As IFN-γ is the main cytokine known to activate macrophages and high IFN-γ production is observed in HTLV-1 infected subjects, one could expect that macrophages from HAM/TSP patients had greater ability to kill an intracellular pathogen, but we did not find that the marked Th1 environment observed in these individuals modified the killing ability of myeloid cells. The gene discussed is IFNG; the disease is tropical spastic paraparesis.