Altered response to and production of TGF-beta by B cells from autoimmune NZB mice

Aberrant expression of interleukin-10 and activation-induced cytidine deaminase in B cells from patients with Behçet's disease

Despite extensive studies, the pathogenesis of Behçet's disease (BD) remains unclear. In particular, the roles of B cells in patients with BD have not been elucidated. Activation-induced cytidine deaminase (AID) is a critical enzyme for immunoglobulin (Ig) heavy chain class switching and somatic hypermutation in B cells and the abnormal expression of AID in various immune conditions has previously been studied. B10 cells, an interleukin (IL)-10-secreting subset of regulatory B cells, function to downregulate inflammation and autoimmunity. Thus, in the present study, the relevance of B cells in patients with BD was investigated. The plasma levels of IL-10 and IgA and the proportions of cluster of differentiation (CD)43+ B cells, excluding naïve B cells, were measured in 16 patients with BD and 16 age- and sex-matched healthy controls (HCs). Additionally, the mRNA levels of IL-10 and AID were assessed in B cells from fresh peripheral blood samples of the BD patients and HCs. The plasma level of IL-10 in patients with BD did not differ significantly from that in HCs. Similarly, there was no significant difference in the plasma level of IgA, although a slight increase was observed in patients with BD compared with that in HCs. There were no differences in CD43+CD19+ B cell numbers between patients with BD and HCs. However, IL-10 mRNA levels were significantly reduced (P<0.05), while AID mRNA levels were significantly increased (P<0.01) in the B cells of patients with BD compared with those in HCs. These results provide insight into the role of B cells in patients with BD.

What do we know about the role of regulatory B cells (Breg) during the course of infection of two major parasitic diseases, malaria and leishmaniasis?

Parasitic diseases, such as malaria and leishmaniasis, are relevant public health problems worldwide. For both diseases, the alarming number of clinical cases and deaths reported annually has justified the incentives directed to better understanding of host's factors associated with susceptibility to infection or protection. In this context, over recent years, some studies have given special attention to B lymphocytes with a regulator phenotype, known as Breg cells. Essentially important in the maintenance of immunological tolerance, especially in autoimmune disease models such as rheumatoid arthritis and experimentally induced autoimmune encephalomyelitis, the function of these lymphocytes has so far been poorly explored during the course of diseases caused by parasites. As the activation of Breg cells has been proposed as a possible therapeutic or vaccine strategy against several diseases, here we reviewed studies focused on understanding the relation of parasite and Breg cells in malaria and leishmaniasis, and the possible implications of these strategies in the course of both infections.

The regulatory role of B cells in autoimmunity, infections and cancer: Perspectives beyond IL10 production

The term regulatory B cells (B regs) is ascribed to a heterogeneous population of B cells with the function of suppressing inflammatory responses. They have been described mainly during the last decade in the context of different immune-mediated diseases. Most of the work on B regs has been focused on IL-10-producing B cells. However, B cells can exert regulatory functions independently of IL-10 production. Here we discuss the phenotypes, development and effector mechanisms of B regs and advances in their role in autoimmunity, infections and cancer.

B-cell modulation of dendritic-cell function: signals from the far side

An appropriate immune response against a specific pathogen requires finely orchestrated interactions between the various cell populations within the immune system. At the same time, immunological tolerance to self must be maintained. DCs play an essential role in achieving these dual requisites. They coordinate adaptive immunity by integrating signals directly emanating from both infectious agents and cells of the immune system. Many such signals, especially those from innate cells and T cells, have been extensively characterized. In contrast, little is known about how B cells modulate function of DCs. B cells produce a variety of cytokines, including IL-10 and IL-6, which are known to influence DC function. In addition, Igs constitute the major secretory products of terminally differentiated B cells (plasma cells). DCs express various types of receptors for binding Ig, such as Fc receptors and C-type lectin receptors. In accordance, Igs can regulate DC function depending on the receptors engaged. Here, we review the emerging immunomodulatory role of cytokines and Ig secreted by B cells. We discuss the evidence for how these B-cell-derived factors may shape the adaptive immune response by directly acting on DCs.

