To characterize the phenotype of FoxP3+ cells in HAM/TSP patients, we investigated the expression levels of Treg associated molecules, and found that the expression of GITR or CTLA-4 in HAM/TSP patients was significantly lower than that in HD (p = 0.0328 or 0.00002, respectively, Figure 5C). Here, CTLA4 is linked to tropical spastic paraparesis.