The role of B cells in lupus pathogenesis

Redox regulation of hepatic NLRP3 inflammasome activation and immune dysregulation in trichloroethene-mediated autoimmunity

Trichloroethene (TCE) exposure is associated with the development of various autoimmune diseases (ADs), including autoimmune hepatitis (AIH) and systemic lupus erythematosus (SLE), potentially through the generation of excessive reactive oxygen and nitrogen species (RONS; oxidative stress). However, the mechanisms by which oxidative stress contributes to these TCE-mediated ADs are not fully understood, and are the focus of current investigation. Female MRL+/+ mice were treated with TCE along with or without antioxidant N-acetylcysteine (NAC) for 6 weeks (TCE, 10 mmol/kg, i. p., every 4th day; NAC, 250 mg/kg/day via drinking water). TCE-treated mice had elevated antinuclear antibodies (ANA) and 4-hydroxynonenal (HNE)-specific circulating immune complexes, suggesting the association of TCE-induced oxidative stress with autoimmune response. In addition, TCE exposure led to prominent lobular inflammation with sinusoid dilation, increased sinusoidal cellularity and increased staining for proliferating cell nuclear antigen (PCNA), confirming inflammatory and hepatocellular cell proliferation. Importantly, TCE exposure resulted in the activation of hepatic inflammasome (NLRP3 and caspase-1) and up-regulation of pro-inflammatory cytokine IL-1β, and these changes were attenuated by NAC supplementation. TCE treatment also led to dysregulation of hepatic immune response as evident from markedly increased hepatic lymphocyte infiltration (especially B cells) and imbalance between Tregs (decreased) and Th17 cells (increased). Interestingly, TCE-mediated dysregulation of various hepatic and splenic immune cells was also effectively attenuated by NAC. Taken together, our findings provide evidence for TCE-mediated inflammasome activation, infiltration of various immune cells, and skewed balance of Treg and Th17 cells in the liver. The attenuation of TCE-mediated hepatic inflammasome activation and immune responses by NAC further supports a critical role of oxidative stress in TCE-mediated inflammation and autoimmunity. These novel findings could help in designing therapeutic strategies for such ADs.

Primary Membranous Glomerulonephritis: The Role of Serum and Urine Biomarkers in Patient Management

The detection of phospholipase A2 receptor (PLA2R) and thrombospondin domain containing 7A THSD7A among primary membranous glomerulonephritis (MGN) patients transformed the diagnosis, treatment monitoring, and prognosis. Anti-PLA2R can be detected in 70-90% of primary MGN patients while anti-THSD7A in 2-3% of anti-PLA2R negative primary MGN patients depending on the technique used. Serum and urine samples are less invasive and non-invasive, respectively, and thus can detect the presence of anti-PLA2R and anti-THSD7A with higher sensitivity and specificity, which is significant in patient monitoring and prognosis. It is better than exposing patients to a frequent biopsy, which is an invasive procedure. Different techniques of detection of PLA2R and THSD7A in patients' urine and sera were reviewed to provide newer and alternative techniques. We proposed the use of biomarkers (PLA2R and THSD7A) in the diagnosis, treatment decision, and follow-up of patients with primary MGN. In addition, other prognostic renal biomarkers like retinol binding protein (RBP) and beta-2 microglobulin were reviewed to detect the progression of renal damage for early intervention.

Modulatory Effect of the Euro-Lupus Low-Dose Intravenous Cyclophosphamide Regimen on Circulating Immune Cells in Systemic Lupus Erythematosus

A Euro-Lupus regimen of low-dose intravenous cyclophosphamide (CFA) is commonly used to treat severe organ manifestations of systemic lupus erythematosus (SLE), particularly lupus nephritis (LN). There are no data on the distributions and dynamics of immune cell populations in patients with various treatment outcomes. The circulating immune cells of 11 female SLE patients were assessed before and after Euro-Lupus regimen (cumulative dose of 3000 mg CFA) by flow cytometry together with those of 16 healthy women. A subanalysis was performed in LN patients who achieved complete remission (CR; n = 3), partial remission (PR; n = 4), and no response (NR; n = 2). In SLE, the Euro-Lupus regimen decreased the percentage and absolute count of B cells; increased the percentage of CD8⁺ T cells, T regulatory cells, neutrophils, and monocyte subsets; and activated T and NK cells compared to healthy controls (P < 0.050). Patients with LN achieving CR had significantly lower proportions of CD27⁺ B memory cells compared to poor responders (PR/NR, P = 0.035). The post-treatment percentages and absolute numbers of B cells, T cells, NK cells, monocytes, and neutrophils showed high inter-individual variability with no association with treatment outcome. Our pilot study revealed the dynamics of changes in immune cell populations in SLE patients during a Euro-Lupus regimen, mainly the lowering of B cells. In LN patients who achieved CR, a lower proportion of CD27⁺ B memory cells was evident compared to poor responders (PR/NR). Further studies on usefulness of monitoring immune cells for treatment response prediction on larger cohorts are needed.

