IL-15 mediated degranulation and IFN-γ production in CD8⁺ T cells of HTLV-I–infected patients. (A) CD107a/IFN-γ expression in CD8⁺ T cells of NDs and HTLV-I–infected patients after culture with rhIL-15. The PBMCs from 3 of each NDs, ACs and HAM/TSP patients were cultured with or without 10 ng/mL rhIL-15 for 12 hours. In HAM/TSP patients, anti–IL-15 was added singly or in combination with rhIL-15 as control. (B) Induction of HTLV-I–specific CD8⁺ T-cell degranulation by IL-15. The top panels show CD107a mobilization in HTLV-I Tax tetramer⁺ CD8⁺ T cells after culture for 12 hours without rhIL-15 (i) and with rhIL-15 (ii). The bottom panels show CD107a mobilization in CMV pp65 tetramer⁺ CD8⁺ T cells after the culture for 12 hours without rhIL-15 (iii) and with rhIL-15 (iv). (C) Inhibitory effects of anti–MHC class I, anti–IL-15, anti–IL-2/15Rβ (Mikβ1) and anti–IL-2Rα (anti-Tac) on degranulation and IFN-γ production in CD8⁺ T cells of HAM/TSP patients. The PBMCs were cultured with antibodies singly or in combination for 24 hours. The amounts of CD107a/IFN-γ productions of CD8⁺ T cells in PBMCs cultured with IgG control were normalized to 100%, and then, those in PBMCs cultured with each antibody were calculated. The graph was prepared from data obtained from 5 HAM/TSP patients. Error bars represent SD. *P < .01, ‡P < .001.