T-cell recognition of HLA-DQ2-bound gluten peptides can be influenced by an N-terminal proline at p-1

Expanding the MAPPs Assay to Accommodate MHC-II Pan Receptors for Improved Predictability of Potential T Cell Epitopes

A critical step in the immunogenicity cascade is attributed to human leukocyte antigen (HLA) II presentation triggering T cell immune responses. The liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based major histocompatibility complex (MHC) II-associated peptide proteomics (MAPPs) assay is implemented during preclinical risk assessments to identify biotherapeutic-derived T cell epitopes. Although studies indicate that HLA-DP and HLA-DQ alleles are linked to immunogenicity, most MAPPs studies are restricted to using HLA-DR as the dominant HLA II genotype due to the lack of well-characterized immunoprecipitating antibodies. Here, we address this issue by testing various commercially available clones of MHC-II pan (CR3/43, WR18, and Tü39), HLA-DP (B7/21), and HLA-DQ (SPV-L3 and 1a3) antibodies in the MAPPs assay, and characterizing identified peptides according to binding specificity. Our results reveal that HLA II receptor-precipitating reagents with similar reported specificities differ based on clonality and that MHC-II pan antibodies do not entirely exhibit pan-specific tendencies. Since no individual antibody clone is able to recover the complete HLA II peptide repertoire, we recommend a mixed strategy of clones L243, WR18, and SPV-L3 in a single immunoprecipitation step for more robust compound-specific peptide detection. Ultimately, our optimized MAPPs strategy improves the predictability and additional identification of T cell epitopes in immunogenicity risk assessments.

Development of a Sequence Searchable Database of Celiac Disease-Associated Peptides and Proteins for Risk Assessment of Novel Food Proteins

Celiac disease (CeD) is an autoimmune enteropathy induced by prolamin and glutelin proteins in wheat, barley, rye, and triticale recognized by genetically restricted major histocompatibility (MHC) receptors. Patients with CeD must avoid consuming these proteins. Regulators in Europe and the United States expect an evaluation of CeD risks from proteins in genetically modified (GM) crops or novel foods for wheat-related proteins. Our database includes evidence-based causative peptides and proteins and two amino acid sequence comparison tools for CeD risk assessment. Sequence entries are based on the review of published studies of specific gluten-reactive T cell activation or intestinal epithelial toxicity. The initial database in 2012 was updated in 2018 and 2022. The current database holds 1,041 causative peptides and 76 representative proteins. The FASTA sequence comparison of 76 representative CeD proteins provides an insurance for possible unreported epitopes. Validation was conducted using protein homologs from Pooideae and non-Pooideae monocots, dicots, and non-plant proteins. Criteria for minimum percent identity and maximum E-scores are guidelines. Exact matches to any of the 1,041 peptides suggest risks, while FASTA alignment to the 76 CeD proteins suggests possible risks. Matched proteins should be tested further by CeD-specific CD4/8+ T cell assays or in vivo challenges before their use in foods.

Ranking of immunodominant epitopes in celiac disease: Identification of reliable parameters for the safety assessment of innovative food proteins

A ranking of gluten T-cell epitopes triggering celiac disease (CD) for its potential application in the safety assessment of innovative food proteins is developed. This ranking takes into account clinical relevance and information derived from key steps involved in the CD pathogenic pathway: enzymatic digestion, epitope binding to HLA-DQ receptors of the antigen-presenting cells and activation of pro-inflammatory CD4 T-cells, which recognizes the HLA-DQ-epitope complex and initiates the inflammatory response. In silico chymotrypsin digestion was the most discriminatory tool for the ranking of gluten T-cell epitopes among all digestive enzymes studied, classifying 81% and 60% of epitopes binding HLA-DQ2.5 and HLA-DQ8 molecules, respectively, with a high risk. A positive relationship between the number of prolines and the risk of gluten T-cell epitopes was identified. HLA-binding data analysis revealed the additional role played by the flanking regions of the 9-mer epitopes whereas the integration of T-cell activation data into the ranking strategy was incomplete because it was difficult to combine results from different studies. The overall ranking proposed in decreasing order of immunological relevance was: α-gliadins > ω-gliadins > hordeins > γ-gliadins ∼ avenins ∼ secalins > glutenins. This novel approach can be considered as a first step to reshape the risk assessment strategy of innovative proteins and their potential to trigger CD.

