In the context of HTLV-1 infected patients, it was demonstrated that, compared to healthy donors or asymptomatic carriers, the HAM/TSP patients are characterized by elevated levels of pro-inflammatory cytokines, such as IL-4, IL-6, IL-8, IFN-γ, and Tumor Necrosis Factor-α (TNF-α) in their plasma (28, 29). This evidence concerns the gene IL4 and tropical spastic paraparesis.