ABSTRACT: In response to microenvironmental cues, macrophages undergo a profound phenotypic transformation acquiring distinct activation phenotypes ranging from pro-inflammatory (M1) to anti-inflammatory (M2). To study how activation phenotype influences phagocytosis and production of reactive oxygen species (ROS) mediated by receptors for IgG antibodies (Fc? receptors) and by CD13, human monocyte-derived macrophages were polarized to distinct phenotypes using IFN-? (M?-IFN-?), IL-4 (M?-IL-4), or IL-10 (M?-IL-10). Phenotypically, M?-IFN-? were characterized as CD14+CD80+CD86+ cells, M?-IL-4 as CD209highCD206+CD11b+CD14low, and M?-IL-10 as CD16+CD163+ cells. Compared to non-polarized macrophages, Fc?RI expression increased in M?-IFN-? and M?-IL-10 and Fc?RIII expression increased in M?-IL-10. None of the polarizing cytokines modified Fc?RII or CD13 expression. Functionally, we found that cytokine-mediated activation significantly and distinctively affected Fc?R- and CD13-mediated phagocytosis and ROS generation. Compared to non-polarized macrophages, Fc?RI-, Fc?RII-, and CD13-mediated phagocytosis was significantly increased in M?-IL-10 and decreased in M?-IFN-?, although both cytokines significantly upregulated Fc?RI expression. IL-10 also increased phagocytosis of Escherichia coli, showing that the effect of IL-10 on macrophage phagocytosis is not specific for a particular receptor. Interestingly, M?-IL-4, which showed poor Fc?R- and CD13-mediated phagocytosis, showed very high phagocytosis of E. coli and zymosan. Coupled with phagocytosis, macrophages produce ROS that contribute to microbial killing. As expected, M?-IFN-? showed significant production of ROS after Fc?RI-, Fc?RII-, or CD13-mediated phagocytosis. Unexpectedly, we found that M?-IL-10 can also produce ROS after simultaneous stimulation through several phagocytic receptors, as coaggregation of Fc?RI/Fc?RII/CD13 induced a belated but significant ROS production. Together, these results demonstrate that activation of macrophages by each cytokine distinctly modulates expression of phagocytic receptors, Fc?R- and CD13-mediated phagocytosis, and ROS production.
