Early in HIV infection, peripheral blood Vδ1 T cell frequency is increased and Vδ2 T cell frequency is decreased, with a reversal of the Vδ1/Vδ2 ratio (which normally favors Vδ2) (44, 49), and the remaining Vδ2 T cells exhibit decreased antigen-induced expression of IFN-γ and TNF-α and decreased proliferative/cytotoxic capacity. This evidence concerns the gene IFNG and HIV infectious disease.