by Kristen Kay

Created on: December 29, 2009

Acquired immunodeficiency syndrome (AIDS) is a disorder caused by the human immunodeficiency virus (HIV). The virus, discovered in 1983, belongs to the lentivirus group. Viruses in this group cause diseases that continue for years.

HIV Virus

The HIV virion, the complete viral particle, is found extracellularly and is capable of infecting a living cell. These virions are so small that a thousand could easily fit on the period at the end of a sentence. Each virion has an envelope consisting of protein and lipids. An inner core of proteins surrounds two RNA strands that are bound to two molecules of the enzyme reverse transcriptase.

The exact process of the HIV life cycle is not completely understood and is still being studied. The surface of the virion is covered with protein studs that protrude from a lipid covering. The studs match proteins on the surface of a host cell. To accept viruses, a cell must have a special receptor protein on the surface, called a CD4 molecule. The CD4 molecule is present on only a few types of body cells, including macrophages and T cells. The T cells are especially susceptible. Once the virion attaches to the surface receptor, a rapid series of events occurs similar to other viruses. The reverse transriptase uses the host cell to produce DNA from its own RNA. The altered DNA can remain in the host cell for years as a silent infection.

When the DNA is activated, the host cell begins to produce viral RNA and eventually new virions to destroy the lymphocytes and infect other cells. The exact cause of the activation is unknown. The incubation period for AIDS depends on the length of time that the virus remains latent.

Effects on the Body

As AIDS progresses the immune system is affected. The T cell is destroyed when HIV reproduces inside its walls. The macrophage, however, reproduces HIV without ill effect to itself. The T cell has a major role in the immune system by helping to prevent infections. The loss of T cells alone does not mean that the HIV-infected person has AIDS. The number of cells can be reduced for years without the patient developing the opportunistic infections that indicate that AIDS is present. Opportunistic infections are those that occur only when an "opportunity" exists, as when the immune system is altered. Individuals with healthy immune systems are not affected. The infections include Pneumocystis carinii pneumonia, candidiasis, cytomegalovirus infection, salmonellosis, and cryptosporidiosis. The AIDS patient

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