UCSF

The cause of allergic disease has been an enigma for millennia. Likely due to its rarity, IgE was the final antibody isotype to be discovered when it was identified as a potent inducer of allergic reactivity. Recent work from our lab and others has revealed that the IgE B lymphocyte program is markedly different from that of other isotypes, being constrained in its generation and longevity. These constraints likely impede the development of allergy, and therefore regulatory breakdown represents a key candidate for how allergy might emerge. Previous work identified TFH-derived cytokines as well as antigen-independent signaling of the IgE BCR as important regulators of IgE responses. However, our studies revealed that these factors cannot completely explain the extent to which IgE antibody production is actively suppressed. Here, we investigated the role of antigen-driven BCR signaling, both in preventing class-switch recombination to IgE and in eliminating class-switched IgE-secreting plasma cells (PCs, this term is used throughout to encompass all antibody-secreting cells including plasmablasts). The bulk of this investigation was carried out with a variety of murine primary B cell culture assays, including experiments using cell trace violet, CRISPR, pharmacologic inhibitors, cell sorting, and Ca2+-sensitive dyes. Critical observations were validated in human B cell cultures or intact mice. In Chapter 2, we show that BCR stimulation preferentially inhibits IgE class-switch recombination (CSR) in a cell division-independent fashion by reducing ε germline transcript (GLT; a prerequisite for CSR). We found that antigen affinity associates inversely with IgE in vitro and in vivo and that antigen positively associates with selectivity for inhibition of IgE versus IgG1 CSR. Dose-dependent and IL-21-synergistic effects of BCR stimulation on IgE CSR were also observed in human cell culture. Meanwhile, in Chapter 3 we demonstrate that IgE and IgM, but not IgG, PCs activate intracellular signaling cascades following antigen exposure. Signaling through the BCR signalosome preferentially eliminates IgE PCs in an affinity-, avidity-, dose-, and time-dependent manner. Using a recently developed transgenic line, we show that selectively impairing BCR signaling in PCs increases IgE PCs in vivo. Conversely, BCR ligation by injection of αIgE or cognate antigen acutely eliminates IgE PCs. Overall, these findings establish a new layer of IgE regulation by antigen-driven BCR signaling, providing a mechanism for constraining IgE responses especially towards high-affinity or prevalent antigens.