Human glycoprotein-2 expressed in Brunner glands - A putative autoimmune target and link between Crohn's and coeliac disease.

Glycoprotein 2 (GP2) is an autoantigen in Crohn's (CD) and coeliac disease (CeD). We assessed GP2-isoform (GP2)-expression in intestinal biopsies of paediatric patients with CD, CeD, ulcerative colitis (UC), and healthy children (HC). Transcription of GP2 was elevated in proximal small intestine in CeD and CD patients (only GP2) compared to jejunum (CeD/CD) and large bowel (CD). CeD patients demonstrated higher duodenal GP2-mRNA levels compared to HC/UC patients whereas CD patients showed higher GP2-mRNA levels compared to UC patients. Duodenal synthesis of only small GP2 isoforms (GP2) was demonstrated in epithelial cells in patients/HC and in Brunner glands (also large isoforms) with a more frequent apical location in CD/CeD patients. All four GP2 isoforms interacted with gliadin and phosphopeptidomannan. Gliadin digestion improved binding to GP2 isoforms. GP2 binding to CeD/CD-related antigens, elevated duodenal GP2-mRNA transcription, and GP2-protein secretion in Brunner glands of CeD/CD patients suggest an autoimmune CeD/CD link.