While reports are varied on the susceptibility of EC CD4+ T cells to HIV-1 infection (29, 30), ECs consistently maintain the balance of CD4+ T helper (Th) 17 cell and regulatory (Treg) subsets similar to that of HIV-1 uninfected individuals, while the ratio of Th17/Treg cells is lower in viremic subjects (31, 32). Here, CD4 is linked to HIV-1 infection.