MiR-183 delivery attenuates murine lupus nephritis-related injuries via targeting mTOR

MicroRNAs (miRNAs) play a vital role in the occurrence and development of many human diseases, including systemic lupus erythematosus (SLE). SLE is an autoimmune disease characterized by the production of autoantibodies against nuclear antigens and multiorgan involvement. Study of miRNAs involved in SLE provides new insights into the pathogenesis of SLE and might lead to the identification of new therapeutic interventions. The aim of this study was to investigate the effect of miR-183 injection on the progression of SLE by using MRL/lpr mouse model. The expression levels of miR-183 and mTOR mRNA were detected by quantitative real-time PCR assay. The effect of miR-183 on the course of spontaneous disease progression in the MRL/lpr mice was examined by intraperitoneal injection of miR-183 into mice and followed by monitoring lifespan, anti-dsDNA antibody levels, urinary albumin levels, blood urea nitrogen (BUN) levels, and Tregs and Th17 cell population. We found that miR-183 injection resulted in reduction of anti-DNA antibody and immune complex component levels, restoration of Tregs and Th17 cell population and prolongation of survival. Our findings suggest that miR-183 injection may serve as an effective therapeutic treatment for delaying or easing pathologic features of SLE.

SNP rs4937333 in the miRNA-5003-Binding Site of the ETS1 3'-UTR Decreases ETS1 Expression

Mutations in and reduced expression of the ETS1 gene may be associated with systemic lupus erythematosus (SLE). Here, we report a replication study to investigate associations of eight ETS1 single-nucleotide polymorphisms in the 3′-untranslated region (3′-UTR) with SLE and their regulation of ETS1 expression in a study population. We found that the rs4937333 T allele was associated with a significantly increased risk of SLE (odds ratio: 1.800, 95% confidence interval: 1.02–3.157, P = 0.040) and with dramatically reduced levels of ETS1 in B cells from SLE subjects. Functionally, the rs4937333 T allele alters the binding affinity between miR-5003 and its ETS1 3′-UTR target, thus enhancing suppression of ETS1 expression. Furthermore, immunoglobulin M-secreting plasmacytes were significantly reduced among B cells with the rs4937333 C allele versus the T allele according to FACS and ELISA. Additionally, miR-5003 expression was higher in B cells than in T cells from SLE patients, and a negative correlation between miR-5003 and ETS1 was found, especially in B cells with the T allele. These findings suggest that the rs4937333 T allele is a risk factor for susceptibility to SLE in the studied population. The rs4937333 T allele may enhance the binding of miR-5003 to ETS1, which probably promotes the involvement of ETS1 in the differentiation of B cells into plasmacytes.

Immunoglobulin Binding Protein 1 as a Potential Urine Biomarker in Patients with Lupus Nephritis

We evaluated the role of immunoglobulin binding protein 1 (IGBP1), a phosphoprotein associated with the B cell receptor (BCR) complex, as a urine biomarker in lupus nephritis (LN). The IGBP1 concentrations in plasma and urine of patients with LN, systemic lupus erythematosus (SLE) without nephritis and healthy controls were estimated by ELISA. IGBP1 expression in the kidneys of LN patients and transplantation donors was detected by immunohistochemistry. Microarray-based global gene expression profile of HK-2 cells with IGBP1 knock-down and fluorescence-activated cell sorting (FACS) for intracellular IGBP1 expression in human peripheral blood mononuclear cells (PBMCs) was performed. Urine IGBP1 levels were elevated significantly in LN patients, and it correlated with the clinical activity indices (complement 3 (C3) level, anti-dsDNA antibodies titer, SLE Disease Activity Index-2000 (SLEDAI-2K) and histological activity index. IGBP1 expression was increased in LN patients as compared to the donors and was detected mainly in the tubules by histopathology. In microarray analysis, several genes related to SLE pathogenesis (PPME1, ROCK2, VTCN1, IL-17R, NEU1, HLA-DM, and PTX3) responded to siRNA-mediated IGBP1 silencing. In FACS, IGBP1 was expressed mainly in the CD14⁺ cells. The overall expression of IGBP1 in PBMCs was higher in LN patients as compared with that in SLE patients without nephritis. Conclusively, urinary IGBP1 may be a novel biomarker reflecting the clinical and histological activities in LN.

