HIV infection is associated with immunosuppression caused by a dramatic reduction in the helper T cell population. The loss of helper T cells may be caused by HIV-induced apoptosis of both infected and uninfected helper T cells. HIV uses the CCR5 chemokine receptor as a coreceptor for macrophage cell entry and upregulates fas-ligand on these cells. CD4 on helper T cells is essential for viral cell entry and infection. Cross-linking of CD4 on the T cell surface may be involved in upregulation of Fas and sensitization of T cells to apoptosis induced by the Fas/Fas-ligand interaction.
