Published in the Bulletin of Experimental Treatments for AIDS July 1998 issue, by the San Francisco AIDS Foundation.

July 1998 Table of Contents

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Glossary

Compiled by Liz Highleyman

ACIDOSIS: a condition that occurs when the kidney cannot adequately process the acids generated during metabolism. The condition is characterized by high levels of acid in the blood and low levels in the urine.

ACUTE RETROVIRAL SYNDROME: a combination of flu-like symptoms (e.g., fever, sore throat, skin rash, headache, nausea, muscle or joint pain) that occurs during or shortly after primary HIV infection.

ADDITIVE TOXICITY: a phenomenon that occurs when 2 or more drugs that cause similar side effects are used together, producing more severe adverse effects.

ADHERENCE: following a prescribed treatment regimen, including correct dosage and number of doses per day, and taking as directed with or without food.

ADRENAL GLAND: an organ located above each kidney that produces various hormones including adrenaline, cortisol and certain androgens.

ADVERSE EVENT: an unwanted toxic reaction or side effect of drug treatment.

ALLERGEN: an agent or substance that stimulates an allergic or hypersensitivity reaction.

AMINO ACID: an organic compound that is a basic structural unit of peptides and proteins.

ANABOLIC STEROID: a natural or synthetic hormone (e.g., testosterone, oxymetholone) that promotes the synthesis of proteins and the building of muscle mass.

ANABOLISM: the building of proteins and muscle mass in the body.

ANAPHYLAXIS: a life-threatening allergic reaction to a foreign antigen. Symptoms include swelling, difficulty breathing and a decrease in blood pressure due to blood vessel dilation.

ANDROGEN: a hormone that has masculinizing effects including stimulation of the development of the male reproductive organs and development of male secondary sex characteristics.

ANEMIA: reduced ability of blood to carry oxygen due to a low hemoglobin level or an abnormality or a reduced number of red blood cells. Symptoms include fatigue and weakness.

ANEMIA OF CHRONIC DISEASE: a mild to moderate type of anemia that often occurs in people with chronic illnesses such as AIDS, cancer or rheumatoid arthritis.

ANGIOGENESIS: the proliferation of new blood vessels.

ANGINA: chest pain caused by reduced flow of blood to the heart muscle.

ANTIBODY (IMMUNOGLOBULIN): a protein secreted by activated plasma cells, which evolve from B-cells, in response to stimulation by an antigen.

ANTIGEN: any agent or substance (e.g., microorganisms or the substances they produce) that stimulates an immune response.

ANTIGEN-PRESENTING CELL: a type of immune system cell (e.g., macrophage) that ingests and breaks up microorganisms and other harmful matter and displays pieces on its surface for recognition by T-cells.

ANTIOXIDANT: a substance that inhibits a chemical reaction by binding with and neutralizing free radicals and other highly reactive (electrically charged) molecules, thus reducing oxidative damage.

ANTIRETROVIRAL: an agent that suppresses the activity or replication of retroviruses such as HIV.

APLASIA: defective development of an organ or tissue, e.g., bone marrow.

APLASTIC ANEMIA: a reduced level of red blood cells due to the inability of stem cells in the bone marrow to produce new cells.

APOPTOSIS: programmed cell death.

ASYMPTOMATIC: not feeling or showing outward signs of infection.

ATHEROSCLEROSIS: "hardening of the arteries" in which cholesterol and other deposits build up on the inner walls of the arteries, limiting the flow of blood.

AUTOIMMUNITY: a condition in which an individual's immune system attacks its own body tissues as if they were foreign matter, possibly leading to autoimmune diseases such as lupus or rheumatoid arthritis.

BAND: an immature neutrophil released into the bloodstream during infection.

BASELINE: a known value (e.g., baseline viral load) against which later measurements can be compared.

BASOPHIL: a type of white blood cell that releases chemicals that slow blood coagulation and mediate allergic reactions.

B-CELL (B-LYMPHOCYTE): an immune system cell that carries out the humoral immune response. B-cells are produced in the bone marrow and mature into plasma cells that produce antibodies.

BIOAVAILABILITY: the extent to which a drug is absorbed and circulated in the body.

BIOPSY: the removal of a small sample of cells or tissue for microscopic examination and/or culture.

BILIRUBIN: a yellow pigment released when red blood cells are broken down. High blood bilirubin levels are indicated by jaundice, a yellowing of the skin and eyes.

BLOOD-BRAIN BARRIER: a set of physical barriers between the blood vessels and the brain which allows only certain substances to pass through.

BONE MARROW: the soft, spongy tissue in the interior of certain bones. Bone marrow contains stem cells and is the site of blood cell production.

BONE MARROW SUPPRESSION: damage to the blood cell-producing stem cells in the bone marrow which may be caused by drugs, toxic chemicals or radiation.

BONE MARROW TRANSFER: a graft of bone marrow from one individual to another to reconstitute the recipient's damaged immune or blood-production system.

BRANCHED-CHAIN DNA ASSAY (bDNA): a test for measuring the amount of virus (viral load) in blood plasma or tissue.