Perennial Ryegrass Contains Gluten-Like Proteins That Could Contaminate Cereal Crops

Background: To ensure safe consumption of gluten-free products, there is a need to understand all sources of unintentional contamination with gluten in the food chain. In this study, ryegrass (Lolium perenne), a common weed infesting cereal crop, is analysed as a potential source of gluten-like peptide contamination.

Materials and Methods: Ten ryegrass cultivars were analysed using shotgun proteomics for the presence of proteins from the prolamin superfamily. A relative quantitative assay was developed to detect ryegrass gluten-like peptides in comparison with those found in 10 common wheat cultivars.

Results: A total of 19 protein accessions were found across 10 cultivars of ryegrass for the protein families of PF00234-Tryp_alpha_amyl, PF13016-Gliadin, and PF03157-Glutenin_HMW. Protein and peptide homology searches revealed that gliadin-like peptides were similar to avenin and gamma-gliadin peptides. A total of 20 peptides, characteristic of prolamin superfamily proteins, were selected for liquid chromatography mass spectrometry (LC-MS) with multiple reaction monitoring (MRM). Only two of the monitored peptides were detected with high abundance in wheat, and all others were detected in ryegrass. Glutenin and alpha-amylase/trypsin inhibitor peptides were reported for the first time in ryegrass and were noted to be conserved across the Poaceae family.

Conclusion: A suite of gluten-like peptides were identified using proteomics that showed consistent abundance across ryegrass cultivars but were not detected in wheat cultivars. These peptides will be useful for differentiating wheat gluten contamination from ryegrass gluten contamination.

Ancestral Wheat Types Release Fewer Celiac Disease Related T Cell Epitopes than Common Wheat upon Ex Vivo Human Gastrointestinal Digestion

Celiac disease (CeD) is an autoimmune enteropathy triggered by immunogenic gluten peptides released during the gastrointestinal digestion of wheat. Our aim was to identify T cell epitope-containing peptides after ex vivo digestion of ancestral (einkorn, spelt and emmer) and common (hexaploid) wheat (Fram, Bastian, Børsum and Mirakel) using human gastrointestinal juices. Wheat porridge was digested using a static ex vivo model. Peptides released after 240 min of digestion were analyzed by liquid chromatography coupled to high-resolution mass spectrometry (HPLC-ESI MS/MS). Ex vivo digestion released fewer T cell epitope-containing peptides from the ancestral wheat varieties (einkorn (n = 38), spelt (n = 45) and emmer (n = 68)) compared to the common wheat varieties (Fram (n = 72), Børsum (n = 99), Bastian (n = 155) and Mirakel (n = 144)). Neither the immunodominant 33mer and 25mer α-gliadin peptides, nor the 26mer γ-gliadin peptide, were found in any of the digested wheat types. In conclusion, human digestive juice was able to digest the 33mer and 25mer α-gliadin, and the 26mer γ-gliadin derived peptides, while their fragments still contained naive T cell reactive epitopes. Although ancestral wheat released fewer immunogenic peptides after human digestion ex vivo, they are still highly toxic to celiac patients. More general use of these ancient wheat variants may, nevertheless, reduce CeD incidence.

Template-based peptide modeling for celiac risk assessment of newly expressed proteins in GM crops

