Identification of cyclophilin as an IgE-binding protein from carrots

BACKGROUND: Plant food allergies have been associated with pollenosis, although most of the causative allergens are as yet undefined. It is important to elucidate the properties of plant food allergens in order to minimize a patient's risks in food selection. The purpose of the present study was to examine and characterize the IgE-binding proteins in carrots as possible allergens by using patients' sera. METHOD: IgE-binding proteins in carrot extract were screened by an immunoblot technique using sera of patients with atopic dermatitis (selected based upon a case history of food allergies). An allergenic protein was purified from carrot extract by chromatographic procedures. The N-terminal amino acid sequence of allergenic protein was determined and subjected to a computer homology search. Cross-reactivity between carrot and birch allergens was examined by immunoblotting. RESULTS AND CONCLUSION: A unique, approximately 20-kDa allergenic protein that reacted with about 14% of patients' sera was isolated and characterized. The N-terminal amino acid sequence of the purified protein was found to be homologous with those of plant cyclophilins. This allergen exhibited a peptidyl-prolyl cistrans isomerase activity, which was inhibited by the conjugation of cyclosporin A. These properties of the allergenic protein isolated from carrot identified it as a cyclophilin, a possible plant food allergen. No cross-reactivity between this 20-kDa carrot allergen and Bet v 7, a birch pollen cylcophilin, was observed.