Production and characterization of rabbit anti-idiotypic antibodies specific to mouse monoclonal anti-human IgE and reacting with IgE-binding factors and lymphocyte receptors for IgE.

A mouse monoclonal antibody specific to human IgE (mAb 75) was employed to immunize a rabbit to obtain anti-idiotypes (aId) bearing the internal image of human IgE determinants and reacting with IgE-binding factors (IgE-BF) and/or lymphocyte receptors for IgE (Fc epsilon R). mAb 75 was selected on the basis of inhibition assays where the binding of mAb 75 to radiolabeled IgE was blocked by IgE-BF. The latter were produced by a lymphoblastoid cell line (RPMI 8866) expressing Fc epsilon R. Sequential samples of rabbit serum, collected during the immunization period, were extensively absorbed on mouse and human Ig-Sepharose 4B. The IgG fractions of the rabbit serum displayed the following activities: (a) they reacted with 125I-labeled mAb 75 but not with other labeled mouse Ig including mAb-aIgE, (b) this binding was inhibited in a dose-dependent fashion by human IgE but not by other human Ig classes nor by heat-inactivated IgE, (c) they reacted with a polyclonal rabbit anti-human IgE and (d) they blocked the binding of 125I-labeled IgE to mAb 75. It was concluded that the rabbit IgG contained aId (RaId) bearing the internal image of heat labile determinants of human IgE. The rosetting of IgE-coated bovine erythrocytes with Fc epsilon R-bearing cells was inhibited by preincubating the receptor-bearing cells with IgG RaId or its F(ab')2 but not with normal rabbit IgG. The ability of RaId to react with IgE-BF as well as with Fc epsilon R was also shown in inhibition experiments where IgE-BF and solubilized Fc epsilon R blocked the binding of mAb 75 to RaId. Finally, Western blot analysis of human colostrum, known to contain IgE-BF, indicated that radioiodinated RaId and IgE identified the same 12-16-kDa molecules corresponding to IgE-BF. It is concluded that RaId expresses the internal image of a heat-labile determinant of IgE which is involved in the binding of IgE to IgE-BF and Fc epsilon R. An alternative interpretation is that RaId reacts with an idiotypic determinant of mAb 75 which is shared by IgE-BF and Fc epsilon R.