Glossary

A

Abscess
An isolated accumulation of pus associated with a localized infection. Abscesses may result in tissue destruction, pain, and swelling; severe abscesses may require surgical drainage.

Adherence
Following a prescribed treatment regimen, including correct dosage, number of doses per day, and dietary restrictions.

Adverse Reaction (Adverse Event, Side Effect)
An unwanted toxic reaction to or side effect of drug treatment (e.g., rash, nausea, peripheral neuropathy, bone marrow suppression, liver, or kidney failure).

Aerobic
Requiring or living in the presence of oxygen (e.g., aerobic bacteria).

AIDS Clinical Trials Group (ACTG)
A NIAID-sponsored group of medical centers, known as AIDS Clinical Trials Units (ACTU), that evaluate treatments for HIV disease and associated illnesses. ACTG studies are designated by number (e.g., ACTG 019).

AIDS-Defining Illness
A condition (e.g., Pneumocystis Carinii pneumonia, toxoplasmosis, Kaposi's sarcoma) that is included in the Center for Disease Control and Prevention's (CDC's) definition of AIDS.

Amylase
An enzyme produced by the salivary glands and the pancreas that helps break down food. An abnormal increase in serum amylase levels may indicate inflammation of the pancreas (pancreatitis).

Anal Intraepithelial Neoplasia (AIN)
The abnormal growth of cells of the anus, which may be a precursor of anal cancer.

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

Antibody (AB, Immunoglobulin, IG)
An immunoglobulin protein secreted by activated plasma cells, which evolve from B-cells. Antibodies are present throughout the blood and tissues; they are produced in response to stimulation by foreign antigens as part of the body's defense against disease. Specific antibodies bind to and act upon specific antigens; the antigen/antibody reaction forms the basis of humoral (TH2) immunity. Neutralizing antibodies destroy or inactivate infectious agents, while enhancing antibodies promote infection.

Antibody Positive
Having antibodies (e.g., against HIV) in the blood, indicating previous exposure to an organism. Typically the terms seropositive and HIV positive are used to mean antibody positive.

Antigen (adjective Antigenic)
Any agent or substance that stimulates an immune response.

Antiretroviral
An agent (e.g., AZT, ddI, nevirapine) that suppresses the activity or replication of retroviruses such as HIV.

Area Under the Curve (AUC)
A measure of drug concentration.

Arm
A group of participants in a clinical trial who receive the same treatment (treatment arm) or placebo (control arm).

Assay
A test, especially one used to detect the presence and/or concentration of a component, drug, or microorganism in the blood or other body fluids or tissues.

As-Treated Analysis
A method of analyzing the results of a clinical trial in which only participants who successfully complete a full course of treatment are analyzed.

B

Baseline
An initial or known value (e.g., CD4 cell count, HIV viral load) against which later measurements can be compared.

Beta Blocker Drugs
One of a large group of medications that obstruct specific nervous system receptors, causing a deceleration of the heart rate, a reduction in blood pressure, and reduced anxiety. Beta blockers are used to treat high blood pressure, angina, and other conditions.

Bilirubin
A pigment produced when the liver processes waste products. A high bilirubin level causes yellowing of the skin.

Bioavailability
The degree to which a drug or other substance is absorbed and circulated in the body; the physiological availability of a drug, as opposed to its chemical potency.

Blinding
A method of conducting clinical trials so that some or all of the participants do not know whether subjects are taking active drug or placebo. Blinding is done to reduce bias in drug trials.

Blood-Brain Barrier
A physical barrier between the blood vessels and the brain that is selectively permeable, i.e., allows only certain substances to pass through.

Body Fat Redistribution Syndrome (BFR)
A set of symptoms related to the loss of fat from certain areas of the body such as the limbs and face (lipodystrophy), possibly accompanied by fat accumulation in other areas such as the abdomen (protease paunch) or back of the neck (buffalo hump).

Branched-Chain DNA Assay (bDNA, Quantiplex HIV RNA Assay)
A test that measures the amount of virus (viral load) in plasma or tissue using a chemical signal, visible as light, that is produced by viral RNA.

Breakthrough
A condition that develops despite measures to prevent it (e.g., PCP that occurs while taking a prophylactic drug). Also, a rise in viral load after it has fallen due to anti-HIV therapy (virological breakthrough).

Buffalo Hump
Dorsocervical (or cervicodorsal) fat pad; an accumulation of fatty tissue on the upper back at the base of the neck.

C

Cardiovascular
Refers to the circulatory system (the heart and blood vessels).

