CD4 and HIV infectious disease: 59% of TB−/HIV− subjects (19/32) and 40% of TB−/HIV+ subjects (14/35) had detectable PPD-specific CD4 T cell responses (cut off: at least 0.05% IFNγ+ CD4 T cells), consistent with previous results that HIV infection is associated with a reduction of PPD-specific CD4 T cell responses [14].