BUBONIC PLAGUE (BLACK DEATH): a disease caused by Yersinia pestis, a bacteria transmitted by fleas carried by rodents. The disease is characterized by swollen lymph nodes, high fever and bleeding under the skin.

BUFFALO HUMP: an accumulation of fatty tissue at the base of the neck that may be a side effect of certain anti-HIV drugs.

CANDIDIASIS: a disease caused by the fungus Candida. Candidiasis may affect the skin, nails and mucous membranes throughout the body including the mouth (thrush), esophagus and vagina.

CCR5: a protein found on certain cells that acts as a receptor site for chemokines and as a co-receptor that enables HIV to enter cells.

CD4 CELL (CD4 LYMPHOCYTE, HELPER T-CELL): a type of white blood cell that carries the CD4 cell surface marker and helps the body fight infection. CD4 cells release cytokines that regulate other immune cells.

CD8 CELL (CD8 LYMPHOCYTE): a type of white blood cell that helps regulate and/or carry out the body's immune response. Two major subsets of T-cells express the CD8 surface marker: suppressor T-cells and cytotoxic T-lymphocytes (CTL).

CELL-MEDIATED IMMUNITY (CELLULAR IMMUNITY, TH1 RESPONSE): the immune response mediated by the Th1 subset of CD4 cells. Cell-mediated immunity is stimulated by cytokines including IL-2 and IL-12, and carried out by cytotoxic T-lymphocytes and macrophages.

CENTRAL NERVOUS SYSTEM (CNS): the brain and spinal cord.

CEREBROSPINAL FLUID (CSF): a clear, nutrient-rich fluid that circulates around and through the brain and spinal cord.

CHEMOKINE: a soluble factor secreted by certain immune system cells that stimulates the activity of other cells. Certain chemokine receptors (e.g., CCR5, CXCR4) are necessary to enable HIV to enter cells.

CHEMOTHERAPY: the use of chemicals or drugs to treat disease; the term is typically used to refer to cancer treatment.

CHOLESTEROL: a fatty substance in animal tissue that is an essential component of cell membranes and nerve fiber insulation.

CHRONIC: slow, persisting over a long period.

CLINICAL TRIAL: an organized procedure for determining the effectiveness of a new drug or therapy by administering the agent to participants under strictly controlled conditions.

COAGULATION: clotting; the transformation of a liquid (e.g., blood) into a solid mass.

COLONY-FORMING UNIT: a precursor cell that develops into mature blood cells.

COLONY-STIMULATING FACTOR (CSF): a cytokine responsible for regulating the production of white blood cells. Types include granulocyte colony-stimulating factor (G-CSF), granulocyte macrophage colony-stimulating factor (GM-CSF) and macrophage colony-stimulating factor (M-CSF).

COLOSTRUM: breast fluid produced prior to milk production that contains antibodies.

COMPLETE BLOOD COUNT (CBC): an inventory of the cellular components of the blood, including red blood cell count and function (including hematocrit and hemoglobin), counts of various types of white blood cells and platelet count.

CONTRAINDICATION: any circumstance or condition that makes a drug or other method of treatment inadvisable in a particular case.

CO-RECEPTOR: a second cell surface receptor required for entry by a pathogen into a cell or initiation of a biological process.

CORONARY ARTERY DISEASE: damage to or blockage of the arteries that provide blood to the heart muscle.

CORTICOSTEROID: one of a group of steroid hormones (e.g., prednisone) produced by the cortex of the adrenal gland or manufactured synthetically. Corticosteroids have anti-inflammatory and immunosuppressive properties.

CROHN'S DISEASE: a chronic type of enteritis, or inflammation of the intestines.

CROSS-RESISTANCE: the development of resistance to one agent (e.g., drug) which also confers resistance to another (often similar) agent.

CRYPTOSPORIDIOSIS: a disease caused by the protozoan Cryptosporidium parvum, which is transmitted to humans by contact with animal feces, ingestion of contaminated food or water, or oral-anal sexual contact. Symptoms include severe diarrhea and weight loss.

CXCR4 (FUSIN): a co-receptor on the surface of certain T-cells that, along with the CD4 molecule, allows HIV to infect a cell.

CYTOCHROME P450 SYSTEM: a system that metabolizes drugs and other foreign substances in the liver by means of enzymes (e.g., CYP3A4) that inhibit or promote metabolic reactions.

CYTOKINE: an intercellular chemical messenger protein (e.g., tumor necrosis factor, interleukin) released by white blood cells. Cytokines facilitate communication among immune system cells.

CYTOMEGALOVIRUS (CMV, HHV-5): a herpesvirus. In immunocompromised individuals CMV may cause retinitis, pneumonia, colitis and/or encephalitis.

CYTOTOXIC T-LYMPHOCYTE (CTL, KILLER T-CELL): an immune system white blood cell that targets and kills cells infected with microorganisms.

DIALYSIS: a procedure for cleansing the blood using membranes to filter out waste elements.

DIETITIAN: a professional specializing in dietetics, the study of nutrition and the use of special diets to prevent and treat disease.

DNA (DEOXYRIBONUCLEIC ACID): a molecule found in the nucleus of cells that encodes genetic information. The particular sequence of 4 chemical building blocks (nucleotides) determines an individual’s unique genetic code.