CD4 Cell (CD4 Lymphocyte, T-Helper Cell, T4 Cell)
A type of white blood cell that carries the CD4 cell surface receptor and helps the body fight infection. CD4 cells release cytokines (chemical messengers) that coordinate a broad range of immune system activities including killer cell activation and antibody production.

CD4 Cell Count (T-Helper Cell Count)
The absolute number of CD4 lymphocytes in one cubic millimeter (mm³) of blood. The CD4 cell count is one indicator of the progression of HIV disease.

CD8 Cell (CD8 Lymphocyte, T8 Cell)
A type of white blood cell that carries the CD8 cell surface marker and helps regulate and/or carry out the body's immune response. Two subsets of T-cells express the CD8 surface marker T-suppressor cells and cytotoxic T-lymphocytes (CTLs).

Cell Line
A specific type of cell that is maintained in vitro for medical and/or research purposes.

Cervicodorsal Fat Pad
See buffalo hump.

Cervicovaginal
Relating to the uterine cervix and the vagina, parts of the female reproductive system.

Cervix (adjective Cervical)
The cylindrical, lower part of the uterus leading into the vagina.

Chemokine
A soluble factor secreted by certain immune system cells that stimulates the activity of other cells. Chemokines have chemoattractant properties and act as messengers between cells. Certain chemokines (e.g., MIP-1 alpha, MIP-1 beta, RANTES) have been shown to affect the activity of HIV; certain chemokine receptors (e.g., CCR5, CXCR4) are necessary to allow HIV to enter host cells.

Cholesterol
A fatty substance in animal tissue that is an essential component of cell membranes and nerve fiber insulation. Cholesterol is important for the metabolism and transport of fatty acids and in the production of hormones and vitamin D. Cholesterol is manufactured by the liver, and is also present in certain foods (e.g., eggs, shellfish). There are two primary types of cholesterol in the blood: low-density lipoprotein (LDL), which is considered a risk factor for heart disease, and high-density lipoprotein (HDL), which is considered protective against heart disease. Very low cholesterol levels may indicate malnutrition.

Chronic
Less intense, slow, persisting over a long period. Contrast with acute.

Coccidioidomycosis (Valley Fever)
A fungal disease acquired by inhaling dust particles containing spores of Coccidioides immitis. The disease affects the upper respiratory tract and lungs, and may sometimes disseminate to visceral organs, bones, skin, and other tissues. Symptoms include cough, fatigue, fever, and weight loss.

Coenzyme Q10 (CoQ10)
A quinone substance that facilitates the production of energy from food and acts as an antioxidant.

Cohort
A group of individuals in a study who share a demographic, clinical, or other statistical characteristic (e.g., age, study site).

Combination Therapy
Simultaneous or alternating administration of two or more therapies.

Coreceptor
A second cell surface receptor required for entry by a pathogen into a host cell or for initiation of a biological process. HIV requires both the CD4 receptor and a coreceptor (e.g., CCR-5 or CXCR-4) to enter a cell.

Cross-Resistance
The development of resistance to one agent (e.g., a drug) that also confers resistance to another agent (e.g., a similar drug of the same class).

Cryptosporidiosis
A disease caused by the protozoan Cryptosporidium parvum, which is transmitted by contact with animal feces, ingestion of contaminated food or water, or oral-anal sexual contact (rimming). It can cause severe, chronic diarrhea, weight loss, and lymphadenopathy.

Cytochrome P450 System
A system that facilitates oxidative metabolism drugs and other substances in the liver by means of enzymes (e.g., CYP3A4) that inhibit or promote metabolic reactions.

Cytokine
An intercellular hormone or chemical messenger protein (e.g., tumor necrosis factor, interleukin) released by white blood cells (e.g., macrophages, T-cells). Cytokines facilitate communication among immune system cells and between immune system cells and the rest of the body.

Cytomegalovirus (CMV, Human Herpesvirus 5)
A herpesvirus. CMV infection often occurs in healthy individuals without causing symptoms. In immunocompromised individuals (usually with CD4 cell counts below 50 cells/mm³), CMV may cause serious illness including retinitis (inflammation of the retina), pneumonia, colitis (inflammation of the large bowel), and encephalitis. CMV may be treated with ganciclovir, foscarnet, or cidofovir.

Cytotoxic T-Lymphocyte (CTL, Killer T-Cell)
A type of white blood cell that bears the CD8 surface marker, and targets and kills cells infected with viruses, bacteria, parasites, and other microorganisms.

D

Dendritic Cell
A type of immune system cell with many branches. Dendritic cells are found in the skin and mucosal membranes. They are typically the first to arrive at sites of injury or infection, where they bind to invaders and transport them to the lymph nodes where the cell-mediated immune response is initiated. Dendritic cells carry the CD4 surface marker, and may be among the first cells to be infected by HIV.

