Quantitation of coeliac toxicity in wheat using genomics and proteomics

Several tests are currently marketed for measuring the amount of gluten in food products and to determine whether products are gluten-free. Of these tests, the Codex Alimentarius approved the R-Biopharm R5 ELISA as the gluten detection standard. This test is based on recognition by a monoclonal antibody (mAb) of five amino acidlong peptide sequences, which are abundantly present in the gliadin proteins of wheat gluten. Another mAb-based test recognises specific peptide sequences of six amino acids (G12 ELISA, Romer Labs). Both tests enable estimating the total amount of gluten (gluten = gliadin x 2) in a wheat product. As the number and composition of coeliac disease (CD) epitopes vary between gliadins and glutenins, among varieties, and between wheat, rye and barley, there is no direct relationship between the estimated gluten content and the presence of CD epitopes. Many research groups have raised epitope-specific T cell clones (TCCs) from patient biopsies that can be used for detection of specific CD-immunogenic gluten epitopes. Such CD epitopes are specific nine amino acid-long peptide sequences rich in prolamin (P) and glutamin (Q) residues. Recently, a list of internationally agreed CD epitopes has been published [1]. Unfortunately, T cell-based tests are mostly qualitative, indicating the presence or absence of a particular epitope, and they are unable to quantitate the overall CD-immunogencity of a given wheat variety. Proper quantitation of CD epitopes is relevant because the amount of non-CDimmunogenic gluten proteins can differ among wheat varieties and genomes (ploidy levels) [2], and the CD-immunogenicity of individual epitopes can be different according to the patient’s sensitivity profile [3,4]. Already a single amino acid substitution in a T cell epitope, especially from proline (P) to serine (S), may abolish T cell binding and thus eliminate the epitope’s CD-immunogenicity [5]. Therefore, gluten detection in the context of coeliac disease should be in line with the internationally agreed list of CD-relevant epitopes. To overcome the shortcomings of mAb-based and T cell-based tests, new approaches are now under development, especially based on genomic and proteomic analysis, aiming at the identification of the profile of CD-immunogenic epitopes of individual wheat species and varieties (for breeding and selection), and at quantitation of CD epitope-containing gluten proteins or fragments in foods (for food diagnostics)