Allergy to birch pollen and apple, and cross-reactivity of the allergens studied with the RAST.

Apple-pulp allergens are unstable, but fresh material can be used for skin testing. In this study stable allergens, probably of a protein nature, were extracted from apple seed and used in radioallergosorbent tests (RAST). Apple-seed allergens were shown by RAST inhibition to cross-react with birch pollen allergen(s). Cross-reactivity may explain the frequent co-occurrence of birch pollen and apple allergy. Approximately 50% of patients in a group with immediate hypersensitivity to birch pollen were also sensitive to apple as judged by a history of symptoms, skin tests with apple-pulp and apple-seed preparations, and apple-seed RAST.