Deoxyribonucleic Acid (DNA)
A molecule that encodes genetic information and is found in the nucleus of cells as a twisted double-stranded chain. The particular sequence of four chemical building blocks (nucleotides) -- adenine, cytosine, guanine, and thymine -- that make up a DNA chain determines the unique genetic code of an individual. See also ribonucleic acid.

Dexa Scan
Dual energy X-ray absorptiometry, a method of determining the composition of body tissues.

Discordant
Not having the same serostatus, for example a couple in which one partner is HIV positive and the other is HIV negative.

DNA (Deoxyribonucleic Acid)
See deoxyribonucleic acid.

Double-Blind
A type of clinical trial in which neither the subject nor the investigator knows what treatment, if any, the subject is receiving.

E

Electrolyte
An electrically charged element or compound (e.g., sodium, potassium) found in body fluids, tissues, and cells. An imbalance of electrolytes can result from prolonged vomiting or diarrhea, and may lead to the disruption of many bodily processes, possibly resulting in muscle weakness, cramps, or seizures.

ELISA
See enzyme-linked immunosorbent assay.

Endocervix (adjective Endocervical)
The inner part of the uterine cervix.

ENV
The gene of HIV that encodes the proteins of the viral envelope; also refers to the proteins produced by that gene.

Enzyme
A protein that induces or accelerates a chemical reaction.

Enzyme-linked Immunosorbent Assay (ELISA)
A laboratory test used to detect the presence of antibodies in the serum. ELISA is used for first-line screening for HIV antibodies; a positive result indicates that antibodies have been detected. The test is sensitive but not specific, and a positive ELISA is typically confirmed using a Western blot assay.

Epidemiology
The study of the frequency, distribution, and behavior of a disease within a population.

Epstein-Barr Virus (EBV, Human Herpesvirus 4)
A herpesvirus. EBV infection is common and usually asymptomatic in children, but may cause infectious mononucleosis in young adults. It is associated with oral hairy leukoplakia, lymphoid interstitial pneumonitis, and some types of cancer in people with HIV disease.

Estradiol
A potent form of estrogen produced by the ovaries, placenta, and testes.

Estrogen
A female sex hormone; a natural or synthetic substance (e.g., estradiol, Premarin) that stimulates the development of female secondary sex characteristics and regulates the reproductive cycle in women. Estrogens are known to affect the immune system.

Ethinyl Estradiol
A semisynthetic estrogen often used in oral contraceptives.

Etiology
The cause of a disease; the study of causes of disease.

F

First-line Treatment
The preferred standard therapy for a particular condition.

Follicle Stimulating Hormone (FSH)
In women, follicle stimulating hormone stimulates the development of ovarian follicles (eggs) and stimulates the release of estrogens.

Follicular Phase
The preovulatory phase of a woman's reproductive cycle during which the follicle grows and high estrogen levels cause the uterine lining to grow.

G

GAG
The gene of HIV that encodes the core proteins of the virus; also refers to the proteins produced by that gene.

Gastrointestinal
Pertaining to the stomach and intestines.

Gene (adjective Genetic)
The unit of heredity. A gene contains hereditary information encoded in the form of DNA and is located at a specific position on a chromosome in a cell's nucleus. Genes determine many aspects of anatomy and physiology by controlling the production of proteins.

Genome (adjective Genomic)
The unique genetic code or hereditary material of an organism, carried by a set of chromosomes in the nucleus of each cell. The human genome contains an estimated 50,000-100,000 genes; the genome of HIV contains nine genes.

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 that make it resistant to a drug. Contrast with phenotype.

Glucocorticoid
A steroid-like substance (e.g., cortisol) capable of influencing metabolism, regulating the immune system, and exerting an anti-inflammatory effect.

Glucose (Blood Sugar)
A form of sugar that is the body's primary fuel; glucose broken down from food can be converted into energy or stored. Abnormally low or high levels of glucose in the blood often indicate metabolic disturbances (e.g., diabetes).

H

HAART
Highly active antiretroviral therapy, a term for potent combination anti-HIV treatment that usually includes a protease inhibitor.

Habitus
Physical or constitutional characteristics.

Half-life
The time required for half of the amount of an agent (e.g., drug, virus, cell type) to be eliminated from the body.

Hemoglobin (Hb)
The red, iron-based pigment in red blood cells that enables them to transport oxygen.

Hepatic
Relating to the liver.

