Concentration dependence of inhibition of phagocytosis by FMLP-activated PMNs by C₂ ceramides and sphingoid bases. Suspended PMNs (2 × 10⁶/mL) were incubated with the indicated doses of lipids for 30 minutes at 22°C, followed by activation with FMLP (100 nmol/L) for 10 minutes at 37°C, and phagocytosis measured as outlined in Materials and Methods. Values represent the mean ± SD for three experiments. The phagocytic index in the absence of lipid (100% control) was 102.3 ± 22.8.