CD4 and tropical spastic paraparesis: Human T-cell leukemia virus type 1 (HTLV-1), a life-long persistent CD4+T -lymphotropic retrovirus, causes an aggressive mature T -cell malignancy termed "adult T-cell leukaemia" (ATL) [1,2] and an inflammatory disease of the central nervous system known as HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) [3,4].