The neurological damages in CNS of HAM/TSP patients is caused by recognition of CD4+HTLV-1 infected cells in the CNS cells by specific CD8+ CTL, resulting in the production of inflammatory cytokines such as IFN-γ, TNF-α and MMP (Jacobson et al., 1990; Wucherpfennig et al., 1992; Kubota et al., 1994; Umehara et al., 1994, 1998). Here, CD4 is linked to tropical spastic paraparesis.