The relationship between CD5-expressing B lymphocytes and serologic abnormalities in rheumatoid arthritis patients and their relatives

Role of B cells as antigen presenting cells

B cells have been long studied for their role and function in the humoral immune system. Apart from generating antibodies and an antibody-mediated memory response against pathogens, B cells are also capable of generating cell-mediated immunity. It has been demonstrated by several groups that B cells can activate antigen-specific CD4 and CD8 T cells, and can have regulatory and cytotoxic effects. The function of B cells as professional antigen presenting cells (APCs) to activate T cells has been largely understudied. This, however, requires attention as several recent reports have demonstrated the importance of B cells within the tumor microenvironment, and B cells are increasingly being evaluated as cellular therapies. Antigen presentation through B cells can be through antigen-specific (B cell receptor (BCR) dependent) or antigen non-specific (BCR independent) mechanisms and can be modulated by a variety of intrinsic and external factors. This review will discuss the pathways and mechanisms by which B cells present antigens, and how B cells differ from other professional APCs.

Chemokine-like factor-like MARVEL transmembrane domain-containing family in autoimmune diseases

The chemokine-like factor (CKLF)-like MARVEL transmembrane domain-containing family (CMTM) is widely expressed in the immune system. Abnormal expression of CMTM is associated with the development of various diseases. This article summarizes the relevant research on the role of the CMTM family in immune disorders. This information will increase our understanding of pathogenesis and identify promising targets for the diagnosis and treatment of autoimmune diseases. The CMTM family is highly expressed in peripheral blood mononuclear cells. CKLF1 may be involved in the development of arthritis through its interaction with C-C chemokine receptor 4. CKLF1 is associated with the pathogenesis of lupus nephritis and psoriasis. Both CMTM4 and CMTM5 are associated with the pathogenesis of systemic lupus erythematosus. CMTM1, CMTM2, CMTM3, and CMTM6 play a role in rheumatoid arthritis, systemic sclerosis, Sjögren syndrome, and anti-phospholipid syndrome, respectively. The CMTM family has been implicated in various autoimmune diseases. Further research on the mechanism of the action of CMTM family members may lead to the development of new treatment strategies for autoimmune diseases.

Regulatory B Cells Are Decreased and Impaired in Their Function in Peripheral Maternal Blood in Pre-term Birth

Preterm birth (PTB) is defined as birth before 37 completed weeks of gestation. The causes of PTB are multiple and complex, the underlying pathophysiology being largely unknown. Interferences in the fine-tuned balance of the maternal immune system have been pointed to as one possible cause of PTB. Regulatory B cells (Breg) are part of the adaptive immune response, and recent data suggest that they may contribute to a healthy pregnancy by their regulatory/suppressive function. We investigated the frequency of Breg cells in peripheral blood of women undergoing PTB and control women immediately before giving birth via cesarean section. We detected an enhanced number of B cells, but a reduced number of Breg cells in women delivering preterm. In addition, the percentage of IL-10-producing B cells was decreased in PTB following stimulation with TLR agonists CpG or LPS, alone or combined with CD40L. This was associated with increased levels of pro-inflammatory cytokines in maternal serum. Moreover, isolated maternal B cells before delivering premature babies secreted higher level of the pro-inflammatory cytokine IL-6. No alterations in the frequency of regulatory T cells were found. Our data indicate that alterations in the number and function of Breg cells in peripheral maternal blood contribute to the immunological changes observed in preterm delivery and suggest these cells as important regulators of maternal immune responses.

B Cell Development and Maturation

Since the identification of B cells in 1965 (Cooper  et al. 1965), three has been tremendous progress in our understanding of B cell development, maturation and function. A number of B cell subpopulations, including B-1, B-2 and regulatory B cells, have been identified. B-1 cells mainly originate from the fetal liver and contain B-1a and B-1b subsets. B-2 cells are derived from the bone marrow (BM) and can be further classified into follicular B (FOB) and marginal zone B (MZB) cells. Regulatory B cells (Bregs) function to suppress immune responses, primarily by production of the anti-inflammatory cytokine IL-10. B cell tolerance is established at several checkpoints, during B cell development in the BM (central tolerance) as well as during B cell maturation and activation in the periphery (peripheral tolerance). This chapter will focus on the regulation of important processes during the development and maturation of B-1 and B-2 cells.

B1a cells play a pathogenic role in the development of autoimmune arthritis

Dysregulated functions of B1 cells have been implicated in the disease progression of various autoimmune disorders, but it remains largely unclear whether B1 cells are involved in the pathogenesis of autoimmune arthritis. In this study, we found that peritoneal B1a cells underwent proliferation and migrated to the inflamed joint tissue with upregulated RANKL expression during collagen-induced arthritis (CIA) development in mice. Adoptive transfer of B1a cells exacerbated arthritic severity and joint damage while intraperitoneal depletion of B1 cells ameliorated both arthritic symptoms and joint pathology in CIA mice. In culture, RANKL-expressing B1a cells significantly promoted the expansion of osteoclasts derived from bone marrow cells, which were in accord with the in vivo findings of increased osteoclastogenesis in CIA mice transferred with B1a cells. Together, these results have demonstrated a pathogenic role of B1a cells in the development of autoimmune arthritis through RANKL-mediated osteoclastogenesis.

RGMb is a novel binding partner for PD-L2 and its engagement with PD-L2 promotes respiratory tolerance

We report that programmed death ligand 2 (PD-L2), a known ligand of PD-1, also binds to repulsive guidance molecule b (RGMb), which was originally identified in the nervous system as a co-receptor for bone morphogenetic proteins (BMPs). PD-L2 and BMP-2/4 bind to distinct sites on RGMb. Normal resting lung interstitial macrophages and alveolar epithelial cells express high levels of RGMb mRNA, whereas lung dendritic cells express PD-L2. Blockade of the RGMb-PD-L2 interaction markedly impaired the development of respiratory tolerance by interfering with the initial T cell expansion required for respiratory tolerance. Experiments with PD-L2-deficient mice showed that PD-L2 expression on non-T cells was critical for respiratory tolerance, but expression on T cells was not required. Because PD-L2 binds to both PD-1, which inhibits antitumor immunity, and to RGMb, which regulates respiratory immunity, targeting the PD-L2 pathway has therapeutic potential for asthma, cancer, and other immune-mediated disorders. Understanding this pathway may provide insights into how to optimally modulate the PD-1 pathway in cancer immunotherapy while minimizing adverse events.

