apoptosis: cellular suicide, also known as programmed cell death. HIV may induce apoptosis in both infected and uninfected immune system cells.
B cells: white blood cells of the immune system that produce infection-fighting proteins called antibodies.
CD4+ T cells: white blood cells that orchestrate the immune response, signalling other cells in the immune system to perform their special functions. Also known as T helper cells, these cells are killed or disabled during HIV infection.
CD8+ T cells: white blood cells that kill cells infected with HIV or other viruses, or transformed by cancer. These cells also secrete soluble molecules that may suppress HIV without killing infected cells directly.
cytokines: proteins used for communication by cells of the immune system. Central to the normal regulation of the immune response.
cytoplasm: the living matter within a cell.
dendritic cells: immune system cells with long, tentacle-like branches. Some of these are specialized cells at the mucosa that may bind to HIV following sexual exposure and carry the virus from the site of infection to the lymph nodes. See also follicular dendritic cells.
enzyme: a protein that accelerates a specific chemical reaction without altering itself.
follicular dendritic cells (FDCs): cells found in the germinal centers (B cell areas) of lymphoid organs. FDCs have thread-like tentacles that form a web-like network to trap invaders and present them to B cells, which then make antibodies to attack the invaders.
germinal centers: structures within lymphoid tissues that contain FDCs and B cells, and in which immune responses are initiated.
gp41: glycoprotein 41, a protein embedded in the outer envelope of HIV. Plays a key role in HIV's infection of CD4+ T cells by facilitating the fusion of the viral and cell membranes.
gp120: glycoprotein 120, a protein that protrudes from the surface of HIV and binds to CD4+ T cells.
gp160: glycoprotein 160, an HIV precursor protein that is cleaved by the HIV protease enzyme into gp41 and gp120.
integrase: an HIV enzyme used by the virus to integrate its genetic material into the host cell's DNA.
Kaposi's sarcoma: a type of cancer characterized by abnormal growths of blood vessels that develop into purplish or brown lesions.
killer T cells: see CD8+ T cells.
lentivirus: "slow" virus characterized by a long interval between infection and the onset of symptoms. HIV is a lentivirus as is the simian immunodeficiency virus (SIV), which infects nonhuman primates.
LTR: long terminal repeat, the RNA sequences repeated at both ends of HIV's genetic material. These regulatory switches may help control viral transcription.
lymphoid organs: include tonsils, adenoids, lymph nodes, spleen and other tissues. Act as the body's filtering system, trapping invaders and presenting them to squadrons of immune cells that congregate there.
macrophage: a large immune system cell that devours invading pathogens and other intruders. Stimulates other immune system cells by presenting them with small pieces of the invaders.
monocyte: a circulating white blood cell that develops into a macrophage when it enters tissues.
opportunistic infection: an illness caused by an organism that usually does not cause disease in a person with a normal immune system. People with advanced HIV infection suffer opportunistic infections of the lungs, brain, eyes and other organs.
pathogenesis: the production or development of a disease. May be influenced by many factors, including the infecting microbe and the host's immune response.
protease: an HIV enzyme used to cut large HIV proteins into smaller ones needed for the assembly of an infectious virus particle.
provirus: DNA of a virus, such as HIV, that has been integrated into the genes of a host cell.
retrovirus: HIV and other viruses that carry their genetic material in the form of RNA and that have the enzyme reverse transcriptase.
reverse transcriptase: the enzyme produced by HIV and other retroviruses that allows them to synthesize DNA from their RNA.
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