Hepatitis
An inflammation of the liver that may be caused by several agents, including viruses, toxins, or drugs. Acute hepatitis is typically characterized by fever, jaundice, fatigue, abdominal tenderness, and elevated liver enzymes. Hepatitis A virus (HAV) causes an inflammatory viral disease with a short incubation period. Hepatitis viruses B (HBV) and C (HCV) can become chronic and may result in liver damage, cirrhosis, or liver cancer. There are also hepatitis viruses D, E, F, and G.

Hepatomegaly
Liver enlargement.

Herpes Simplex Virus (HSV-1, HSV-2, Human Herpesvirus 1, 2)
A herpesvirus that causes recurring lesions. Herpes simplex virus type 1 (HSV-1) usually produces blisters on the lips or in the mouth (cold sores or fever blisters). HSV type 2 (HSV-2) is usually sexually transmitted and generally produces lesions in the genital or anal area. Both HSV-1 and HSV-2 are treated with acyclovir; ganciclovir or foscarnet are used to treat acyclovir-resistant HSV.

Histoplasmosis
A fungal infection acquired by inhaling spores of the fungus Histoplasma capsulatum, which are present in soil or dust. The disease most often affects the lungs, where it produces a tuberculosis-like inflammation, but may also disseminate. Symptoms include cough, fever, and weight loss. The disease may be life-threatening in indiviuals with suppressed immune systems.

Hormone
A chemical messenger (e.g., adrenaline, testosterone) involved in the regulation and coordination of cellular and bodily functions.

Human Papillomavirus (HPV)
A papovavirus, many strains of which cause warts, including condylomata acuminata (genital warts). Certain strains of HPV (e.g., 16, 18) are associated with cervical, anal, and oral cancer.

Hypermenorrhea
Unusually frequent or heavy menstrual bleeding.

I

Immunology (adjective Immunologic)
The study and/or treatment of disorders that involve the immune system (e.g., cancer, HIV disease, autoimmune diseases).

Incidence (Incidence Rate)
The number of new cases of a disease or condition in a specific population during a given period of time. The incidence rate is determined by dividing the number of new cases by the total population.

Incubation Period
The period of time between an initial exposure to an infectious agent and the development of symptoms of disease, during which the infection is established in the body.

Insulin
A peptide hormone produced in the pancreas. Insulin enables the body to metabolize and use glucose (sugar). Lack of or insensitivity to insulin results in diabetes.

Intent-to-Treat Analysis
Analysis that requires the inclusion of all randomized subjects, regardless of whether they remain on protocol for the duration of the study.

Interferon-Alpha (Intron-A, Roferon-A)
A type of interferon produced in response to viral infection. Genetically engineered interferon-alpha is used to treat Kaposi's sarcoma, anogenital warts, and chronic hepatitis B and C, and is under study as an anti-HIV therapy. Side effects include flu-like symptoms, anemia, and neutropenia.

Intermittent
Occurring sporadically or in phases.

In Vitro
Latin for "in glass." Refers to studies done in a test tube or culture medium in the laboratory.

In Vivo
Latin for "in the body of a living organism." Refers to studies done using human or animal subjects.

K

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 purplish or brownish lesions, and is associated with a herpesvirus (KSHV or HHV-8).

L

Lactic Acidosis
A buildup of lactic acid (a byproduct of carbohydrate metabolism) in bodily tissues.

Latency (adjective Latent)
The state in which a pathogenic organism is present in the body but not actively replicating or causing illness.

Lean Body Mass
Muscle and organ tissue.

Leukopenia
An abnormally low number of white blood cells in the circulating blood.

Leutenizing Hormone (LH)
A hormone produced by the pituitary gland that acts with FSH (follicle stimulating hormone) to stimulate ovulation, and androgen and progesterone secretion.

Lipid
A fat.

Lipodystrophy
A loss of fatty tissue, usually in the limbs and face. The term is sometimes used to refer to any type of body fat redistribution.

Lipoprotein
A compound composed of protein and fats.

Log
Refers to quantities in factors of ten. A log change is an exponential or ten-fold increase or decrease (e.g., a change from ten to 100 is a 1-log increase).

Long-Term Nonprogressor (LTNP)
An individual who has been infected with HIV for several years (7-10 or more years) but does not exhibit immune system decline or have opportunistic diseases. About 10% of persons with HIV disease seem to be LTNPs.

Luteal Phase
The postovulatory phase of a woman's menstrual cycle. See also ovulation.

Lymphocyte
A type of white blood cell (e.g., T-cell, B-cell, natural killer cell) that plays a part in immune defense.

