ABSTRACT
Human erythrocytes exposed to appropriate concentrations of H(2)O(2) for 1h became susceptible to the binding and phagocytosis by macrophages. The binding was inhibited by anti-band 3 serum and prevented by pretreatment of erythrocytes with a polylactosamine-cleaving enzyme endo-beta-galactosidase, indicating that polylactosaminyl sugar chains of band 3 are recognized by macrophages. The macrophage receptor involved was suggested to be nucleolin, a recently identified macrophage surface protein recognizing sialylpolylactosaminyl-chain clusters on early apoptotic cells, because anti-nucleolin antibody and a soluble form of recombinant nucleolin blocked the recognition. Treatment of erythrocytes with caspase inhibitors Z-VAD-fmk or Z-DQMD-fmk (caspase 3 selective) before the oxidation resulted in lowered binding of the oxidized erythrocytes to macrophages, suggesting that actions of caspases, particularly those of caspase 3, are prerequisite for the membrane changes leading to band 3 aggregation. Moreover, the cytosolic caspase 3 was found to be activated by H(2)O(2), and the extent of the activation correlated well with the susceptibility of the oxidized erythrocytes to the macrophage recognition. These results suggest that oxidative stress renders the erythrocytes susceptible to clearance by macrophages through activation of caspases leading to band 3 aggregation.
