Apple allergy across Europe:: How allergen sensitization profiles determine the clinical expression of allergies to plant foods

Background: Allergy to a plant food can either result from direct sensitization to that food or from primary sensitization to pollen, latex, or another food. Objective: We sought to investigate the primary sensitizers in apple allergy across Europe, the individual allergens involved, and whether these differences determine the clinical presentation. Methods: Patients (n = 389) with positive case histories and skin prick test responses to fresh apple were selected in the Netherlands, Austria, Italy, and Spain. Skin prick tests and RASTs to a panel of pollens and plant foods were performed, as well as RASTs to Bet v 1 and the apple allergens Mal d 1, 2, 3, and 4. Results: In the Netherlands, Austria, and Italy apple allergy is mild (> 90% isolated oral symptoms) and related to birch pollinosis and sensitization to Bet v 1 and its apple homologue, Mal d 1, which has an odds ratio of local reactions of 2.85 (95% CI, 1.47-5.55). In Spain apple allergy is severe (> 35% systemic reactions) and related to peach allergy and sensitization to Mal d 3 (nonspecific lipid transfer protein), which has an odds ratio of systemic reactions of 7.76 (95% CI, 3.87-15.56). Conclusion: The analysis of individual apple allergens in a clinical context has provided insight into the sensitization pathway and into the intrinsic risk an allergen bears to induce mild or severe food allergy. Clinical implications: Information on the sensitization pathway is essential to develop preventive strategies in food allergy. The application of individual food allergens with a known intrinsic risk will improve the prognostic value of diagnostic tests.