Furthermore, decreased expression levels of CTL antigen-4 (CTLA-4), a Treg-associated immune-suppressive molecule, and glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR) have also been observed on the CD4+CD25+ T cells of HAM/TSP patients [30,34]. The gene discussed is TNFRSF18; the disease is tropical spastic paraparesis.