Teach Online Glossary

Definitions are given by the full name of the term or generic name of the drug, not by the abbreviation or brand name. For example, the definition of KS will be found under Kaposi's Sarcoma. The only abbreviations commonly used within definitions are HIV, AIDS, RNA, DNA, and FDA.

Terms used that are defined elsewhere in the Glossary are in CAPITALS.

The drug chart lists alternative names for commonly prescribed medications.

< K >

K Cell: A type of nonspecific LYMPHOCYTE that seeks out and kills any cells coated with any ANTIBODY. (The cells become coated because they are infected with VIRUS and display viral PROTEINS on their surface membranes.)

Kaplan-Meier Curve: a method for analyzing a therapy's EFFICACY or TOXICITY by graphically displaying "survival" or the occurrence of a study ENDPOINT or dropout. The Kaplan-Meier curve displays a statistical estimate of the percent of people receiving a given therapeutic REGIMEN who, at each observation point after entering a trial, continue to do acceptably well on their assigned therapy. Plotting the curves for a trial's different treatment ARMS on the same chart yields a comparison of the various regimens.

Kaposi's Sarcoma (KS): an AIDS-DEFINING ILLNESS consisting of individual cancerous lesions caused by an overgrowth of blood vessels. KS typically appears as pink or purple painless spots or nodules on the surface of the skin or oral cavity. KS also can occur internally, especially in the intestines, LYMPH NODES and lungs, and in this form is life-threatening. KS is most likely triggered by a species of HERPES VIRUS similar to EPSTEIN-BARR VIRUS (see HHV-8). Up to now, KS has been treated with ALPHA INTERFERON, radiation therapy (outside the oral cavity), and various systemic and intralesional cancer CHEMOTHERAPIES. Possible antiviral remedies, such as CIDOFOVIR and FOSCARNET, are now being examined, as well as TOPICAL treatments.

Kaposi's Sarcoma Herpes Virus: see HHV-8.

Karnofsky Performance Score: a scale for analyzing a patient's ability to perform certain ordinary tasks: 100 - normal, no complaints; 70 - unable to carry on normal activity; 50 - requires considerable assistance; 40 - disabled; 30 - hospitalization recommended.

Ketoconazole (Nizoral): an antifungal medication available in pill and liquid form that is effective against a variety of fungal infections such as oral, vaginal and esophageal THRUSH and cryptococcosis (see CRYPTOCOCCUS). Persons taking ketoconazole must have their liver function tested periodically because of the slight danger of serious liver damage.

Kidney Stone: a painful solid mass in the kidney or urinary system, caused by the solidification or precipitation of a dissolved substance in the urine.

Killer Cell: a generalized name for IMMUNE SYSTEM cells that kill cancerous and VIRUS-infected cells. Among the killer cells are killer T CELLS (CYTOTOXIC T LYMPHOCYTES), NATURAL KILLER CELLS and K CELLS.



KSHV: see HHV-8.


< L >

Lactic Acidosis: a rare but deadly metabolic disorder. Symptoms can include weight loss, fatigue, malaise, nausea, vomiting, abdominal pain, shortness of breath and low SERUM bicarbonate levels. NUCLEOSIDE ANALOGS have been associated with mitochondrial toxicity, which can lead to lactic acidosis.

Lactobacillus: BACTERIA that create lactic acid.

Lactose Intolerance: the inability to digest milk products due to the lack of the ENZYME lactase, which breaks down milk sugar (lactose).

Lamivudine (3TC, Epivir): a NUCLEOSIDE ANALOG from GlaxoSmithKline with anti-HIV and anti-HEPATITIS B activity. Most common SIDE EFFECTS are nausea, headache, fatigue, diarrhea and ANEMIA.

Langerhans Cell: the type of DENDRITIC CELL found in the skin.

Last Observation Carried Forward (LOCF): a type of data analysis in CLINICAL TRIALS in which the last results before a subject drops out of the trial are counted as if they occurred at the end of the trial. Used when data are missing due to loss to follow-up.

Late Breaker: a presentation at a scientific conference that was submitted too late to be included in the original program but that was deemed to merit inclusion in the conference.

Latency: a QUIESCENT period during a disease process. Clinical latency is an ASYMPTOMATIC period in the early years of HIV infection. The period of latency is characterized in the peripheral blood by stable, slightly depressed CD4 CELL COUNTS and low HIV levels. Research indicates that HIV remains quite active in the LYMPH NODES during this period. Cellular latency is a condition that exists in some cells after HIV has integrated its GENOME into the cell's DNA but has not yet begun to replicate. Cellular latency may last for years, making the eradication of HIV from the body unlikely.

