Paul A. Blair

CD19+CD24hiCD38hi B Cells Exhibit Regulatory Capacity in Healthy Individuals but Are Functionally Impaired in Systemic Lupus Erythematosus Patients

The immunosuppressive function of regulatory B cells has been shown in several murine models of chronic inflammation, including collagen-induced arthritis, inflammatory bowel disease, and experimental autoimmune encephalomyelitis. Despite interest in these cells, their relevance to the maintenance of peripheral tolerance in humans remains elusive. Here, we demonstrate that human CD19(+)CD24(hi)CD38(hi) B cells possessed regulatory capacity. After CD40 stimulation, CD19(+)CD24(hi)CD38(hi) B cells suppressed the differentiation of T helper 1 cells, partially via the provision of interleukin-10 (IL-10), but not transforming growth factor-beta (TGF-beta), and their suppressive capacity was reversed by the addition of CD80 and CD86 mAbs. In addition, CD19(+)CD24(hi)CD38(hi) SLE B cells isolated from the peripheral blood of systemic lupus erythematosus (SLE) patients were refractory to further CD40 stimulation, produced less IL-10, and lacked the suppressive capacity of their healthy counterparts. Altered cellular function within this compartment may impact effector immune responses in SLE and other autoimmune disorders.

Selective Targeting of B Cells with Agonistic Anti-CD40 Is an Efficacious Strategy for the Generation of Induced Regulatory T2-Like B Cells and for the Suppression of Lupus in MRL/lpr Mice

We have previously reported that IL-10+ regulatory B cells, known to play an important role in controlling autoimmunity and inflammatory disorders, are contained within the transitional 2 immature (T2) B cell pool (T2 Bregs). Therapeutic strategies facilitating their enrichment or enhancing their suppressive activity are highly attractive. In this study, we report that agonistic anti-CD40 specifically targets T2 B cells and enriches Bregs upon short-term in vitro culture. Although transfer of unmanipulated T2 B cells, isolated from mice with established lupus, failed to confer protection to diseased mice, transfer of in vitro anti-CD40-generated T2 B cells (T2-like-Bregs) significantly improved renal disease and survival by an IL-10-dependent mechanism. T2-like-Bregs readily accumulated in the spleen after transfer, suppressed Th1 responses, induced the differentiation of IL-10+CD4+T cells, and conveyed a regulatory effect to CD4+T cells. In addition, in vivo administration of agonistic anti-CD40, currently on trial for the treatment of cancer, halted and reversed established lupus. Taken together, our results suggest a novel cellular approach for the amelioration of experimental lupus.

Regulatory B cells in autoimmunity: developments and controversies

Over a decade has now passed since the concept of B cells with a regulatory function was resurrected—B cells that produce antibodies with a suppressive effect were first reported in the 1960s and suppressor B cells in the 2000s. In the meantime, some aspects of regulatory B (BREG)-cell biology have been elucidated. Not only have scientists begun to unravel the mechanism of how BREG cells suppress immune responses and which cells they target, but their ontogeny and development has also begun to be determined. To date, key roles for BREG cells have been identified in the regulation of several immune-mediated processes, including autoimmunity and responses to infectious disease and cancer. This Review highlights these advances in the study of BREG cells, and outlines what is known about their phenotype as well as their suppressive role in autoimmunity from studies in both mice and humans. A particular emphasis is placed on BREG-cell function in rheumatic diseases.

A Regulatory Feedback between Plasmacytoid Dendritic Cells and Regulatory B Cells Is Aberrant in Systemic Lupus Erythematosus.

