TLR-9 Activation of Marginal Zone B Cells in Lupus Mice Regulates Immunity Through Increased IL-10 Production

Regulatory functions of innate-like B cells

Innate-like B cells (ILBs) are heterogeneous populations of unconventional B cells with innate sensing and responding properties. ILBs in mice are composed of B1 cells, marginal zone (MZ) B cells and other related B cells. ILBs maintain natural IgM levels at steady state, and after innate activation, they can rapidly acquire immune regulatory activities through the secretion of natural IgM and IL-10. Thus, ILBs constitute an important source of IL-10-producing regulatory B cells (Bregs), which have been shown to play critical roles in autoimmunity, inflammation and infection. The present review highlights the latest advances in the field of ILBs and focuses on their regulatory functions. Understanding the regulatory activities of ILBs and their underlying mechanisms could open new avenues in manipulating their functions in inflammatory, infectious and other relevant diseases.

Regulatory B cells from hilar lymph nodes of tolerant mice in a murine model of allergic airway disease are CD5+, express TGF-β, and co-localize with CD4+Foxp3+ T cells

In a biphasic, ovalbumin (OVA)-induced murine asthma model where allergic airway disease is followed by resolution and the development of local inhalational tolerance (LIT), transforming growth factor (TGF)-β-expressing CD5(+) B cells were selectively expanded locally in hilar lymph nodes (HLN) of LIT mice. LIT HLN CD5(+) B cells, but not LIT HLN CD5(-) B cells, induced expression of Foxp3 in CD4(+)CD25(-) T cells in vitro. These CD5(+) regulatory B cells (Breg) and CD4(+)Foxp3(+) T cells demonstrated similar increases in expression of chemokine receptors (CXCR4 and CXCR5) and co-localized in HLN B cell zones of LIT mice. The adoptive transfer of LIT HLN CD5(+) B cells, but not LIT HLN CD5(-) B cells, increased the number of CD4(+)Foxp3(+) T cells in the lung and inhibited airway eosinophilia in this OVA model. Thus, Breg in HLNs of LIT mice reside in a CD5(+) TGF-β-producing subpopulation and co-localize with CD4(+)Foxp3(+) T cells.

The role of B lymphocytes in the progression from autoimmunity to autoimmune disease

Autoimmunity, defined as the presence of autoreactive T and/or B lymphocytes in the periphery, is a frequent and probably even physiological condition. It is mainly caused by the fact that the central tolerance mechanisms, which are responsible for counter-selection of autoreactive lymphocytes, are not perfect and thus a limited number of these autoreactive cells can mature and enter the periphery. Nonetheless, autoreactive cells do not lead automatically to autoimmune disease as evidenced by a multitude of experimental and human data sets. Interestingly, the progression from autoimmunity to autoimmune disease is not only determined by the degree of central tolerance leakage and thus the amount of autoreactive lymphocytes in the periphery, but also by peripheral mechanism of activation and control of the autoreactive cells. In this review, we discuss the contribution of peripheral B lymphocytes in this process, ranging from activation of T cells and epitope spreading to control of the autoimmune process by regulatory mechanisms. We also discuss the parallels with the role of B cells in the induction and control of alloimmunity in the context of organ transplantation, as more precise knowledge of the pathogenic antigens and time of initiation of the immune response in allo- versus auto-immunity allows better dissection of the exact role of B cells. Since peripheral mechanisms may be easier to modulate than central tolerance, a more thorough understanding of the role of peripheral B cells in the progression from autoimmunity to autoimmune disease may open new avenues for treatment and prevention of autoimmune disorders.

Regulation of B-cell responses by Toll-like receptors

The discovery of host-encoded gene products that sense molecular patterns in infectious microbes, and the demonstration of their role in triggering innate and adaptive immune responses, has been a key milestone in our understanding of immunology. Twenty-three years after Janeway first outlined the fundamental concepts of the 'pattern recognition' model, and 15 years since the identification of Toll-like receptors (TLRs) as pattern recognition receptors (PRRs), new insights continue to be revealed, and questions remain. For example, innate immune responses to microbes that are mediated by PRRs have historically been viewed as the domain of innate immune cell populations such as dendritic cells and macrophages. New evidence, however, has pointed to the role of B-cell-intrinsic TLR activation in shaping antibody responses. These studies have revealed that TLRs regulate a complex transcriptional network that controls multiple steps in the development of antigen-specific antibodies. This review covers these recent developments regarding the role of TLRs in B-cell gene expression and function in vitro and in vivo, and highlights the remaining challenges in the field, with particular emphasis on the role of TLRs in antibody responses to viral infection. A more complete understanding of how TLRs regulate antibody responses will lead to improved vaccine design.

Autoimmunity in wiskott-Aldrich syndrome: an unsolved enigma

Wiskott-Aldrich Syndrome (WAS) is a severe X-linked Primary Immunodeficiency that affects 1-10 out of 1 million male individuals. WAS is caused by mutations in the WAS Protein (WASP) expressing gene that leads to the absent or reduced expression of the protein. WASP is a cytoplasmic protein that regulates the formation of actin filaments in hematopoietic cells. WASP deficiency causes many immune cell defects both in humans and in the WAS murine model, the Was(-/-) mouse. Both cellular and humoral immune defects in WAS patients contribute to the onset of severe clinical manifestations, in particular microthrombocytopenia, eczema, recurrent infections, and a high susceptibility to develop autoimmunity and malignancies. Autoimmune diseases affect from 22 to 72% of WAS patients and the most common manifestation is autoimmune hemolytic anemia, followed by vasculitis, arthritis, neutropenia, inflammatory bowel disease, and IgA nephropathy. Many groups have widely explored immune cell functionality in WAS partially explaining how cellular defects may lead to pathology. However, the mechanisms underlying the occurrence of autoimmune manifestations have not been clearly described yet. In the present review, we report the most recent progresses in the study of immune cell function in WAS that have started to unveil the mechanisms contributing to autoimmune complications in WAS patients.

Integration of B cell responses through Toll-like receptors and antigen receptors

Unlike other immune cells, B cells express both an antigen-specific B cell receptor (BCR) and Toll-like receptors (TLRs). Dual BCR and TLR engagement can fine-tune functional B cell responses, directly linking cell-intrinsic innate and adaptive immune programmes. Although most data regarding B cell-specific functions of the TLR signalling pathway have been obtained in mice, the discovery of patients with a deficiency in this pathway has recently provided an insight into human B cell responses. Here, we highlight the importance of the integration of signalling pathways downstream of BCRs and TLRs in modulating B cell function, focusing when possible on B cell-intrinsic roles.

