Our finding that the ability of the acute viruses (w2 for BR24 and w1 for CA28) to bind CD4 and to infect CD4low cells in both macaques is decreased is consistent with these reports in human, and suggests that CD4+ T cells expressing high amounts of the receptor may be the earliest and preferred targets of virus infection and depletion in vivo, leaving only cells with lower CD4 levels available during the post-acute phase of infection. This evidence concerns the gene CD4 and infection.