Identification of complement C3 as an autoantigen in inflammatory bowel disease

OBJECTIVE: Autoantibodies against goblet cells in the gastrointestinal mucosa have been described in patients with inflammatory bowel disease (IBD) but a corresponding autoantigen has not yet been identified. The aim of this study was to identify such an antigen. METHODS: First, 10 candidate autoantigens were discarded based on double stainings of appendiceal sections and a mucin-producing cell line (HT29-mtx). Second, an appendiceal cDNA library was immunoscreened with IBD sera. RESULTS: Three out of 48 positive clones were identified as complement C3. Using immunoprecipitation of in vitro transcribed and translated C3, seven of 17 primary sclerosing cholangitis patient sera, 15 of 65 IBD sera, and none out of 54 sera from healthy blood donors showed C3 immunoreactivity. The results were confirmed using western blot and an enzyme-linked immunosorbent assay with alternative sources of C3 protein. CONCLUSION: In conclusion, we have identified complement C3 as a potential autoantigen in IBD and primary sclerosing cholangitis.