Transglutaminase 2 at the Interface of Gene Regulation and Antigen Processing in HLA-Restricted Immunity of Celiac Disease

Celiac disease (CD) is an immune-mediated enteropathy triggered by dietary gluten in genetically predisposed individuals. Although HLA-DQ2 and HLA-DQ8 are the primary genetic determinants of susceptibility, they are not sufficient to explain disease onset and progression. A key molecular event in CD pathogenesis is the post-translational modification of gluten peptides by transglutaminase 2 (TG2), which enhances their binding to HLA-DQ molecules and promotes CD4+ T cell activation. TG2 also acts as the principal autoantigen, driving the production of anti-TG2 autoantibodies through linked recognition mechanisms. Beyond its enzymatic activity, TG2 is tightly regulated by gene regulatory mechanisms, including cytokine-driven transcription, epigenetic modulation, and stress-responsive signaling pathways. These processes determine TG2 expression and activity in the intestinal mucosa, thereby influencing the efficiency of gluten peptide modification and antigen presentation. Here, we propose that TG2 operates at the interface between gene regulation and antigen processing, linking transcriptional control of TGM2 to HLA-restricted immune activation. In this framework, disease susceptibility arises from the coordinated interaction between HLA-dependent peptide presentation, TG2-mediated modification of gluten epitopes, and regulation of TG2 expression within the intestinal mucosa. This integrated model provides a mechanistic basis for disease heterogeneity and identifies TG2 as a central regulatory node and potential therapeutic target in CD.