When compared to ACs, HAM/TSP patients have higher levels of spontaneous lymphocyte proliferation (Sakai et al., 2001; Pinto et al., 2011), increased HTLV-1 expression, and importantly, a higher frequency of HTLV-1 specific CD8+ T-cells (Kubota et al., 2000; Yamano et al., 2002), which are thought to be critical mediators of central nervous system (CNS) injury. This evidence concerns the gene CD8A and tropical spastic paraparesis.