The interaction of monomeric and complexed mouse monoclonal IgG with rat basophilic leukemia cells: a subset of IgG molecules can bind to RBL cell Fc receptors for IgG.

Rat basophilic leukemia (RBL) cells were shown to bind mouse monoclonal (MC) IgE and certain mouse monomeric IgG1 and IgG2b monoclonal antibodies (MAb) by using a haptenated sheep red blood cell (SRBC) rosetting assay. Rosette formation was antibody concentration dependent with all three immunoglobulin isotypes, but at least 100 times more IgG than IgE was required to form a similar number of rosettes. It was shown by FACS analysis and rosette formation that a subset (8/23) of the IgG MC was able to bind to RBL cells as monomers. However, the majority 15/23 did not bind or bound weakly (less than 25% rosettes) unless in the form of antigen-antibody complexes. As complexes, all IgG subclasses except IgG3 could produce rosettes with RBL cells. None of the IgM or IgA MC tested formed rosettes, even in complexed form. By inhibition studies it is demonstrated that mouse IgG1, IgG2a, and IgG2b MC bind to the same Fc receptor. Mouse IgE was only partially able to inhibit IgG-dependent rosettes at high concentrations, and none of the IgG MC were able to inhibit IgE-dependent rosettes. These results suggest that the interaction of mouse IgG is quite specific for the RBL cell FcG receptor. Because deaggregated polyclonal mouse IgG was a weak inhibitor of MC IgG sensitization of RBL cells, the results are discussed in terms of the heterogeneity and possible abnormality of some MAb.