CD4 and tropical spastic paraparesis: It has been demonstrated that HTLV-1 Tax-specific CD8+ T cells as well as CD4+ T cells expressing HTLV-1 Tax proteins were detected in the parenchyma of HAM/TSP spinal cords, suggesting that the interaction between HTLV-1-specific CTLs and HTLV-1-infected CD4+ T cells may cause bystander damage to resident cells in the CNS [82].