Lack of crossreaction with Bet v 1 in patients sensitized to Dau c 1, a carrot allergen

Background: Pollen-related food allergies to fresh fruit and vegetables are a well-known clinical phenomenon. Allergens related to Bet v 1 are responsible for these cross-reactions. Objective: To characterize the allergen recognized by four carrot-allergic patients. Methods: Sera from four patients showing strong immediate systemic reactions after contact or ingestion of raw carrot were studied by immunoblotting, The 18-kD allergen, named Dau c 1, was isolated by ethanol precipitation and specific extraction after SDS-PAGE and its N-terminal amino acid sequence was determined. Results: All the patients had significant levels of specific IgE to carrot, but no specific IgE to birch pollen was detected in any of them. IgE immunodetection with the sera only recognized a single band of around Is kD in raw carrot and in celery (with weaker reaction). No reactive band was found with birch pollen. These results were confirmed using a polyclonal anti-carrot antiserum. The carrot IgE-binding protein had a pi of 4.2 and its N-terminal sequence was homologous to that of Bet v 1 and to allergens previously described in celery and other foods. The four patients studied were not sensitized to birch pollen and three of them tolerated fruit ingestion. Conclusion: The whole study indicated that a sensitization to Dau c 1 induces IgE antibodies that do not cross-react with birch pollen allergens.