Molecular composition and biological activity of commercial birch pollen allergen extracts

Commercial extracts used for diagnosis and treatment of allergy are currently prepared from natural allergen sources. The aim of this study was to analyse birch pollen allergen extracts produced for in vivo diagnosis of birch pollen allergy regarding their contents of individual birch pollen allergens (Bet v 1, Bet v 2 and Bet v 4). Protein contents were measured and the allergen composition was analysed by immunoblotting using antibody probes specific for Bet v 1, Bet v 2 and Bet v 4 in birch pollen extracts from five manufacturers of allergen extracts. The contents of the major birch pollen allergen, Bet v 1, were quantified with a specific two-site binding enzyme-linked immunosorbent assay with nanogram sensitivity for Bet v 1. The biological activities of the allergen extracts were evaluated by skin prick testing in birch pollen allergic patients and compared with their sensitization profiles. A more than 10-fold variation regarding total protein contents (23.1-314 mu g mL(-1)) and also regarding the amounts of the major birch pollen allergen, Bet v 1 (1.62-19.6 mu g mL(-1)) was found. The highly cross-reactive Bet v 4 allergen was absent in three of the five tested extracts. Furthermore, varying skin test results were obtained in birch pollen allergic patients with the allergen extracts. Commercial birch pollen extracts exhibit a considerable variability regarding allergen contents and hence deliver varying in vivo test results. These problems might be overcome with recombinant allergen-based preparations.