Design, synthesis and evaluation of gluten peptide analogues as inhibitors of the HLA/DQ8-mediated celiac immune response

The immune response induced by gluten is the result of molecular mechanisms involving gliadin peptides, DQ2 or DQ8 glycoproteins, and the interaction with T lymphocyte receptors. DQ8-glia-α1 is an immunodominant peptide present in gliadin from wheat Triticum spelta that interacts with the DQ8 protein, as proven through transgenic mouse models. The research was carried out by performing a computational analysis aimed at finding antagonistic peptides of the DQ8-glia-α1 peptide, i.e. peptides obtained by varying its amino acids to maintain or even enhance the binding towards DQ8 and at the same time to prevent an immune response by a reduced interaction with the T lymphocyte receptors. Crystallographic structures of DQ8 and three different T-cell receptors were taken as experimental starting systems, the peptide-protein interaction was modelled by molecular dynamics simulations and molecular interaction field calculations, and the optimal mutations of the peptide sequence were identified by using multivariate analysis. The method provided a list of nine immunodominant peptide candidates, which were produced by chemical synthesis and validated by tests on transgenic mice. The results showed that immunization with the peptide (DQ8-glia-α1, designated M1) induced in vitro antigen-specific secretion of IFN-γ restricted to the M1 peptide alone. M1 also stimulated antigen-specific secretion of the regulatory cytokine IL-10. A peptide (i.e., M10) was identified as a potential therapeutic molecule for down-regulating the inflammatory condition triggered by the DQ8-glia-α1 immunodominant peptide in CD.