DOSE-RANGING TRIAL: a clinical trial in which different doses of a drug are compared to determine which dosage has the best balance of high efficacy and low toxicity.

DOUBLE-BLIND: a type of clinical trial in which neither the subject nor the investigator knows what treatment, if any, the subject is receiving.

EFFICACY: effectiveness.

ENDOCRINE SYSTEM: a system of ductless glands that regulates bodily functions via hormones secreted into the bloodstream. The endocrine system includes the hypothalamus, pituitary gland, thyroid, adrenal glands and gonads (ovaries and testes).

ENDPOINT: a direct marker of disease progression.

ENZYME: a protein that induces or accelerates a chemical reaction.

EOSINOPHIL: a type of white blood cell that plays a role in allergic reactions and defense against parasites.

ERYTHROBLASTOSIS FETALIS: a condition in which antibodies from an Rh- mother attack the red blood cells of a developing Rh+ fetus.

ERYTHROCYTE: a mature red blood cell that contains hemoglobin. Red blood cells transport oxygen to the tissues of the body.

ERYTHROPOIETIN (EPO): a hormone produced by the kidney that stimulates the production of red blood cells. Genetically engineered EPO (epoietin alfa, brand names Procrit and Epogen) is used to treat anemia due to chronic kidney failure or drug toxicity.

EXPANDED ACCESS: an FDA program that allows distribution of experimental drugs to people with life-threatening illness who have failed or cannot tolerate approved therapies, are unable to participate in clinical trials and have no other treatment options.

FLAVONOID: a plant extract with biological activity.

FOLIC ACID: a B complex vitamin important for red blood cell production. Folate is a salt or ester of folic acid. Deficiency can cause loss of taste and anemia.

FOOD AND DRUG ADMINISTRATION (FDA): the U.S. federal agency responsible for regulating the development, use and safety of drugs, medical devices, food, cosmetics and related products.

FORMULARY: a list of approved or available drugs.

GALL BLADDER: an organ in the abdomen in which bile is stored.

GAMMA GLOBULIN: a preparation of antibodies injected to prevent or treat infection.

GASTROINTESTINAL: relating to the stomach and intestines.

GENE THERAPY: an approach to preventing and/or treating disease by replacing, removing or introducing genes, or otherwise manipulating genetic material.

GENOTYPE (adjective GENOTYPIC): the specific genetic makeup or "blueprint" of an organism. Genotypic resistance testing determines whether an organism's genetic structure contains certain mutations.

GLUCOSE-6-PHOSPHATE DEHYDROGENASE (G6PD) DEFICIENCY: a disorder in which a missing enzyme leads to the destruction of red blood cells.

GP120: a glycoprotein (sugar/protein compound) on the outer envelope of HIV. Gp120 binds to CD4 receptors and enables HIV to enter certain cells.

GRAFT-VERSUS-HOST DISEASE (GVHD): a condition in which transplanted donor immune tissue (e.g., bone marrow) attacks the tissues of the new host's body.

GRANULOCYTE: a type of white blood cell (basophil, eosinophil, neutrophil) that contains granules of toxic chemicals that are released to kill microorganisms and mediate allergic reactions.

GRANULOCYTE COLONY-STIMULATING FACTOR (G-CSF): a cytokine that stimulates the production of granulocytes, a type of white blood cell. Genetically engineered G-CSF (filgrastim, brand name Neupogen) is used to treat neutropenia.

GRANULOCYTE MACROPHAGE COLONY-STIMULATING FACTOR (GM-CSF): a cytokine that stimulates growth of granulocytes and macrophages, types of white blood cells. Genetically engineered GM-CSF (sargramostim, brand name Leukine) is used to stimulate white blood cell production, e.g., following a bone marrow transplant.

GRANULOCYTOPENIA: abnormally low numbers of granulocytes in the circulating blood, which may lead to an increased risk of bacterial infection. In practice the term is used to mean neutropenia.

GYNECOMASTIA: abnormally extensive development of breast tissue in males.

HAART: highly active antiretroviral therapy, a term for potent combination anti-HIV treatment usually including a protease inhibitor drug.

HALF-LIFE: the time required for half of the amount of an agent (e.g., drug, virus) to be eliminated from the body.

HEMATOCRIT (HCT): the percentage of red blood cells in a given amount of whole blood. The hematocrit reflects the oxygen-carrying capacity of the blood.

HEMATOPOIESIS: the production of new blood cells in the bone marrow.

HEMOGLOBIN: the red, iron-based pigment in red blood cells that enables them to transport oxygen. Also refers to a test of the amount of hemoglobin in red blood cells.

HEMOLYSIS: the breakdown or destruction of red blood cells.

HEMOLYTIC ANEMIA: a low red blood cell count due to destruction of the cells.

HEPATITIS: an inflammation of the liver that may be caused by several agents, including viruses, toxins and drugs. Acute hepatitis is typically characterized by fever, jaundice, fatigue, abdominal tenderness and elevated liver enzymes. Hepatitis A virus causes an inflammatory viral disease with a short incubation period. Hepatitis B and C virus can become chronic and may result in liver damage, cirrhosis and/or liver cancer.

