The role of the macrophage in apoptosis: hunter, gatherer, and regulator.

Clearance of cellular corpses is a critical feature of apoptosis in vivo during development, tissue homeostasis, and resolution of inflammation. As the professional phagocytes of the body, macrophages play a key role in this process. By recognizing emerging signals using several different receptors, macrophages engulf apoptotic cells swiftly and efficiently. In addition, the binding of apoptotic cells profoundly down-regulates the ability of the macrophage to produce inflammatory mediators by inducing the release of antiinflammatory mediators. Finally, macrophages may actually induce cell death in specific cells during embryogenesis. Abnormalities of apoptotic cell clearance may contribute to the pathogenesis of chronic inflammatory diseases, including those of autoimmune etiology. It is also possible that certain malignant tumor cells co-opt the mechanisms for apoptotic cell clearance to avoid immune surveillance by subverting macrophage and dendritic cell responses.