Lavage: the process of washing out an internal organ or cavity for treatment or to obtain a sample.

L-Carnitine: a naturally occurring cell constituent that modulates fat METABOLISM, in particular the mitochondrial intake of LIPID derivatives. L-carnitine has been proposed as a treatment for WASTING SYNDROME and the MYOPATHY associated with AZT (ZIDOVUDINE).


Lean Body Mass: the body's muscle and organ tissue.

Lecithinized Superoxide Dismutase (PC-SOD): a synthetic version of superoxide dismutase (SOD), one of the more potent ANTIOXIDANTS produced by the body.

Lentivirus: a subgroup of the RETROVIRUS family that includes HIV and is characterized by long periods of clinical LATENCY after infection.

Lesion: a disturbed area of tissue - a wound, ulcer, injury, nodule or tumor on the skin or elsewhere.


Leukocyte: any of the various white blood cells, which together make up the IMMUNE SYSTEM. NEUTROPHILS, LYMPHOCYTES and MONOCYTES are all leukocytes.

Leukocytosis: an abnormally high number of LEUKOCYTES, or white blood cells, in the blood. This condition can occur during many types of infection and INFLAMMATION.

Leukopenia: an abnormally low number of total LEUKOCYTES, or white blood cells, circulating in the blood, frequently the result of drug-induced BONE MARROW SUPPRESSION.


Libido: sex drive.

Licorice: see GLYCYRRHIZIN.

Ligand: any molecule that binds to the surface of another molecule, such as an immune cell RECEPTOR. For examples of receptors see CCR5, CXCR-4, CD4.

Limit of Detection: refers to the SENSITIVITY of a quantitative diagnostic test, such as the VIRAL LOAD ASSAY. The limit of detection is the level below which the test can no longer accurately measure the amount of a substance, such as HIV RNA. If a person has an "undetectable" viral load, it does not mean that HIV is no longer present, but rather, that the test is not sensitive enough to measure the amount (see also RESERVOIR). Also called the limit of quantification.

Limit of Quantification: see LIMIT OF DETECTION.


Lipid: a fatty substance.

Lipitor: see ATORVASTATIN.

Lipodystrophy: a disturbance of fat METABOLISM that involves the absence of fat and/or the abnormal distribution of fat in the body. Currently, "lipodystrophy" is not clearly defined and the term is used to refer to a variety of SYNDROMES, including wasting in the face and extremities, an accumulation of abdominal fat and breast enlargement. The cause is unknown, but it could be a result of HIV infection and/or ANTIRETROVIRAL therapy.

Lipomas: tumors consisting of fat cells.

Lipomatosis: A disorder characterized by deposits of fat beneath the skin of the neck, upper body, arms and legs. The origin is uncertain, but it is thought to be genetic. Lipomatosis often occurs in conjunction with alcoholic liver disease, macrocytic ANEMIA and PERIPHERAL NEUROPATHY. It usually affects men and is most common in the Mediterranean.

Lipoprotein: a chemical compound made of fat and PROTEIN. Lipoproteins are found in the blood, where they carry CHOLESTEROL.

Liposome: microscopic globules of LIPIDS manufactured to enclose medications. The liposome's fatty layer is supposed to protect and confine the enclosed drug until the liposome adheres to the outer membrane of target cells. By delivering treatments directly to the cells needing them, drug EFFICACY may be increased while overall TOXICITY is reduced.

Liposuction: a surgical procedure in which fat deposits are suctioned from specific parts of the body, e.g., the abdomen, buttocks, hips, thighs, or back. Liposuction is sometimes used to treat truncal adiposity or BUFFALO HUMP, although results can vary.


Liver Function Test (LFT): a test that measures the blood SERUM level of any of several ENZYMES produced by the liver. An elevated liver function test is a sign of possible liver damage.


Log (Logarithm): formally, the number of times ten must be multiplied with itself to equal a certain number. For example, log 5 is 100,000 (10 x 10 x 10 x 10 x 10). VIRAL LOAD is often reported in terms of log. In addition, logs are used to measure changes in viral load. For example, a reduction in viral load from 100,000 to 1,000 copies/ml is a 2.0 log (or 99 percent) reduction (100,000 divided by 100 [2.0 log or 10 x 10] equals 1,000). Note that while a one log reduction is a ten-fold difference, a half log change is not a five-fold difference, rather a change of 3.16-fold (the square root of ten) because 100.5 or 101⁄2 = 3.16.

Logarithm: see LOG.

