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Monoclonal antibodies specific to the alpha-subunit of the mast cell's Fc epsilon R block IgE binding and trigger histamine release.

In an attempt to block the interactions between IgE and its receptor on mast cells (Fc epsilon R), we have established anti-Fc epsilon R monoclonal antibodies (mAb) by fusion of myeloma cells with mouse splenocytes immunized with irradiated rat basophilic leukemia (RBL) cells. Two anti-Fc epsilon R mAb were obtained (denoted 4.7 and 5.14) that could specifically bind to RBL and mast cells. This binding could be inhibited by IgE. The mAb and their F(ab')2 fragments inhibited 125I-IgE binding to RBL cell and triggered cell degranulation. The Fab' fragments, on the other hand, could only inhibit IgE binding but did not stimulate cell degranulation. Furthermore, these monovalent fragments inhibited RBL and mast cell degranulation induced by IgE-antigen complexes both in vitro and in vivo in the passive cutaneous anaphylaxis reaction. The number of mAb 4.7 and 5.14 molecules bound per RBL cells was similar to that of IgE; nevertheless, mAb 4.7 and 5.14 recognized different epitopes on the IgE receptor. Immunoprecipitation and immunoblotting analysis demonstrated that the mAb reacted with the alpha-subunit of the Fc epsilon R. Our findings establish the anti-Fc epsilon R mAb as a useful reagent for the isolation and characterization of the Fc epsilon R's alpha-subunit and the monomeric (Fab') for blocking the IgE-Fc epsilon R interactions.