IFNG and tropical spastic paraparesis: These Treg-like ATL cells do not produce IFN-γ [31,36] contrary to the HTLV-I infected CD4+CD25+ cells in the neuro-inflammatory HTLV-I Associated Myelopathy/Tropical Spastic Paraparesis (HAM/TSP), which display a non-Treg phenotype with decreased expression of Foxp3 and increased levels of IFN- γ [37-41].