Newly expressed proteins in genetically modified (GM) crops are subject to celiac disease risk assessment according to EFSA guidelines. Amino acid identity matches between short peptides (9aa) and known celiac restricted epitopes are required to be further evaluated through peptide modeling; however, validated methods and criteria are not yet available. In this investigation, several structures of HLA-DQ2.5/peptide/TCR (T-cell receptor) complexes were analyzed and two template-based peptide molding software packages were evaluated using various peptides including ones not associated with celiac disease. Structural characterization indicates that residues at P(position)1, P2, P5, P8, and P9 in the 9aa restricted epitopes also contribute to the binding of celiac peptides to the HLA-DQ2.5 antigen in addition to the presence of the motif Q/EX₁PX₂ starting at P4 or P6. The recognition of the HLA-DQ2.5/peptide complex by TCR is through specific interactions between the residues in the restricted epitopes and some loop structures in the TCR. The template-based software package GalaxyPepDock seems to be suitable for the application of peptide modeling when an estimated accuracy value of >0.95 combined with >160 interaction similarity score are used as a threshold for biologically meaningful in silico binding. Nevertheless, caution should be exercised when applying peptide modeling to celiac disease risk assessment until methods are rigorously validated and further evaluated to demonstrate its value in the risk assessment of newly expressed proteins in GM crops.

Characterization and Relative Quantitation of Wheat, Rye, and Barley Gluten Protein Types by Liquid Chromatography-Tandem Mass Spectrometry

The consumption of wheat, rye, and barley may cause adverse reactions to wheat such as celiac disease, non-celiac gluten/wheat sensitivity, or wheat allergy. The storage proteins (gluten) are known as major triggers, but also other functional protein groups such as α-amylase/trypsin-inhibitors or enzymes are possibly harmful for people suffering of adverse reactions to wheat. Gluten is widely used as a collective term for the complex protein mixture of wheat, rye or barley and can be subdivided into the following gluten protein types (GPTs): α-gliadins, γ-gliadins, ω5-gliadins, ω1,2-gliadins, high- and low-molecular-weight glutenin subunits of wheat, ω-secalins, high-molecular-weight secalins, γ-75k-secalins and γ-40k-secalins of rye, and C-hordeins, γ-hordeins, B-hordeins, and D-hordeins of barley. GPTs isolated from the flours are useful as reference materials for clinical studies, diagnostics or in food analyses and to elucidate disease mechanisms. A combined strategy of protein separation according to solubility followed by preparative reversed-phase high-performance liquid chromatography was employed to purify the GPTs according to hydrophobicity. Due to the heterogeneity of gluten proteins and their partly polymeric nature, it is a challenge to obtain highly purified GPTs with only one protein group. Therefore, it is essential to characterize and identify the proteins and their proportions in each GPT. In this study, the complexity of gluten from wheat, rye, and barley was demonstrated by identification of the individual proteins employing an undirected proteomics strategy involving liquid chromatography-tandem mass spectrometry of tryptic and chymotryptic hydrolysates of the GPTs. Different protein groups were obtained and the relative composition of the GPTs was revealed. Multiple reaction monitoring liquid chromatography-tandem mass spectrometry was used for the relative quantitation of the most abundant gluten proteins. These analyses also allowed the identification of known wheat allergens and celiac disease-active peptides. Combined with functional assays, these findings may shed light on the mechanisms of gluten/wheat-related disorders and may be useful to characterize reference materials for analytical or diagnostic assays more precisely.

Update 2020: nomenclature and listing of celiac disease-relevant gluten epitopes recognized by CD4+ T cells

Celiac disease is caused by an abnormal intestinal T cell response to cereal gluten proteins. The disease has a strong human leukocyte antigen (HLA) association, and CD4⁺ T cells recognizing gluten epitopes presented by disease-associated HLA-DQ allotypes are considered to be drivers of the disease. This paper provides an update of the currently known HLA-DQ restricted gluten T cell epitopes with their names and sequences.

Assessment of the potential allergenicity of genetically-engineered food crops

An extensive safety assessment process exists for genetically-engineered (GE) crops. The assessment includes an evaluation of the introduced protein as well as the crop containing the protein with the goal of demonstrating the GE crop is "as-safe-as" non-GE crops in the food supply. One of the evaluations for GE crops is to assess the expressed protein for allergenic potential. Currently, no single factor is recognized as a predictor for protein allergenicity. Therefore, a weight-of-the-evidence approach, which accounts for a variety of factors and approaches for an overall assessment of allergenic potential, is conducted. This assessment includes an evaluation of the history of exposure and safety of the gene(s) source; protein structure (e.g. amino acid sequence identity to human allergens); stability of the protein to pepsin digestion in vitro; heat stability of the protein; glycosylation status; and when appropriate, specific IgE binding studies with sera from relevant clinically allergic subjects. Since GE crops were first commercialized over 20 years ago, there is no proof that the introduced novel protein(s) in any commercialized GE food crop has caused food allergy.

