5 research outputs found
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B cell receptor signaling is a critical regulator of IgE responses
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
The p300 and CBP Transcriptional Coactivators Are Required for β-Cell and α-Cell Proliferation
MicroRNA-directed pathway discovery elucidates an miR-221/222-mediated regulatory circuit in class switch recombination.
MicroRNAs (miRNAs, miRs) regulate cell fate decisions by post-transcriptionally tuning networks of mRNA targets. We used miRNA-directed pathway discovery to reveal a regulatory circuit that influences Ig class switch recombination (CSR). We developed a system to deplete mature, activated B cells of miRNAs, and performed a rescue screen that identified the miR-221/222 family as a positive regulator of CSR. Endogenous miR-221/222 regulated B cell CSR to IgE and IgG1 in vitro, and miR-221/222-deficient mice exhibited defective IgE production in allergic airway challenge and polyclonal B cell activation models in vivo. We combined comparative Ago2-HITS-CLIP and gene expression analyses to identify mRNAs bound and regulated by miR-221/222 in primary B cells. Interrogation of these putative direct targets uncovered functionally relevant downstream genes. Genetic depletion or pharmacological inhibition of Foxp1 and Arid1a confirmed their roles as key modulators of CSR to IgE and IgG1
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Interferon gamma constrains type 2 lymphocyte niche boundaries during mixed inflammation.
Allergic immunity is orchestrated by group 2 innate lymphoid cells (ILC2s) and type 2 helper T (Th2) cells prominently arrayed at epithelial- and microbial-rich barriers. However, ILC2s and Th2 cells are also present in fibroblast-rich niches within the adventitial layer of larger vessels and similar boundary structures in sterile deep tissues, and it remains unclear whether they undergo dynamic repositioning during immune perturbations. Here, we used thick-section quantitative imaging to show that allergic inflammation drives invasion of lung and liver non-adventitial parenchyma by ILC2s and Th2 cells. However, during concurrent type 1 and type 2 mixed inflammation, IFNÎł from broadly distributed type 1 lymphocytes directly blocked both ILC2 parenchymal trafficking and subsequent cell survival. ILC2 and Th2 cell confinement to adventitia limited mortality by the type 1 pathogen Listeria monocytogenes. Our results suggest that the topography of tissue lymphocyte subsets is tightly regulated to promote appropriately timed and balanced immunity