M

Macaque
A family of monkey species (e.g., rhesus, pigtail, cynomolgus) often used in scientific research. Macaques can be infected with simian immunodeficiency virus (SIV) and are used as an animal model for AIDS.

Macrophage
A large scavenger white blood cell that ingests and processes degenerated cells and foreign invaders. The long-lived macrophages can harbor large quantities of HIV, and may act as viral reservoirs.

Magnetic Resonance Imaging (MRI)
A sensitive, noninvasive method for viewing soft tissues of the body using a strong magnetic field.

Maternal-Fetal Barrier
The placental barrier. See placenta.

MBChB
Bachelor of Medicine, Bachelor of Surgery.

Mean
A statistical measurement of the central tendency, or average, of a set of values. Contrast with median.

Median
The number within a series that is preceded and followed by an equal number of values. Contrast with mean.

Menstrual Cycle
The reproductive cycle of female humans characterized by a monthly discharge of blood, mucus, and tissues from the uterus. This cycle involves changes to the uterine wall during the rest of the month including a few days of fertility after an ovum (egg) is released from an ovary.

Microbe
A tiny living organism (e.g., bacterium, protozoan, fungus), especially those that cause disease.

Microbicide
An agent that inactivates, kills, or destroys microbes. Vaginal and anal microbicides are under study as a means of preventing HIV transmission.

Micronutrient
A trace element; an organic compound, small amounts of which are essential for physical health, growth, and metabolism.

Mitochondria (singular Mitochondrion)
Rod-shaped or oval organelles in the cytoplasm of a cell that produce most of the cell's energy.

Molecule
A small unit of matter made up of atoms. A molecule is the smallest unit of a substance that retains its unique characteristics.

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 (Kissing Disease)
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.

Multivariate Analysis
A statistical analysis technique in which multiple variables are analyzed separately to determine the contribution made by each variable to an observed result. Contrast with univariate analysis.

Mutation
A change in the character of a gene that is perpetuated when a cell divides or a virus replicates. A mutant is a new strain of an organism produced by a genetic mutation.

Mycobacterium Avium Complex (MAC)
An opportunistic disease caused by Mycobacterium avium or Mycobacterium intracellulare (sometimes referred to as Mycobacterium avium-intracellulare or MAI), bacteria found in soil and water. In immunosuppressed persons, the bacteria can infect the lymph nodes, intestines, bone marrow, liver, spleen, spinal fluid, lungs, and the gastrointestinal tract, and may become disseminated. MAC is the most common bacterial infection in persons with advanced AIDS (usually with CD4 cell counts below 5,075 cells/mm³). Symptoms include diarrhea, wasting, fever, night sweats, fatigue, and spleen enlargement. Clarithromycin is used as treatment and prophylaxis for MAC.

N

Nadir
The lowest point. The term is used to refer to the lowest CD4 cell count a person ever reaches before the count increases due to anti-HIV treatment.

Naive
Inexperienced. The term is used to describe an individual who has never taken a certain drug or class of drugs (e.g., AZT-naive, antiretroviral-naive) or to refer to an undifferentiated immune system cell.

Natal
Relating to birth.

Natural Killer Cell (NK Cell)
A type of white blood cell that attacks and kills tumor cells and cells infected with microorganisms. Unlike cytotoxic T-lymphocytes, NK cells are nonspecific and attack infected cells without regard to specific antigens or MHC receptor configuration.

NEF
A gene of HIV that influences viral replication and may help HIV evade host defenses; also refers to the protein produced by that gene.

Neuropathy (adjective Neuropathic)
Damage to the nerves; an inflammatory or degenerative condition of the nervous system. See also peripheral neuropathy.

NNRTI
See non-nucleoside reverse transcriptase inhibitor.

Non-Nucleoside Reverse Transcriptase Inhibitor (NNRTI)
A drug (e.g., nevirapine, delavirdine, efavirenz) that binds with and inhibits the action of the HIV reverse transcriptase enzyme, thus blocking viral transcription and replication.

Norethindrone
A synthetic hormone with actions similar to progesterone but functioning as a more potent inhibitor of ovulation.

NRTI
See nucleoside reverse transcriptase inhibitor.

Nucleoside Analog
See nucleoside reverse transcriptase inhibitor.

Nucleoside Reverse Transcriptase Inhibitor (NRTI, also known as Nucleoside Analog)
A compound (e.g., AZT, ddI, ddC, d4T, 3TC) that mimics one of the building blocks of DNA. These compounds suppress retroviral replication by interfering with the reverse transcriptase enzyme.

O

Open-Label
Refers to a drug trial that is not randomized and not blinded; both participants and investigators know what drug is being tested and what dosages are being used.