T Cells in Celiac Disease

Celiac disease is a human T cell-mediated autoimmune-like disorder caused by exposure to dietary gluten in genetically predisposed individuals. This review will discuss how CD4 T cell responses directed against an exogenous Ag can cause an autoreactive B cell response and participate in the licensing of intraepithelial lymphocytes to kill intestinal epithelial cells. Furthermore, this review will examine the mechanisms by which intraepithelial cytotoxic T cells mediate tissue destruction in celiac disease.

How Looking for Celiac‐Safe Wheat Can Influence Its Technological Properties

Because of the continuous increase in the prevalence of gluten‐related disorders, selection of wheat with a low content of immunogenic gluten epitopes could be an innovative alternative for prevention. In this review, the focus is on literature data concerning the deallergenization tools of wheat, which are mainly related to breeding approaches (classic and advanced) and processing operations (germination and fermentation). Until now, no safe wheat genotype has been identified, whereas decreasing wheat allergenicity is possible. On the other hand, the decrease of gluten or some of its epitopes can strongly affect technological properties. Thus, obtaining celiac‐safe gluten without affecting the technological properties of wheat could be considered as a new challenge that scientists will be facing. Celiac‐safe wheat‐based product development could be a great revolution in the market of foods for special medical purposes. The present paper is aiming to: (a) review the strategies and the approaches used, or that can be used, for developing low allergenic wheat: their utilities and limits were also discussed and (b) screen the impact of gluten reduction or removal on the quality of wheat end‐use products.

Identification of novel antibody-reactive detection sites for comprehensive gluten monitoring

Certain cereals like wheat, rye or barley contain gluten, a protein mixture that can trigger celiac disease (CD). To make gluten-free diets available for affected individuals the gluten content of foodstuff must be monitored. For this purpose, antibody-based assays exist which rely on the recognition of certain linear gluten sequence motifs. Yet, not all CD-active gluten constituents and fragments formed during food processing/fermentation may be covered by those tests. In this study, we therefore assayed the coverage of reportedly CD-active gluten components by currently available detection antibodies and determined the antibody-inducing capacity of wheat gluten constituents in order to provide novel diagnostic targets for comprehensive gluten quantitation. Immunizations of outbred mice with purified gliadins and glutenins were conducted and the linear target recognition profile of the sera was recorded using synthetic peptide arrays that covered the sequence space of gluten constituents present in those preparations. The resulting murine immunorecognition profile of gluten demonstrated that further linear binding sites beyond those recognized by the monoclonal antibodies α20, R5 and G12 exist and may be exploitable as diagnostic targets. We conclude that the safety of foodstuffs for CD patients can be further improved by complementing current tests with antibodies directed against additional CD-active gluten components. Currently unrepresented linear gluten detection sites in glutenins and α-gliadins suggest sequences QQQYPS, PQQSFP, QPGQGQQG and QQPPFS as novel targets for antibody generation.

A Grounded Guide to Gluten: How Modern Genotypes and Processing Impact Wheat Sensitivity

The role of wheat, and particularly of gluten protein, in our diet has recently been scrutinized. This article provides a summary of the main pathologies related to wheat in the human body, including celiac disease, wheat allergy, nonceliac wheat sensitivity, fructose malabsorption, and irritable bowel syndrome. Differences in reactivity are discussed for ancient, heritage, and modern wheats. Due to large variability among species and genotypes, it might be feasible to select wheat varieties with lower amounts and fewer types of reactive prolamins and fructans. Einkorn is promising for producing fewer immunotoxic effects in a number of celiac research studies. Additionally, the impact of wheat processing methods on wheat sensitivity is reviewed. Research indicates that germination and fermentation technologies can effectively alter certain immunoreactive components. For individuals with wheat sensitivity, less-reactive wheat products can slow down disease development and improve quality of life. While research has not proven causation in the increase in wheat sensitivity over the last decades, modern wheat processing may have increased exposure to immunoreactive compounds. More research is necessary to understand the influence of modern wheat cultivars on epidemiological change.

