Antigen Presentation to Celiac Lesion-Derived T Cells of a 33-Mer Gliadin Peptide Naturally Formed by Gastrointestinal Digestion

Abstract

Celiac disease is an HLA-DQ2-associated disorder characterized by intestinal T cell responses to ingested wheat gluten proteins. A peptide fragment of 33 residues (α2-gliadin 56–88) produced by normal gastrointestinal proteolysis contains six partly overlapping copies of three T cell epitopes and is a remarkably potent T cell stimulator after deamidation by tissue transglutaminase (TG2). This 33-mer is rich in proline residues and adopts the type II polyproline helical conformation in solution. In this study we report that after deamidation, the 33-mer bound with higher affinity to DQ2 compared with other monovalent peptides harboring gliadin epitopes. We found that the TG2-treated 33-mer was presented equally effectively by live and glutaraldehyde-fixed, EBV-transformed B cells. The TG2-treated 33-mer was also effectively presented by glutaraldehyde-fixed dendritic cells, albeit live dendritic cells were the most effective APCs. A strikingly increased T cell stimulatory potency of the 33-mer compared with a 12-mer peptide was also seen with fixed APCs. The 33-mer showed binding maximum to DQ2 at pH 6.3, higher than maxima found for other high affinity DQ2 binders. The 33-mer is thus a potent T cell stimulator that does not require further processing within APC for T cell presentation and that binds to DQ2 with a pH profile that promotes extracellular binding.

Igs as Substrates for Transglutaminase 2: Implications for Autoantibody Production in Celiac Disease

“…However, no IL-2 could be detected in the absence of T cells (data not shown), verifying that IL-2 production in this assay is dependent on T cell activation. The results obtained by overnight incubation with 33merE peptide together with T cells show that all A20 cells are equally capable of presenting deamidated peptide following unspecific uptake or direct binding to surface HLA molecules (33). However, when the cells were pulsed with TG2 and 33merQ peptide or with TG2-33-mer complexes for 1 h prior to incubation with T cells, only cells with a TG2-specific BCR presented the deamidated peptide.…”

Inhibition of HLA-DQ2-Mediated Antigen Presentation by Analogues of a High Affinity 33-Residue Peptide from α2-Gliadin

“…Its extreme resistance to breakdown by luminal proteases and intestinal brush-border enzymes allows it to persist for a considerable duration in the upper small intestine, the primary affected region of the gastrointestinal tract in a Celiac Sprue patient (15). Not only does this peptide have a high affinity for HLA-DQ2, it is displayed on the surface of antigen presenting cells with unusual robustness (16,17). Not surprisingly, it is a potent proliferative trigger of glutenresponsive T cells from small intestinal biopsy samples of all DQ2 Celiac Sprue patients tested thus far.…”

“…A Pro-and Gln-rich 33-mer peptide from α2-gliadin, LQLQPFPQPELPYPQPELPYPQPELPYPQPQPF (transglutaminase-catalyzed Gln→Glu changes underlined), is a particularly interesting lead peptide for this purpose (15)(16)(17). Its extreme resistance to breakdown by luminal proteases and intestinal brush-border enzymes allows it to persist for a considerable duration in the upper small intestine, the primary affected region of the gastrointestinal tract in a Celiac Sprue patient (15).…”

Secretory IgA mediates retrotranscytosis of intact gliadin peptides via the transferrin receptor in celiac disease

“…The adaptive immune response is orchestrated by CD4 + T cells recognizing various deamidated gliadin peptides ( 3 ), including a 33-mer (peptide 56-88 [p56-88]) ( 4 ), bound to HLA-DQ2/8 molecules ( 5 ). p56-88 is a powerful immunodominant gliadin peptide extremely resistant to gastrointestinal digestion and has far higher T cell stimulatory potency than its 12-mer counterparts ( 6 ). The innate immune response in CD is triggered by a distinct set of gliadin peptides: one prototype innate peptide is p31-49, common to the N terminus of A-gliadins and shown to be toxic for CD patients both in vitro and in vivo ( 7 -9 ).…”