Effect of RBCs on neutrophil apoptosis. Neutrophils were cultured for varying times (A) or 16 hours (B) in RPMI 1640 containing 5% FCS in the presence or absence of 1:10 to 1:1000 RBCs. Apoptotic cells were identified by morphology on light microscopy and % apoptosis was obtained from 300 counts per experiment. Data represents mean ± SEM of 6 experiments. ** P < .01 versus cells in the absence of RBCs.