CD4 and HIV infectious disease: This concept is not limited to CD4+ T cells as TRAIL-mediated apoptosis has also been implicated in inhibiting memory B-cell reconstitution in successfully treated HIV patients.37In vitro exposure of peripheral blood mononuclear cells to IFN-α also upregulates the expression of pro-apoptotic molecules Bak and Fas (CD95) on CD4+ T cells and subsequently promotes Fas-mediated apoptosis of T cells from HIV patients.38 Bak is upregulated on CD4+ T cells in chronic HIV infection, and its expression is associated with CD4+ T-cell loss.38