HIV Effects on the Immune System

HIV Effects on the Immune System

The pathogenesis of HIV is basically a struggle between HIV replication and the immune responses of the patient, via cell-mediated and immune-mediated reactions. The HIV viral burden directly and indirectly mediates CD4+ T-cell destruction. There is destruction of mature CD4+ cells; CD4+ progenitor (biological ancestor) cells in bone marrow, the thymus, and peripheral lymphoid organs; as well as CD4+ cells within the nervous system. The result of this destruction is failure of T-cell production and eventual immune suppression.

There are many mechanisms of CD4+ cell depletion by HIV infection. Direct HIV-mediated cytopathic (characterized by a pathological change in the function or form of a cell) effects include single-cell killing as well as cell fusion, or syncytium formation. The syncytium is a fusion of multiple uninfected CD4+ cells with one HIV-infected CD4+ cell via CD4-gp120 interaction. This fusion results in a multinucleated syncytium, or giant cell, which may ultimately serve as a means to produce many virions. HIV can infect many types of cells. The spread of HIV outside lymphoid organs to the brain, spinal cord, lung, colon, liver, and kidney usually occurs late during illness.