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

Background

Celiac 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.

Results

A 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.

Conclusions

Evaluating 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).

Nomenclature and listing of celiac disease relevant gluten T-cell epitopes restricted by HLA-DQ molecules

Celiac disease is caused by an abnormal intestinal T-cell response to gluten proteins of wheat, barley and rye. Over the last few years, a number of gluten T-cell epitopes restricted by celiac disease associated HLA-DQ molecules have been characterized. In this work, we give an overview of these epitopes and suggest a comprehensive, new nomenclature.

Are ancient durum wheats less toxic to celiac patients? A study of α-gliadin from Graziella Ra and Kamut

In the present paper, the controversial hypothesis suggesting ancient grains might show lower immunogenic properties and therefore the possibility to introduce them in the diet of wheat-sensitive people, including celiac patients, was investigated. The immunogenic potential of the ancient durum wheats Graziella Ra and Kamut was studied by comparison to the durum accessions Cappelli, Flaminio, Grazia and Svevo. Experiments were carried out with two monoclonal antibodies (mAbs) raised against α-gliadin peptides p31–49 and p56–75 (the latter containing the overlapping DQ2-Glia-α1 and DQ2-Glia-α2 epitopes), toxic for celiac patients. For all accessions, a few α-gliadin alleles were also cloned, sequenced and translated into aminoacid sequences. Several aminoacid substitutions or deletions were detected in p31–49, DQ2-Glia-α1 and DQ2-Glia-α2 epitopes, nevertheless, ELISA constantly showed antibody-antigen positive reactions which led us to suggest that mAbs binding was not apparently affected by polymorphisms. Moreover, a few substitutions were also observed in DQ2-Glia-α3 and DQ8-Glia-α1 epitopes. Although some DQ2-Glia-α1 and DQ2-Glia-α2 variants evidenced herein were previously reported to have a diminished or abolished T cell stimulatory capacity, present results cannot confirm that ancient durum wheats would be less CD-toxic. In conclusion, we strongly advice celiac patients from consuming ancient wheats including Graziella Ra or Kamut.

Immunogenicity characterization of two ancient wheat α-gliadin peptides related to coeliac disease

The immunogenic potential of α-gliadin protein from two ancient wheats was studied with reference to coeliac disease. To this aim we investigated Graziella Ra® and Kamut® (the latter is considered an ancient relative of modern durum wheat) in comparison to four durum wheat accessions (Senatore Cappelli, Flaminio, Grazia and Svevo). ELISA and Western Blot analyses - carried out by two monoclonal antibodies raised against the α-gliadin peptides p31-49 (LGQQQPFPQQPYPQPQPF) and p56-75 (LQLQPFPQPQLPYPQPQLPY) containing a core region (underlined) reported to be toxic for coeliac patients - always showed an antibody-antigen positive reaction. For all accessions, an α-gliadin gene has also been cloned and sequenced. Deduced amino acid sequences constantly showed the toxic motifs. In conclusion, we strongly recommend that coeliac patients should avoid consuming Graziella Ra® or Kamut®. In fact their α-gliadin not only is as toxic as one of the other wheat accessions, but also occurs in greater amount, which is in line with the higher level of proteins in ancient wheats when compared to modern varieties.

Functionality of lactic acid bacteria peptidase activities in the hydrolysis of gliadin-like fragments

AIMS

To evaluate the role of the peptidase activities from sourdough lactic acid bacteria (LAB) in the degradation of alpha-gliadin fragments.

METHODS AND RESULTS

Different proline-containing substrates were hydrolysed by LAB indicating pro-specific peptidase activities. Lactobacillus plantarum CRL 775 and Pediococcus pentosaceus CRL 792 displayed the highest tri- and di-peptidase activities, respectively. Lactobacillus plantarum strains hydrolysed more than 60%alpha-gliadin fragments corresponding to the 31-43 and 62-75 amino acids in the protein after 2 h. None of the LAB strains alone could hydrolyse 57-89 alpha-gliadin peptide; however, the combination of L. plantarum CRL 775 and P. pentosaceus CRL 792 led to hydrolysis (57%) of this peptide in 8 h.