Induction and maintenance of protective CD8+ T cells against malaria liver stages: implications for vaccine development

CD8+ T cells against malaria liver stages represent a major protective immune mechanism against infection. Following induction in the peripheral lymph nodes by dendritic cells (DCs), these CD8+ T cells migrate to the liver and eliminate parasite infected hepatocytes. The processing and presentation of sporozoite antigen requires TAP mediated transport of major histocompatibility complex class I epitopes to the endoplasmic reticulum. Importantly, in DCs this process is also dependent on endosome-mediated cross presentation while this mechanism is not required for epitope presentation on hepatocytes. Protective CD8+ T cell responses are strongly dependent on the presence of CD4+ T cells and the capacity of sporozoite antigen to persist for a prolonged period of time. While human trials with subunit vaccines capable of inducing antibodies and CD4+ T cell responses have yielded encouraging results, an effective anti-malaria vaccine will likely require vaccine constructs designed to induce protective CD8+ T cells against malaria liver stages.

B cells exposed to enterobacterial components suppress development of experimental colitis

BACKGROUND

B cells positively contribute to immunity by antigen presentation to CD4(+) T cells, cytokine production, and differentiation into antibody secreting plasma cells. Accumulating evidence implies that B cells also possess immunoregulatory functions closely linked to their capability of IL-10 secretion.

METHODS

Colitis development was followed in CD4(+) CD25(-) T cell transplanted SCID mice co-transferred with B cells exposed to an enterobacterial extract (ebx-B cells). B and T cell cytokine expression was measured by flow cytometry and enzyme-linked immunosorbent assay (ELISA).

RESULTS

We demonstrate that splenic B cells exposed to ebx produce large amounts of IL-10 in vitro and express CD1d and CD5 previously known to be associated with regulatory B cells. In SCID mice transplanted with colitogenic CD4(+) CD25(-) T cells, co-transfer of ebx-B cells significantly suppressed development of colitis. Suppression was dependent on B cell-derived IL-10, as co-transfer of IL-10 knockout ebx-B cells failed to suppress colitis. Ebx-B cell-mediated suppression of colitis was associated with a decrease in interferon gamma (IFN-γ)-producing T(H) 1 cells and increased frequencies of Foxp3-expressing T cells.

CONCLUSIONS

These data demonstrate that splenic B cells exposed to enterobacterial components acquire immunosuppressive functions by which they can suppress development of experimental T cell-mediated colitis in an IL-10-dependent way.

Essential role for B cells in transplantation tolerance

T lymphocytes are the primary targets of immunotherapy in clinical transplantation. However, B lymphocytes are detrimental to graft survival by virtue of their capacity to present antigen to T cells via the indirect pathway of allorecognition and the generation of donor specific alloantibody. Furthermore, the long-term survival of organ allografts remains challenged by chronic rejection, a process in which activated B cells have been found to play a significant role. Therefore, the achievement of transplantation tolerance will likely require induction of both T and B cell tolerance to alloantigens. Moreover, human and animal investigations have shown that subsets of B cells, Transitional and Regulatory, are inherently tolerogenic. Developing therapeutic strategies that exploit these populations may be key to achieving transplantation tolerance. In this review we describe the current evidence for the essential role of B cells in transplant tolerance and discuss emerging B cell directed strategies to achieve allograft tolerance.

Regulatory T-cells: diverse phenotypes integral to immune homeostasis and suppression

Regulatory T-cells (T(REG)) are diverse populations of lymphocytes that regulate the adaptive immune response in higher vertebrates. T(REG) delete autoreactive T-cells, induce tolerance, and dampen inflammation. T(REG) cell deficiency in humans (i.e., IPEX [Immunodysregulation, Polyendocrinopathy and Enteropathy, X-linked syndrome]) and animal models (e.g., "Scurfy" mouse) is associated with multisystemic autoimmune disease. T(REG) in humans and laboratory animal species are similar in type and regulatory function. A molecular marker of and the cell lineage specification factor for T(REG) is FOXP3, a forkhead box transcription factor. CD4(+) T(REG) are either natural (nT(REG)), which are thymus-derived CD4(+)CD25(+)FOXP3(+) T-cells, or inducible (i.e., Tr1 cells that secrete IL-10, Th3 cells that secrete TGF-β and IL-10, and Foxp3(+) Treg). The proinflammatory Th17 subset has been a major focus of research. T(H)17 CD4(+) effector T-cells secrete IL-17, IL-21, and IL-22 in autoimmune and inflammatory disease, and are dynamically balanced with T(REG) cell development. Other lymphocyte subsets with regulatory function include: inducible CD8(+) T(REG), CD3(+)CD4(-)CD8(-) T(REG) (double-negative), CD4(+)Vα14(+) (NKT(REG)), and γδ T-cells. T(REG) have four regulatory modes of action: secretion of inhibitory cytokines (e.g., IL-10 and TGF-β), granzyme-perforin-induced apoptosis of effector lymphocytes, depriving effector T-cells of cytokines leading to apoptosis, or inhibition of dendritic cell function. The role of T(REG) in mucosal sites, inflammation/infection, pregnancy, and cancer as well as a review of T(REG) as a modulatory target in drug development will be covered.

Immune regulatory function of B cells

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.

B Cell in Autoimmune Diseases

The role of B cells in autoimmune diseases involves different cellular functions, including the well-established secretion of autoantibodies, autoantigen presentation and ensuing reciprocal interactions with T cells, secretion of inflammatory cytokines, and the generation of ectopic germinal centers. Through these mechanisms B cells are involved both in autoimmune diseases that are traditionally viewed as antibody mediated and also in autoimmune diseases that are commonly classified as T cell mediated. This new understanding of the role of B cells opened up novel therapeutic options for the treatment of autoimmune diseases. This paper includes an overview of the different functions of B cells in autoimmunity; the involvement of B cells in systemic lupus erythematosus, rheumatoid arthritis, and type 1 diabetes; and current B-cell-based therapeutic treatments. We conclude with a discussion of novel therapies aimed at the selective targeting of pathogenic B cells.

