Critical roles of IL-4 on induction and maintenance of alternative activation in BMDMs. BMDMs were incubated with IL-4 for 2 days; then the cells were incubated with (IL-4 continuous group) or without (IL-4 medium group) IL-4 for the indicated time. (A) The mRNA levels of Ym1 (Chi3l3), FIZZ1 (Retnla), and Arginase 1 (Arg1) were analyzed by quantitative RT-PCR. The data shown are “fold induction” relative to that in untreated cells. (B) Expressions of Ym1, FIZZ1, and Arginase 1 (Arg1) were measured by immunoblotting. Gapdh was used as a loading control. (C) The mRNA levels of iNOS (Nos2) were analyzed by quantitative RT-PCR. The data shown are “fold induction” relative to that in untreated cells. #P < .05 compared with the level on day 0. (D) Expression of phosphorylated (pY)-STAT6 was measured by immunoblotting. Gapdh was used as a loading control. Data are representative of 3 independent experiments (A-D) and are expressed as mean ± SEM (A,C). *P < .05, **P < .01, ***P < .001, compared with IL-4 medium group.