ABSCESS: Inflamed tissue, including an area of pus.

ACCELERATED APPROVAL: Expedited process for FDA approval of treatments for serious or life-threatening conditions.

ACQUIRED IMMUNODEFICIENCY SYNDROME (AIDS): The most severe manifestation of infection with HIV. The CDC lists numerous opportunistic infections and neoplasms (cancers) that, in the presence of HIV infection, constitute an AIDS diagnosis. In 1993, the CDC expanded the criteria for an AIDS diagnosis to include CD4 cell count at or below 200 cells/mm³ in the presence of HIV infection. In persons (age 5 and older) with normally functioning immune systems, CD4 cell counts usually range from 800 to 1,500 cells/mm³. Persons living with AIDS often have infections of the lungs, brain, eyes, and other organs, debilitating weight loss, diarrhea, and malignancies.

ACTG: See AIDS Clinical Trials Group.

ACTIVE IMMUNITY: Immunity produced by the body in response to stimulation by a disease-causing organism or other antigen, such as a vaccine.

ACUPUNCTURE: A Chinese medical treatment involving the insertion of very fine sterile needles into the body at specific points according to a mapping of “energy pathways.” Historically, acupuncture is one component of an overall program of Chinese medicine that includes theory, practice, diagnosis, physiology, and the use of herbal preparations. Acupuncture is used to control pain and to treat other conditions such as allergies or addiction withdrawal. See Alternative Medicine.

ACUTE HIV INFECTION: The four- to seven-week period of rapid viral replication following exposure to HIV. During acute infection, high levels of plasma HIV RNA (viral load) disseminate throughout the body, accompanied by a sharp drop in CD4 cell count. An estimated 30% to 60% of individuals with acute HIV infection develop a syndrome characterized by fever, malaise, lymphadenopathy, pharyngitis, headache, myalgia, and, sometimes, rash. Usually within 30 to 50 days after acute infection, seroconversion and a broad HIV-1-specific immune response occur. Also called primary HIV infection.

ADAP: See AIDS Drug Assistance Programs.

ADENOPATHY: Any disease involving or causing enlargement of glandular tissues, especially one involving the lymph nodes.

ADENOSINE: A nucleoside combining the base adenine with D-ribose. One of the building blocks of DNA and RNA.

ADENOVIRUS: Any virus from the family Adenoviridae. More than 40 adenoviruses are known to infect people, causing upper respiratory tract, gastrointestinal, and eye infections.

ADHERENCE: Taking medications or undergoing other treatment as prescribed, including frequency and food restrictions. Nearly-perfect adherence to anti-HIV regimens is typically required to avoid the development of drug resistance. Also called compliance.

ADJUVANT: A substance added to a drug formulation that facilitates or modifies the action of the principal ingredient. May be used in HIV therapies or for HIV vaccines. Examples of adjuvants include Freund incomplete adjuvant and Montanide incomplete seppic adjuvant.

ADVERSE EVENT: An unwanted effect, especially as defined in clinical trials. Specifically, drug-related adverse events are those that are considered by the investigators to be caused by the study drug. Also called adverse reactions.

AEROSOLIZED: A form of drug administration in which the agent is turned into a fine spray or mist and inhaled.

AETC: See AIDS Education and Training Centers.

AFEBRILE: Without fever; having a normal body temperature.

AGAMMAGLOBULINEMIA: Absence or low levels of the gamma fraction of serum globulin. Commonly used to describe absence of immunoglobulins in general. See Antibodies.

AIRBORNE TRANSMISSION: Process by which an infectious agent passes through the air to infect susceptible individuals by droplet infection (eg, sneezing, coughing).

ALANINE AMINOTRANSAMINASE (ALT): A liver enzyme that plays a role in protein metabolism. Elevated serum levels of ALT are a sign of liver damage from disease or drugs. Also called serum glutamic-pyruvic transaminase (SGPT).

ALBUMIN: A protein component of blood serum.

ALKALINE PHOSPHATASE: An enzyme normally present in certain cells within the liver, bone, kidneys, intestine, and placenta. When the cells are destroyed in those tissues, more of the enzyme leaks into the blood, and levels rise in proportion to the severity of the condition. Measurement of this enzyme is used as an indication of the health of the liver.

ALLERGY: An immediate or delayed immune reaction caused by exposure to an antigen (allergen).

ALOPECIA: Partial or complete hair loss. Certain chemotherapeutic cancer drugs cause hair loss because these agents target rapidly dividing cells, including hair cells.

ALTERNATIVE MEDICINE: A broad category of treatment systems (eg, chiropractic, herbal medicine, acupuncture, homeopathy, naturopathy, and spiritual devotions) or culturally based healing traditions such as Chinese, Ayurvedic, and Christian Science. Alternative medicine is also referred to as complementary medicine. Holistic medicine is a narrower term.

ALUM: Potassium aluminum sulfate, or ammonium aluminum sulfate, used especially as an emetic (an agent that induces vomiting), an astringent (a substance that contracts tissues), and a styptic (a substance that tends to check bleeding by contracting the tissues or blood vessels).

ALVEOLUS: A small cavity or socket. Pulmonary alveoli are thin-walled saclike ends of bronchioles where gas exchange takes place.

AMEBIASIS: An inflammation of the intestines caused by infestation with Entameba histolytica (a type of ameba) and characterized by frequent loose stools flecked with blood and mucus.

AMINO ACID: Any of a class of nitrogen-containing acids. Some 20 amino acids are commonly found in animals and humans. Chains of amino acids synthesized by living systems are called polypeptides (up to about 50 amino acids) and proteins (more than 50 amino acids). See Peptide; Proteins.

AMYLASE: An enzyme secreted by the salivary glands and the pancreas that helps in the digestion of carbohydrates. Elevated levels may be a sign of pancreatitis.

ANABOLIC: Pertaining to anabolism, the metabolic process of building tissue from simpler molecules.

ANALOG: In chemistry, a compound with a structure similar to that of another compound but differing from it in respect to certain components or structural makeup, which may have a similar or opposite action metabolically.

ANAMNESTIC RESPONSE: The heightened immunologic reaction elicited by a second or subsequent exposure to particular antigen such as a pathogenic microorganism (eg, bacterium, fungus).

ANAPHYLACTIC SHOCK: A life-threatening allergic reaction characterized by a swelling of body tissues (including the throat) and a sudden decline in blood pressure.

ANDROGEN: A natural or synthetic hormone, such as androsterone or testosterone, with masculizing effects.

ANEMIA: A lower than normal number of red blood cells.

ANERGY: 1. The loss or weakening of the body’s immunity to an irritating agent, or antigen. Anergy can be thought of as the opposite of allergy, which is an overreaction to a substance. The strength of the body’s immune response is often quantitatively measured by means of a skin test in which a solution containing an antigen known to cause a response, such as mumps or candida, is injected immediately under the skin. Patients may be so immunologically suppressed that they are unable to produce cutaneous (skin) delayedtype hypersensitivity reaction (DTH). Such patients usually do not test positive for tuberculosis on a tuberculin skin test (or Mantoux test). The lack of a reaction to these common antigens indicates anergy. 2. Researchers have found that CD4 cells in cell culture can be turned off by contact with the HIV envelope, leaving them unable to respond to further immune system stimulation.

ANGINA: A severe, often constricting pain, usually referring to chest pain.

ANGIOGENESIS: The process of forming new blood vessels. Angiogenesis is essential for tumor growth.

ANOREXIA: Lack or loss of appetite that causes significant weight loss.

ANOSCOPY: A visual examination of the anal canal with an anoscope.

ANTAGONISM: Opposing action between agents (eg, drugs), or when the combined effect is less than the effect of one of the agents alone.

ANTENATAL: See Prenatal.

ANTI-IDIOTYPE: An antibody that recognizes and binds to another antibody (idiotype).

ANTIARRHYTHMIC: A drug or procedure that counters or prevents cardiac arrhythmia.

ANTIBIOTIC: A substance derived from mold or bacteria that inhibits the growth of other microorganisms (such as bacteria or fungi). Antibiotics are used to treat infectious diseases.

ANTIBODIES: Molecules in the blood or secretory fluids that tag, destroy, or neutralize bacteria, viruses, or other harmful toxins (see Antigens). They are members of a class of proteins known as immunoglobulins, which are produced and secreted by B lymphocytes in response to stimulation by antigens. An antibody is specific to an antigen.

ANTIBODY-DEPENDENT CELL-MEDIATED CYTOTOXICITY (ADCC): An immune response in which antibodies bind to target cells, identifying them for attack by the immune system.

ANTIEMETIC: A drug used to treat nausea or vomiting.

ANTIFOLATE: An agent that inhibits intracellular production of folinic acid.

ANTIGEN: Any substance that antagonizes or stimulates the immune system to produce antibodies (ie, proteins that fight antigens). Antigens are often foreign substances such as bacteria or viruses.

ANTINEOPLASTIC: Inhibiting or preventing the growth of tumor cells.

ANTIRETROVIRAL AGENTS: Substances used against retroviruses such as HIV.

ANTISENSE DRUG: A synthetic length of DNA, RNA, or molecules with similar structure containing a nucleotide base sequence complementary to the genetic sequence that it is supposed to inactivate. Antisense drugs are designed to lock into and block viral genetic instructions, marking them for destruction by cellular enzymes. This prevents the building of new virus or the infection of new cells.

ANTITOXINS: Antibodies that recognize and inactivate toxins produced by certain bacteria, plants, or animals.

ANTIVIRAL: A substance or process that destroys or weakens a virus or interferes with its ability to replicate.

APHASIA: Loss of ability to speak or understand speech.

APHTHOUS ULCER: A painful oral or esophageal sore on a mucous membrane. The size of an ulcer can range from several millimeters to 2 cm in diameter and can occur as single or multiple lesions. Also called canker sores, recurrent ulcerative stomatitis, or ulcerative stomatitis.

APOPTOSIS: Cellular suicide or programmed cell death. HIV may induce apoptosis in both infected and uninfected immune system cells. Normally when CD4 cells mature in the thymus gland, a small proportion of these cells are unable to distinguish self from nonself. Because these cells would otherwise attack the body’s own tissues, they receive a biochemical signal from other cells that results in apoptosis. See Tumor Necrosis Factor.

AREA UNDER THE CURVE (AUC): In pharmacokinetics, a mathematical calculation to evaluate the body’s total exposure over time to a given drug. In a graph plotting how drug concentration in the blood changes after dosing, the drug concentration variable lies on the y-axis and time lies on the x-axis. The area between a drug concentration curve and the x-axis for a designated time interval is the AUC. AUCs are used as a guide for dosing schedules and to compare the different drugs’ availability in the body.

ARM: One group of participants in a comparative clinical trial, all of whom receive the same treatment. The other arm(s) receive(s) a different treatment.

ARRHYTHMIA: A change in the heartbeat’s rhythm.

ARTHRALGIA: Pain in a joint, not inflammatory in character.

ASPARTATE AMINOTRANSAMINASE (AST): A liver enzyme that plays a role in protein metabolism. Elevated serum levels of AST are a sign of liver damage from disease or drugs. Also called SGOT (Serum Glutamic-Oxaloacetic Transaminase).

ASSAY: A test to detect the presence, absence, or quantity of an agent (such as a drug or viral load).

ASSEMBLY AND BUDDING: Final stages of the viral life cycle. Viral core proteins, enzymes, and RNA (see Ribonucleic Acid) gather just inside the cell’s membrane, while the viral envelope proteins aggregate within the membrane. An immature viral particle is formed and then pinches off from the cell, acquiring an envelope and the cellular and HIV proteins from the cell membrane. The immature viral particle then undergoes processing by an HIV enzyme called protease to become an infectious virus.

ASTHENIA: Weakness.

ASYMPTOMATIC: Without symptoms. In HIV/AIDS literature, this term is often used to describe someone who has a positive reaction to one of several tests for HIV antibodies but who shows no clinical symptoms of the disease.

ATAXIA: Lack of voluntary muscle coordination.

ATTENUATED: Weakened or decreased.

AUTOANTIBODY: 1. An antibody that is active against some of the tissues of the organism that produced it. 2. An antibody directed against the body’s own tissue.

AUTOIMMUNE DISEASE: A condition that results when the immune system responds against a person’s own tissues or cells.

AUTOIMMUNIZATION: Inducing immunity against the body’s own tissues.

AUTOINOCULATION: A secondary infection originating from a focus of infection already in the body.

AUTOLOGOUS: Pertaining to the same organism or one of its parts; originating within an organism itself (eg, reserving your blood for your future surgery is an autologous transfusion).

AZOTEMIA: Abnormally high concentrations of urea and other nitrogenous substances in the blood.

B CELL: See B Lymphocyte.

B LYMPHOCYTE (B CELL): One of the two major classes of lymphocytes, B lymphocytes are blood cells of the immune system derived from bone marrow and spleen. During infections, these cells are transformed into plasma cells that produce large quantities of antibody directed at specific pathogens. When antibodies bind to foreign proteins, such as those that occur naturally on the surfaces of bacteria, they mark the foreign cells for elimination by other cells of the immune system. This process occurs through interactions with various types of T-cells and other components of the immune system.

BACTEREMIA: Viable bacteria in the circulating blood.

BACTERICIDAL (BACTERIOCIDAL): Capable of killing bacteria.

BACTERIOSTATIC: Capable of inhibiting or slowing the reproduction of bacteria.

BACTERIUM: A single-celled prokaryotic microorganism. Many bacteria cause disease.

BACULOVIRUS: A virus that infects insects; used in the production of some HIV vaccines. See Vaccine.

BASAL CELL: A skin cell in the deepest layer of the stratified epithelium.

BASELINE: 1. Information gathered at the beginning of a study against which variations found in the study are measured. 2. A known value or quantity with which an unknown is compared when measured or assessed. 3. The initial time point in a clinical trial, just before a volunteer starts to receive the experimental treatment undergoing testing. At this reference point, measurable values such as CD4 count are recorded. Safety and efficacy of a drug are often determined by monitoring changes from the baseline values.

BASOPHIL: A type of white blood cell filled with granules of toxic chemicals that can digest microorganisms.

BILE: A fluid secreted by the liver and passed to the small intestine where it aids in the emulsification and absorption of fats.

BILIRUBIN: A red pigment in liver bile, blood, and urine. Bilirubin is a product of hemoglobin breakdown in red blood cells. It is removed from the blood and processed by the liver, which secretes it into the digestive tract. Measuring bilirubin levels is one way to assess the liver’s health. The normal level of bilirubin in the blood is 0.1 to 1.5 mg/L. An elevated level of bilirubin in blood (hyperbilirubinemia) indicates liver disease or drug-induced liver impairment.

BINDING ANTIBODY: As related to HIV infection, an antibody that attaches to some part of HIV. Binding antibodies may or may not adversely affect the virus.

BIOAVAILABILITY: The extent to which a drug is absorbed into the bloodstream.

BIOELECTRICAL IMPEDANCE ANALYSIS (BIA): A test for measuring various bodily characteristics, including body fat and body cell mass.

BIOLOGICAL RESPONSE MODIFIERS (BRM): Substances, either natural or synthesized, that boost, direct, or restore normal immune defenses. BRMs include interferons, interleukins, hormones, and monoclonal antibodies.

BIOPSY: Surgical removal of a piece of tissue from a living organism for microscopic examination to make a diagnosis (eg, to determine whether abnormal cells such as cancer cells are present).

BIOTECHNOLOGY: 1. Using living organisms or their products to make or modify a substance. Techniques include recombinant DNA (see Genetic Engineering) and hybridoma technology. 2. Industrial application of biological research, particularly in fields such as recombinant DNA or gene splicing, which produces synthetic hormones or enzymes by combining genetic material from different species.

BLINDED STUDY: A clinical trial in which participants are unaware as to whether they are in the experimental or control arm of the study. See Double-Blind Study.

BLOOD-BRAIN BARRIER: A barrier created by brain capillaries that prevents many substances from leaving the blood and crossing the capillary walls into the brain tissues. Certain compounds can readily cross the blood-brain barrier; others can not.

BODY FLUIDS: Any fluid in the human body, such as blood, urine, saliva (spit), sputum, tears, semen, breast milk, or vaginal secretions. Only blood, semen, breast milk, and vaginal secretions have been linked directly to HIV transmission.

BONE MARROW SUPPRESSION: A side effect of many anticancer and antiviral drugs, including AZT. Leads to a decrease in white blood cells, red blood cells, and platelets. Such reductions, in turn, result in anemia, bacterial infections, and spontaneous or excess bleeding.

BONE MARROW: Soft tissue located in the cavities of the bones where blood cells such as erythrocytes, leukocytes, and platelets are formed.

BOOSTER: A second or later dose of a vaccine given to increase the immune response to the original dose.

BRANCHED DNA ASSAY (BDNA TEST): A test for measuring the amount of HIV (as well as other viruses) in blood plasma. The test uses a method that creates a luminescent signal whose brightness depends on the amount of viral RNA present. Test results are calibrated in numbers of virus particle equivalents per milliliter of plasma. The bDNA test is similar in results but not in technique to the PCR test. See Viral Load.

BREAKTHROUGH INFECTION: An infection, caused by the infectious agent the vaccine is designed to protect against, that occurs during the course of a vaccine trial. These infections may be caused by exposure to the infectious agent before the vaccine has taken effect, or before all doses of the vaccine have been given.

BRONCHIOALVEOLAR: Related to the bronchioles and alveoli of the lungs.

BRONCHITIS: Inflammation of the lungs’ bronchial tubes.

BRONCHOSCOPY: Visual examination of the bronchial passages of the lungs through the tube of an endoscope (usually a curved flexible tube containing fibers that carry light down the tube and project an enlarged image up the tube to the viewer) that is inserted into the upper lungs. Can be used for extraction of material from the lungs. See Endoscopy.

BUCCAL: Related to the cheek or mouth.

BUDDING: See Assembly and Budding.

CACHEXIA: General ill health and malnutrition, marked by weakness and emaciation, and usually associated with serious disease. See AIDS Wasting Syndrome.

CANDIDA: A yeastlike fungus commonly found in the normal flora of the mouth, skin, intestinal tract, and vagina, which can become clinically infectious in immunocompromised persons.

CARCINOGEN: A cancer-producing substance.

CARCINOMA: A malignant tumor.

CARDIOMYOPATHY: A disease of the heart muscles.

CARNITINE: A compound involved in transferring fatty acids across mitochondrial membranes.

CARRIER: A person who harbors an infectious disease (such as hepatitis) without any clinical signs of it and is a potential source of infection.

CAT SCAN: See CT Scan.

CATHETER: A tubular medical device for insertion into canals, vessels, passageways, or body cavities, usually to permit injection (eg, through an intravenous catheter into a vein), to withdraw fluids, or to keep a passage open.

