Human T cell leukemia virus type 1 (HTLV-1) is a retrovirus that causes an aggressive neoplasm of mature CD4+ T cells called adult T cell leukemia (ATL), as well as a variety of inflammatory diseases including uveitis, infectious dermatitis, Sjögren’s syndrome, and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) [1–8]. Here, CD4 is linked to tropical spastic paraparesis.