By Ingrid Grasmo
Severe allergic reactions to deamidated gluten (DG) in individuals tolerant to wheat are linked to a separate phenotype of wheat allergy, suggest study findings.
"DG allergy is a separate entity, characterized by a homogenous immunoglobulin (Ig)E response. This entity is a direct consequence of present technologies applied to industrial food products," say Sandra Denery-Papini (Biopolymeres, leurs Interactions et Assemblages, Nantes, France) and co-authors.
For the study, the researchers assayed sera from 15 patients with a confirmed allergy to DG and nine patients allergic to wheat proteins (WPs).
Findings from the immunologic assay showed that patients with DG allergy had significantly higher IgE sera reactivity to native ω2-gliadins compared with other fractions, and to deamidated ω2-, γ-, and total gliadins relative to other deamidated fractions or respective native fractions.
Comparison of the triggering potential in a humanized rat basophilic leukemia model showed that degranulation was significantly more common among patients allergic to DG compared with WP (75 vs 56%).
In contrast to patients with WP allergy who showed low degranulation percentages, the degranulation percentage was strong (over 25%) in sera from patients allergic to DG. Furthermore, only deamidation of ω2-gliadins increased the response intensity or decreased the reactivity threshold in these patients.
Mapping of epitopes detected by IgE from patients allergic to DG revealed that the sequences detected with the highest intensity and by the larger number of sera all included the octapeptide QPQQPFPQ.
To address the effect of deamidation, the researchers then substituted four glutamine residues with glutamic acids at their different positions and found that the peptide detected with the highest intensity was QPEEPFPE, with substitutions at positions Q3 or Q4, and Q8.
"Deamidated ω2-gliadins or the dominant IgE-binding epitope QPEEPFPE could be used as tools for the diagnosis of this new allergy," conclude the researchers in Allergy.
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