Aging in the absence of HIV-1 infection was not significantly associated with a difference in the number of CD31-CD4+ naïve T-cells (an average of 178 cells/mm3 and 188 cells/mm3 in the younger and older groups respectively; interaction p = 0.7476), consistent with previous reports by our group [27] and others [45], demonstrating that HIV-1 infection is associated with negative effects on this subset that are distinct from aging. Here, CD4 is linked to HIV-1 infection.