To investigate the relationship between the expression level of HBZ mRNA and the antibody response against HBZ in Japanese HTLV-1-infected individuals with different clinical status (i.e., HAM/TSP, ATL, and AC), we quantified the expression of HBZ mRNA in PBMCs and anti-HBZ Abs in plasma. This evidence concerns the gene DDX41 and tropical spastic paraparesis.