Carrot allergy: Double-blinded, placebo-controlled food challenge and identification of allergens

Background: Allergic reactions to carrot affect up to 25% of food-allergic subjects. Clinical manifestations of carrot allergy and IgE responses to ca rrot proteins, however, have never been studied in subjects with carrot all ergy confirmed by means of double-blinded, placebo-controlled food challeng e (DBPCFC). Objective: The purposes of this investigation were to confirm clinically re levant sensitizations to carrot by means of DBPCFC, to validate current dia gnostic methods, and to identify IgE-reactive carrot proteins in patients w ith true allergy. Methods: DBPCFCs were performed in 26 subjects with histories of allergic r eactions to carrot. Patients underwent skin prick tests with carrot extract , fresh carrot, and various pollen extracts. Specific IgE to carrot, celery , birch, and mugwort pollen and to rBet v 1, rBet v 2, and rBet v 6 were me asured through use of the CAP method. Carrot allergens were identified by m eans of immunoblotting and blotting inhibition. Results: Twenty of 26 patients had positive DBPCFC results. The sensitivity of the determination of carrot-specific IgE antibodies through use of the CAP method (greater than or equal to0.7 kU/L) was 90%, the sensitivity for skin prick testing with commercial extracts was 26%, and the sensitivity fo r prick-to-prick tests with raw carrot was 100%. The Bet v 1-related major carrot allergen Dau c 1 was recognized by IgE from 85% of patients; 45% wer e sensitized to cross-reactive carbohydrate determinants and 20% to carrot profilin. In 1 subject, a Bet v 6-related carrot allergen was recognized. I n 4 patients, IgE binding to Dau c I was not inhibited or was weakly inhibi ted by rBet v 1 or birch pollen extract. Conclusion: This study confirmed the allergenicity of carrot by means of DB PCFC. DBPCFC-positive patients had exclusively specific IgE antibodies to b irch pollen-related carrot allergens, Dan c 1 being the major allergen. The lack of inhibition of IgE binding to Dau c 1 by birch allergens in a subgr oup of patients might indicate an secondary immune response to new epitopes on the food allergen that are not cross-reactive with Bet v 1.