Regulatory B cells (Breg cells) differentiate in response to inflammation and subsequently restrain excessive immune responses via the release of interleukin-10 (IL-10). However, the precise inflammatory signals governing their differentiation remain to be elucidated. Here we show that the gut microbiota promotes the differentiation of Breg cells in the spleen as well as in the mesenteric lymph nodes. Perturbation of the gut microbiome imposed either by antibiotic treatment or by changes in the sterility of housing conditions reduces the number and function of Breg cells. Following the induction of arthritis, IL-1β and IL-6 are produced only in conventionally housed mice and both cytokines directly promote Breg cell differentiation and IL-10 production. Mice lacking IL-6 receptor (IL-6R) or IL-1 receptor 1 (IL-1R1) specifically on B cells have a reduced number of IL-10-producing B cells and develop exacerbated arthritis compared to control animals. Thus, in response to inflammatory signals induced by both the gut flora and arthritis, Breg cells increase in number and restrain excessive inflammation.

SummaryRegulatory T cells (Tregs) are crucial in mediating immune homeostasis and promoting the establishment and maintenance of peripheral tolerance. However, in the context of cancer their role is more complex, and they are thought to contribute to the progress of many tumours. As cancer cells express both self-and tumour-associated antigens, Tregs are key to dampening effector cell responses, and therefore represent one of the main obstacles to effective anti-tumour responses. Suppression mechanisms employed by Tregs are thought to contribute significantly to the failure of current therapies that rely on induction or potentiation of anti-tumour responses. This review will focus on the current evidence supporting the central role of Tregs in establishing tumour-specific tolerance and promoting cancer escape. We outline the mechanisms underlying their suppressive function and discuss the potential routes of Tregs accumulation within the tumour, including enhanced recruitment, in-situ or local proliferation, and de-novo differentiation. In addition, we review some of the cancer treatment strategies that act, at least in part, to eliminate or interfere with the function of Tregs. The role of Tregs is being recognized increasingly in cancer, and controlling the function of these suppressive cells in the tumour microenvironment without compromising peripheral tolerance represents a significant challenge for cancer therapies.

Regulatory B cells (Bregs) is a term that encompasses all B cells that act to suppress immune responses. Bregs contribute to the maintenance of tolerance, limiting ongoing immune responses and reestablishing immune homeostasis. The important role of Bregs in restraining the pathology associated with exacerbated inflammatory responses in autoimmunity and graft rejection has been consistently demonstrated, while more recent studies have suggested a role for this population in other immune-related conditions, such as infections, allergy, cancer, and chronic metabolic diseases. Initial studies identified IL-10 as the hallmark of Breg function; nevertheless, the past decade has seen the discovery of other molecules utilized by human and murine B cells to regulate immune responses. This new arsenal includes other anti-inflammatory cytokines such IL-35 and TGF-β, as well as cell surface proteins like CD1d and PD-L1. In this review, we examine the main suppressive mechanisms employed by these novel Breg populations. We also discuss recent evidence that helps to unravel previously unknown aspects of the phenotype, development, activation, and function of IL-10-producing Bregs, incorporating an overview on those questions that remain obscure.

SummaryRegulatory B cells (Bregs) play a critical role in the control of autoimmunity and inflammation. IL-10 production is the hallmark for the identification of Bregs. However, the molecular determinants that regulate the transcription of IL-10 and control the Breg developmental program remain unknown. Here, we demonstrate that aryl hydrocarbon receptor (AhR) regulates the differentiation and function of IL-10-producing CD19+CD21hiCD24hiBregs and limits their differentiation into B cells that contribute to inflammation. Chromatin profiling and transcriptome analyses show that loss of AhR in B cells reduces expression of IL-10 by skewing the differentiation of CD19+CD21hiCD24hiB cells into a pro-inflammatory program, under Breg-inducing conditions. B cell AhR-deficient mice develop exacerbated arthritis, show significant reductions in IL-10-producing Bregs and regulatory T cells, and show an increase in T helper (Th) 1 and Th17 cells compared with B cell AhR-sufficient mice. Thus, we identify AhR as a relevant contributor to the transcriptional regulation of Breg differentiation.

B cells have a central role in many autoimmune diseases, including in those with renal involvement, as well as in the immunological response to kidney transplantation. The majority of studies of B cells have focused on their pathological role as antibody producers. However, these cells have broad functions in immune responses beyond immunoglobulin secretion, including antigen presentation to T cells and cytokine production. Importantly, not all B cell subsets enhance immune responses. Regulatory B (Breg) cells attenuate inflammation and contribute to the maintenance of immune tolerance. Breg cells are numerically deficient and/or dysfunctional in several autoimmune diseases that can affect the kidney, including systemic lupus erythematosus and anti-neutrophil cytoplasmic antibody-associated vasculitis, as well as in some groups of renal transplant recipients with alloimmune graft damage. B cell-targeting biologics have been trialled with promising results in diverse immune-mediated renal conditions. These therapies can affect both pro-inflammatory B cells and Breg cells potentially limiting their long-term efficacy. Future strategies might involve the modulation of inflammatory B cells in combination with the stimulation of regulatory subsets. Additionally, the monitoring of individual B cell subsets in patients may lead to the discovery of novel biomarkers that could help to predict disease relapse or progression.