ABSCESS: Inflamed tissue, including an area of pus.

ABSOLUTE CD4 CELL COUNT (T4 COUNT): See CD4 Cell Count.

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.

ADMINISTRATION (ROUTE OF ADMINISTRATION): How a drug or therapy is introduced into the body. Systemic administration means that the drug goes throughout the body (usually carried in the bloodstream), and includes oral (by mouth), intravenous (injection into a vein, IV), intramuscular (injections 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 maligtion into a muscle, IM), intrathecal (into the spinal canal), subcutaneous (beneath the skin, sc), and rectal administration. Local administration means that the drug is applied or introduced into the specific area affected by the disease, such as application directly onto the affected skin surface (topical administration). The effects of most therapies depend upon the ability of the drug to reach the affected area; thus the route of administration and consequent distribution of a drug in the body are important determinants of its effectiveness.

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.

AGENCY FOR HEALTH CARE POLICY AND RESEARCH (AHCPR): An agency of the Department of Health and Human Services supporting activities to enhance health-care services and improve access to them.

AHCPR: See Agency for Health Care Policy and Research.

AIDS CLINICAL TRIALS GROUP (ACTG): A group of U.S. medical centers that evaluate treatment for HIV and HIV-associated infections. ACTG studies-both adult and pediatric-are sponsored by the National Institute of Allergy and Infectious Diseases and the National Institute of Child Health and Human Development (for many of the pediatric studies) of the National Institutes of Health.

AIDS DRUG ASSISTANCE PROGRAMS (ADAP): State-based programs funded in part by Title II of the Ryan White CARE Act that provide therapeutics (including devices necessary to administer pharmaceuticals) to treat HIV disease or prevent the serious deterioration of health, including treatment of opportunistic infections. ADAP formularies and eligibility criteria are determined state by state with a focus on serving low-income individuals.

AIDS EDUCATION AND TRAINING CENTERS (AETC): The Health Resources and Services Administration (HRSA) supports a network of 15 regional centers that serve as resources for educating health professionals in prevention, diagnosis, and care of HIV-positive patients. The centers train primary caregivers to incorporate HIV prevention strategies into their clinical priorities, along with diagnosis, counseling, and care of HIV-positive persons and their families.

AIDS RESEARCH ADVISORY COMMITTEE (ARAC): A board that advises and makes recommendations to the Director, National Institute of Allergy and Infectious Diseases, on all aspects of HIV-related research, vaccine development, pathogenesis, and epidemiology.

AIDS WASTING SYNDROME: Involves involuntary loss of 10% of baseline body weight plus either chronic diarrhea (two loose stools per day for more than 30 days) or chronic weakness and documented fever (for 30 days or more, intermittent or constant) in the absence of a concurrent illness or condition other than HIV infection that would explain the findings.

AIDS-DEFINING ILLNESS: Any one of a number of serious diseases that, if experienced by a person with HIV, is sufficient for a diagnosis of AIDS. According to the CDC, some AIDS-defining illnesses are PCP, MAC, AIDS wasting syndrome, KS, and invasive cervical cancer. A CD4 cell count <200 cells/mm³ is an AIDS-defining condition.

AIDS-RELATED CANCERS: Several cancers are more common or more aggressive in persons living with HIV. These malignancies include lymphomas, KS, and anogenital cancers that primarily affect the anus and the cervix. HIV, or the immune suppression it induces, appears to play a role in the development of these cancers.

AIDS: See Acquired Immunodeficiency Syndrome.

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.

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.

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.