Characterization of the human erythrocyte complement receptor CR1 (C3b receptor) by epitope mapping |
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| Authors: | R Prohaska G R Adolf |
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| Affiliation: | 1. Dept. of Immunology, Erasmus MC, University Medical Center Rotterdam, Wytemaweg 80 3015 CN, Rotterdam, The Netherlands;2. Dept. of Laboratory Medicine, Medical Immunology, University of Groningen, University Medical Center Groningen, Hanzeplein 1, 9700 RB, Groningen, The Netherlands;3. Dept. of Pediatrics, Beatrix Children''s Hospital, University of Groningen, University Medical Centre Groningen, Hanzeplein 1,9700 RB, Groningen, The Netherlands |
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| Abstract: | 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. |
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