CNTN2 and tropical spastic paraparesis: Interestingly, CSF/serum antibody index of anti-Gag and anti-Tax were significantly elevated in HAM/TSP patients while ACs had a significantly lower CSF/serum antibody index of all HTLV-1 antigens; this suggests that antibody responses for HTLV-1 Gag and Tax might be generated in HAM/TSP patients according to increases of viral expression or immune activation while antibody responses against these HTLV-1 antigens might be well controlled in the CSF of ACs.