CD4 and infection: A direct infection of skeletal muscle fibers by HTLV-1 was described in a case of polymyositis with co-infection by HTLV-1 and HIV-1, but this study was quickly contradicted by the evidence of the real integration of the HTLV-1 provirus in internal mononuclear inflammatory cells (mainly CD4+ T cells) that have infiltrated skeletal muscle [49,50].