Opportunistic Infection (OI)
A disease caused by a microorganism that does not normally cause illness in a person with a healthy immune system, but that may cause serious disease when the immune system is weakened. Common OIs in HIV positive people include Pneumocystis carinii pneumonia (PCP), Mycobacterium avium complex (MAC), and cytomegalovirus (CMV) infection.

Organelle
One of the specialized small organs of a living cell (e.g., mitochondria).

Ovary
One of the two female gonads located within the abdomen on either side of the uterus. The ovaries are the site of egg (ovum) storage and maturation.

Ovulation
The process by which an ovum (egg) is discharged from an ovary.

Oxidative Stress
Increased levels of free radicals and other oxidation-promoting molecules associated with disease, immune response, and aging. When the production of pro-oxidants exceeds the cellular supply of antioxidants, harmful effects may result including cell membrane damage, cell death, and damage to genetic material resulting in mutations.

P

P450
See cytochrome P450 system.

Pancytopenia
An abnormally low level of all types of blood cells, typically due to bone marrow damage.

Papanicolaou Smear (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. An abnormal Pap smear suggests increased risk of developing cancer.

Peripheral Neuropathy
Damage to the peripheral nerves, usually involving the feet and hands, and sometimes the legs, arms, and face. Symptoms may include numbness, tingling or burning sensations, pain, abnormal reflexes, weakness, and partial paralysis. Peripheral neuropathy is a side effect of HIV as well as several anti-HIV drugs (e.g., ddC, ddI, and d4T).

P-Glycoprotein
A family of plasma membrane proteins which, when overexpressed, can cause multidrug resistance.

pH
A logarithmic scale used to describe the acidity or alkalinity of a solution; a measure of the hydrogen concentration of a solution. Water has a neutral pH of 7. A pH below 7 is acidic; a pH above 7 is alkaline (or basic).

Pharmacological
See pharmacology.

Pharmacology
The science of drugs, their sources, and how they work.

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 is susceptible to a specific drug in a test tube. Contrast with genotype.

Phosphorylation
The addition of a phosphate group to a compound by an enzyme (e.g., thymidine kinase, tyrosine kinase). Phosphorylation is an essential step in many cellular processes.

Placebo
An inert, inactive substance; a "sugar pill." Experimental therapies are compared with placebo in many clinical trials.

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 circulating blood that carries blood cells and nutrients throughout the body, removes metabolic wastes, and is a medium for chemical communications between different parts of the body.

Pneumocystis Carinii Pneumonia (PCP)
A life-threatening opportunistic type of pneumonia believed to be caused by a protozoan. PCP is a common infection that can cause severe illness in immunocompromised people (especially those with CD4 cell counts of fewer than 200 cells/mm³); it remains a leading cause of death in people with AIDS. Symptoms include dry cough, fever, chest tightness, and shortness of breath. Pneumocystis carinii can also infect other parts of the body. First-line treatment and primary prophylaxis is TMP-SMX (Bactrim, Septra); other treatments and prophylaxes include dapsone, pentamidine, and atovaquone.

Polymerase Chain Reaction (PCR) Assay
A highly sensitive test that can detect small amounts of DNA or RNA (genetic material) in a blood or tissue sample using an amplification technique that multiplies the existing DNA/RNA so that it can more easily be detected. PCR assays are used to determine viral loads in persons infected with HIV.

Postexposure Prophylaxis (PEP)
Drug therapy given immediately following exposure to an infectious organism, done in an attempt to prevent the infection from taking hold in the body.

Prenatal
The period preceding birth, during which the fetus develops in the uterus.

Prevalence (Prevalence Rate)
The proportion of individuals with a condition in a specific population during a given time. The prevalence rate is determined by dividing the number of people with the condition by the total population.

Prodrug
An inactive form of a drug that exerts its effects after metabolic processes within the body convert it to a usable or active form.

Progesterone
A female steroid hormone with anti-estrogen effects. Progesterone prepares the uterus for the development of the fertilized ovum and maintains the uterus throughout pregnancy. Synthetic progesterone is used as a contraceptive.

Progestin
A hormone produced by the corpus luteum, placenta, or adrenal cortex (or synthetically manufactured) that has progesterone-like effects. Synthetic progestin is used as a contraceptive.

Prolactin
A pituitary hormone that stimulates the secretion of breast milk.

Proliferation
Rapid reproduction or replication.

Prophylaxis (PX)
Therapy that helps to prevent a disease or condition before it occurs (primary prophylaxis) or recurs (secondary prophylaxis).

Prospective Study
A study that looks forward in time. Participants are selected and their progression is followed over time.

