Translational Mini-Review Series on B Cell-Directed Therapies: Recent advances in B cell-directed biological therapies for autoimmune disorders

Nomogram Based on Inflammatory Factor to Predict Therapeutic Response of Thrombocytopenia in Patients with Primary Sjögren's Syndrome

Objective

Thrombocytopenia is a common manifestation of blood system involvement in primary Sjögren's syndrome (pSS) patients, and the treatment approach involves glucocorticoids and immune agents. However, a proportion of patients do not respond well to this therapy and failed to achieve remission. Accurate prediction of therapeutic response in pSS patients with thrombocytopenia is of great significance for improving the prognosis. This study aims to analyze the influencing factors of no remission to treatment in pSS patients with thrombocytopenia and establish an individualized nomogram to predict the treatment response of patients.

Materials and Methods

The demographic data, clinical manifestations and laboratory examinations of 119 patients with thrombocytopenia pSS in our hospital were retrospectively analyzed. According to the 30-day treatment response, patients were divided into remission group and non-remission group. Logistic regression was used to analyze the influencing factors related to the treatment response of patients, and then a nomogram was further established. The discriminative ability and clinical benefit of the nomogram were evaluated by receiver operating characteristic (ROC) curve, calibration chart and decision curve analysis (DCA).

Results

After treatment, there were 80 patients in the remission group and 39 in the non-remission group. Comparative analysis and multivariate logistic regression analysis identified hemoglobin (P=0.023), C3 level (P=0.027), IgG level (P=0.040), and bone marrow megakaryocyte counts (P=0.001) as independent predictors of treatment response. The nomogram was constructed based on the above four factors, and the C-index of the model was 0.882 (95% CI 0.810-0.934). The calibration curve and DCA proved that the model has better performance.

Conclusion

The nomogram incorporating hemoglobin, C3 level, IgG level, and bone marrow megakaryocyte counts could be used as an auxiliary tool to predict the risk of treatment non-remission in pSS patients with thrombocytopenia.

The immunomodulatory effect of koumine on B cells under dependent and independent responses by T cells

Dysregulated activation of polyclonal B cells and production of pathogenic antibodies are involved in the development of rheumatoid arthritis (RA). Therefore, targeted B cell therapy is effective against RA. Gelsemium elegans (Gardn. & Champ.) Benth., a toxic plant widely distributed in Southeast Asia, has been used for treating rheumatoid pain, neuropathic pain, spasticity, skin ulcers, and cancers for many years in traditional Chinese medicine. Koumine, an alkaloid monomer from Gelsemium elegans Benth., exerts therapeutic effects against RA. However, whether koumine affects B cells remains unknown. In this study, the effect of koumine on B cells under T cell-independent (TI) and T cell-dependent (TD) immune responses is investigated in vitro and in vivo. Mouse primary B cells were obtained by immunomagnetic bead sorting, and immunomodulatory effects of koumine on the activation, proliferation, and differentiation of B cells were determined in TI and TD models induced by lipopolysaccharide (LPS) and anti-CD40 antibodies in vitro, respectively. The humoral immune responses of TI and TD were established using NP-AECM-FICOLL and NP-CGG in C57BL/6J mice, respectively. We found that koumine inhibited B cell differentiation in the TI model and inhibited B cell activation and proliferation in the TD model in vitro. Koumine also inhibited antibody secretion in TI immune response, TD initial immune response, and in TD secondary immune response. Our results reveal that koumine has a direct and indirect immune regulatory effect on B cells, showing that it can directly inhibit the differentiation and secretion of autoantibodies after abnormal activation of B cells, and indirectly inhibit the activation and proliferation of TD B cells to reduce the secretion of antibodies. It may be an important mechanism for its anti-RA effect in mice, providing a rationale and laboratory data support for the application of koumine in anti-human RA therapy.

A novel modified vaccination technique produces IgG antibodies that cause complement-mediated lysis of multiple myeloma cells carrying CD38 antigen

Objectives were to: 1) induce a lytic IgG antibody (ab) response (via the so called `third vaccination method') against CD38 antigen (ag) residing on the extra-cellular domain of multiple myeloma (MM) cells in recipient rabbits, by combining the CD38 ag with donor-derived anti-CD38 ag lytic IgG ab into an immune complex (IC); and 2) determine whether abs produced would cause complement-mediated lysis (in vitro) of human MM cells containing CD38 ag. The vaccine was created in a two-step process. First, ab (rabbit anti-CD38 ag IgG ab) was raised in donor rabbits by injections of low molecular weight soluble CD38 ag in Freund's complete adjuvant (FCA) and aqueous solution. Second, transfer of pathogenic lytic IgG ab response into recipient rabbits was achieved by injections of ICs composed of CD38 ag and homologous anti-CD38 ag IgG ab. Consequently, recipient rabbits produced the same ab with the same specificity against the target ag as was present in the inoculum, namely agglutinating, precipitating and lytic (as demonstrated in vitro). In an in vitro study, in the presence of complement, donor and recipient rabbits' immune sera caused lysis of CD38 ag associated human MM cells. The most effective lytic ab response causing sera were those from donor rabbits injected with CD38 ag in FCA and those from rabbits injected with ICs, especially when they were administered in adjuvants. These results provided proof of concept that the third vaccination method has good potential as a stand-alone and efficacious method of controlling cancer.