CBCT: See Community-Based Clinical Trial.

CCR5: A chemokine receptor found on some immune cells. CCR5 receptors, along with CD4 receptors, are required for macrophagetropic HIV to enter a cell. People who lack CCR5 receptors appear to have a decreased susceptibility to HIV infection, and those who are infected progress more slowly to AIDS.

CD4 CELL COUNT: A test to evaluate the immune system. Specifically, this count measures the number of immune system cells (eg, T lymphocytes and monocytes) that have CD4 receptors. The count is determined by a blood test and measured by the number of CD4 cells per cubic millimeter of blood. Normal CD4 counts range from 800-1,500 cells/mm³ (athough this range varies among experts). According to the CDC, a CD4 count at or below 200 cells/mL is an AIDSdefining condition.

CD4 CELLS (T4 CELLS): 1. A type of T cell involved in protecting against viral, fungal, and protozoal infections. These cells normally orchestrate the immune response, signaling other cells in the immune system to perform their special functions. Also known as T helper cells. 2. HIV’s preferred targets are cells that have a docking molecule called “cluster designation 4” (CD4) on their surfaces. Cells with this molecule are known as CD4-positive (or CD4+) cells. Destruction of CD4 lymphocytes is the major cause of the immunodeficiency observed in AIDS, and decreasing CD4 lymphocyte levels appears to be the best indicator for developing opportunistic infections. Although CD4 counts fall, the total T cell level remains fairly constant through the course of HIV disease, because of a concomitant increase in the CD8 cells. The ratio of CD4 to CD8 cells is therefore an important measure of disease progression. See CD8 (T8) Cells; Immunodeficiency.

CD4 PERCENTAGE: The percentage of lymphocytes that are CD4 cells. A common method of evaluating immune system status, CD4 percentage is typically more reliable than CD4 counts.

CD8 (T8) CELLS: Protein embedded in the cell surface of suppressor T lymphocytes. Also called cytotoxic T lymphocytes (CTLs). Some CD8 cells recognize and kill cancerous cells and those infected by intracellular pathogens (some bacteria, viruses, and mycoplasma).

CDC: See Centers for Disease Control and Prevention.

CELL LINES: Specific cell types artificially maintained in the laboratory (ie, in vitro) for scientific purposes.

CELL-MEDIATED IMMUNITY (CMI): This branch of the immune system exists primarily to deal with viruses that are more insidious than bacteria because they invade the host (eg, human) cells, where they can hide from the antibodymaking cells of the immune system. With this system, the response to foreign material is performed by specific defense cells, such as killer T cells, macrophages, and other white blood cells rather than by antibodies.

CELLULAR IMMUNITY: See Cell-Mediated Immunity.

CELLULITIS: Inflammation of the subcutaneous, loose connective tissue.

CENTERS FOR DISEASE CONTROL AND PREVENTION (CDC): The Department of Health and Human Services agency with the mission to promote health and quality of life by preventing and controlling disease, injury, and disability. The CDC operates eleven centers including the National Center for HIV, STD, and TB prevention. The CDC assesses the status and characteristics of the HIV epidemic and conducts epidemiological, laboratory, and surveillance investigations. The CDC supports the design, implementation, and evaluation of prevention activities for HIV/AIDS and maintains various HIV/AIDS information services.

CENTRAL NERVOUS SYSTEM (CNS) DAMAGE (BY HIV INFECTION): The central nervous system is composed of the brain, spinal cord, and the meninges (protective membranes surrounding them). Although HIV infects monocytes and macrophages, they appear to be relatively resistant to killing. These cells travel throughout the body and carry HIV to various organs, especially the lungs and the brain. Persons living with HIV often experience abnormalities in the central nervous system. Investigators have hypothesized that an accumulation of HIV in brain and nerve cells or the inappropriate release of cytokines or toxic byproducts of these cells may be to blame for the neurological manifestations of HIV disease.

CEREBRAL: Pertaining to the cerebrum, the main portion of the brain.

CEREBROSPINAL FLUID (CSF): Fluid that bathes the brain and the spinal cord. A sample of this fluid is often removed from the body for diagnostic purposes by a lumbar puncture (spinal tap).

CERVICAL CANCER: A neoplasm of the uterine cervix that can be detected in the early curable stage by the Papanicolaou (Pap) test. See Cervical Dysplasia; Cervix; Pap Smear.

CERVICAL DYSPLASIA: Abnormality in the size, shape, and organization of adult cells of the cervix. Often a precursor lesion for cervical cancer. Studies indicate an increase in prevalence of cervical dysplasia among women living with HIV. Additional studies have documented that a higher prevalence is associated with greater immune suppression. HIV infection may also adversely affect the clinical course and treatment of cervical dysplasia and cancer.

CERVICAL INTRAEPITHELIAL NEOPLASIA (CIN1, CIN2, CIN3): Dysplasia of the cervix epithelium, often premalignant (ie, precancerous), characterized by various degrees of hyperplasia, abnormal keratinization (forming horny epidermal tissue), and condylomata. Considerable evidence implicates human papilloma virus (HPV) in the development of CIN. Immunosuppression may also play an important role in facilitating infection or persistence of HPV in the genital tract and progression of HPV-induced neoplasia. See Condyloma; Neoplasm.

CERVICOVAGINAL LAVAGE (CVL): A method of “washing” the vaginal cavity to test the resulting fluid, eg, to determine viral load in a woman’s genital tract secretions.

CERVIX: The lower, cylindrical terminus of the uterus that juts into the vagina and contains a narrow canal connecting the upper and lower parts of a woman’s reproductive tract.

CHANCRE: The primary syphilis lesion, occurring at the site of cutaneous or mucosal infection. It begins 10-30 days after infection and breaks down into an ulcer, healing slowly after 4 to 6 weeks.

CHANCROID: A highly contagious sexually transmitted disease caused by the Hemophilus ducreyi bacterium. It appears as a pimple, chancre, sore, or ulcer on the skin of the genitals. The lesion appears after an incubation period of three to five days and may facilitate HIV transmission.

CHART REVIEW: A retrospective method of collecting data that involves reviewing medical records.

CHEILITIS: Inflammation of the lips.

CHEMOKINES: Also called beta chemokines. Studies of the relationship between HIV and these immune system chemicals have shown the complex exchanges that take place when HIV and white blood cells meet. Chemokines are intracellular messenger molecules secreted by CD8 cells whose major function is to attract immune cells to sites of infection. Recent research has shown that HIV-1 needs access to chemokine receptors on the cell surface to infect the cell. Several chemokines-called RANTES, MIP-1A and MIP-1B-interfere with HIV replication by occupying these receptors. Findings suggest that one mechanism these molecules use to suppress HIV infectivity is to block the process of fusion used by the virus to enter cells.

CHEMOPROPHYLAXIS: The use of chemical agents to prevent infectious disease.

CHEMOTHERAPY: Treatment of disease or mental illness using drugs. Often used in reference to cancer. Chemotherapy for cancer involves cytotoxic drugs that target rapidly dividing cells. This treatment commonly has adverse side effects that may include the temporary loss of the body’s natural immunity to infections, hair loss (alopecia), digestive upset, and a general feeling of illness.

CHLAMYDIA: A sexually transmitted disease (STD). The most common sexually transmitted bacterium (Chlamydia trachomatis) that infects the reproductive system. The infection is frequently asymptomatic (ie, shows no symptoms), but if left untreated, can cause sterility in women.

CHOLANGITIS: Inflammation of the bile duct(s).

CHOLELITHIASIS: The production of gallstones.

CHOLESTASIS: An obstruction in the bile duct.

CHRONIC IDIOPATHIC DEMYELINATING POLY NEUROPATHY (CPID): Chronic, spontaneous loss or destruction of myelin. Myelin is a soft, white, somewhat fatty material that forms a thick sheath around the core of myelinated nerve fiber. Patients show progressive, usually symmetric weakness in the upper and lower extremities. Patients with clinical progression of the syndrome after four to six weeks by definition have CPID. Treatment in most centers consists of giving IV-immune globulin for four to five days or plasmapheresis (five to six exchanges over two weeks).

CHRONIC: A continuous or persistent condition of long duration.

CIRCULATING IMMUNE COMPLEXES: See Immune Complex.

CIRCUMORAL PARESTHESIA: An abnormal touch sensation, such as burning or prickling around the mouth, often in the absence of an external stimulus. See Paresthesia.

CIRRHOSIS: End-stage liver disease caused by hepatitis, alcoholism, or an obstruction of bile flow. Cirrhosis can cause jaundice, gastrointestinal problems, edema, liver failure, and death.

CLEARANCE: The removal of drugs or other substances from blood by the kidneys.

CLINICAL ALERT: The National Institutes of Health in conjunction with the editors of several biomedical journals publish those bulletins on urgent cases by which timely and broad dissemination of results of clinical trials could prevent morbidity (sickness) and mortality (death). The Clinical Alert does not become a barrier to subsequent publication of the full research paper. Clinical Alerts are widely distributed electronically through the National Library of Medicine and through standard mailings.

CLINICAL ENDPOINT: See Endpoint.

CLINICAL LATENCY: The state or period of an infectious agent, such as a virus or bacterium, living or developing in a host without producing clinical symptoms. Pertaining to HIV infection, infected individuals usually exhibit a period of clinical latency with little evidence of disease, but viral load studies show that the virus is never truly latent (dormant). Even early in the disease, HIV is active within lymphoid organs, where large amounts of virus become trapped in the follicular dendritic cell network. Surrounding tissues are areas rich in CD4 cells. These cells increasingly become infected, and viral particles accumulate both in infected cells and as free virus.

CLINICAL PRACTICE GUIDELINES: Standards for physicians to adhere to in prescribing care for a given condition or illness.

CLINICAL TRIAL: A scientifically designed and executed investigationof the effects of a drug (or vaccine) administered to human volunteers. The goal is to define the safety, clinical efficacy, and pharmacological effects (including toxicity, side effects, incompatibilities, or interactions) of the drug. The U.S. government, through the FDA, requires strict testing of all new drugs and vaccines prior to their approval for use as therapeutic agents. See entries for Phase I, II, III, and IV Trials.

CLINICAL: Pertaining to or founded on observation and treatment

CLONE: 1. A group of genetically identical cells or organisms descended from a common ancestor. 2. To produce genetically identical copies. 3. A genetically identical replication of a living cell that is valuable for the investigation and reproduction of test cultures.

CMAX: The maximum concentration of a drug in the body after dosing.

CMIN: The minimum concentration of a drug in the body after dosing.

CNS: See Central Nervous System.

CODON: A sequence of three nucleotides of messenger RNA that determines the addition of a particular amino acid to, or termination of, a polypeptide chain during protein synthesis. See Ribonucleic Acid.

COFACTORS: 1. Substances, microorganisms, or characteristics of individuals that may influence the progression of disease or the likelihood of becoming ill. 2. A substance, such as a metallic ion or coenzyme, that must be associated with an enzyme for the enzyme to function. 3. A situation or activity that may increase an HIV-positive person’s susceptibility to AIDS. Examples of cofactors are

COGNITIVE IMPAIRMENT: Loss of the ability to process, learn, and remember information.

COHORT: In epidemiology, a group of individuals with some characteristics in common.

COLITIS: Inflammation of the colon.

COLONOSCOPY: An examination of the interior of the colon using a colonoscope. Also called coloscopy.

COLPOSCOPY: An examination of the vagina and cervix using an endoscope, primarily to identify areas of cervical dysplasia in women with abnormal Pap smears.

COMBINATION THERAPY: As it pertains to HIV/AIDS, two or more drugs used together to achieve optimum results control HIV infection. Typically, at least three drugs from two different classes are used. An example of combination therapy is two nucleoside analogs (such as 3TC and AZT) plus either a protease inhibitor or a non-nucleoside reverse transcriptase inhibitor. See Synergism.

COMMUNITY-BASED CLINICAL TRIAL (CBCT): A clinical trial conducted primarily through primary-care physicians rather than academic research facilities.

COMPASSIONATE USE: A method of providing experimental therapeutics (including experimental drugs) prior to final FDA approval for use in humans. This procedure is used with very sick individuals who have no other treatment options. Often, case-by-case approval must be obtained from the FDA for compassionate use of a drug or therapy.

COMPLEMENT CASCADE: A precise sequence of events, usually triggered by an antigen-antibody complex, in which each component of the complement system is activated in turn. See Antibodies; Antigen.

COMPLEMENT: A group of proteins in normal blood serum and plasma that, in combination with antibodies, causes the destruction of antigens, particularly bacteria and foreign blood cells.

COMPLEMENTARY THERAPY: A range of services designed to complement traditional medical practice as part of a practitioner’s primary care plan for an individual.

COMPLETE BLOOD COUNT (CBC): A test often used to monitor people with HIV. A CBC measures the number of red blood cells, white blood cells, and platelets.

COMPLIANCE: See Adherence.

CONCOMITANT DRUGS: Drugs that are taken together. Certain concomitant medications may have adverse interactions.

CONDYLOMA (CONDYLOMA ACUMINATUM): A papilloma with a central core of connective tissue in a treelike structure covered with epithelium, usually occurring on the mucous membrane or skin of the external genitals or in the perianal (tissue surrounding the anus) region. Although the lesions are usually few, they may aggregate to form large, cauliflower-like masses. Caused by the human papilloma virus (see HPV), condyloma is infectious and autoinoculable (ie, capable of being transmitted by inoculation from one part of the body to another). Also called genital warts, venereal warts, or verruca acuminata.

CONJUNCTIVA: A thin mucous membrane on the inner surface of the eyelids.

CONTAGIOUS: In the context of HIV, any infectious disease transmitted by casual contact between persons. Casual contact can be defined as normal day-to-day contact among people at home, school, work, or in the community. A contagious pathogen (eg, chicken pox) can be transmitted by casual contact. An infectious pathogen, on the other hand, is transmitted by direct or intimate contact (eg, sex). HIV is infectious, not contagious.

CONTRAINDICATION: A specific circumstance when the use of certain treatments could be harmful.

CONTROLLED TRIALS: A control is a standard against which experimental observations are evaluated. In clinical trials, one group of patients is given an experimental drug, while another group (the control group) is given either a standard treatment for the disease or a placebo.

CORECEPTORS: A pair of cell surface proteins with which

CORTICOSTEROID: A natural steroid that comes from the cortex or adrenal gland, or a synthetic version. Corticosteroids can reduce swelling, pain, and other manifestations of inflammation.

CPID: See Chronic Idiopathic Demyelinating Polyneuropathy.

CREATININE: A protein found in muscles and blood and excreted by the kidneys in the urine. Creatinine levels in the blood or urine provide a measure of kidney function.

CROSS-RESISTANCE: The phenomenon in which a microbe that has acquired resistance to one drug through direct exposure subsequently has resistance to one or more other drugs to which it has not been exposed. Cross-resistance arises because the biological mechanism of resistance to several drugs is the same and arises through identical genetic mutations.

CRYOTHERAPY: Using liquid nitrogen to freeze and destroy a lesion or growth; sometimes used to induce scar formation and healing to prevent further spread of a condition (eg, warts or Molluscum contagiosum).

CRYSTALLURIA: The presence of crystals in the urine.

CT SCAN (CT OR COMPUTED TOMOGRAPHY): Radiography (using X ray) in which a three-dimensional image of a body structure is constructed by computer from a series of cross-sectional images made along an axis. (Once called computerized axial tomography or CAT scan; these terms are now obsolete.) See Magnetic Resonance Imaging (MRI).

CTL: See Cytotoxic T Lymphocyte.

CUTANEOUS: Of, pertaining to, or affecting the skin.

CXCR4: Also known as fusin, CXCR4 is a G-protein-linked chemokine receptor. A variety of CD4+ and CD4- cells, including those from the spleen, brain, and lungs, express CXCR4. Early in the epidemic, researchers discovered the primary HIV receptor, the CD4 molecule. A second molecule, CXCR4, is also required for certain strains of HIV to fuse with and enter into cells. Studies indicate a multistage interplay between HIV and two receptors on white blood cells. After binding to the receptor CD4, the virus fuses with CXCR4; this double clasp may then signal the receptors to move the virus into the cell.

CYP 3A4: A liver enzyme that is part of the cytochrome P450 system and metabolizes many drugs.

CYTIDINE: A nucleoside combining the base cytosine with D-ribose. One of the building blocks of DNA and RNA.

CYTOCHROME P450 SYSTEM: A set of liver enzymes that metabolize drugs and other substances. Some drugs inhibit or stimulate this system, which affects the breakdown and, therefore, blood levels of other drugs in the body. In such cases, dose adjustments may be necessary.

CYTOKINES: Proteins produced by white blood cells that act as chemical messengers between cells. They can stimulate or inhibit the growth and activity of various immune cells. HIV replication is regulated by a delicate balance among the body’s own cytokines. By altering that balance, one can influence the replication of the virus in the test tube and potentially even in the body. See Interleukins; Tumor Necrosis Factor.

CYTOPENIA: Deficiency in the cellular elements of the blood.

CYTOPLASMA: All of the substance of a cell other than the nucleus.

CYTOSINE: One of the four ringed, nitrogen-containing bases that make up RNA and DNA.

CYTOTOXIC T LYMPHOCYTE (CTL): A lymphocyte that kills foreign cells marked for destruction by the cellular immune system. See CD8 (T8) Cells.

CYTOTOXIC: An agent or process that is toxic to cells (ie, suppresses cell function or causes cell death).

DATA AND SAFETY MONITORING BOARD (DSMB): An independent committee, composed of community representatives and clinical research experts, that reviews data while a clinical trial is in progress to ensure that participants are not exposed to undue risk. A DSMB may recommend that a trial be stopped if there are safety concerns or if the trial objectives have been achieved.

DELETION: In genetics, any spontaneous elimination of a section of genetic material (ie, from a chromosome) either in nature or in the laboratory. A deletion is a type of mutation.

DEMENTIA: Chronic intellectual impairment (ie, loss of mental capacity) with organic origins that affects a person’s ability to function in a social or occupational setting.

DEMYELINATION: Destruction, removal, or loss of the myelin sheath of a nerve or nerves.

DENDRITE: Any of the usual branching protoplasmic processes that conduct impulses toward the body of a nerve cell. See Protoplasm.

DENDRITIC CELLS: Patrolling immune system cells that may begin the HIV disease process by carrying the virus from the site of the infection to the lymph nodes, where other immune cells become infected. Dendritic cells travel through the body and bind to foreign invaders-such as HIV-especially in external tissues, such as the skin and the membranes of the gut, lungs, and reproductive tract. They then ferry the foreign substance to the lymph nodes to stimulate T cells and initiate an immune response. In laboratory experiments, the dendritic cells that carry HIV also bind to CD4 cells, thereby allowing HIV to infect the CD4 cells. CD4 cells are the primary immune system cells targeted by HIV and depleted during HIV infection.

