Interaction of human IgE with Fc epsilon RI alpha exposes hidden epitopes on IgE

Background: Binding of human IgE via the f heavy-chain constant region doma in 3 (C epsilon 3) to the alpha-chain of its high affinity receptor (Fc eps ilon Rl alpha) is a key event in mediating allergic reactions. We wanted to identify epitopes within C epsilon 3 that are stable to denaturation and t o evaluate whether such structures are involved in receptor binding. The ex istence of stable epitopes would facilitate the generation of compounds tha t inhibit the IgE-Fc epsilon-Rl alpha interaction. Methods: Monoclonal anti -human IgE-antibodies against recombinant bacterially synthesized C epsilon 3, which is known to be partly misfolded, were raised in mice. These antib odies were probed for binding to native, immobilized and receptor-bound IgE , respectively, providing tools for the identification of the indicated sta ble epitopes. Results: Two of the generated antibodies (8E7, 3G9) discrimin ate between IgE in solution and IgE attached to Fc epsilon Rl alpha, pointi ng towards a steric rearrangement within C epsilon 3 induced upon receptor binding. The described antibodies represent tools for studying the mechanis m of the Fc epsilon-Fc epsilon Rl alpha interaction and may be of diagnosti c value since serum IgE from various human donors was differently recognize d by 8E7, which is indicative for naturally occurring IgE molecules with di fferent steric conformation. Conclusion: The presented data support the hyp othesis of a conformational change within ISE C epsilon 3 upon receptor bin ding by showing that monoclonal antibodies raised against recombinant C eps ilon 3 differently recognize soluble and receptor-bound IgE. The presence o f an IgE portion in sera of human donors that is rscognized by 8E7 indicate s the existence of IgE molecules in different steric conformations in human blood, which may be related to pathologic parameters. Copyright (C) 1999 S . Karger AG. Basel.