IFNG and tropical spastic paraparesis: Although Th2 and Treg CD4+CD25+CCR4+ T cells in healthy individuals are known to be immunosuppressive [26], we demonstrated that in HAM/TSP patients, HTLV-1-infected CD4+CD25+CCR4+ T cells overproduce Th1 cytokines such as IFN-γ and produce low levels of suppressive cytokines such as IL-4 and IL-10.