Long-Term Nonprogressor: an individual who has been infected with HIV for at least seven to twelve years (different authors use different time spans) and yet retains a CD4 CELL COUNT within the normal range and no evidence of disease progression.

Long-Term Survivor: a looser term than LONG-TERM NONPROGRESSOR that indicates any person with any stage of HIV infection, including AIDS, who has been stable over a period of years.

Long Terminal Repeat (LTR): the genetic material at each end of a genetic sequence. When the HIV genes are integrated into a cell's own GENOME, the LTR interacts with cellular and viral factors to initiate the transcription of the HIV DNA into an RNA form that is packaged in new VIRUS particles. Activation of the LTR is a major step in triggering HIV replication.

Longitudinal Study: a study that follows patients over an extended period of time.


Lopinavir (Kaletra, LPV): a PROTEASE INHIBITOR made by Abbott Laboratories. Kaletra (LPV/r) is a combination of lopinavir and a low dose of RITONAVIR, a drug that improves blood levels of lopinavir.

Lotrimin: see CLOTRIMAZOLE.

Lovastatin: a CHOLESTEROL-lowering drug.

Low Density Lipoprotein (LDL) Cholesterol: a LIPOPROTEIN that contains more fat than PROTEIN, often called "bad cholesterol."



Lumbar Puncture (LP): insertion of a needle into the lower spinal canal to obtain a sample of CEREBROSPINAL FLUID. Also called a spinal tap.

Lymph Fluid: a transparent, slightly yellow fluid that carries LYMPHOCYTES to and from the LYMPH NODES and helps to collect foreign MICROBES. Lymph is derived from tissue fluids. The fluid passes through the lymphatic ducts and then enters the bloodstream.

Lymph Gland: see LYMPH NODE.

Lymph Node: small bean-sized organs made up mostly of densely packed LYMPHOCYTES, LYMPH FLUID and connective tissue. Clusters of lymph nodes are widely distributed in the body and are essential to the functioning of the immune system. They are the main sites where acquired immune responses are launched (see IMMUNE SYSTEM and NAIVE T CELL). Lymph nodes are connected with each other, other lymphoid tissue and the blood by the LYMPHATIC VESSELS.

Lymphadenopathy: swelling or enlargement of the LYMPH NODES due to infection or cancer. The swollen nodes may be palpable or visible from outside the body.

Lymphatic Vessels: a body-wide network of channels, similar to the blood vessels, that transports LYMPH FLUID to the lymphoid tissue and into the bloodstream.

Lymphocyte: white blood cells that mature and reside in the lymphoid organs and are responsible for the acquired immune response (see IMMUNE SYSTEM). The two major types of lymphocytes are T CELLS and B CELLS.

Lymphoid Interstitial Pneumonitis (LIP): a type of pneumonia that affects 35 to 40 percent of children with AIDS and causes hardening of the lung membranes involved in absorbing oxygen. LIP is an AIDS-DEFINING ILLNESS in children.

Lymphoid Tissue: the organs of the lymph system throughout the body, including the BONE MARROW, THYMUS, LYMPH NODES, SPLEEN, tonsils, PEYER'S PATCHES and LYMPHOCYTE aggregates on mucosal surfaces.

Lymphokine: a substance produced by LYMPHOCYTES to precipitate various immune reactions. Lymphokines include the INTERFERONS and INTERLEUKINS and are a subset of the CYTOKINE family.

Lymphoma: a cancer of the LYMPHOID TISSUE, largely a solid tumor with cells arising from proliferating LYMPHOCYTES. Symptoms may include LYMPH NODE swelling, weight loss and fever. Some examples of lymphomas are BURKITT'S LYMPHOMA, HODGKIN'S DISEASE and NON-HODGKIN'S LYMPHOMA. Treatment involves radiation therapy (radiotherapy), CHEMOTHERAPY or both.

Lymphoproliferative Response: a specific IMMUNE RESPONSE that entails rapid T CELL replication. Standard ANTIGENS, such as tetanus toxoid, that elicit this response are used in lab tests of immune competence.

Lysis: the splitting and dissolution of cellular or viral material by chemical action.

< M >



Macrophage: a large scavenger cell that ingests degenerated cells and foreign organisms. Macrophages exist in large numbers throughout the body and contribute to the development of acquired immunity by acting as ANTIGEN PRESENTING CELLS. They also ingest and destroy foreign matter coated with ANTIBODIES. Macrophages can be infected by HIV.

Macrophage Inflammatory Protein-1 Alpha and Beta (MIP-1a, MIP-1b): CHEMOKINES that bind to the CCR5 RECEPTOR site and interfere with HIV's fusion with uninfected cells.

