HTLV-1 infection is the established cause of adultt-cell leukemia/lymphoma (ATL), an aggressive malignancy of CD4+ lymphocytes; HTLV-1 associated myelopathy (HAM)/tropical spastic paraparesis (TSP), a demyelinating inflammatory disease of the spinal cord; and HTLV-1 uveitis (HU), defined as uveitis of undetermined etiology in an HTLV-1 carrier. Here, CD4 is linked to tropical spastic paraparesis.