TPI1 and celiac disease: Other examples of experimentally determined structures with tilted TCR engagement of Class II MHCs include two TCRs that interact with insulin B and IAg7 [38], two human TCRs that interact with a mutant form of human triosephosphate isomerase peptide presented by HLA-DR1 [49,50], and a human TCR (S2) that interacts with the HLA-DQ2-gliadin antigen in celiac disease [51].