AIDS is believed to be the result of infection with a retrovirus that adversely affects cells carrying the CD4 (OKT4) protein. These include white blood cells of the Helper T-cell lineage. Now officially called Human Immunodeficiency Virus (HIV), the virus has been previously referred to as HTLV-III, LAV, ARV, and several other designations.
The virus is not by itself fatal, however, the virus impairs the immune system of the host and impairs the body's resistance to opportunistic infections. Opportunistic infections are infections with organisms generally incapable of causing disease in persons with healthy immune systems, but which may be fatal in persons with compromised immune systems.
If one molecule in the immune system, whose absence would be most damaging to the system, had to be selected it would be Cellular Determinant 4 (CD4). This molecule acts as the receptor for the virus' entry into the cell and is crucial for this to occur. CD4 is commonly found on cells of the Helper T-cell variety but has also been found on some Killer T-cells, Macrophages ( Mononuclear phagocytes ), in an unknown cell type in the brain, and in human colorectal cells.
A diagnosis of AIDS is made according to a very strict guidelines established by the Centers for Disease Control (CDC). The presence of the HIV virus and other symptoms not qualifying a diagnosis as AIDS result in a diagnosis of AIDS Related Complex or Condition (ARC). An assymptomatic case with the HIV virus present is referred to as "HIV Positive".
While it is unknown exactly what percentage of the latter two groups will progress to a full-blown diagnosis of AIDS, a recently proposed redefinition of AIDS would result in an increase in the number of AIDS cases of approximately 25% by reclassifying a number of persons currently listed as ARC patients.
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