Differential impact of Toll-like receptor signaling on distinct B cell subpopulations

B cells exhibit a range of functional responses following TLR engagement including immunoglobulin and cytokine production, proliferation, antigen presentation and migration. However, B cell intrinsic TLR responses appear to be precisely programmed based upon the developmental stage of the cell. B cell subpopulations classified as innate immune cells including marginal zone and B-1 B cells exhibit robust responses to TLR stimulation. In contrast, activation of other B cell subsets is constrained via a variety of developmentally regulated events. In this review we provide an overview of TLR responses in murine and human B cells and specifically highlight patterns of TLR expression and developmentally regulated functional responses.

B cell-derived IL-10 does not regulate spontaneous systemic autoimmunity in MRL.Fas(lpr) mice

B cells contribute to the pathogenesis of chronic autoimmune disorders, like systemic lupus erythematosus (SLE), via multiple effector functions. However, B cells are also implicated in regulating SLE and other autoimmune syndromes via release of IL-10. B cells secreting IL-10 were termed "Bregs" and were proposed as a separate subset of cells, a concept that remains controversial. The balance between pro- and anti-inflammatory effects could determine the success of B cell-targeted therapies for autoimmune disorders; therefore, it is pivotal to understand the significance of B cell-secreted IL-10 in spontaneous autoimmunity. By lineage-specific deletion of Il10 from B cells, we demonstrated that B cell-derived IL-10 is ineffective in suppressing the spontaneous activation of self-reactive B and T cells during lupus. Correspondingly, severity of organ disease and survival rates in mice harboring Il10-deficient B cells are unaltered. Genetic marking of cells that transcribe Il10 illustrated that the pool of IL-10-competent cells is dominated by CD4 T cells and macrophages. IL-10-competent cells of the B lineage are rare in vivo and, among them, short-lived plasmablasts have the highest frequency, suggesting an activation-driven, rather than lineage-driven, phenotype. Putative Breg phenotypic subsets, such as CD1d(hi)CD5(+) and CD21(hi)CD23(hi) B cells, are not enriched in Il10 transcription. These genetic studies demonstrated that, in a spontaneous model of murine lupus, IL-10-dependent B cell regulation does not restrain disease and, thus, the pathogenic effects of B cells are not detectably counterbalanced by their IL-10-dependent regulatory functions.

B cells and autoimmunity

There is a growing appreciation for the role for B cells in autoimmune disorders in which inflammation is driven by T cells, in addition to the well-established role for B cells in autoimmune disorders characterized by pathogenic auto-antibodies. Current information on tolerance checkpoints in B cells, B cell depletion, BAFF blockade, regulatory B cells and clonal ignorance mediated by the SIAE/Siglec pathway will be reviewed.

Maturation and function of human dendritic cells are regulated by B lymphocytes

Mature dendritic cells (DCs) are stimulators of T-cell immune response, whereas immature DCs support T-cell tolerance. Murine B cells can inhibit the production of IL-12 by DCs and thereby hinder the inflammatory response. Notwithstanding the importance of this modulation, only a few studies are available in humans. Here, we have developed an in vitro model of cocultures to assess its significance. We establish that human activated B cells restrained the development of monocytes into immature DCs and their differentiation into mature DCs. In addition, they decreased the density of HLA-DR from mature DCs, the expression of CD80 and CD86 coactivation molecules, the production of IL-12p70 required for antigen presentation and Th1 differentiation, and inhibited the DC-induced T-cell proliferation. These modulations were mediated by CD19(+)IgD(low)CD38(+)CD24(low)CD27(-) B cells and needed direct cell-to-cell contacts that involved CD62L for the control of CD80 and CD86 expression and a soluble factor for the control of IL-12 production. Moreover, mature DCs from patients with systemic lupus erythematosus displayed insensitivity to the regulation of IL-12. Overall, it appears that human B cells can regulate DC maturation and function and that inefficient B-cell regulation may influence an improper balance between an effector inflammatory response and tolerance induction.

Immune-regulatory mechanisms in systemic autoimmune and rheumatic diseases

Systemic autoimmune and rheumatic diseases (SAIRDs) are thought to develop due to the failure of autoimmune regulation and tolerance. Current therapies, such as biologics, have improved the clinical results of SAIRDs; however, they are not curative treatments. Recently, new discoveries have been made in immune tolerance and inflammation, such as tolerogenic dendritic cells, regulatory T and B cells, Th 17 cells, inflammatory and tolerogenic cytokines, and intracellular signaling pathways. They lay the foundation for the next generation of the therapies beyond the currently used biologic therapies. New drugs should target the core processes involved in disease mechanisms with the aim to attain complete cure combined with safety and low costs compared to the biologic agents. Re-establishment of autoimmune regulation and tolerance in SAIRDs by the end of the current decade should be the final and realistic target.

Primary B cell repertoire remodeling to achieve humoral transplantation tolerance

The current mainstay of immunotherapy in clinical transplantation is T lymphocyte directed. However, it has long been appreciated that the emergence of an alloimmune response mounted by the B lymphocyte compartment and detectable as donor-specific antibodies is a critical challenge to long-term graft survival. Thus, achieving robust transplantation tolerance will require induction of tolerance in both the T- and B-cell compartments. Here we propose that the natural developmental propensity of the B-lymphocyte compartment acquisition of tolerance to self-antigens can be recapitulated to achieve humoral transplantation tolerance. It is our contention B-lymphocyte directed induction immunotherapy would be an important component of emerging strategies for induction of Transplantation tolerance.

In vivo administration of ligands for chicken toll-like receptors 4 and 21 induces the expression of immune system genes in the spleen

Toll-like receptors (TLRs) are a group of conserved proteins that play an important role in pathogen recognition in addition to the initiation and regulation of innate and adaptive immune responses. To date, several TLRs have been identified in chickens, each recognizing different ligands. TLR stimulation in chickens has been shown to play a role in host-responses to pathogens. However, the mechanisms through which TLRs modulate the chicken immune system have not been well examined. The present study was conducted to characterize the kinetics of responses to TLR4 and TLR21 stimulation in chickens following intramuscular injections of their corresponding ligands, lipopolysaccharide (LPS) and CpG oligodeoxynucleotides (ODNs), respectively. To this end, relative expression of cytokine genes in the spleen was determined at 2, 6, 12 and 24 h after injection of TLR ligands. The results indicated that LPS strongly induced the up-regulation of some immune system genes early on in the response to treatment, including interferon (IFN)-γ, interleukin (IL)-10, and IL-1β. Furthermore, treatment with CpG ODN promoted the up-regulation of major histocompatibility complex (MHC)-II, IFN-γ and IL-10. The response to CpG ODN appeared to be somewhat delayed compared to the response to LPS. Moreover, we found a significant increase in IFN-α gene expression in response to LPS but not CpG ODNs. Future studies may be aimed to further characterize the molecular mechanisms of TLR activation in chickens or to exploit TLR agonists as vaccine adjuvants.

