Clearance: The cast and often forgotten stage of apoptosis

Engulfment by a phagocyte is the final common event in the life of most apo ptotic cells. Phagocytosis of apoptotic bodies prior to their lysis prevent s the release of potentially toxic or immunogenic intracellular contents an d activates an anti-inflammatory response, at least in macrophages. We are beginning to understand the mechanisms by which macrophages and other phago cytes recognize apoptotic cells in vitro, but we are a long way from determ ining their relative importance in vivo. The involuting mammary gland under goes massive cell loss by apoptosis. The dying alveolar epithelial cells ca n be shed into the lumen or can be phagocytosed by macrophages and viable e pithelial cells. Yet we know virtually nothing about the mechanisms mediati ng recognition and uptake in the mammary gland. It is likely that clearance of apoptotic cells is critical to normal remodeling of the gland in prepar ation for the next wave of lactation. The mammary gland, therefore, provide s an ideal organ in which to study the mechanisms and consequences of apopt otic cell clearance in vivo.