Perforin-positive CD8⁺ T cells and HTLV-1 proviral load in HTLV-1 infection. (Left panels) There was a marginal negative correlation between the percentages of perforin-positive CD8⁺ T cells and HTLV-1 proviral load (PVL) in whole HTLV-1–infected patients (HAM/TSP + HVCs; P = .046, r = −0.29 by Spearman rank correlation analysis), but not in patients with HAM/TSP or in HVCs alone. (Right panels) There was a significant negative correlation between the percentages of perforin-positive CD8⁺ T cells and HTLV-1 PVL in whole HLA-A*02–positive HTLV-1–infected patients (HAM/TSP + HVCs; P = .003, r = −0.58) and in HVCs alone (P = .024, r = −0.64), but not in patients with HAM/TSP (P = .15, r = −0.35). The x axis denotes percentage of perforin-positive CD8⁺ T cells, and the y axis denotes HTLV-1 PVL (copy number of HTLV-1 tax per 10⁴ PBMCs = [(copy number of tax)/(copy number of β-actin/2)] × 10⁴). Data were analyzed by Spearman rank correlation. The solid line represents a least-squares regression line.