Bet v 1 homologues in strawberry identified as IgE‐binding proteins and presumptive allergens

Abstract
Background: No strawberry allergen has so far been identified and characterized. Methods: Serum samples were collected from patients with a suggestive case history of adverse reactions to strawberry and other fruits. Extracts from fresh and frozen strawberries were analysed by sodium dodecyl sulphate‐polyacrylamide gel electrophoresis (SDS‐PAGE), Western blotting and mass spectrometry. Patient blood samples were analysed for inhibition of IgE binding and basophil degranulation. Results: Several IgE‐binding proteins could be detected. In more than half of the patient sera, a 20/18‐kDa doublet band was observed in Western blotting. These two bands were excised and analysed by mass spectrometry showing the presence of proteins belonging to the Bet v 1 family of allergens. Inhibition of the IgE binding to the 20/18‐kDa doublet was obtained by addition of two recombinantly expressed allergens belonging to the Bet v 1 family (Bet v 1 and Mal d 1) and strawberry protein extract. In a cell‐based assay of patient blood samples, basophil degranulation could be induced by strawberry protein extract and by Bet v 1 and Mal d 1. Conclusions: We conclude that strawberry homologues to Bet v 1 may be allergens of importance for adverse reactions to strawberry.