Basophile Activation Testing (BAT) in Hazelnut Allergy (Hazelnut BAT Study)

Inclusion Criteria: Primary Inclusion criteria: * Male and female subjects, age ≥ 14 years * Informed Consent as documented by signature Secondary inclusion criterion * Group A: positive case history of allergic reaction(s) to hazelnut positive double-blind placebo-controlled food challenge with hazelnut or positive titrated open food challenge with hazelnut or unambiguous case history of an anaphylactic reaction after hazelnut will be included without provocation * Group B:positive skin test (SPT) with birch pollen and hazelnut and negative food provocation with hazelnut. * Group C: negative case history of hazelnut and birch allergy and negative skin test (SPT) with hazelnut and birch pollen and negative food provocation with hazelnut Exclusion Criteria: * Drugs not allowed due to interference with the food challenge (or shortest interval between last treatment and food challenge): corticosteroids systemically (2 weeks), antihistamines (3 days), beta blocker (1 day), angiotensin converting enzyme (ACE) inhibitors (2 days), omalizumab (2 months) * Women who are pregnant * Lack of safe contraception * Uncontrolled asthma, forced expiratory volume (1 second) \<70% predicted value * Acute allergic disease * Chronic urticaria * Mastocytosis * Other clinically significant concomitant disease states * Known or suspected non-compliance, drug or alcohol abuse, * Inability to follow the procedures of the study * Participation in another study with investigational drug within the 30 days preceding and during the present study