HEPATOMEGALY: liver enlargement.

HERPES SIMPLEX VIRUS (HSV): a herpesvirus that causes recurring lesions. HSV type 1 usually produces blisters on the lips or in the mouth ("cold sores"); HSV type 2 is usually sexually transmitted and produces lesions in the genital and/or anal area.

HERPESVIRUS: a group of viruses that includes herpes simplex virus types 1 and 2, varicella-zoster virus, Epstein-Barr virus, cytomegalovirus, human herpesvirus types 6 and 7, and Kaposi's sarcoma-associated herpesvirus.

HHV-8: see Kaposi's sarcoma-associated herpesvirus.

HORMONE: a chemical messenger involved in the regulation and coordination of cellular and bodily functions.

HUMAN CHORIONIC GONADOTROPIN (HCG): a hormone secreted by the placenta that maintains pregnancy during the early development of the fetus.

HUMAN CHORIONIC GONADOTROPIN-ASSOCIATED FACTOR (HAF): a substance associated with human chorionic gonadotropin that has been shown to shrink Kaposi's sarcoma tumors, lower blood levels of HIV and stimulate blood cell production.

HUMAN PAPILLOMAVIRUS (HPV): a papovavirus. Many strains of HPV cause warts, including condylomata acuminata (genital warts). Certain strains (e.g., 16, 18) are associated with cervical and anal cancer.

HUMORAL IMMUNITY (TH2 RESPONSE): the immune response mediated by the Th2 subset of CD4 cells. Humoral immunity is stimulated by cytokines including IL-4 and IL-6, and carried out by plasma cells (derived from B-cells) which produce antibodies.

HYDROXYUREA: a drug that interferes with viral replication by inhibiting a host cell enzyme called ribonucleotide reductase, resulting in a reduction of the supply of the building blocks needed to make new DNA.

HYPERGLYCEMIA: high blood sugar (glucose).

HYPERSENSITIVITY REACTION: an exaggerated immune response to an antigen, drug, etc.

HYPERSPLENISM: a condition in which an enlarged spleen removes too many blood cells from circulation.

HYPERTENSION: high blood pressure.

HYPOTONY: low pressure, e.g., in the eye.

HYPOXIA: a reduced level of oxygen reaching body tissues.

IDIOPATHIC: refers to a disease or condition of unknown cause or origin.

ILEUM: the final, long and narrow segment of the small intestine that empties into the colon.

IMMUNE SYSTEM: the body's defense system that protects against foreign invaders (e.g., microorganisms) and cancerous cells. Immune system organs include the lymph nodes, spleen, thymus, tonsils and bone marrow.

IMMUNIZATION (VACCINATION): a process by which a person is protected against the adverse effects of infection by a disease-causing microorganism by exposing the person to a small amount of the killed or inactivated organism or to pieces of the organism.

IMMUNOGLOBULIN: see antibody.

IMMUNOSUPPRESSION: reduction in immune system function.

IMMUNOTHERAPY (IMMUNE-BASED THERAPY): a therapy that attempts to modify or enhance immune response, or to reconstitute a damaged immune system.

INCIDENCE: the number of new cases of a disease or condition in a specific population during a given period of time.

INDUCTION: the initiation phase of a particular therapy.

INFLAMMATION: the body's response to tissue injury or infection, which typically includes increased vessel dilation and permeability, resulting in redness, swelling, heat and pain.

INTERLEUKIN (IL): a cytokine (chemical messenger) secreted by immune system blood cells that regulates a range of immune functions.

INTRINSIC FACTOR: a substance produced by the lining of the intestine that enables the absorption of vitamin B₁₂.

IN UTERO: in the uterus; typically refers to events that occur in the womb before birth.

IN VITRO: Latin for "in glass"; refers to work done in a test tube or culture medium in the laboratory.

IN VIVO: Latin for "in the body of a living organism"; refers to work done using human or animal subjects.

IRON DEFICIENCY ANEMIA: the most common type of anemia, caused by a lack of iron, which is needed to produce the hemoglobin in red blood cells.

JAUNDICE: a yellowish discoloration of the skin and whites of the eyes caused by the increased breakdown of red blood cells. Jaundice is associated with liver damage.

KAPOSI'S SARCOMA (KS): an abnormal or cancerous proliferation of cells of the blood and/or lymph vessels causing tumors on the skin, mucous membranes and/or internal organs. KS typically appears as pink or purple, flat or raised lesions.

KAPOSI’S SARCOMA-ASSOCIATED HERPESVIRUS (KSHV, HHV-8): a sexually transmitted herpesvirus that is associated with Kaposi's sarcoma.

KERATOCONJUNCTIVITIS: inflammation of the cornea and conjunctival membrane of the eye.

KIDNEY STONE (NEPHROLITHIASIS): an accumulation of substances (e.g., drug crystals, minerals) in the kidney, which may lead to blockage and pain in the flanks, back or groin.

LACTOSE INTOLERANCE: a digestive disturbance characterized by cramps that results from the lack of a digestive enzyme (lactase) that breaks down the sugar (lactose) in milk.

