Characterization of the human erythrocyte complement receptor CR1 (C3b receptor) by epitope mapping.
Monoclonal antibodies and an anti-idiotypic serum against human complement receptor CR1 (C3b receptor, immune adherence receptor) were used to identify CR1 and some of its proteolytic fragments by an immunoblotting technique. The anti-idiotypic serum had a specificity for the C3b-binding site, as could be shown by its cross-reactivity with complement factor H. The monoclonal antibodies GARP-4 and GARP-37 were specific for epitopes located nearby the ligand-binding site, because they blocked the immune adherence reaction. For the immunoblotting technique, it was essential to use non-reducing conditions, since reduction of CR1 destroyed the epitopes. Therefore, mainly large (disulphide-linked) fragments of CR1 were obtained. A chymotryptic fragment of Mr 56,000 identified by GARP-4, was the smallest cleavage product to be associated with the C3b-binding domain. Different proteases gave CR1 degradation products of similar Mr, indicating the presence of distinct domains, three of which had a Mr approximately 38,000. A schematic model of CR1 substructure was deduced from the epitope mapping data.
D000911:Antibodies, Monoclonal / Q000276:immunology; D000918:Antibody Specificity; D001665:Binding Sites; D003180:Complement C3b Inactivator Proteins / Q000276:immunology; D017242:Complement Factor H; D003429:Cross Reactions; D000939:Epitopes / Q000276:immunology; D004912:Erythrocytes / Q000032:analysis*; D006801:Humans; D011951:Receptors, Complement / Q000276:immunology*; D017463:Receptors, Complement 3b
D000911:Antibodies, Monoclonal; C493495:CFH protein, human; D003180:Complement C3b Inactivator Proteins; D000939:Epitopes; D011951:Receptors, Complement; D017463:Receptors, Complement 3b; D017242:Complement Factor H