The CD4+ memory T cells are the main population infected by HIV-1 [56,57], and depletion of this population during HIV-1 infection is instigated either directly via productive infection leading to caspase-3-dependent apoptosis or indirectly, via non-productive infection of bystander CD4+ T cells, resulting in caspase-1-dependent pyroptosis [58,59]. Here, CD4 is linked to infection.