IFNG and tropical spastic paraparesis: Although it has been demonstrated that CD4+CD25+ T cells in HAM/TSP patients exhibit reduced Foxp3 expression and Treg suppression [30–33] and that HTLV-1-infected CD4+ T cells in HAM/TSP patients produce Th1 cytokines (IFN-γ) [16,30], it has also been observed that CCR4 selectively overexpresses on HTLV-1-infected T cells in HAM/TSP patients [54].