Protease Inhibitor (PI)
A drug (e.g., saquinavir, ritonavir, indinavir, nelfinavir, amprenavir) that blocks the action of the HIV protease enzyme, thereby preventing viral replication. Unlike reverse transcriptase inhibitors, protease inhibitors can inhibit HIV replication in cells that are already infected.

Protocol
A plan that states the specifics of a clinical trial, such as the hypothesis to be tested, drug(s) to be used, method(s) of administration, length of the trial, endpoint(s) to be used, and characteristics of participants (e.g., inclusion/exclusion criteria).

Psychostimulant
A drug that causes increased responsiveness of the mind.

Q

Quiescent
Refers to a state of resting, inactivity, or latency.

R

Randomized Trial
An experiment in which subjects with particular characteristics are assigned by chance to different treatment or control arms. Randomization is done to cancel out the influence of factors that are not under study.

Rebound
An increase in viral load following a previous decrease due to anti-HIV therapy.

Receptor
A specific binding site on a cell's surface or interior. When chemical messengers bind to receptors, various cellular functions are activated or inhibited. Many drugs exert their effects by binding to receptors and altering normal cellular communication. Viruses enter cells by fusing with receptors on the cell surface, often in conjunction with certain genes (MHC molecules) and/or coreceptors.

Renal
Pertaining to the kidneys.

Reservoir
A site where an infectious agent collects and multiplies; resting CD4 cells are reservoirs of HIV.

Resistance
The mutation of a microorganism in such a way that it loses its sensitivity to a drug; a resistant organism can function and replicate despite the drug's presence. Contrast with susceptible. Genotypic and phenotypic resistance tests are used to measure whether an organism is resistant to a drug. See also cross-resistance.

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.

Ribonucleic Acid (RNA)
A single-stranded nucleic acid that encodes genetic information. RNA takes the place of DNA in retroviruses such as HIV. The presence of HIV RNA in the plasma indicates that the virus is actively replicating.

RNA
See ribonucleic acid.

S

Second-Line Treatment
The second preferred therapy for a particular condition used when a first-line treatment fails or when a person cannot tolerate the side effects of first-line drugs.

Semen
A whitish, viscid fluid ejaculated from the penis containing spermatozoa and secretions from the prostate gland.

Sensitivity
The ability of an organism to be affected by a drug or other agent (e.g., a virus is sensitive to AZT if AZT is able to prevent viral replication). Sensitivity also refers to a statistical measure of the accuracy of a screening test, i.e., how likely a test is to label as positive those who have a disease or condition.

Seroconversion
The development of antibodies directed against an antigen; the change in a person's antibody status from negative to positive. Vaccine-induced seroconversion is not an infection.

Seronegative
Having a blood test that does not indicate infection with a microorganism (e.g., HIV), either by the presence of antibodies or antigen.

Seropositive
Having a blood test result that indicates infection with a microorganism (e.g., HIV). A test may detect either antibodies to an organism (antibody positive) or the organism or its proteins (antigen positive).

Sexually Transmitted Disease (STD, Venereal Disease)
A disease (e.g., gonorrhea, syphilis, chlamydiasis, herpes) that is transmitted through sexual contact.

Simian Immunodeficiency Virus (SIV)
A viral infection endemic to African green monkeys and able to infect various primates. SIV is similar to HIV-2.

Somatic
Relating to the physical body.

Spermicide
An agent (e.g., nonoxynol-9) that immobilizes or kills spermatozoa; spermicides are also often used to kill HIV and other organisms.

Standard Therapy
A therapy that is FDA-approved for a specific condition and is widely used as first-line treatment for that condition.

Steatosis
Tissue degeneration (e.g., in the liver) caused by the buildup of fat in the cells.

Strain
A specific genetic variant of a particular organism.

Subcutaneous
Beneath the skin; subdermal.

Subtype (Clade)
A phylogenetically distinct strain of a microorganism. There are at least 11 subtypes of HIV-1 classified into two groups: group M (containing subtypes A through J) and group O. Subtype B is predominant in the U.S. There are five known subtypes of HIV-2 (A-E). See also strain.

Suppression
The cessation of detectable viral replication in a person's blood.

Surrogate Marker
A marker or sign that can serve in place of a clinical endpoint such as disease progression or death. Surrogate markers for HIV disease may be virologic (e.g., viral load), immunologic (e.g., CD4 cell count), or clinical (e.g., weight loss).

Susceptible
Vulnerable to or potentially able to contract a disease. Also refers to a microorganism that is vulnerable to the effects of a drug. Contrast with resistance.