Inhibition and promotion of tumor growth with adeno-associated virus carcinoembryonic antigen vaccine and Toll-like receptor agonists

Carcinoembryonic antigen (CEA) is a cancer vaccines target. Several feature of recombinant adeno-associated virus (rAAV) are attractive for vaccine applications. Combining other viral vector vaccines with Toll like receptor (TLR) agonists enhances antitumor immunity. Wild-type and CEA transgenic (Tg) mice were immunized with rAAV expressing CEA, the TLR9 agonist, ODN1826, and the TLR7 agonist, imiquimod. Mice were challenged with MC38 colon tumor cells and MC38 cells expressing CEA. rAAV-CEA immunization combined with ODN1826 or imiquimod enhanced CEA-specific T-helper-1 immunity and protected against tumor challenge in wild-type but not in CEA-Tg mice. In contrast, immunization with rAAV-CEA in CEA-Tg mice could abrogate the antitumor effects of ODN1826 and promote tumor growth. Compared to wild-type, CEA-Tg mice were characterized by a greater myeloid suppressor cell and T-helper 2 response to TLR agonists and to syngeneic tumors. Depleting PDCA1+ plasmacytoid dendritic cells and Gr1+ myeloid cells increased anti-CEA immune responses in CEA-Tg mice to rAAV-CEA-ODN1826 immunization; depleting CD25+ T cells did not. There are differences in the response of wild-type and CEA-Tg mice to rAAV-CEA, TLR agonists, and syngeneic tumor. In CEA-Tg mice tumor growth can be promoted with rAAV-CEA and TLR agonists. Dendritic and myeloid cells play a regulatory role.

Regulatory B cells are identified by expression of TIM-1 and can be induced through TIM-1 ligation to promote tolerance in mice

T cell Ig domain and mucin domain protein 1 (TIM-1) is a costimulatory molecule that regulates immune responses by modulating CD4+ T cell effector differentiation. However, the function of TIM-1 on other immune cell populations is unknown. Here, we show that in vivo in mice, TIM-1 is predominantly expressed on B rather than T cells. Importantly, TIM-1 was expressed by a large majority of IL-10-expressing regulatory B cells in all major B cell subpopulations, including transitional, marginal zone, and follicular B cells, as well as the B cell population characterized as CD1d(hi)CD5+. A low-affinity TIM-1-specific antibody that normally promotes tolerance in mice, actually accelerated (T cell-mediated) immune responsiveness in the absence of B cells. TIM-1+ B cells were highly enriched for IL-4 and IL-10 expression, promoted Th2 responses, and could directly transfer allograft tolerance. Both cytokine expression and number of TIM-1+ regulatory B cells (Bregs) were induced by TIM-1-specific antibody, and this was dependent on IL-4 signaling. Thus, TIM-1 is an inclusive marker for IL-10+ Bregs that can be induced by TIM-1 ligation. These findings suggest that TIM-1 may be a novel therapeutic target for modulating the immune response and provide insight into the signals involved in the generation and induction of Bregs.

L2pB1: a new player in autoimmunity

L2pB1 cells (PD-L2positive B1 cells) are a newly discovered subpopulation of B1 B cells. L2pB1 cells are noted for the expression of PD-L2 (CD273, B7-DC), a ligand for the inhibitory receptor PD-1, which distinguishes this subpopulation from other B1 B cells that lack PD-L2, namely, L2nB1 cells (PD-L2negative B1 cells). PD-L2 gene expression is regulated differently in B1 B cells as compared to macrophages and dendritic cells. L2pB1 cells share many commonly known B1 cell features with L2nB1 cells. These include spontaneous IgM secretion, constitutive ERK activation, elevated co-stimulatory molecule expression, skewing of T cell differentiation, and unique proliferative responsiveness (to LPS, PMA, but not anti-IgM). However, L2pB1 cells express a biased Ig repertoire that is enriched for self-reactivity as compared with L2nB1 cells. Further, L2pB1 cells present antigen more potently than L2nB1 cells. In addition, L2pB1 cells switch Ig isotype more readily from IgM to IgG1 and IgG2b upon cytokine stimulation. Moreover, increased numbers of L2pB1 cells are present in murine models of lupus and this correlates with increased serum anti-dsDNA titers. These characteristics suggest that L2pB1 cells may play a pathophysiological role in autoimmune dyscrasias. In this report we review the special features of L2pB1 cells and how they may contribute to autoimmunity.

Human T cells induce their own regulation through activation of B cells

Regulatory functions for B lymphocytes have been reported in murine models of autoimmune diseases in which B-cell deficient mice were shown to exhibit exacerbated disease. The B cells responsible for the immune regulations were identified as a subpopulation of interleukin 10-secreting cells. However, the mechanism of induction and the characteristics of regulatory B cells in humans have been hardly studied. This study reports that regulation of T cell responses can be induced by B cells following CD40-dependent cognate interaction. T cell proliferation and cytokine production were differentially regulated. Thus, CD40-induced regulatory B cells partially inhibited T cell proliferation following CD40 interaction without requirement of soluble factor. In contrast, modulation of Th1 differentiation resulted from CD80- and CD86-dependent interactions and from IL-10 production. The suppressive effects were mediated by CD19(high)IgD+CD38(high)CD24(high)CD5(high) B cells and appeared to be indirect, through the induction of regulatory T cells as indicated by the appearance of Foxp3+CD4+CD25+T cells. These data suggest that activation signals from T cells initiate regulatory properties in B cells that modulate T cell responses involving regulatory T cells. Finally, studies in autoimmune patients revealed that regulation of T cell proliferation was defective in systemic lupus erythematosus but efficient in other diseases. Restoration of efficient B-cell regulatory activity could provide innovative B-cell based treatment of autoimmune diseases.

