Characterization of new rat anti-mouse IgE monoclonals and their use along with chimeric IgE to further define the site that interacts with FcϵRII and FcϵRI

Three rat monoclonal antibodies specific for mouse IgE (C12B9, 23G3, and B1E3) were established by using monoclonal anti-DNP mouse IgE (mIgE) as immunogen. These antibodies, as well as a fourth, (R1E4) were characterized. It was found that one antibody (C12B9) recognizes an allotypic determinant (Igh-7a) found on the Cϵ, chain of mIgE. Antibody cross-blocking studies and epitope mapping studies using recombinant mIgE indicated that 3 antibodies (C12B9, R1E4 and 23G3) were directed against the Cϵ3 domain while one (B1E3) was directed against the Cϵ4 domain. A highly specific sandwich RIA for mIgE was developed using these antibodies. Use of these monoclonal anti-mIgE antibodies in conjunction with recombinant chimeric mIgE-human IgG1 molecules, demonstrated that the Cϵ3 domain is important in the binding of mIgE to the murine B cell FcϵRII as well as to the murine mast cell FcϵRI. The presence of the Cϵ4 domain influenced the binding of the recombinant IgE to the FcϵRII; in contrast to the Cϵ4 domain had no effect on binding to the FcϵRI.