Structural Analysis of Human IgE Monoclonal Antibody Epitopes on Dust Mite Allergen Der P 2

Background: Human IgE (hIgE) mAbs against major mite allergen Der p 2 developed using human hybridoma technology were used for IgE epitope mapping and analysis of epitopes associated with the hIgE repertoire. Objective: We sought to elucidate the new hIgE mAb 4C8 epitope on Der p 2 and compare it to the hIgE mAb 2F10 epitope in the context of the allergenic structure of Der p 2. Methods: X-ray crystallography was used to determine the epitope of anti-Der p 2 hIgE mAb 4C8. Epitope mutants created by targeted mutagenesis were analyzed by immunoassays and in vivo using a human high-affinity IgE receptor (Fc epsilon RI alpha)-transgenic mouse model of passive systemic anaphylaxis. Results: The structure of recombinant Der p 2 with hIgE mAb 4C8 Fab was determined at 3.05 angstrom. The newly identified epitope region does not overlap with the hIgE mAb 2F10 epitope or the region recognized by 3 overlapping hIgE mAbs (1B8, 5D10, and 2G1). Compared with wild-type Der p 2, single or double 4C8 and 2F10 epitope mutants bound less IgE antibodies from allergic patients by as much as 93%. Human Fc epsilon RI alpha-transgenic mice sensitized by hIgE mAbs, which were susceptible to anaphylaxis when challenged with wild-type Der p 2, could no longer cross-link Fc epsilon RI epsilon RI to induce anaphylaxis when challenged with the epitope mutants. C onclusions: These data establish the structural basis of allergenicity of 2 hIgE mAb nonoverlapping epitopes on Der p 2, which appear to make important contributions to the hIgE repertoire against Der p 2 and provide molecular targets for future design of allergy therapeutics.