Engagement of the B cell receptor for antigen differentially affects B cell responses to Toll-like receptor-7 agonists and antagonists in BXSB mice

Nucleic acid sensors of the Toll-like receptor (TLR) family play a well-established role in the pathogenesis of lupus. This is particularly true for a single-stranded RNA-sensing TLR-7 receptor, as lupus mice lacking TLR-7 show ameliorated disease. Cytosine-guanosine dinucleotide (CpG)-DNA-sensing TLR-9, conversely, has a complex regulatory role in systemic lupus erythematosus (SLE). Much less is known about whether signals through the B cell receptor for antigen (BCR) may affect the ability of B cells to respond to suboptimal TLR-7 agonists and antagonists. We studied this question in prediseased BXSB male and female B cells. We found that male B cells responded more vigorously to numerous TLR-7 ligands and this responsiveness was enhanced further upon co-engagement of the BCR. This synergy was seen primarily with the interleukin (IL)-6 secretion. A number of 32-mer inhibitory oligonucleotides (INH-ODNs) with a nuclease-resistant phosphorothioate backbone were capable of blocking TLR-7, but not BCR-induced B cell activation, with an inhibitory concentration (IC)(50) of approximately 100 nm. Surprisingly, while the presence of a single TGC motif at the 5' end of an ODN did not increase its inhibitory capacity, INH-ODNs containing multiple TGC motifs had greater inhibitory potency. When BCR and TLR-7 were co-engaged, INH-ODNs showed a differential effect on B cell activation. Whereas apoptosis protection and G1-M entry completely escaped suppression, IL-6 secretion remained sensitive to inhibition, although with a 10-fold lower potency. Our results suggest that while TLR-7 antagonists may be considered as lupus therapeutics, simultaneous co-engagement of the TLR-7 and BCR might favour autoreactive B cell survival. This hypothesis needs further experimental validation.

B cells in spontaneous autoimmune diseases of the central nervous system

B cells and their secreted products participate in the intricate network of pathogenic and regulatory immune responses. In human autoimmune diseases like rheumatoid arthritis, systemic lupus erythematosus and type 1 diabetes, a role for B cells and antibodies is well established. However, in multiple sclerosis (MS), despite the presence of autoantibodies, B cells were less considered as a major participant of autoimmune processes, until recently. Several lines of evidence now indicate a more active role for B cells in disease pathogenesis. In this review, we discuss the diverse roles of B cells in autoimmune diseases with particular focus on multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE) as well as the recently generated spontaneous EAE mouse models.

Decreased production of interleukin-10 and transforming growth factor-β in Toll-like receptor-activated intestinal B cells in SAMP1/Yit mice

A unique subset of B cells expressing interleukin-10 (IL-10) and transforming growth factor-β (TGF-β) plays an essential role in preventing inflammation and autoimmunity. We investigated the presence of this cell subset in intestines and its role in the pathogenesis of ileitis using SAMP1/Yit and age-matched control AKR/J mice. Mononuclear cells were isolated from mesenteric lymph nodes (MLNs) and the expressions of B220, CD1d, CD5, Toll-like receptor 4 (TLR4) and TLR9 in isolated cells were analysed. Purified B cells were stimulated with lipopolysaccharide (LPS) or CpG-DNA, then IL-10 and TGF-β(1) expressions were examined by enzyme immunoassay and flow cytometry. Production of IL-1β by TLR-mediated macrophages co-cultured with or without purified MLN B cells from SAMP1/Yit and AKR/J mice was evaluated. In addition, interferon-γ (IFN-γ) production in intestinal T cells co-cultured with MLN B cells were also assessed in SAMP1/Yit and AKR/J strains. The production levels of IL-10 and TGF-β(1) stimulated by LPS and CpG-DNA were significantly lower in B cells separated from MLNs from the SAMP1/Yit strain. B cells expressing IL-10 and TGF-β(1) were mainly located in a population characterized by the cell surface marker CD1d(+) . Interleukin-1β production by TLR-activated macrophages co-cultured with MLN B cells from SAMP1/Yit mice was significantly higher than that of those from AKR/J mice. Interestingly, IFN-γ production by T cells was noted only when they were co-cultured with SAMP1/Yit but not the AKR/J B cells. These results are the first to show that disorders of regulatory B-cell function under innate immune activation may cause disease pathogenesis in a murine model of Crohn's disease.

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 (B(REG))-cell biology have been elucidated. Not only have scientists begun to unravel the mechanism of how B(REG) 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 B(REG) 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 B(REG) 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 B(REG)-cell function in rheumatic diseases.

Regulation of the activity of an adeno-associated virus vector cancer vaccine administered with synthetic Toll-like receptor agonists

Recombinant adeno-associated virus (rAAV) is being tested as a vaccine vector, but the cellular immune responses elicited in animal tumor models have not been completely protective. The adjuvant effects of the TLR7 agonist, imiquimod, and the TLR9 agonist, ODN1826, were tested with rAAV expressing the melanoma antigen, Trp2. Mice immunized with rAAV-TRP2 and either TLR agonist alone generated T-helper-1 antitumor immune responses. Antitumor activity in all experiments was still incomplete. Furthermore, antitumor activity was not achieved when the combination of ODN1826 and imiquimod was used as adjuvant. In vitro, the combination increased IL-10 production by dendritic cells. In vivo, the combination reduced T-helper-1 response and dendritic cell activation and increased myeloid suppressor cells; regulatory T cells were not significantly modulated. Depletion of myeloid derived suppressor cells enhanced the antitumor activity of immunization with rAAV-TRP2 and the imiquimod-ODN1826 combination; depletion of regulatory T cells did not. TLR7 and TLR9 agonists can be used to enhance the immune response to rAAV immunogens, but antagonism can be observed when combined. Suppressor mechanisms, including those mediated by myeloid cells, may negatively regulate the antitumor immune response.

Cell type-specific regulation of IL-10 expression in inflammation and disease

IL-10 plays an essential part in controlling inflammation and instructing adaptive immune responses. Consequently, dysregulation of IL-10 is linked with susceptibility to numerous infectious and autoimmune diseases in mouse models and in humans. It has become increasingly clear that appropriate temporal/spatial expression of IL-10 may be the key to how IL-10 contributes to the delicate balance between inflammation and immunoregulation. The mechanisms that govern the cell type- and receptor-specific induction of IL-10, however, remain unclear. This is due largely to the wide distribution of cellular sources that express IL-10 under diverse stimulation conditions and in a variety of tissue compartments. Further complicating the issue is the fact that human IL-10 expression patterns appear to be under genetic influence resulting in differential expression and disease susceptibility. In this review, we discuss the cellular sources of IL-10, their link to disease phenotypes and the molecular mechanisms implicated in IL-10 regulation.