The role of autoimmunity in premature ovarian failure

Premature ovarian failure (POF) is a heterogeneous syndrome with several causative factors. Autoimmune mechanisms are involved in pathogenesis of 4-30 % of POF cases. The present review focuses on the role of autoimmunity in the pathophysiology of POF. The evidences for an autoimmune etiology are: demonstration of ovarian autoantibodies, the presence of lymphocytic oophoritis, and association with other autoimmune disorders. Several ovarian antigenic targets have been identified in POF patients. The oocyte seems to be the most often targeted cell. Lymphocytic oophoritis is widely present in POF associated adrenal insufficiency. Addison's disease is one of the most common autoimmune disorders associated with POF. Early detection of this potentially life threatening disease was recommended in several studies. The gold standard for detecting autoimmune POF is ovarian biopsy. This procedure is not recommended due to unknown clinical value, expense, and risks. Several immunoassays have been proposed as substitute diagnostic tools. Nevertheless, there is no clinically proven sensitive and specific serum test to confirm the diagnosis of autoimmune POF or to anticipate the patient's chance of developing POF or associated diseases. Some authors suggested the possible effects of immuno-modulating therapy on the resumption of ovarian function and fertility in a selected group of autoimmune POF patients. However, in most instances, this treatment fails to reverse the course of the disease. Numerous studies illustrated that standard treatment outcome for infertility is less effective in the presence of ovarian autoimmunity. The antibody-induced damage could be a pathogenic factor. Nevertheless, the precise cause remains obscure.

Achieving incompatible transplantation through desensitization: current perspectives and future directions

The application of life-saving transplantation is severely limited by the shortage of organs, and histoincompatibility. To increase transplant rates in sensitized patients, new protocols for HLA and blood type incompatible (ABOi) desensitization have emerged. These approaches require significant desensitization using intravenous immunoglobulin, rituximab and plasma exchange. In addition, the development of donor-specific antibody responses post transplant is the major cause of allograft failure with return to dialysis. This increases patient morbidity/mortality and cost. Immunotherapeutic agents used for desensitization evolved from drug development in oncology and autoimmune diseases. Currently, there is a renaissance in development of novel drugs likely to improve antibody reduction in transplantation. These include agents that inactivate IgG molecules, anticytokine antibodies, costimulatory molecule blockade, anticomplement agents and therapies aimed at the plasma cell.

Sjögren's syndrome: still not fully understood disease

Primary Sjögren's syndrome is an autoimmune disorder with external exocrine glands dysfunction and multiorgan involvement. The pathogenesis of primary Sjogren’s syndrome is still unclear; however, our knowledge of the involvement of different cells (e.g., B and T cells, macrophages and dendritic cells) and pathways (BAFF/APRIL and interferons) leading to the development of autoimmunity is continually expanding. For clinicians, the most frequent symptoms are dryness of eyes and mouth, but often the patients have musculoskeletal symptoms and systemic manifestations. However, the increased risk of lymphoproliferative disorders in this group of patients, most commonly B-cell marginal zone lymphoma, is particularly important. Recent separation of IgG4-related diseases and attempts to create further diagnostic criteria for pSS testify to the difficulties, and at the same time a large interest, in understanding the disease so as to allow the effective treatment. This article draws attention to the problems faced by the clinician wishing to securely identify pSS by using accurate laboratory biomarkers and useful imaging tools and predict the development of complications associated with this, still not fully understood, autoimmune disease.

Role of BAFF/BAFF-R axis in B-cell non-Hodgkin lymphoma

B-cell activating factor (BAFF), as a member of the tumor necrosis factor (TNF) ligand family, plays important roles in B-cell homeostasis, tolerance, and malignancy. BAFF binds to three receptors of TNF, TACI, BCMA and BAFF-receptor (BAFF-R). In particular, the BAFF/BAFF-R pathway is crucial to the survival and growth of mature normal and malignant B-cells. BAFF is displayed on the cell surface or is released in a soluble form after cleavage from the plasma membrane. BAFF-R as the main BAFF receptor is expressed mainly on B-cells. Aberrant BAFF expression was found in malignant B-cells from B-cell non-Hodgkin lymphoma (B-NHL) patients, which protects these cells from spontaneous or drug-induced apoptosis and stimulated NF-κB activation via autocrine and/or paracrine pathways. However, the mechanisms involved in the gene expression and regulation of BAFF or BAFF-R has not been elucidated. More importantly, the design of reagents able to counteract BAFF/BAFF-R pathways may be of therapeutic value for B-NHL. Results of ongoing clinical trials with BAFF or BAFF-R antagonists are eagerly awaited.

