Acute HIV infection    The 4-to-7-week period of rapid viral replication immediately following exposure.

Acyclovir (Acycloguanosine.)    A nucleoside analog antiviral drug used to treat the symptoms of herpes simplex  virus infection, herpes zoster (shingles), and sometimes  acute varicella zoster virus (chicken pox). Also known as  Zovirax.

AIDS    Acquired Immune Deficiency Syndrome is an infectious viral disease that results in damage to the immune system in otherwise healthy individuals.

AIDS antibody test    A test to determine if an individual has antibodies to HIV, the virus that causes AIDS. Presence of HIV-specific antibodies indicates that the person has been exposed to HIV and has raised an immune response, but it does not tell if the person is still infected. The most common test is the ELISA tests. A backup test called the Western blot is also used.

AIDS Clinical Trials Group (ACTG)   Composed of a number of U.S. medical centers that evaluate treatment for HIV and HIV-associated infections. ACTG studies -- both adult and pediatric -- are sponsored by the National Institute of Allergy and Infectious Diseases (see) and the National Institute of Child Health and Human Development (for many of the pediatric studies) of the National Institutes of Health.

AIDS dementia complex (ADC)    A degenerative neurological condition attributed to HIV infection, characterized by a group of clinical presentations including loss of coordination, mood swings and loss of inhibitions, and widespread cognitive dysfunctions. It is the most common central nervous system complication of HIV infection. Characteristically, it manifests itself after the patient develops major opportunistic infections or AIDS-related cancers. However, patients can also have this syndrome before these major systemic complications occur. The cause of ADC has not been determined exactly, but it may result from HIV infection of cells or inflammatory reactions to such infections.

Alpha interferon   A protein that the body produces in response to infections. In persons who are HIV positive, elevated interferon levels are regarded as an indication of disease progression. Genetically engineered alpha interferon has been approved by the FDA as a treatment for Kaposi's Sarcoma. See Interferon.

Antibiotics   Compounds that are effective against infection by microorganisms such as bacteria, fungi and protozoa. They are generally ineffective against viral infections.

Antibody   A protein produced by a B-lymphocyte that specifically binds a particular antigen. This leads to attack by the immune system.

Antigen   A molecule or substance against which a specific immune response is raised.

Antivirals   Compounds that are effective in treating virus infections.

Asymptomatic AIDS carriers   Individuals infected with HIV who do not show any sign of disease. The may be capable of infecting others.

Azidothymidine (AZT)   An antiviral that is effective in treating HIV infection. It works by preferentially inhibiting the action of reverse transcriptase during HIV replication.  Also called Retrovir or zidovudine.

Bacteria   Small single-cell microorganisms that can cause diseases.

B-lymphocytes   One of several kinds of lymphocyte. B-lymphocytes secrete antibodies that are specific for particular antigens.

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

Blinded study   A clinical trial in which participants are unaware as to whether they are in the experimental or control arm of the study.

Blood-brain barrier    A selective barrier (obstacle) between brain blood vessels and brain tissues whose effect is to restrict what may pass from the blood into the brain. Certain compounds readily cross the blood-brain barrier; others are completely blocked.

CD4 protein/cells   A surface protein that is characteristic of T-helper lymphocytes (aka T-cells.) These T-cells help the immune system orchestrate its special functions. CD4 protein is the cell receptor for HIV. HIV's preferred targets are cells that have a docking molecule called "cluster designation 4" (CD4) on their surfaces. Cells with this molecule are known as CD4-positive (or CD4+) cells. Destruction of CD4+ lymphocytes is the major cause of the immunodeficiency observed in AIDS, and decreasing CD4+ lymphocyte levels appear to be the best indicator for developing opportunistic infections. Although CD4 counts fall, the total T cell level remains fairly constant through the course of HIV disease, due to a concomitant increase in the CD8+ cells. The ratio of CD4+ to CD8+ cells is therefore an important measure of disease progression.

CD8 (T8) protein/cells   A protein embedded in the cell surface of suppressor T lymphocytes (see). 1. Also called cytotoxic T cells (see). Some CD8 cells
recognize and kill cancerous cells and those infected by intracellular pathogens (some bacteria, viruses, and mycoplasma). These cells are called cytotoxic T lymphocytes (see). 2. Also called T-suppressor cells. Immune cells that shut down the immune response after it has effectively wiped out invading organisms. Sensitive to high concentrations of circulating lymphokines (see), T8 cells release their own lymphokines when an immune response has achieved its goal, signaling all other participants to cease their coordinated attack. A number of B lymphocytes (see) remain in circulation in order to fend off a possible repeat attack by the invading organism. With HIV, however, the immune system's response system does not work. T4 cells (see) are dysfunctional, lymphokines proliferate in the bloodstream, and T8 cells compound the problem by misreading the oversupply of lymphokines as meaning that the immune system has effectively eliminated the invader. So while HIV is multiplying, T8 cells are simultaneously attempting to further shut down the immune system. The stage is set for normally repressed infectious agents, such as PCP or CMV, to proliferate unhindered and to cause disease.