Macrophage-Tropic HIV (M-Tropic, CCR5-using HIV, NSI HIV): refers to strains of HIV that have an affinity for infecting MACROPHAGES as well as CD4 CELLS. When entering new cells, M-tropic HIV usually binds to the CCR5 RECEPTOR in addition to the CD4 receptor. This type of HIV is generally a non-syncytia-inducing (NSI) virus (see SYNCYTIUM), it is the type of HIV that is transmitted sexually, and it is generally predominant until late stage disease.

Macula: the pigmented central area or "yellow spot" of the RETINA that is adjacent to the optic nerve. It is the most sensitive area of the retina and contains the FOVEA, a region that is responsible for detailed central vision.

Magnetic Resonance Imaging (MRI): a noninvasive, non-x-ray diagnostic technique based on the magnetic fields of hydrogen atoms in the body. MRI provides computer-generated images of the body's internal tissues and organs.

MAI (Mycobacterium Intercellulare): see MYCOBACTERIUM AVIUM COMPLEX.

Maintenance Therapy: extended drug therapy, usually at a diminished dose, administered after a disease has been brought under control. Maintenance therapy is utilized when a complete cure is not attainable, and a disease is likely to recur if therapy is halted. It is used for CHRONIC infections and tumors. So far, attempts at using maintenance therapy for HIV have been unsuccessful. See also INDUCTION THERAPY.

Major Histocompatibility Complex (MHC): two classes of molecules on cell surfaces. MHC class I molecules exist on all cells and hold and present foreign ANTIGENS to CD8 CYTOTOXIC T LYMPHOCYTES if the cell is infected by a VIRUS or other MICROBE. MHC class II molecules are found on the IMMUNE SYSTEM's ANTIGEN PRESENTING CELLS and display antigen to activate CD4 CELLS.

Malabsorption: inability of the GASTROINTESTINAL TRACT to absorb food, drugs or any substance needed to maintain good health; if not countered, leads to weight loss and AIDS WASTING SYNDROME.

Malaise: a vague feeling of discomfort or uneasiness, often the result of infection or a drug's SIDE EFFECTS.

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

Manifestation: the outward sign that an illness is present; a symptom or condition.


Marinol (Dronabinol): an appetite stimulant composed of TETRAHYDROCANNABINOL (THC), the major psychoactive ingredient in marijuana (see CANNABIS).

Masked: see BLINDED.

Mast Cell: an IMMUNE SYSTEM cell filled with granules of inflammatory chemicals such as histamine. This cell is believed to play a leading role in generating the symptoms of allergy.


"Me Too" Drug: an informal term used to describe a drug that offers little or no benefit over a similar drug that has already been approved by the FDA.

Mean: see AVERAGE.

Median: the midpoint in a series of numbers; half the data values are above the median, and half are below. For example, in the odd series 1, 4, 9, 12 and 33, 9 is the median. In the even series 1, 4, 10, 12, 33 and 88, 11 is the median (halfway between 9 and 12). Note, the median is not necessarily the same as the AVERAGE (or mean). For example, the median of 2, 6, 10, 22 and 40 is 10 but the average is 18.

Medulla: the inner portion of an organ.


Megadosing: medical treatment with very large doses of a naturally occurring, supposedly nontoxic substance, usually a VITAMIN.

Mega-HAART: the use of six or more ANTIRETROVIRALS to treat HIV, typically some or all of which have been used previously by the individual.

Megestrol Acetate (Megace): an appetite stimulant approved for the treatment of weight loss in people with AIDS. Megestrol acetate is a synthetic version of the female hormone PROGESTERONE. Most of the weight gain it leads to has been found to be fat rather than PROTEIN. Possible SIDE EFFECTS include HYPERGLYCEMIA, occasional impotence and decreased LIBIDO in men and uterine bleeding in women.

Memory T Cell: a T CELL that bears RECEPTORS for a specific foreign ANTIGEN encountered during a prior infection or vaccination. After an infection or a vaccination, some of the T cells that participated in the response remain as memory T cells, and can rapidly mobilize and clone themselves should the same antigen be re-encountered during a subsequent infection.

Men Who Have Sex with Men (MSM): a term created to include MSM who do not identify as gay or bisexual.

Meninges: the membranes that envelope the brain and the spinal cord.

Meningitis: INFLAMMATION of the MENINGES. It may be caused by a BACTERIUM, FUNGUS or VIRUS.

Mepron: see ATOVAQUONE.