Orientation-specific attachment of polymeric microtubes on cell surfaces

Tubular particles presenting heterogeneous regions of chemistry on the tube-ends versus the side are fabricated and are shown to control the particle orientation on the surface of live lymphocytes. Controlling the orientation of anisotropic microparticles on cell surfaces is of interest for biomedical applications and drug delivery in particular, since it can be used to promote or resist particle internalization.

Common variable immunodeficiency unmasked by treatment of immune thrombocytopenic purpura with Rituximab

Background

Hypogammaglobulinemia may be part of several different immunological or malignant conditions, and its origin is not always obvious. Furthermore, although autoimmune cytopenias are known to be associated with common variable immunodeficiency (CVID) and even may precede signs of immunodeficiency, this is not always recognized. Despite novel insight into the molecular immunology of common variable immunodeficiency, several areas of uncertainty remain. In addition, the full spectrum of immunological effects of the B cell depleting anti-CD20 antibody Rituximab has not been fully explored. To our knowledge this is the first report of development of CVID in a patient with normal immunoglobulin prior to Rituximab treatment.

Case presentation

Here we describe the highly unusual clinical presentation of a 34-year old Caucasian male with treatment refractory immune thrombocytopenic purpura and persistent lymphadenopathy, who was splenectomized and received multiple courses of high-dose corticosteroid before treatment with Rituximab resulted in a sustained response. However, in the setting of severe pneumococcal meningitis, hypogammaglobulinemia was diagnosed. An extensive immunological investigation was performed in order to characterize his immune status, and to distinguish between a primary immunodeficiency and a side effect of Rituximab treatment. We provide an extensive presentation and discussion of the literature on the basic immunology of CVID, the mechanism of action of Rituximab, and the immunopathogenesis of hypogammaglobulinemia observed in this patient.

Conclusions

We suggest that CVID should be ruled out in any patient with immune cytopenias in order to avoid diagnostic delay. Likewise, we stress the importance of monitoring immunoglobulin levels before, during, and after Rituximab therapy to identify patients with hypogammaglobulinemia to ensure initiation of immunoglobulin replacement therapy in order to avoid life-threatening invasive bacterial infections. Recent reports indicate that Rituximab is not contra-indicated for the treatment of CVID-associated thrombocytopenia, however concomitant immunoglobulin substitution therapy is of fundamental importance to minimize the risk of infections. Therefore, lessons can be learned from this case report by clinicians caring for patients with immunodeficiencies, haematological diseases or other autoimmune disorders, particularly, when Rituximab treatment may be considered.

CD22 and autoimmune disease

CD22 is a 140-kDa member of the Siglec family of cell surface proteins that is expressed by most mature B-cell lineages. As a co-receptor of the B-cell receptor (BCR), it is known to contribute to the sensitive control of the B-cell response to antigen. Cross-linking of CD22 and the BCR by antigen triggers the phosphorylation of CD22, which leads to activation of signaling molecules such as phosphatases. Signal transduction pathways involving CD22 have been explored in a number of mouse models, some of which have provided evidence that in the absence of functional CD22, B cells have a "hyperactivated" phenotype, and suggest that loss of CD22 function could contribute to the pathogenesis of autoimmune diseases. Modulating CD22 activity has therefore been suggested as a possible therapeutic approach to such diseases. For example, the novel CD22-targeting monoclonal antibody epratuzumab is currently under investigation as a treatment for the connective tissue disorder systemic lupus erythematosus (SLE).

Novel approaches in the treatment of myositis and myopathies

The inflammatory myopathies are a heterogeneous group of disorders characterized by muscle weakness and inflammation. Although no standard therapeutic guidelines exist, traditional treatment has included corticosteroids and a variety of second-line immunosuppressants. As treatment of refractory disease has been difficult, newer agents and approaches have been used with varying response. The advent of standardized treatment response criteria by the International Myositis Assessment and Clinical Studies (IMACS) group has helped investigators to evaluate and compare clinical trial outcomes in a more rigorous fashion. The use of intravenous immunoglobulin (IVIG), rituximab, biologic agents including tumor necrosis factor (TNF) inhibitors, stem-cell transplantation, gene therapy, and vascular occlusion resistance training are reviewed here. As our understanding of disease pathogenesis at the immunologic, genetic, and molecular level expands, the discovery of novel therapeutic targets hold promise for the successful treatment of these conditions.