DEOXYRIBONUCLEIC ACID (DNA): The reproducible doublestranded molecular chain that contains cellular and viral genes. The embodiment of hereditary metabolic information, DNA uses four nucleotides to encode the molecular sequence of structural proteins, enzymes and growth factors.

DEOXYRIBONUCLEOTIDE: A nucleotide that contains deoxyribose and is a component of DNA.

DEPARTMENT OF HEALTH AND HUMAN SERVICES (HHS): The U.S. government’s principal agency for protecting the health of all Americans and providing essential human services, especially for those who are least able to help themselves. HHS includes some 250 programs, administered by 10 principal operating divisions such as CDC, FDA, and NIH. HHS works closely with state and local governments, and many HHS-funded services are provided at the local level by state or county agencies or through private sector grantees.

DERMATITIS: Inflammation of the skin.

DIABETES MELLITUS: A chronic metabolic disorder caused by absolute or relative insulin deficiency. The more common form, diabetes mellitus type 2, is characterized by insulin resistance in peripheral tissues and a defect in insulin secretion by beta cells. Diabetes mellitus is an independent risk factor for cardiovascular disease.

DIAGNOSIS: The determination of the presence of a specific disease or infection, usually accomplished by evaluating clinical symptoms and laboratory tests.

DIAPHORESIS: Perspiration, especially profuse perspiration.

DIPLOPIA: Double vision.

DISEASES (NIAID): An NIH institute that conducts and supports research to study the causes of allergic, immunologic, and infectious diseases, and to develop better means of preventing, diagnosing, and treating illnesses. NIAID is responsible for the federally funded, national basic research program in AIDS. It supports basic research, epidemiology, and natural history studies; blood screening tests; drug discovery and development; vaccine development and testing; and treatment studies, some directly and some through contracts and cooperative agreements with other institutions. It administers the Adult and Pediatric AIDS Clinical Trial Group (ACTG) network of testing units at hospitals around the country and the Community Programs for Clinical Research on AIDS (CPCRA), a community-based network of AIDS treatment research centers.

DISSEMINATED: Spread (eg, of a disease) throughout the body.

DISTAL: Located away from the center of the body.

DIURETIC: Something which increases the production of urine.

DNA: See Deoxyribonucleic Acid.

DOMAIN: A region of a gene or gene product. See Gene.

DORMANCY: See Latency.

DOSE-ESCALATING TRIAL: A clinical trial in which drug amounts increase over time or across different arms. Dose-escalating trials are used to determine the highest, most tolerable and effective dose of a drug.

DOSE-LIMITING ADVERSE EVENT: An adverse event serious enough to warrant a reduction in a drug’s dose.

DOSE-RANGING STUDY: A clinical trial in which two or more doses of a drug are tested against each other to determine which dose works best and is least harmful.

DOSE-RESPONSE RELATIONSHIP: The relationship between the dose of an agent (such as a drug), or the extent of exposure, and a physiological response. A dose-response effect means that as the dose increases, so does the effect.

DOUBLE-BLIND STUDY: A clinical trial design in which neither the participating individuals nor the study staff know which patients are receiving the experimental drug and which are receiving a placebo or another therapy. Double-blind trials are thought to produce objective results, since the doctor’s and patient’s expectations about the experimental drug do not affect the outcome. See Blinded Study.

DRUG RESISTANCE: The ability of some disease-causing microorganisms, such as bacteria, viruses, and mycoplasma, to adapt themselves, to grow, and to multiply even in the presence of drugs that usually kill them. See Cross-Resistance.

DRUG-DRUG INTERACTION: A modification of the effect of a drug when administered with another drug. The effect may be an increase or a decrease in the action of either substance, or it may be an adverse effect that is not normally associated with either drug.

DSMB: See Data and Safety Monitoring Board.

DUAL-ENERGY X-RAY ABSORPTIOMETRY (DEXA): A method of scanning the body to determine bone density and fat distribution.

DYSPEPSIA: Digestive upset, which can include nausea, vomiting, and heartburn.

DYSPLASIA: Any abnormal development of tissues or organs. In pathology, alteration in size, shape, and organization of adult cells.

DYSPNEA: Difficult or labored breathing. It is also called DYSMNOEA.

DYSURIA: Difficult or painful urination.

EDEMA: An abnormal swelling resulting from the accumulation of fluid in the spaces between tissues.

EFFICACY: The maximum ability of a drug or treatment to produce a result regardless of dosage. A drug passes efficacy trials if it is effective at the dose tested and against the illness for which it is prescribed. In the procedure mandated by the FDA, phase II clinical trials gauge efficacy, and phase III trials confirm it.

ELISA (ENZYME-LINKED IMMUNOSORBENT ASSAY): A type of enzyme immunoassay (EIA) to determine the presence of antibodies to HIV in the blood or oral fluids. Repeatedly reactive (ie, two or more) ELISA test results should be validated with an independent supplemental test of high specificity. In the United States the validation test used most often is the Western Blot test.

EMPIRICAL: Based on experimental data, not on a theory.

ENCEPHALITIS: A brain inflammation of viral or other microbial origin. Symptoms include headache, neck pain, fever, nausea, vomiting, and nervous system problems. Several types of opportunistic infections can cause encephalitis.

END-STAGE DISEASE: Final period or phase in the course of a disease leading to death.

ENDEMIC: Pertaining to diseases associated with particular locales or population groups.

ENDOGENOUS: Relating to or produced by the body.

ENDOSCOPY: Viewing the inside of a body cavity (eg, colon) with an endoscope, a device using flexible fiber optics.

ENDOTOXIN: A toxin present inside a bacterial cell.

ENDPOINT: A category of data used to compare the outcomes in different arms of a clinical trial. Common endpoints are severe toxicity, disease progression, or-especially in HIV disease-surrogate markers, such as CD4 count. Sometimes death is used as an endpoint. The term is confusing because it often incorrectly implies that patients in a study are no longer followed after they experience an endpoint. This is obviously true when the event is death, but need not be so for nonfatal events. In fact, the design of the trial may require continued treatment and follow-up of patients over the entire course of the trial, regardless of the number of nonfatal “endpoints” observed.

ENTERAL: Through or within the intestines or gastrointestinal tract.

ENTERIC: Pertaining to the intestine.

ENTERITIS: Inflammation of the intestine.

ENTEROPATHY: An intestinal disease.

ENTEROTOXIN: A toxic substance that causes gastrointestinal upset. Cholera toxin is an example of an enterotoxin.

ENTRY INHIBITOR: A drug that interferes with HIV’s ability to enter a cell.

ENV: An HIV gene that codes for the protein gp160, the precursor of the envelope proteins gp120 and gp41. See gp160; gp120; gp41.

ENVELOPE: In virology, a protein covering that packages the virus’s genetic information. The outer coat, or envelope, of HIV is composed of two layers of fatlike molecules called lipids taken from the membranes of human cells. Embedded in the envelope are numerous cellular proteins, as well as mushroom-shaped HIV proteins that protrude from the surface. Each mushroom is thought to consist of a cap made of four glycoprotein molecules called gp120, and a stem consisting of four gp41 molecules embedded in the envelope. The virus uses these proteins to attach to and infect cells.

ENZYME: A cellular protein whose shape allows it to hold together several other molecules in close proximity to each other. In this way, enzymes catalyze chemical reactions of other substances with little expenditure of energy and without being changed themselves.

EOSINOPHIL: A type of white blood cell, called granulocyte, that can digest microorganisms. The granules can be stained by eosin, an acid dye, for microscopic examination.

EOSINOPHILIC FOLLICULITIS: An inflammatory reaction around hair follicles, characterized by very itchy papules (small elevations or bumps on the skin) that may grow together to form plaques. The cause of this condition in persons with AIDS has yet to be established; it involves invasion of the follicles by eosinophils. Partially successful treatment has been reported with ultraviolet light, steroids, antihistamines, and itraconazole.

EPIDEMIC: A disease that spreads rapidly through a demographic segment of the population, such as everyone in a given geographic area (eg, a military base) or everyone of a certain age or sex (eg, the children or women of a region). Epidemic diseases can be spread from person to person or from a contaminated source, such as food or water.

EPIDEMIOLOGIC SURVEILLANCE: The ongoing and systematic collection, analysis, and interpretation of data about a disease or health condition. As part of a surveillance system to monitor the HIV epidemic in the U.S., the CDC, in collaboration with state and local health departments, other federal agencies, blood collection agencies, and medical research institutions, conducts standardized HIV seroprevalence surveys in designated subgroups of the U.S. population. Collecting blood samples for the purpose of surveillance is called serosurveillance.

EPIDEMIOLOGY: The study of incidence and distribution and control of a disease in a population.

EPISTAXIS: Nosebleed.

EPITHELIUM: The covering of the internal and external organs of the body. Also the lining of vessels, body cavities, glands, and organs. It consists of cells bound together by connective tissue and varies in the number of layers and the kinds of cells.

EPITOPE: A unique shape or marker carried on an antigen’s surface that triggers a corresponding antibody response. See Antibodies; Antigen.

EPSTEIN-BARR VIRUS (EBV): A herpeslike virus that causes one of the two kinds of mononucleosis (the other is caused by CMV). It infects the nose and throat and is contagious. EBV lies dormant in the lymph glands and has been associated with Burkitt’s lymphoma and hairy leukoplakia.

EQUIPOISE: An ethical requirement of clinical trials, equipoise means that the researchers are not certain which arm will receive the best treatment.

ERYTHEMA MULTIFORME: A skin disease characterized by popular (small, solid, usually conic elevations of the skin) or vesicular lesions (blisters) and reddening or discoloration of the skin, often in concentric zones about the lesion. Associated with many infections, collagen disease, drug sensitivities, allergies, and pregnancy. A severe form of this condition is Stevens-Johnson syndrome.

ERYTHEMA: Redness or inflammation of the skin or mucous membranes.

ERYTHROCYTES: Red blood cells whose major function is to carry oxygen to cells.

ERYTHROPOIETIN: A glycoprotein that stimulates production of red blood cells.

ETIOLOGY: The study or theory of the factors that cause disease.

EUPHORIA: A feeling of elation or well-being.

EXCIPIENT: An inactive ingredient added to a drug (ie, in pill form) to dilute it or to give it form or consistency.

EXCLUSION/INCLUSION CRITERIA: The medical or social standards determining whether a person may or may not be allowed to enter a clinical trial. For example, some trials may not include persons with chronic liver disease, or may exclude persons with certain drug allergies; others may exclude men or women or include only persons with a lowered T cell count.

EXOGENOUS: Developed or originating outside the body.

EXOTOXIN: A toxic substance, secreted by bacteria and released outside the bacterial cell.

EXPANDED ACCESS: Refers to any of the FDA procedures, such as compassionate use, parallel track, and treatment IND, that distribute experimental drugs to patients who are failing on currently available treatments for their condition and also are unable to participate in ongoing clinical trials.

EXPRESSION SYSTEM: In HIV vaccine production, cells into which an HIV gene has been inserted to produce specific HIV proteins.

FAILURE: Relating to HIV/AIDS, the inability to suppress and/or maintain HIV at undetectable levels. Treatment failure can be caused by many factors, including the development of resistance or nonadherence.

FALLOPIAN TUBES: Part of the female reproductive system. A pair of ducts opening at one end into the uterus and at the other end into the peritoneal cavity, over the ovary. Each tube serves as a passage through which the ovum (egg) is carried to the uterus and through which spermatozoa (sperm) move out toward the ovary.

FAS LIGAND: A cell surface molecule belonging to the tumor necrosis factor family, which binds to its receptor Fas, inducing apoptosis. Various cells express Fas, whereas Fas ligand is expressed predominantly on natural killer cells and activated T-cells. Fas and Fas ligand are involved in antiviral immune responses, elimination of tumor cells, and regulation of lymphocyte development.

FDA: See Food and Drug Administration.

FDC: See Follicular Dendritic Cells.

FEBRILE: Marked by fever.

FIRST-LINE TREATMENT: The preferred therapy for a particular condition.

FLOATERS: Drifting dark spots within the field of vision. Floaters can be caused by infection with CMV retinitis, but also can appear in people as a normal part of the aging process.

FOLIC ACID: A crystalline vitamin of the B complex that is used especially in the treatment of nutritional anemias. It occurs in green plants, fresh fruit, liver, and yeast. Also called folacin, folate, and vitamin B9.

FOLINIC ACID: Also called citrovorum factor. A metabolically active form of folic acid that has been used in cancer therapy to protect normal cells against methotrexate-a cancer chemotherapy agent. Also used to treat megaloblastic anemias.

FOLLICLE: A small anatomical sac, cavity, or deep narrow-mouthed depression (eg, a hair follicle).

FOLLICULAR DENDRITIC CELLS (FDC): Cells found in the germinal centers of lymphoid organs. FDCs have threadlike tentacles that form a weblike network to trap invaders and present them to other cells of the immune system for destruction. See Lymphoid Organs.

FOMITE: An inanimate object that can harbor pathogenic microorganisms and thus serve as an agent of transmission of infection.

FOOD AND DRUG ADMINISTRATION (FDA): The Department of Health and Human Services agency responsible for ensuring the safety and effectiveness of drugs, biologics, vaccines, and medical devices used (among others) in the diagnosis, treatment, and prevention of HIV infection, AIDS, and AIDS-related opportunistic infections. The FDA also works with the blood banking industry to safeguard the nation’s blood supply.

FREE DRUG: Drug that has not entered cells and can be found in the blood or other bodily fluids.

FREUND’S ADJUVANT: See Adjuvant.

FULMINATING: Occurring quickly and severely.

FUNCTIONAL ANTIBODY: An antibody that binds to an antigen and has an effect. For example, neutralizing antibodies inactivate HIV or prevent it from infecting other cells.

FUNGEMIA: Fungal infection disseminated through the bloodstream.

FUNGUS: 1. One of a group of primitive, nonvascular organisms including mushrooms, yeasts, rusts, and molds. 2. Fungi, which were once classified as plants, have since been reclassified as unmoving organisms that lack chlorophyll. Some fungi are single-celled but differ from bacteria in that they have a distinct nucleus and other cellular structures. Reproduction is accomplished by spores. Mycologists (scientists working with fungi) estimate that there are 100,000 species of fungi, ranging from baker’s yeast to dermatophytes (fungi that cause ringworm and athlete’s foot) to potentially invasive species such as Candida albicans and Aspergillus. As many as 150 of these organisms have now been linked to animal or human diseases.

FUSIN: See CXCR4.

FUSION MECHANISM: Fusion is an integral step in the process whereby HIV enters cells. Researchers have found that in addition to the primary receptor, the CD4 molecule, other cofactors, such as CCR5 and CXCR4, are needed in order for HIV to fuse with the membranes of the immune system cells.

GALLSTONE: A hard mass of cholesterol, calcium bilirubinate, and calcium carbonate formed in the gallbladder or biliary passages.

GAMMA GLOBULIN: 1. One of the proteins in blood serum that contains antibodies. 2. Passive immunizing agents obtained from pooled human plasma. See Globulins, Immunoglobulins.

GAMMA INTERFERON: A T cell-derived stimulating substance that suppresses virus reproduction, stimulates other T cells, and activates macrophage cells.

GANGLION: A mass of nervous tissue, composed principally of nerve-cell bodies, usually lying outside the central nervous system.

GASTRITIS: Inflammation of the stomach’s mucous membranes.

GASTROENTERITIS: Inflammation of the lining membrane of the stomach and intestines.

GASTROINTESTINAL (GI): Relating to the stomach and intestine.

GENE THERAPY: Any of a number of experimental treatments in which cell genes are altered. Some gene therapies attempt to provoke new immune activity; some try to render cells resistant to infection; and others involve the development of enzymes that destroy viral or cancerous genetic material within cells.

GENE: 1. A unit of DNA that carries information for the biosynthesis of a specific product in the cell. 2. Ultimate unit by which inheritable characteristics are transmitted to succeeding generations in all living organisms. Genes are contained by, and arranged along the length of, the chromosome. The gene is composed of deoxyribonucleic acid (DNA). Each chromosome of a species has a definite number and arrangement of genes, which govern both the structure and metabolic functions of the cells and thus of the entire organism. Genes provide information for the synthesis of enzymes and other proteins and specify when these substances are to be made. Alteration of either gene number or arrangement can result in mutation (a change in the inheritable traits).

GENETIC ENGINEERING: New research techniques that manipulate the DNA (genetic material) of cells. The genesplicing technique, which produces recombinant DNA, is a method of transporting selected genes from one species to another. The genes, which are actually portions of molecules of DNA, are removed from the donor (insect, plant, mammal, or other organism) and spliced into the genetic material of a virus; the virus is then allowed to infect recipient bacteria. In this way the bacteria become recipients of both viral and foreign genetic material. When the virus replicates within the bacteria, large quantities of the foreign as well as viral material are made.

GENITAL ULCER DISEASE: Ulcerative lesions on the genitals usually caused by a sexually transmitted disease such as herpes, syphilis, or chancroid. The presence of genital ulcers may increase the risk of transmitting HIV.

GENITAL WARTS: See Condyloma.

GENITOURINARY TRACT: The organs concerned with the production and excretion of urine and those concerned with reproduction. Also called genitourinary system, urogenital system, or urogenital tract.

GENOME: The complete set of genes in the chromosomes of each cell of a particular organism.

GENOTYPE: An organism’s genetic makeup.

GENOTYPIC ASSAY: A test that determines the genotype of an organism, such as a virus. With respect to HIV, a genotypic assay can provide information about viral mutations, which is potentially useful in determining an effective drug regimen.

GERMINAL CENTERS: One of a series of follicles or cavities around the periphery of lymph nodes. Germinal centers are the site of antibody production and are populated mostly by B cells but include a few T cells and macrophages. As HIV infection progresses, the germinal centers gradually decay.

GIARDIASIS: A common protozoal infection of the small intestine, spread via contaminated food and water and direct person-to-person contact.

GLOBULINS: Simple proteins found in the blood serum, which contain various molecules central to the immune system function. See Immunoglobulin.

GLUCOSE: A naturally occurring sugar found in fruits and honey.

GLYCOPROTEIN: A conjugated protein in which the nonprotein group is a carbohydrate (eg, a sugar molecule); also called glucoprotein.

GP120: Glycoprotein 120, a protein that protrudes from the surface of HIV and binds to CD4 cells. In a two-step process that allows HIV to breach the membrane of T cells, gp120-CD4 complex refolds to reveal a second structure that binds to CCR5, one of several chemokine co-receptors used by the virus to gain entry into T cells.

GP160: Glycoprotein 160, a precursor of HIV envelope proteins gp41 and gp120.

