A high number of birch pollen-allergic individuals develop hypersensitivity reactions to certain foods, e.g. apples. This food allergy is due to immunological cross-reactivity. Birch pollen-related foods contain proteins, e.g. Mal d 1 in apple, that are structurally related with the major birch pollen allergen, Bet v 1. Hence IgE antibodies and T lymphocytes specific for Bet v 1 recognize these food proteins which results in activation of the immune system and, consequently, in clinical symptoms.

In the present study the investigators intend to investigate if and how the consumption of birch pollen-related food allergens affects birch pollen allergy. In other words, the investigators are interested to analyse whether Bet v 1-related food allergens activate Bet v 1-specific memory cells and thus, contribute to the maintenance of the pollen allergy outside the pollen season. Data obtained in this study will help to clarify the immunological and clinical role of cross-reactivity between pollen and food allergies and will reveal whether avoidance of such foods should be recommended for the patients. Finally, novel approaches for diagnosis and therapy of pollen-related food allergens can be developed.

Inclusion Criteria:

• Otherwise healthy birch pollen allergic (rhinoconjunctivitis)persons
• Positive SPT and RAST to birch pollen
• Sensitized to Bet v 1

Exclusion Criteria:

• Persons suffering from malignancies, autoimmune and cardiopulmonary diseases
• Anemia
• Hyper-IgE syndrome
• Treatment with ß-blockers, permanent treatment with antihistaminics, leucotriene antagonists, corticosteroids

otherwise healthy birch pollen allergic (rhinoconjunctivitis)persons suffering also from oral allergy syndrome to apple.