Backround and aims: The aetiopathogenesis of Crohn’s disease (CD), an inflammatory bowel disease (IBD), is not yet fully understood. Autoimmune mechanisms are thought to play a role in the development of CD, but the target antigens and the underlying pathways have not been sufficiently identified.
Methods: Based on data from immunoblotting and matrix-assisted laser desorption ionisation time-of-flight (MALDI-TOF) mass spectrometry, the major antigenic target of pancreatic autoantibodies (PAB), which are specific for CD, was identified. Specificity of autoantibody reactivity was confirmed by enzyme-linked immunosorbent assays (ELISA) and indirect immunofluorescence (IIF) using purified rat and human recombinant GP2 synthesised in transiently transfected mammalian HEK 293 cells. Real-time polymerase chain reaction (rt-PCR) and IIF were used to detect mRNA and antigen localisation in human colon biopsies.
Results: The major zymogen granule membrane glycoprotein 2 (GP2) was identified as the autoantigen of PAB in CD. PAB-positive CD patient sera (n=42) displayed significantly higher IgG reactivity to rat GP2 in ELISA than PAB-negative sera (n=31), ulcerative colitis (UC) patient sera (n=49), and blood donor sera (n=69) (p<0.0001, respectively). Twenty eight (66%) and 18 (43%) of 42 PAB-positive sera demonstrated IgG and IgA reactivity to human recombinant GP2 in IIF, respectively. Patients with PAB-negative CD (n=31) were not reactive. GP2 mRNA transcription was significantly higher in colon biopsies from CD patients (n=4) compared to UC patients (n=4) (p=0.0286). Immunochemical staining confirmed GP2 expression in human colon biopsies from CD patients.
Conclusion: Anti-GP2 autoantibodies constitute novel CD-specific markers, the quantification of which could significantly improve the serological diagnosis of IBD. The expression of GP2 in human enterocytes suggests an important role for anti-GP2 response in the pathogenesis of CD.