Regulatory B cells: evidence, developmental origin and population diversity

The adaptive immune system has developed several highly effective mechanisms in order to avoid excessive or unwanted reactions and promote resolution of immune activation. An emerging, significant body of evidence indicates that B cells can actively modulate immune responses by mechanisms that do not directly involve the production of antibodies. B cells appear to have the capacity to both induce and suppress immune effector mechanisms and they exert these functions both by contact-dependent interactions and through the secretion of cytokines. In this review we will focus on the regulatory suppressive function of several recently described B cell populations, functionally defined "regulatory B cells" or Breg cells. We will first outline the evidence that has led to their identification and then we will summarize current hypotheses on their ontogeny and possible lineage relationship.

Susceptibility to experimental autoimmune encephalomyelitis is associated with altered B-cell subsets distribution and decreased serum BAFF levels

B cells possess the ability to regulate either pathogenic or protective events in several autoimmune diseases such as multiple sclerosis (MS) and its experimental model, experimental autoimmune encephalomyelitis (EAE). Given the extensive use of B-cell-targeting treatments, it appears crucial to more precisely define the dual role of B cells in the progression of the disease. In the present study, we explored the impact of EAE induction on the distribution of potential regulatory B-cell subsets (CD5(+) B1a, marginal zone and transitional 2 B cells) over critical time points in the relapsing-remitting EAE model, SJL/J (H2s). The same approach was carried out in B10.S mice that are resistant to EAE induction, (H2s). The comparative data obtained from these experiments showed that the homeostasis of the regulatory B-cell subsets is altered during the EAE preclinical and acute phases. These observations were associated with a distortion of the BAFF response. All these data suggest the existence of a close relationship between B-cell homeostasis, BAFF response and the susceptibility to develop EAE.

B cell therapies for rheumatoid arthritis: beyond B cell depletion

Initially suggested by the presence of rheumatoid factor autoantibodies, multiple pathogenic roles for B cells (both antibody-mediated and antibody-independent) in rheumatoid arthritis (RA) now are supported by a growing body of experimental observations and human studies. The pathogenic significance of B cells in this disease also has been established conclusively by the proven benefit of Rituximab-induced B cell depletion in RA patients refractory to tumor necrosis factor (TNF) blockade. This article reviews the rationale for the use of B cell-targeting therapies in RA and discusses the caveats and limitations of indiscriminate B cell depletion as currently applied, ncluding incomplete depletion of pathogenic B cells and elimination of protective B cells. Finally, it presents alternative therapeutic strategies that exploit current knowledge of B cell activation, survival, and differentiation to provide more selective B cell and plasma cell targeting.

TLR1/2, TLR7, and TLR9 signals directly activate human peripheral blood naive and memory B cell subsets to produce cytokines, chemokines, and hematopoietic growth factors

Recently, it has been reported that using multiple signals, murine and human B cells secrete several cytokines with pro-inflammatory and immunoregulatory properties. We present the first comprehensive analysis of 24 cytokines, chemokines, and hematopoietic growth factors production by purified human peripheral blood B cells (CD19+), and naive (CD19+CD27-) and memory (CD19+CD27+) B cells in response to direct and exclusive signaling provided by toll-like receptor (TLR) ligands Pam3CSK (TLR1/TLR2), Imiquimod (TLR7), and GpG-ODN2006 (TLR9). All three TLR ligands stimulated B cells (CD19+) to produce cytokines IL-1α, IL-1β, IL-6, TNF-α, IL-13, and IL-10, and chemokines MIP-1α, MIP-1β, MCP-1, IP-10, and IL-8. However, GM-CSF and G-CSF production was predominantly induced by TLR2 agonist. Most cytokines/chemokines/hematopoietic growth factors were predominantly or exclusively produced by memory B cells, and in general, TLR2 signal was more powerful than signal provided viaTLR7 and TLR9. No significant secretion of eotaxin, IFN-α, IFN-γ, IL-2, IL-3, IL-4, IL-5, IL-7, IL-15, IL-17, IL-12p40, IL-12p70, and TNF-β (lymphotoxin) was observed. These data demonstrate that human B cells can be directly activated viaTLR1/TLR2, TLR7, and TLR9 to induce secretion of cytokines, chemokines, and hematopoietic growth factors and suggest a role of B cells in immune response against microbial pathogenesis and immune homeostasis.

Regulatory B cells in autoimmune diseases and mucosal immune homeostasis

B lymphocytes contribute to physiological immunity through organogenesis of secondary lymphoid organs, presentation of antigen to T cells, production of antibodies, and secretion of cytokines. Their role in several autoimmune diseases, mainly as producers of pathogenic antibodies, is also well known. However, certain subsets of B cells are emerging as the important regulatory cell populations in both mouse and human. The regulatory functions of B cells have been demonstrated in a variety of mouse models of autoimmune diseases including collagen-induced arthritis (CIA), experiment autoimmune encephalomyelitis (EAE), anterior chamber-associated immune deviation (ACAID), diabetes, contact hypersensitivity (CHS), and intestinal mucosal inflammation. Accumulating evidence from both mouse and human studies confirms the existence of regulatory B cells, and is beginning to define their mechanisms of action. In this article, we first review the history of B cells with regulatory function in autoimmune diseases, and summarize the current understanding about the characterizations of such B-cell subsets. We then discuss the possible regulatory mechanisms of B cells, and specifically define the role of regulatory B cells in immune homeostasis in the intestine.

Nucleic acid sensing receptors in systemic lupus erythematosus: development of novel DNA- and/or RNA-like analogues for treating lupus

Double-stranded (ds) DNA, DNA- or RNA-associated nucleoproteins are the primary autoimmune targets in SLE, yet their relative inability to trigger similar autoimmune responses in experimental animals has fascinated scientists for decades. While many cellular proteins bind non-specifically negatively charged nucleic acids, it was discovered only recently that several intracellular proteins are involved directly in innate recognition of exogenous DNA or RNA, or cytosol-residing DNA or RNA viruses. Thus, endosomal Toll-like receptors (TLR) mediate responses to double-stranded RNA (TLR-3), single-stranded RNA (TLR-7/8) or unmethylated bacterial cytosine (phosphodiester) guanine (CpG)-DNA (TLR-9), while DNA-dependent activator of IRFs/Z-DNA binding protein 1 (DAI/ZBP1), haematopoietic IFN-inducible nuclear protein-200 (p202), absent in melanoma 2 (AIM2), RNA polymerase III, retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5) mediate responses to cytosolic dsDNA or dsRNA, respectively. TLR-induced responses are more robust than those induced by cytosolic DNA- or RNA- sensors, the later usually being limited to interferon regulatory factor 3 (IRF3)-dependent type I interferon (IFN) induction and nuclear factor (NF)-kappaB activation. Interestingly, AIM2 is not capable of inducing type I IFN, but rather plays a role in caspase I activation. DNA- or RNA-like synthetic inhibitory oligonucleotides (INH-ODN) have been developed that antagonize TLR-7- and/or TLR-9-induced activation in autoimmune B cells and in type I IFN-producing dendritic cells at low nanomolar concentrations. It is not known whether these INH-ODNs have any agonistic or antagonistic effects on cytosolic DNA or RNA sensors. While this remains to be determined in the future, in vivo studies have already shown their potential for preventing spontaneous lupus in various animal models of lupus. Several groups are exploring the possibility of translating these INH-ODNs into human therapeutics for treating SLE and bacterial DNA-induced sepsis.

