IL-4 signaling in macrophages promotes an M2 phenotype important for the resolution of inflammation. (A-B) The number of IL-4–producing macrophages (A) or NKT cells (B) during the course of peritonitis in WT mice was determined by ICS and flow cytometry. At least 3 mice were examined for each time point. (C) Peritoneal macrophages were cultured ex vivo for 48 hours, and expression of M2 markers Arg1, Ym1, and Fizz1 were quantified by quantitative polymerase chain reaction. Data represent 2 independent experiments. (D) Expression of M2 markers in day 3 WT and Il4^−/− peritoneal macrophages were determined and compared as described in (C). Each dot represents data from 1 mouse. (E) Severity of sodium periodate–induced peritonitis in WT or I14ra^L/−LysM^Cre mice was scored by enumeration of peritoneal cells at days 0, 3, and 4. (F) Expression of Ym1 in mice from (E) was measured by quantitative polymerase chain reaction.