B cells are regarded for their capacity to produce antibody. However, recent advances in B cell biology have capitalized on old findings and demonstrated that B cells also release a broad variety of cytokines. As with T helper cells, B cells can be classified into subsets according to the cytokine milieu that they produce. One functional B cell subset, regulatory B cells (Bregs), has recently been shown to contribute to the maintenance of the fine equilibrium required for tolerance. Bregs restrain the excessive inflammatory responses that occur during autoimmune diseases or that can be caused by unresolved infections. Pivotal to Breg function is interleukin-10 (IL-10), which inhibits proinflammatory cytokines and supports regulatory T cell differentiation. This review reports and discusses the factors that are important for Breg differentiation and for their effector function in both mouse and human.

Immune Regulatory Function of B Cells

https://www.cell.com/immunity/pdf/S1074-7613(15)00134-X.pdf

Regulatory B Cells: Origin, Phenotype, and Function

These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer-reviewed by leading experts in the field, making this an essential research companion.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (second edition)

Interleukin-10 (IL-10)-producing regulatory B (Breg) cells suppress autoimmune disease, and increased numbers of Breg cells prevent host defense to infection and promote tumor growth and metastasis by converting resting CD4(+) T cells to regulatory T (Treg) cells. The mechanisms mediating the induction and development of Breg cells remain unclear. Here we show that IL-35 induces Breg cells and promotes their conversion to a Breg subset that produces IL-35 as well as IL-10. Treatment of mice with IL-35 conferred protection from experimental autoimmune uveitis (EAU), and mice lacking IL-35 (p35 knockout (KO) mice) or defective in IL-35 signaling (IL-12Rβ2 KO mice) produced less Breg cells endogenously or after treatment with IL-35 and developed severe uveitis. Adoptive transfer of Breg cells induced by recombinant IL-35 suppressed EAU when transferred to mice with established disease, inhibiting pathogenic T helper type 17 (TH17) and TH1 cells while promoting Treg cell expansion. In B cells, IL-35 activates STAT1 and STAT3 through the IL-35 receptor comprising the IL-12Rβ2 and IL-27Rα subunits. As IL-35 also induced the conversion of human B cells into Breg cells, these findings suggest that IL-35 may be used to induce autologous Breg and IL-35(+) Breg cells and treat autoimmune and inflammatory disease.

Interleukin-35 induces regulatory B cells that suppress autoimmune disease.

The relevance of regulatory B cells in the maintenance of tolerance in healthy individuals or in patients with immune disorders remains understudied. In healthy individuals, CD19(+)CD24(hi)CD38(hi) B cells suppress CD4(+)CD25(-) T cell proliferation as well as the release of interferon-γ and tumor necrosis factor-α by these cells; this suppression is partially mediated through the production of interleukin-10 (IL-10). We further elucidate the mechanisms of suppression by CD19(+)CD24(hi)CD38(hi) B cells. Healthy CD19(+)CD24(hi)CD38(hi) B cells inhibited naive T cell differentiation into T helper 1 (T(H)1) and T(H)17 cells and converted CD4(+)CD25(-) T cells into regulatory T cells (T(regs)), in part through the production of IL-10. In contrast, CD19(+)CD24(hi)CD38(hi) B cells from patients with rheumatoid arthritis (RA) failed to convert CD4(+)CD25(-) T cells into functionally suppressive T(regs) or to curb T(H)17 development; however, they maintained the capacity to inhibit T(H)1 cell differentiation. Moreover, RA patients with active disease have reduced numbers of CD19(+)CD24(hi)CD38(hi) B cells in peripheral blood compared with either patients with inactive disease or healthy individuals. These results suggest that in patients with active RA, CD19(+)CD24(hi)CD38(hi) B cells with regulatory function may fail to prevent the development of autoreactive responses and inflammation, leading to autoimmunity.

CD19+CD24hiCD38hi B cells maintain regulatory T cells while limiting TH1 and TH17 differentiation.

IL-10–producing B cells, also known as regulatory B cells (Bregs), play a key role in controlling autoimmunity. In this study, we report that chimeric mice specifically lacking IL-10–producing B cells (IL-10−/−B cell) developed an exacerbated arthritis compared with chimeric wild-type (WT) B cell mice. A significant decrease in the absolute numbers of Foxp3 regulatory T cells (Tregs), in their expression level of Foxp3, and a marked increase in inflammatory Th1 and Th17 cells were detected in IL-10−/− B cell mice compared with WT B cell mice. Reconstitution of arthritic B cell deficient (μMT) mice with different B cell subsets revealed that the ability to modulate Treg frequencies in vivo is exclusively restricted to transitional 2 marginal zone precursor Bregs. Moreover, transfer of WT transitional 2 marginal zone precursor Bregs to arthritic IL-10−/− mice increased Foxp3+ Tregs and reduced Th1 and Th17 cell frequencies to levels measured in arthritic WT mice and inhibited inflammation. In vitro, IL-10+/+ B cells established longer contact times with arthritogenic CD4+CD25− T cells compared with IL-10−/− B cells in response to Ag stimulation, and using the same culture conditions, we observed upregulation of Foxp3 on CD4+ T cells. Thus, IL-10–producing B cells restrain inflammation by promoting differentiation of immunoregulatory over proinflammatory T cells.

Mice Lacking Endogenous IL-10–Producing Regulatory B Cells Develop Exacerbated Disease and Present with an Increased Frequency of Th1/Th17 but a Decrease in Regulatory T Cells

Contrasting results have emerged from studies performed using IL-12p35(-/-) mice. Animals lacking the IL-12p35 subunit can either be protected from or develop exacerbated autoimmune diseases, intracellular infections, and delayed-type hypersensitivity responses. In this study, we report that mice lacking the IL-12p35 subunit develop a significantly milder Ag-induced arthritis compared with wild-type (WT) mice. Lack of severe inflammation is accompanied by an increase in the mRNA levels of the Ebi-3 and p28 subunits and increased secretion of IL-27 and IL-10. This anti-inflammatory environment contributed to increased differentiation of regulatory T and B cells with intact suppressive function. Furthermore, IL-12p35(-/-) mice display reduced numbers of Th17 cells compared with WT arthritic mice. Neutralization of IL-27, but not the systemic administration of IL-12, restored inflammation and Th17 to levels seen in WT mice. The restoration of disease phenotype after anti-IL-27 administration indicates that the IL-12p35 subunit acts as negative regulator of the developing IL-27 response in this model of arthritis.

Rita Vasconcellos

Papers

Mice Lacking Endogenous IL-10–Producing Regulatory B Cells Develop Exacerbated Disease and Present with an Increased Frequency of Th1/Th17 but a Decrease in Regulatory T Cells

IL-12p35 Subunit Contributes to Autoimmunity by Limiting IL-27–Driven Regulatory Responses