Temporal course of responsiveness to anti-Fas IgM ligation. Neutrophils (1 × 10⁶/mL) were incubated with LPS (1 μg/mL) (A) or cross-linked with antibodies to CD11b (8 μg/mL) (B) for 0, 1, or 4 hours, washed, and then incubated with anti-Fas IgM (100 ng/mL for 1 hour). Apoptosis was assessed by flow cytometry at 18 hours after incubation with LPS or CD11b ligation. *P < .05 versus control, ρ P < .05 versus Fas (100 ng/mL). Results are the mean ± SD for n = 5 experiments with four separate donors of neutrophils.