Celiac disease T-cell epitopes from gamma-gliadins: immunoreactivity depends on the genome of origin, transcript frequency, and flanking protein variation

Abstract

BackgroundCeliac disease (CD) is caused by an uncontrolled immune response to gluten, a heterogeneous mixture of wheat storage proteins. The CD-toxicity of these proteins and their derived peptides is depending on the presence of specific T-cell epitopes (9-mer peptides; CD epitopes) that mediate the stimulation of HLA-DQ2/8 restricted T-cells. Next to the thoroughly characterized major T-cell epitopes derived from the α-gliadin fraction of gluten, γ-gliadin peptides are also known to stimulate T-cells of celiac disease patients. To pinpoint CD-toxic γ-gliadins in hexaploid bread wheat, we examined the variation of T-cell epitopes involved in CD in γ-gliadin transcripts of developing bread wheat grains.ResultsA detailed analysis of the genetic variation present in γ-gliadin transcripts of bread wheat (T. aestivum, allo-hexaploid, carrying the A, B and D genome), together with genomic γ-gliadin sequences from ancestrally related diploid wheat species, enabled the assignment of sequence variants to one of the three genomic γ-gliadin loci, Gli-A1, Gli-B1 or Gli-D1. Almost half of the γ-gliadin transcripts of bread wheat (49%) was assigned to locus Gli-D1. Transcripts from each locus differed in CD epitope content and composition. The Gli-D1 transcripts contained the highest frequency of canonical CD epitope cores (on average 10.1 per transcript) followed by the Gli-A1 transcripts (8.6) and the Gli-B1 transcripts (5.4). The natural variants of the major CD epitope from γ-gliadins, DQ2-γ-I, showed variation in their capacity to induce in vitro proliferation of a DQ2-γ-I specific and HLA-DQ2 restricted T-cell clone.ConclusionsEvaluating the CD epitopes derived from γ-gliadins in their natural context of flanking protein variation, genome specificity and transcript frequency is a significant step towards accurate quantification of the CD toxicity of bread wheat. This approach can be used to predict relative levels of CD toxicity of individual wheat cultivars directly from their transcripts (cDNAs).

Expansion of the gamma-gliadin gene family in Aegilops and Triticum

“…Figure 1 presents a schematic overview of the structure of gamma-gliadins, after [9] and [27]. The sequences of the predicted intact proteins varied in length considerably due to variation in the length of the repetitive domain (II) and the length of the glutamin-rich domain (IV).…”

Targeting of prolamins by RNAi in bread wheat: effectiveness of seven silencing‐fragment combinations for obtaining lines devoid of coeliac disease epitopes from highly immunogenic gliadins

“…The DQ2.5-glia-a3 epitope, downstream of the 33-mer fragment, was the least abundant probably due to its digestibility with Trypsin. Because c-gliadins contain 5-10 epitopes per sequence (Salentijn et al, 2012), a high number of these epitopes was identified in almost all lines analysed, most prevalent being the epitopes DQ2.5-glia-c4c/DQ8-glia-c1a and DQ2.5-glia-c5. In general, a lower number of CD epitopes was observed in transgenic lines generated using two plasmids, with the exception of Plasmid Combination 6.…”

Genome-wide analysis of complex wheat gliadins, the dominant carriers of celiac disease epitopes

“…Bioinformatic analysis of protein sequences has frequently been employed to detect the presence of CD epitopes in different gliadins. The results show that different types of gliadins differ substantially in the CD epitopes contained, with the α-gliadins specified by Gli-B2 containing very few CD epitopes51024252627. However, this type of analysis has not been reported for δ-gliadins, which are recognized only recently2829, nor has it been conducted for all of the gliadins accumulated in a single bread wheat variety.…”