Molecular Characterization of Bip 1, a Monoclonal Antibody That Modulates IgE Binding to Birch Pollen Allergen, Bet v 1

Bet v 1 and homologous proteins represent major cross-reactive allergens for more than 95% of tree pollen-, fruit-, and vegetable-allergic individuals. To study the interaction of Bet v 1 and the immune system, we characterized a Bet v 1-specific mAb, Bip 1. Soluble rBip 1 Fabs were expressed in Escherichia coli and purified by affinity chromatography using immobilized Bet v 1. Bip 1 Fabs displayed a cross-reactivity to homologous allergens comparable with that of IgE Abs from allergic patients. Preincubation of Bet v 1 with Bip 1 led to an up to fivefold increase of allergic patients' IgE binding to Bet v 1. This enhancement in IgE binding may be interpreted as stabilization of a Bet v 1 state, in which certain IgE epitopes are better applicable. It also shows that allergic patients possess IgE Abs directed against different Bet v 1 conformations. The modulation of Ab binding to a given Ag by other Abs was observed also for human Bet v 1-specific IgG Abs, and may represent a novel mechanism for the regulation of specific humoral immune responses in a complex network.