PD-1 expression on virus-specific CD8+ T lymphocytes in ACs, carriers with collagen disease (CCs) and HAM/TSP. Percentage of PD-1 expression on CD8+ lymphocytes and HTLV-1-, CMV-, EBV-specific CD8+ lymphocytes in AC, CC, HAM/TSP and healthy donors (HDs). Horizontal bars indicate the mean percentage of PD-1-positive cells. The number below each subject is the mean±SD. *P<0.001; **P<0.01 (Significant differences by Mann-Whitney U test).