GP41: Glycoprotein 41, a protein embedded in the outer envelope of HIV. Plays a key role in HIV’s infection of CD4 cells by facilitating the fusion of the viral and cell membranes.

GRADE 1-4: Adverse events are categorized from Grade 1 to Grade 4. Grade 1 adverse events are usually transient and have little impact on a person’s day-to-day life. Grade 4 adverse events are intolerable, irreversible, or pose a threat of death.

GRANULOCYTE: A type of white blood cell filled with granules of compounds that digest microorganisms. Granulocytes are part of the innate immune system and have broad-based activity. They do not respond only to specific antigens, as do B cells and T cells. Basophils, eosinophils, and neutrophils are all granulocytes.

GRANULOCYTOPENIA: A lack or low level of granulocytes in the blood. Often used interchangeably with neutropenia.

GROWTH FACTOR: A molecule that has an effect on proliferation and maturation of cells. These proteins can also influence the growth rate of some cancers.

GUANOSINE: A nucleoside combining the base guanine with D-ribose. One of the building blocks of DNA and RNA.

HAART: See Highly Active Antiretroviral Therapy.

HALF-LIFE: The time required for the body to eliminate half the amount of a drug.

HEALTH RESOURCES AND SERVICES ADMINISTRATION (HRSA): An agency in the Department of Health and Human Services that puts primary health-care providers and services in the places they are needed most. HRSA administers the Ryan White CARE Act Titles I, II, III(b), IV, SPNS, and AETCs (see Ryan White CARE Act) to provide treatment and services for those affected by HIV/AIDS. HRSA administers programs to demonstrate how communities can organize their health-care resources to develop an integrated, comprehensive, culturally competent system to care for those with AIDS and HIV infection. HRSA also administers education and training programs for health-care providers and community service workers who care for persons living with HIV/AIDS.

HELPER T CELLS: Lymphocytes bearing the CD4 marker that are responsible for many immune system functions, including turning antibody production on and off.

HELPER/SUPPRESSOR RATIO (OF T CELLS): T cells are lymphocytes (white blood cells) that are formed in the thymus and are part of the immune system. They have been found to be abnormal in persons with AIDS. The normal ratio of helper T cells (CD4 cells) to suppressor T cells (CD8 cells) is approximately 2

HEMATOCRIT: A laboratory measurement that determines the percentage of packed red blood cells in a given volume of blood. In women, red blood cells are normally 37 to 47 percent of the blood, and in men, red blood cells are normally 40 to 54 percent of the blood.

HEMATOTOXIC: Poisonous to the blood or bone marrow.

HEMATURIA: The presence of blood or red blood cells in the urine.

HEMODIALYSIS: Usually a treatment for end-stage liver disease, hemodialysis involves the use of a machine to perform the liver’s normal functions.

HEMOGLOBIN: The component of red blood cells that carries oxygen.

HEMOLYSIS: The rupture of red blood cells.

HEMOPHILIA: An inherited disease that affects mostly males and prevents normal blood clotting. It is treated by lifelong injections of a synthetic version of the clotting factor lacking in persons with the disease.

HEPATIC: Pertaining to the liver.

HEPATITIS: Inflammation of the liver. May be caused by bacterial or viral infection, parasitic infestation, alcohol, drugs, toxins, or transfusion of incompatible blood. Although many cases of hepatitis are not a serious health threat, the disease can become chronic and sometimes lead to liver failure and death.

HEPATOMEGALY: Enlargement of the liver.

HEPATOTOXICITY: Liver toxicity. Drugs that cause liver damage are hepatotoxic.

HERPETIFORM: Resembling herpes.

HHS: See Department of Health and Human Services.

HIGH-DENSITY LIPOPROTEIN CHOLESTEROL (HDL-C): A lipoprotein that takes cholesterol from the blood for breakdown by the liver. HDL contains more protein than fat.

HIGHLY ACTIVE ANTIRETROVIRAL THERAPY (HAART): Combination therapy against HIV, which typically includes three drugs from at least two different classes.

HIRSUTISM: Excessive bodily and facial hair.

HISTOCOMPATIBILITY TESTING: A method of matching self-antigens from tissue of a potential transplant donor with those of a recipient. The closer the match, the better the chance that the transplant will not be rejected. See Human Leukocyte Antigens.

HIV DISEASE: After contracting HIV, a person undergoes acute HIV infection, a period that lasts 4 to 7 weeks. HIV disseminates throughout the body and the number of CD4 cells plummets. The body then evokes an immune response, resulting in a decrease in detectable viremia and a prolonged period of clinical latency that lasts about ten years on average. During clinical latency, the CD4 cell count steadily declines until it reaches a critical level, below which there is substantial risk of OIs. See Acquired Immunodeficiency Syndrome; Human Immunodeficiency Virus Type 1; Acute HIV Infection.

HIV SETPOINT: The equilibrium viral load that arises after acute infection and reflects the balance between HIV replication and immune activity. This equilibrium is stable for some years. Without anti-HIV therapy, the magnitude of the setpoint correlates with the speed of disease progression.

HIV VIRAL LOAD: See Viral Load.

HIV-1: See Human Immunodeficiency Virus Type 1.

HIV-2: See Human Immunodeficiency Virus Type 2.

HLA: See Human Leukocyte Antigens.

HOLISTIC MEDICINE: Healing traditions that promote the protection and restoration of health through theories reputedly based on the body’s natural ability to heal itself and by understanding the various ways body components affect each other and are influenced by the environment.

HOMOLOGOUS: Similar in appearance or structure, but not necessarily in function.

HORMONE: An active chemical substance formed in one part of the body and carried in the blood to other parts of the body, where it stimulates or suppresses cell and tissue activity. See Pituitary Gland.

HOST FACTORS: The body’s potent mechanisms for containing HIV, including immune system cells called CD8 cells.

HOST: A plant or animal harboring another organism.

HRSA: See Health Resources and Services Administration.

HTLV-I: See Human T Cell Lymphotropic Virus Type I.

HTLV-II: See Human T Cell Lymphotropic Virus Type II.

HUMAN IMMUNODEFICIENCY VIRUS TYPE 1 (HIV-1): 1. The retrovirus isolated and recognized as the etiologic agent (cause) of AIDS. HIV-1 is classified as a lentivirus in a subgroup of retroviruses. See Lentivirus; Retrovirus. Most viruses and all bacteria, plants, and animals have genetic codes made up of DNA, which uses RNA to build specific proteins. The genetic material of a retrovirus such as HIV is RNA. HIV inserts its own RNA into the host cell DNA, preventing the host cell from carrying out its natural functions and turning it into an HIV “factory.”

HUMAN IMMUNODEFICIENCY VIRUS TYPE 2 (HIV-2): A virus closely related to HIV-1 that also causes AIDS. It was first isolated in West Africa. Although HIV-1 and HIV-2 are similar in their viral structure, modes of transmission, and resulting opportunistic infections, they differ in their geographic patterns of infection.

HUMAN LEUKOCYTE ANTIGENS (HLA): Markers that identify cells as “self” and prevent the immune system from attacking them.

HUMAN T CELL LYMPHOTROPIC VIRUS TYPE I (HTLV-I): HTLV-I and HTLV-II, like all retroviruses, are single-stranded RNA viruses that replicate through a DNA intermediate. HTLV-I has an affinity for T lymphocytes; it appears to be the causative agent of certain T cell leukemias, T cell lymphomas, and HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP).

HUMAN T CELL LYMPHOTROPIC VIRUS TYPE II (HTLVII): A virus closely related to HTLV-I, HTLV-II is found predominantly in injection drug users and Native Americans, as well as Caribbean and South American Indian groups. HTLV-II has not been clearly linked to any disease, but has been associated with several cases of myelopathy/tropical spastic paraparesis (HAM/TSP)-like neurological disease.

HUMORAL IMMUNITY: The branch of the immune system that relies primarily on antibodies.

HYBRID: Offspring produced from mating plants or animals from different species, varieties, or genotypes.

HYBRIDOMA: A hybrid cell produced by the fusion of an antibody-producing lymphocyte with a tumor cell. Hybridomas are used in the production of monoclonal antibodies.

HYPERBILIRUBINEMIA: Excess bilirubin in the blood.

HYPERGAMMAGLOBULINEMIA: Abnormally high levels of immunoglobulins in the blood. Common in persons with HIV.

HYPERGLYCEMIA: High blood sugar.

HYPERKALEMIA: High levels of potassium in the blood.

HYPERLIPIDEMIA: High levels of lipids in the blood.

HYPERPLASIA: Abnormal increase in the elements composing a part (as tissue cells).

HYPERSENSITIVITY: An exaggerated immune response to a foreign agent. Some hypersensitivity reactions can be fatal.

HYPERTENSION: High blood pressure.

HYPERTRIGLYCERIDEMIA: High triglyceride levels in the blood.

HYPOGAMMAGLOBULINEMIA: Abnormally low levels of immunoglobulins. See Antibodies.

HYPOGLYCEMIA: Low blood sugar.

HYPOTENSION: Low blood pressure.

HYPOTHESIS: A specific statement or proposition, stated in a testable (researchable) form, predicting a particular relationship among multiple variables.

HYPOXIA: Reduction of oxygen supply to tissue.

IDIOPATHIC: Without a known cause.

IDIOTYPES: The unique and characteristic parts of an antibody’s variable region, which can themselves serve as antigens. See Antibodies; Antigen.

IDU: Injection drug use or user.

IHS: See Indian Health Service.

IMMUNE COMPLEX: Clusters formed when antigens and antibodies bind together.

IMMUNE DEFICIENCY: A breakdown or inability of certain parts of the immune system to function, thus making people susceptible to certain diseases that they would not ordinarily develop.

IMMUNE RESPONSE: The immune system’s reaction against foreign substances.

IMMUNE SYSTEM: The body’s complicated natural defense against disruption caused by invading foreign agents (eg, microbes, viruses). There are two aspects of the immune system’s response to disease

IMMUNE THROMBOCYTOPENIC PURPURA (ITP): Also idiopathic immune thrombocytopenic purpura. A condition in which the body produces antibodies against the platelets in the blood, which are cells responsible for blood clotting. ITP is very common in persons infected with HIV.

IMMUNITY: A natural or acquired resistance to a specific disease. Immunity may be partial or complete, long lasting or temporary.

IMMUNIZATION: Administration of antigenic components of an infectious agent to stimulate a protective immune response.

IMMUNOCOMPETENT: 1. Capable of developing an immune response. 2. Possessing a normal immune system.

IMMUNOCOMPROMISED: Refers to an immune system in which the ability to resist or fight off infections and tumors is subnormal.

IMMUNODEFICIENCY: Breakdown in immunocompetence when certain parts of the immune system no longer function. This condition makes a person more susceptible to certain diseases.

IMMUNOGEN: A substance, also called an antigen, capable of provoking an immune response.

IMMUNOGENICITY: The ability of an antigen or vaccine to stimulate an immune response.

IMMUNOGLOBULIN (IG): A general term for antibodies, which bind onto invading organisms, leading to their destruction. There are five classes

IMMUNOGLOBULIN A (IGA): An immunoglobulin found in body fluids such as tears and saliva and in the respiratory, reproductive, urinary, and gastrointestinal tracts. IgA protects the body’s mucosal surfaces from infection.

IMMUNOGLOBULIN G (IGG): The prominent type of immunoglobulin existing in the blood.

IMMUNOMODULATOR: Any substance that influences the immune system. See Interleukins; Immunostimulant; Immunosuppression.

IMMUNOSTIMULANT: Any agent or substance that triggers or enhances the body’s defense; also called immunopotentiator.

IMMUNOSUPPRESSION: A state of the body in which the immune system is damaged and does not perform its normal functions. Immunosuppression may be induced by drugs (eg, in chemotherapy) or result from certain disease processes, such as HIV infection.

IMMUNOTHERAPY: Treatment aimed at reconstituting an impaired immune system.

IMMUNOTOXIN: A plant or animal toxin (ie, poison) that is attached to a monoclonal antibody and used to destroy a specific target cell.

IN UTERO: Within the uterus.

IN VITRO (“IN GLASS”): An artificial environment created outside a living organism (eg, a test tube or culture dish) to study a disease or process.

IN VIVO (“IN LIFE”): Studies conducted within living organisms (eg, animal or human studies).

INCIDENCE: The number of new cases (eg, of a disease) occurring in a given population over a certain period.

INCLUSION/EXCLUSION CRITERIA: The medical or social standards determining whether a person may or may not be allowed to enter a clinical trial. For example, some trials may exclude persons with chronic liver disease or with certain drug allergies; others may exclude men or women, or include only persons with a lowered T cell count.

INCUBATION PERIOD: The time interval between the initial infection with a pathogen (eg, HIV) and the appearance of the first symptom or sign of disease.

IND: See Investigational New Drug.

INDIAN HEALTH SERVICE (IHS): The federal agency charged with administering the health programs for American Indians and Alaska Natives (AI/AN), who are enrolled members of federally recognized Indian tribes.

INFECTION: The state or condition in which the body (or part of the body) is invaded by an infectious agent (eg, a bacterium, fungus, or virus), which multiplies and produces an injurious effect (active infection). As related to HIV

INFECTIOUS: An infection capable of being transmitted by direct or intimate contact (eg, sex).

INFORMED CONSENT: The permission granted by a participant in a research study (including medical research) after he/she has received comprehensive information about the study. This is a statement of trust between the institution performing the research procedure and the person (eg, a patient) on whom the research procedures are to be performed. This includes the type of protection available to people considering entering a drug trial. Before entering the trial, participants must sign a consent form that contains an explanation of: (a) why the research is being done, (b) what the researchers want to accomplish, (c) what will be done during the trial and for how long, (d) what the risks associated with the trial are, (e) what benefits can be expected from the trial, (f) what other treatments are available, and (g) the participant’s right to leave the trial at any time. Informed consent also pertains to situations where certain tests need to be performed. See Clinical Trial.

INFUSION: The process of administering therapeutic fluid to an individual by slowly injecting a dilute solution of the compound into a vein. Infusions are often used when the digestive system does not absorb appreciable quantities of a drug or when the drug is too toxic or the volume is too large to be given by quick injection.

INHIBITOR: As it pertains to drug design, a drug that slows or blocks physiologic, chemical, or enzymatic action.

INHIBITORS (NRTIS): Also called nucleoside or nucleotide analogs (nucleotide analogs are phosphorylated nucleoside analogs). These anti-HIV drugs include AZT, 3TC, d4T, ddC, ddI, abacavir, and tenofovir (a nucleotide analog). These agents block reverse transcription by acting as chain terminators.

INHIBITORY CONCENTRATION 50 (IC50): The concentration of drug needed to reduce HIV replication in cell culture by 50%.

INHIBITORY CONCENTRATION 90 (IC90): The concentration of drug needed to reduce HIV replication in cell culture by 90%.

INHIBITORY QUOTIENT: Minimum blood level obtained divided by the IC50.

INOCULATION: The introduction of a substance (inoculum; eg, a vaccine, serum, or virus) into the body to produce or to increase immunity to the disease or condition associated with the substance. See Vaccine.

INSTITUTIONAL REVIEW BOARD (IRB): A committee of physicians, statisticians, researchers, community advocates, and others that ensures that a clinical trial is ethical and that the rights of study participants are protected. All clinical trials in the U.S. must be approved by an IRB before they begin. Every institution that conducts or supports biomedical or behavioral research involving humans must, by federal regulation, have an IRB that initially approves and periodically reviews the research so as to protect the rights of people.

INSULIN: A hormone that controls blood sugar levels. Diabetes is caused by a lack of insulin or resistance to insulin.

INTEGRASE: A little-understood enzyme that plays a vital role in the HIV-infection process. Integrase inserts HIV’s genes into a cell’s normal DNA. It operates after reverse transcriptase has created a DNA version of the RNA form of HIV genes present in virus particles. Substances that inhibit integrase are being studied in HIV-positive patients.

INTEGRATION: The process by which the different parts of an organism are made a functional and structural whole, especially through the activity of the nervous system and of hormones. As related to HIV

INTENT TO TREAT: Analysis of clinical trial results that includes all data from patients in the groups to which they were randomized (ie, assigned through random distribution) even if they never received the treatment.

INTERLEUKINS: Multifunctional cytokines synthesized by lymphocytes, monocytes, macrophages, and other cells. Cytokines are small, hormonelike molecules that regulate the intensity and duration of the immune response and mediate cell-to-cell communication. Once the structure of a cytokine is determined, it is renamed interleukin.

INTERNATIONAL UNIT (IU): The amount of a substance (eg, vitamins, hormones, enzymes, drugs) that produces a specific effect, as defined by an international body and accepted internationally.

INTERSTITIAL: Relating to or situated in the small, narrow spaces between tissues or parts of an organ.

INTRACELLULAR CONCENTRATION: The concentration (eg, of a drug) within a cell.

INTRACELLULAR: Within a cell.

INTRACRANIAL: Within the cranium.

INTRAMUSCULAR (IM): Injected directly into a muscle.

INTRAOCULAR: Within the eyeball.

INTRAPARTUM: During labor and childbirth.

INTRATHECAL: Injected into the fluid surrounding the spinal cord.

INTRAVENOUS (IV): Of or pertaining to the inside of a vein, as of a thrombus. Injection directly into a vein.

INTRAVITREAL: Within the vitreous humor of the eye.

INVESTIGATIONAL NEW DRUG (IND): The status of an experimental drug after the FDA agrees that it can be tested in people.

IRB: See Institutional Review Board.

ISOLATE: An individual (as a spore or a single organism), viable part of an organism (as a cell), or a strain that has been separated (as from diseased tissue, contaminated water, or the air) from the whole. Also, a pure culture produced from such an isolate. A particular strain of HIV taken from a patient.

ITP: See Immune Thrombocytopenic Purpura.

IDIOPATHIC: Without a known cause.

IDIOTYPES: The unique and characteristic parts of an antibody’s variable region, which can themselves serve as antigens. See Antibodies; Antigen.

IDU: Injection drug use or user.

IHS: See Indian Health Service.

IMMUNE COMPLEX: Clusters formed when antigens and antibodies bind together.

IMMUNE DEFICIENCY: A breakdown or inability of certain parts of the immune system to function, thus making people susceptible to certain diseases that they would not ordinarily develop.

IMMUNE RESPONSE: The immune system’s reaction against foreign substances.

IMMUNE SYSTEM: The body’s complicated natural defense against disruption caused by invading foreign agents (eg, microbes, viruses). There are two aspects of the immune system’s response to disease

IMMUNE THROMBOCYTOPENIC PURPURA (ITP): Also idiopathic immune thrombocytopenic purpura. A condition in which the body produces antibodies against the platelets in the blood, which are cells responsible for blood clotting. ITP is very common in persons infected with HIV.

