Detection of specific IgE against linear epitopes from Gal d 1 has additional value in diagnosing hen's egg allergy in adults

Abstract

Background: Although hen's egg allergy is more prevalent in children, up to 0.6% of adults from different European countries suffer from a persistent or newly onset hen's egg allergy, making accurate diagnosis in adults necessary. However, sensitization to hen's egg extracts, components and linear epitopes is solely studied in children.

Methods: Hen's egg allergic (n = 16) and tolerant (n = 19) adults were selected by sensitization towards recombinant components rGal d 1 and/or 3. Sensitization profiles towards egg white and yolk extract and the native components Gal d 1, 2, 3 and 4 were respectively evaluated with the ImmunoCAP or the EUROLINE system. Characterization of linear epitopes was performed with a peptide microarray containing 15mer peptides representing the entire sequence of mature Gal d 1 and 3.

Results: Overall, sIgE titres against hen's egg extracts and single components overlapped largely between allergic and tolerant adults. Although the median sIgE/sIgG4 ratio to Gal d 1 was increased in allergic adults, the range was comparable between both groups. Clinically relevant sensitization to Gal d 1 was confirmed by sIgE-binding to the linear epitopes aa30-41, aa39-50 or aa84-95 in 6/13 allergic adults, mainly suffering from objective symptoms. In comparison, these epitopes were recognized by 1/15 tolerant patient. Only a few linear epitopes were detected for Gal d 3, suggesting a greater importance of conformational epitopes for the recognition of Gal d 3.

Conclusion and clinical relevance: Specific IgE-binding to linear epitopes of Gal d 1 is highly specific in identifying hen's egg allergic adults with objective symptoms.

Keywords: IgE; food allergy; hen; linear epitopes's egg.

Figure 1

Sensitization profiles of tolerant and allergic patients to hen´s egg extracts and components. A, sIgE levels to egg white and egg yolk extract measured with the ImmunoCAP system (kU/L) split by allergic and tolerant patients; represented with the median. B, sIgE and sIgG4 levels to native hen's egg components Gal d 1, Gal d 2, Gal d 3 and Gal d 4 measured with the EUROLINE‐immunoblot (EL‐intensities, RU) split by allergic and tolerant patients; represented with the median. C, Log‐transformed sIgE/IgG4 ratios to native hen's egg components Gal d 1, Gal d 2, Gal d 3 and Gal d 4 resulting from the measures shown in b); represented with the median

Figure 2

Linearization effects sIgE‐binding to Gal d 3. A, Comparison of IgE‐binding capacity between native (EL) and linearized Gal d 1 and Gal d 3 (WB); the number of bound IgE is divided into categories defined as low , moderate and high . B, original WB showing sIgE‐binding to the recombinant components rGal d 1 and rGal d 3

Figure 3

Peptide and epitope analysis derived from Gal d 1 and Gal d 3. A + B, Heatmap of Gal d 1 and Gal d 3 showing the IgE (green) and IgG4 (red) epitope recognition pattern of 13 hen's egg allergic and 15 hen's egg tolerant adults expressed as mean z‐scores. Epitopes recognized by sIgE and sIgG4 from the same individual are shown in rows underneath each other. Surface‐exposed epitopes of Gal d 3 are indicated with a red star and patients suffering from objective symptoms are highlighted with a green star