LEAN BODY MASS: muscle and organ tissue.

LEUKEMIA: a cancerous disease of the blood characterized by the proliferation of white blood cells.

LEUKOCYTE: an immune system white blood cell (e.g., monocyte, neutrophil, B-cell, T-cell). White blood cells are involved in the body's defense against infections and cancer.

LEUKOPENIA: an abnormally low number of white blood cells in the circulating blood.

LIMIT OF DETECTION: the lower boundary of an assay (e.g., a viral load test). The limit of detection is the level below which a test cannot measure the presence of a component (e.g., HIV RNA).

LIPID: a fat.

LIPODYSTROPHY: changes in body shape typically characterized by loss of fatty tissue in the limbs and face and redistribution of fat to the trunk, abdomen or back of the neck.

LIVER ENZYME: a protein produced by the liver (e.g., ALT, AST) that catalyzes various physiological reactions. Abnormally high levels of liver enzymes in the blood may indicate liver damage.

LIVER FUNCTION TEST: a blood test that measures levels of liver enzymes to indicate how well the liver is working .

LOG: refers to quantities in factors of 10. A log change is an exponential or 10-fold increase or decrease (e.g., going from 10 to 100 is a 1-log increase).

LUPUS (SYSTEMIC LUPUS ERYTHEMATOSUS): an autoimmune disease characterized by swelling in many parts of the body and associated with inflammation of the connective tissue, especially in the joints.

LYMPH NODE: small, bean-sized organs located throughout the body. Lymph nodes filter out antigens and are the site of immune activation.

LYMPHATIC SYSTEM: a network of capillary-like vessels, ducts, nodes and organs that helps maintain the fluid environment of the body and coordinates immune responses. The lymphoid organs include the lymph nodes, spleen, thymus, tonsils and adenoids.

LYMPHOCYTE: a type of white blood cell (T-cell, B-cell or natural killer cell) that plays a part in immune defense.

LYMPHOCYTIC LINEAGE: a type of precursor blood cell that develops into lymphocytes (B-cells and T-cells).

LYMPHOCYTOPENIA (LYMPHOPENIA): a reduced number of lymphocytes, a type of white blood cell.

MACROPHAGE: a large scavenger white blood cell that ingests and processes degenerated cells and foreign invaders. Macrophages are derived from monocytes that leave the blood to migrate into the tissues. Specialized macrophages protect the skin, lungs (alveolar macrophages), brain (microglia), liver (Kupffer cells) and other tissues. The long-lived macrophages act as reservoirs of HIV.

MACROPHAGE COLONY-STIMULATING FACTOR (M-CSF): a cytokine that stimulates the production of macrophages, a type of white blood cell.

MAINTENANCE THERAPY: preventive therapy that follows successful initial treatment of an illness.

MALAISE: a generalized feeling of illness and discomfort; a "flu-like" feeling.

MAST CELL: a type of immune system cell, related to the basophil, that resides in bodily tissues. Mast cells release histamine and heparin, chemicals which are involved in allergic reactions and blood clotting.

MEGAKARYOCYTE (THROMBOBLAST): a large precursor cell in the bone marrow that divides to form platelets.

MEGALOBLASTIC ANEMIA (MACROCYTIC ANEMIA): a type of anemia characterized by large, misshapen, short-lived red blood cells, due to a lack of vitamin B₁₂ or folic acid.

MEMORY CELL: a B-cell or T-cell that remains after an initial immune response and is primed to respond to a subsequent attack by the same invader in the future.

METABOLISM (adjective METABOLIC): the process of building the body's molecular structures from nutrients (anabolism) and breaking them down for energy production (catabolism).

MICROBICIDE: an agent that inactivates, kills or destroys microbes.

MICROCYTIC HYPOCHROMIC ANEMIA: a type of anemia characterized by small red blood cells that contain a reduced amount of hemoglobin.

MOLLUSCUM CONTAGIOSUM: a viral skin condition characterized raised, flesh-colored lesions with a central depression.

MONOCYTE: a large white blood cell that plays a role in immune defense. Monocytes circulate in the bloodstream; when they migrate to the tissues, they mature into macrophages.

MONONUCLEOSIS: an infectious disease caused by the Epstein-Barr virus that is easily transmitted via saliva. The disease is characterized by a sore throat, fatigue and possibly swollen lymph nodes or a swollen spleen.

MONOTHERAPY: the use of a single drug or other therapy.

MUTATION: a change in the character of a gene that is perpetuated when a cell or virus divides. A mutant is a new organism produced by a gene mutation.

MYASTHENIA GRAVIS: an autoimmune disease that targets nerve-muscle junctions, resulting in weakness and paralysis.

MYCOBACTERIUM AVIUM COMPLEX (MAC): an opportunistic disease caused by Mycobacterium avium or Mycobacterium intracellulare, bacteria found in soil and water.

MYELOCYTIC LINEAGE: a type of precursor blood cell that develops into monocytes, macrophages and granulocytes.

MYELOMA: a type of cancer of the bone marrow.

MYOPATHY: inflammation or degeneration of the muscles which may cause pain or weakness.