IMMUNITY: A natural or acquired resistance to a specific disease. Immunity may be partial or complete, long lasting or temporary.

IMMUNIZATION: Administration of antigenic components of an infectious agent to stimulate a protective immune response.

IMMUNOCOMPETENT: 1. Capable of developing an immune response. 2. Possessing a normal immune system.

IMMUNOCOMPROMISED: Refers to an immune system in which the ability to resist or fight off infections and tumors is subnormal.

IMMUNODEFICIENCY: Breakdown in immunocompetence when certain parts of the immune system no longer function. This condition makes a person more susceptible to certain diseases.

IMMUNOGEN: A substance, also called an antigen, capable of provoking an immune response.

IMMUNOGENICITY: The ability of an antigen or vaccine to stimulate an immune response.

IMMUNOGLOBULIN (IG): A general term for antibodies, which bind onto invading organisms, leading to their destruction. There are five classes

IMMUNOGLOBULIN A (IGA): An immunoglobulin found in body fluids such as tears and saliva and in the respiratory, reproductive, urinary, and gastrointestinal tracts. IgA protects the body’s mucosal surfaces from infection.

IMMUNOGLOBULIN G (IGG): The prominent type of immunoglobulin existing in the blood.

IMMUNOMODULATOR: Any substance that influences the immune system. See Interleukins; Immunostimulant; Immunosuppression.

IMMUNOSTIMULANT: Any agent or substance that triggers or enhances the body’s defense; also called immunopotentiator.

IMMUNOSUPPRESSION: A state of the body in which the immune system is damaged and does not perform its normal functions. Immunosuppression may be induced by drugs (eg, in chemotherapy) or result from certain disease processes, such as HIV infection.

IMMUNOTHERAPY: Treatment aimed at reconstituting an impaired immune system.

IMMUNOTOXIN: A plant or animal toxin (ie, poison) that is attached to a monoclonal antibody and used to destroy a specific target cell.

IN UTERO: Within the uterus.

IN VITRO (“IN GLASS”): An artificial environment created outside a living organism (eg, a test tube or culture dish) to study a disease or process.

IN VIVO (“IN LIFE”): Studies conducted within living organisms (eg, animal or human studies).

INCIDENCE: The number of new cases (eg, of a disease) occurring in a given population over a certain period.

INCLUSION/EXCLUSION CRITERIA: The medical or social standards determining whether a person may or may not be allowed to enter a clinical trial. For example, some trials may exclude persons with chronic liver disease or with certain drug allergies; others may exclude men or women, or include only persons with a lowered T cell count.

INCUBATION PERIOD: The time interval between the initial infection with a pathogen (eg, HIV) and the appearance of the first symptom or sign of disease.

IND: See Investigational New Drug.

INDIAN HEALTH SERVICE (IHS): The federal agency charged with administering the health programs for American Indians and Alaska Natives (AI/AN), who are enrolled members of federally recognized Indian tribes.

INFECTION: The state or condition in which the body (or part of the body) is invaded by an infectious agent (eg, a bacterium, fungus, or virus), which multiplies and produces an injurious effect (active infection). As related to HIV

INFECTIOUS: An infection capable of being transmitted by direct or intimate contact (eg, sex).

INFORMED CONSENT: The permission granted by a participant in a research study (including medical research) after he/she has received comprehensive information about the study. This is a statement of trust between the institution performing the research procedure and the person (eg, a patient) on whom the research procedures are to be performed. This includes the type of protection available to people considering entering a drug trial. Before entering the trial, participants must sign a consent form that contains an explanation of: (a) why the research is being done, (b) what the researchers want to accomplish, (c) what will be done during the trial and for how long, (d) what the risks associated with the trial are, (e) what benefits can be expected from the trial, (f) what other treatments are available, and (g) the participant’s right to leave the trial at any time. Informed consent also pertains to situations where certain tests need to be performed. See Clinical Trial.

INFUSION: The process of administering therapeutic fluid to an individual by slowly injecting a dilute solution of the compound into a vein. Infusions are often used when the digestive system does not absorb appreciable quantities of a drug or when the drug is too toxic or the volume is too large to be given by quick injection.

INHIBITOR: As it pertains to drug design, a drug that slows or blocks physiologic, chemical, or enzymatic action.

INHIBITORS (NRTIS): Also called nucleoside or nucleotide analogs (nucleotide analogs are phosphorylated nucleoside analogs). These anti-HIV drugs include AZT, 3TC, d4T, ddC, ddI, abacavir, and tenofovir (a nucleotide analog). These agents block reverse transcription by acting as chain terminators.

INHIBITORY CONCENTRATION 50 (IC50): The concentration of drug needed to reduce HIV replication in cell culture by 50%.

INHIBITORY CONCENTRATION 90 (IC90): The concentration of drug needed to reduce HIV replication in cell culture by 90%.

INHIBITORY QUOTIENT: Minimum blood level obtained divided by the IC50.

INOCULATION: The introduction of a substance (inoculum; eg, a vaccine, serum, or virus) into the body to produce or to increase immunity to the disease or condition associated with the substance. See Vaccine.

INSTITUTIONAL REVIEW BOARD (IRB): A committee of physicians, statisticians, researchers, community advocates, and others that ensures that a clinical trial is ethical and that the rights of study participants are protected. All clinical trials in the U.S. must be approved by an IRB before they begin. Every institution that conducts or supports biomedical or behavioral research involving humans must, by federal regulation, have an IRB that initially approves and periodically reviews the research so as to protect the rights of people.

INSULIN: A hormone that controls blood sugar levels. Diabetes is caused by a lack of insulin or resistance to insulin.

INTEGRASE: A little-understood enzyme that plays a vital role in the HIV-infection process. Integrase inserts HIV’s genes into a cell’s normal DNA. It operates after reverse transcriptase has created a DNA version of the RNA form of HIV genes present in virus particles. Substances that inhibit integrase are being studied in HIV-positive patients.

INTEGRATION: The process by which the different parts of an organism are made a functional and structural whole, especially through the activity of the nervous system and of hormones. As related to HIV

INTENT TO TREAT: Analysis of clinical trial results that includes all data from patients in the groups to which they were randomized (ie, assigned through random distribution) even if they never received the treatment.

INTERLEUKINS: Multifunctional cytokines synthesized by lymphocytes, monocytes, macrophages, and other cells. Cytokines are small, hormonelike molecules that regulate the intensity and duration of the immune response and mediate cell-to-cell communication. Once the structure of a cytokine is determined, it is renamed interleukin.

INTERNATIONAL UNIT (IU): The amount of a substance (eg, vitamins, hormones, enzymes, drugs) that produces a specific effect, as defined by an international body and accepted internationally.

INTERSTITIAL: Relating to or situated in the small, narrow spaces between tissues or parts of an organ.

INTRACELLULAR CONCENTRATION: The concentration (eg, of a drug) within a cell.

INTRACELLULAR: Within a cell.

INTRACRANIAL: Within the cranium.

INTRAMUSCULAR (IM): Injected directly into a muscle.

INTRAOCULAR: Within the eyeball.

INTRAPARTUM: During labor and childbirth.

INTRATHECAL: Injected into the fluid surrounding the spinal cord.

INTRAVENOUS (IV): Of or pertaining to the inside of a vein, as of a thrombus. Injection directly into a vein.

INTRAVITREAL: Within the vitreous humor of the eye.

INVESTIGATIONAL NEW DRUG (IND): The status of an experimental drug after the FDA agrees that it can be tested in people.

IRB: See Institutional Review Board.

ISOLATE: An individual (as a spore or a single organism), viable part of an organism (as a cell), or a strain that has been separated (as from diseased tissue, contaminated water, or the air) from the whole. Also, a pure culture produced from such an isolate. A particular strain of HIV taken from a patient.

ITP: See Immune Thrombocytopenic Purpura.

JAUNDICE: Yellow pigmentation of the skin and whites of the eyes caused by elevated blood levels of bilirubin. The condition is associated with either liver or gallbladder disease or excessive destruction of red blood cells.

KARNOFSKY SCALE: A performance scale between 0 and 100 for rating a person’s usual activities; used to evaluate a patient’s progress after a therapeutic procedure. A score of 100 signifies normal physical abilities with no evidence of disease. Decreasing numbers indicate a reduced ability to perform daily living activities.

KILLER T CELLS: Because viruses lurk inside host (eg, human) cells where antibodies cannot reach them, the only way they can be eliminated is by killing the infected host cell. To do this, the immune system uses a kind of white blood cell, called killer T cells. These cells act only when they encounter another cell that carries a “marker” (ie, a protein) that links it to a foreign protein-that of the invading virus. Killer T cells can themselves become infected by HIV or other viruses, or transformed by cancer. Also known as cytotoxic T cells (or cytotoxic T lymphocytes). See Natural Killer Cell; Null Cell; T Cell.

KUPFFER CELLS: Specialized macrophages in the liver.

LACTIC ACIDOSIS: High levels of lactic acid in the blood, which is potentially fatal. Symptoms include nausea, vomiting, fatigue, and shortness of breath. The use of nucleoside analogs can contribute to lactic acidosis.

LAI: A group of closely related HIV isolates that includes the LAV, IIIB, and BRU strains of HIV. Used in HIV vaccine development.

LAK CELLS: Lymphocytes transformed in the laboratory into lymphokine activated killer cells, which attack tumor cells.

LANGERHANS CELLS: Dendritic cells in the skin that pick up an antigen and transport it to the lymph nodes.

LAS: See Lymphadenopathy Syndrome.

LATENCY: An inactive or resting period during a disease process. Clinical latency is an asymptomatic period in the early years of HIV infection. The latency period is characterized in the peripheral blood by near-normal CD4 counts. Recent research indicates that HIV remains quite active in the lymph nodes during this period. Cellular latency is the period after HIV has integrated its genome into a cell’s DNA but has not yet begun to replicate.

LAV (LYMPHADENOPATHY ASSOCIATED VIRUS): See Human Immunodeficiency Virus Type I.

LAVAGE: Washing a body cavity or internal organ to obtain a sample or as a part of treatment.

LD50 (LETHAL DOSE 50): The amount of a substance sufficient to kill 50% of the test animals. Also called the median lethal dose.

LEAN BODY MASS: The portion of the body that is made up by muscle and organ tissue.

LENTIVIRUS: “Slow” virus characterized by a long interval between infection and the onset of symptoms. HIV is a lentivirus, as is the simian immunodeficiency virus (SIV) that infects nonhuman primates.

LESION: A general term to describe an area of altered tissue (eg, the infected patch or sore in a skin disease).

LEUKOCYTES: Any of the various white blood cells that together make up the immune system. Neutrophils, lymphocytes, and monocytes are all leukocytes.

LEUKOCYTOSIS: An abnormally high number of leukocytes in circulation. This condition can occur during acute infection, inflammation, hemorrhage, and other conditions. Generally, a cell count greater than 10,000 cells/mm³ indicates leukocytosis.

LEUKOPENIA: An abnormally low number of white blood cells in circulation. The lower limit is generally regarded as 4,000 to 5,000 cells/mm³.

LIMIT OF QUANITIFICATION: The lowest level that a test can measure. For example, some viral load tests cannot measure below <400 or 50 copies/mL, which is therefore their limit of quantification. See Sensitivity.

LIP: See Lymphoid Interstitial Pneumonitis.

LIPID: Any of a group of fats and fatlike compounds, including sterols, fatty acids, and many other substances.

LIPOATROPHY: Loss of subcutaneous fat, eg, in the face and limbs.

LIPODYSTROPHY: Defective metabolism of fat. Includes fat loss, such as wasting in the face, arms, and legs, and fat redistribution, such as fat accumulation in the upper back or trunk.

LIPOSOME: A spherical particle in an aqueous (watery) medium (eg, inside a cell) formed by a lipid bilayer enclosing an aqueous compartment. Microscopic globules of lipids are manufactured to enclose medications. The liposome’s fatty layer is supposed to protect and confine the enclosed drug until the liposome binds with the outer membrane of target cells. By delivering treatments directly to the cells needing them, drug efficacy may be increased while overall toxicity is reduced.

LIVE VECTOR VACCINE: As pertaining to HIV, a vaccine that uses an attenuated (weakened) virus or bacterium to carry pieces of HIV into the body to directly stimulate a cell-mediated immune response.

LIVER FUNCTION TEST: A test that measures the blood serum level of any of several enzymes (eg, ALT, AST) produced by the liver. An elevated liver function test is a sign of possible liver damage.

LOG: Changes in viral load are often reported as logarithmic or “log changes.” This mathematical term denotes a change in value of what is being measured by a factor of 10. For example, if the baseline viral load by PCR were 20,000 copies/mL plasma, then a 1-log increase equals a 10-fold (10 times) increase, or 200,000 copies/mL plasma. A 2-log increase equals 2,000,000 copies/mL plasma, or a 100-fold increase. Using the same starting point of 20,000 copies/mL plasma, a 1-log decrease means that the viral load has dropped to 2,000 copies/mL. A 2-log decrease equals a viral load of 200 copies/mL plasma. An easy way to figure out log changes is either to drop the last “0” or add “0” to the original number.

LONG TERMINAL REPEAT SEQUENCE (LTR): The genetic material at each end of the HIV genome. When the HIV genome is integrated into a cell’s own genome, the LTR interacts with cellular and viral factors to trigger the transcription of the HIV-integrated HIV DNA genes into an RNA form that is packaged in new virus particles. Activation of LTR is a major step in triggering HIV replication.

LONG-TERM NONPROGRESSORS: Individuals who have been living with HIV for at least 7 to 12 years (different authors use different time spans) and have stable CD4 cell counts of 600 or more cells per cubic millimeter of blood, no HIV-related diseases, and no previous antiretroviral therapy.

LONGITUDINAL STUDY: A study that follows volunteers over time.

LOW-DENSITY LIPOPROTEIN (LDL): A lipoprotein that carries cholesterol from the liver to body tissues. LDL contains more fat than protein.

LTR: See Long Terminal Repeat Sequence.

LUMBAR PUNCTURE: A procedure in which sero-spinal fluid from the subarachnoid space in the lumbar region is tapped for examination. Also known as spinal tap.

LUMBAR: 1. Lower back region. 2. Of, relating to, or constituting the vertebrae between the thoracic vertebrae and the sacrum region. The sacrum is the triangular bone made up of five fused vertebrae and forming the posterior section of the pelvis. The thorax is the part of the human body between the neck and the diaphragm, partially encased by the ribs and containing the heart and lungs (ie, the chest).

LYMPH NODES: Small, bean-sized organs of the immune system, distributed widely throughout the body. Lymph fluid is filtered through the lymph nodes in which all types of lymphocytes take up temporary residence. Antigens that enter the body find their way into lymph or blood and are filtered out by the lymph nodes or spleen respectively, for attack by the immune system.

LYMPH: A transparent, slightly yellow fluid that carries lymphocytes. Lymph is derived from tissue fluids collected from all parts of the body and is returned to the blood via lymphatic vessels.

LYMPHADENOPATHY SYNDROME (LAS): Swollen, firm, and possibly tender lymph nodes. The cause may range from an infection such as HIV, the flu, or mononucleosis to lymphoma (cancer of the lymph nodes).

LYMPHATIC VESSELS: A body-wide network of channels, similar to the blood vessels, that transport lymph to the immune organs and into the bloodstream.

LYMPHOCYTE: A white blood cell. Present in the blood, lymph, and lymphoid tissue. See B Lymphocyte; T Cells.

LYMPHOID INTERSTITIAL PNEUMONITIS (LIP): A type of pneumonia that affects 35 to 40 percent of children with AIDS, which causes hardening of the lung membranes involved in absorbing oxygen. LIP is an AIDS-defining illness in children. The etiology (cause) of LIP is not clear. There is no established therapy for LIP, but the use of corticosteroids for progressive LIP has been advocated.

LYMPHOID ORGANS: Include tonsils, adenoids, lymph nodes, spleen, thymus, and other tissues. These organs act as the body’s filtering system, trapping invaders (ie, foreign particles, such as bacteria and viruses) and presenting them to squadrons of immune cells that congregate there. Within these lymphoid tissues, immune activity is concentrated in regions called germinal centers, where the threadlike tentacles of follicular dendritic cells (FDCs) form networks that trap invaders.

LYMPHOKINES: 1. Products of the lymphatic cells that stimulate the production of disease-fighting agents and the activities of other lymphatic cells. Among the lymphokines are gamma interferon and interleukin-2. 2. Nonantibody mediators of immune responses, released by activated lymphocytes.

LYMPHOMAGENESIS: The development of lymphoma.

LYMPHOPROLIFERATIVE RESPONSE: A specific immune response that entails rapid T cell replication. Standard antigens that elicit this response, such as tetanus toxoid, are used in lab tests of immunocompetency.

LYSIS: Rupture and destruction of a cell.

MACROPHAGE: A large immune cell that devours invading pathogens and other intruders. Stimulates other immune cells by presenting them with small pieces of the invader. Macrophages can harbor large quantities of HIV without being killed, acting as reservoirs of the virus.

MACROPHAGETROPIC VIRUS: HIV strains that preferentially infect macrophages in cell culture experiments. They readily fuse with cells that have both CD4 and CCR5 molecules on their surfaces, whereas the same viral isolates fail to fuse with cells expressing only CD4. These isolates are the main strains found in patients during the symptom-free stage of HIV disease.

MAGNETIC RESONANCE IMAGING (MRI): A noninvasive, non-X ray diagnostic technique-also called nuclear magnetic resonance or NMR-based on the magnetic fields of hydrogen atoms in the body. MRI provides computer-generated images of the body’s internal tissues and organs.

MAINTENANCE THERAPY: Drug therapy for an extended period after the initial disease has been brought under control. Maintenance therapy is usually used to keep a disease such as an opportunistic infection from recurring.

MAJOR HISTOCOMPATIBILITY COMPLEX (MHC): Two classes of molecules on cell surfaces. MHC class I molecules exist on all cells and hold and present foreign antigens to CD8 cytotoxic T lymphocytes if the cell is infected by a virus or other microbe. MHC class II molecules are the billboards of the immune system. Peptides derived from foreign proteins are inserted into MHC’s binding groove and displayed on the surface of antigen-presenting cells. These peptides are then recognized by T lymphocytes so that the immune system is alerted to the presence of foreign material. See Histocompatibility Testing.

MALAISE: A generalized, nonspecific feeling of discomfort.

MALIGNANT: Refers to cells or tumors growing in an uncontrolled fashion. Such growths may spread to and disrupt nearby normal tissue, or reach distant sites via the bloodstream. By definition, cancers are always malignant, and the term “malignancy” implies cancer. See Metastasis.

MANDATORY REPORTING: System under which a physician is required by law to inform health authorities when a specified illness is diagnosed. Mandatory reporting is required for AIDS in all 50 states.

