CD4 and HIV infectious disease: Frequencies of Cytomegalovirus (CMV) (100) and Mycobacterium tuberculosis (M.tb)-specific CD4+ T cell responses (101) are significantly lower in HIV infected individuals relative to healthy individuals and, despite clearly detectable HIV-specific CD8+ T cell responses, little to no HIV-specific CD4+ T cell proliferation is detectable in untreated HIV infection (100).