FOXP3 and tropical spastic paraparesis: Further, the increased IFN-γ production and decreased IL-17 production in CD4+CD25+CCR4+Foxp3− T cells of HAM/TSP patients (Figures 4 and 5) suggests that HTLV-1 expression may also contribute to the differentiation of Th1 versus Th17 CD4+ T cells.