Degradation of Opsonized Erythrocytes by Mouse Macrophages‘

The role of the complement receptor type 3 (CR3) on thioglycollate-elicited peritoneal macrophages (TG-PM) in the destruction of opsonized particles was studied. We found that sheep red blood cells (E) that were opsonized with an IgM monoclonal antiForssman antibody and complement (E-IgM-C) were lysed by TG-PM, whereas there was little lysis of E pretreated with either the antibody or the eomplement source alone. Furthermore, this lysis could be inhibited by anti-CR3 monoclonal antibodies that had previously been shown to inhibit binding of E IgM-C to the CR3. Kinetic studies of phagocytosis and lysis indicated that lysis of E1gM-C occurs after phagocytosis, suggesting that lysis is an intracellular event. Further findings suggested that intracellular lysis was promoted by CR3 bound to the phagocytosed target, because a monoclonal antiCR3 antibody decreased the rate of phagocytosis of E-IgM-C but not its magnitude, whereas the rate and extent of lysis were strikingly inhibited. Furthermore, TG-PM that had already internalized unopsonized E selectively lysed EIgM-C that were added later. These data confirm that the interaction of the CR3 with its ligand on E-1g”C promotes rapid phagocytosis, and further suggest that the CR3 facilitates degradation of the target particle once internalization has occurred.