PT with heat-processed apple peel extract to detect LTP hypersensitivity.

Background: Allergen-resolved diagnosis of food allergy may be essential in the clinical practice, particularly in patients allergic to foods that may contain both labile and stable allergens. However, presently available diagnostic tests are not useful in this sense.
Objective: To assess the clinical usefulness of SPT with a heat-processed apple peel extract as an easily available means to detect hypersensitivity to lipid transfer protein (LTP), an extremely stable and potentially hazardous apple allergen.
Methods: Raw and heat-processed (100 degrees C x 10 min) apple peel extract (100 microg/ml) were used to carry out SPT in 23 patients with apple-allergy, 15 of which considered as probably sensitized to labile allergens (Maid 1, Mal d 4) and 8 to stable allergens (Mal d 3, LTP), respectively on the basis of the presence/absence of IgE reactivity to birch pollen. IgE reactivity to the heat-processed apple peel extract was further analyzed by immunoblot.
Results: Altogether SPT with raw apple extract scored positive in 20/23 (87%) patients, including 12/15 patients considered as probably sensitized to labile allergens and 8/8 patients considered as probably sensitized to LTP. In contrast, the heat-processed apple extract induced a wheal-and-flare reaction only in the 8 (100%) presumptive LTP reactors. Immunoblot analysis showed IgE reactivity to a 10 kDa protein (LTP) in heat-processed apple extract.
Conclusion: The heat-resistance of stable apple allergens like LTP can be usefully exploited to prepare extracts for allergen-resolved diagnosis in-vivo.