MAST CELL: A granulocyte found in tissue. The contents of the mast cells, along with those of basophils, are responsible for the symptoms of allergy.

MEDIAN: The midpoint value in a series; the median is not necessarily the same as the mean.

MEDICAID: Federal/state health-care program for persons below the poverty level.

MEDICARE: Federal health insurance program for persons 65 years of age or older, the disabled, and those with end-stage renal disease.

MELANOMA: A malignant tumor produced by the pigment-producing cells of the skin. It begins as a dark skin lesion and may spread rapidly to other areas on the skin and within the body.

MEMORY T CELLS: A subset of T lymphocytes that have been exposed to specific antigens and can then proliferate (ie, reproduce) on subsequent immune system encounters with the same antigen.

MENINGES: Membranes surrounding the brain or spinal cord. Part of the blood-brain barrier. See Meningitis.

MENINGITIS: An inflammation of the meninges (membranes surrounding the brain or spinal cord), which may be caused by a bacterium, fungus, or virus.

MESSENGER RNA: Also referred to as mRNA. A form of RNA that carries the genetic code for a particular protein from the DNA in the cell’s nucleus to a ribosome in the cytoplasm and acts as a template, or pattern, for the formation of that protein.

META-ANALYSIS: A statistical analysis of data combined from two or more studies.

METABOLIC DISORDER: A disturbance in the buildup, breakdown, or excretion of substances.

METABOLISM: The sum of the processes by which a particular substance is handled (as by assimilation and incorporation, or by detoxification and excretion) in the living body.

METABOLITE: Any substance produced by metabolism or by a metabolic process.

METASTASIS: Transfer of a disease-producing agent (eg, cancer cells or bacteria) from an original site of disease to another part of the body, with development of a similar lesion in the new location (eg, spread of cancer from an original site to other sites in the body).

MHC: See Major Histocompatibility Complex.

MICROBES: Microscopic living organisms, including bacteria, protozoa, viruses, and fungi.

MICROBICIDE: An agent (eg, a chemical or an antibiotic) that destroys microbes. New research is being carried out to evaluate the use of rectal and vaginal microbicides to inhibit the transmission of sexually transmitted diseases, including HIV.

MICROENCAPSULATED: Surrounded by a thin layer of protection. A means of protecting a drug or vaccine from rapid breakdown.

MITOCHONDRIA: Membrane-enclosed cellular compartments that are the major source of a cell’s energy. Mitochondria accomplish this by oxidizing the products of carbohydrate and lipid metabolism. Mitochondria contain some independent DNA genes and are reproduced as needed by the cell they reside in.

MITOCHONDRIAL TOXICITY: Damage to the mitochondria, often characterized by muscular weakness and fatigue. It can lead to life-threatening conditions, such as lactic acidosis. Nucleoside analogs may cause mitochondrial toxicity.

MN: A strain of HIV used in vaccine development.

MOLECULE: The smallest particle of a compound that has all the chemical properties of that compound. Molecules are made up of two or more atoms, either of the same element or of two or more different elements. Ionic compounds, such as common salt, are made up not of molecules, but of ions arranged in a crystalline structure. Unlike ions, molecules carry no electrical charge. Molecules differ in size and molecular weight as well as in structure.

MONOCLONAL ANTIBODIES: Antibodies produced in the laboratory by a hybridoma or antibody-producing cell source for a specific antigen. Monoclonal antibodies are useful as tools for identifying specific protein molecules.

MONOCYTE: A large white blood cell that ingests microbes or other cells and foreign particles. When a monocyte enters tissues, it develops into a macrophage.

MONONEURITIS MULTIPLEX (MM): A rare type of neuropathy that has been described with HIV infection. It may fall into two different categories. One type occurs during the early period of the infection and has a more benign outcome. The second form occurs later and is more aggressive, leading to progressive paralysis and death in some patients. It has been suggested that MM is related to multifocal cytomegalovirus (CMV) infection.

MONOTHERAPY: Treatment with one drug, as opposed to combination therapy (ie, the use of two or more drugs).

MONOVALENT VACCINE: A vaccine specific for only one antigen.

MORBIDITY: Illness or disease.

MORTALITY: Death.

MRI: See Magnetic Resonance Imaging.

MUCOCUTANEOUS: Anything that pertains to mucous membranes and the skin (eg, mouth, eyes, vagina, lips, or anal area).

MUCOSA: See Mucous Membrane.

MUCOSAL IMMUNITY: Resistance to infection across the mucous membranes. Dependent on immune cells and antibodies present in the lining of the urogenital tract, gastrointestinal tract, and other parts of the body exposed to the environment.

MUCOUS MEMBRANE: Moist layer of tissue lining the digestive, respiratory, urinary, and reproductive tracts-all the body cavities with openings to the outside world except the ears.

MUTATION: In biology, a sudden change in a gene or unit of hereditary material that results in a new inheritable characteristic. In higher animals and many higher plants, a mutation may be transmitted to future generations only if it occurs in germ (sex cells); body cell mutations cannot be inherited. Changes within the chemical structure of single genes may be induced by exposure to radiation, temperature extremes, and certain chemicals. The term “mutation” may also be used to include losses or rearrangements of segments of chromosomes, the long strands of genes. Mutations, which can establish new traits in a population, are important in evolution. As related to HIV

MYALGIA: Diffuse muscle pain, usually accompanied by malaise (vague feeling of discomfort or weakness).

MYCOBACTERIUM: Any bacterium of the genus Mycobacterium or a closely related genus.

MYCOPLASMA: 1. Smallest free-living organisms known to infect humans. Mycoplasma cause a variety of illnesses, especially of the lungs and sexual organs. 2. Any microorganism of the genus Mycoplasma, also called pleuropneumonia-like organism.

MYCOSIS: Any disease caused by a fungus.

MYELIN: A substance that sheathes nerve cells, acting as an electric insulator that facilitates the conduction of nerve impulses. See Chronic Idiopathic Demyelinating Polyneuropathy.

MYELOPATHY: Any disease of the spinal cord.

MYELOSUPPRESSION: Suppression of bone marrow activity, causing decreased production of red blood cells (anemia), white blood cells (leukopenia), or platelets (throm-bocytopenia). Myelosuppression is an effect of some drugs, such as AZT.

MYELOTOXIC: Destructive to bone marrow.

MYOCARDIAL: Refers to the heart’s muscle mass.

MYOPATHY: Progressive muscle weakness. Myopathy may arise as a toxic reaction to AZT or as a direct consequence of HIV infection.

NAIVE T-CELL: Immune cells (either CD4+ T-helper lymphocytes or CD8+ cytotoxic lymphocytes) that respond to antigens that the body has not encountered before. After naive Tcells have fought off disease, a portion of them become memory cells, which can quickly respond to a reintroduction of the relevant pathogen.

NATIONAL CANCER INSTITUTE (NCI): An NIH institute with the overall mission of conducting and supporting research, training, and disseminating health information with respect to the causes, diagnosis, and treatment of cancer. NCI also performs these functions for HIV-related cancers.

NATIONAL INSTITUTE OF CHILD HEALTH AND HUMAN DEVELOPMENT (NICHD): An NIH institute that conducts and supports research on the reproductive, developmental, and behavioral processes that determine the health of children, adults, families, and populations. Thus, NICHD supports clinical research related to the transmission of HIV from infected mothers to their offspring, the progression of disease in HIV-positive infants and children, and the testing of potential therapies and preventatives for this population.

NATIONAL INSTITUTES OF HEALTH (NIH): A multi-institute agency of the Department of Health and Human Services, NIH is the federal focal point for health research. It conducts research in its own laboratories and supports research in universities, medical schools, hospitals, and research institutions throughout this country and abroad.

NATIONAL LIBRARY OF MEDICINE (NLM): An NIH institute, NLM is one of three U.S. national libraries. It is the world’s largest research library in a single scientific and professional field (ie, medicine). In the HIV/AIDS area, NLM provides electronic and print information services including the online services AIDSLINE, AIDSTRIALS, and AIDSDRUGS.

NATURAL HISTORY STUDY: Study of the natural development of something (such as an organism or a disease) over a period of time.

NATURAL KILLER CELL (NK CELL): A type of lymphocyte. Like cytotoxic T cells, NK cells attack and kill tumor cells and protect against a wide variety of infectious microbes. They are “natural” killers because they do not need additional stimulation or to recognize a specific antigen in order to attack and kill. Persons with immunodeficiencies such as those caused by HIV infection have a decrease in natural killer cell activity.

NDA: See New Drug Application.

NECROLYSIS: Shedding of surface components of tissue, such as cells from internal body surfaces, due to death of a portion of tissue.

NECROSIS: Death of tissue.

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NEONATAL: The first four weeks of life after birth.

NEOPLASM: An abnormal and uncontrolled growth of tissue; a tumor.

NEPHROLITHIASIS: The formation of small stones or sediment in the kidney.

NEPHROTOXIC: Poisonous to the kidneys.

NEURALGIA: A sharp, shooting pain along a nerve pathway.

NEUROLOGICAL COMPLICATIONS OF AIDS: See Central Nervous System (CNS) Damage.

NEUROPATHY: The name given to a group of disorders involving nerves. Symptoms range from a tingling sensation or numbness in the toes and fingers to paralysis. It is estimated that 35 percent of persons with HIV disease have some form of neuropathy.

NEUROTOXIC: Toxic to the nervous system or the nerves.

NEUTRALIZATION: The process by which an antibody binds to specific antigens, thereby “neutralizing” the microorganism.

NEUTRALIZING ANTIBODY: An antibody that keeps a virus from infecting a cell, usually by blocking receptors on the cell or the virus.

NEUTRALIZING DOMAIN: The section of the HIV envelope protein gp120 that elicits antibodies with neutralizing activities.

NEUTROPENIA: An abnormal decrease in the number of neutrophils (the most common type of white blood cells) in the blood. The decrease may be relative or absolute. Neutropenia may also be associated with HIV infection or may be drug-induced.

NEUTROPHIL: Also called polymorphonuclear neutrophil (PMN) leukocyte. A white blood cell that plays a central role in defense of a host against infection. Neutrophils engulf and kill foreign microorganisms.

NEW DRUG APPLICATION (NDA): An application submitted by the manufacturer of a drug to the FDA-after clinical trials have been completed-for a license to market the drug for a specified indication.

NIAID: See National Institute of Allergy and Infectious Diseases.

NIGHT SWEATS: Extreme sweating during sleep. Although they can occur with other conditions, night sweats are also a symptom of HIV disease.

NIH: See National Institutes of Health.

NK CELL: See Natural Killer Cell.

NNRTI: See Non-nucleoside Reverse Transcriptase Inhibitors.

NON-NUCLEOSIDE REVERSE TRANSCRIPTASE INHIBITORS (NNRTIS): The third class of anti-HIV drugs, NNRTIs bind near reverse transcriptase’s active site and subsequently inhibit its polymerase activity. Approved NNRTIs include delavirdine, efavirenz, and nevirapine.

NONPROGESSOR: See Long-Term Nonprogressors.

NRTI: See Nucleoside/Nucleotide Reverse Transcriptase Inhibitors.

NUCLEIC ACID: Organic substance, found in all living cells, in which the hereditary information is stored and from which it can be transferred. Nucleic acid molecules are long chains that generally occur in combination with proteins. The two chief types are DNA (deoxyribonucleic acid), found mainly in cell nuclei, and RNA (ribonucleic acid), found mostly in cytoplasm.

NUCLEOLI: Bodies in the nucleus that become enlarged during protein synthesis and contain the DNA template for ribosomal RNA. See Ribonucleic Acid; Ribosome.

NUCLEOSIDE ANALOG: A type of synthetic antiviral drug, such as AZT, ddI, ddC, d4T, or 3TC, whose makeup constitutes a defective version of a natural nucleoside. Nucleoside analogs may take the place of the natural nucleosides, blocking the completion of a viral DNA chain during infection of a new cell by HIV. The HIV enzyme reverse transcriptase is more likely to incorporate the nucleoside analogs into the DNA it is constructing than is the DNA polymerase normally used for DNA creation in cell nuclei. See Nucleic Acid.

NUCLEOSIDE: A building block of DNA or RNA, the genetic material found in living organisms. See Nucleic Acid.

NUCLEOTIDE ANALOGS: See Nucleoside/Nucleotide Reverse Transcriptase Inhibitors.

NUCLEOTIDE: Nucleic acid chains are composed of subunits called nucleotides. Nucleosides are related to nucleotides, the subunits of nucleic acids; however, nucleosides do not carry the phosphate groups of the nucleotides.

NUCLEUS: 1. The central controlling body within a living cell, usually a spherical unit enclosed in a membrane and containing genetic codes for maintaining the life systems of the organism and for issuing commands for growth and reproduction. 2. The nucleus of a cell is essential to such cell functions as reproduction and protein synthesis. It is composed of nuclear sap and a nucleoprotein-rich network from which chromosomes and nucleoli arise, and is enclosed in a definite membrane.

NULL CELL: A lymphocyte that develops in the bone marrow and lacks the characteristic surface markers of the B and T lymphocytes. Null cells represent a small proportion of the lymphocyte population. Stimulated by the presence of antibody, null cells can attack certain cellular targets directly and are known as natural killer (NK) cells.

NYMPHOMINIC: Excessive sex desire in Woman.

OBSERVATIONAL STUDY: A study that involves observing without altering or influencing that which is being observed. Observational studies are prone to bias, but can be useful in creating hypotheses and determining the natural history of a disease.

OCULAR: Pertaining to the eye.

OFF-LABEL USE: Use of a drug for a disease or condition other than the specific disease or condition for which the FDA approved it.

OFFICE OF AIDS RESEARCH (OAR): An office within the National Institutes of Health (NIH) that coordinates AIDS research in all of the participating NIH institutes.

ONCOLOGY: The study of tumors.

OPEN-LABEL TRIAL: A clinical trial in which doctors and participants know which drug or vaccine is being administered.

OPHTHALMOSCOPY: An examination of the eye, using an ophthalmoscope, to identify CMV retinitis and other conditions. Also called funduscopy.

OPPORTUNISTIC INFECTIONS: Illnesses caused by various organisms, some of which usually do not cause disease in persons with normal immune systems. Persons living with advanced HIV infection suffer opportunistic infections of the lungs, brain, eyes, and other organs. Opportunistic infections common in persons diagnosed with AIDS include Pneumocystis carinii pneumonia; Kaposi’s sarcoma; cryptosporidiosis; histoplasmosis; other parasitic, viral, and fungal infections; and some types of cancer.

ORGANELLE: A specialized “organ” of a cell, such as the mitochondria, the Golgi complex, the endoplastic reticulum, the lyso-somes, and the centrioles.

OROPHARYNGEAL: Relating to that division of the pharynx between the soft palate and the epiglottis. The pharynx is a tube that connects the mouth and nasal passages with the esophagus, the connection to the stomach. The epiglottis is a thin, valve-like structure that covers the glottis, the opening of the upper part of the larynx, during swallowing.

ORPHAN DRUGS: An FDA category that refers to medications used to treat diseases and conditions that rarely occur. Therefore, there is little financial incentive for the pharmaceutical industry to develop such medications. Orphan drug status gives a manufacturer specific financial incentives to develop and provide such medications.

P-VALUE: See Statistically Significant.

P24: A bullet-shaped core made of another protein that surrounds the viral RNA within the envelope of HIV. The p24 antigen test looks for the presence of this protein in a patient’s blood. A positive result for the p24 antigen suggests active HIV replication. p24 found in the peripheral blood is also thought to correlate with the amount of virus in the peripheral blood. Measurement of p24 levels in the blood has been used to monitor viral activity, although this is not considered a very accurate method because of the existence of the p24 antibody that binds with the antigen and makes it undetectable. See Branched DNA Assay.

PACKAGE INSERT: A document approved by the FDA and furnished by the manufacturer of a drug for use when dispensing the drug (it is inserted into the package). The document indicates approved uses, contraindications, and potential side effects.

PALLIATIVE CARE: Palliative care is an approach to life-threatening chronic illnesses, especially at the end of life. Palliative care combines active and compassionate therapies to comfort and support patients and their families who are living with life-ending illness. Palliative care strives to meet physical needs through pain relief and maintaining quality of life while emphasizing the patient’s and family’s rights to participate in informed discussion and to make choices. This patient- and family-centered approach uses the skills of interdisciplinary team members to provide a comprehensive continuum of care including spiritual and emotional needs.

PALLIATIVE: A treatment that provides symptomatic relief but not a cure.

PANCREAS: A gland situated near the stomach that secretes a digestive fluid into the intestine through one or more ducts and also secretes the hormone insulin.

PANCREATITIS: Inflammation of the pancreas. An occasional side effect of treatment with ddI, pancreatitis can result in severe, debilitating abdominal pain and death. Its onset can be predicted by rises in blood levels of the pancreatic enzyme amylase, as well as increases in blood triglycerides.

PANCYTOPENIA: Deficiency of erythrocytes, all types of white blood cells, and platelets in the circulating blood.

PANDEMIC: A disease prevalent throughout an extensive region, country, or continent, or throughout the world. See Epidemic.

PAP SMEAR: A method for the early detection of cancer and other abnormalities of the female genital tract, especially of the cervix, employing scraped as well as exfoliated cells (cells that have been shed into the vaginal fluid) and a special staining technique for microscopic examination that differentiates diseased tissue. Formerly known as Papanicolaou Smear after George Papanicolaou, the American cytologist who developed this method.

PAPILLOMA: 1. A benign tumor (as a wart or condyloma) resulting from an overgrowth of epithelial tissue on papillae of vascularized connective tissue (as of the skin). 2. An epithelial tumor caused by a virus. See Condyloma; Epithelium.

PARALLEL TRACK: A system of distributing experimental drugs to patients who are unable to participate in ongoing clinical efficacy trials and have no other treatment options. See Clinical Trial.

PARASITE: A plant or animal that lives and feeds on or within another living organism (a host), causing some degree of harm to the host.

PARENCHYMA: The tissue of an organ (as distinguished from supporting or connective tissue).

PARENTERAL: Not in or through the digestive system. For example, parenteral can pertain to blood being drawn from a vein in the arm or introduced into that vein via a transfusion (intravenous), or to injection of medications or vaccines through the skin (subcutaneous) or into the muscle (intramuscular).

PARESTHESIA: Abnormal sensations such as burning, tingling, or a “pins-and-needles” feeling. Paresthesia may constitute the first group of symptoms of peripheral neuropathy, or it may be a limited drug side effect that does not worsen with time. Circumoral paresthesia affects the area around the mouth.

PASSIVE IMMUNOTHERAPY: Process in which individuals with advanced disease (who have low levels of HIV antibody production) are infused with plasma rich in HIV antibodies or an immunoglobulin concentrate (HIVIG) from such plasma. The plasma is obtained from asymptomatic HIVpositive individuals with high levels of HIV antibodies.

