Identification of immunodominant epitopes of alpha-gliadin in HLA-DQ8 transgenic mice following oral immunization

• Published in: Journal of Immunology Vol. 175; no. 12; pp. 8087 - 8095
• Main Authors: Senger, Stefania, Maurano, Francesco, Mazzeo, Maria F, Gaita, Marcello, Fierro, Olga, David, Chella S, Troncone, Riccardo, Auricchio, Salvatore, Siciliano, Rosa A, Rossi, Mauro
• Format: Journal Article
• Language: English
• Published: United States 15-12-2005
• Subjects: Amino Acid Sequence; Animals; CD4-Positive T-Lymphocytes - immunology; CD4-Positive T-Lymphocytes - metabolism; Celiac Disease - immunology; Cytokines - analysis; Cytokines - metabolism; Disease Models, Animal; Escherichia coli; Gliadin - immunology; HLA-DQ Antigens - genetics; Hordeum vulgare; Humans; Immunization; Immunodominant Epitopes - chemistry; Mice; Mice, Transgenic; Peptide Fragments - administration & dosage; Peptide Fragments - immunology; Peptide Mapping; Triticum aestivum; Wheat Hypersensitivity - immunology
• ISSN: 0022-1767; 1550-6606; 1365-2567
• DOI: 10.4049/jimmunol.175.12.8087

Celiac disease, triggered by wheat gliadin and related prolamins from barley and rye, is characterized by a strong association with HLA-DQ2 and HLA-DQ8 genes. Gliadin is a mixture of many proteins that makes difficult the identification of major immunodominant epitopes. To address this issue, we expressed in Escherichia coli a recombinant alpha-gliadin (r-alpha-gliadin) showing the most conserved sequence among the fraction of alpha-gliadins. HLA-DQ8 mice, on a gluten-free diet, were intragastrically immunized with a chymotryptic digest of r-alpha-gliadin along with cholera toxin as adjuvant. Spleen and mesenteric lymph node T cell responses were analyzed for in vitro proliferative assay using a panel of synthetic peptides encompassing the entire sequence of r-alpha-gliadin. Two immunodominant epitopes corresponding to peptide p13 (aa 120-139) and p23 (aa 220-239) were identified. The response was restricted to DQ and mediated by CD4+ T cells. In vitro tissue transglutaminase deamidation of both peptides did not increase the response; furthermore, tissue transglutaminase catalyzed extensive deamidation in vitro along the entire r-alpha-gliadin molecule, but failed to elicit new immunogenic determinants. Surprisingly, the analysis of the cytokine profile showed that both deamidated and native peptides induced preferentially IFN-gamma secretion, despite the use of cholera toxin, a mucosal adjuvant that normally induces a Th2 response to bystander Ags. Taken together, these data suggest that, in this model of gluten hypersensitivity, deamidation is not a prerequisite for the initiation of gluten responses.