A role for CMTM7 in BCR expression and survival in B-1a but not B-2 cells

B-1 cells are an important cell population for the production of natural antibodies and front-line host defense. Here, we show that the MARVEL-domain-containing membrane protein CMTM7 (CKLF-like MARVEL transmembrane domain-containing 7) plays a critical role in BCR expression and survival in B-1a cells. We analyzed lymphocyte development in Rag1⁻/⁻ mice reconstituted with Cmtm7(flox/⁺) fetal liver cells because of the unexpected lethality of the Cmtm7(flox/⁺) heterozygotes. We found a mild reduction of serum IgM and a significantly reduced B-1a population in the peritoneal cavity of Rag1⁻/⁻ mice reconstituted with Cmtm7(flox/⁺) cells compared with those reconstituted with wild-type (WT) cells. The reduction of B-1a cells in Cmtm7(flox/⁺) mice was associated with reduced BCR expression and increased spontaneous cell death in these cells. In addition, both B-1a and B-1b cells derived from Cmtm7(flox/⁺) fetal liver cells contained a lower frequency of cells capable of spontaneously differentiating into IgM-secreting plasma cells than did those derived from WT fetal liver cells. Furthermore, Cmtm7(flox/⁺) B-1a and B-1b cells responded poorly to LPS-induced proliferation. In striking contrast to the defects in B-1 cells, Cmtm7(flox/⁺) B-2 cells did not show obvious abnormalities when compared with WT B-2 cells. These results demonstrate a specific role for CMTM7 in BCR expression and survival in B-1a cells.

Serologic factors in early relapse of IgG4-related orbital inflammation after steroid treatment

PURPOSE

To determine whether serologic factors correlate with early relapse in cases of IgG4-related orbital inflammation, a lymphoproliferative disorder.

DESIGN

Retrospective cohort study.

METHODS

We examined the orbital images and serum data of 30 patients with (n=24) or without (n=6) corticosteroid treatment before and after corticosteroid treatment and 6 months after discontinuation of corticosteroid treatment.

RESULTS

Seven patients (23%) (all with corticosteroid treatment) had elevated serum levels of rheumatoid factor. Of the 24 patients with corticosteroid treatment, 24 (100%) showed regression of the lesion, but 8 of the 24 (33%) showed relapse. The serum IgG4 levels before and after corticosteroid treatment were not significantly different between the relapsed and nonrelapsed groups (P=.5 and P=.2, respectively). However, the incidence of patients who were rheumatoid factor-positive was significantly higher in the relapsed group (P=.02). The 6 patients without corticosteroid treatment showed minor proliferation or regression of the lesion at the 6-month follow-up.

CONCLUSIONS

The serum rheumatoid factor level may correlate with proliferative activity in IgG4-related orbital inflammation.

Pathogenic and physiological autoantibodies in the central nervous system

In this article, we review the current knowledge on pathological and physiological autoantibodies directed toward structures in the central nervous system (CNS) with an emphasis on their regulation and origin. Pathological autoantibodies in the CNS that are associated with autoimmunity often lead to severe neurological deficits via inflammatory processes such as encephalitis. In some instances, however, autoantibodies function as a marker for diagnostic purposes without contributing to the pathological process and/or disease progression. The existence of naturally occurring physiological autoantibodies has been known for a long time, and their role in maintaining homeostasis is well established. Within the brain, naturally occurring autoantibodies targeting aggregated proteins have been detected and might be promising candidates for new therapeutic approaches for neurodegenerative disorders. Further evidence has demonstrated the existence of naturally occurring antibodies targeting antigens on neurons and oligodendrocytes that promote axonal outgrowth and remyelination. The numerous actions of physiological autoantibodies as well as their regulation and origin are summarized in this review.

Phenotype and function of CD25-expressing B lymphocytes isolated from human umbilical cord blood

BACKGROUND

We have shown that approximately 30% of human peripheral blood B-cells express CD25. B cells expressing CD25 display a mature phenotype belonging to the memory B-cell population and have a better proliferative and antigen-presenting capacity. The aim of the present study was to characterize the CD25-expressing subset of B cells in human cord blood.

MATERIAL AND METHODS

Mononuclear cell fraction from human cord blood (n=34) and peripheral adult blood (n=22) was sorted into CD20+CD25+ and CD20+CD25- B-cell populations. Phenotype and function of these B-cell populations were compared using flow cytometry, proliferation, cytokine production, and immunoglobulin secretion.

RESULTS

CD25-expressing B cells are a limited population of cord blood mononuclear cells representing 5% of the CD20+ B cells. They are characterised by high expression of CD5 in cord blood and CD27 in adult blood. CD25-expressing B cells express a functional IL-2 receptor and high levels of CC-chemokine receptors and spontaneously produce antibodies of IgG and IgM subclass.

CONCLUSIONS

CD25 expression is a common denominator of a specific immunomodulatory B-cell subset ready to proliferate upon IL-2 stimulation, possibly ready to migrate and home into the peripheral tissue for further differentiation/action.

B cell depletion in autoimmune diabetes: insights from murine models

INTRODUCTION

The incidence of type 1 diabetes (T1D) is rising for reasons that largely elude us. New strategies aimed at halting the disease process are needed. One type of immune cell thought to contribute to T1D is the B lymphocyte. The first Phase II trial of B cell depletion in new onset T1D patients indicated that this slowed the destruction of insulin-producing pancreatic beta cells. The mechanistic basis of the beneficial effects remains unclear.

