Allergens in raw and roasted hazelnuts (Corylus avellana) and their cross-reactivity to pollen

Hazelnuts (HNs), widely distributed in sweets, provoke one of the most frequent pollen-associated food allergies. In this study HN allergens were investigated and immunologically characterized, focussing on their heat stability and cross-reactivity with known allergenic structures. Therefore, 27 sera from HN-allergic patients and 28 sera from children with positive CAP classes for HN and birch pollen were submitted to immunoblot and immunoblot inhibition. The major HN allergen was found to present a molecular mass of about 17-18 kDa, and to share IgE epitopes with Bet v 1, the major birch pollen allergen. This allergen was recognized by IgE of 93% of our HN-allergic patients and by 79% of sensitized children. A 48 kDa glycoprotein was identified as a minor HN allergen with cross-reactive carbohydrate determinants. The major N-glycan species was determined by matrix assisted laser desorption mass spectrometry to be Man(3)XylGlcNAc(2). IgE binding to this protein was detected in sera of 41% of the allergic patients and 61% of the children. Partial N-terminal sequencing demonstrated similarity to legume storage proteins. The IgE reactivity of this structure was partially resistant to heating. The rat basophil leukaemia cell mediator release assay was used for estimation of cross-sensitization between HN and birch pollen, confirming the finding that HNs contain a heat-resistant allergenicity without cross-reactivity to birch pollen allergens.