A study of cross-reactivity between citrus fruit and pollen allergens in oral allergy syndrome and food-dependent exercise-induced anaphylaxis in Japan

Objectives: Oral allergy syndrome (OAS) associated with citrus fruits has been previously reported. However, in Japan, although rare, citrus allergy is also associated with food-dependent exercise-induced anaphylaxis (FDEIA). This study was done to determine whether different allergens may be involved in these two responses, and to examine cross-reactivity between popular citrus fruits and local pollen allergens. Methods:Twelve patients were studied who had a history of OAS (8 cases) or FDEIA (4 cases), and had positive IgE antibody titers or tested positive with a skin prick test to citrus antigens. Serum immunodetection assays and immunoblot inhibition assays were performed with extracted Valencia orange (rCit s 2), selected antigens in white birch pollen (WBP) and orchard grass pollen (OGP). Results: Immunodetection assays demonstrated an allergen associated with OAS as the 14-kDa protein, Cit s 2. An as yet unidentified 54-kDa protein was demonstrated in FDEIA patients. Cross-reactivity between orange and pollen antigens was confirmed by the following results: 1) Significant correlations between serum specific IgE levels for orange and OGP, 2) Immunoblot inhibition with WBP and OGP pollen antigens against rCit s 2. In Immunoblot inhibition, WBP and OGP both pollen antigens inhibited against rCit s 2. Conclusion: The main allergen of OAS induced by orange was Cit s 2, which has cross-reactivity with WBP and/or OGP in Japanese patients with orange allergy. IgE-binding protein pattern in patients with FDEIA induced by orange were different from that in OAS. A 54-kDa protein was assumed to be a candidate for clinically relevant allergens in the development of the FDEIA.