Meta-Analysis: a method of summarizing previous research by reviewing and combining results from multiple CLINICAL TRIALS. Meta-analyses are attempted when previous studies were too small individually to achieve meaningful or statistically significant results. Because combining data from disparate groups is problematic, meta-analyses usually are considered more suggestive than definitive.

Metabolism: the buildup, breakdown and excretion of substances, commonly used to refer to the breakdown of food (or drugs) and its transformation into energy.

Metformin (Glucophage): a drug used to treat high blood sugar.

Methadone: an oral or INTRAVENOUS OPIATE commonly used to control symptoms of withdrawal from heroin.

Metronidazole (Flagyl): an ANTIBIOTIC used to treat a variety of infections.


Microbe: a microscopic organism, such as a BACTERIA, FUNGUS, PROTOZOA or VIRUS.

Microbicide: an agent that destroys MICROBES. TOPICAL microbicides, applied to mucosal surfaces, act as chemical barriers to prevent the spread of sexually transmitted diseases. Several compounds are under investigation to block HIV infection.

Micronutrient: a VITAMIN or mineral that the body must obtain from outside sources. Micronutrients are essential to the body in small amounts because they are either components of ENZYMES or act as coenzymes in managing chemical reactions.

Microsporidiosis: an intestinal infection that causes diarrhea and wasting in people with HIV. It results from two different species of microsporidia, a protozoal parasite. Two common organisms that cause it are Enterocytozoon and Septata. Among the possible treatments are THALIDOMIDE and ALBENDAZOLE.


Mitochondria: a rod-shaped or oval body in cells that is the site of energy production by means of OXIDATION. Mitochondrial function can be interrupted by NUCLEOSIDE ANALOGS (LAMIVUDINE [3TC], STAVUDINE [D4T]) due to inhibition of gamma INTERFERON and DNA POLYMERASE, leading to lactic acidosis.

Mitogen: a substance that induces cell division.

Mitosis: the process of cell division.


Molluscum Contagiosum: a skin condition caused by a pox virus infection, distinguished by small dome-shaped papules (bumps) on the face, upper trunk or extremities. Current treatment is mainly cosmetic. It often involves application of liquid nitrogen to the papules as a means of excising them.

Monoclonal Antibody: an ANTIBODY produced by laboratory cultures of a single CELL LINE. The antibodies are all identical, binding with the same EPITOPE.

Monocyte: a large white blood cell that can leave the blood vessels and enter body tissue, at which point it becomes a MACROPHAGE.

Mononeuritis Multiplex (MM): a rare type of NEUROPATHY that causes patchy areas of movement and asymmetrical sensory abnormalities. MM tends to occur during the ASYMPTOMATIC, early period of HIV infection, but a more severe type, attributed to CYTOMEGALOVIRUS (CMV) infection, has been observed in people with advanced AIDS.

Mononucleosis: an infection caused by the EPSTEIN-BARR VIRUS (EBV) that leads to an increase in mononuclear LEUKOCYTES. Mononucleosis can be spread by saliva and is also known as the "kissing disease" (or simply "mono"). Symptoms include fever, fatigue, sore throat and swollen LYMPH NODES.

Monotherapy: the use of a single drug or therapy to treat a disease or condition.

Morbidity: having an illness or disease.

Mortality: death.




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

Multi-Drug Resistant Tuberculosis (MDR-TB): a strain of TUBERCULOSIS (TB) that does not respond to two or more standard anti-TB drugs. MDR-TB usually arises when treatment is intermittent, thus permitting replication and allowing an accumulation of MUTATIONS in the TB BACTERIA that confer broader and broader drug RESISTANCE.

Multiple Regression Analysis: a statistical method used with one dependent variable and more than one independent variable.

Multivariate Analysis: a statistical analysis that involves more than one dependent variable.

Murine: of or relating to rodents, especially mice.

Mutagen: an agent that has a tendency to increase MUTATIONS.

Mutation: any alteration, loss, gain or exchange of genetic material within a cell or VIRUS. Mutations are perpetuated in succeeding generations of that cell or virus (or of an entire multicellular organism if the mutated cell is a sperm, egg or spore). They can occur spontaneously or in response to environmental factors, including drug therapy. See also RESISTANCE.

Myalgia: pain in one or more muscles.

Myambutal: see ETHAMBUTAL.

Mycelex: see CLOTRIMAZOLE.

Mycobacterium: a group of BACTERIA with many disease-causing members. The causative agents for TUBERCULOSIS, leprosy and MYCOBACTERIUM AVIUM COMPLEX (MAC) all belong to this group.

