This excessive immune response is associated with high expression of the HTLV-1 tax protein, overproduction of the pro-inflammatory cytokine IFN-γ, decrease in Foxp3 expression, and suppression of regulatory T cell function in infected T cells of patients with HAM (Yamano et al., 2002, 2009; Araya et al., 2014). This evidence concerns the gene IFNG and tropical spastic paraparesis.