Prolonged effects of short-term anti-CD20 B cell depletion therapy in murine systemic lupus erythematosus

OBJECTIVE

Although B cells are implicated in the pathogenesis of systemic lupus erythematosus, the role of B cell depletion (BCD) as a treatment is controversial, given the variable benefit in human disease. This study was undertaken to test the effects of BCD therapy in a murine lupus model to better understand the mechanisms, heterogeneity, and effects on disease outcomes.

METHODS

(NZB x NZW)F(1) female mice with varying degrees of disease severity were treated with an anti-mouse CD20 (anti-mCD20) antibody (IgG2a), BR3-Fc fusion protein (for BAFF blockade), or control anti-human CD20 monoclonal antibody (approximately 10 mg/kg each). Tissue samples were harvested and analyzed by flow cytometry. The development and extent of nephritis were assessed by monitoring proteinuria (using a urine dipstick) and by immunohistochemical analysis of the kidneys. Serum immunoglobulin levels were measured by enzyme-linked immunosorbent assay.

RESULTS

After a single injection of anti-mCD20, BCD was more efficient in the peripheral blood, lymph nodes, and spleen compared with the bone marrow and peritoneum of normal mice as well as younger mice with lupus. Since depletion of the marginal zone and peritoneal B cells was incomplete and variable, particularly in older mice with established nephritis, a strategy of sequential weekly dosing was subsequently used, which improved the extent of depletion. BAFF blockade further enhanced depletion in the spleen and lymph nodes. Early BCD therapy delayed disease onset, whereas BCD therapy in mice with advanced disease reduced the progression of nephritis. These effects were long-lasting, even after B cell reconstitution occurred, and were associated with a reduction in T cell activation but no significant change in autoantibody production.

CONCLUSION

The lasting benefit of a short course of BCD therapy in lupus-prone mice with an intact immune system and established disease highlights the validity of this treatment approach.

B-cell receptor for antigen modulates B-cell responses to complex TLR9 agonists and antagonists: implications for systemic lupus erythematosus

The capacity to make secondary structures significantly affects the ability of Toll-like receptor 9 (TLR9) agonists and antagonists to either induce or block TLR9-dependent activation in B cells. However, it has a minor impact on TLR9-induced activation in interferon alpha (IFNα)-producing dendritic cells. Based on the ability of inhibitory oligodeoxynucleotides to form predictable secondary structures, we have classified TLR9-antagonists into Class R ('restricted', palindromic) and Class B ('broadly reactive', linear) oligodeoxynucleotides. In non-autoreactive B cells, Class R oligodeoxynucleotides are at least 10-fold less potent TLR9-inhibitors. We wanted to determine whether engagement of the B-cell receptor for antigen could overcome this restriction. Here we show that in non-autoreactive mouse B cells, B-cell receptor for antigen engagement increased the potency of Class R oligodeoxynucleotides for TLR9 activation at least 10-fold, making it equal in potency to linear oligodeoxynucleotides. However, this enhanced potency was selective for TLR9-induced B-cell cycling and apoptosis protection while TLR9-induced IL-6, an event that strongly depends on signaling via late endosomes, still required 10 times more Class R oligodeoxynucleotides. Thus, pathway-specific effects of Class R oligodeoxynucleotides for TLR9/B-cell receptor for antigen co-stimulated B cells may have therapeutic advantages over non-selective targeting of B cells, a strategy that may be seen as a potential therapy for human systemic lupus erythematosus.

B cells as therapeutic targets in SLE

The use of B-cell targeted therapies for the treatment of systemic lupus erythematosus (SLE) has generated great interest owing to the multiple pathogenic roles carried out by B cells in this disease. Strong support for targeting B cells is provided by genetic, immunological and clinical observations that place these cells at the center of SLE pathogenesis, as initiating, amplifying and effector cells. Interest in targeting B cells has also been fostered by the successful use of similar interventions to treat other autoimmune diseases such as rheumatoid arthritis, and by the initial promise shown by B-cell depletion to treat SLE in early studies. Although the initial high enthusiasm has been tempered by negative results from phase III trials of the B-cell-depleting agent rituximab in SLE, renewed vigor should be instilled in the field by the convergence of the latest results using agents that inhibit B-cell-activating factor (BAFF, also known as BLyS and tumor necrosis factor ligand superfamily, member 13b), further analysis of data from trials using rituximab and greatly improved understanding of B-cell biology. Combined, the available information identifies several new avenues for the therapeutic targeting of B cells in SLE.

A double-edged sword in B-cell-targeted therapy for inflammatory diseases

Cells of the immune system, including B cells, perform inflammatory functions against microbial invasion, accompanied by anti-inflammatory responses to avoid host damage. B-cell-depletion therapy using anti-CD20 monoclonal antibodies against inflammatory diseases has beneficial or adverse effects depending on the timing and/or microenvironment in which they are used. To achieve effective B-cell-targeted therapy, it is necessary to identify and understand the modes of action of pathogenic and regulatory B cells, which include antibody production, formation of immune complexes, cytokine and chemokine production, cytotoxic killing, lymphoid neogenesis and antigen presentation. B cells interact with multiple cells, including dendritic cells, T cells and natural killer T cells, creating a complex regulatory network. Specific targeting of B-cell subsets and/or their interaction partners might lead to clinical benefits with minimal host damage.