Mycobacterium Avium Complex (MAC): a serious OPPORTUNISTIC CONDITION caused by two similar BACTERIA (Mycobacterium avium and Mycobacterium intercellulare) found in the soil and dust particles. In AIDS, MAC can spread through the bloodstream to infect LYMPH NODES, BONE MARROW, liver, SPLEEN, spinal fluid, lungs and intestinal tract. Typical symptoms of MAC include night sweats, weight loss, fever, fatigue, diarrhea and enlarged spleen. MAC is usually found in people with CD4 CELL COUNTS below 95. CLARITHROMYCIN, AZITHROMYCIN, ETHAMBUTAL, RIFAMPIN, clofazimine and RIFABUTIN are some of the ANTIBIOTICS commonly used in MAC prevention and treatment. (Treatment of active infection usually involves combination therapy.)

Mycobacterium Intercellulare (MAI): see MYCOBACTERIUM AVIUM COMPLEX.

Mycobutin: see RIFABUTIN.

Mycoplasma: a group of BACTERIA, some of whose members cause disease in animals and humans. Mycoplasma are very simple one-celled organisms without an outer membrane. They penetrate and infect individual cells. Most commonly, mycoplasma causes pneumonia.

Mycosis: any disease caused by a FUNGUS.

Myelin: a fatty substance that covers and protects the nerves.

Myelitis: INFLAMMATION of the spinal cord.

Myelopathy: any disease affecting the spinal cord.

Myelosuppression: see BONE MARROW SUPPRESSION.

Myelotoxic: destructive to BONE MARROW.

Myocardial: refers to the heart's muscle mass.

Myopathy: progressive muscle weakness. Myopathy may arise as a toxic reaction to AZT (ZIDOVUDINE) or as a consequence of HIV infection itself.

< N >



N-Acetylcysteine (NAC): a naturally occurring substance that is metabolized into the AMINO ACID CYSTEINE. Cysteine is one of the three components of the major cellular ANTIOXIDANT GLUTATHIONE, and people with HIV have decreased levels of this compound. Taking NAC will restore glutathione levels, but it remains to be proven whether this increase in glutathione has clinical benefit. See also OXIDATIVE STRESS.

Nadir: the lowest point.

Naive T Cell: a T CELL arising from the IMMUNE SYSTEM'S production of fresh cells in the BONE MARROW. Naive T cells respond to newly encountered PATHOGENS containing ANTIGENS the immune system has not processed before. The naive T cells' activation and proliferation create an acquired immune response (see IMMUNE SYSTEM) to the newly encountered pathogenic agent. After the disease is eradicated, a portion of the T cell population engendered by the activated naive T cells constitute a reservoir of memory cells, which proliferate and respond very quickly to any recurrence of the disease. See also MEMORY T CELL.

Nandralone Decanoate (Deca Durabolin): an injectable synthetic ANABOLIC STEROID being studied for the treatment of AIDS-related WASTING SYNDROME.


National Cancer Institute (NCI): a branch of the NATIONAL INSTITUTES OF HEALTH (NIH) that oversees considerable research in HIV and AIDS-related malignancies.

National Institute of Allergy and Infectious Diseases (NIAID): the federal agency that is responsible for a great deal of the government-sponsored AIDS research. NIAID is a branch of the NATIONAL INSTITUTES OF HEALTH (NIH).

National Institute of Mental Health (NIMH): a branch of the NATIONAL INSTITUTES OF HEALTH (NIH) that oversees neurologic and psychologic research.

National Institutes of Health (NIH): the federal agency responsible for overseeing government-sponsored biomedical research. It is divided into 24 institutes and research centers.

Natural History of Disease: the course of a disease when left untreated.

Natural History Study: a study that observes the development of a disease over time.

Natural Killer (NK) Cell: a type of LYMPHOCYTE that attacks and destroys foreign, VIRUS-infected and cancerous cells. NK cells are not targeted at specific ANTIGENS the way CYTOTOXIC T LYMPHOCYTES are. They are part of the innate rather than the acquired immune response (see IMMUNE SYSTEM).




NebuPent: see PENTAMIDINE.

Nef: an HIV regulatory PROTEIN. HIV without nef appears to have lessened capacity to infect new cells. Nef also blocks HIV-infected cells from expressing CD4 and MAJOR HISTOCOMPATIBILITY COMPLEX (MHC) class I molecules on their surfaces, thus limiting the IMMUNE SYSTEM's ability to recognize and kill these cells.

Nelfinavir (Viracept): a PROTEASE INHIBITOR from Agouron / Pfizer, FDA-approved for adults and children over two years old. Nelfinavir should be taken two or three times a day with a meal or light snack. Its most common SIDE EFFECT is diarrhea. Nelfinavir can reduce blood levels of oral contraceptives and increase blood levels of other protease inhibitors.