Selective APRIL blockade delays systemic lupus erythematosus in mouse

SLE pathogenesis is complex, but it is now widely accepted that autoantibodies play a key role in the process by forming excessive immune complexes; their deposits within tissues leading to inflammation and functional damages. A proliferation inducing ligand (APRIL) is a member of the tumor necrosis factor (TNF) superfamily mediating antibody-producing plasma cell (PC)-survival that may be involved in the duration of pathogenic autoantibodies in lupus. We found significant increases of APRIL at the mRNA and protein levels in bone marrow but not spleen cells from NZB/W lupus mice, as compared to control mice. Selective antibody-mediated APRIL blockade delays disease development in this model by preventing proteinuria, kidney lesions, and mortality. Notably, this was achieved by decreasing anti-DNA and anti-chromatin autoantibody levels, without any perturbation of B- and T-cell homeostasis. Thus, anti-APRIL treatment may constitute an alternative therapy in SLE highly specific to PCs compared to other B-cell targeting therapies tested in this disease, and likely to be associated with less adverse effects than any anti-inflammatory and immunosuppressant agents previously used.

Relevance of rituximab therapy in pemphigus vulgaris: analysis of current data and the immunologic basis for its observed responses

Treatment of pemphigus vulgaris (PV) patients with rituximab therapy has not been critically evaluated. This article will provide in significant detail the available data to date, in order to provide a clinical and immunologic basis for clinicians to decide how best to treat recalcitrant PV patients with rituximab. PV is an autoimmune blistering disorder that affects the skin and mucous membranes. The immunopathology is well characterized, including the target antigens. PV patients have traditionally been treated with systemic corticosteroids and adjuvant immunosuppressive therapies. Clinical remission has been achieved in roughly 30% of patients. However, many patients experience severe side effects from this immunosuppression, including death. B-cell depletion therapy with rituximab therapy has been used to treat several autoimmune diseases including PV. In this article, we examined the data on 153 patients with PV who have been treated with rituximab. Our focus is on the clinical response of the patients with emphasis on adjuvant therapies, dosing regimens, potential adverse events and mechanism of action related to B-cell modulation during therapy. Importantly, the use of rituximab has increased clinical remission rates to 65% including many patients who were able to discontinue all systemic medications. Finally, an expert commentary is provided, which includes suggestions for optimizing current therapy and recommends the future direction of the field. The authors strongly endorse the use of rituximab in treatment of PV patients, particularly those nonresponsive to or who develop serious side effects to conventional therapy. Proper monitoring of patients including peripheral B-cell counts and overt signs of infection are warranted, given the potential for prolonged B-cell depletion.

Primary B-cell deficiencies reveal a link between human IL-17-producing CD4 T-cell homeostasis and B-cell differentiation

IL-17 is a pro-inflammatory cytokine implicated in autoimmune and inflammatory conditions. The development/survival of IL-17-producing CD4 T cells (Th17) share critical cues with B-cell differentiation and the circulating follicular T helper subset was recently shown to be enriched in Th17 cells able to help B-cell differentiation. We investigated a putative link between Th17-cell homeostasis and B cells by studying the Th17-cell compartment in primary B-cell immunodeficiencies. Common Variable Immunodeficiency Disorders (CVID), defined by defects in B-cell differentiation into plasma and memory B cells, are frequently associated with autoimmune and inflammatory manifestations but we found no relationship between these and Th17-cell frequency. In fact, CVID patients showed a decrease in Th17-cell frequency in parallel with the expansion of activated non-differentiated B cells (CD21(low)CD38(low)). Moreover, Congenital Agammaglobulinemia patients, lacking B cells due to impaired early B-cell development, had a severe reduction of circulating Th17 cells. Finally, we found a direct correlation in healthy individuals between circulating Th17-cell frequency and both switched-memory B cells and serum BAFF levels, a crucial cytokine for B-cell survival. Overall, our data support a relationship between Th17-cell homeostasis and B-cell maturation, with implications for the understanding of the pathogenesis of inflammatory/autoimmune diseases and the physiology of B-cell depleting therapies.

Clinical significance of B cell-activating factor in autoimmune pancreatitis

OBJECTIVES

Overexpression of B Cell-activating factor (BAFF) is involved in autoimmunity, but little is known about its role in autoimmune pancreatitis (AIP). The aim of this study was to investigate the role of BAFF in the diagnosis and pathogenesis of AIP.

