IFNG and tropical spastic paraparesis: Furthermore, CD4+CD25+CCR4+ T cells, which mainly include suppressive T cell subsets such as Th2 and Treg in HTLV-1-seronegative healthy controls [26], become Th1-like cells with overproduction of IFN-γ and production of low levels of IL-4 and IL-10 (Figures 4 and 5) in patients with HAM/TSP.