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The Immunology of Aids Introduction Although HIV was first identified in 1983, studies of previously stored blood samples indicate that the virus entered the U.S. population sometime in the late 1970s. Worldwide, an estimated 27.9 million people had become HIV-infected through mid-1996, and 7.7 million had developed AIDS, according to the World Health Organization (WHO). AIDS is a disease of the immune system, and is caused by Human Immuno deficiency Virus (HIV). HIV targets and infects T-helper cells and macrophages. After infection, replication of the virus occurs within the T-helper cells. The cells are lysed and the new viruses are released to infect more T-helper cells. The course of the disease results in the production of massive numbers of virus (1 billion/day) over the full course of the disease. The T- helper cells are infected, and rapidly destroyed both by virus and by cytotoxic T cells. T-helper cells are replaced with nearly a billion produced per day. Over many years (average may be 10), the T-helper cell population is depleted and the body loses its ability to mount an immune response against infections. Thus, we mount a very strong immune response against the virus for a long time, but the virus is produced at a very high rate and ultimately overcomes the ability of the immune system to respond. Since HIV belongs to a class of viruses called retroviruses, it has genes composed of ribonucleic acid (RNA) molecules. Like all viruses, HIV can replicate only inside host cells, commandeering the cell's machinery to reproduce. However, only HIV and other retroviruses, once inside a cell, use an enzyme called reverse transcriptase to convert their RNA into DNA, which can be incorporated into the host cell's genes. HIV belongs to a subgroup of retroviruses known as lenti-viruses, or "slow" viruses. The course of infection with these viruses is characterized by a long interval, up to 12 years or more,...