The engulfment of apoptotic leukocytes (efferocytosis) by macrophages during the resolution of inflammation is essential for homeostasis and results in macrophage reprogramming/immune-silencing. Here, we show CD11bhigh macrophages convert to CD11blow ones and stop efferocytosing apoptotic PMN after reaching an engulfment threshold in vivo. In addition, CD11blow macrophages are distinct from either M1 or M2 in their protein expression profile and display pro-resolving properties, such as diminished responses to different TLR ligands ex vivo and propensity to emigrate from resolving inflammation sites to lymphoid organs. Of interest, we found the pro-resolving lipid mediators resolvin E1 and D1, as well as the glucocorticoid dexamethasone (Dex) and the lectin galectin-1 enhance satiated-efferocytosis and consequently CD11blow macrophage conversion from their CD11bhigh counterparts. Deficiency in the atypical chemokine receptor D6 resulted in delayed satiation and reduced immune-silencing of macrophages, and inhibits their departure from resolving inflammation sites. In sum, satiated-efferocytosis is a novel phagocyte property of CD11blow macrophages that is regulated by pro-resolving mediators. Moreover, satiated-efferocytosis is required for CD11blow macrophage emigration from resolving inflammation sites and the return of tissue homeostasis. Thus, satiated-efferocytosis is essential for the completion of timely- and spatially-coordinated resolution of acute inflammation.
- Copyright © 2013 by The American Association of Immunologists, Inc.