T helper type 9 cell response and its role in the neurological clinic of patients with Human T-lymphotropic virus 1.

Human T-lymphotropic virus 1 (HTLV-1) affects 5-10 million individuals worldwide. Most of those infected with this virus remain asymptomatic; however, 0.25%-4% of individuals develop HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), while 2%-4% develop adult T-cell leukemia/lymphoma (ATLL).