IgE binding to unique hazelnut allergens : Identification of non pollen-related and heat-stable hazelnut allergens eliciting severe allergic reactions

Usually hazelnut allergic patients suffer from the tree pollen associated oral allergy syndrome (OAS) caused by cross-reactive structures. Anaphylactic reactions elicited by hazelnuts happen rarely but are of high clinical significance. Considering that hazelnuts are ingredients in processed foods, hazelnuts may play an important role as hidden allergens for these high risk patients. Therefore, we analyzed the IgE reactivity of a young woman with severe allergic reactions after ingestion of hazelnuts without any association to tree pollen allergy. The aim of this study was to identify and characterize these potent hazelnut-specific allergens. We compared these allergens to structures displayed by sera from patients with a completely or partially non pollen-related hazelnut allergy and with birch pollen-related hazelnut allergy. None of the sera had a clinical history of anaphylaxis. Special emphasis was placed on the heat stability and cross-reactivity of these allergens. Using Western blotting with extract from birch pollen and EAST inhibition techniques we were able to show that the allergens in the serum sample of the young woman were not cross-reactive with birch pollen. Immunoblot experiments with extracts from native and heated hazelnuts and EAST inhibition tests further characterized these allergens to be heat-stable. Unlike the IgE binding pattern of the sera from the patients with pollen-related hazelnut allergy, low molecular weight proteins below 10 kDa were identified by the sera from the patients without pollinosis. Since the binding pattern of the serum sample of the young woman was different from that of the sera from patients without pollen allergy but less severe symptoms, we assume an association between single non pollen-dependent hazelnut allergens in the low molecular range and severe allergic reactions. These results enable us to approach a subgroup of hazelnut allergens which we believe to be responsible for anaphylactic reactions in hazelnut allergic patients after ingestion of heat-stable hazelnut structures in processed food stuff, independent of pollinosis.