Continuous apple consumption induces oral tolerance in birch-pollen-associated apple allergy.

BACKGROUND Patients with birch pollen allergy (major allergen: Bet v 1) have often an associated oral allergy syndrome (OAS) to apple, which contains the cross-reactive allergen Mal d 1. As successful birch pollen immunotherapy does not consistently improve apple related OAS symptoms, we evaluated whether regular apple consumption has an effect on OAS and immune parameters of Mal d 1 or Bet v 1 allergy. METHODS A total of 40 patients with a clear history of birch pollen rhinoconjunctivitis and associated OAS to apple were included in an open, randomized, controlled clinical trial: 27 patients consumed daily defined amount of apple (1-128 g), doubling the amount every two to three weeks, while 13 patients remained untreated. Primary endpoint was the proportion of patients that achieved tolerance to at least 128 g of apple at the end of the study after 8 months. Exploratory endpoints were questionnaire about cross-reactive food and pollen allergy symptoms, conjunctival provocation test with birch pollen and Bet v 1, and in vitro tests (tIgE, sIgE, and IgG4 to Mal d 1 and Bet v 1; basophil activation test with both allergens). RESULTS Seventeen of 27 patients in active group and none of 13 patients in control group (P = 0.0001) could tolerate a whole apple after the intervention. However, differences in endpoints reflecting systemic immune reactivity did not reach statistical significance. CONCLUSION In patients with OAS to apple, tolerance can be safely induced with slowly, gradually increasing consumption of apple. However, the observation of a relapse after discounting of apple consumption and absence of immunologic changes suggest that induced tolerance is only transient.