Anti-alpha-gliadin antibodies (AGA) in the serum of coeliac children and controls recognize an identical collection of linear epitopes of alpha-gliadin

Abstract

Anti-gliadin antibodies can be found in the serum of patients with overt and subclinical coeliac disease, but also in that of some controls. The aim of the present study was to identify the linear epitopes of the alpha-gliadin molecule to which the humoral response is directed. Therefore, the IgG and IgA antibody reactivity against an overlapping set of synthetic peptides covering the entire sequence of alpha-gliadin was measured in the sera from patients with coeliac disease, from controls with elevated titres of anti-gliadin antibodies and from healthy children using an ELISA technique. The antibodies mainly recognize peptides derived from the N-terminal region of alpha-gliadin, containing the motif QPFXXQXPY. Reactivity was also detected against two other synthetic peptides, which do not contain this motif and represent a sequence encoded further to the C-terminal region of alpha-gliadin. Anti-gliadin antibodies in sera from patients with coeliac disease and from controls recognize the same linear epitopes. Thus, serological investigation of the specificity of these antibodies using a peptide ELISA does not allow discrimination between patients and controls.

Fig. 1

IgG and IgA against gliadin in the sera of 12 children with coeliac disease (CoD) while on a gluten-containing diet (GCD), while on a gluten-free diet (GFD), and in sera of controls (group I, CI; n = 11; group II, CII; n = 11). The OD 450 at serum dilution 1:1600 for IgG and 1:100 for IgA is presented. The geometric mean value for each group is indicated by the horizontal line.

Fig. 2

Percentage of sera with antibody reactivity against synthetic peptides of α-gliadin (peptide set 1). Sera were analysed at a dilution of 1:500 for antibodies of the IgG class and 1:200 for antibodies of the IgA class. Reactivity to a distinct peptide was considered to be present according to the criteria formulated in Patients and Methods. Results are shown for IgG (a–c) and IgA (d–f) class antibodies in the sera of children with coeliac disease (CoD) while on a gluten-containing diet or, if sera were not available at that time, while on a gluten-free diet (a, n = 29 sera; d, n = 26 sera) and for control children from groups I (b, n = 24 sera; e, n = 24 sera) and II (c, n = 11 sera; f, n = 11 sera). ▾, ▴, •, The most commonly recognized region and peptides, respectively.

Fig. 3

Percentage of sera with IgA against synthetic peptides of α-gliadin (peptide set 2). Sera were analysed at a dilution of 1:200 and IgA reactivity to a distinct peptide was considered to be present according to the criteria formulated in Patients and Methods. Results are shown for children with coeliac disease (CoD) while on a gluten-containing diet (a, n = 10) and for the individuals of group II (b, n = 11). ▪, Responses to the five immunodominant peptides emerging from peptide set 1; □, responses to their respective truncated derivatives (see also Table 1).