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

Background: The IgE-mediated activation of effector cells and antigen-presenting cells through the high-affinity receptor for IgE (FceRI) 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 FceRI, 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 FceRI 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 FceRI. Using this molecular model, we identified a nonanaphylactic anti-human IgE antibody fragment (Fab12), which blocked the IgE-FceRI 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.)