HIV receptors and cellular tropism.

Viruses use specific cell surface receptors to bind to and subsequently gain entry into their host cells. Some retroviruses such as HIV-1 and HIV-2 utilize one receptor for high-affinity binding (CD4), and a separate coreceptor to mediate fusion of the viral envelope with the cell membrane (CCR5 or CXCR4). The identification of these receptors explains the cellular tropism of HIV, and hence its pathogenesis leading to immune deficiency (T-helper cell depletion), the wasting syndrome (macrophage infection), and dementia (microglia infection). HIV can infect cells by membrane fusion at the cell surface and by receptor-mediated endocytosis. Knowledge of the HIV receptors has led to practical developments such as inhibitory drugs, reasons for genetic resistance to infection, and should inform the judicious choice of candidate vaccines.