Identification of allergens in oilseed rape (Brassica napus) pollen

Background: Pollen from oilseed rape (OSR), Brassica napus, an increasingly cultivated oilplant from the Brassicaceae, has been recognized as a potential cause of allergic sensitization. Allergens have been hardly investigated. Methods: We characterized IgE binding proteins in OSR pollen by immunoblot, immunoblot inhibition and specific monoclonal antibodies using sera from 89 patients sensitized to OSR, Results: Two low-molecular-weight allergens of 6/8 kD and 14 kD as well as a high molecular-weight cluster (27-69 kD) comprising six cross-reactive peptides could be identified. The three allergens were recognized by 50, 34 and 80% of patients, respectively. Immunoblot IgE binding to OSR could be totally inhibited by rye pollen and moderately by birch pollen (6/8 and 14 kD) while mugwort had little effect. An anti-profilin-specific monoclonal antibody bound specifically to a 14-kD protein in OSR. Binding to the 6/8-kD rape allergen could be effectively inhibited by rAln g 2, a calcium-binding protein from alder. Periodate treatment led to a significant reduction in IgE binding to the 27 to 69-kD OSR allergens indicating that carbohydrate determinants are involved in IgE binding. OSR proteins were capable to quench IgE binding to timothy grass pollen proteins of greater than or equal to 60 kD suggesting that grass pollen group 4 allergens cross-react with the 27 to 69-kD cluster in OSR. Conclusions: The data demonstrate that OSR pollen is allergenic and indicate that the identified allergens represent cross-reacting homologues of well-known pollen allergens, i.e. calcium-binding proteins, profilins, and high-molecular-weight glycoproteins. Via cross-reactivity, exposure to OSR pollen may be a prolonging and aggravating factor in underlying birch and grass pollen allergy.