In the present study, to investigate host factors regulating HTLV-1-mediated lymphoproliferative and inflammatory diseases, we established IL-2-dependent HTLV-1-infected T-cell lines (ILTs) from patients with ATL and HAM/TSP, and characterized their cytokine production, viral protein expression, and proliferative abilities. This evidence concerns the gene IL2 and tropical spastic paraparesis.