NAIVE: inexperienced. The term is used to describe an individual who has never taken a certain drug (e.g., AZT-naive) or to refer to undifferentiated immune system cells.

NATURAL KILLER CELL (NK CELL): a type of white blood cell that attacks and kills tumor cells and cells infected with microorganisms.

NEOPLASM: a tumor or growth; tissue that develops abnormally or grows more rapidly than normal and lacks structural organization and functional coordination with normal tissue.

NEPHROTOXICITY: the property of being poisonous or harmful to the kidneys.

NEUTROPENIA: an abnormally low number of neutrophils in the circulating blood, leading to susceptibility to infection.

NEUTROPHIL: the most common type of white blood cell. Neutrophils are phagocytes that engulf and destroy bacteria and fungi.

NITRITE INHALANT (POPPERS): a volatile chemical preparation (e.g., amyl nitrite, isobutyl nitrite) that dilates blood vessels and is often used as a sexual enhancer.

NITROGLYCERIN: a chemical that dilates blood vessels, typically used to treat angina pain.

NON-NUCLEOSIDE REVERSE TRANSCRIPTASE INHIBITOR (NNRTI): a drug (e.g., delavirdine, nevirapine, efavirenz) that binds to and inhibits the action of the HIV reverse transcriptase enzyme, thus blocking viral transcription and replication.

NUCLEOSIDE ANALOG (also known as NUCLEOSIDE REVERSE TRANSCRIPTASE INHIBITOR, NRTI): a compound (e.g., AZT, ddI, ddC, d4T, 3TC, abacavir) that mimics one of the building blocks of DNA. These compounds suppress retroviral replication by interfering with the reverse transcriptase enzyme; the synthetic nucleosides cause premature termination when they are inserted into the viral DNA chain being built.

OFF-LABEL: use of an FDA-approved drug for an indication other than that for which it was approved.

OPEN-LABEL: refers to a drug trial in which both participants and investigators know what drug is being tested and what dosages are being used.

OPHTHALMOLOGY: the medical specialty relating to the treatment of diseases and disorders of the eye.

OPPORTUNISTIC INFECTION (OI): a disease (e.g., PCP, MAC, CMV disease) caused by a microorganism that does not normally cause illness in a person with a healthy immune system, but which may cause serious disease when the immune system is suppressed.

PALLOR: paleness.

PANCREATITIS: inflammation of the pancreas, a digestive gland in the abdominal cavity. Symptoms may include abdominal pain, nausea, constipation and jaundice.

PANCYTOPENIA: an abnormally low level of all types of blood cells, typically due to bone marrow damage.

PAP SMEAR: a procedure in which a specimen of cells is taken from the uterine cervix or anus, prepared on a slide and examined under a microscope for abnormal cell growth.

PARVOVIRUS: a family of viruses which infect rapidly growing tissues.

PATHOGEN: any disease-causing agent, especially a microorganism.

PATHOGENESIS: the origin and development of a particular disease, including the specific events involved, bodily tissues or systems affected, mechanisms of damage and timing of the course of disease.

PCR: see polymerase chain reaction.

PERINATAL HIV TRANSMISSION (PHT, VERTICAL TRANSMISSION): the transmission of HIV from mother to child. Perinatal transmission may occur in utero (in the womb), intrapartum (during birth) or postpartum (after birth, via breast-feeding).

PERIPHERAL NEUROPATHY: a disorder of the peripheral nerves, usually involving the feet, hands and sometimes the legs, arms and face. Symptoms may include numbness, tingling or burning sensations, pain, abnormal reflexes, weakness and partial paralysis.

PERIPHERAL SMEAR: a blood test that involves looking at the size and shape of blood cells under a microscope.

PERNICIOUS ANEMIA: a type of anemia caused by the inability of the intestine to absorb vitamin B₁₂, which is needed to produce red blood cells.

PHAGOCYTOSIS: the process of engulfing harmful matter in the body, carried out by scavenger white blood cells called phagocytes (e.g., neutrophils, macrophages).

PHARMACOKINETICS: the action of drugs in the body, including the processes of absorption, metabolism, transformation, distribution to tissues and elimination.

PHASE I TRIAL: the first step in human testing of a new drug; these trials evaluate drug safety and toxicity at different dose levels in a small number of volunteers.

PHASE II TRIAL: the second step in the evaluation of a new drug in humans; these trials evaluate drug effectiveness and compare doses in more participants than Phase I studies.

PHASE III TRIAL: the third step in human drug testing; these trials are designed to support and verify information gathered in Phase I and II trials, and involve many more volunteers. Phase III trials may compare the drug being tested to other therapies or to placebo.

PHENOTYPE (adjective PHENOTYPIC): visible characteristics and/or behavior that result from the interaction of an organism’s genetic "blueprint" (genotype) and the environment. Phenotypic resistance testing determines whether an organism responds to a specific drug in a test tube.

PLACEBO-CONTROLLED TRIAL: a trial of an experimental therapy in which an inactive substance or mock therapy (placebo) is given to one group while the treatment being tested is given to another, and the results obtained in the different groups are compared.