AREAS COVERED

Studies of B cell depletion and deficiency in animal models of T1D. How B cells can influence T cell-dependent autoimmune diabetes in animal models. The heterogeneity of B cell populations and current evidence for the potential contribution of specific B cell subsets to diabetes, with emphasis on marginal zone B cells and B1 B cells.

EXPERT OPINION

B cells can influence the T cell response to islet antigens and B cell depletion or genetic deficiency is associated with decreased insulitis in animal models. New evidence suggests that B1 cells may contribute to diabetes pathogenesis. A better understanding of the roles of individual B cell subsets in disease will permit fine-tuning of therapeutic strategies to modify these populations.

Role of PIR-B in autoimmune glomerulonephritis

PIR-B, an inhibitory receptor expressed on murine B cells and myeloid cells, regulates humoral and cellular immune responses via its constitutive binding to the ligand, MHC class I molecules, on the same cells (cis) or on different cells (trans). Although it has been speculated that PIR-B is important for maintaining peripheral tolerance, PIR-B single deficiency does not cause overt autoimmune diseases. Recently, however, the combination of its deficiency with the Fas lpr mutation was found to result in augmented production of autoantibodies such as IgG rheumatoid factor and anti-DNA IgG, leading to glomerulonephritis in mice. Although the precise molecular mechanism for the overall scenario is unclear, PIR-B was found to suppress TLR9-mediated production of naturally autoreactive antibodies by innate B cells or B-1 cells by inhibiting the activation of Bruton's tyrosine kinase. Thus, PIR-B is an important regulator of innate immunity mediated by TLR9 in B-1 cells, which can otherwise provoke autoimmunity when overactivated.

Reduced Fas ligand-expressing splenic CD5+ B lymphocytes in severe collagen-induced arthritis

Introduction

The objective was to study immune regulation in a mouse model of rheumatoid arthritis that exhibits considerable heterogeneity of disease activity.

Methods

T-cell receptor transgenic mice, in which nearly all CD4⁺ T cells recognize a single peptide of type II collagen, were immunized with collagen and observed for development of arthritis for 4 weeks. At 28 days post-immunization, splenocytes were analyzed by flow cytometry and in vitro assays for markers of immune activation and regulation.

Results

Disease severities ranging from 0 to 12 (on a 12-point scale) were observed. Among splenic lymphocyte populations, only the CD5⁺ B-cell subset displayed a decrease in relative numbers as arthritis severity increased. Splenic CD5⁺ B cells expressed higher levels of Fas ligand (FasL) than did CD4⁺ T cells or CD5^- B cells in all mice, and antigen-dependent T-cell death correlated with higher levels of CD5⁺ B cells in cocultures. Ratios of interleukin (IL)-17 to interferon-gamma production were higher in antigen-driven cultures of splenocytes from severely arthritic mice compared to mildly or nonarthritic mice. A correlation was established between the reduced production of IL-17 in antigen-driven T-cell/B-cell cocultures and FasL, but not IL-10. Confirmation of the direct killing effect of B cells on T cells was demonstrated using an antigen-specific T hybridoma cell line.

Conclusions

Reduced numbers of splenic FasL⁺ CD5⁺ B cells correlated with increasing arthritis severity and decreased T-cell death in a T-cell receptor transgenic mouse model of collagen-induced arthritis. These 'killer' B cells may provide a novel mechanism for inducing T-cell death as a treatment for arthritis.

Augmented TLR9-induced Btk activation in PIR-B-deficient B-1 cells provokes excessive autoantibody production and autoimmunity

Pathogens are sensed by Toll-like receptors (TLRs) expressed in leukocytes in the innate immune system. However, excess stimulation of TLR pathways is supposed to be connected with provocation of autoimmunity. We show that paired immunoglobulin (Ig)-like receptor B (PIR-B), an immunoreceptor tyrosine-based inhibitory motif-harboring receptor for major histocompatibility class I molecules, on relatively primitive B cells, B-1 cells, suppresses TLR9 signaling via Bruton's tyrosine kinase (Btk) dephosphorylation, which leads to attenuated activation of nuclear factor kappaB p65RelA but not p38 or Erk, and blocks the production of natural IgM antibodies, including anti-IgG Fc autoantibodies, particularly rheumatoid factor. The autoantibody production in PIR-B-deficient (Pirb(-/-)) mice was further augmented in combination with the Fas(lpr) mutation, which might be linked to the development of autoimmune glomerulonephritis. These results show the critical link between TLR9-mediated sensing and a simultaneously evoked, PIR-B-mediated inhibitory circuit with a Btk intersection in B-1 cells, and suggest a novel way toward preventing pathogenic natural autoantibody production.

CD19+CD5+ B cells in primary IgA nephropathy

The source of IgA and the mechanism for deposition of IgA in the mesangium remain unknown for primary IgA nephropathy. Because CD19(+)CD5(+) B cells are important producers of IgA and contribute to several autoimmune diseases, they may play an important role in IgA nephropathy. In this study, flow cytometry, quantitative PCR, and confocal microscopy were used to assess the frequency, distribution, Ig production, CD phenotypes, cytokine production, and sensitivity to apoptosis of CD19(+)CD5(+) B cells in the peripheral blood, peritoneal fluid, and kidney biopsies of 36 patients with primary IgA nephropathy. All patients with IgA nephropathy were significantly more likely to have CD19(+)CD5(+) B cells in the peripheral blood, peritoneal fluid, and kidney biopsies than were five control subjects and 10 patients with active systemic lupus erythematosus. The 33 patients who had IgA nephropathy and responded to treatment demonstrated a significant decrease in CD19(+)CD5(+) B cells in the peripheral blood, peritoneal fluid, and kidney (all P < 0.01). In the three patients who had IgA nephropathy and did not respond to treatment, the frequency of CD19(+)CD5(+) B cells did not change. CD19(+)CD5(+) B cells isolated from patients with untreated IgA nephropathy expressed higher levels of IgA, produced more IFN-gamma, and were more resistant to CD95L-induced apoptosis than cells isolated from control subjects and patients with lupus; these properties reversed with effective treatment of IgA nephropathy. In conclusion, these results strongly suggest that CD19(+)CD5(+) B cells play a prominent role in the pathogenesis of primary IgA nephropathy.

