A large fraction of the T-cell pool in the body is harbored in the gut-associated lymphoid tissue (GALT) [3], which has been identified as a primary anatomical site for CD4+ T-cell depletion in both HIV-1-infected patients [4]–[6] and SIV-infected nonhuman primates [1], [2], [7], [8]; yet, the loss of CD4+ T cells within the early phase of infection appears to be a systemic phenomenon that involves all secondary lymphoid organs [1], [9], [10]. Here, CD4 is linked to infection.