Abstract
Human T-cell lymphotropic virus type I (HTLV-I) infection is associated with a variety of human diseases. In particular, there are two major diseases caused by HTLV-I infection. One is an aggressive neoplastic disease called adult T-cell leukemia (ATL), and another is a chronic progressive inflammatory neurological disease called HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). It is still unknown why one virus causes these different diseases. With regard to HAM/TSP, virus-host immunological interactions are an considered to be important cause of this disease. Coexisting high HTLV-I proviral load and HTLV-I-specific T cells (CD4+ T cells and CD8+ T cells) is an important feature of HAM/TSP. Histopathological studies indicate the existence of an inflammatory reaction and HTLV-I-infected cells in the affected lesions of HAM/TSP. Therefore, the immune response to HTLV-I probably contributes to the inflammatory process of the central nervous system lesions in HAM/TSP patients.