COOPERATION EFFECT OF EXTERNALIZED PHOSPHATIDYLSERINE AND OXIDIZED PHOSPHOLIPIDS ON CLEARANCE OF APOPTOTIC CELLS BY MACROPHAGES

To investigate the role of externalized phosphatidylserine(PS) and oxidized phospholipids on the clearance of apoptotic cells by macrophage,red blood cells(RBCs) containing different apoptotic signals(externalized PS or/and oxidized phospholipids) were prepared by incubation of normal or N-ethylmaleimide pre-treated RBCs with liposomes containing PS or/and oxidized phospholipids,the ratio of binding and phagocytosis of these modified RBCs by mouse peritoneal macrophages were measured by counting binding or phagocytotic positive macrophages under microscope.The results showed that PS externalization alone caused either by incorporation with liposome containing PS or by pre-treatment with N-ethylmaleimide significantly increased the ratio of binding by macrophages,but had no significantly influence on the ratio of phagocytosis.However,when both PS and oxidized phospholipids(either oxidized PS or oxidized phosphatidylcholine) were incorporated into normal RBCs or oxidized phospholipids were incorporated into N-ethylmaleimide pre-treated RBCs,not only the ratio of binding by macrophages increased significantly,but also the ratio of phagocytosis significantly increased.These results imply that externalization of PS might be responsible for the binding of apoptotic cells with macrophage,and oxidized phospholipids might trigger the further phagocytosis.The cooperation of them is required for the clearance of apoptotic cells by macrophages.