MAPPING OF THE HIGH-AFFINITY FC-EPSILON RECEPTOR-BINDING SITE TO THE 3RD CONSTANT REGION DOMAIN OF IGE

Indentification of the precise region(s) on the IgE molecule that take part in the binding of IgE to its high affinity receptor (Fc-epsilon-RI) may lead to the design of IgE analogues able to block the allergic response. To localize the Fc-epsilon-RI-binding domain of mouse IgE, we attempted to confer on human IgE, which normally does not bind to the rodent receptor, the ability to bind to the rat Fc-epsilon-RI. Employing exon shuffling, we have expressed chimeric epsilon-heavy chain genes composed of a mouse (4-hydroxy-3-nitrophenyl)acetic acid (NP)-binding V(H) domain, and human C-epsilon in which various domains were replaced by their murine counterparts. This has enabled us to test the Fc-epsilon-binding of each mouse IgE domain while maintaining the overall conformation of the molecule. All of the chimeric IgE molecules which contain the murine C-epsilon-3, bound equally to both the rodent and human receptor, as well as to monoclonal antibodies recognizing a site on IgE which is identical or very close to the Fc-epsilon-RI binding site. Deletion of the second constant region domain did not impair either the binding capacity of the mutated IgE or its ability to mediate mast cell degradation. These results assign the third epsilon domain of IgE as the principal region involved in the interaction with the Fc-epsilon-RI.