Summary Signals controlling the generation of regulatory B (Breg) cells remain ill-defined. Here we report an “auto”-regulatory feedback mechanism between plasmacytoid dendritic cells (pDCs) and Breg cells. In healthy individuals, pDCs drive the differentiation of CD19+CD24hiCD38hi (immature) B cells into IL-10-producing CD24+CD38hi Breg cells and plasmablasts, via the release of IFN-α and CD40 engagement. CD24+CD38hi Breg cells conversely restrained IFN-α production by pDCs via IL-10 release. In systemic lupus erythematosus (SLE), this cross-talk was compromised; pDCs promoted plasmablast differentiation but failed to induce Breg cells. This defect was recapitulated in healthy B cells upon exposure to a high concentration of IFN-α. Defective pDC-mediated expansion of CD24+CD38hi Breg cell numbers in SLE was associated with altered STAT1 and STAT3 activation. Both altered pDC-CD24+CD38hi Breg cell interactions and STAT1-STAT3 activation were normalized in SLE patients responding to rituximab. We propose that alteration in pDC-CD24+CD38hi Breg cell interaction contributes to the pathogenesis of SLE.

Regulatory B cells in CVID patients fail to suppress multifunctional IFN-γ+TNF-α+CD4+ T cells differentiation

Common variable immunodeficiency (CVID) refers to primary hypogammaglobulinemia with unknown pathogenesis. Although there is evidence for intrinsic B cell defects in some CVID patient groups, various abnormalities in cytokine production by T cells in CVID patients are frequently observed. Here, we demonstrate a relationship in the production of pro-inflammatory Th1 cytokines and regulatory B cells producing IL-10 between CVID patients and healthy controls. We describe CD19(+)CD24(hi)CD38(hi)IL-10(+) regulatory B cells generated after T cell stimulation of human peripheral blood lymphocytes ex vivo are able to suppress IFN-γ(+)TNF-α(+) producing CD4(+) T cells. This process is impaired in CVID patients, who present with both low numbers of CD19(+)CD24(hi)CD38(hi)IL-10(+) B cells and increased numbers of IFN-γ(+)TNF-α(+)CD4(+) T cells. Disruption of the regulatory B cell response to T cell stimulation explains the excessive T cell activation regarded as an immunoregulatory abnormality that is a frequent finding in CVID patients.

Editorial: regulatory B cells: are we really ready to manipulate them for the benefit of patients with autoimmune diseases?

B cells are known primarily for their ability to produce antibodies and secondarily for their activation of T cells via protein-antigen presentation. However, recently it has been shown that B cells can interact with and activate other cells of the immune system, such as invariant natural killer T (iNKT) cells via lipid-antigen presentation (1). In addition, B cells can produce a vast array of cytokines in response to a variety of stimuli (2). Thus, B cells differentiating in the presence of inflammation or following priming by Th1 cells can produce high levels of proinflammatory cytokines (tumor necrosis factor , interferon), which in turn, contribute to the maintenance/efficacy of inflammatory response against specific pathogens (3). Conversely, B cells triggered by Th2 cells differentiate into B cells producing interleukin-4 (IL-4) and IL-13 (3). Recently, another subset of B cells has been described which exhibits regulatory capacity chiefly via the release of IL-10 and/or transforming growth factor (2). These B cells with suppressive functions are commonly referred to as Breg cells. Breg cells exert their regulatory functions both by secretion of cytokines, predominantly IL-10, and by direct cell–cell contact, in which CD80 and CD86 play a pivotal role. In rheumatoid arthritis (RA), the important cellular targets of Breg cell suppression include CD4 T cells, monocytes, and iNKT cells (4). Breg cells directly suppress the proliferation of effector T cells and modulate the production of proinflammatory cytokines by naive and memory T cells. Some of the targeted T cells are then converted into bona fide Treg cells that further contribute to the inhibition of proinflammatory immune responses (4). Therefore, Breg cells initiate an immunoregulatory cascade that if perturbed, at least in mice, leads to a severe arthritis. Currently, IL-10 is largely used as a surrogate marker for Breg cells. However, it is important to remember that IL-10 produced by B cells also acts as an autocrine growth/survival factor. Therefore, the enumeration of B cells producing IL-10 must be complemented with multiple functional assays in order to generate an accurate understanding of the role played by Breg cells in autoimmunity. To date, there are no definitive markers that uniquely identify Breg cells. In mice, the majority of reported Breg cells express high levels of CD1d, CD24, and CD21 but variable levels of CD5, CD10, and CD23 (2,5). Similarly, in studies in humans, high levels of expression of CD1d and CD24 are often associated with IL-10–producing B cells (6,7). While the quest for the identification of unique Breg cell markers continues, the data available in the literature suggest that Breg cells are not a single homogenous population but that various subtypes can be identified under different inflammatory conditions, including populations that share characteristics with both immature and mature B cells. In this issue of Arthritis & Rheumatology, Daien et al investigate the presence of IL-10–producing B cells (here termed B10 cells) in RA patients (8). Taking account of the fact that a variety of phenotypes have been proposed for human Breg cells, Daien et al first investigate the presence of B10 cells in peripheral blood from healthy controls. They report that B10 cells are not confined to any one of the proposed phenotypes but can be detected in several subsets following in vitro stimulation with the Toll-like receptor 9 ligand CpG. In particular, the highest percentages of B10 cells are found in CD24CD38 and CD24CD27 B cell subsets; however, given that CD24CD27 B cells make up a larger percentage of peripheral blood B cells, the authors calculate that there will be significantly higher numbers of CD24CD27 B10 cells in vivo. Interestingly, when correlating the numbers of CD24CD27 B cells with disease activity, they find that the percentClaudia Mauri, PhD, Paul A. Blair, PhD: University College London, London, UK. Address correspondence to Claudia Mauri, PhD, or Paul A. Blair, PhD, Division of Medicine, University College London, 5 University Street, London WC1E 6JF, UK. E-mail: c.mauri@ucl.ac.uk or p.blair@ucl.ac.uk. Submitted for publication March 10, 2014; accepted in revised form April 8, 2014.

