Published online before print March 21, 2006
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Inflammation Repair Group, MRC Centre for Inflammation Research, Queens Medical Research Institute, Edinburgh, United Kingdom
1Correspondence: Inflammation Repair Group, MRC Centre for Inflammation Research, C2.05 Queens Medical Research Institute, Little France Crescent, Edinburgh EH16 4TJ, UK. E-mail: simon.brown{at}ed.ac.uk
Phagocyte integrins, by binding "bridging" molecules, mediate the ingestion of late apoptotic cells and apoptotic bodies by mechanisms that remain obscure. We recently reported that human monocyte-derived macrophages capture viable and apoptotic human leukocytes through homophilic interactions involving CD31 and that CD31 then promotes the engulfment of apoptotic cells or the detachment of viable cells. We now report that CD31 homophilic interactions between phagocyte and target cells lead to activation of phagocyte
5ß1 integrin and the engulfment of apoptotic Jurkat T lymphocytes via a fibronectin (Fn) "bridge." Although Fn and serum served as an opsonin for ß1 integrin-dependent phagocytosis of apoptotic leukemic T cells, they failed to do so for neutrophils. Given the complexities and inherent variability of working with primary cells, we have refined our model to show that ligation of CD31 on THP-1 macrophages also regulates ß1 integrin-dependent phagocytosis of Fn-coated Latex beads. Thus, selective "tethering" of apoptotic leukocytes by phagocyte CD31 not only discriminates dying from viable cells but also selectively activates phagocyte integrins for the engulfment of apoptotic cells.
Key Words: acute-phase reactants macrophages adhesion molecules
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