Elevated frequency of IFN-γ producing HTLV-1 infected CD4+CD25+CCR4+ T cells with proinflammatory features is found in HAM/TSP patients and this is associated with the disease pathogenesis (Araya et al., 2014; Yamano and Coler-Reilly, 2017). This evidence concerns the gene CCR4 and tropical spastic paraparesis.