HLA-DQ Molecules as Affinity Matrix for Identification of Gluten T Cell Epitopes

Abstract

Even though MHC class II is a dominant susceptibility factor for many diseases, culprit T cell epitopes presented by disease-associated MHC molecules remain largely elusive. T cells of celiac disease lesions recognize cereal gluten epitopes presented by the disease-associated HLA molecules DQ2.5, DQ2.2, or DQ8. Employing celiac disease and complex gluten Ag digests as a model, we tested the feasibility of using DQ2.5 and DQ2.2 as an affinity matrix for identification of disease-relevant T cell epitopes. Known gluten T cell epitope peptides were enriched by DQ2.5, whereas a different set of peptides was enriched by DQ2.2. Of 86 DQ2.2-enriched peptides, four core sequences dominated. One of these core sequences is a previously known epitope and two others are novel epitopes. The study provides insight into the selection of gluten epitopes by DQ2.2. Furthermore, the approach presented is relevant for epitope identification in other MHC class II–associated disorders.

T Cells in Celiac Disease

“…Gluten-reactive T cells of DQ2.2 CD patients were found not to respond to DQ2.5 restricted T-cell epitopes (35). Rather T-cell clones of DQ2.2 patients recognized a unique set of gluten epitopes that commonly had a serine residue at position P3 (35, 36). This finding corresponded with studies of the peptide binding preference of DQ2.5 and DQ2.2; DQ2.2 uniquely utilizes serine as an anchor at position P3 (22, 37).…”

T-cell and B-cell immunity in celiac disease

“…These long gluten peptides can cross the epithelial layer and get in touch with the inductive part of the immune system. The importance of proteolytic resistance on the selection of T-cell responses has recently been substantiated by the observation that T-cell epitopes that are most frequently recognized remain more often intact after enzymatic digestion than T-cell epitopes that are infrequently recognized [26].…”

“…This led to the prediction that different gluten epitopes would be presented in HLA-DQ2.2-expressing patients. Indeed, the two HLA-DQ2 variants select for distinct sets of gluten peptides for presentation to CD4 þ T cells [7, 26,39]. This difference in epitope selection is governed by distinct binding specificity of the two HLA-DQ2 variants.…”

“…Peptides binding to HLA-DQ2.2 use P3 as a major anchor where there is preference for serine, threonine and asparatic acid. Interestingly, the three characterized DQ2.2 restricted gluten epitopes to date all have serine at P3 [7, 26,39]. The remarkable difference in risk between the two variants is likely explained by quantitative differences in the amount of gluten peptides that are able to form stable complexes with each of the two HLA-DQ molecules.…”

Small Bowel, Celiac Disease and Adaptive Immunity

“…Recent research has revealed that this indeed is the case [26]. Using HLA molecules as affinity matrix for isolation of DQ2.2-binding peptides of gluten digests, three DQ2.2 epitopes were identified [27], one of which was previously characterized as an immunodominant epitope [28]. Characteristically, these epitopes all have serine at position P3.…”