IFNG and tropical spastic paraparesis: Human T-lymphotropic virus type 1-associated myelopathy/tropical spastic paraparesis patients show extremely high cellular and humoral acquired immune responses, such as high frequencies of Tax-specific CD8+ T cells in peripheral blood and CSF (Jacobson et al., 1990; Nagai et al., 2001); high antibody titer to HTLV-1 (Ishihara et al., 1994; Akahata et al., 2012); and increased production of proinflammatory cytokines such as IL-6, IL-12, and IFN-γ (Furuya et al., 1999).