CONCLUSIONS

The capacity of LAB strains to degrade alpha-gliadin fragments was not correlated to individual peptidase activities. Several strains separately degraded the 31-43 and 62-75 alpha-gliadin fragments, while the 57-89 peptide degradation was associated with the combination of peptidase profiles from pooled LAB strains. This is the first report on the peptide hydrolase system of sourdough pediococci and its ability to reduce alpha-gliadin fragments.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study contributes to a better knowledge of sourdough LAB proteolytic system and its role in the degradation of proline-rich alpha-gliadin peptides involved in celiac disease.

Peptide length significantly influences in vitro affinity for MHC class II molecules

Background

Class II Major Histocompatibility Complex (MHC) molecules have an open-ended binding groove which can accommodate peptides of varying lengths. Several studies have demonstrated that peptide flanking residues (PFRs) which lie outside the core binding groove can influence peptide binding and T cell recognition. By using data from the AntiJen database we were able to characterise systematically the influence of PFRs on peptide affinity for MHC class II molecules.

Results

By analysing 1279 peptide elongation events covering 19 distinct HLA alleles it was observed that, in general, peptide elongation resulted in increased MHC class II molecule affinity. It was also possible to determine an optimal peptide length for MHC class II affinity of approximately 18–20 amino acids; elongation of peptides beyond this length resulted in a null or negative effect on affinity.

Conclusion

The observed relationship between peptide length and MHC class II affinity has significant implications for the design of vaccines and the study of the epitopic basis of immunological disease.

Functional inhibition related to structure of a highly potent insulin-specific CD8 T cell clone using altered peptide ligands

Insulin-reactive CD8 T cells are amongst the earliest islet-infiltrating CD8 T cells in NOD mice. Cloned insulin B15–23-reactive cells (designated G9C8), restricted by H-2K^d, are highly diabetogenic. We used altered peptide ligands (APL) substituted at TCR contact sites, positions (p)6 and 8, to investigate G9C8 T cell function and correlated this with structure. Cytotoxicity and IFN-γ production assays revealed that p6G and p8R could not be replaced by any naturally occurring amino acid without abrogating recognition and functional response by the G9C8 clone. When tested for antagonist activity with APL differing from the native peptide at either of these positions, the peptide variants, G6H and R8L showed the capacity to reduce the agonist response to the native peptide. The antagonist activity in cytotoxicity and IFN-γ production assays can be correlated with conformational changes induced by different structures of the MHC-peptide complexes, shown by molecular modeling. We conclude that p6 and p8 of the insulin B15–23 peptide are very important for TCR stimulation of this clone and no substitutions are tolerated at these positions in the peptide. This is important in considering the therapeutic use of peptides as APL that encompass both CD4 and CD8 epitopes of insulin.

Analysis of the binding of gluten T-cell epitopes to various human leukocyte antigen class II molecules

Celiac disease is a prevalent disorder of the small intestine that is caused by an inflammatory reaction to dietary gluten in genetically susceptible individuals. More than 90% of patients express the HLA-DQ2 molecule, whereas DQ8 is carried by most of the remaining patients. DQ2- and DQ8-mediated presentation of gluten peptides to CD4+ T cells is a key event in the pathogenesis of the disease. The association of celiac disease with these human leukocyte antigen (HLA) molecules is explained by a preferential binding of gluten peptides to these HLA molecules, although the actual data on this in the literature are scarce. The objective of this study was to test this hypothesis. A panel of peptides representing DQ2-restricted gluten T-cell epitopes was tested for binding to various HLA class II molecules using various experimental approaches. The results demonstrate that the gluten T-cell epitopes mainly bind to the DQ2 molecule.

