Mucosal Autoimmunity to Cell-Bound GP2 Isoforms Is a Sensitive Marker in PSC and Associated With the Clinical Phenotype

Abstract

Introduction: Zymogen granule glycoprotein 2 (GP2) was demonstrated as first autoimmune mucosal target in primary sclerosing cholangitis (PSC) associated with disease severity. Autoantibodies to four GP2 isoforms (aGP21−4) were found in patients with inflammatory bowel diseases but reactivity against specific GP2 epitopes has not been investigated in PSC yet. Hence, the prevalence of aGP21−4 and their association with the PSC phenotype for risk prediction were examined.Methods: GP2 isoforms were stably expressed as glycosylphosphatidyl - inositol-anchored molecules in the membrane of HEp-2 cells and used as autoantigenic targets in indirect immunofluorescence assay (IFA). aGP21−4 IgA and IgG were detected by IFA in 212 PSC patients of four European university hospitals and 145 controls comprising 95 patients with cystic fibrosis and 50 healthy subjects.Results: Combined aGP21 and aGP24 IgA testing with a sensitivity of 66.0% and a specificity of 97.9% resulted in the best diagnostic performance (Youden index: 0.64) regarding all aGP2 and combinations thereof. aGP24 IgA positivity is significantly associated with the presence of cirrhosis in PSC (p = 0.0056). Logistic regression revealed the occurrence of aGP21 IgA (odds ratio [OR] 1.38, 95% confidence interval [CI]: 1.03–1.86) and aGP24 IgA (OR 1.52, 95%CI: 1.07–2.15) along with male gender (OR 0.51, 95%CI: 0.27–0.97) and older age (OR 1.03 95%CI: 1.01–1.05) as significant risks for the concomitant presence of cirrhosis in PSC.Conclusions: Combined aGP21 and aGP24 IgA analysis is preferred to single aGP2 isoform analysis for sensitive PSC autoantibody testing. Positivity for aGP21 and aGP24 IgA is associated with cirrhosis in PSC and could be used for risk stratification.

The search for the Holy Grail: autoantigenic targets in primary sclerosing cholangitis associated with disease phenotype and neoplasia

“…Combined testing for IgA to GP2 isoforms 1 (large isoform) and 4 (small isoform) was superior to the analysis of autoAbs to just one GP2 isoform and resulted in a sensitivity of 66% in the 212 patients with PSC [104]. AutoAbs to GP2 isoforms 1 and 4 were independent risk predictors for the severity of disease (occurrence of cirrhosis) after adjusting for age and gender [104].…”

“…These GP2 isoforms encompass two larger and two smaller isoforms whereby the large and small isoforms differ in only three amino acids (valine-proline-arginine) [64]. Intriguingly, autoAbs to all four GP2 isoforms, which were expressed as glycosylphosphatidylinositol (GPI)-anchored membrane molecules in a human cell line, could be determined by IFA in patients with PSC from four European university hospitals [104]. Combined testing for IgA to GP2 isoforms 1 (large isoform) and 4 (small isoform) was superior to the analysis of autoAbs to just one GP2 isoform and resulted in a sensitivity of 66% in the 212 patients with PSC [104].…”

“…Intriguingly, autoAbs to all four GP2 isoforms, which were expressed as glycosylphosphatidylinositol (GPI)-anchored membrane molecules in a human cell line, could be determined by IFA in patients with PSC from four European university hospitals [104]. Combined testing for IgA to GP2 isoforms 1 (large isoform) and 4 (small isoform) was superior to the analysis of autoAbs to just one GP2 isoform and resulted in a sensitivity of 66% in the 212 patients with PSC [104]. AutoAbs to GP2 isoforms 1 and 4 were independent risk predictors for the severity of disease (occurrence of cirrhosis) after adjusting for age and gender [104].…”

Anti‐glycoprotein 2 (anti‐GP2) IgA and anti‐neutrophil cytoplasmic antibodies to serine proteinase 3 (PR3‐ANCA): antibodies to predict severe disease, poor survival and cholangiocarcinoma in primary sclerosing cholangitis

“…These isoforms differ by 3 amino acids (valine-proline-arginine) 30 and were previously described in PSC. 23 All assays were carried out according to the manufacturer's instruc-…”

“…Other studies identified IgA against the pancreatic major zymogen granule glycoprotein 2 (GP2) as a marker of disease severity in PSC. [21][22][23][24] Anti-GP2 antibodies (anti-GP2) are members of the family of pancreatic autoantibodies directed against proteins predominantly expressed in the exocrine pancreas. 25 In total, four human GP2 isoforms (GP2 1−4 ) were identified and both IgA, as well as IgG autoantibodies were detected in humans.…”