Immunologic characterization of monoclonal antibodies that modulate human IgE binding to the major birch pollen allergen Bet v 1

Background: Bet v 1 and homologous proteins represent major allergens for almost 95% of patients allergic to tree pollen and approximately 70% of those allergic to fruits and vegetables. As yet, no continuous (sequential) IgE epitopes have been determined for Bet v 1, and evidence has accumulated that Bet vl IgE epitopes belong to the conformational (discontinuous) type, Objective: A panel of 85 mouse monoclonal anti-Bet v 1 antibodies was raised as a tool with which to study the interaction of human IgE antibodies with Bet v 1. Methods: The epitopes of selected monoclonal antibodies (mAbs) were characterized by mapping with synthetic overlapping peptides and by cross-competition experiments, Cross-reactivity of Bet v I-specific mAbs with tree and plant food allergens was investigated by Western blotting. The influence of Bet v 1-specific mAbs on the IgE-Bet v I interaction was studied by competition assays with immobilized purified recombinant Bet v 1 and by basophil histamine release experiments. Results: Antibodies that increased the IgE binding to Bet v I up to fivefold could be defined, whereas others inhibited IgE binding to Bet v 1 up to 99% and competed with the Bet v 1-induced histamine release from patients' basophils. Conclusion: The activity of the enhancing antibodies is interpreted as a stabilization of Bet v 1 states/IgE epitopes, which are either more accessible for certain IgE antibodies or are recognized with higher affinity. Those mAbs that competed with the Bet v 1-IgE interaction, if humanized or produced as recombinant antibody fragments, might be considered as potential tools for local allergy therapy.