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P280. Anti glycoprotein-2 antibody in pediatric inflammatory bowel disease and celiac disease: prevalence, diagnostic value and variation at follow-up

M. Vallorani1, S. Gatti1, V. Romagnoli1, L. Marinelli2, G. Ciarrocchi2, C. Catassi1, 1Università Politecnica delle Marche, Department of Pediatrics, Ancona, Italy, 2Ospedali Riuniti, University Hospital, Central Analytical Laboratory, Ancona, Italy

Background

The zymogen granule membrane glycoprotein (GP2) has been recognized as the major antigenic target of Crohn's disease (CD) specific anti-pancreatic antibodies (PAB). Reactivity to anti-GP2 has been showed in 30% and 10% of adults patients with CD and ulcerative colitis (UC), respectively. Previous studies revealed an association of anti GP2 with ileo-colonic location, stricturing tendency and perianal disease in adults with inflammatory bowel disease (IBD) [1]. As reported in a single study the reactivity of antibodies anti-GP2 in Celiac Disease was 13%. The prevalence, the significance, association with clinical parameters and variation over time in antibodies levels has never been investigated in pediatric gastrointestinal (GI) diseases.

Methods

Anti-GP2 IgG and IgA and ASCA IgG and IgA were determined by enzyme-linked immunosorbent assay (ELISA) in sera of 34 pediatric IBD patients (15 CD, 19 UC, median age 10.5 yrs) and 25 children with Celiac Disease (at diagnosis), prospectively recruited at the Department of Pediatrics (Università Politecnica delle Marche), from Dec 2011 to Sep 2013. Data were compared with a control group of 24 children with functional GI disorders. Furthermore 15 IBD patients (7CD and 8UC) were prospectively tested for anti-GP2 at the follow-up. According to previous studies a value >20 U/ml for both tests was considered positive.

Results

Overall the prevalence of anti GP2 antibody (IgA and/or IgG) was 33.3% in CD, 4% in Celiac Disease and 0% both in UC and in the control group. In the CD group, 5 had anti GP2-IgG and 2 showed both GP2-IgG and IgA reactivity; ASCA were positive in 66.7% and co-occurrence of ASCA and anti-GP2 was detected in 26.7%. In CD patients no association of anti GP2 positivity was found either with phenotype or location. Diagnostic sensitivity and specificity of anti-GP2 were 33.3% and 100% in the CD group, while considering together ASCA and anti-GP2 reactivity, sensitivity for CD raised to 73.3%. At the follow-up (median time: 1.8 yrs) we found persistence of negative anti-GP2 values in all IBD patients, except one. Interestingly, in one patient (positive at first determination), we could demonstrate a reduction in anti-GP2 IgG titer (from 30.2 U/ml to 13.5 U/ml), during anti-TNF alpha treatment.

Conclusion

Anti-GP2 antibodies are highly specific for CD also in children. The association with other serological markers (ASCA) increases the sensitivity for CD detection. Anti-GP2 could find an important role as part of a serological diagnostic panel, particularly in cases of IBD of Unclassified type. The possible implication of anti-GP2 antibodies in pathogenesis and evolution of IBD needs further investigations.

1. Somma V, Ababneh H, Ababneh A, Gatti S, Romagnoli V, Bendia E, Conrad K, Bogdanos DP, Roggenbuck D, Ciarrocchi G, (2013), The Novel Crohn's Disease Marker Anti-GP2 Antibody Is Associated with Ileocolonic Location of Disease, Gastroenterology Reasearch and Practice.