PATHOGEN: Any disease-producing microorganism or material.

PATHOGENESIS: The origin and development of a disease.

PBMC: See Peripheral Blood Mononuclear Cell.

PCR: See Polymerase Chain Reaction.

PELVIC INFLAMMATORY DISEASE (PID): Gynecological condition caused by an infection (usually sexually transmitted) that spreads from the vagina to the upper parts of a woman’s reproductive tract in the pelvic cavity. PID can cause abscesses and constant pain almost anywhere in the genital tract. If left untreated, it can cause infertility or more frequent menstrual periods. Severe cases may even spread to the liver and kidneys, causing dangerous internal bleeding and death.

PEPTIDE (ALSO POLYPEPTIDE): Biochemical formed by the linkage of up to about 50 amino acids to form a chain. Longer chains are called proteins. The amino acids are coupled by a peptide bond, a special linkage in which the nitrogen atom of one amino acid binds to the carboxyl carbon atom of another. Many peptides, such as the hormones vasopressin and ACTH, have physiological or antibacterial activity.

PERIANAL: Around the anus.

PERINATAL TRANSMISSION: Transmission of a pathogen, such as HIV, from mother to baby before, during, or after the birth process.

PERINATAL: Events that occur at or around the time of birth.

PERIORAL: Around the mouth.

PERIPHERAL BLOOD MONONUCLEAR CELL (PBMC): Cells in the bloodstream with one nucleus. Generally refers to lymphocytes and macrophages.

PERSISTENT GENERALIZED LYMPHADENOPATHY (PGL): Chronic, diffuse, noncancerous lymph node enlargement. Typically it has been found in persons with persistent bacterial, viral, or fungal infections. PGL in HIV infection is a condition in which lymph nodes are chronically swollen in at least two areas of the body for three months or more with no obvious cause other than the HIV infection.

PGL: See Persistent Generalized Lymphadenopathy.

PHAGOCYTE: A cell that is able to ingest and destroy foreign matter, including bacteria.

PHAGOCYTOSIS: The process of ingesting and destroying a virus or other foreign matter by phagocytes. See Macrophage; Monocyte.

PHARMACOKINETICS: The processes (in a living organism) of absorption, distribution, metabolism, and excretion of a drug or vaccine.

PHASE I TRIALS: Involve the initial introduction of an investigational new drug into humans. Phase I trials are closely monitored and may be conducted in patients or healthy volunteers. The studies are designed to determine the metabolism and pharmacologic actions of the drug in humans, safety, side effects associated with increasing doses, and if possible, early evidence of effectiveness. The trials can also include studies of structure-activity relationships, mechanisms of action in humans, and use of the investigational drug as a research tool to explore biological phenomena or disease processes. The total number of patients included in phase I studies varies but is generally in the range of 20 to 80. Sufficient information should be obtained in the trial to permit design of well-controlled, scientifically valid phase II studies.

PHASE II TRIALS: Include controlled clinical studies of effectiveness of the drug for a particular indication or indications in patients with the disease or condition under study, and determination of common, short-term side effects and risks associated with the drug. Phase II studies are typically well controlled, closely monitored, and usually involve no more than several hundred patients.

PHASE III TRIALS: Expanded controlled and uncontrolled studies. They are performed after preliminary evidence of drug effectiveness has been obtained. They are intended to gather additional information about effectiveness and safety that is needed to evaluate the overall benefit-risk relationship of the drug and to provide adequate basis for physician labeling. These studies usually include anywhere from several hundred to several thousand volunteers.

PHASE IV TRIALS: Postmarketing studies, carried out after licensure of the drug. Generally, a phase IV trial is a randomized, controlled trial that is designed to evaluate the long-term safety and efficacy of a drug for a given indication. Phase IV trials are important in evaluating AIDS drugs because many drugs for HIV infection have been given accelerated approval with small amounts of clinical data about the drugs’ effectiveness.

PHENOTYPE: The physical expression of an organism’s genotype.

PHENOTYPIC (RESISTANCE): See Resistance.

PHENOTYPIC ASSAY: A test performed in vitro that measures HIV’s ability to replicate in the presence of antiretroviral drugs. Higher amounts of drug indicate resistance.

PHOTOSENSITIVITY: Heightened skin response to sunlight or ultraviolet light (rapid burning when exposed to the sun).

PITUITARY GLAND: Small, oval endocrine gland that lies at the base of the brain. It is called the master gland because the other endocrine glands depend on its secretions for stimulation. The pituitary has two distinct lobes, anterior and posterior. The anterior lobe secretes at least six hormones

PLACEBO EFFECT: A physical or emotional change occurring after a substance is taken or administered that is not the result of any special property of the substance. The change may be beneficial, reflecting the expectations of the patient and, often, the expectations of the person giving the substance.

PLACEBO-CONTROLLED STUDY: A method of investigating drugs in which an inactive substance (the placebo) is given to one group of patients, while the drug being tested is given to another group. The results obtained in the two groups are then compared to see if the investigational treatment is more effective in treating the condition.

PLACEBO: An inactive substance (may look like the real medication) against which investigational treatments are compared for efficacy and safety. See Placebo-Controlled Study.

PLASMA CELLS: Large antibody-producing cells that develop from B cells. See Antibodies; B Lymphocyte.

PLASMA: Ten percent of the blood that contains nutrients, electrolytes (dissolved salts), gases, albumin, clotting factors, wastes, and hormones.

PLASMAPHERESIS: The selective removal of certain proteins or antibodies from the blood (followed by reinjection of the blood). This process is sometimes used in the treatment of some peripheral neuropathies and is an integral part of passive immunotherapies for HIV.

PLATELETS: Active agents of inflammation when damage occurs to a blood vessel. They are not actually cells, but fragments released by megakaryocyte cells. A megakaryocyte is a large cell in the bone marrow whose function is to produce platelets. When vascular damage (ie, damage to blood vessels) occurs, the platelets stick to the vascular walls, forming clots to prevent the loss of blood. Thus, it is important to have adequate numbers of normally functioning platelets to maintain effective coagulation (clotting) of the blood. There are drugs that can potentially alter the platelet count, making it necessary to monitor the count. Also, some persons living with HIV develop thrombocytopenia-a condition characterized by a platelet count of less than 100,000 cells/mm³ of blood. The normal value for men is 154,000-354,000 cells/mm³. For women, it is 162,000-380,000 cells/mm³.

POLYMERASE CHAIN REACTION (PCR): 1. A laboratory process that selects a DNA segment from a mixture of DNA chains and rapidly replicates it; used to create a large, readily analyzed sample of a piece of DNA. It is used in DNA fingerprinting and in medical tests to identify diseases from the infectious agent’s DNA. 2. As related to HIV-also called RT-PCR-a sensitive laboratory technique that can detect and quantify HIV in a person’s blood or lymph nodes. PCR works by repeatedly copying genetic material using heat cycling and enzymes similar to those used by cells.

POLYMERASE: Any of several enzymes that catalyze the formation of DNA or RNA from precursor substances in the presence of preexisting DNA or RNA templates.

POLYNEURITIS: Inflammation of many nerves at once.

POLYPEPTIDE: See Peptide.

POLYSACCHARIDE: A complex carbohydrate such as cellulose, starch, or glycogen.

POLYVALENT VACCINE: A vaccine that is active against multiple viral strains.

POST-EXPOSURE PROPHYLAXIS: Taking antiretrovirals immediately (within 72 hours) after exposure to HIV to prevent the establishment of infection.

POSTPARTUM: After birth.

PPD TEST: See Purified Protein Derivative.

PRECLINICAL: Refers to the testing of experimental drugs in the test tube or in animals-the testing that occurs before trials in humans may be carried out.

PRECURSOR CELLS: Cells from which natural processes form other cells.

PRENATAL: Immediately before birth.

PREVALENCE: A measure of the proportion of people in a population affected with a particular disease at a given time.

PRIMARY ENDPOINT: See Endpoint.

PRIMARY HIV INFECTION: See Acute HIV Infection.

PROCTITIS: Inflammation of the rectum.

PRODROME: A symptom that indicates the onset of a disease.

PRODRUG: A compound that the body converts into active drug.

PROGENITOR: Parent or ancestor.

PROPHYLAXIS: Treatment to prevent the onset of a particular disease (“primary” prophylaxis), or the recurrence of symptoms in an existing infection that has been brought under control (“secondary” prophylaxis, maintenance therapy).

PROSPECTIVE STUDY: A study designed to follow participants forward in time, rather than retrospectively.

PROTEASE INHIBITORS: HIV protease is an enzyme essential to the replicative life cycle of HIV. The three-dimensional molecular structure of the HIV protease has been fully determined. Pharmaceutical developers therefore are able to rationally design drugs to inhibit the enzyme and thus interfere with replication of the virus. These drugs act by preventing cleavage of HIV viral polyproteins into active proteins; this occurs during the process by which HIV normally replicates. The drugs bind to the enzyme’s active site, blocking cleavage of the polyprotein.

PROTEASE: An enzyme that breaks down proteins into their component peptides. HIV’s protease breaks apart long strands of viral protein into the separate proteins making up the viral core. The enzyme acts as new virus particles are budding off a cell membrane. Protease is the first HIV protein whose three-dimensional structure has been characterized. See Proteins.

PROTEINS: Highly complex organic compounds found in all living cells. Protein is the most abundant class of all biological molecules, comprising about 50 percent of cellular dry weight. Structurally, proteins are large molecules composed of one or more chains of varying amounts of the same 22 amino acids that are linked by peptide bonds. Each protein is characterized by a unique and invariant amino acid sequence. The information for the synthesis of the specific amino acid sequence in a protein, from free amino acids, is carried by the cell’s nucleic acid.

PROTEINURIA: Excessive protein in the urine.

PROTOCOL: The detailed plan for conducting a clinical trial. It states the trial’s rationale, purpose, drug or vaccine dosages, length of study, routes of administration, who may participate (see Inclusion/Exclusion Criteria), and other aspects of trial design.

PROTOPLASM: The entire contents of a live cell.

PROTOZOA: Large group of one-celled (unicellular) animals, including amebas. Some protozoa cause parasitic diseases in people with AIDS, notably toxoplasmosis and cryptosporidiosis.

PROVIRUS: Viral genetic material in the form of DNA that has been integrated into the host genome. When HIV is dormant in human cells, it is in a proviral form.

PRURITIS: Itching.

PSEUDOVIRION: A viruslike particle.

PSYCHOSTIMULANT: An antidepressant or mood-elevating drug.

PSYCHOTROPIC: A drug that affects the mind, emotions, or behavior.

PULMONARY: Pertaining to the lungs.

PURIFIED PROTEIN DERIVATIVE (PPD): Material used in the tuberculin skin test (see Tuberculin Skin Test); the most common test for exposure to Mycobacterium tuberculosis, the bacterium that causes TB. PPD is sometimes used synonymously with TST. In the PPD test, a small amount of TB protein is injected under the skin. If patients have been previously infected, they will mount a delayed-type hypersensitivity reaction, characterized by a hard red bump called an induration.

PWA: Person with AIDS.

PYURIA: Pus in the urine.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

QUALITY OF LIFE: Expression used in speaking of issues relating to normalizing the life of a chronically ill individual. In defining quality of life, health-care providers must consider not only the physical responses to medical therapy, but also the psychological implications of illness for both the patient and family. The overriding goal of care should be to relieve suffering and increase patient well-being.

RADIOLOGY: The science of diagnosis and/or treatment using radiant energy. Includes X rays, CT scan, and destruction of tumors by radiation.

RANDOMIZED TRIAL: A study in which participants are randomly (ie, by chance) assigned to one of two or more treatment arms or regimens of a clinical trial. Occasionally placebos are utilized. Randomization minimizes the differences among groups by equally distributing people with particular characteristics among all the trial arms.

REACTOGENICITY: The capacity to produce adverse reactions.

REBOUND: Increases in viral load above a set limit for a period of time. For example, a person may be rebounding if his or her viral load is <400 copies/mL for several months and subsequently >400 copies/mL at three consecutive clinic visits. These parameters vary among doctors. “Blips” are transient increases.

RECEPTOR: A molecule on the surface of a cell that serves as a recognition or binding site for antigens, antibodies, or other cellular or immunological components.

RECHALLENGE: To introduce a drug again after an initial adverse result. For example, if someone has an allergic reaction to a drug, he or she may be rechallenged by taking a smaller dose and building up to a normal dose.

RECOMBINANT DNA: See Biotechnology; Genetic Engineering.

RECOMBINANT: An organism whose genome contains integrated genetic material from a different organism. Also used in relation to compounds produced by laboratory or industrial cultures of genetically engineered living cells. The cells’ genes have been altered to give the capability of producing large quantities of the desired compound for use as a medical treatment. Recombinant compounds are often altered versions of naturally occurring substances.

REFRACTORY: Resistant to treatment; difficult to treat.

REGIMEN: A program of treatment, including doses and scheduling.

REGULATORY GENES: As related to HIV

REGULATORY T CELLS: T cells that direct other immune cells to perform special functions. The chief regulatory cell, the CD4 cell or T helper cell, is HIV’s chief target.

REMISSION: The lessening of the severity or duration of outbreaks of a disease, or the abatement (diminution in degree or intensity) of symptoms altogether over a period of time.

RENAL: Pertaining to the kidneys.

RESERVOIR: A part of the body that may contain HIV and that is not easily penetrated by drugs. Examples include macrophages, lymphocytes, the brain, and testes.

RESISTANCE: Reduction in a pathogen’s sensitivity to a particular drug. Resistance is thought to result usually from a genetic mutation. In HIV, such mutations can change the structure of viral enzymes and proteins so that an antiviral drug can no longer bind with them as well as it used to. Resistance detected by searching a pathogen’s genetic makeup for mutations thought to confer lower susceptibility is called “genotypic resistance.” Resistance found by successfully growing laboratory cultures of the pathogen in the presence of a drug is called “phenotypic resistance.”

RETICULOENDOTHELIAL CELLS: A system of interstitial cells that includes all the phagocytic cells, which trap and consume foreign agents, except the leukocytes circulating in the bloodstream. This system forms a network throughout the body and is another of the body’s defense systems against invading organisms in the connective tissues of the body. See Phagocyte.

RETINA: Light-sensitive tissue at the back of the eye that transmits visual impulses via the optic nerve to the brain. See Retinitis.

RETINAL DETACHMENT: Condition in which a portion of the retina becomes separated from the inner wall of the eye. In AIDS patients, it can result from retinal disease such as CMV retinitis. The condition can rapidly lead to vision loss but is treatable by adding silicone to the eye’s vitreous humor to increase the pressure on the retina.

RETINITIS: Inflammation of the retina, linked in AIDS to cytomegalovirus infection. Untreated, it can lead to blindness.

RETINOPATHY: Noninflammatory degenerative disease of the retina.

RETROSPECTIVE STUDY: A study based on the review of medical records of patients.

RETROVIRUS: A type of virus that, when not infecting a cell, stores its genetic information on a single-stranded RNA molecule instead of the more usual double-stranded DNA. HIV is an example of a retrovirus. After a retrovirus penetrates a cell, it constructs a DNA version of its genes using a special enzyme called reverse transcriptase. This DNA then becomes part of the cell’s genetic material.

REV: One of the regulatory genes of HIV. Three HIV regulatory genes- tat, rev, and nef-and three so-called auxiliary genes-vif, vpr, and vpu-contain information necessary for the production of proteins that control the virus’s ability to infect a cell, produce new copies of the virus, or cause disease. See nef; tat.

REVERSE TRANSCRIPTASE: This enzyme of HIV-and other retroviruses-converts the single-stranded viral RNA into DNA, the form in which the cell carries its genes. Antiretrovirals such as NRTIs and NNRTIs inhibit this stage of the viral life cycle.

RHABDOMYOLYSIS: A serious and potentially fatal disease involving destruction or degeneration of skeletal muscle.

RIBONUCLEIC ACID (RNA): 1. A nucleic acid, found mostly in the cytoplasm-rather than the nucleus-of cells. RNA, like the structurally similar DNA, is a chain made up of subunits called nucleotides. RNA plays several roles in determining the synthesis of proteins. Messenger RNA replicates the DNA code for a protein and moves to sites in the cell called ribosomes. There, the much shorter transfer RNA (tRNA) assembles amino acids to form the protein specified by the messenger RNA. Most forms of RNA (including messenger and transfer RNA) consist of a single nucleotide strand, but a few forms of viral RNA that function as carriers of genetic information (instead of DNA) are double-stranded. Some viruses, such as HIV, carry RNA instead of the more usual genetic material DNA. See Cytoplasma; Retrovirus.

RIBOSOME: A cytoplasmic cellular structure, composed of ribonucleic acid and protein, that functions in the synthesis of protein. Ribosomes interact with messenger RNA and transfer RNA to join together amino acid units into a polypeptide chain according to the sequence determined by the genetic code.

RITONAVIR ENHANCEMENT: The use of ritonavir with other drugs, especially with other protease inhibitors, to increase their blood levels.

RNA: See Ribonucleic Acid.

ROUTE OF ADMINISTRATION: See Administration.

RT-PCR (REVERSE TRANSCRIPTASE POLYMERASE CHAIN REACTION): An FDA-approved test to measure viral load. The test is also known as PCR (see Polymerase Chain Reaction).

RYAN WHITE CARE ACT: Through the Ryan White Comprehensive AIDS Resources Emergency (CARE) Act, health-care and support services are provided for persons living with HIV/AIDS. HRSA administers this Act, which was authorized by Congress.

SAFER SEX: Sexual activity conducted in such a way that transmission of HIV infection is minimized by reducing the exchange of body fluids (eg, consistent use of condoms, avoiding unprotected vaginal and anal intercourse).

SALVAGE THERAPY: A drug regimen that is initiated after other regimens have failed. Often, salvage therapy is used to refer to regimens designed to combat highly resistant HIV. Also called rescue therapy.

SARCOMA: A malignant (cancerous) tumor of the skin and soft tissue.

SATYRIASIS: Excessive sex desire in man.

SEBORRHEIC DERMATITIS: A chronic inflammatory disease of the skin of unknown cause or origin, characterized by moderate erythema; dry, moist, or greasy scaling; and yellow crusted patches on various areas, including the midparts of the face, ears, supraorbital regions, umbilicus (the navel), genitalia, and especially the scalp. Seborrheic dermatitis in patients infected with HIV responds to a variety of therapies but tends to reoccur. Topic antifungal agents and corticosteroids suppress the process, but therapy must be applied repeatedly.

SENSITIVITY: 1. The minimum detection limit of an assay. 2. The degree to which a pathogen is susceptible to a drug. A virus that is not resistant to a drug is sensitive to that drug.

