Background/Aims: A strong association exists between ulcerative colitis and primary sclerosing cholangitis (PSC). Previously, the presence of a unique epitope shared by colon and biliary epithelial cells was shown by using the novel monoclonal antibody (MAb) 7E12H12 developed against a colonic epithelial protein. In the present study, the presence of circulating autoantibody in PSC against this peptide was examined. Methods: Sera from 16 patients with PSC, 13 with primary biliary cirrhosis, 6 with secondary biliary stricture, and 6 with chronic liver diseases and 10 normal subjects were used. An inhibition immunoperoxidase assay using the 7E12H12 MAb was developed against sections of bile duct and gallbladder. Sera were also examined in an enzyme-linked immunosorbent assay (ELISA) against the gallbladder extract enriched in 7E12H12-reactive protein. Results: About two thirds of the sera from patients with PSC blocked the binding of 7E12H12 MAb on the bile duct and gallbladder, whereas non-PSC sera did not. In the ELISA, 93% of PSC sera had circulating immunoglobulin G antibodies against the enriched gallbladder extract. The reactivity of sera from the PSC group was significantly (P < 0.01 to P < 0.0001) higher than in each of the non-PSC groups. Conclusions: Sera from patients with PSC contains autoantibodies against a cross-reactive peptide shared by colon and biliary epithelial cells.
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