In HAM/TSP and ATL patients, most of CD4+CD25+CCR4+ T cells are infected with HTLV-I (87-88) and the ratio of THAM cells (CCR4+Foxp3– with IFN-γ production) to Treg cells (CCR4+Foxp3+ with no cytokine production) in the CD4+CD25+CCR4+ T cell subset are higher in HAM/TSP patients compared with ATL patients (87). Here, IFNG is linked to tropical spastic paraparesis.