Celiac disease: antibody recognition against native and selectively deamidated gliadin peptides.

BACKGROUND: Selective deamidation of glutamine residues by tissue transglutaminase (tTG) turns gliadin peptides into stronger activators of T cells from celiac disease (CD) patients. We examined the possibility that these modified peptides could be more specific epitopes for circulating antibodies than are native peptides. METHODS: Two native synthetic peptides and their respective modified sequences were used as antigens for ELISA assays: peptide-1, with residues 56-75 of alpha-type gliadin; and peptide-2, with residues 134-153 of gamma-type gliadin. We examined 40 CD patients [31 not being treated with a gluten-free diet (GFD) and 9 being treated with a GFD] and 30 non-CD patients. RESULTS: An enhanced response against deamidated peptides was observed in 4 (IgA) and 22 (IgG) of 31 untreated CD patients for peptide-1 and in 25 (IgA) and 29 (IgG) patients for peptide-2. Higher anti-gliadin antibody and anti-tTG IgA concentrations correlated with increased IgA reactivity to modified peptides. Among the nine treated CD patients, eight also displayed an improved IgG signal for the deamidated sequence. Deamidation of peptides did not increase the reactivity of non-CD sera. CONCLUSIONS: Selective deamidation specifically increases circulating antibody recognition of gliadin peptides in CD patients. This suggests that deamidated gliadin peptides are more specific CD B-cell epitopes than native peptides; this finding may be relevant for designing improved diagnostic tests.

[Serological diagnosis of celiac disease: anti-gliadin peptide antibodies and tissue anti-transglutaminase]. / Diagnóstico serológico de la enfermedad celíaca: anticuerpos anti-péptidos de síntesis de gliadina y anti-transglutaminasa de tejido.

Serological markers currently used for the diagnosis of celiac disease are anti-gliadin (AG) and anti-endomysium (AE) antibodies. Recently tissue transglutaminase (tTG) was identified as the specific autoantigen for endomysial antibodies. The aim of this work was to determine sensitivity and specificity of ELISA tests developed by using defined molecular structures as capture antigen for AG and AE antibodies. Three synthetic peptides, from the amino terminal region of alpha gliadin, were used as immobilized antigens for AG, and the transglutaminase from guinea pig liver for AE. A total of 80 sera from celiac patients, non celiac disease controls and healthy controls were examined. Age range was 7 months to 14 years. A sensitivity of 97% and a specificity of 86% was obtained for IgG determined by using as antigen one of the three synthetic peptides (corresponding to residues 31-55 of alpha gliadin). Therefore, this peptide appears as a highly sensitive antigen and more specific than gliadin. The best result, showing 100% of sensitivity and specificity, was obtained for IgA anti-tTG, thus pointing out the relevance of these antibodies as serological markers for celiac disease.