An in vitro Model for the Allergen–IgE–FcεRI Interaction

Abstract

Background: The interaction of immune complexes consisting of allergens and allergen–specific IgE with the high–affinity Fcε receptor represents the key event in the induction of symptoms in type I allergic individuals. Immediate–type symptoms result from the release of biological mediators due to allergen–induced cross–linking of FcεRI receptors on mast cells and basophils, whereas FcεRI–mediated presentation of allergen–IgE complexes may contribute to late–phase symptoms through enhanced T cell activation. The interaction of allergens/allergen–specific IgE/FcεRI represents, therefore, an important target for therapeutic intervention strategies in type I allergy. Methods and Results: A molecular model of the allergen–IgE–FcεRI interaction was established. It consists of recombinant purified Bet v 1, the major birch pollen allergen, a chimeric Bet v 1 specific monoclonal IgE antibody, and the baculovirus–expressed purified human alpha chain of FcεRI. The chimeric Bet v 1–specific IgE antibody consists of the light chain and the heavy chain variable region of a mouse monoclonal Bet v 1 specific antibody, Bip 1, and the constant region of human IgE. The interaction of rBet v 1, chimeric Bip 1, and human alpha chain was investigated by overlay experiments. Nitrocellulose–immobilized recombinant alpha chains was incubated with chimeric Bip 1 and, for control purposes, with mouse–derived Bip 1. Bound chimeric Bip 1 was detected with ¹²⁵I–labeled rBet v 1. The specific interaction of rBetv 1, chimeric Bip 1, and recombinant human alpha chain is demonstrated. We thus establish a molecular model of the allergen/IgE/alpha chain interaction. The usefulness of the described in vitro system is exemplified by the identification of a mouse monoclonal antihuman IgE antibody which blocked the IgE–alpha chain interaction. Conclusions: The module system consisting of rBet v 1, chimeric Bip 1, and recombinant alpha chain may be used for the identification of competitors of the allergic effector reaction by means of high throughput screening of compounds or by combinatorial chemistry.