T cells from celiac disease lesions recognize gliadin epitopes deamidated in situ by endogenous tissue transglutaminase

Celiac disease is an HLA-DQ2-associated disorder characterized by intestina l T cell responses to ingested wheat gliadins. Initial studies used gliadin that had been subjected to non-enzymatic deamidation during pepsin/trypsin digestion to enrich for the gliadin-specific T cells in small intestinal c eliac biopsies. These T cells recognized synthetic gliadin peptides only af ter their deamidation in vitro by purified tissue transglutaminase (tTG). H owever, as these studies used a deamidated antigen for re-stimulation prior to testing for antigen specificity, this raised the possibility that T cel ls specific for native epitopes had not been expanded in vitro and had thus been overlooked. To address this possibility and to look for more direct e vidence that endogenous tTG mediates deamidation of gluten in the celiac le sions, we have here used a minimally deamidated chymotrypsin-digest of glia din to challenge biopsies and then investigated the specificity of the T ce ll lines derived from them. Interestingly, these T cell lines only barely r esponded to the chymotrypsin-digested gliadins, but efficiently recognized the in vitro tTG-treated variants of the same gliadins. Moreover, the addit ion of a tTG-inhibitor during the gliadin challenge often resulted in T cel l lines with abolished or reduced responses to deamidated gliadin. These da ta demonstrate that DQ2- restricted T cells within adult celiac lesions pre dominantly recognize deamidated gliadin epitopes that are formed in situ by endogenous tTG.