CHARACTERIZATION OF APPLE 18-KD AND 31-KD ALLERGENS BY MICROSEQUENCING AND EVALUATION OF THEIR CONTENT DURING STORAGE AND RIPENING

Patients with tree pollinosis frequently report allergic reactions aft er ingestion of apples. The severity of apple allergy has been related to the variety of apples and their degree of maturity. To generate a serum pool that is representative of various IgE-binding patterns of a pple-allergic sera, serum samples from 34 patients allergic to tree po llens were screened. Only 24 serum samples reacted to the apple extrac t. Pooled serum was used to identify allergens in apples. An efficient and consistent extraction method for apple fruits was used to compare the immunoreactivities of extracts of different varieties (McIntosh, Red Delicious, Granny Smith, and Golden Delicious) of freshly picked a nd store-purchased apples. We found that Golden Delicious apples had t he greatest amount of 18 kd allergen, which has been reported to be a potent IgE-binding apple allergen. Store-purchased apples contained hi gher concentrations of the 18 kd allergen than freshly picked apples. In our study only 37.5% of sera reacted to the 18 kd protein, whereas 75% of the sera reacted to a 31 kd allergen. Other immunoreactive band s in apple extracts included proteins of 50, 38, 16, 14, and 13 kd. Th e amino-terminal amino acid sequences of the two major allergens, 18 k d and 31 kd, were determined. These sequences shared approximately 50% identity with disease resistance proteins of various plants or Bet v 1 in birch tree pollens. The appearance of various allergens was also investigated in mature apples during storage. The amount of 18 kd alle rgen increased significantly when apples were stored at 4 degrees C. H owever, under controlled atmospheric conditions in which oxygen- and c arbon dioxide-induced ripening were regulated, the amount of 18 kd all ergen remained unaffected. Because ripening and maturation were not as sociated with increases in 18 kd allergen content, the observed change s might be induced by factors related to disease resistance.