Allergen-mediated crosslinking of IgE antibodies bound to effector cells (eg, mast cells and basophils) through the high-affinity receptor for IgE

antigen-presenting cells through the high-affinity receptor for IgE (FcεRI) represents a key pathomechanism in type I allergy and many forms of asthma. Objective: We sought to establish an in vitro molecular model for the interaction of human FcεRI, IgE, and the corresponding allergen and to identify monoclonal anti-human IgE antibodies with a therapeutic profile different from previously established anti-IgE antibodies. Methods: Human FcεRI α chain, a human monoclonal allergen-specific IgE antibody (chimeric Bip 1), and the corresponding allergen, the major 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 microscopic analysis, and in vitro cultivated human basophils, we characterized mouse anti-human IgE antibodies. Results: We established a molecular model for the interaction of human IgE with FcεRI. Using this molecular model, we identified a nonanaphylactic anti-human IgE antibody fragment (Fab12), which blocked the IgE-FcεRI 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 antibodies, as well as for the depletion of IgEbearing cells. (J Allergy Clin Immunol 2001;108:409-16.)