Clearance: The Last and Often Forgotten Stage of Apoptosis
Engulfment by a phagocyte is the final commonevent in the life of most apoptotic cells. Phagocytosisof apoptotic bodies prior to their lysis prevents therelease of potentially toxic or immunogenicintracellular contents and activates an anti-inflammatoryresponse, at least in macrophages. We are beginning tounderstand the mechanisms by which macrophages and otherphagocytes recognize apoptotic cells in vitro, but we are a long way from determining theirrelative importance in vivo. The involuting mammarygland undergoes massive cell loss by apoptosis. Thedying alveolar epithelial cells can be shed into the lumen or can be phagocytosed by macrophages andviable epithelial cells. Yet we know virtually nothingabout the mechanisms mediating recognition and uptake inthe mammary gland. It is likely that clearance of apoptotic cells is critical to normalremodeling of the gland in preparation for the next waveof lactation. The mammary gland, therefore, provides anideal organ in which to study the mechanisms and consequences of apoptotic cell clearance invivo.
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