Impact of native, heat-processed and encapsulated hazelnuts on the allergic response in hazelnut-allergic patients

Pollen-associated food allergy is common. However, systemic reactions or even life-threatening anaphylaxis are rare. The aim of this study was to investigate the clinical impact of native, heat-processed and encapsulated hazelnuts (HN) in patients with proven HN allergy. One hundred and thirty-two patients with a positive history of HN allergy were recruited. Sensitization was confirmed by a skin prick test (SPT) and sIgE against HN. After an HN-free diet, double-blind placebo-controlled challenges were performed with increasing amounts of native and roasted HN. A subset of patients were given HN capsules to circumvent the oral mucosa. Basophil activation was measured by flow cytometry before and after provocation but also ex vivo using native and roasted HN extracts. Three groups of HN-allergic patients were identified depending on their clinical reaction pattern. The dosages by which allergic reactions were elicitated varied for native HN from 0.01 to 2.0 g, with a median of 0.1 g, for roasted HN from 0.01 to 10.0 g, with a median of 0.23 g, and for encapsulated HN from 0.1 to 3.0 g, with a median of 0.3 g. Accordingly, the SPT was more frequently positive and resulted in greater weal reactions if native HN was used. This finding was confirmed by ex vivo basophil activation showing that significantly higher allergen extract concentrations (roasted > native) were necessary to induce 50% basophil activation. Our data show that heat processing of HN reduces its allergenicity. SPT but also the basophil activation test can be used to determine the reactivity of an allergen extract.