Different kinetics of blimp-1 induction in B cell subsets revealed by reporter gene

The transcriptional repressor Blimp-1 (B lymphocyte-induced maturation protein 1) has been described as a "master regulator" of B cell differentiation into Ab-secreting cells (ASCs). Although there is mounting evidence for the importance and necessity of Blimp-1 in plasma cell development, there is uncertainty as to the role it plays in B cell differentiation of B cell subsets and the way in which it may interact with other transcription factors such as Pax5 and Bcl6 during ASC differentiation. Using a mouse expressing GFP under the control of the Blimp-1 regulatory elements (Blimp-1(GFP/+)), we examined the kinetics of Blimp-1 up-regulation in purified B cell subsets following activation. B1 cells showed the most rapid and pronounced up-regulation of Blimp-1 in response to the mitogens tested, followed by marginal zone B cells and then conventional B2 cells. Interestingly, only B1 cells substantially up-regulated Blimp-1 expression in response to CpG. B1 cells secreted negligible Ig upon isolation but were able to up-regulate Blimp-1 and initiate Ig secretion within 28 h of stimulation. Also of interest, B1 cells have a transcriptional factor profile that is intermediate between a naive B cell and an ASC, indicative of the semiactivated state of B1 cells. Transferred naive Blimp-1(GFP/+) B1 and B2 cells both gave rise to ASCs in the bone marrow, suggesting no intrinsic barriers to B1 cell entry into the long-lived ASC compartment.

B cell conducts the lymphocyte orchestra

The interest for B cells has recently been revived. They normally play a role in the development, the regulation, as well as the activation of lymphoid architecture: they regulate dendritic cells and T-cell subsets function through cytokine production. Receptor editing is also essential in B cells and aids in preventing autoimmunity. Both abnormalities in the distribution of B-cell subsets and clinical benefit response to B-cell depletion in autoimmune states illustrate their importance. A new area has thus been reached, whereby B lymphocytes return as a significant contributor to autoimmune disorders.

B-1 B lymphocytes require Blimp-1 for immunoglobulin secretion

B-1 B cells produce circulating natural antibodies that provide “innate-like” protection against bacterial and viral pathogens. They also provide adaptive responses to blood and air-borne pathogens. B lymphocyte–induced maturation protein 1 (Blimp-1) is a transcriptional repressor that is required for the formation of B-2–derived antibody-secreting plasma cells. In this study, we used mice lacking Blimp-1 in the B cell lineage to show that Blimp-1 is not necessary for the formation or self-renewal of B-1 B cells but that Blimp-1 is required for normal immunoglobulin (Ig) secretion by B-1 cells. B-1 cells lacking Blimp-1 do not repress Pax5 mRNA and do not induce X-box binding protein 1, and μ secreted mRNA normally, showing that B-1 and B-2 cells both use a common pathway for Ig secretion. Blimp-1–deficient B-1 B cells are also defective in providing early protection against influenza infection.

Signals from a self-antigen induce positive selection in early B cell ontogeny but are tolerogenic in adults

Positive and negative signals from self-Ags shape the B cell repertoire and the development of distinct B cell subsets, but little is known about what distinguishes these signals. To address this question, we have studied the development of anti-hen egg lysozyme MD4 Ig transgene B cells while systematically varying the level, distribution, and timing of exposure to different forms of hen egg lysozyme as a self-Ag. This process has allowed us to explore the effects of Ag independent of BCR specificity. Our findings show how the selection of autoreactive B cells is a competitive process involving immunogenic and tolerogenic forms of self-Ags. Due to a developmental switch during B cell ontogeny, autoreactive anti-hen egg lysozyme MD4 Ig transgene B cells are negatively selected by self-Ags in adult bone marrow but susceptible to positive selection by some of the same self-Ags in fetal and neonatal life. However, the persistence of B1 cells and IgM autoantibodies from early ontogeny enables autoreactive B cells from the adult bone marrow to escape negative selection. Our data suggest that this rescue may be due to the clearance or masking of self-Ag by IgM autoantibody. We discuss the implications of these findings in terms of B cell selection and the maintenance of self-tolerance during early and adult life.

B lymphocytes on the front line of autoimmunity

The paradigm that B cell response to self antigens (Ag) is promoted by antibodies (Ab) has become unsatisfactory. Studies over the last decade have indeed revealed that B cells serve extraordinarily diverse functions within the immune system other than Ab production. They normally play a role in the development in the regulation, as well as the activation of lymphoid architecture, regulating dentritic cells and T cell subsets function through cytokine production. Receptor editing is also essential in B cells and aids in preventing autoimmunity. Both abnormalities in the distribution of B cells subsets and clinical benefit response to B cell depletion in autoimmune states illustrate their importance. Transgenic animal models have demonstrated that sensitivity of B cells to Ag receptor cross-linking correlates to autoimmunity: negative signaling by CD5 and CD22 in maintaining tolerance through recruitment of phosphatase has thus been documented. In short, a new area has been reached, whereby B lymphocytes return as a significant contributor to autoimmune disorders.

Implications for induction of autoimmunity via activation of B-1 cells by Helicobacter pylori urease

Besides various gastroduodenal diseases, Helicobacter pylori infection may be involved in autoimmune disorders like rheumatoid arthritis (RA) or idiopathic thrombocytopenic purpura. Such autoimmune disorders are often associated with autoreactive antibodies produced by B-1 cells, a subpopulation of B lymphocytes. These B-1 cells are mainly located in the pleural cavity or mucosal compartment. The existence of H. pylori urease-specific immunoglobulin A (IgA)-producing B cells in the mucosal compartment and of their specific IgM in the sera of acutely infected volunteers suggests the possibility that urease stimulates mucosal innate immune responses. Here, we show for the first time that purified H. pylori urease predominantly stimulates the B-1-cell population rather than B-2 cells, which produce antigen-specific conventional antibodies among splenic B220(+) B cells. The fact that such stimulation of B-1 cells was not affected by the addition of polymyxin B indicates that the effect of purified H. pylori urease was not due to the contamination with bacterial lipopolysaccharide. Furthermore, the production of various B-1-cell-related autoreactive antibodies such as IgM-type rheumatoid factor, anti-single-stranded DNA antibody, and anti-phosphatidyl choline antibody was observed when the splenic B cells were stimulated with purified H. pylori urease in vitro. These findings suggest that H. pylori components, urease in particular, may be among the environmental triggers that initiate various autoimmune diseases via producing autoreactive antibodies through the activation of B-1 cells. The findings shown here offer important new insights into the pathogenesis of autoimmune disorders related to H. pylori infection.

