CD38 and HIV-1 infection: In the case of CD4+ T cells, both activated subpopulations exhibit a higher susceptibility to infection [4], [5], whereas for CD8+ T cells, high frequency of HLA-DR+CD38- is associated with seroconversion during continued HIV-1 exposure [27], suggesting that by reducing the frequency of these different cells, VitD might decrease the HIV-1 infection risk.