A molecular model of type I allergy: Identification and characterization of a nonanaphylactic anti-human IgE antibody fragment that blocks the IgE-Fcepsilon RI interaction and reacts with receptor-bound IgE

Background: The IgE-mediated activation of effector cells and antigen-prese nting cells through the high-affinity receptor for IgE (Fc epsilon RI) repr esents a key pathomechanism in type 1 allergy and many forms of asthma. Objective: We sought to establish an in vitro molecular model for the inter action of human Fc epsilon RI, IgE, and the corresponding allergen and to i dentify monoclonal anti-human IgE antibodies with a therapeutic profile dif ferent from previously established anti-IgE antibodies. Methods: Human Fc epsilon RI alpha chain, a human monoclonal allergen-speci fic IgE antibody (chimeric Bip 1), and the corresponding allergen, the majo r birch pollen allergen Bet v 1, were produced as recombinant proteins and analyzed by means of circular dichroism and native overlays, respectively. Using this molecular model, as well as negative stain immunoelectron micros copic analysis, and in vitro cultivated human basophils, we characterized m ouse anti-human IgE antibodies. Results: We established a molecular model for the interaction of human IgE with FeeRl. Using this molecular model, we identified a nonanaphylactic ant i-human IgE antibody fragment (Fab12), which blocked the IgE-Fe epsilon RI interaction and reacted with effector cell-bound IgE. Conclusion: Fab12 represents a candidate molecule for therapy of atopy and asthma because it can be used for the depletion of circulating IgE antibodi es, as well as for the depletion of IgE-bearing cells.