Characterization of the Small Intestinal Lesion in Celiac Disease by Label-Free Quantitative Mass Spectrometry

Global characterization of tissue proteomes from small amounts of biopsy material has become feasible because of advances in mass spectrometry and bioinformatics tools. In celiac disease (CD), dietary gluten induces an immune response that is accompanied by pronounced remodeling of the small intestine. Removal of gluten from the diet abrogates the immune response, and the tissue architecture normalizes. In this study, differences in global protein expression of small intestinal biopsy specimens from CD patients were quantified by analyzing formalin-fixed, paraffin-embedded material using liquid chromatography-mass spectrometry and label-free protein quantitation. Protein expression was compared in biopsy specimens collected from the same patients before and after 1-year treatment with gluten-free diet (n = 10) or before and after 3-day gluten provocation (n = 4). Differential expression of proteins in particular from mature enterocytes, neutrophils, and plasma cells could distinguish untreated from treated CD mucosa, and Ig variable region IGHV5-51 expression was found to serve as a CD-specific marker of ongoing immune activation. In patients who had undergone gluten challenge, coordinated up-regulation of wound response proteins, including the CD autoantigen transglutaminase 2, was observed. Our study provides a global and unbiased assessment of antigen-driven changes in protein expression in the celiac intestinal mucosa.

Serologic assay for diagnosis of celiac disease based on a patient-derived monoclonal antigliadin antibody

BACKGROUND & AIMS

Patients with celiac disease can be identified based on the detection of serum antibodies to deamidated gliadin peptides (DGPs). Recombinant human monoclonal antibodies (hmAb) against gliadin are produced by cloning antibody genes from single IgA-producing plasma cells isolated from lesions of patients with celiac disease. We developed an assay to identify patients with celiac disease based on the ability of antibodies from their serum to inhibit the binding of a gliadin-specific hmAb (1002-1E03) to a specific peptide antigen (inhibition assay).

METHODS

We selected 2 peptides (a 34-mer and a 26-mer) found in ω-gliadins and low-molecular-weight glutenins that had been identified as specific targets of the hmAb 1002-1E03 from a digest of gliadin treated by transglutaminase 2. These peptides contained repeat sequence motifs; their interaction with hmAb 1002-1E03 was assessed in an amplified luminescent proximity homogeneous inhibition assay. We also tested peptides we created that included 3 repeated sequence motifs. Serum samples from untreated patients diagnosed with celiac disease (n = 106) and 2 control groups (198 blood donors, 151 patients with Crohn's disease) were analyzed using the assay, as well as in conventional commercial assays that measure IgA against transglutaminase 2 (TG2) or IgG against DGP.

RESULTS

In our inhibition assays, the 34-mer peptide showed the best results, and identified patients with celiac disease with 86.8% sensitivity and 98.6% specificity. Its diagnostic accuracy was comparable with that of commercial anti-DGP IgG (sensitivity, 87.9%; specificity, 98.0) and anti-TG2 IgA (sensitivity, 81.1%; specificity, 98.9) assays, and it detected most of the patients with anti-TG2 IgA-negative celiac disease without a significant decrease in specificity. Combined use of the anti-ω34 and the anti-TG2 assays produced specificity and sensitivity values of 95.3% and 98.0%, respectively.

CONCLUSIONS

We developed an antigliadin inhibition assay that identifies patients with celiac disease with high levels of specificity and sensitivity. It may prove useful as an adjunct to the current assay for anti-TG2 IgA.

Small bowel, celiac disease and adaptive immunity

BACKGROUND

Celiac disease is a multifactorial and polygenic disease with autoimmune features. The disease is caused by an inappropriate immune response to gluten. Elimination of gluten from the diet leads to disease remission, which is the basis for today's treatment of the disease. There is an unmet need for new alternative treatments.

KEY MESSAGES

Genetic findings point to adaptive immunity playing a key role in the pathogenesis of celiac disease. MHC is by far the single most important genetic factor in the disease. In addition, a number of non-MHC genes, the majority of which have functions related to T cells and B cells, also contribute to the genetic predisposition, but each of them has modest effect. The primary MHC association is with HLA-DQ2 and HLA-DQ8. These HLA molecules present gluten epitopes to CD4+ T cells which can be considered to be the master regulators of the immune reactions that lead to the disease. The epitopes which the T cells recognize are usually deamidated, and this deamidation is mediated by the enzyme transglutaminase 2 (TG2). Celiac disease patients have disease-specific antibodies. In addition to antibodies to gluten, these include autoantibodies to TG2. Antibodies to deamidated gluten are nearly as specific for celiac disease as the anti-TG2 antibodies. Both types of antibodies appear only to be produced in subjects who are HLA-DQ2 or HLA-DQ8 when they are consuming gluten.

CONCLUSION

It is hardly coincidental that TG2 is implicated in T-cell epitope formation and at the same time a target for autoantibodies. Understanding this connection is one of the major challenges for obtaining a complete understanding of how gluten causes tissue destruction and remodeling of the mucosa in the small bowel.

Different binding motifs of the celiac disease-associated HLA molecules DQ2.5, DQ2.2, and DQ7.5 revealed by relative quantitative proteomics of endogenous peptide repertoires

Celiac disease is caused by intolerance to cereal gluten proteins, and HLA-DQ molecules are involved in the disease pathogenesis by presentation of gluten peptides to CD4⁺ T cells. The α- or β-chain sharing HLA molecules DQ2.5, DQ2.2, and DQ7.5 display different risks for the disease. It was recently demonstrated that T cells of DQ2.5 and DQ2.2 patients recognize distinct sets of gluten epitopes, suggesting that these two DQ2 variants select different peptides for display. To explore whether this is the case, we performed a comprehensive comparison of the endogenous self-peptides bound to HLA-DQ molecules of B-lymphoblastoid cell lines. Peptides were eluted from affinity-purified HLA molecules of nine cell lines and subjected to quadrupole orbitrap mass spectrometry and MaxQuant software analysis. Altogether, 12,712 endogenous peptides were identified at very different relative abundances. Hierarchical clustering of normalized quantitative data demonstrated significant differences in repertoires of peptides between the three DQ variant molecules. The neural network-based method, NNAlign, was used to identify peptide-binding motifs. The binding motifs of DQ2.5 and DQ7.5 concurred with previously established binding motifs. The binding motif of DQ2.2 was strikingly different from that of DQ2.5 with position P3 being a major anchor having a preference for threonine and serine. This is notable as three recently identified epitopes of gluten recognized by T cells of DQ2.2 celiac patients harbor serine at position P3. This study demonstrates that relative quantitative comparison of endogenous peptides sampled from our protein metabolism by HLA molecules provides clues to understand HLA association with disease.