CTL-induced platelet apoptosis was found in some ITP patients. Platelets were gated by (A) forward scatter (FS) and side scatter (SS), and labeled with (B) phycoerythrin-cyano dye 5–conjugated mouse anti-human CD41a. (C) The apoptosis of platelets from 1 ITP patient was 8.15% (cultured alone) and 13.28% (cultured with autologous CTLs), respectively. (D) Thirty-eight ITP patients were divided into 2 groups. CTL-induced platelet apoptosis in the cytotoxic group (23 patients) was significantly higher than that of healthy controls (3.32% ± 1.38% vs 0.27% ± 0.43%, P < .01), whereas that in the noncytotoxic group (15 patients) was not different from healthy controls (0.14% ± 0.38% vs 0.27% ± 0.43%, P = .23). *P < .01.