- In this study, the role of Igs in the recognition and removal of oxidatively damaged human red blood cells (RBCs) was investigated. Phagocytosis of normal RBCs exposed to the oxidative hemolytic agent phenylhydrazine (Phz) and of glucose-6-phosphate dehydrogenase (G6PD)- deficient RBCs by murine macrophages was examined. A 40-fold increase in phagocytosis of RBCs treated with 3 mmol/L Phz was obtained both in the absence and presence of autologous serum, indicating that binding of autologous antibodies to the oxidized cells is not essential for phagocytosis. Yet, a basal number of IgG molecules was found to be present on the RBCs, as determined both by binding of 125I protein A and fluorescein isothiocyanate-antihuman Ig to the cells. Macrophage Fc receptors were found to be involved in the recognition of the RBCs, because phagocytosis was partially inhibited by incubating macrophages with bovine serum albumin (BSA) anti-BSA complexes, aIg (aggregated Igs), and anti-Fc receptor II monoclonal antibodies. Galactose/mannose inhibited phagocytosis of oxidized RBCs additively to aIg. Because phagocytosis was decreased when Phz-RBCs were incubated with F(ab')2 fragments of antihuman antibodies, it is suggested that the basal amount of Igs bound to the cells plays a role in the recognition of Phz- RBCs. G6PD-deficient RBCs were recognized and phagocytosed by murine macrophages without preexposure to oxidants in vitro (mean of 19 RBCs/100 macrophages). This phagocytosis was not affected by the addition of serum and was inhibited by incubating macrophages with galactose/mannose and the various Fc receptor blockers. A positive correlation between hemoglobin content and the number of cell-bound Igs to each patient erythrocytes was found. These results support the involvement of both an Fc and a lectin-like macrophage receptor in the recognition and phagocytosis of Phz-oxidized and G6PD-deficient RBCs and suggest opsonization as a possible physiologic process for the removal of severe damaged RBCs.