SEPSIS: The presence of harmful microorganisms or associated toxins in the blood and tissues. See Septicemia.

SEPTICEMIA: The systemic disease associated with sepsis. Blood poisoning.

SEROCONVERSION: The development of antibodies to a particular antigen. When people develop antibodies to HIV, they “seroconvert” from antibody-negative to antibody-positive. It may take from as little as one week to several months or more after infection with HIV for antibodies to the virus to develop. After antibodies to HIV appear in the blood, a person should test positive on antibody tests. See Incubation Period; Window Period.

SEROLOGIC TEST: Any of several tests that are performed on the clear portion of blood. Often refers to a test that determines the presence of antibodies to antigens such as viruses.

SERONEGATIVE: Lacking antibodies to HIV in the blood; testing negative for HIV.

SEROPOSITIVE: Having HIV antibodies in the blood; testing positive for HIV.

SEROPREVALENCE: As related to HIV infection, the proportion of persons who have serologic (ie, pertaining to serum) evidence of HIV infection at any given time. See Serum.

SEROSTATUS: Results of a blood test for specific antibodies.

SERUM: The clear, thin, and sticky fluid portion of the blood that remains after coagulation (clotting). Serum contains no blood cells, platelets, or fibrinogen.

SET POINT: See HIV Set Point.

SEXUALLY TRANSMITTED DISEASE (STD): Also called venereal disease or VD (an older public health term). Sexually transmitted diseases are infections spread by the transfer of organisms from person to person during sexual contact. In addition to the “traditional” STDs (syphilis and gonorrhea), the spectrum of STDs now includes HIV infection, which causes AIDS; Chlamydia trachomatis infections; human papilloma virus (HPV) infection; genital herpes; chancroid; genital mycoplasmas; hepatitis B; trichomoniasis; enteric infections; and ectoparasitic diseases (ie, diseases caused by organisms that live on the outside of the host’s body).

SF-2: A strain of HIV used in vaccine development.

SGOT (SERUM GLUTAMIC-OXALOACETIC TRANSAMINASE): See Aspartate Aminotransaminase (AST).

SGPT (SERUM GLUTAMIC-PYRUVIC TRANSAMINASE): See Alanine Aminotransaminase (ALT).

SHINGLES: See Varicella-Zoster Virus.

SHIV: Genetically engineered hybrid virus having an HIV envelope and an SIV core. See Genetic Engineering; Hybrid; Simian Immunodeficiency Virus (SIV).

SIDE EFFECTS: The actions or effects of a drug (or vaccine) other than those desired. The term usually refers to undesired or negative effects, such as headache, skin irritation, or liver damage. Experimental drugs must be evaluated for both immediate and long-term side effects.

SIMIAN IMMUNODEFICIENCY VIRUS (SIV): An HIV-like virus that infects monkeys, chimpanzees, and other nonhuman primates.

SINUSITIS: Inflammation of the mucous membrane of any sinus, especially of the nasal sinuses.

SIV: See Simian Immunodeficiency Virus.

SPINAL TAP: See Lumbar Puncture.

SPLEEN: Large lymphatic organ in the upper left of the abdominal cavity. Closely associated with the circulatory system, the spleen culls damaged, worn-out, or potentially dangerous cells from the blood. It also produces lymphocytes and stores excess red blood cells.

SPLENOMEGALY: An enlarged spleen.

SPUTUM ANALYSIS: Method of detecting certain infections (especially tuberculosis) by culturing of sputum-the mucous matter that collects in the respiratory and upper digestive passages and is expelled by coughing.

STANDARD OF CARE: Treatment regimen or medical management based on state-of-the-art patient care.

STATISTICALLY SIGNIFICANT: The likelihood that a result (eg, of a clinical trial) is caused by something other than mere chance. Significance is defined by an appropriately small p value, almost always set at p<0.05. A statistically significant finding may not necessarily be clinically significant, ie, it does not have a measurable impact on patients’ symptoms.

STD: See Sexually Transmitted Disease.

STEATOSIS: Fatty degeneration. Hepatic steatosis is fatty degeneration of the liver.

STEM CELLS: Cells from which all blood cells derive. Bone marrow is rich in stem cells. Clones of stem cells may become any one of the repertoire of immune cells depending upon what cytokines and hormones they are exposed to.

STERILIZING IMMUNITY: An immune response that completely eliminates an infection.

STEROID: Member of a large family of structurally similar lipid substances. Steroid molecules have a basic skeleton consisting of four interconnected carbon rings. Different classes of steroids have different functions. All the natural sex hormones are steroids. Anabolic steroids increase muscle mass. Anti-inflammatory steroids (or corticosteroids) can reduce swelling, pain, and other manifestations of inflammation.

STEVENS-JOHNSON SYNDROME: A severe and sometimes fatal form of erythema multiforme characterized by severe skin manifestations; conjunctivitis (eye inflammation), which often results in blindness; Vincent’s angina (trench mouth); and ulceration of the genitals and anus.

STOMATITIS: Inflammation of the mucous membrane of the mouth. Causes may include mechanical trauma, irritants, allergy, vitamin deficiency, or infection.

STRAIN: Subgroup of a species (also called taxon).

STRUCTURED TREATMENT INTERRUPTION: A planned, temporary suspension of HIV treatment, in consultation with a physician.

SUBARACHNOID SPACE: The space through which the spinal fluid circulates.

SUBCLINICAL INFECTION: An infection, or phase of infection, without readily apparent symptoms or signs of disease.

SUBCUTANEOUS (SC): Beneath the skin or introduced beneath the skin (eg, subcutaneous injections).

SUBUNIT HIV VACCINE: A genetically engineered vaccine that is based on only part of the HIV molecule.

SULFA DRUG: A sulfonamide drug used to treat bacterial infections. These drugs inhibit the action of p-aminobenzoic acid, a substance bacteria need in order to reproduce. Sulfa drugs are now used primarily in the treatment of urinary tract infections and ulcerative colitis. In the HIV area, the sulfa drug sulfadiazine is used in combination with pyrimethamine as standard therapy for toxoplasmosis. Trimethoprim is used in combination with another sulfa drug, sulfamethoxazole, against PCP.

SULFONAMIDES: Synthetic derivatives of paminobenzene sulfonamide. See Sulfa Drug.

SUPERANTIGEN: Investigators have proposed that a molecule known as a superantigen, made either by HIV or an unrelated agent, may stimulate massive quantities of CD4 cells at once, rendering them highly susceptible to HIV infection and subsequent cell death. See Antigen.

SUPPRESSOR PHENOMENON: Process whereby CD8 cells not only kill HIV-infected cells directly by a process called cytolysis, but also secrete soluble factors that suppress HIV replication in both blood and lymph nodes. It appears that CD8 cells secrete signaling molecules, called beta-chemokines (see Chemokines), which normally recruit inflammatory cells to the site of an infection. Three of these beta-chemokines, RANTES, MIP-1a, and MIP-1b, appear to block HIV replication by occupying receptors necessary for the entry of some strains of HIV into their target cells.

SUPPRESSOR T CELLS: (T8, CD8) Subset of T cells that halts antibody production and other immune responses.

SURROGATE MARKER: Laboratory tests that may predict a patient’s clinical outcome or indicate whether a drug is effective without having to rely on the traditional clinical endpoints of death or development of a major opportunistic infection. Surrogate markers under study in HIV disease include CD4 counts, CD4/CD8 cell ratios, and viral load.

SURVEILLANCE: See Epidemiologic Surveillance.

SUSCEPTIBLE: Vulnerable or predisposed to a disease.

SYMPTOMS: Any perceptible, subjective change in the body or its functions that indicates disease or phases of disease, as reported by the patient.

SYNCYTIA (“GIANT CELLS”): Dysfunctional multicellular clumps formed by cell-to-cell fusion. Cells infected with HIV may also fuse with nearby uninfected cells, forming balloonlike giant cells called syncytia. In test tube experiments, these giant cells have been associated with the death of uninfected cells. The presence of so-called syncytia-inducing variants of HIV has been correlated with rapid disease progression in HIV-positive individuals.

SYNDROME: A group of symptoms as reported by the patient and signs as detected in an examination that together are characteristic of a specific condition.

SYNERGISM, SYNERGISTIC: An interaction between two or more treatments (eg, drugs) that produces or enhances an effect that is greater than the sum of the effects produced by the individual treatments.

SYNTHESIS: 1. In chemistry, the formation of a compound from simpler compounds or elements. 2. The production of a substance (eg, as in protein synthesis) by the union of chemical elements, groups, or simpler compounds, or by the degradation (ie, breakdown) of a complex compound.

SYPHILIS: A disease-primarily sexually transmitted-resulting from infection with the spirochete Treponema pallidum (a bacterium). Syphilis can also be acquired in the uterus during pregnancy.

SYSTEMIC: Relating to the whole body instead of an individual part. A systemic therapy is one to which the entire body is exposed. Local therapy targets only the affected tissues.

T CELLS (T LYMPHOCYTES): T cells are white blood cells, derived from the thymus gland, that participate in a variety of cell-mediated immune reactions. Three fundamentally different types of T cells are recognized

T LYMPHOCYTE PROLIFERATION ASSAY: Measures the strength of response of T memory cells, a subgroup of T lymphocytes, to HIV.

T LYMPHOCYTES: See T Cells.

T4 CELL: See CD4 Cells.

T8 CELL: See CD8 (T8) Cells.

TABES DORSALIS: A syphilitic disorder that involves wasting, pain, lack of coordination, and sensory disorders.

TACHYPNEA: Increase in the rate of respiration.

TAT: One of the regulatory genes of HIV. Three HIV regulatory genes- tat, rev, and nef-and three so-called auxiliary genes-vif, vpr, and vpu-contain information necessary for the production of proteins that control the virus’s ability to infect a cell, produce new copies of the virus, or cause disease. The tat gene is thought to enhance virus replication. See nef; rev.

TEMPLATE: In biology, a molecule (eg, DNA) that serves as a pattern for the generation of another macromolecule (eg, messenger RNA). See Ribonucleic Acid.

TERATOGENICITY: Producing physical defects in offspring in utero (ie, birth defects). Teratogenicity is a potential side effect of some drugs, such as thalidomide.

TESTOSTERONE: Naturally occurring male hormone. When administered as a drug it can cause gain in lean body mass, increased sex drive, and possibly aggressive behavior. Many men with HIV have low testosterone levels.

TH1 RESPONSE: An acquired immune response whose most prominent feature is high cytotoxic T lymphocyte activity relative to the amount of antibody production. The Th1 response is promoted by CD4 “Th1” T-helper cells. See Th2 Response.

TH2 RESPONSE: An acquired immune response whose most prominent feature is high antibody production relative to the amount of cytotoxic T lymphocyte activity. The Th2 response is promoted by CD4 “Th2” T-helper cells. See Th1 Response.

THERAPEUTIC HIV VACCINE: Also called treatment vaccine. A vaccine designed to boost the immune response to HIV in people already infected with the virus. A therapeutic vaccine is different from a preventive vaccine, which is designed to prevent a disease from becoming established in a person.

THYMIDINE: A nucleoside combining the base thymine with D-ribose. One of the building blocks of DNA.

THYMOSIN: A polypeptide hormone of the thymus gland that influences the maturation of T cells destined for an active role in cell-mediated immunity.

THYMUS: A mass of glandular tissue (lymphoid organ) found in the upper chest under the breastbone in humans. The thymus is essential to the development of the body’s system of immunity beginning in fetal life (ie, before birth). The thymus processes white blood cells (see Lymphocytes), which kill foreign cells and stimulate other immune cells to produce antibodies. An important function of the thymus is to weed out lymphocytes that react to proteins produced by the body (self-antigens), thus preventing autoimmune disease. The gland grows throughout childhood until puberty and then gradually decreases in size. See Thymosin.

THYROID: An endocrine gland that produces hormones, including thyroxine and triiodothyronine.

TINNITUS: Noises (eg, ringing, roaring, whistling) in the ears.

TISSUE: A collection of similar cells and the intercellular substances surrounding them. The four basic tissues in the body are epithelial, connective, muscle, and nerve tissue.

TITER (ALSO “TITRE”): A laboratory measurement of the concentration of a substance in solution.

TOXICITY: The extent, quality, or degree of being poisonous.

TRANSAMINASE: A liver enzyme. A laboratory test that measures transaminase levels is used to assess the health of the liver.

TRANSCRIPTION: The process of constructing a messenger RNA molecule, using a DNA molecule as a template, with the resulting transfer of genetic information to the messenger RNA. As related to HIV

TRANSDERMAL: Through the skin, eg, a medication that is applied to the skin as a patch.

TRANSFER FACTOR: A fraction of white blood cells that apparently “transfers” capability to mount an immune response to a specific antigen.

TRANSFUSION: 1. The process of transfusing fluid (such as blood) into a vein. 2. The transfer of whole blood or blood products from one individual (the donor) to another (the receptor).

TRANSLATION: The complex process by which information encoded in messenger RNA is translated into protein.

TRANSMISSION (OF HIV): HIV is spread most commonly by sexual contact with an infected partner. The virus can enter the body through the mucosal lining of the vagina, vulva, penis, rectum or, rarely, the mouth during oral sex. The likelihood of transmission increases when these linings are damaged by ulcers or inflammation as a result of other sexually transmitted diseases. HIV also is spread through contact with infected blood, most often by the sharing of drug needles or syringes contaminated with minute quantities of blood containing the virus. Children can contract HIV from their infected mothers either during pregnancy or birth, or postnatally, through breast-feeding. In developed countries, HIV is now only rarely transmitted by transfusion of blood or blood products because of screening measures.

TREATMENT IND: A program to provide experimental treatments to a class of patients who lack satisfactory alternative treatments. IND stands for Investigational New Drug application, which is part of the FDA approval process to market a new prescription drug in the United States.

TREATMENT-EXPERIENCED: Someone who has taken a drug, class of drugs, or type of drug previously. Commonly signifies in the HIV/AIDS literature that a person has had previous experience on HAART or a component of HAART.

TREATMENT-NAIVE: Having never taken a drug, class of drugs, or type of drug previously. Commonly signifies in the HIV/AIDS literature that a person has not had previous experience on HAART or a component of HAART.

TRIGLYCERIDE: The basic structure of most fats and oils. It is composed of glycerol and three chains of fatty acids. Often refers to a type of blood lipid.

TROUGH LEVEL: The lowest level of a drug in blood plasma.

TUBERCULIN SKIN TEST (TST): A purified protein derivative of the tubercle bacilli, called tuberculin, is introduced into the skin by scratch, puncture, or intradermal injection. If a raised, red, or hard zone forms surrounding the test site, the person is said to be sensitive to tuberculin, and the test is read as positive. See Purified Protein Derivative.

TUMOR NECROSIS FACTOR (TNF): A cytokine, produced by macrophages, which helps activate T cells. It may also stimulate HIV activity. TNF levels are very high in persons with HIV, and the molecule is suspected to play a part in HIV-related wasting, neuropathy, and dementia. TNF triggers a biochemical pathway that leads to the programmed form of cell suicide known as apoptosis. It also activates a key molecule that can block this very pathway, and so set up a delicate life-death balance within the cell.

UNDETECTABLE: Below the limit of detection (or quantification).

UREA: The primary end product of nitrogen metabolism in mammals, formed in the liver and excreted in the urine.

V3 LOOP: Section of the gp120 protein on the surface of HIV. Appears to be important in stimulating neutralizing antibodies.

VACCINATION: Inoculation of a substance (vaccine) into the body for the purpose of producing active immunity against a disease.

VACCINE: A preparation of killed virus, living attenuated (weakened) virus, or living, fully virulent virus administered to produce or artificially increase immunity to a disease. Subunit vaccines comprise only part of the pathogen. Most candidate AIDS vaccines to date have been of this type.

VACCINIA: The poxvirus that causes cowpox and is used for vaccination against smallpox. It is used as a vector in HIV vaccine research to transport HIV genes into the body.

VARIABLE REGION: The part of an antibody’s structure that differs from one antibody to another.

VARICELLA-ZOSTER VIRUS (VZV): A virus in the herpes family that causes chicken pox during childhood and may reactivate later in life to cause herpes zoster (shingles) in immunosuppressed adults. Also called herpes zoster.

VASCULITIS: Inflammation of a blood vessel or lymph vessel.

VASOCONSTRICTION: Narrowing of the blood vessels.

VECTOR: A nonpathogenic bacterium or virus used to transport an antigen into the body to stimulate protective immunity (eg, in vaccine).

VERTICAL TRANSMISSION: Transmission of a pathogen such as HIV from mother to child during pregnancy or birth.

VIRAL BURDEN: See Viral Load.

VIRAL CORE: 1. Typically a virus contains an RNA or DNA core of genetic material surrounded by a protein coat. 2. As related to HIV: Within HIV’s envelope is a bullet-shaped core made of another protein, p24, that surrounds the viral RNA. Each strand of HIV RNA contains the virus’ nine genes. Three of these—gag, pol, and env—are structural genes that contain information needed to make structural proteins. The env gene, for example, codes for gp160, a protein that is later broken down to gp120 and gp41. See Surrogate Marker.

VIRAL CULTURE: A laboratory method for growing viruses.

VIRAL ENVELOPE: As related to HIV

VIRAL LOAD TEST: As related to HIV: Test that measures the quantity of HIV RNA in the blood. Results are expressed as the number of copies per milliliter of blood plasma. Measures of viral load CD4 cells are used to determine when to initiate and/or therapy. See Viral Load.

VIRAL LOAD: The amount of HIV in the circulating blood. Monitoring a person’s viral load is important because of the apparent correlation between the amount of virus in the blood and disease severity

VIREMIA: The presence of virus in the bloodstream. See Sepsis.

VIRICIDE: Any agent that destroys or inactivates a virus.

VIRILIZATION: A girl, woman, or prepubescent male acquiring masculine characteristics.

VIRION: A virus particle existing freely outside a host cell. A mature virus particle.

VIROLOGY: The study of viruses and viral disease.

VIRUS: An infectious agent that is dependent upon a host cell for replication. The complete virus particle (virion) comprises DNA or RNA, protected by a protein shell or capsid, and sometimes covered by an envelope. Virions range in size from 15 to several hundred nanometers. When viruses enter a living plant, animal, or bacterium, they replicate using the host cell’s metabolic machinery. After the infected host cell makes viral components and virus particles are released, the host cell is often dissolved. Some viruses do not kill cells but transform them into a cancerous state; some cause illness and then seem to disappear, while remaining latent and later causing another, sometimes much more severe, form of disease. In humans, viruses cause diseases such as measles, mumps, yellow fever, poliomyelitis, influenza, and the common cold. Some viral infections can be treated with drugs.

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