IgH isotype-specific B cell receptor expression influences B cell fate. Mus musculus breed:C57BL/6 x 129

Immunoglobulin heavy chain (IgH) isotypes (e.g. IgM, IgG and IgE) are generated as secreted/soluble antibodies (sIg) or as membrane-bound (mIg) B cell receptors (BCR) through alternative RNA splicing. IgH isotype dictates soluble antibody function, but how mIg isotype influences B cell behavior is not well defined. We examined IgH isotype-specific BCR function by analyzing naturally switched B cells from wild type mice, as well as by engineering polyclonal Ighγ1/γ1 and Ighε/ε mice, which initially produce IgG1 or IgE from their respective native genomic configurations. We found that B cells from wild type mice, as well as Ighγ1/γ1 and Ighε/ε mice, produce transcripts that generate IgM, IgG1, and IgE in an alternative splice form bias hierarchy, regardless of cell stage. In this regard, we found that mIgμ>mIgγ1>mIgε—and that these expression differences influence respective BCR densities and developmental fitness. Restrained B cell development from Ighγ1/γ1 and Ighε/ε mice was proportional to sIg/mIg ratios, and was rescued by enforced expression of the respective mIgs. In addition, artificially enhancing BCR signal strength permitted IgE+ memory B cells—which essentially do not exist under normal conditions—to provide long-lived memory function, suggesting that quantitative BCR signal weakness contributes to restraint of IgE B cell responses. Thus, our results indicate that IgH isotype-specific mIg/BCR dosage may play a larger role in B cell fate than previously anticipated.