Return to What, How, and When Page

AIDS: Advanced infection with HIV, marked by certain conditions that do not occur in people with healthy immune systems, or by a decrease in CD4 cells below the level of 200 copies per microliter of blood.

CD4 cells: White blood cells that help direct the body's infection-fighting cells. They're named after the CD4 molecules they carry on their surface. Also called T helper cells.

CD4 count: The number of CD4 cells in a tiny drop of blood (a microliter, or about 1/5000th of a teaspoon). Because HIV attacks CD4 cells, their number falls as the infection gets more serious.

clinical trial: A study of the effects of one or more drugs in people.

compassionate use program: A plan through which the maker of a new drug can give that drug to some people who need it even before it is approved by the Food and Drug Administration (FDA). Such programs often include people outside the United States.

cross-resistance: Resistance of HIV to more than one drug at the same time.

enzyme: A kind of protein that causes chemical changes inside cells.

genetic: Having to do with genes, tiny segments of chemicals inside all viruses and cells that carry the information needed to make proteins that perform basic functions (such as the replication of viruses).

HIV: The human immunodeficiency virus. It attacks infection-fighting blood cells (CD4 cells) and other cells and causes AIDS.

immune system: The network of organs and cells in the body that recognizes and fights off infections and other "foreign" invaders.

infectious: Having the ability to infect (get inside) uninfected cells.

protease: An enzyme that HIV uses to make new copies of itself inside infected cells.

protease inhibitor (PRO-tee-aze in-HIB-it-ter): A drug that stops protease from making new copies of HIV that can infect other cells.

proteins: Complex compounds that are a major part of cells in all plants and animals. Their makeup depends on the particular genes inside each cell. The genes of viruses such as HIV also make specific proteins inside infected cells.

proteinase inhibitor: Another name for protease inhibitor, often used in Europe.

resistance: The ability of HIV to change its chemical (or genetic) structure so that it resists the effects of drugs.

replication: The process by which HIV makes new copies of itself inside infected cells.

reverse transcriptase (ri-VERS tran-SKRIP-taze): An HIV enzyme that lets the virus's genetic message get inside the genetic machinery of infected cells.

reverse transcriptase inhibitor: A drug that stops reverse transcriptase from doing its job efficiently inside infected cells.

side effects: The unwanted (sometimes harmful) effects of drugs.

T helper cells: White blood cells that help direct the body's infection-fighting cells. Also called CD4 cells.

This information was generously provided by:
International Association of Physicians in AIDS Care ©1996