IFNG and tropical spastic paraparesis: Patients with HAM/TSP present an infiltrate of infected T-lymphocytes and cytotoxic T-lymphocytes (CTL) specific for viral antigens in their cerebrospinal fluid, in addition to increased proinflammatory cytokine (IFN-γ, TNF-α) and chemokine (CXCL-9 and CXCL-10) production [5, 6].