Oxidation and erythrocyte senescence

Direct macrophage recognition of an externalized phosphatidylserine signal on senescent erythrocytes is a process of erythrophagocytic clearance that is in line with the general clearance process of all other circulating cell s that become apoptotic, Advances in deciphering this process suggest that oxidation of the erythrocyte's hemoglobin, the salient target of the free r adicals encountered in the circulatory environment, may drive subsequent st eps. The progressive accumulation of oxidized hemoglobin covalently bound t o the membrane skeleton not only disrupts membrane organization but also th reatens eventual phospholipid oxidation via a calcium-promoted quasi-lipoxy genase activity. The emergence on the cell surface of a threshold concentra tion of oxidized phospholipids, principally phosphatidylserine, signals rec ognition by the CD36 macrophage receptor. (C) 2000 Lippincott Williams & Wi lkins, Inc.