To support further the involvement of CD244/CD48 signaling on CD8+ T cells in HTLV-I-infected patients, the distribution of CD244 was visualized on cytotoxic lymphocytes (perforin+ cells) of patients with HAM/TSP after 8 hours in vitro culture when both perforin+ cells and polarizing perforin+ cells were most frequently visualized. Here, CD244 is linked to tropical spastic paraparesis.