To determine whether HTLV-1 expression contributes to the differential fate of HTLV-1-infected CD4+CD25+CCR4+ T cells between HAM/TSP and ATL patients, differences in the HTLV-1 proviral load and the HTLV-1 tax mRNA and HTLV-1 HBZ mRNA expression of these populations were analyzed (Figure 6). This evidence concerns the gene CD4 and tropical spastic paraparesis.