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.