HBZ and tropical spastic paraparesis: While the significance of PVL in determining the course of HTLV-1 infections and transformation of ACs to ATLL and/or HAM/TSP patients is already determined (Nagai et al., 1998; Iwanaga et al., 2010), the role of HBZ and Tax expression and their balance in the outcome of HTLV-1 infection is also strongly suggested by comparing their levels between ACs, HAM/TSP, and ATLL patients.