LTB₄ modulates phagocytosis of IgG-SRBCs but not apoptotic cells. Mouse peritoneal macrophages were pretreated in the absence (open bars) or presence of MK 886 (1 μM; 10 minutes) or LTB₄ (10 and 100 nM; 2 minutes) prior to the addition of IgG-SRBCs (panels A and C) or apoptotic thymocytes (panels D and F), respectively. Peritoneal macrophages harvested from WT or 5-LO gene knockout mice (5-LO^–/–) were challenged with IgG-SRBCs (B) or apoptotic thymocytes (E). *P < .05 compared with respective controls (ANOVA followed by Bonferroni t test). Results are the mean ± SEM of triplicate determinations from n = 2-3 separate experiments.