ISOLATION AND CHARACTERIZATION OF THE 18-KDA MAJOR APPLE ALLERGEN ANDCOMPARISON WITH THE MAJOR BIRCH POLLEN ALLERGEN (BET-V-I)

The major allergen from birch pollen, Bet v I, and the cross-reacting 18-kDa major allergen from Golden Delicious and Granny Smith apples we re isolated by micropreparative SDS-PAGE followed by electroelution. I n the case of apples, highly active, low-temperature extracts were use d. The purity of the allergens was checked by analytic SDS-PAGE and im munoblotting with allergic patients' sera, as well as by N-terminal am ino acid microsequencing, and the allergens were found to be very pure . The strong immunologic activity of the isolates was determined by th e enzyme allergosorbent test (EAST) and EAST inhibition assays; this a ctivity was, in the case of Bet v I, similar to that of a preparation obtained by monoclonal antibody affinity chromatography. The allergeni c potency of Bet v I and of the cross-reactive apple allergen was dete rmined by EAST inhibition and dose-related histamine release. With bot h assay systems, the allergenic reactivity of Bet v I was considerably higher than that of the major apple allergen. Furthermore, skin prick tests with the purified allergens and with whole allergenic extracts were performed on a group of 33 patients suffering from birch-pollen a nd apple hypersensitivity, and on a control group of 10 patients. The frequency of positive prick test results in the allergic patient group ranged from 73% for the major allergen from Golden Delicious apples t o 97% with Bet v I and whole birch pollen extract, respectively. In co ntrast to our low-temperature extracts, commercial prick test solution s of four different manufacturers were found to be unreliable for the diagnosis of apple allergy. The skin test results again indicated the strong immunologic activity of the allergen isolates and the predomina nce of the major allergens in context with birch-polIen and apple hype rsensitivity. Taken together, the results support the view that the 18 -kDa major allergen represents most of the allergenicity of the the ap ple fruit, and that all allergenic epitopes of the apple proteins are present on Bet v I.