The Intestinal T Cell Response to α-Gliadin in Adult Celiac Disease Is Focused on a Single Deamidated Glutamine Targeted by Tissue Transglutaminase

Abstract

The great majority of patients that are intolerant of wheat gluten protein due to celiac disease (CD) are human histocompatibility leukocyte antigen (HLA)-DQ2+, and the remaining few normally express HLA-DQ8. These two class II molecules are chiefly responsible for the presentation of gluten peptides to the gluten-specific T cells that are found only in the gut of CD patients but not of controls. Interestingly, tissue transglutaminase (tTG)-mediated deamidation of gliadin plays an important role in recognition of this food antigen by intestinal T cells. Here we have used recombinant antigens to demonstrate that the intestinal T cell response to α-gliadin in adult CD is focused on two immunodominant, DQ2-restricted peptides that overlap by a seven-residue fragment of gliadin. We show that tTG converts a glutamine residue within this fragment into glutamic acid and that this process is critical for T cell recognition. Gluten-specific T cell lines from 16 different adult patients all responded to one or both of these deamidated peptides, indicating that these epitopes are highly relevant to disease pathology. Binding studies showed that the deamidated peptides displayed an increased affinity for DQ2, a molecule known to preferentially bind peptides containing negatively charged residues. Interestingly, the modified glutamine is accommodated in different pockets of DQ2 for the different epitopes. These results suggest modifications of anchor residues that lead to an improved affinity for major histocompatibility complex (MHC), and altered conformation of the peptide–MHC complex may be a critical factor leading to T cell responses to gliadin and the oral intolerance of gluten found in CD.

Diagnostic efficacy of the ELISA test for the detection of deamidated anti‐gliadin peptide antibodies in the diagnosis and monitoring of celiac disease

“…The persistence of demand for AGA tests has led some manufacturers to develop new AGA ELISA tests that use deamidated gliadin peptides as antigen. Some studies have demonstrated that the immune response to gliadin in CD patients is directed against limited portions of the protein structure, and that the epitopic core of these sequences is constituted by the tripeptide PEQ (28,29). The aim of our study was to compare the diagnostic performance of a new ELISA test using synthetic gliadin peptides and an ELISA test using extracted gliadin for assaying AGA IgA and IgG in a group of celiac patients and controls with different clinical and serological characteristics.…”

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

“…Serine at P3 was recently shown to be critical for stable binding of the DQ2.2-glut-L1 epitope (7). To investigate whether the serine residue in the DQ2.2-glia-a1 and DQ2.2-glia-a2 peptides was also located at the P3 position, we determined their binding registers by analyzing lysine-substituted analogs (15) (Fig. 8).…”

“…Typically the gluten peptides that are recognized by T cells of CD patients are posttranslationally modified (13,14). The enzyme transglutaminase 2 (TG2) converts certain residues in gluten peptides from glutamine to glutamate and this deamidation process improves the ability of DQ2.5, DQ2.2, and DQ8 to bind and present the peptides to T cells (15)(16)(17).…”

Celiac Disease: a model autoimmune disease with gene therapy applications

“…36 It was demonstrated that this 'digestionresistant' section of a-gliadin has a high affinity for tTG deamidation and the up to 6 T-cell epitopes, including the ones previously described by Sollid's group. 37 Other players in the pathogenesis of CD If the central role of the adaptive (T cell) recognition of gluten/gliadin (as a paradigm a-gliadin) is without any question at the basis of the pathogenesis of CD, there are other important players that should be considered in the equation. Indeed, if the local activation of lamina propria CD4+ HLA class II (DQ2 or DQ8) restricted T cells is well documented and now clearly understood in its 'molecular basis', other immunological diseasespecific changes are observed in the small intestine of celiac patients.…”