Chancroid   A highly contagious sexually transmitted disease caused by the Hemophilus ducreyi bacterium. It  appears as a pimple, chancre, sore, or ulcer on the skin of the genitals. The lesion appears after an incubation period of 3 to 5 days and may help the transmission of HIV.

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

Chemotherapy    The treatment, mostly of cancer, using drugs that attack cancerous cells. This treatment commonly has adverse side effects that may include the temporary loss of the body's natural immunity to infections, loss of hair, digestive upset, and a general feeling of illness. Although unpleasant, the adverse effects of treatment are tolerated considering the life-threatening nature of the cancers.

Chlamydia    A sexually transmitted disease (STD) The most common sexually transmitted bacterium (Chlamydiatrachomatis) that infects the reproductive system. In fact, in 1995, chlamydia was the most common STD in the United States. The infection is frequently asymptomatic (i.e., shows no symptoms), but if left untreated, can cause sterility in women.

Chronic Idiopathic Demyelinating Polyneuropathy (CIPD)   Chronic, spontaneous loss or destruction of myelin. Myelin is a soft, white, somewhat fatty material that forms a thick sheath around the core of myelinated nerve fiber. Patients with CIPD show progressive, usually symmetric weakness in the upper and lower extremities.

Clinical latency   The state or period of an infectious agent, such as a virus or bacterium, living or developing in a host without producing clinical symptoms. Pertaining to HIV infection, infected individuals usually exhibit a period of clinical latency with little evidence of disease, but viral load studies show that the virus is never truly latent (dormant). Even early in the disease, HIV is active within lymphoid organs.

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

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

Contagious   In the context of HIV, has come to be more popularly known as any infectious disease capable of being transmitted by casual contact from person to another. Casual contact can be defined as normal day-to-day contact among people at home, school, work, or in the community. A contagious pathogen (e.g., chicken pox) can be transmitted by casual contact. An infectious pathogen, on the other hand, is transmitted by direct or intimate contact (e.g., sex). HIV is infectious, not contagious.

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

Cryptosporidiosis   A gastrointestinal disease caused by the microscopic protozoan parasite Cryptosporidium parvum. It is recognized as one of the three most common diarrhea-causing intestinal pathogens in the world. Transmission occurs by the oral-fecal route.

Cyotmegalovirus (CMV)   A herpes virus that is a common cause of opportunistic diseases in persons with AIDS and other persons with immune suppression. While CMV can infect most organs of the body, persons with AIDS are most susceptible to CMV retinitis (disease of the eye; see) and colitis (disease of the colon).

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

Dementia   Loss of mental function due to damaged brain cells and brain inflammation. In AIDS-afflicted patients this is referred to as AIDS-related dementia (ARD).

Desensitization    Gradually increasing the dose of a medicine in order to overcome severe reactions. Desensitization procedures have become popular when administering Bactrim to persons with a history of adverse reactions to the drug. Bactrim (see TMP/SMX) is an important drug against PCP (see) infection.

Dose ranging study   A clinical trial (see) in which two or more doses of an agent (such as a drug) are tested against each other to determine which dose works best and is least harmful.

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

Double-blind study   A clinical trial (see) design in which neither the participating individuals nor the study staff know which patients are receiving the experimental drug and which are receiving a placebo (see) or another therapy. Double-blind trials are thought to produce objective results, since the doctor's and patient's expectations about the experimental drug do not affect the outcome.

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

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

ELISA   (Enzyme-Linked Immunosorbent Assay.) A type of enzyme immunoassay (EIA) to determine the presence of antibodies (see) to HIV in the blood or oral fluids. Repeatedly reactive (i.e., two or more) ELISA test results should be validated with an independent supplemental test of high specificity. In the United States the validation test used most often is the Western Blot (see) test.

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

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

Envelope   In virology, a protein covering that packages the virus's genetic information. The outer coat, or envelope, of HIV is composed of two layers of fat-like molecules called lipids (see) taken from the membranes of human cells. Embedded in the envelope are numerous cellular proteins, as well as mushroom-shaped HIV proteins that protrude from the surface. The virus uses these proteins to attach to and infect cells.

Enzyme   A cellular protein whose shape allows it to hold together several other molecules in close proximity to each other. In this way, enzymes are able to induce chemical reactions in other substances with little expenditure of energy and without being changed themselves. Basically, an enzyme acts as a catalyst.