Classification, mechanisms of action, and therapeutic applications of inhibitory oligonucleotides for Toll-like receptors (TLR) 7 and 9

Our immune defense depends on two specialized armed forces. The innate force acts as an alarm mechanism that senses changes in the microenvironment through the recognition of common microbial patterns by Toll-like receptors (TLR) and NOD proteins. It rapidly generates an inflammatory response aimed at neutralizing the intruder at the mucosal checkpoint. The innate arm also communicates this message with more specialized adaptive forces represented by pathogen-specific B cells and T cells. Interestingly, B cells also express some innate sensors, like TLR7 and TLR9, and may respond to bacterial hypomethylated CpG motifs and single-stranded RNA viruses. Intracellular nucleic acid sensing TLRs play an important role in the pathogenesis of Systemic Lupus Erythematosus (SLE). In this review, we describe recent achievements in the development of oligonucleotide—(ODN)-based inhibitors of TLR9 and/or TLR7 signaling. We categorize these novel therapeutics into Classes G, R, and B based on their cellular and molecular targets. Several short ODNs have already shown promise as pathway-specific therapeutics for animal lupus. We envision their future use in human SLE, microbial DNA-dependent sepsis, and in other autoinflammatory diseases.

Am"B"valent: anti-CD20 antibodies unravel the dual role of B cells in immunopathogenesis

Accumulating evidence has designated B cells as central players in the pathogenesis of immune diseases. In the late 1990s, anti-CD20 monoclonal antibodies were developed for the treatment of B-cell non-Hodgkin lymphomas, offering the opportunity to efficiently deplete the B-cell compartment for therapeutic immunointerventions. Several studies have since established the beneficial effect of this drug on the course of a wide range of immune diseases. However, paradoxically, it has also been reported that rituximab sometimes worsens the symptoms of the very same conditions. The explanation that reconciles such apparently conflicting results has recently emerged from basic studies, which demonstrate that (1) B cells are also endowed with immune-regulatory properties and (2) the opposing contributions of B cells may overlap during the course of the disease. Caution should therefore be exercised when considering B-cell depletion because the therapeutic effect will depend on the relative contributions of the opposing B-cell activities at the time of the drug administration.

Toll-like receptors--sentries in the B-cell response

Toll-like receptors (TLR) play a central role in the initiation of the innate immune response to pathogens. Upon recognition of molecular motifs specific for microbial molecules TLR mediate pro-inflammatory cytokine secretion and enhance antigen presentation; in B cells they further promote expansion, class switch recombination and immunoglobulin secretion. As a result of their adjuvant properties, TLR ligands have become an integral component of antimicrobial vaccines. In spite of this, little is known of the direct effects of TLR engagement on B-lymphocyte function. The scope of this review is to outline the differences in TLR expression and reactivity in murine and human B-cell subsets and to provide an overview of the currently available literature. We will further discuss the possible roles of TLR in regulating B-cell effector functions and shaping antibody-mediated defence against microbial pathogens in vivo.

CD19(+)CD24(hi)CD38(hi) 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.

CpG-enhanced CD8+ T-cell responses to peptide immunization are severely inhibited by B cells

Synthetic peptides encoding protective pathogen-derived epitopes represent--in principle--an ideal approach to T-cell vaccination. Empirically, however, these strategies have not been successful. In the current study, we profiled the early activation of CD8+ T cells by MHC class I-restricted peptide immunization to better understand the biology of this response. We found that CD8+ T cells proliferated robustly in response to low doses of short synthetic peptides in PBS, but failed to acquire effector function or form memory populations in the absence of the TLR ligand CpG. CpG was unique among TLR ligands in its ability to enhance the response to peptide and its adjuvant effects had strict temporal requirements. Interestingly, CpG treatment modulated T-cell expression of the surface receptors PD-1 and CD25, providing insight into its possible adjuvant mechanism. The effects of CpG on peptide immunization were dramatically enhanced in the absence of B cells, demonstrating a unique system of regulation of T-cell responses by these lymphocytes. The results reported here provide insight into the complex response to a simple vaccination regimen, as well as a framework for a rational peptide-based vaccine design to both exploit and overcome targeted aspects of the immune response.

Regulatory B cells shape the development of Th2 immune responses in BALB/c mice infected with Leishmania major through IL-10 production

Recent evidence indicates that B cells are required for susceptibility to infection with Leishmania major in BALB/c mice. In this study, we analyzed the role of the IL-10 produced by B cells in this process. We showed that B cells purified from the spleen of BALB/c mice produced IL-10 in response to stimulation with L. major in vitro. In vivo, early IL-10 mRNA expression is detected after L. major infection in B cells from draining lymph nodes of susceptible BALB/c, but not of resistant C57BL/6 mice. Although adoptive transfer of naive wild-type B cells prior to infection in B cell-deficient BALB/c mice restored Th2 cell development and susceptibility to infection with L. major of these otherwise resistant mice, adoptive transfer of IL-10(-/-) B cells mice did not. B cells stimulated by L. major, following in vitro or in vivo encounter, express the CD1d and CD5 molecules and the IL-10 produced by these cells downregulate IL-12 production by L. major-stimulated dendritic cells. These observations indicate that IL-10 secreting B cells are phenotypically and functionally regulatory B cells. Altogether these results demonstrate that the IL-10 produced by regulatory CD1d+ CD5+ B cells in response to L. major is critical for Th2 cell development in BALB/c mice.

Insights into the heterogeneity of human B cells: diverse functions, roles in autoimmunity, and use as therapeutic targets

B cells are critical players in the orchestration of properly regulated immune responses, providing protection against infectious agents without inflicting autoinflammatory damage. A balanced B cell compartment is also essential to create protective immunity in response to vaccines. This difficult compromise is achieved through the finely regulated participation of multiple B cell populations with different antibody-dependent and independent functions. Both types of functions allow B cells to powerfully modulate other components of the innate and adaptive immune system. For the most part, however, the necessary division of labor among different B cell populations is poorly understood. B cell dysfunction has been implicated in multiple autoimmune conditions. The physiological importance and complexity of B cell functions has been brought to the fore in recent years by the success of rituximab-based B cell depletion therapy (BCDT) in multiple autoimmune diseases including rheumatoid arthritis (RA) and multiple sclerosis (MS) which are conventionally viewed as T-cell mediated conditions. Given the widespread utilization of BCDT in malignant and autoimmune diseases and the key role of B cells in both protective immunity and pathogenic autoimmunity, a better understanding of B cell functions is of the essence and a focus of the research in our division. We are investigating these issues through a variety of approaches, including the study of the phenotype and function of human B cell populations in health, their perturbation in autoimmune disease states, the effects of targeted biologic therapies, and the study of relevant murine models.