Neonate: a newborn, typically up to four weeks of age.

Neoplasia: the abnormal growth of new tissue, consisting of a NEOPLASM or tumor.

Neoplasm: literally, a new growth. An abnormal growth of tissue, a tumor.

Neopterin: a substance present in BODILY FLUIDS that is elevated when the IMMUNE SYSTEM is activated. SERUM or CEREBROSPINAL FLUID neopterin levels were measured in early studies as a SURROGATE MARKER for HIV disease.

Nephritis: INFLAMMATION of the kidneys.

Nephrolithiasis: the formation of sediment or small stones in the kidneys. See also KIDNEY STONE.

Nephrotoxicity: damage to the kidneys.

Nerve Growth Factor (NGF): a naturally produced substance that has many roles in the maintenance of nerves and nerve cells, especially sensory ones. Synthetic, RECOMBINANT NGF is a proposed therapy for HIV- and drug-associated NEUROPATHIES.


Neurologic: relating to the nervous system, including the brain.

Neuron: one of the electrically active cells that transmit signals within the brain or nervous system.

Neuropathy: disease or INFLAMMATION and degeneration of the nerves. See PERIPHERAL NEUROPATHY.

Neuropsychologic Tests: tests designed to measure certain aspects of brain function, such as memory, concentration, attention and visual/motor skills.

Neurotransmitter: a substance secreted by excited nerve cells (NEURONS) that conveys the nerve signal to another nerve cell across the gap, or synapse, between the two cells.

Neutralizing Antibody: ANTIBODIES that can directly block the infective capacity of a microorganism, particularly a VIRUS' ability to penetrate cells.

Neutrexin: see TRIMETREXATE.

Neutropenia: a shortage of NEUTROPHILS in the blood.

Neutrophil: a type of GRANULOCYTE that is especially protective against bacterial and fungal infections. Neutrophils are also called polymorphonuclear cells (PMNs) because of their internal structure.

Nevirapine (Viramune): Boehringer Ingelheim's NON-NUCLEOSIDE REVERSE TRANSCRIPTASE INHIBITOR (NNRTI). Nevirapine is FDA-approved for treatment of HIV-infected adults in combination with NUCLEOSIDE ANALOGS. Possible SIDE EFFECTS include severe rash, fever and liver impairment. Nevirapine interacts with many other drugs.

New Drug Application (NDA): an application to the FDA asking for approval to market a new drug.






Nizoral: see KETOCONAZOLE.



Noncompleter Equals Failure (NC=F): the most conservative type of analysis in which participants who drop out of a CLINICAL TRIAL are considered to have failed therapy.

Noncompliant: refers to a patient who is unwilling or unable to follow a treatment REGIMEN as prescribed.

Non-Hodgkin's Lymphoma (NHL): a LYMPHOMA made up of B CELLS and characterized by nodular or diffuse tumors that may appear in the stomach, liver, brain or BONE MARROW. After KAPOSI'S SARCOMA, NHL is the most common opportunistic cancer in people with AIDS.

Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI): a member of a class of compounds, including DELAVIRDINE, NEVIRAPINE and EFAVIRENZ, that acts to directly combine with and block the action of HIV's REVERSE TRANSCRIPTASE enzyme. In contrast, NUCLEOSIDE ANALOGS block reverse transcriptase by capping the unfinished DNA chain that the ENZYME is constructing.

Nonoxynol-9: an anti-microbial agent present in some spermicides and lubricants. Nonoxynol-9 has been shown to irritate mucosal linings, which may possibly facilitate HIV infection and its use is not recommended as an MICROBICIDE.

Non-Syncytium-Inducing HIV: see SYNCYTIUM; T-TROPIC HIV.

Norvir: see RITONAVIR.


NSI Virus (Non-Syncytium-Inducing HIV): see SYNCYTIUM; T-TROPIC HIV.


Nucleic Acid Sequence-Based Amplification (NASBA): an ASSAY used to detect HIV VIRAL LOAD in blood PLASMA.

Nucleoside: a combination of one of five single or double ringed "bases" and a sugar (ribose for RNA or deoxyribose for DNA). These molecular units are the building blocks of DNA and RNA, the genetic material found in living organisms. Before being added to a DNA or RNA sequence, nucleosides must have a phosphate group added (see PHOSPHORYLATION).

