Macrophage phagocytosis of wound neutrophils

Resolution of acute inflammation is thought to require the recognition and phagocytosis of apoptotic neutrophils (PMN) through receptor-ligand interactions with macrophages (Mphi). This hypothesis was tested in rat wounds by quantifying apoptosis in freshly harvested and aged-in-culture PMN taken from wounds 1-3 days after injury and by using these wound PMN as phagocytic targets for wound, immune-activated peritoneal, and resident peritoneal Mphi. Less than 6% of freshly harvested PMN exhibited characteristics of apoptosis. On aging in culture, day 1 PMN did not undergo apoptosis, whereas 41+/-1 and 29+/-1% of day 2 and 3 PMN, respectively, developed apoptosis, which corresponded to increased ingestion by Mphi. All three Mphi populations engaged different receptor-ligand pairs for the recognition and phagocytosis of PMN. Results indicate the resistance of early wound PMN to age-induced apoptosis, demonstrate wound-Mphi phagocytosis of wound PMN, and identify distinct receptor utilization by wound and other Mphi to ingest wound PMN.