Background: Previous studies have demonstrated insufficient sensitivity of commercially available celeriac extract reagents in the diagnosis of celeriac allergy.
Objective: We sought to assess the diagnostic performance of specific IgE determination based on recombinant and purified natural celeriac allergens in comparison with an extract-based assay and to investigate interference by IgE to cross-reactive carbohydrate determinants and its biologic activity.
Methods: Twenty-four subjects with a positive double-blind, placebo-controlled food challenge result to celeriac; 20 atopic control subjects with birch pollen allergy who tolerated celeriac; and 20 nonatopic subjects were enrolled. IgE binding was investigated for celeriac allergens (rApi g 1.01, rApi g 4, and nApi g 5), extract reagents (celeriac, birch, mugwort, and timothy grass pollen), birch pollen allergens (rBet v 1 and rBet v 2), and cross-reactive carbohydrate determinants by means of ImmunoCAP analysis. Biologic activity of allergens was determined based on basophil mediator release.
Results: Component-resolved ImmunoCAP analysis considerably increased the sensitivity to detect celeriac-specific IgE by 20%. Sensitization to carbohydrate structures was detected in 38% of patients with celeriac allergy, and there was an excellent correlation between sensitization to the glycoprotein Api g 5 and isolated glycan. Positive results among atopic control subjects were mainly caused by protein allergens, whereas the effect of carbohydrate epitopes was marginal. The ability of allergens to induce mediator release decreased in the order Bet v 1 > Api g 1 > Api g 5, confirming the low biologic activity of IgE to carbohydrate epitopes.
Conclusion: Component-resolved diagnosis allowed an increase in diagnostic sensitivity from 67% to 88% compared with extract-based diagnosis. Sensitization to Api g 5 was attributable to its glycan moieties but did not interfere with diagnostic specificity.