Nucleoside Analog (Nucleoside Analog Reverse Transcriptase Inhibitor, NRTI): a type of ANTIVIRAL drug, such as AZT (ZIDOVUDINE), ddI (DIDANOSINE), ddC (DIDEOXYCYTIDINE) or d4T (STAVUDINE), whose structure constitutes a defective version of a natural NUCLEOSIDE. Nucleoside analogs may take the place of the natural nucleosides, blocking the completion of a viral DNA chain during infection of a new cell by HIV. The HIV enzyme REVERSE TRANSCRIPTASE is more likely to incorporate nucleoside analogs into the DNA it is constructing than is the DNA POLYMERASE that cells normally use for DNA construction.

Nucleoside Analog Reverse Transcriptase Inhibitor: see NUCLEOSIDE ANALOG.

Nucleotide: a building block of RNA and DNA that consists of a base, a sugar, and a phosphate group. A phosphorylated nucleoside (see NUCLEOSIDE and PHOSPHORYLATION).

Nucleotide Analog: TENOFOVIR, ADEFOVIR, CIDOFOVIR and other ANTIVIRAL compounds that function exactly like NUCLEOSIDE ANALOGS but are pre-activated through the addition of a phosphate group during their synthesis. This PHOSPHORYLATION is supposed to enhance the drug levels and activity achieved within cells. Nucleotide analogs typically are active against a wide range of VIRUSES, including HERPES VIRUSES, HEPATITIS B and sometimes HIV.

Nystatin: an antifungal drug used primarily as a topical agent for oral CANDIDIASIS (THRUSH).

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Observational Study: a study that does not involve randomization but where available data are nonetheless analyzed to make treatment comparisons. Observational studies are subject to bias, which may render their conclusions less reliable than those obtained by well controlled randomized CLINICAL TRIALS. Still, they may be useful for hypothesis generation and defining the natural history of disease.

Octoxynol: a chemical used in spermicides.

Octreotide Acetate (Sandostatin): an antidiarrheal drug.

Ocular: relating to the eye.

Odynophagia: pain when swallowing.

Off-Label: use of a drug for a disease or condition other than the INDICATION for which it was approved by the FDA. For example, many doctors prescribe PAROMOMYCIN for CRYPTOSPORIDIOSIS, although it is not approved for treating this disease.


OI (Opportunistic Infection): see OPPORTUNISTIC CONDITION.

Oocysts: the first stage in the life cycle of a parasitic PROTOZOAN.

Open-Label Trial: a study in which both researchers and participants know what drugs a person is taking and at what dose. Compare BLINDED.

Opiate: a natural or synthetic derivative of opium that has similar ANALGESIC and sedative effects.

Opportunistic Condition: an infection or cancer that occurs especially or exclusively in persons with weak IMMUNE SYSTEMS due to AIDS, cancer or immunosuppressive drugs such as CORTICOSTEROIDS or CHEMOTHERAPY. KAPOSI'S SARCOMA (KS), PNEUMOCYSTIS CARINII PNEUMONIA (PCP), TOXOPLASMOSIS and CYTOMEGALOVIRUS are all examples of opportunistic conditions. Also more loosely termed "opportunistic infection"(OI).

Oral Candidiasis: see THRUSH.

Oral Hairy Leukoplakia (OHL): a white lesion that appears on the side of the tongue and inside cheeks. The lesion appears raised, with a ribbed or "hairy" surface. OHL occurs mainly in people with declining immunity and may be caused by EPSTEIN-BARR VIRUS infection.

Organic Molecule: a molecule that comes, or came, from a living thing.

Orphan Drug: a status granted by the FDA to unpatentable medications developed for rare diseases. Orphan drug status gives the drug's manufacturer a seven-year right to exclusively market the compound. This protection of unpatentable orphan drugs encourages their development by greatly increasing their profitability.

Osteoporosis: loss of bone density due to depletion of calcium and bone PROTEIN.

Oxandrin: see OXANDROLONE.

Oxandrolone (Oxandrin): an oral ANABOLIC STEROID approved by the FDA in 1962 as a general remedy for weight loss in a variety of conditions including CHRONIC infection. Now being studied as treatment for AIDS-related WASTING SYNDROME.

Oxidation: a chemical reaction resulting from exposure to oxygen or other electron-seizing atoms or molecular combination of atoms (see FREE RADICALS). On the cellular level, oxidative reactions are the source of energy, but free radicals and other oxidizing agents can damage cellular components, such as membranes, and interfere with cells' regulatory systems.

Oxidative Stress: a highly oxidized environment within cells that is thought to promote HIV replication because cells are forced into a highly activated state due to loss of control of their regulatory systems.

Oxymetholone (Anadrol): an anabolic-androgenic STEROID used to treat ANEMIA.

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