METHODS

Patients with AIP (n = 19) were compared with 2 disease control groups (chronic pancreatitis [n = 17] and pancreatic cancer [n = 15]) and a healthy subject group (n = 19). Serum BAFF levels were assessed using an enzyme-linked immunosorbent assay. The expressions of BAFF and BAFF receptor in the pancreatic tissue of patients with AIP were estimated using immunohistochemistry.

RESULTS

Mean serum BAFF levels were higher in the patients with AIP than in the patients with chronic pancreatitis, the patients with pancreatic cancer, and the healthy subjects (P < 0.0001 for all groups). Using the cutoff value of 1389 pg/mL, the sensitivity and specificity to differentiate AIP from disease and healthy controls were 89.5% and 92.2%, respectively. Glucocorticoid therapy decreased serum BAFF levels below 1389 pg/mL in all patients with AIP (P < 0.0001). B Cell-activating factor and BAFF receptor were expressed on cells infiltrating the pancreas of patients with AIP.

CONCLUSIONS

B Cell-activating factor could be a novel marker for diagnosis and treatment response in AIP and may contribute to its pathogenesis.

Citrullination of CNS proteins in the pathogenesis of multiple sclerosis

Multiple sclerosis is a chronic immune-mediated disease of the CNS. Although it is a predominantly T-cell mediated condition, B cells and autoreactive antibodies play an important role in its pathogenesis, with the presence of oligoclonal immunoglobulins in the cerebrospinal fluid being an important diagnostic indicator. The target of these immunoglobulins has not yet been fully characterized. However, post-translational modifications of CNS-specific proteins are thought to contribute to their production through the generation of novel epitopes. One post-translational modification in particular, the conversion of the amino acid arginine to the nonstandard amino acid, citrulline, has been increasingly described in the literature as a factor in the pathogenesis of this condition. In this article, we summarize and discuss the current knowledge on citrullination in multiple sclerosis, the importance of this in relation to its pathogenesis and, potentially, its diagnosis.

Tumor-associated macrophages as major source of APRIL in gastric MALT lymphoma

Lymphoid hyperplasia of gastric mucosa associated with Helicobacter pylori (HP) infection represents a preneoplastic condition of the mucosa associated lymphoid tissue (MALT), which may evolve to a B-cell lymphoma. While it is well established that the initial neoplastic proliferation of B cells is antigen-driven and dependent on the helper activity of HP-specific T cells, it needs to be elucidated which cytokine or soluble factor(s) promote B-cell activation and lymphomagenesis. Herein, we originally report that gastric MALT lymphoma express high levels of a proliferation inducing ligand (APRIL), a novel cytokine crucial in sustaining B-cell proliferation. By immunohistochemistry, we demonstrate that APRIL is produced almost exclusively by gastric lymphoma-infiltrating macrophages located in close proximity to neoplastic B cells. We also show that macrophages produce APRIL on direct stimulation with both HP and HP-specific T cells. Collectively, our results represent the first evidence for an involvement of APRIL in gastric MALT lymphoma development in HP-infected patients.

Potential impact of B cells on T cell function in multiple sclerosis

Multiple sclerosis is a chronic debilitating autoimmune disease of the central nervous system. The contribution of B cells in the pathoetiology of MS has recently been highlighted by the emergence of rituximab, an anti-CD20 monoclonal antibody that specifically depletes B cells, as a potent immunomodulatory therapy for the treatment of MS. However, a clearer understanding of the impact B cells have on the neuro-inflammatory component of MS pathogenesis is needed in order to develop novel therapeutics whose affects on B cells would be beneficial and not harmful. Since T cells are known mediators of the pathology of MS, the goal of this review is to summarize what is known about the interactions between B cells and T cells, and how current and emerging immunotherapies may impact B-T cell interactions in MS.

Successful outcome using rituximab as the only immunomodulation in Henoch-Schonlein purpura: case report

In the current report, we describe a patient with moderate nephritis and severe skin Henoch Schönlein purpura (HSP) who has been treated with rituximab. Complete and sustained skin and renal remission resulted from the treatment. Thus, further studies are required to confirm the efficacy of rituximab as first-line treatment in HSP, and it might be an interesting new therapeutic option.

Functional and clinical aspects of the B-cell-activating factor (BAFF): a narrative review

B-cell-activating factor (BAFF) influences peripheral B-cell survival, maturation and immunoglobulin class-switch recombination and has a range of potential clinical implications. Biological functions of BAFF and its relevance in various clinical disorders including currently investigated BAFF-targeting therapies are reviewed and discussed based on PubMed search of relevant articles. Serum levels of BAFF are increased in autoimmune diseases including autoimmune hepatitis and primary biliary cirrhosis where BAFF concentrations are related to titres of autoantibodies and disease progression. Increased BAFF levels are found in synovial, bronchoalveolar and gut lavage fluids, suggesting local class switching and immunoglobulin production. Clinical relevance and diagnostic potential of BAFF are also noted in patients with allergic diseases, malignancies and infections including hepatitis C virus. BAFF antagonists are promising new therapeutic agents, currently being tried in B-cell-related autoimmune diseases. Serum level of BAFF may indicate disease mechanisms and the degree of activity. Determination of BAFF in different body compartments like synovium, airways and gut may also have clinical implications. Results of ongoing clinical trials with BAFF antagonists are eagerly awaited.

