ENTPD1 and tropical spastic paraparesis: CD39+CD25+CD4+ T cells from HAM/TSP produce significantly higher levels of not only IFN-γ but also TNF-α and IL-2 and more importantly dual TNF-α+IL-2+ production within the CD39+CD25+ subset when compared to HTLV-1 asymptomatic carriers or uninfected subjects.