Diagnostic value of anti-GP2 antibodies determined in serum and coprofiltrates in children with inflammatory bowel disease

Abstract

Inflammatory bowel diseases (IBD), such as Crohn’s disease (CD) and ulcerative colitis (UC), are characterized by chronically recurring inflammation of intestinal wall and are associated with a significant decrease in the quality of life. A spectrum of genetic variants associated with Crohn’s disease is described. Intestinal dysbiosis (DB) may be the triggering factor of the disease. Glycoprotein 2 (GP2), the main protein of pancreatic zymogen granules, is secreted into the intestines with digestive enzymes. Anti-GP2 antibodies were found in the serum of patients with CD. The aim of the present study was to investigate the levels of anti-GP2 antibodies in serum and feces of children with IBD compared with the DB group. Serums and coprofiltrates from 110 children (64 boys and 46 girls) at the age of 12.3 (2.6-17.9) years were studied; 36 patients with CD, 30 patients with UC. A comparison group consisted of 44 patients with DB. IgG and IgA antibodies against GP2 were tested with ELISA. Nonparametric statistics methods are applied, the results are presented as percentages and medians (Me (Q0.25-Q0.75)). The serum levels of anti-GP2 IgA antibodies were 9.97 (3.35-13.45) U/ml for the CD patients, 6.08 (2.71-14.26) U/ml for UC and 2. 94 (2.29-6.41) U/ml for DB. The levels of anti-GP2 IgG antibodies in serum were 6.16 (3.26-18.4) U/ml for CD, 5.26 (2.97-7.52) U/ml for UC, and for DB 5.23 (2.53-8.85) U/ml. The cut-off threshold concentration for anti-GP2 IgG antibodies was 13.8 U/ml, with sensitivity of 63.2%, specificity 100%, and for IgA 5.63 U/ml, with sensitivity of 60.5% and specificity of 78.8%, thus being lower than the calculated cut-off for adults (20 U/ml). The levels of anti-GP2 IgG in coprofiltrates in children of comparison group were 1.99 (1.26-3.04) U/ml; in the patients with CD, 23.5 (16.15-29.3) U/ml, and in children with UC, 20.45 (13.63-25.5) units/ml (p < 0.001). The cut-off value amounted 8.0 U/ml, with 100% sensitivity and 100% specificity. Concentrations of anti-GP2 IgA in coprofiltrates of patients with IBD did not significantly differ from DB patients. Moreover, the concentration of sIgA in the coprofiltrates of patients with IBD was significantly higher than their level in DB group. The anti-GP2 IgA/sIgA ratio was significantly lower in patients with CD (0.326 (0.23-0.512)), and UC (0.327 (0.205-0.435)), than in patients with DB (2.332 (1.575-3.523)) (p < 0.001); the cut-off level was 0.784, with a sensitivity of 97.7% and specificity of 98.6%. It is discussed, whether fecal anti-GP2 IgA antibodies should be considered as protective, supporting intestinal homeostasis, whereas anti-GP2 IgG antibodies are pathogenetically significant for development of IBD. Thus, using a non-invasive method for determining anti-GP2 antibodies in stool, when exceeding the cut-off for IgG, and reduction of IgA/sIgA ratio below the cut-off, one may differentiate IBD from DB with a similar symptoms at the onset of disease, with 100% sensitivity and 100% specificity.