M2A and M2C Macrophage Subsets Ameliorate Inflammation and Fibroproliferation in Acute Lung Injury Through Interleukin 10 Pathway.

The role of M2 macrophages in the resolution and fibroproliferation of acute lung injury (ALI) is poorly understood. In this study, we investigated the effects of two M2 macrophage subtypes, M2a induced by interleukin (IL)-4/IL-13 and M2c induced by IL-10/transforming growth factor (TGF)-β, on the pathogenesis of ALI. M2a and M2c were adoptively transferred into LPS-induced ALI mice model. Data showed that Vybrant-labeled macrophages appeared in the lungs of ALI mice. Subsequently, we observed that both subsets significantly reduced lung inflammation and injury including a reduction of neutrophil influx into the lung and an augmentation of apoptosis. Interestingly, M2c macrophages more effectively suppressed indices of lung injury than M2a macrophages. M2c macrophages were also more effective than M2a in reduction of lung fibrosis. In addition, we found that M2c but not M2a macrophages increased IL-10 level in lung tissues of the recipient ALI mice partially mediated by activating the JAK1/STAT3/SOCS3 signaling pathway. After blocking IL-10, these superior effects of M2c over M2a were abolished. These data imply that M2c are more potent than M2a macrophages in protecting against lung injury and subsequent fibrosis due to their ability to produce IL-10. Therefore, reprogramming macrophages to M2c subset may be a novel treatment modality with transitional potential.