PLACENTA: the organ that connects the fetus and the mother's uterus and enables the exchange of oxygen and nutrients.

PLASMA: the fluid, non-cellular portion of blood.

PLASMA CELL: an immune system cell that develops from a B-cell and produces antibodies against a specific antigen.

PLASMAPHERESIS: a process by which certain elements are removed from whole blood and the remaining blood is returned to the circulation.

PLATELET: see thrombocyte.

PLURIPOTENT STEM CELL: see stem cell.

PNEUMOCYSTIS CARINII PNEUMONIA (PCP): a life-threatening opportunistic type of pneumonia caused by a protozoan.

PNEUMONITIS: inflammation of the lungs.

POLYMERASE CHAIN REACTION (PCR): a highly sensitive test that uses an amplification technique to detect small amounts of DNA or RNA (genetic material) in blood or tissue samples.

POPPERS: see nitrite inhalant.

POSTEXPOSURE PREVENTION (PEP): drug therapy given immediately following exposure to an infectious organism in an attempt to prevent the infection from taking hold in the body.

PRECURSOR CELL: a cell that develops into a mature blood cell.

PREVALENCE: the number of individuals with a condition in a specific population.

PRIMARY HIV INFECTION (PHI): the initial introduction of HIV into the body; the earliest stage of HIV disease.

PROGNOSIS: a forecast of the probable course and/or outcome of a disease.

PROGRESSIVE MULTIFOCAL LEUKOENCEPHALOPATHY (PML): a rapidly progressing, often fatal brain disease believed to be caused by the JC papovavirus. PROPHYLAXIS (adjective PROPHYLACTIC): therapy that helps to prevent a disease before it occurs (primary prophylaxis) or recurs (secondary prophylaxis).

PROTEASE: an enzyme that cleaves proteins; HIV protease allows replication of the virus.

PROTEASE INHIBITOR: a drug (e.g., saquinavir, indinavir, ritonavir, nelfinavir, amprenavir) that blocks the action of the HIV protease enzyme, thereby preventing viral replication.

PROTOZOAN: an acellular or 1-celled microorganism, several types of which can cause disease in humans.

RANDOMIZED TRIAL: an experiment arranged so as to produce a chance distribution of subjects into different treatment groups or arms.

RECEPTOR: a specific protein-binding site on a cell's surface or interior. Viruses enter cells by fusing with receptors on a cell’s surface.

RECOMBINANT: produced by genetic engineering.

REFRACTORY: resistant to treatment.

REGIMEN: a formalized schedule by which drugs are administered, including the amount of drug and the number of doses in a time period.

REMISSION: an abatement in the severity of disease symptoms; a period during which symptoms are reduced or eliminated.

REPLICATION: multiplication or reproduction.

RESERVOIR: a site where an infectious agent collects and multiplies; macrophages and lymph nodes are thought to be HIV reservoirs.

RESISTANCE: the mutation of a microorganism in such a way that it loses its sensitivity to a drug.

RETICULOCYTE: an immature red blood cell that still contains intracellular organelles.

RETINITIS: inflammation of the retina, the light-sensitive tissue at the back of the eyeball, that may lead to the loss of vision. Cytomegalovirus (CMV) infection is a common cause of retinitis in people with HIV disease.

RETROVIRUS: a class of enveloped viruses that have their genetic material in the form of RNA and use the reverse transcriptase enzyme to translate their RNA into DNA.

REVERSE TRANSCRIPTASE (RT): a viral enzyme that allows a retrovirus to translate its genetic material (in the form of RNA) into DNA, which is then integrated into the chromosomes of the host cell.

REVERSE TRANSCRIPTASE INHIBITOR (RTI): a drug that blocks retroviral replication by interfering with the reverse transcriptase enzyme. RTI include nucleoside analogs (e.g., AZT, ddI, 3TC, abacavir) and non-nucleoside reverse transcriptase inhibitors (e.g., nevirapine, delavirdine, efavirenz).

RNA (RIBONUCLEIC ACID): a single-stranded nucleic acid made up of nucleotides. Messenger RNA (mRNA) is involved in the transcription of genetic information and the production of new proteins.

RT-PCR: see polymerase chain reaction.

SALVAGE THERAPY: emergency treatment with experimental or non-standard drugs for an illness that has not responded to standard therapy.

SENSITIVITY: the ability of an organism to be affected by a drug. Also, a statistical measure of the accuracy of a screening test.

SEPSIS: the presence of pathogenic organisms or their toxins in the blood.

SEROCONVERSION: the development of antibodies directed against a microorganism; the change in a person's antibody status from negative to positive.

SEXUALLY TRANSMITTED DISEASE (STD): a disease (e.g., gonorrhea, syphilis, chlamydiasis) that is transmitted through sexual contact.

SHINGLES (HERPES ZOSTER): a condition characterized by painful blisters that typically appear in a linear distribution on the skin. Shingles is caused by reactivation of a previous infection with the varicella-zoster virus (VZV) that causes chickenpox.

SICKLE CELL ANEMIA: a type of anemia in which abnormal hemoglobin molecules form crystals inside red blood cells, causing them to get stuck in small blood vessels and sometimes to burst.

