Autoantigens in Inflammatory Bowel Disease and Primary Sclerosing Cholangitis

Abstract: Inflammatory bowel disease (IBD) comprises diseases that are characterized by chronic or relapsing inflammation of the gastrointestinal tract. Primary sclerosing cholangitis (PSC) is an extraintestinal manifestation in IBD. Immunoreactivity against an autoantigen that is expressed both in the gastrointestinal tract and the biliary tract could be the link between these diseases. A possible source of such an antigen is goblet cells.Immunostainings of normal human tissues using IBD patient sera showed goblet cell immunoreactivity against goblet cells in all parts of the gastrointestinal tract. The most frequent immunostaining was found against goblet cells in the appendix against which 84% (42/50) of IBD patients compared to 8% (4/50) of healthy blood donors showed immunoreactivity. To identify the corresponding antigen we used three different approaches, investigation of immunoreactivity to different candidate proteins compared to IBD sera, immunoscreening of an appendiceal cDNA library, and immunoprecipitation of protein lysates from mucin producing cells followed by SDS-PAGE and 2D gel electrophoresis. These approaches led to the identification of several candidate autoantigens of which complement C3 is the most promising.A novel staining pattern with strong immunoreactivity to granules and the apical membrane of biliary epithelial cells was identified with 35% (12/34) of PSC sera compared to none of healthy controls (n=28). Screening of a cDNA library from normal human choledochus identified PDZ domain containing 1 (Pdzk1) and Glutathion S transferase theta 1 (GSTT1) as potential candidates. Pdzk1 is an interesting candidate which is expressed in the intestinal tract and bile ducts. GSTT1 antibodies were not specific for PSC and are thought to develop as an alloimmune response in patients with the GSTT1-null genotype.In conclusion, we have identified specific immunoreactivity to goblet cells and biliary epithelial cells using sera from patients with IBD and PSC respectively. We have also identified several potential autoantigens.