Circulating and intrahepatic antiviral B cells are defective in hepatitis B

B cells are increasingly recognized as playing an important role in the ongoing control of hepatitis B virus (HBV). The development of antibodies against the viral surface antigen (HBV surface antigen [HBsAgs]) constitutes the hallmark of resolution of acute infection and is a therapeutic goal for functional cure of chronic HBV (CHB). We characterized B cells directly ex vivo from the blood and liver of patients with CHB to investigate constraints on their antiviral potential. Unexpectedly, we found that HBsAg-specific B cells persisted in the blood and liver of many patients with CHB and were enriched for T-bet, a signature of antiviral potential in B cells. However, purified, differentiated HBsAg-specific B cells from patients with CHB had defective antibody production, consistent with undetectable anti-HBs antibodies in vivo. HBsAg-specific and global B cells had an accumulation of CD21–CD27– atypical memory B cells (atMBC) with high expression of inhibitory receptors, including PD-1. These atMBC demonstrated altered signaling, homing, differentiation into antibody-producing cells, survival, and antiviral/proinflammatory cytokine production that could be partially rescued by PD-1 blockade. Analysis of B cells within healthy and HBV-infected livers implicated the combination of this tolerogenic niche and HBV infection in driving PD-1hiatMBC and impairing B cell immunity.

B Cell Activation and B Cell Tolerance

Upon exposure to an antigen, whether microbial or following vaccination, naive B cells undergo a series of activation and maturation steps that drive their differentiation into memory or plasma cells, and result in the production of antibodies that target the invading organism. Upon re-encounter with an antigen, both plasma and memory B cells promptly respond by releasing antibodies. The stochastic nature of B cell development yields cells with a diverse repertoire, a significant proportion of which recognize self-antigen at the earliest stages of differentiation. However, the immune system has evolved an exquisite series of checkpoints that discriminate self- from non-self-antigens, thus preventing undesirable activation of autoreactive B cells. In this chapter we describe the events and mechanisms by which B cells achieve a fine balance between activation and tolerance and how defects in the maintenance of this balance can increase the risk of autoimmunity.