Regulatory B cells and allergic diseases

B cells are generally considered to positively regulate immune responses by producing antigen-specific antibodies. B cells are classified into classical CD5^- conventional B cells and CD5⁺ B1 cells. The latter produce multi-specific autoantibodies and are thought to be involved in autoimmune diseases. However, evidence supporting a B cell negative regulatory function has accumulated over the past 30 years. Multiple reports have suggested that absence, or loss, of regulatory B cells exacerbates symptoms of both allergic (including contact hypersensitivity and anaphylaxis) and autoimmune (such as experimental autoimmune encephalomyelitis, chronic colitis, and collagen-induced arthritis) diseases, and in lupus-like models of autoimmunity. Regulatory B cells are characterized by production of the negative regulatory cytokines, IL-10 and TGF-β. IL-10-producing B cells were the first regulatory B cells to be recognized and were termed 'B10' cells. IL-10-producing regulatory B cells are of the CD19⁺CD5⁺IgM^hiIgD^loCD1d^hi type. Recently, a TGF-β-producing regulatory B cell subset, Br3, has been shown to be related to immune tolerance in food allergies. Moreover, forkhead box P3 (Foxp3)-expressing B cells have also been identified in humans and may act as regulatory B cells (Bregs). The functional image of regulatory B cells is similar to that of regulatory T cells. Because of the proliferative and apoptotic responses of Br1 and Br3 cells in immune tolerance in non-IgE-mediated food allergy, reciprocal roles and counter-regulatory mechanisms of Br1 and Br3 responses are also suspected. Additionally, different roles for regulatory B and T cells at different time points during initiation and progression of autoimmune disease are described.

Allergen-specific transforming growth factor-β-producing CD19+CD5+ regulatory B-cell (Br3) responses in human late eczematous allergic reactions to cow's milk

CD19(+)CD5(+) regulatory B cells produce transforming growth factor β (TGF-β) in both mouse and human B-cell leukemias. In this study, TGF-β was uniquely produced by normal human regulatory B cells. TGF-β-producing regulatory B-cell (Br3) responses were characterized through allergic responses to cow's milk. In total, 10 subjects allergic to milk and 13 milk-tolerant subjects were selected following double-blinded, placebo-controlled food challenges. Their peripheral blood mononuclear cells were stimulated in vitro with casein. Following allergen stimulation, the percentage of Br3s among CD5(+) B cells decreased from 11.5% ± 13.7% to 8.0% ± 9.6% (P = 0.042, n = 5) in the milk-allergy group and increased from 14.7% ± 15.6% to 18.9% ± 20.1% (P = 0.006, n = 7) in the milk-tolerant group. However, the numbers of Br3s increased only in the milk-tolerant group, from 1,954 ± 1,058 to 4,548 ± 1,846 per well (P = 0.026), whereas the numbers of Br3s in the milk-allergy group were unchanged [2,596 ± 823 to 2,777 ± 802 per well (P = 0.734)]. The numbers of apoptotic events were similar to the numbers of total Br3 responses. The percentage of non-TGF-β-producing CD5(+) B cells with apoptotic changes increased from 13.4% ± 17.1% to 16.4% ± 20.3% (P = 0.047, n = 5) in the milk-allergy group and remained unchanged [from 9.9% ± 11.9% to 9.3% ± 11.4% (P = 0.099, n = 7)] in the milk-tolerant group. Using carboxyfluorescein succinimidyl ester labeling, we observed that the percentage of proliferating Br3s among CD5(+) B cells was unchanged [from 6.1% ± 2.8% to 6.4% ± 2.9% (P = 0.145)] in the milk-allergy group and increased from 6.8% ± 3.9% to 10.2% ± 5.3% (P = 0.024) in the milk-tolerant group. In conclusion, Br3s proliferated in response to allergen stimulation in the milk-tolerant group and not in the milk-allergy group. TGF-β-producing regulatory B cells (Br3) may be involved in allergy tolerance by negatively regulating the immune system with TGF-β, and this negative regulation may be controlled by apoptosis.

Presence of Foxp3-expressing CD19(+)CD5(+) B Cells in Human Peripheral Blood Mononuclear Cells: Human CD19(+)CD5(+)Foxp3(+) Regulatory B Cell (Breg)

Foxp3 is a transcript factor for regulatory T cell development. Interestingly, Foxp3-expressing cells were identified in B cells, especially in CD19(+)CD5(+) B cells, while those were not examined in CD19(+)CD5(-) B cells. Foxp3-expressing CD5(+) B cells in this study were identified in human PBMCs and were found to consist of 8.5±3.5% of CD19(+)CD5(+) B cells. CD19(+)CD5(+)Foxp3(+) B cells showed spontaneous apoptosis. Rare CD19(+)CD5(+) Foxp3(+) regulatory B cell (Breg) population was unveiled in human peripheral blood mononuclear cells and suggested as possible regulatory B cells (Breg) as regulatory T cells (Treg). The immunologic and the clinical relevant of Breg needs to be further investigated.

