Signaling pathways involved in macrophage FcγR- or SR-mediated phagocytosis. Phagocytosis of WT Ox-RBCs or IgG-opsonized WT RBCs by RPM was studied in the presence or absence of (A) the p38 MAPK-inhibitor SB203580 (30 μM; n = 8), the ERK1/2-inhibitor PD98059 (30 μM; n = 4), the tyrosine kinase–inhibitor genistein (100 μM; n = 4), or the PI3 kinase–inhibitor LY294002 (50 μM; n = 4); (B) the Src kinase family–inhibitor PP2 (10 μM; n = 3), or the inactive control substance PP3 (10 μM; n = 3); or (C) the Syk tyrosine kinase–inhibitor piceatannol (25 μM; n = 3). In the controls, equal amounts of dimethylsulfoxide (DMSO) were added. Macrophages were preincubated with the indicated inhibitors at 37°C for 30 minutes prior to addition of RBCs in the presence of 10% FCS for another 30 minutes. Following lysis of uningested RBCs, phagocytosis was determined as described in the legend to Figure 1. Data are mean plus or minus SEM for the indicated number of experiments. *P < .05; **P < .01; and ***P < .001, using the Student t test for paired comparisons.