PRF1 and tropical spastic paraparesis: Sabouri et al. reported that the frequency of perforin and GzmB+CD8+, CD8+CD28-and CD8+CD27-T cells in PBMCs of HAM/TSP and HTLV-1carriers is lower than healthy controls (HCs), and a marginal negative correlation was observed between percent perforin-positive CD8+ T cells and HTLV-1 PVL in all HTLV-1infected subjects (including patients with HAM/TSP and ACs).