In patients with HAM/TSP, high HTLV-I Tax expression is mainly detected in CD4+ T cells after ex vivo culture, but dendritic cells and CD14+ cells can also express HTLV-I Tax, consistent with the observation that HTLV-I infects dendritic cells to effectively transfer cell-free virus to CD4+ T cells [18,19]. This evidence concerns the gene CD4 and tropical spastic paraparesis.