Highly efficient gluten degradation by lactobacilli and fungal proteases during food processing: new perspectives for celiac disease

Presently, the only effective treatment for celiac disease is a life-long gluten-free diet. In this work, we used a new mixture of selected sourdough lactobacilli and fungal proteases to eliminate the toxicity of wheat flour during long-time fermentation. Immunological (R5 antibody-based sandwich and competitive enzyme-linked immunosorbent assay [ELISA] and R5 antibody-based Western blot), two-dimensional electrophoresis, and mass spectrometry (matrix-assisted laser desorption ionization-time of flight, strong-cation-exchange-liquid chromatography/capillary liquid chromatography-electrospray ionization-quadrupole-time of flight [SCX-LC/CapLC-ESI-Q-TOF], and high-pressure liquid chromatography-electrospray ionization-ion trap mass spectrometry) analyses were used to determine the gluten concentration. Assays based on the proliferation of peripheral blood mononuclear cells (PBMCs) and gamma interferon production by PBMCs and intestinal T-cell lines (iTCLs) from 12 celiac disease patients were used to determine the protein toxicity of the pepsin-trypsin digests from fermented wheat dough (sourdough). As determined by R5-based sandwich and competitive ELISAs, the residual concentration of gluten in sourdough was 12 ppm. Albumins, globulins, and gliadins were completely hydrolyzed, while ca. 20% of glutenins persisted. Low-molecular-weight epitopes were not detectable by SCX-LC/CapLC-ESI-Q-TOF mass spectrometry and R5-based Western blot analyses. The kinetics of the hydrolysis of the 33-mer by lactobacilli were highly efficient. All proteins extracted from sourdough activated PBMCs and induced gamma interferon production at levels comparable to the negative control. None of the iTCLs demonstrated immunoreactivity towards pepsin-trypsin digests. Bread making was standardized to show the suitability of the detoxified wheat flour. Food processing by selected sourdough lactobacilli and fungal proteases may be considered an efficient approach to eliminate gluten toxicity.

Celiac disease: pathogenesis of a model immunogenetic disease

Celiac disease is characterized by small-intestinal mucosal injury and nutrient malabsorption in genetically susceptible individuals in response to the dietary ingestion of wheat gluten and similar proteins in barley and rye. Disease pathogenesis involves interactions among environmental, genetic, and immunological factors. Although celiac disease is predicted by screening studies to affect approximately 1% of the population of the United States and is seen both in children and in adults, 10%-15% or fewer of these individuals have been diagnosed and treated. This article focuses on the role of adaptive and innate immune mechanisms in the pathogenesis of celiac disease and how current concepts of immunopathogenesis might provide alternative approaches for treating celiac disease.

Advances in celiac disease

PURPOSE OF REVIEW

Increasing numbers of atypical or asymptomatic cases of celiac disease are being diagnosed. This review aims to summarize recent critical research in celiac disease.

RECENT FINDINGS

Alternative candidate genes outside of the human leukocyte antigen complex continue to be identified, whilst innate and adaptive immune responses to key gliadin epitopes are now both recognized to be important in celiac disease pathogenesis.

SUMMARY

Serological tests and small bowel biopsy remain the cornerstones of diagnosis. Treatment options other than the restrictive gluten-free diet remain limited.

Deamidated Gliadin Peptides as Targets for Celiac Disease‐Specific Antibodies

Celiac disease (CD) is an (auto)immunologically mediated intestinal intolerance against proteins from wheat (gluten) and related cereal proteins. Tissue transglutaminase (tTG) has been identified as the autoantigen in CD. Although ultimate diagnosis is based on histological analysis of small intestinal mucosa obtained via tissue biopsy, assessment of autoantibodies can provide substantial help in the evaluation of CD. Gliadin antibodies are directed against the native disease-provoking cereal proteins. Despite their initial usefulness, these antibodies have lost diagnostic importance due to their poor specificity and sensitivity as CD markers. Recently, it was found, however, that gliadin antibodies from sera of patients with active CD preferentially recognized deamidated gliadin peptides. The use of deamidated gliadin peptides in immunoassays has significantly improved the usefulness of gliadin antibodies in diagnosis of CD to that observed with autoantibody assay methods (endomysium antibodies, antibodies against tTG). The antibody epitopes (B-cell epitopes) reflect substrate specificity of tTG and resemble peptide sequences known to be strongly T-cell stimulatory (T-cell epitopes) in CD. The assay applying deamidated gliadin peptides measures a new species of antibodies, which is different from conventional gliadin antibodies as well as from autoantibodies and will likely provide new information on pathophysiological mechanisms of CD.

