Saturated‐efferocytosis generates pro‐resolving CD11blow macrophages: Modulation by resolvins and glucocorticoids

During the resolution phase of inflammation, apoptotic leukocytes are efferocytosed by macrophages in a nonphlogistic fashion that results in diminished responses to bacterial moieties and production of anti‐inflammatory cytokines. Complement receptor 3 and pro‐resolving lipid mediators promote the engulfment of apoptotic leukocytes by macrophages. Here, we present evidence for the emergence of pro‐resolving, CD11blow macrophages in vivo during the resolution of murine peritonitis. These macrophages are distinct from the majority of peritoneal macrophages in terms of their functional protein expression profile, as well as pro‐resolving properties, such as apoptotic leukocyte engulfment, indifference to TLR ligands, and emigration to lymphoid organs. Notably, we also found macrophages convert from the CD11bhigh to the CD11blow phenotype upon interaction with apoptotic cells ex vivo. In addition, we found that the pro‐resolving lipid mediators resolvin E1 and D1, and the glucocorticoid dexamethasone regulated pro‐resolving macrophage functions in vivo. This regulation culminated in a novel pro‐resolving function, namely reducing the apoptotic leukocyte ingestion requirement for CD11blow macrophage generation. These new phenotype and molecular pathway markers define the new satiated macrophage. Thus, we suggest that satisfying efferocytosis generates CD11blow macrophages that are essential for complete nonphlogistic containment of inflammatory agents and the termination of acute inflammation.