Therapeutic targeting of B cells for rheumatic autoimmune diseases

Autoreactive B cells are characterized by their ability to secrete autoantibodies directed against self-peptides. During the last decade, it has become increasingly apparent that B lymphocytes not only produce autoantibodies but also exert important regulatory roles independent of their function as antibody-producing cells. This is especially relevant in the context of autoimmunity, because autoreactive B cells have been shown to possess the ability to activate pathogenic T cells, to produce pro-inflammatory cytokines, and to promote the formation of tertiary lymphoid tissue in target organs. The production of monoclonal antibodies against B-cell-surface molecules has facilitated the characterization of several distinct B lymphocyte subsets. These cell-surface molecules have not only served as useful cell differentiation markers but have also helped to unravel the important biological functions of these cells. Some of these molecules, all of which are expressed on the cell surface, have proven to be effective therapeutic targets. In both animal models and in clinical assays, the efficient elimination of B lymphocytes has been shown to be useful in the treatment of rheumatoid arthritis and other autoimmune diseases. The treatment of most rheumatic autoimmune diseases relies mainly on the use of cytotoxic immunosuppressants and corticosteroids. Although this has resulted in improved disease survival, patients may nonetheless suffer severe adverse events and, in some cases, their relapse rate remains high. The increasing need for safer and more effective drugs along with burgeoning new insights into the pathogenesis of these disorders has fueled interest in biological agents; clinical trials involving the B-cell depletion agent rituximab have been especially promising. This article reviews the current knowledge of B-cell biology and pathogenesis as well as the modern therapeutic approaches for rheumatic autoimmune diseases focusing in particular on the targeting of B-cell-specific surface molecules and on the blocking of B-cell activation and survival.

B cells--masters of the immunoverse

The immune system involves the complex interplay between many different cell types. Over the last decade, T cells, dendritic cells (DC) and macrophages have all been implicated as the key regulator cells of the immunological response, linking innate and adaptive immunity. The forgotten cell in this discourse has been the B-cell. Long considered as simple antibody production units dictated to by T-cells, recent years have begun to shift this assumption. The discovery that numerous B-cell subsets exist, with specific regulatory functions capable of modulating T-cell and chronic inflammatory responses has revealed a hitherto unappreciated role of B-cells. In particular, these ideas have been developed in light of the surprisingly successful responses delivered in autoimmune settings following depletion of B-cells with the anti-CD20 antibody rituximab. Here we summarise the history of the humble B-cell and discuss some of the key recent findings that lead us to propose it as an important regulator of ongoing immune responses and as such, one of the masters of the immunoverse.

A case for regulatory B cells in controlling the severity of autoimmune-mediated inflammation in experimental autoimmune encephalomyelitis and multiple sclerosis

Multiple sclerosis (MS) is considered to be a T cell-mediated autoimmune disease that results in the presence of inflammatory lesions/plaques associated with mononuclear cell infiltrates, demyelination and axonal damage within the central nervous system (CNS). To date, FDA approved therapies in MS are thought to largely function by modulation of the immune response. Since autoimmune responses require many arms of the immune system, the direct cellular mechanisms of action of MS therapeutics are not definitively known. The mouse model of MS, experimental autoimmune encephalomyelitis (EAE), has been instrumental in deciphering the mechanism of action of MS drugs. In addition, EAE has been widely used to study the contribution of individual components of the immune system in CNS autoimmunity. In this regard, the role of B cells in EAE has been studied in mice deficient in B cells due to genetic ablation and following depletion with a B cell-targeted monoclonal antibody (mAb) (anti-CD20). Both strategies have indicated that B cells regulate the extent of EAE clinical disease and in their absence disease is exacerbated. Thus a new population of "regulatory B cells" has emerged. One reoccurring component of regulatory B cell function is the production of IL-10, a pleiotropic cytokine with potent anti-inflammatory properties. B cell depletion has also indicated that B cells, in particular antibody production, play a pathogenic role in EAE. B cell depletion in MS using a mAb to CD20 (rituximab) has shown promising results. In this review, we will discuss the current thinking on the role of B cells in MS drawing from knowledge gained in EAE studies and clinical trials using therapeutics that target B cells.

