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Background: Fruits are a major cause of food allergy in adults. Lipid transfer proteins (LTP) are implicated in severe allergic reactions to fruits, but little is known about LTP content in different cultivars., Objective: Determination of the levels of LTP in a wide range of apple cultivars., Methods: LTP was measured in apples from 53 cultivars grown in Italy and 35 grown in The Netherlands, using three different immunoassays: a competitive ELISA (cELISA), a sandwich ELISA (sELISA) and a RAST inhibition (RI). Selected cultivars were evaluated using the basophil histamine release test (BHR), skin prick test (SPT) and double-blind, placebo-controlled food challenge (DBPCFC)., Results: LTP levels measured with the three immunoassays were significantly correlated, as judged by Pearson's correlation (0.61 < Rp < 0.65; p < 0.0001), but differed with respect to the actual quantities: 3.4-253.2 (sELISA), 2.7-120.2 (cELISA) and 0.4-47.3 microg/g tissue (RI). Between cultivars, LTP titers varied over about a two-log range. Pilot in vitro and in vivo biological testing (BHR, SPT and DBPCFC) with selected cultivars supported the observed differences in LTP levels., Conclusions: Around 100-fold differences in LTP levels exist between apple cultivars. Whether the lowest observed levels of LTP warrant designation as hypo-allergenic requires more extensive confirmation by oral challenges. Determination of cultivar variation in LTP levels provides important information for growers and consumers. Comparison to earlier reported Mal d 1 levels in the same cultivars reveals that a designation as low allergenic does not always coincide for both allergens., (Copyright 2007 S. Karger AG, Basel.)

Background: Assessment of allergenicity of foods is important for allergic consumers and regulators. Immunoassays to measure major food allergens are widely applied, often giving variable results. Using the major apple allergen Mal d 1 as a model, we aimed to establish at the molecular level why different immunoassays for assessing allergenicity of apple cultivars produce conflicting outcomes., Methods: Mal d 1 was measured in 53 cultivars from Italy and 35 from The Netherlands, using four different immunoassays. Purified Mal d 1 standards were molecularly characterized by size-exclusion chromatography (SEC) and mass spectrometry (MS)., Results: Three immunoassays using an identical standard gave similar results. Minor differences in sample preparation already resulted in significant loss of allergenicity. The fourth assay, using a different Mal d 1 standard, gave 10- to 100-fold lower outcomes. By SEC, this standard was shown to be almost fully aggregated. This aggregation was accompanied by a decrease of the mass of the Mal d 1 molecule by approximately 1 kDa as analyzed by MS. The deviating immunoassay was shown to selectively recognize this aggregated form of Mal d 1, whereas the other three assays, including the one based on IgE antibody recognition, preferentially bound non-aggregated allergen., Conclusions: Variable and poorly controllable major allergen modification in both extracts and standards hamper accurate allergenicity assessments of fruits.