Is targeted chemotherapy an alternative to immunotherapy in chronic lymphocytic leukemia?

Although molecular remission is now detected, it is still unknown whether we have the tools to cure B cell chronic lymphocytic leukemia (referred to as CLL). Nonetheless, several new therapeutic approaches have been introduced in cancer therapy during the last decade, including antiangiogenic therapy, apoptosis-inducing treatment and inhibition of heat shock proteins, farnesyl transferase, tyrosine kinases and proteasomes. These modalities may also be considered in CLL, but additional experimental characterization is required. Further characterization and development of CLL animal models should be a part of this preclinical work (especially xenografting in NOD/SCID animals, but also murine leukemia) to allow a more extensive evaluation prior to clinical trials. Animal models are particularly important for preclinical comparison of pharmacological effects between different disease compartments and for in vivo evaluation of antileukemic immune reactivity. However, T cell targeting therapy seems to have several advantages in comparison to other approaches: (1) based on the current clinical experience one would expect low toxicity for several of these strategies, especially vaccine treatment; (2) several studies have demonstrated that autologous T cells can recognize CLL cells; (3) experimental and clinical evidence suggests that immunotherapy can be combined with chemotherapy. Thus, T cell therapy has a relatively strong scientific basis that justifies further clinical studies of immunotherapy in CLL. Although several of the new pharmacological agents seem to have immunosuppressive effects, at least some of them (e.g. heat shock protein 90 inhibitors, proteasome inhibitors, inhibition of angiogenesis) appear to affect T cells only at relatively high concentrations and may thus be used in combination with immunotherapy.

Establishment of a novel human B-CLL-like xenograft model in nude mouse

We have developed a novel murine model for B-CLL by engrafting human prolymphocytic leukemia (PLL) or B-CLL cell line cells (JVM-3 and MEC-2 cell lines, respectively) into nude mice. Not only treatment of the mice was a prerequisite for the success of the graft, but also for the first time, females appeared to accept the cells more easily than males. Surprisingly, tumoral murine models for B-CLL could be established with PLL cells but not with B-CLL cells. JVM-3 cells were efficiently transplanted into nude mice through subcutaneous or intravenous routes. Irradiated female mice appeared to be the optimal recipients for tumor growth. Such murine models for human B-CLL may help the development of therapeutic agents.

Transforming growth factor-beta (TGF-beta)-resistant B cells from chronic lymphocytic leukemia patients contain recurrent mutations in the signal sequence of the type I TGF-beta receptor

B cell chronic lymphocytic leukemia (B-CLL) is the most common leukemia in western societies, and is currently incurable. B cells of some B-CLL patients are resistant to the anti-proliferative effects of transforming growth factor-beta (TGF-beta). Herein, we identified two mutations within the putative signal sequence of TGF-beta type I receptor (TbetaR-I) gene of TGF-beta-resistant B-CLL patients (i.e., a Leu12Gln substitution together with an in-frame single Ala deletion). Although TbetaR-I mutants were expressed to the cell surface and interacted normally with TGF-beta-bound TbetaR-II, their expression significantly reduced gene transcription stimulated by TGF-beta, suggesting a causal relationship in the development of TGF-beta-resistant B-CLL. Screening of additional B-CLL patients solely for the presence of TbetaR-I signal sequence mutations showed that these mutations correlated with and predicted for B-CLL patient insensitivity to TGF-beta. Our results demonstrate that TGF-beta-resistant B-CLL is linked to signal sequence mutations within the TbetaR-I gene, and may eventually be employed as a prognostic indicator in B-CLL.