Cell-cell interactions in rheumatoid arthritis synovium

Understanding the pathogenesis of joint inflammation and destruction in rheumatoid arthritis involves dissection of the cellular and molecular interactions that occur in synovial tissue. Development of effective targeted therapies has been based on progress in achieving such insights. Safer and more specific approaches to treatment could flow from discovery of cell-cell interaction pathways that are specific to inflammation of the joint and less important in the defense against systemic infection. This article highlights selected cell-cell interactions in rheumatoid arthritis synovium that may be worthy of evaluation as future therapeutic targets.

Pharmacological inhibition of TLR9 activation blocks autoantibody production in human B cells from SLE patients

OBJECTIVES

Toll-like receptor 9 (TLR9), which recognizes hypomethylated DNA [cytosine-phosphate-guanine (CpG)], plays a role in the maintenance of serological memory and has been recently implicated in the pathogenesis of SLE. We previously reported that in vitro TLR9 triggers memory B-cell differentiation into antibody-producing cells, and that the MyD88-inhibitor ST2825 blocks TLR9-induced plasma cell (PC) generation. Here, we investigated whether memory B cells produce autoantibodies in SLE patients with active disease or in clinical remission, and whether ST2825 could inhibit PC generation in SLE patients.

METHODS

Peripheral blood mononuclear cells from 10 SLE patients in clinical remission and 2 with active SLE were cultured in the presence of CpG with or without ST2825. Phenotypical analysis of CpG-stimulated cells was performed by flow cytometry. Supernatants were collected to measure antibody production by ELISA and to detect autoantibodies by IF.

RESULTS

CpG-induced TLR9 stimulation caused autoantibody secretion in patients with active disease and in the majority of patients in clinical remission. Inhibition of MyD88 completely blocked the de novo generation of PCs and the secretion of autoantibodies.

CONCLUSIONS

Autoreactive B cells persist in SLE patients during disease remission in the circulating B-cell memory pool. TLR9-dependent activation of memory B cells by pathogens could be one of the mechanisms triggering relapses in SLE. Compounds targeting the TLR/MyD88 pathway may be used as novel therapeutic tools to treat acute disease and to prevent relapses in SLE patients.

Epstein-Barr virus latent infection and BAFF expression in B cells in the multiple sclerosis brain: implications for viral persistence and intrathecal B-cell activation

A cardinal feature of multiple sclerosis (MS) is the persistent intrathecal synthesis of antibodies. Our previous finding that a large fraction of B cells infiltrating the MS brain are infected with Epstein-Barr virus (EBV) raises the possibility that this virus, because of its ability to establish a latent infection in B cells and interfere with their differentiation, contributes to B-cell dysregulation in MS. The aim of this study was to gain further insight into EBV latency programs and their relationship to B-cell activation in the MS brain. Immunohistochemical analysis of postmortem MS brain samples harboring large EBV deposits revealed that most B cells in white matter lesions, meninges, and ectopic B-cell follicles are CD27+ antigen-experienced cells and coexpress latent membrane protein 1 and latent membrane protein 2A, 2 EBV-encoded proteins that provide survival and maturation signals to B cells. By combining laser-capture microdissection with preamplification reverse transcription-polymerase chain reaction techniques, EBV latency transcripts (latent membrane protein 2A, EBV nuclear antigen 1) were detected in all MS brain samples analyzed. We also found that B cell-activating factor of the tumor necrosis factor family is expressed in EBV-infected B cells in acute MS lesions and ectopic B-cell follicles. These findings support a role for EBV infection in B-cell activation in the MS brain and suggest that B cell-activating factor of the tumor necrosis factor family produced by EBV-infected B cells may contribute to this process resulting in viral persistence and, possibly, disruption of B-cell tolerance.

Autoantigens in ovarian autoimmunity associated with unexplained infertility and premature ovarian failure

OBJECTIVE

To identify ovarian autoantigens associated with ovarian autoantibodies.

DESIGN

Hypothesis-generating prospective study.

SETTING

Urban infertility referral centers and academic research institution.

PATIENT(S)

Seventy-four patients with infertility, 19 patients with premature ovarian failure (POF), and 16 healthy control women.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Identification of autoantigens.

RESULT(S)

To identify major antigens for ovarian autoimmunity, sera from 74 women with unexplained infertility were screened for ovarian autoantibodies (AOAs) by immunoassay and one-dimensional Western blot. The majority of sera had immunoreactions at 50-56 kDa. Six representative positive infertility sera were used to identify antigens between 40 and 60 kD by two-dimensional Western blot and mass spectrometry. Antigens included aldehyde (retinal) dehydrogenases (ALDH1A1, ALDH1A2, and ALDH7A1), protein disulfide isomerase A3, vimentin, α-enolase, phosphoglycerate dehydrogenase, and selenium-binding protein 1 (SBP1). Sixty percent (24 out of 40) of infertility and POF sera were positive for recombinant ALDH1A1, SBP1, or enolase; 80.7% (21 out of 26) of AOA-positive sera had antibodies to one or more of the three antigens, and only 7% (1 out of 14) of AOA-negative sera had antibodies to recombinant proteins.

