Macrophage phagocytosis of neutrophils at inflammatory/infectious foci: a cooperative mechanism in the control of infection and infectious inflammation

Macrophages and neutrophils possess overlapping and complementary features associated to their common origin and subsequent specialization during myelopoiesis. That specialization results in macrophage lineage being limited in antimicrobial capacity and cytotoxicity comparatively with the neutrophil lineage. These and other features of mature macrophages and neutrophils, like different lifespan and tissue localization, promote their particular lifestyles and prompt a functional partnership for cooperation in the protective antimicrobial host defense. This partnership includes reciprocal recruitment to infected sites, cooperative effector antimicrobial activities, and pro-resolving anti-inflammatory effects. One modality of the cooperative effector antimicrobial activities involves the phagocytosis by the macrophage of apoptosing neutrophils and of nonapoptosing neutrophils expressing "eat-me" signals. This cooperative interaction results in the enhancement of the comparatively limited macrophage antimicrobial capacity by the acquisition and use of potent neutrophil microbicidal molecules. Here, data are reviewed that suggest that this is a process actively engaging the two professional phagocytes. Phagocytosis of neutrophils by macrophages at inflammatory/infectious foci accumulates two effects beneficial to the protective host immune response: help in the control of the infection and prevention of neutrophil autolysis, effects that converge to accelerate the resolution of the infection-associated inflammation.