Rheumatoid Factors: Good or Bad for You?

BACKGROUND

Rheumatoid factors (RFs) are autoantibodies associated with rheumatoid arthritis. They can be detected in normal individuals, although transiently. This dichotomy has led to questions about the origins and types of RFs. Recently it has been shown that B cells that produce RFs only do so when activated by two signals, one from engagement of the B-cell receptor and the other from recognition of a pathogen-associated molecular pattern through a Toll-like receptor (TLR). These autoantibodies thus link the innate and acquired immune responses.

OBJECTIVE

Through a review of the literature, an examination of the current knowledge of RF induction is presented. The focus is on a discussion of a beneficial or detrimental role for RFs in normal individuals and in those with chronic disease.

RESULTS

What makes RF 'good' in some cases and 'bad' in others may reflect the type of RF produced. Low-affinity polyreactive IgM RFs are probably beneficial as they aid in the clearance of immune complexes that are more efficiently cleared, and the RF B cell can act as an antigen-presenting cell and stimulate host defense. However, large amounts of high-affinity RFs found in patients with chronic disease may be harmful by participation in a vicious cycle of autoantibody production by stimulation of self lymphocytes, and/or deposition in blood vessels thus causing vasculitis.

CONCLUSIONS

Whether RFs are beneficial or detrimental depends on the context in which they are expressed, the type and amount of RF produced, whether the response is perpetuated by TLR ligation and whether other cells are stimulated either directly or indirectly by RF-positive B cells.

B Lymphocytes Are Required for Development and Treatment of Autoimmune Diseases

Recent studies have revealed that B cells serve extraordinarily diverse functions within the immune system in addition to antibody production. These functions contribute to autoimmunity. They initiate the development of lymphoid architecture and regulate dendritic and T-cell function through cytokine production. Receptor editing is also essential to prevent autoimmunity. Both abnormalities in the distribution of B-cell subsets and the benefits of ablative B-cell therapy of autoimmune states confirm their importance. Results from transgenic models have demonstrated that the sensitivity of B cells to antigen receptor cross-linking correlates to autoimmunity, with particular reference to negative signaling by CD5 and CD22. These mechanisms maintain tolerance by recruiting src-homology 2 domain-containing protein tyrosine phosphatase-1. These findings open new prospects for immunotherapy of autoimmune diseases.

Reduced proviral loads during primo-infection of sheep by Bovine Leukemia virus attenuated mutants

Background

The early stages consecutive to infection of sheep (e.g. primo-infection) by Bovine leukemia virus mutants are largely unknown. In order to better understand the mechanisms associated with this period, we aimed at analyzing simultaneously three parameters: B-lymphocytosis, cell proliferation and viral replication.

Results

Sheep were experimentally infected either with a wild type BLV provirus or with selected mutants among which: a virus harboring an optimalized LTR promoter with consensus cyclic AMP-responsive elements, two deletants of the R3 or the G4 accessory genes and a fusion-deficient transmembrane recombinant. Seroconversion, as revealed by the onset of an anti-viral antibody response, was detected at 3 to 11 weeks after inoculation. At seroconversion, all sheep exhibited a marked increase in the numbers of circulating B lymphocytes expressing the CD5 and CD11b cluster of differentiation markers and, interestingly, this phenomenon occurred independently of the type of virus. The net increase of the absolute number of B cells was at least partially due to accelerated proliferation as revealed, after intravenous injection of bromodeoxyuridine, by the higher proportion of circulating BrdU+ B lymphocytes. BLV proviral DNA was detected by polymerase chain reaction in the leucocytes of all sheep, as expected. However, at seroconversion, the proviral loads were lower in sheep infected by the attenuated proviruses despite similar levels of B cell lymphocytosis.

Conclusions

We conclude that the proviral loads are not directly linked to the extent of B cell proliferation observed during primo-infection of BLV-infected sheep. We propose a model of opportunistic replication of the virus supported by a general activation process of B lymphocytes.

Rheumatoid factors: host resistance or autoimmunity?

Rheumatoid factors (RFs), autoantibodies that bind to the Fc portion of IgG, are important in the immune response. RF-committed B-cells exist in the circulating lymphocyte pool in a high frequency (approximately 1-2 %) in normal individuals and in patients with pathological conditions associated with the sustained levels of circulating RF, such as rheumatoid arthritis (RA), Sjogren's syndrome (SS), and mixed cryoglobulinemia, associated with hepatitis C virus infection. RFs are induced by many infectious entities (viruses, bacteria, parasites) as a consequence of a secondary immune response to the pathogen, but usually the response is transient. It is likely that RFs play an important role in the host's defense against infection, both at the cellular level, where the RF B-cell can be an antigen presenting cell which can promote the antipathogen response, and at the humoral level, where RFs can contribute to the mopping up of the IgG antipathogen antibodies by contributing to immune complex formation and clearance. There has been much research on RFs in chronic pathological conditions, and the literature pertaining to their origin, structure, binding specificities, and possible roles in disease are discussed. The importance of the host defense, sometimes at the expense of an autoimmune response, is a balance that needs to be considered in light of a possible outcome of health or disease.

