Lipid transfer proteins (LTPs) are the major allergens in patients sensitive to Rosaceae (apple, peach, apricot, cherry, plum, and pear) who are not allergic to birch pollen.
The purpose of this study was to find a sensitive, specific, and relatively easy method for detection of LTP-sensitive patients.
We studied 36 persons who experienced oral allergy syndrome after the ingestion of fruits in the family Rosaceae. This study cohort was divided into two groups: 18 without allergy to birch pollen (patients) and 18 with birch pollen allergy (control subjects). All were tested by skin prick tests (SPTs) with fresh Golden Delicious apple, fresh peach, and extracts of peel and pulp from both fruits. Their specific IgE reactivities against peach peel extract were further investigated by immunoblot analysis.
All 18 subjects in the control group showed strongly positive skin reactions with both fresh apple and fresh peach, whereas no skin reactivity was found with extracts from peach peel, peach pulp, or apple pulp. Extract of apple peel produced positive skin reactions in 17 of 18 control subjects; however, the wheals were generally smaller than those induced by fresh fruits. Immunoblot analysis showed no reactivity for peach peel extract. In contrast, the SPTs with fresh fruits showed that some of the 18 patients had strongly positive reactions, but others had weak reactions or negative responses. Further, in a high proportion of the patients, consecutive SPT with fresh apple yielded inconsistent results. In all patients, SPTs with extracts from apple pulp and peach pulp were negative, whereas SPTs with peel extracts were strongly positive in all patients. In most patients, the wheal area induced by SPT with peel extracts was larger than that induced by SPTs with fresh fruits. Immunoblot analysis showed that serum specimens from all 18 patients reacted with a 10-kD protein in peach peel. This is the molecular mass of LTPs.
In birch pollen-allergic patients, the SPTs with fresh foods still remains the most reliable method of diagnosing vegetable food hypersensitivity. In contrast, in patients not allergic to birch pollen, the most reliable strategy for detection of patients sensitive to LTPs is skin prick testing with properly prepared fruit peel extracts. The loss of Bet v 1- and Bet v 2-like structures, which probably occurs during extraction, may facilitate immediate identification of the relevant allergen.