Sourdough lactobacilli and celiac disease

Celiac disease (CD) is one of the most common food intolerance. The only effective treatment for CD is a strict adherence to a gluten-free diet throughout the patient's lifetime. Gluten-free products are not widely available and are usually more expensive than their gluten-containing counterparts. There is, therefore, an urgent need to develop safe and effective therapeutic alternatives, to develop high-quality gluten-free products and to investigate the potential of the bread making biotechnology following ancient protocols which include long-time fermentation by selected sourdough lactic acid bacteria. This review describes the most relevant results related to biotechnologies that use selected sourdough lactic acid bacteria and probiotics as starters for sourdough fermentation to investigate their potential to decrease the risk of gluten contamination in gluten-free products. As shown by studies in vitro on celiac intestinal tissue and in vivo on CD patients, the bacterial proteolytic activity is rather promising not only as currently demonstrated for eliminating traces of contaminant gluten but probably also in perspective for the manufacture of tolerated baked goods.

Celiac disease--sandwiched between innate and adaptive immunity

Celiac disease (CD) patients are intolerant to gluten, proteins in wheat, and related cereals. Virtually all patients are human leukocyte antigen (HLA)-DQ2 or HLA-DQ8 positive and several studies have demonstrated that CD4 T cells specific for (modified) gluten peptides bound to these HLA-DQ molecules are found in patients but not in control subjects. These T cell responses are therefore thought to be responsible for disease development. Many immunogenic gluten peptides which may relate to the disease-inducing properties of gluten have now been identified. In addition, gluten can stimulate IL-15 production that ultimately leads to NKG2D-mediated epithelial cell killing. However, CD develops in only a minority of HLA-DQ2 and HLA-DQ8 individuals. This may be attributed to the default setting of the intestinal immune system: induction and maintenance of tolerance to dietary components and commensal flora. Although at present it is unknown why tolerance in CD is not established or broken, both environmental and genetic factors have been implicated. There is strong evidence for the existence of genes or gene variants on chromosomes 5, 6, and 19 that predispose to CD. In addition, type I interferons have been implicated in development of several autoimmune disorders, including CD. Thus, viral infection and/or tissue damage in the intestine may cause inflammation and induce protective Th1-mediated immunity leading to loss of tolerance for gluten. Once tolerance is broken, a broad gluten-reactive T cell repertoire may develop through determinant spreading. This may be a critical step toward full-blown disease.

Advances in celiac disease

PURPOSE OF REVIEW

This article primarily aims to review critically research in all aspects of celiac disease over the last year. As always, there has been a wealth of relevant papers.

RECENT FINDINGS

The role of genetics in disease susceptibility is slowly becoming more clearly defined and a more detailed understanding of the disease processes at the molecular level is paving the way towards the development of specific targeted therapies.

SUMMARY

Despite recent advances in our understanding of celiac disease, the gluten-free diet remains the only current viable therapy and even with advances in serological tests and markers, the duodenal biopsy remains the gold standard for diagnosis and monitoring of the response to therapy.

Celiac disease: caught between a rock and a hard place

Celiac disease (CD) is an intestinal disorder caused by an intolerance to gluten, proteins in wheat. CD is an HLA-associated disease: virtually all patients express HLA-DQ2 or HLA-DQ8. Recent work has shown that these disease-predisposing HLA-DQ molecules bind enzymatically modified gluten peptides and these HLA-DQ peptide complexes trigger inflammatory T-cell responses in the small intestine that lead to disease. In addition, gluten induces innate immune responses that contribute to the tissue damage that is characteristic for CD. Thus, CD patients are caught between a rock and a hard place: the disease is caused by a combination of adaptive and innate immune responses that both are triggered by gluten. These findings explain the disease-inducing properties of gluten and provide valuable clues for the development of alternative treatment modalities for patients. They also may be of relevance for our understanding of other multifactorial disorders including IBD and HLA-associated autoimmune diseases.