Origins and functions of B-1 cells with notes on the role of CD5

Whether B-1a (CD5+) cells are a distinct lineage derived from committed fetal/neonatal precursors or arise from follicular B-2 cells in response to BCR ligation and other, unknown signals remains controversial. Recent evidence indicates that B-1a cells can derive from adult precursors expressing an appropriate specificity when the (self-) antigen is present. Antibody specificity determines whether a B cell expressing immunoglobulin transgenes has a B-2, B-1a or marginal zone (MZ) phenotype. MZ cells share many phenotypic characteristics of B-1 cells and, like them, appear to develop in response to T independent type 2 antigens. Because fetal-derived B cell progenitors fail to express terminal deoxynucleotidyl transferase (TdT) and for other reasons, they are likely to express a repertoire that allows selection into the B-1a population. As it is selected by self-antigen, the B-1 repertoire tends to be autoreactive. This potentially dangerous repertoire is also useful, as B-1 cells are essential for resistance to several pathogens and they play an important role in mucosal immunity. The CD5 molecule can function as a negative regulator of BCR signaling that may help prevent inappropriate activation of autoreactive B-1a cells.

Recent progress in the understanding of B-cell functions in autoimmunity

Our early concepts of the normal role of B cells in immunity focused on their ability to produce antibodies (Ab) and in the case of autoimmune diseases autoAbs, some of which were pathogenic. Over the past 10 years, it has became apparent that B cells display a variety of characteristics, other than Ab production, which could contribute to autoimmunity. They normally play a role in the development of lymphoid architecture, regulating T-cell subsets and dendritic cell (DC) function through cytokine production, and in activation of T cells. Receptors editing is also important in B cells which aids in immunity to infection and, possibly, prevention of autoimmunity. Transgenic animal models have now shown that B cells are necessary for many autoimmune diseases although their Ab products are not required in some cases. Negative signalling by CD5 and other molecules, such as CD22, in maintaining tolerance through recruitment of src-homology two domain-containing protein tyrosine phosphatase-1 has also been documented. In fact, we have now reached a new era whereby the B cell has returned as an important contributor to autoimmune disorders, so that the race is on to characterize signalling regulation via the B-cell receptor and coreceptors. Identification of such molecules and their potential defects should lead to effective ways of controlling the immune response and in particular preventing the development of autoimmune states. The classical view of B cells in the biology of immune responses to infectious and self-antigens (Ag) that they promote immunity primarily by producing Ab turns out to be rather naïve. Indeed, studies over the last few years indicate that this view is far from complete, and suggest that B lymphocytes have extraordinarily diverse functions within the immune system. Furthermore, it is becoming increasingly clear that the pathogenesis of autoimmune diseases cannot solely be accounted for by T cells, and intrinsic abnormalities of B cells have been described in such conditions. In this brief review we highlight some recent observations in the context of B lymphocyte in pathophysiology, and focus on their revival as pivotal players the pathophysiology in autoimmune diseases. Yet, it remains difficult to provide a model of how important B cells are in immunity and autoimmunity.

Prevalence of joint complaints amongst individuals with Dupuytren's disease--from the Reykjavík study

It has been reported that Dupuytren's disease is very uncommon amongst patients with rheumatoid arthritis (RA). We investigated the prevalence of different joint complaints in a cohort of 1297 males, aged 46-74 years, participating in a prospective longitudinal health survey. Joint complaints were less frequently observed in men with Dupuytren's disease than in those who did not have any signs of this disease. When adjusted for age the Dupuytren's patients had less frequently history of morning stiffness (odds ratio (OR)=0.65; 95% confidence interval (CI)=0.44-0.98, P=0.04), joint swelling (OR=0.52; 95% CI=0.27-1.00, P=0.05), and attendance to doctors due to rheumatic disorders (OR=0.44; 95% CI=0.15-0.86, P=0.02) than those who did not have clinical signs of Dupuytren's disease. Furthermore, these associations were even stronger after adjustment for other potential confounding factors, such as smoking, lipids, diabetes, education, and occupation. The reason for a negative association between Dupuytren's disease and joint complaints is not clear but genetic and immunological factors may be important.

CD5 expression in human B-cell populations

The origin of CD5+ B cells remains controversial. The differential response to ligation of CD5 resulting in apoptosis or proliferation provides insight into its roles in distinct human B cells. Here, Pierre Youinou, Christophe Jamin and Peter Lydyard review current knowledge of B-1 and B-2 cells, and propose that CD5 has different functions when expressed by different B-cell subpopulations.

An NFAT-Dependent Enhancer Is Necessary for Anti-IgM-Mediated Induction of Murine CD5 Expression in Primary Splenic B Cells

CD5 is a 67-kDa membrane glycoprotein the expression of which in murine splenic B cells is induced by surface IgM cross-linking. To analyze this induction, we transiently transfected primary splenic B cells with luciferase reporter constructs driven by various wild-type and mutated CD5 5′-flanking sequences. The transfected cells were subsequently cultured in medium with or without F(ab′)2 anti-IgM (anti-IgM), and luciferase expression was assayed. Using this approach, we identified a 122-bp enhancer element necessary for anti-IgM-mediated induction of the CD5 promoter. Electrophoretic mobility shift assays indicated that four inducible and four constitutive complexes form on the enhancer fragment in nuclear extracts of primary B cells. Supershift assays revealed that two of the inducible complexes contained NFATc. Point mutations that abolished NFAT binding severely impaired enhancer function. Thus, CD5 is a target of NFAT in B cells. A third inducible complex required an intact H4TF-1 site. One of several constitutive complexes required an intact Ebox site while a second required an intact putative ets binding site. Mutation of the H4TF-1, Ebox, and Ets sites, in the presence of wild-type NFAT sites, significantly reduced the activity of the enhancer. Therefore, the induction of B cell CD5 expression requires NFAT binding and binding to at least one of three additional sites in the CD5 enhancer.

