Birch pollen-related food allergy: Clinical aspects and the role of allergen-specific IgE and IgG₄ antibodies

Background: Patients with birch pollen allergy often develop allergic reactions to plant foods. Objective: To evaluate the prevalence, main symptoms, and triggers of birch pollen-related food allergy and the role of food-specific IgG₄ antibodies in food tolerance. Methods: Food-induced symptoms were evaluated in 225 individuals with birch pollen allergy by using a standardized questionnaire. IgE and IgG₄ levels specific for the major birch pollen allergen Bet v 1 and birch profilin Bet v 2 and the Bet v 1 homologs in apple (Mal d 1) and hazelnut (Cor a 1) were quantified by ImmunoCAP. Mock-treated and IgG-depleted sera from patients tolerating hazelnuts in food challenges were compared for their inhibitory activity for binding of Cor a 1-IgE complexes to B cells. Results: In total, 73% of the study population experienced food allergy, which was perennial in 86% of the affected individuals. The oral allergy syndrome was the main clinical manifestation. However, more than 58% of the patients also experienced food-induced rhinoconjunctivitis. Apples and hazelnuts were identified as the most frequent triggers. Food allergy correlated with IgE reactivity to Bet v 1 but not to Bet v 2. Mal d 1-specific and Cor a 1-specific IgG₄/IgE ratios were significantly higher in food-tolerant individuals than individuals with food allergy. Sera from IgG₄-positive food-tolerant patients possessed IgG-dependent IgE-inhibitory activity. Conclusion: Birch pollen-related food allergy is highly prevalent and often perennial. High food allergen-specific IgG₄/IgE ratios seem associated with food tolerance, potentially because specific IgG₄ blocks IgE binding to food allergens. Thus, the presence of food allergen-specific IgG₄ antibodies is no diagnostic marker for birch pollen-related food allergy.