Essential role for STIM1 in macrophage FcγR-dependent calcium signaling and phagocytosis, but not MCP-1 production. (A) PM cells of Stim1^+/+ and Stim^−/− chimeric mice were stained with Alexa 647–conjugated FcγRI, FcγRIII, and FcγRIV-specific mAbs in combination with PE-F4/80 and analyzed by fluorescence-activated cell sorting (FACS). Data shown are MFI (± SD; n = 4, **P < .01). (B) Fura-2–loaded PM were incubated with 10 μg/mL 2.4G2 for 4 minutes followed by addition of 20 μg/mL cross-linking anti–rat IgG antibodies and monitoring of [Ca²⁺]_i. Representative measurements (left) and maximal (Δ[Ca²⁺]_i ± SD, n = 5 per group) are shown. (C-E) PM cells were incubated with uncoated (control) or IgG2-coated MRBC. (C) To study binding, incubations were performed for 4 hours at 4°C. To study phagocytosis (D) and MCP-1 release (E), incubations were performed for 4 hours at 37°C followed by the lysis of extracellular MRBC. (C,D) The percentage of positive cells that formed rosettes with more than 3 erythrocytes or ingested more than 1 erythrocyte was assessed microscopically. The results shown are mean (± standard error of the mean [SEM]) of 2 independent experiments performed in duplicate (**P < .001).