IFNG and tropical spastic paraparesis: It has been demonstrated that HTLV-I-specific CD8+ clones derived from HAM/TSP patients secret IFN-γ, TNF-α, IL-16, macrophage-inflammatory protein-1α (MIP-1α) and 1β (MIP-1β), and matrix metalloproteinase-9 (MMP-9) (61).