title: Functional cooperation of C3b-acceptors, Fc gamma-receptors and cell-surface proteases on macrophages.
abstract: Macrophages are FcR-positive cells, synthetize complement components and express proteolytic enzymes on their surface. In this paper a functional cooperation of C3b acceptor (C3bA) sites, which bind covalently nascent C3b molecules via their metastable binding site, IgG FcRs and cell surface proteases are described and the possible importance of this cooperation in regulation of immune response is discussed. It was found that isolated monocytes did not express C3bA in contrast to cultured macrophages which showed immune adherence positivity. Stimulation of macrophages resulted in enhanced expression of C3bA. C3 synthetized by macrophages was shown to be cleaved by cellular proteases which resulted in the binding of nascent C3b to C3bA. C3bA-nascent C3b interaction inhibited FcR-dependent effector functions, such as immune complex phagocytosis and antibody-dependent cellular cytotoxicity.
mesh_terms: D000818:Animals; D000920:Antibody-Dependent Cell Cytotoxicity; D000936:Antigen-Antibody Complex / Q000378:metabolism; D001665:Binding Sites; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D003179:Complement C3b / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008262:Macrophage Activation; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D009000:Monocytes / Q000276:immunology; D010447:Peptide Hydrolases / Q000378:metabolism*; D010587:Phagocytosis; D011961:Receptors, Fc / Q000276:immunology*; D017452:Receptors, IgG
chemical_list: D000936:Antigen-Antibody Complex; D011961:Receptors, Fc; D017452:Receptors, IgG; D003179:Complement C3b; D010447:Peptide Hydrolases