CD4 and infection: Although data on pulmonary immune perturbations during primary acute HIV infection is scarce, in vitro experiments on human lung lymphocytes and in vivo animal SIV models suggest that during the acute phase of infection pulmonary interstitial CD4 T-cells are more severely and rapidly depleted compared to the blood compartment that is largely due to CCR5+ memory CD4 T-cells’ high susceptibility to CCR5-topic HIV-1 infection, which make up the vast majority of the lung CD4 T-cell pool (54, 55).