To address whether CD14+ cells promote HTLV-I production in CD4+ T cells of patients with HAM/TSP, we examined HTLV-I Tax expression of CD4+CD25+ T cells and CD4+CD25- T cells cocultured with or without autologous CD14+ cells of patients with HAM/TSP, compared to those of ACs. The gene discussed is CD4; the disease is tropical spastic paraparesis.