The study of circulating CD5 positive B lymphocytes in Chinese patients with rheumatoid arthritis

Circulating CD5+ B lymphocytes were studied in 39 Chinese patients with rheumatoid arthritis (RA). Blood cells were stained with anti-CD5 and anti-CD19 monoclonal antibodies and were analyzed by flow cytometry. The results showed that there was no elevation of CD5+ B cells in RA patients when compared with 41 healthy control subjects. The circulating levels of CD5+ B cell correlated neither with serum titers of rheumatoid factor (RF) nor with disease activities in these patients. The CD5+ B cell levels remained relatively constant after a serial follow-up for 12 months. The similar pattern of epitope density of CD5 antigens also existed in the same patients. Although most studies in Caucasians revealed increased levels of CD5+ B cells in RA patients, measurements of this marker were not useful for the evaluation of disease activities in Chinese patients. Levels of CD5+ B cells may reflect more individual genetic background and may play a minor role in the flare-up of activities in Chinese patients with RA.

B lymphocytes and humoral immune responses in rheumatoid arthritis

Although the etiology of rheumatoid arthritis (RA) remains unknown at present, major evidence implicates humoral immune mechanisms in the pathophysiology of this disease. The primary lesions occur in the synovium and are characterized by immunological activation and chronic inflammation. Activated B cells and plasma cells secrete antibodies including rheumatoid factors and anticollagen antibodies. These antibodies give rise to immune complex formation and activation of the inflammatory cascade. There is no evidence that rheumatoid factor secreting B cells act as antigen presenting cells and present immune complex to T cells, leading to perpetuation of the inflammatory response.

Anti CD5 sustains the proliferative response of IgM-activated human CD5+ B cells

The CD5 molecule is expressed by most T cells but it is present on a minor B cell subset. Whilst several studies have provided information on the physiological role of T cell CD5, the functional role of CD5 on B lymphocytes remains unclear. To address this question, tonsillar CD5+ B cells were sorted by dual-colour fluorescence and FACS. Sorted cells were stimulated with polyclonal anti-IgM antibodies (Ab), and monoclonal (MoAb) F(ab')2 fragments of anti-CD5. Proliferative responses were evaluated by enumeration of Ki-67 positive cells using quantitative flow cytometry. Co-stimulation with anti-CD5 MoAb for 3 days did not affect the anti-IgM and IL2-induced proliferation of CD5+ B cells. This was seen under conditions where the anti-CD5 was soluble, adsorbed to the microwells or cross-linked by anti-mouse antibodies. Fewer CD25+ cells were detected, however, in the presence of anti-CD5. In contrast, the proliferative response of CD5+ B cells prestimulated for 3 days with IL-2 and anti-IgM, was sustained in a further 3-day culture period when anti-CD5 was added. It is concluded that CD5 occupancy might provide an additional signal to activated CD5+ B cells favouring their proliferation and differentiation into autoantibody secreting cells.

Low molecular weight IgM and CD5 B lymphocytes in rheumatoid arthritis

OBJECTIVES

To evaluate the role of low molecular weight (LMW) IgM and CD5 B cells in rheumatoid arthritis (RA) and to explore the possibility that LMW IgM is derived selectively from this subset of B cells.

METHODS

LMW IgM in sera and culture supernatants was detected by a sensitive immunoblot technique with an enhanced chemiluminescence detection system. CD5 B cells were determined by FACScan cytometry. In vitro studies were established in culture plates containing pokeweed mitogen with or without 2-mercaptoethanol (2-ME). Supernatants were obtained from CD5 positive hybridomas and CD5 negative hybridomas. Other immunological indices were measured by laser nephelometry.

RESULTS

Circulating LMW IgM was detected in all rheumatoid patients with significantly higher levels being observed in sero-positive patients. LMW IgM correlated significantly with total IgM and RF. Peripheral blood mononuclear cells (PBMC) from the majority of the patients with RA secreted LMW IgM in vitro as did mononuclear cells from a synovial fluid sample. The addition of low concentrations of 2-ME to the culture medium enhanced the proportions of secreted monomeric IgM. In contrast, PBMC from healthy subjects secreted only trace quantities of LMW IgM. In RA no significant correlations were observed between CD5 B cells and LMW IgM and RF. LMW IgM could be detected in the supernatants from both CD5+ and CD5- B cell lines. Finally, CD5 B cells were not significantly elevated in RA and levels remained constant over time.

CONCLUSION

LMW IgM exists in high concentrations in RA sera and synovial fluid. Serum level correlates with RF and IgM. In vitro studies have suggested that the occurrence of LMW IgM may be due to an intrinsic defect(s) in the assembly of the IgM pentameric molecule. LMW IgM is unlikely to be derived solely from CD5 B cells.

CD5+ B cells and the immune system

The CD5+ B-cell population is prominent in early life and may play a key role in the ontogeny of the immune system. Transplantation studies in mice are in support of CD5+ B cells as a separate lineage from CD5- B cells. In both mice and men there is evidence in favour of CD5 being an activation antigen rather than a lineage marker, but the jury is still out! The frequency of CD5+ B cells appears to be under genetic influence. CD5+ B cells are receptive to many cytokines including IL-2 and IL-5 and themselves produce a number of cytokines especially IL-10. The function of the CD5 molecule on B cells is presently unknown but it might be involved in interaction with CD72 on other B cells. CD5+ B cells generally utilise minimally mutated germ-line genes and produce low avidity auto- and polyreactive antibodies (natural antibodies) generally of the IgM class.

Anti-"dividing cell antigen" autoantibody: a novel antinuclear antibody pattern related to histones in systemic lupus erythematosus

This study aims to describe a novel antinuclear antibody directed to proteins only accessible during the mitosis: anti-"dividing cell antigen" (DCA) antibody. A total of 709 disease-associated and control sera was tested by indirect immunofluorescence using a variety of cell lines as substrate. Cells were treated with enzymes and antibodies absorbed with nuclear antigens. Antibodies to DNA, histone subfractions, and synthetic peptides were evaluated using enzyme-linked immunosorbent assays. Cell extracts were electrophoresed before and after synchronization and sera tested on the blots. The anti-DCA antibody was demonstrated in 10 of 183 SLE patients but virtually never in other connective tissue diseases. The DCA was sensitive to HCl and proteolytic enzymes and the anti-DCA binding inhibited by histones H2A and H2B. Differences of anti-H2A and anti-H2B were observed between anti-DCA antibody-positive and anti-DCA antibody-negative sera, and antibodies specific for the 1-15 region of H2A, the 1-25 region of H2B and the 1-29 region of H4 were more frequent in the former sera than in the latter. The anti-DCA antibody was shown to react with a 60-kDa protein. Our findings suggest that the anti-DCA antibody is directed to a protein complex containing H2A and H2B.