Epidemiology   The study of patterns of disease occurrence in populations and the factors affecting them.

Epstein-Barr virus (EBV)   A herpes-like virus that causes one of the two kinds of mononucleosis (the other is caused by CMV, see). It infects the nose and throat and is contagious. EBV lies dormant in the lymph glands and has been associated with Burkitt's lymphoma and hairy leukoplakia.

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

Fungi   Microorganisms that may exist as single cells or be organized into simple multicellular organisms.

Harm-reduction model    An educational model that emphasizes how sexually active people or intravenous drug users can protect themselves with clean needles and condoms. (Cf. Abstinence model)

Helper T-lymphocytes   T-lymphocytes that help T-killer and B-lymphocytes respond to antigens. Destruction of T-helper lymphocytes is the major problem in AIDS.

HIV (Human Immunodeficiency Virus)    The virus almost universally believed to cause AIDS. The predominant form of HIV in North America, Europe, and central Africa is called HIV-1. A closely related retrovirus found in western Africa is called HIV-2.

Immune system   The circulating cells and serum fluids in blood that provide continuous protection from foreign infectious agents.

Incidence   The proportion of a population that develops new cases of a disease during a particular time period.

Incubation   The period between infection by a microorganism and appearance of disease symptoms.

Kaposi sarcoma   A normally rare cancer that develops frequently in AIDS patients.

Killer (a.k.a. cytotoxic) T-lymphocytes   T-lymphocytes that kill target cells they bind to.

Latency   A state of virus infection in which the virus’s genetic material remains hidden in the cell, but no virus is produced. The latent virus may become reactivated at a later time. HIV can establish latent infection.

Lymphadenopathy syndrome (LAS)   Persistently enlarged lymph nodes or swollen glands, sometimes an early sign of HIV infection that is progressing.

Lymphatic circulation   A secondary circulatory system that lymphocytes circulate through. Lymph channels drain fluid from tissues into lymph nodes, where B- and T-lymphocytes are located. T- lymphocytes are produced in the lymph glands in response to infection.

Lymphocytes   Cells of the immune system that respond specifically to foreign substances. The two classes of lymphocytes are B-lymphocytes and T-lymphocytes.

Macrophages   One kind of phagocyte. Macrophages generally attack cells infected with viruses.

Medicaid   A program of medical aid designed for those unable to afford regular medical service and financed by the state and federal governments.

Medicare  A government program of medical care esp. for the aged.

Non-lytic infection   Infection of a cell by a virus that results in production of virus, but survival of the cell. Most retroviruses normally carry out non-lytic infections. HIV infections of macrophages is non-lytic.

Opportunistic infections   Infections by common microorganisms that usually do not cause problems in healthy individuals. Opportunistic infections are the major health problems for AIDS patients.

Pandemic disease   An infectious disease present on many continents simultaneously.

Phagocytes   Cells of the immune system that eat foreign cells or infected cells. There are two kinds of phagocytes: macrophages and neutrophils (a.k.a. granulocytes).

Primary immune response The immune response that follows exposure to an infection or an antigen for the first time. There is a lag period before antibodies are produced.

Protozoa   Large single-cell microorganisms that can cause disease.

PWA   Person with AIDS.

Retrovir    AZT

Red blood cells   Blood cells that are responsible for carrying oxygen and carbon dioxide to and from the tissues.

Reverse transcriptase An enzyme that is unique to all retroviruses. It reads the genetic information of the retrovirus, which is RNA, and makes a DNA copy.

Secondary immune response   An immune response that follows exposure to an infection or an antigen that the immune system has already encountered. The strength of the response is greater, it occurs more rapidly, and it lasts longer.

Seroconversion   Infection with the HIV virus detectable in the blood.

Seronegative   HIV is not detectable in the blood.

Seropositive   HIV is detectable in the blood.

STD    Any of various diseases transmitted by direct sexual contact that include the classic venereal diseases (as syphilis, gonorrhea, and chancroid) and other diseases (as hepatitis A, hepatitis B, giardiasis, and AIDS) that are often or sometimes contracted by other than sexual means

Viral envelopes   Structures that surround some virus particles resembling membranes around cells. Viral envelopes contain virus-specific proteins that are important in binding cell receptors. Viral envelope proteins are major targets for the immune system.

Viruses   Small infectious agents They are parasites that must grow inside cells.

White blood cells (leukocytes)   All non-red blood cells. Leukocytes consist of a variety of blood cells including lymphocytes, neutrophils, eosinophils, macrophages, and megakaryocytes.

Zidovudine    AZT.