In vitro quantification of anti-red blood cell antibody production in idiopathic autoimmune haemolytic anaemia: effect of mitogen and cytokine stimulation

The immunopathogenic mechanisms underlying idiopathic autoimmune haemolytic anaemia (AIHA) are still unknown, although regulatory cytokines are thought to play an important role. We investigated cytokine production by mitogen-stimulated whole blood cultures from 21 patients with AIHA and from 22 age- and sex-matched controls. In parallel experiments, we studied the effect of mitogen and cytokine stimulation on anti-red blood cell (RBC) IgG antibody production, assessed as both binding on autologous RBCs and secretion in culture supernatants. To quantify anti-RBC antibody, we set up a sensitive and quantitative solid phase competitive immunoassay. The results showed that in AIHA patients production of interleukin (IL)-4, IL-6 and IL-13 was significantly increased, whereas that of interferon (IFN)-gamma was reduced. Multivariate analysis showed that IFN-gamma was the only independent factor significantly associated with the reduced T-helper-1-like cytokine profile. Patients with active haemolysis showed further reduction of IFN-gamma and IL-2 production and increased secretion of transforming growth factor (TGF)-beta. In AIHA patients, mitogen stimulation, as well as IL-6, significantly increased autologous anti-RBC-binding relative to unstimulated cultures. Mitogen stimulation and addition of IL-4, IL-6, IL-10, IL-13 and TGF-beta significantly increased both autologous anti-RBC binding and antibody secretion in AIHA patients compared with controls. The results suggest that a reduced T-helper-1- and a predominant T-helper-2-like profile and elevated TGF-beta levels might play a role in the immunopathogenesis of AIHA. Furthermore, our competitive anti-RBC antibody was able to detect anti-RBC antibody production in some direct antiglobulin test (DAT)-negative AIHA patients.

Disruption of the IFN-gamma cytokine network in chronic lymphocytic leukemia contributes to resistance of leukemic B cells to apoptosis

Recent evidence indicates that the slowly expanding population of CD5+ B cells that characterizes chronic lymphocytic leukemia (CLL) results primarily from defects in responses to cytokines that regulate apoptosis (e.g. I1-4, TGF-beta, IFN-alpha, IFN-gamma). We have now demonstrated not only that the enhanced anti-apoptotic effect of IFN-gamma on these neoplastic B cells is apparently mediated through increased levels of IFN-gamma receptors but also that there are increased numbers of IFN-gamma-expressing CD4 and CD8 T cells in these patients. This is the strongest evidence to date that multiple alterations in the IFN-gamma cytokine network contribute to the pathogenesis of CLL.

CD5 B cells and B-cell malignancies

Over the past year, progress has been made in understanding of the physiology and disease associations of CD5+ (B1) B cells, although their exact role in pathogenesis remains unclear. Earlier studies on the negative function of CD5 within the B-cell receptor complex have been substantiated, and it seems likely that soon the signaling pathways used by this coreceptor will be elucidated. Progress in diagnosis, physiology, and etiopathogenesis of CD5+ malignancies has been made, particularly in B-cell chronic lymphocytic leukemia. The low-level expression of surface immunoglobulin has been explained by the mutations that occur in the associated CD79b. Two new potential tumor-suppressor genes have been identified in the hot spot of chromosome 13q, which provides an exciting step forward in understanding of the etiopathogenesis of some B-cell chronic lymphocytic leukemia. Activated signal transducers for activation of transcription factors molecules have been shown to be phosphorylated on different amino acids in B1 and chronic lymphocytic leukemia tumors, although the significance of this is, as yet, unclear. Finally, aberrant expression of CD40L by chronic lymphocytic leukemia T cells may contribute to the immunodeficiency that develops in these patients.

Aberrant responses of human lymphocytic neoplasms to cytokine regulation

Studies in this laboratory have recently focused on two hemic neoplasms: B cell chronic lymphocytic leukemia (B-CLL) and a T cell disorder, Sézary syndrome. These tumors do not have consistent cytogenetic or molecular genetic alterations, and so we have concentrated on their response to and production of various regulatory cytokines. Although B-CLL cells show variable proliferative responses when exposed to transforming growth factor beta (TGF beta), these cells have consistently shown resistance to the pro-apoptotic effects of this cytokine. Also, interleukin 4 (IL4), IL5, and interferon-gamma (IFN gamma) all show a consistently increased protective effect against apoptosis in B-CLL cells as compared to normal human B cells. Thus, a defect in apoptosis appears to be an important factor in the pathogenesis of CLL. By contrast, the neoplastic T cells of Sézary syndrome show a consistent resistance to the antiproliferative effects of TGF beta, suggesting that aberrant proliferation is more important than apoptosis in this disorder. In both neoplasms, we have shown that the defective responses to cytokines are in some instances related to alterations in receptor expression, but this has not been true in all circumstances, and other stages in the signaling pathways are being investigated. As we define more precisely the specific defects that contribute to the clonal expansion of these neoplasms, the findings may ultimately lead to improved clinical control of these disorders.