SIDE EFFECT: an unwanted adverse reaction to a drug treatment (e.g., rash, nausea, peripheral neuropathy, bone marrow suppression, liver or kidney failure).

SIMIAN IMMUNODEFICIENCY VIRUS (SIV): a virus, similar to HIV, that infects monkeys.

SPECIFIC IMMUNITY: a form of immune system activity carried out by B-cells and T-cells, which each react to a specific antigen.

SPLEEN: an immune system organ located in the abdominal cavity. The spleen is a blood-producing organ in the fetus, and removes old red blood cells and platelets from circulation.

SPLENECTOMY: surgical removal of the spleen.

SPLENOMEGALY: enlargement of the spleen.

SPRUE: an intestinal disease.

STATISTICAL SIGNIFICANCE: the probability that an observed outcome of an experiment or trial is not due to chance alone.

STEM CELL: a precursor cell in the bone marrow from which all blood cells are derived.

STEROID: a family of substances that share a similar chemical structure, including certain hormones (e.g., testosterone) and various drugs.

STRAIN: a specific genetic variant of an organism.

STROKE: a cerebrovascular accident, in which the blood flow to the brain is interrupted.

SUBTYPE: a distinct form of a microorganism.

SUBUNIT: a piece or small part of a larger unit. Subunit HIV vaccines are vaccines that contain a piece of HIV.

SUPPOSITORY: a medicated tablet that is inserted into the rectum or vagina.

SYNERGY: the action of 2 or more drugs working together to produce an effect greater than the expected combined effect of the same agents used separately.

SYSTEMIC: affecting the whole body; not localized.

T-CELL (T-LYMPHOCYTE): a type of white blood cell that matures in the thymus and carries out the cell-mediated immune response. There are 3 major types of T-cells: helper (CD4) T-cells, suppressor (CD8) T-cells and killer T-cells (cytotoxic T-lymphocytes or CTL).

TESTOSTERONE: a steroid hormone produced by the testes and adrenal glands. Testosterone is required for sperm production, the development of the male reproductive organs, and the emergence of male secondary sexual characteristics. The hormone is also required for the buildup of lean muscle mass.

THALASSEMIA: an inherited disease characterized by small, abnormal red blood cells. The disease is due to the inability to properly incorporate hemoglobin into newly forming cells.

THROMBOCYTE (PLATELET): a type of blood cell that facilitates normal blood clotting.

THROMBOCYTOPENIA: an abnormally low number of platelets, which may result in abnormal bleeding and bruising.

THROMBOCYTOPENIC PURPURA: a condition, caused by a lack of platelets, characterized by bleeding from small blood vessels, leading to numerous bruises under the skin.

THROMBOPOIETIN (TPO): a cytokine that stimulates the production of megakaryocytes and their division into platelets.

THYMUS: an immune system organ in the upper chest where T-cells mature.

TOXICITY (adjective TOXIC): the quality of being poisonous or harmful; often used to refer to drug side effects.

TOXIN: a harmful or poisonous agent.

TRANSFUSION: the transfer of blood or blood components from one individual to another.

TUBERCULOSIS (TB): an infectious disease caused by Mycobacterium tuberculosis that typically affects the lungs, but may also occur in other organs (extrapulmonary TB).

UNDETECTABLE: a term used to describe a viral load that is below the level of detection of the test being used.

VACCINE: a preparation that contains an infectious agent or its components which is administered to stimulate an immune response that will protect a person from illness due to that agent. Agents used in vaccines may be whole killed (inactivated) organisms, live-attenuated (weakened) organisms or artificially manufactured pieces of an organism. A therapeutic vaccine is given after infection and is intended to reduce or arrest disease progression. A preventive vaccine is intended to prevent initial infection.

VARICELLA-ZOSTER VIRUS (VZV, HUMAN HERPESVIRUS 3): a herpesvirus that initially causes chickenpox and may reactivate later to cause herpes zoster (shingles).

VIRAL LOAD (VIRAL BURDEN): the amount of virus in the blood or other tissues. The presence of HIV RNA indicates that the virus is replicating. Changes in viral load may be used to gauge drug effectiveness and disease progression. Viral load is measured using assays such as the RT-PCR or branched-chain DNA (bDNA) tests.

VIREMIA: the presence of virus in the blood or plasma.

VIRULENCE (adjective VIRULENT): aggressiveness, ability to cause disease.

VIRUS: a minute organism that cannot grow or reproduce outside of a host cell. During replication a virus integrates its genetic material (DNA or RNA) into the host cell and takes over the cell's biological mechanisms to reproduce new virus particles.

VITAMIN B₁₂ (COBALAMIN): a vitamin of the B complex that is necessary for the production of healthy red blood cells.

WASTING SYNDROME: a condition characterized by atrophy of lean body mass and involuntary weight loss of more than 10% of normal body weight.

WESTERN BLOT: a laboratory blood test for specific antibodies. The Western blot test is more accurate than the ELISA test, and is used as a confirmatory test if an ELISA test is positive.

WILD-TYPE: the normal, typical form of a virus before genetic mutation takes place.

Page last updated 8 July 1998

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