CD4 and HIV-1 infection: The preferential depletion of naïve T cells in blood and lymphoid tissues (LT) [3], where they mainly reside, also poses particular difficulties for attributing depletion simply to direct mechanisms of viral infection or indirect mechanisms of activation-induced cell death (AICD), since (1) naïve CD4+ T cells are resistant to HIV-1 infection and (2) AICD should primarily affect the activated effector and memory populations [12]–[14].