ERVW-1 and tropical spastic paraparesis: The mean anti-Env antibody titer in the HAM/TSP patients was 345,176 ± 232,983 LU, while the ATLL and asymptomatic HTLV-I-infected patients had mean titers of 82,825 ± 125,784 LU and 61,310 ± 109,976 LU, respectively.