CD4 and tropical spastic paraparesis: Additionally, the antiviral Th1 phenotype is also dominant among HTLV-1-specific CD4+ T-cells in patients with HAM/TSP (Goon et al., 2002), and higher frequency of IFN-γ, TNF-α, and IL-2 secreting CD4+ T-cells has been demonstrated in patients with HAM/TSP compared to ACs with a similar PVL (Goon et al., 2002, 2003).