Mitochondrial toxins inhibit IL-4-induced arginase activity. Microglial cells were treated with rotenone or 3-NP and stimulated with 10 ng/ml IL-4 for 24 hrs, and arginase expression was analysed by western blot. A representative blot is shown in (a). Quantification of three western blots (b). Microglial cells were treated with rotenone or 3-NP and stimulated with 10 ng/ml IL-4 for 32 hrs. Arginase activity was quantified after 5 h as described in Methods (c). Values are mean ± SEM for independent arginase activity measurements. n = 16-22 wells (i.e., 8-11 separate experiments performed in duplicate); ***, p < 0.001, significantly different from corresponding basal (ANOVA followed by Bonferroni's Multiple Comparison test).