In Northern and Central Europe, birch pollen allergy is one of the most important causes of allergic rhino-conjunctivitis and bronchial asthma. In addition, birch pollen allergy is frequently associated with food allergies to fruits, legumes and nuts due to IgE cross-reactivity between the major birch pollen allergen, Bet v 1, and homologous food allergens from the pathogenesis-related proteins subfamily PR-10. Up to now, only one allergen with low sequence identity to Bet v 1 outside the PR-10 subfamily, Act d 11 from kiwi fruit, has been published. Therefore, one aim of this thesis was to assess the allergenicity of the cytokinin-specific binding protein from mung bean, which is distantly related to Bet v 1, and the significance of its low sequence identity for cross-reactivity.
Birch pollen allergic patients were recruited in two allergy outpatient clinics in Vienna, interviewed on their allergic reactions and tested for pollen and food allergies by common in vitro and in vivo diagnosis. Allergens were expressed in Escherichia coli and purified through chromatographic methods. Allergen-specific immunoglobulin levels were measured by ELISA and cross-reactivity determined by inhibition assays. Additionally, basophil degranulation assays were performed to evaluate allergenicity.
We identified cytokinin-specific binding protein as a novel allergen in mung bean sprouts. It was designated Vig r 6.0101 by the IUIS Allergen Nomenclature Subcommittee. Vig r 6 bound IgE from 32% of sera from 60 unselected birch pollen allergic patients and from 63% of 19 patients who were additionally sensitised to mung bean sprouts. Furthermore, we demonstrated its cross-reactivity with Bet v 1 and the PR-10 subfamily member from mung beans, Vig r 1, and its capability of activating basophils sensitised with patients' sera.
Diagnosis of food allergy is complicated by the fact that food allergen- specific IgE is often not associated with allergic reactions. Moreover, the role of other immunoglobulins in the birch pollen-plant food syndrome has been rarely investigated. Therefore, another aim of this thesis was to compare antibody binding of Bet v 1-related allergens from different foods and to evaluate the clinical relevance of allergen- specific IgE, IgG and IgA in the context of food allergy.
All 35 tested birch pollen allergic patients' sera contained IgE specific for Bet v 1, Cor a 1 from hazelnut, Mal d 1 from apple and Pru p 1 from peach, which are allergens with high sequence identities to Bet v 1. In contrast, lower sequence identities and lower IgE binding were observed for Gly m 4 from soybean, Vig r 1 and Api g 1.01 from celeriac. Sera from allergic and non-allergic patients contained allergen-specific IgA, although the allergic group showed higher levels. However, we detected no significant correlation between allergen-specific Ig levels and food-associated symptoms with the only exception of elevated Api g 1.01-specific IgE in celeriac allergic patients. In addition, Mal d 1- specific IgA and Api g 1.01-specific IgE, IgG4 and IgA were significantly associated with higher frequencies of the respective food allergies.
To conclude, cross-reactivity can occur among allergens with high and low sequence identity as long as IgE binding epitopes are sufficient similar. Therefore, distantly related proteins are promising targets to study cross-reactivity and IgE binding epitopes regarding future allergy diagnosis.