CONCLUSION(S)

ALDH1A1 and SBP1 are unique to ovarian autoimmunity associated with infertility and POF, and may provide the basis for specific tests to identify patients with ovarian autoimmunity.

Basophils and the T helper 2 environment can promote the development of lupus nephritis

In systemic lupus erythematosus (SLE), self-reactive antibodies can target the kidney (lupus nephritis), leading to functional failure and possible mortality. We report that activation of basophils by autoreactive IgE causes their homing to lymph nodes, promoting T helper type 2 (T(H)2) cell differentiation and enhancing the production of self-reactive antibodies that cause lupus-like nephritis in mice lacking the Src family protein tyrosine kinase Lyn (Lyn(-/-) mice). Individuals with SLE also have elevated serum IgE, self-reactive IgEs and activated basophils that express CD62 ligand (CD62L) and the major histocompatibility complex (MHC) class II molecule human leukocyte antigen-DR (HLA-DR), parameters that are associated with increased disease activity and active lupus nephritis. Basophils were also present in the lymph nodes and spleen of subjects with SLE. Thus, in Lyn(-/-) mice, basophils and IgE autoantibodies amplify autoantibody production that leads to lupus nephritis, and in individuals with SLE IgE autoantibodies and activated basophils are factors associated with disease activity and nephritis.

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.

Effector and regulatory B cells: modulators of CD4+ T cell immunity

B cells are essential for humoral immunity, but the role that they have in regulating CD4(+) T cell responses remains controversial. However, new data showing that the transient depletion of B cells potently influences the induction, maintenance and reactivation of CD4(+) T cells, with the recent identification of antibody-independent functions of B cells, have reinvigorated interest in the many roles of B cells in both infectious and autoimmune diseases. In this Review, we discuss recent data showing how effector and regulatory B cells modulate CD4(+) T cell responses to pathogens and autoantigens.

Role of platelets in neuroinflammation: a wide-angle perspective

OBJECTIVES

This review summarizes recent developments in platelet biology relevant to neuroinflammatory disorders. Multiple sclerosis (MS) is taken as the "Poster Child" of these disorders but the implications are wide. The role of platelets in inflammation is well appreciated in the cardiovascular and cancer research communities but appears to be relatively neglected in neurological research.

ORGANIZATION

After a brief introduction to platelets, topics covered include the matrix metalloproteinases, platelet chemokines, cytokines and growth factors, the recent finding of platelet PPAR receptors and Toll-like receptors, complement, bioactive lipids, and other agents/functions likely to be relevant in neuroinflammatory diseases. Each section cites literature linking the topic to areas of active research in MS or other disorders, including especially Alzheimer's disease.

CONCLUSION

The final section summarizes evidence of platelet involvement in MS. The general conclusion is that platelets may be key players in MS and related disorders, and warrant more attention in neurological research.

B-cell biology and related therapies in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex disease characterized by numerous autoantibodies and clinical involvement in multiple organ systems. The immunologic events triggering the onset and progression of clinical manifestations have not yet been fully defined, but a central role for B cells in the pathogenesis has been brought to the fore in the last several years. The breakdown of B-cell tolerance is likely a defining and early event in the disease process and may occur by multiple pathways, including alterations in factors that affect B-cell activation thresholds, B-cell longevity, and apoptotic cell processing. Antibody-dependent and -independent mechanisms of B cells are important in SLE. Thus, autoantibodies contribute to autoimmunity by multiple mechanisms including immune complex mediated type III hypersensitivity reactions, type II antibody-dependent cytotoxicity, and by instructing innate immune cells to produce pathogenic cytokines including interferon alpha, tumor necrosis factor, and interleukin 1. Recent data have highlighted the critical role of toll-like receptors as a link between the innate and adaptive immune system in SLE immunopathogenesis. Given the large body of evidence implicating abnormalities in the B-cell compartment in SLE, there has been a therapeutic focus on developing interventions that target the B-cell compartment. Several different approaches to targeting B cells have been used, including B-cell depletion with monoclonal antibodies against B-cell-specific molecules, induction of negative signaling in B cells, and blocking B-cell survival and activation factors. Overall, therapies targeting B cells are beginning to show promise in the treatment of SLE and continue to elucidate the diverse roles of B cells in this complex disease.