IL4 and tropical spastic paraparesis: Among the diseases related to HTLV-I, extensive studies have been performed on the pathogenesis of HAM/TSP and various reports have shown that HTLV-I infection in such cases is accompanied by the spontaneous proliferation of T-cells and the production of high levels of pro-inflammatory cytokines such as IL-2, IL-4, IL-6, TNF-α, IL-1α, IL-1β, IFN-γ in serum and CSF and spinal cord injuries in infected patients (4,5,7-11).