Celiac disease is associated with a CD4+ T-cell response to epitopes of gliadin presented by HLA-DQ2 or -DQ8 class II MHC molecules. These epitopes are present in a 33-mer peptide of wheat alpha-gliadin, residues 56-88, which is resistant to digestion and forms a substrate for tissue transglutaminase (TG2), generating the glutamic acid residues essential for binding to HLA-DQ2. The immunogen corresponds to a deamidated form of a region that includes the T-cell epitopes, including the immunodominant PQPQLPY region and two PXPQP motifs associated with binding to IgA from patients with celiac disease. Complete homology exists between residues 63-73, 70-80 and 77-87 of wheat alpha gliadin. This antibody cross-reacts fully with the non-deamidated peptide KLQPFPQPQLPYPQPQ