Expression of CD5 and CD72 on T and B cell subsets in rheumatoid arthritis and Sjögren's syndrome

A minority of B cells express the CD5 marker, which is found on virtually all T cells, and CD72 has been defined as the CD5 ligand on the B cell membrane. The mean fluorescence intensity (MFI) of the CD5 molecules was shown to be higher on CD4+CD29+ than CD4+CD45RA+ in peripheral blood (PB) and synovial fluid (SF) of rheumatoid arthritis (RA) patients (P < 0.0001 and < 0.001), and PB of Sjögren's syndrome (SS) patients and normal controls (P < 0.02 and < 0.03). This MFI declined once the CD4 expressed HLA-DR in PB of SS patients (P < 0.004) and normal controls (P < 0.02) or CD25 in PB of RA (P < 0.004) and SS patients (P < 0.0004). There was a correlation between the CD5 MFI on CD4+CD45RA+ and CD4+CD29+ in RA (P < 0.001) as well as SS (P < 0.0007) PB. The CD72 MFI was impressively higher on CD5+ than CD5- B cells in PB and SF of RA patients (P < 0.0001 and P < 0.005) and PB of SS patients (P < 0.005) and normal controls (P < 0.005). Our data suggest that, in association with CD4CD29, CD5 is involved in CD5+B/CD5+ B cell interactions in non-organ-specific autoimmune diseases.

Human CD5-positive B cells in lymphoid malignancy and connective tissue diseases

The current literature on human CD5-positive B cells (CD5 + B cells) has been analysed, with a special emphasis on non organ-specific auto-immune diseases. Malignant cells of most of the chronic lymphoid leukaemias of the B cell lineage express the CD5 molecule. Antibodies of the IgM class produced by leukaemic B cells are multispecific auto-antibodies. The CD5 + B cell subset may be expanded in non organ-specific autoimmune diseases, such as rheumatoid arthritis, primary Sjögren's syndrome, systemic lupus erythematosus. This holds true for various conditions, including organ-specific auto-immune diseases. Since auto-immune features are common in lymphoproliferative disorders, and the latter be a complication in non organ-specific auto-immune diseases, CD5 + B cells may represent an intermediary between these auto-immune diseases and B cell lymphoproliferations. Studies on the regulation of CD5 + B cell production and function are likely to shed light on the aetiology of, and pathogenetic mechanisms operating in the different disease states.

CD5+ B lymphocytes and T-cell subsets in a case of juvenile rheumatoid arthritis

Recent research has demonstrated that CD5+ B lymphocytes have an important role in autoimmune and rheumatic diseases. In a case of juvenile rheumatoid arthritis (JRA), we observed the behavior of these cells and other subpopulations of T lymphocytes of peripheral blood before and after therapy with thymopentin (TP5). All the lymphocyte subpopulations returned to normal range, except the CD5+ B cells, where the percentage remained abnormally high (60%). These data suggest that CD5+ B cells can be a useful monitoring index and confirm their important role in the pathogenesis of juvenile rheumatoid arthritis.

Increase in CD5+ B Cells in Juvenile Rheumatoid Arthritis

OBJECTIVE

To investigate the association between CD5+ B cell expression and IgM rheumatoid factor (IgM-RF) in juvenile rheumatoid arthritis (JRA).

METHODS

CD5+ B cell levels analyzed by flow cytometry and IgM-RF expression determined by enzyme-linked immunosorbent assay were compared in children with JRA, children with other collagen vascular diseases, and healthy controls.

RESULTS

Children with polyarticular JRA had expanded populations of CD5+ B cells, and expansion of CD5+ B cells and IgM-RF both correlated with disease activity.

CONCLUSION

The results indicate that an expanded CD5+ B cell population leads to IgM-RF production in patients with polyarticular JRA, as well as patients with RA.

Anti-Epstein-Barr virus-nuclear antigen-1, -2A and -2B antibodies in rheumatoid arthritis patients and their relatives

We have examined serum antibodies to Epstein-Barr virus Nuclear Antigen (EBNA)-1, -2A and -2B, in addition to antibodies to viral capsid antigen and early antigen in 100 rheumatoid arthritis patients and 50 of their relatives. Using indirect immunofluorescence on transfected cells and Western-blot technique, we have found increased frequency and titres of antibodies to EBNA-2B in patients and, to a lesser degree, in their family members, whereas other anti-Epstein-Barr virus antibodies appeared to be similar to controls. Cross-inhibition experiments were carried out and show that antibodies to EBNA-2A are distinct from those to -2B, and vice versa.

Cell-free CD5 in patients with rheumatic diseases

Since an increased frequency of CD5+ B cells has been reported in rheumatoid arthritis (RA) and primary Sjögren's syndrome (SS), and the expression of the molecule was reduced on the T cells of some SS patients, we hypothesised that there would be an accelerated turnover of CD5 in these disorders. We describe a novel enzyme-linked immunosorbent assay for measuring cell-free (CF) CD5, using rabbit F(ab')2 anti-CD5 antibody as capture agent and monoclonal anti-CD5 antibody as revealing agent. It was established that CF-CD5 was detectable in RA and SS sera, as opposed to sera from patients with ankylosing spondylitis and normal controls. The level of CF-CD5 did not correlate with rheumatoid factor in RA patients but was significantly higher (P less than 0.05) in SS patients with extraglandular manifestations than in those with glandular disease. Three of the latter patients with significantly increased levels of CD5-negative T cells did not have a particularly high proportion of CF-CD5 in these sera.