Symptomatic
Showing outward signs of a disease.

Synergy (Synergism, adjective Synergistic)
An interaction between agents (e.g., drugs) that produces an effect greater than the combined effects of the same agents used separately.

T

T-Cell (T-Lymphocyte)
A type of white blood cell that matures in the thymus and carries out the cell-mediated immune response. Three major types of T-cells are helper (CD4) T-cells, suppressor (CD8) T-cells, and killer (CD8) T-cells (cytotoxic T-lymphocytes, or CTLs).

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.

Third-Line Treatment
The third preferred therapy for a particular condition; used when the patient fails or cannot tolerate the side effects of the first- and second-line treatments.

Thrombocytopenia
An abnormally low number of platelets; the condition may result in abnormal bleeding and bruising. The normal platelet range is 150,000-300,000 per millimeter of blood. Thrombocytopenia may be controlled by the administration of certain cytokines or by removal of the spleen.

Thymus (adjective Thymic)
A lymphoid organ located in the chest behind the sternum. The thymus is a source of T-cell production in the fetus and the site of T-cell maturation and differentiation, i.e., where the cells learn to recognize antigens.

Thyroid Gland
An organ at base of the neck that produces thyroxin and other hormones.

Toxicity (adjective Toxic)
The quality of being poisonous or harmful; often used to refer to side effects of drugs.

Toxoplasmosis
An opportunistic infection caused by the microscopic protozoan Toxoplasma gondii, found in undercooked meat and cat feces. Symptoms may include headache, lymphadenopathy, malaise, muscle pain, and fever. A common manifestation of the disease is toxoplasmic encephalitis (cerebral toxoplasmosis), characterized by brain swelling, confusion, lethargy, seizures, and coma; the eyes, heart, and lungs may also be affected. Toxoplasmosis is treated with pyramethamine, usually in combination with other drugs; TMP-SMX may be used as prophylaxis.

Trichomoniasis (TV)
Infection with the protozoan parasite Trichomonas vaginalis. Trichomoniasis may be asymptomatic, especially in men; in women symptoms may include vaginal irritation, itching, discharge, and painful urination.

Triglyceride
A combination of glycerol and fatty acid that circulates in the blood.

Tuberculosis (TB)
An infectious disease caused by Mycobacterium tuberculosis that typically affects the lungs (pulmonary TB), but may also occur in other organs (extrapulmonary TB). Transmission generally occurs through inhalation of aerosolized sputum droplets. A combination of four chemotherapeutic drugs is standard therapy. Multidrug-resistant tuberculosis (MDRTB) is resistant to several standard drugs and requires more aggressive treatment.

Tumor Necrosis Factor (TNF, Cachectin)
A cytokine (chemical messenger) that can destroy tumors. When chronically elevated, as may occur in HIV disease, TNF-alpha (one type of TNF) may lead to fever, anorexia, hypermetabolism, and wasting. TNF-alpha may block the production of enzymes that digest fats, leading to the breakdown of muscle tissue. In laboratory tests TNF-alpha has been shown to stimulate HIV replication.

U

Undetectable (Unquantifiable)
A term used to describe a viral load that is below the level of detection of the test being used.

Univariate Analysis
A statistical analysis that considers only one factor or variable at a time. Contrast with multivariate analysis.

Uterus (Womb)
The muscular pelvic organ of the female reproductive system in which the fetus develops.

V

Vagina
The passage from the uterus to the outside of the body, part of the female reproductive system; the "birth canal."

Viral Breakthrough
See breakthrough.

Viral Load (Viral burden)
The amount of virus in the blood or body 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 tests such as polymerase chain reaction (PCR) or branched-chain DNA (bDNA), and is typically expressed as the number of copies of RNA per milliliter (mL) of blood plasma.

Viral Replication
Multiplication or reproduction of a virus in a person's blood.

Viral Suppression
The cessation of detectable viral replication in a person's blood.

Viremia
The presence of virus in the blood.

Virological Failure
Treatment breakthrough; an increase in viral load after it has been suppressed with antiretroviral drugs.

Virology
The study of viruses and diseases caused by viruses.

Virus
Any of a large group of minute organisms 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 viral particles. Various families of viruses infect humans, animals, plants, and bacteria.

W

Western Blot
A laboratory blood test for specific antibodies (e.g., to HIV). The Western blot assay is more accurate than the ELISA, and is used as a confirmatory test if an ELISA is positive.

Wild Type (adjective Wild-Type)
The normal, typical phenotype of a virus or other organism before genetic mutation takes place.

World Health Organization (WHO)
An organization of the United Nations concerned with worldwide public health.

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