RasGRP3 in peripheral blood mononuclear cells is associated with disease activity and implicated in the development of systemic lupus erythematosus

This study examined the relationship between the expression of Ras guanyl nucleotide-releasing protein 3 (RasGRP3) and disease activity in systemic lupus erythematosus (SLE) and explored the possible mechanisms in MRL/lpr mice. We detected the expression of RasGRP3 in peripheral blood mononuclear cells (PBMCs) of SLE patients (n=26) and healthy controls (n=20) by employing RT-PCR and studied the association between the mRNA expression of RasGRP3 in PBMCs and the clinical findings. We also measured the protein level of RasGRP3 in PBMCs by Western blotting (n=10). In addition, we isolated the B cells from PBMCs with magnetic bead separation and determined the RasGRP3 expression by RT-PCR (n=10). Furthermore, we extracted spleen B cells from MRL/lpr mice and knocked down RasGRP3 by siRNA transfection to study the role of RasGRP3 in the pathway of B cell receptor (BCR) activation and the production of pro-inflammatory cytokines. Compared with healthy volunteers, the expression of RasGRP3 was significantly elevated in PBMCs and purified B cells from SLE patients. The mRNA expression of RasGRP3 in PBMCs was positively correlated with SLE disease activity index (SLEDAI). Moreover, silencing RasGRP3 could inhibit Akt and Erk1/2 activation in marginal zone (MZ) and follicular (FO) B cells of MRL/lpr mice. Additionally, the production of pro-inflammatory cytokines, such as interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), was decreased whereas activation of caspase-3 cleavage was induced in vitro. In conclusion, over-expression of RasGRP3 is associated with disease activity and might be involved in the pathogenesis of SLE.

Sirtuins in B lymphocytes metabolism and function

Sirtuins (SIRTs) are NAD+-dependent histone deacetylases and play a role in virtually all cell biological processes. As SIRTs functions vary according to their subtypes, they can either activate or inhibit signaling pathways upon different conditions or tissues. Recent studies have focused on metabolic effects performed by SIRTs in several cell types since specific metabolic pathways (e.g., aerobic glycolysis, oxidative phosphorylation, β-oxidation, glutaminolysis) are used to determine the cell fate. However, few efforts have been made to understand the role of SIRTs on B lymphocytes metabolism and function. These cells are associated with humoral immune responses by secreting larger amounts of antibodies after differentiating into antibody-secreting cells. Besides, both the SIRTs and B lymphocytes are potential targets to treat several immune-mediated disorders, including cancer. Here, we provide an outlook of recent studies regarding the role of SIRTs in general cellular metabolism and B lymphocytes functions, pointing out the future perspectives of this field.

Innate and adaptive signals enhance differentiation and expansion of dual-antibody autoreactive B cells in lupus

Autoreactive B cells have a major function in autoimmunity. A small subset of B cells expressing two distinct B-cell-antigen-receptors (B_2R cells) is elevated in many patients with systematic lupus erythematosus (SLE) and in the MRL(/lpr) mouse model of lupus, and is often autoreactive. Here we show, using RNAseq and in vitro and in vivo analyses, signals that are required for promoting B_2R cell numbers and effector function in autoimmune mice. Compared with conventional B cells, B_2R cells are more responsive to Toll-like receptor 7/9 and type I/II interferon treatment, display higher levels of MHCII and co-receptors, and depend on IL-21 for their homeostasis; moreover they expand better upon T cell-dependent antigen stimulation, and mount a more robust memory response, which are characteristics essential for enhanced (auto)immune responses. Our findings thus provide insights on the stimuli for the expansion of an autoreactive B cell subset that may contribute to the etiology of SLE.

Cutting Edge: Deletion of Ezrin in B Cells of Lyn-Deficient Mice Downregulates Lupus Pathology

Genetic deletion of the Src family tyrosine kinase Lyn in mice recapitulates human systemic lupus erythematosus, characterized by hyperactive BCR signaling, splenomegaly, autoantibody generation, and glomerulonephritis. However, the molecular regulators of autoimmunity in Lyn-deficient mice and in human lupus remain poorly characterized. In this study, we report that conditional deletion of the membrane-cytoskeleton linker protein ezrin in B cells of Lyn-deficient mice (double knockout [DKO] mice) ameliorates B cell activation and lupus pathogenesis. B cells from DKO mice respond poorly to BCR stimulation, with severe downregulation of major signaling pathways. DKO mice exhibit reduced splenomegaly as well as significantly lower levels of autoantibodies against a variety of autoantigens, including dsDNA, histone, and chromatin. Leukocyte infiltration and deposition of IgG and complement component C3 in the kidney glomeruli of DKO mice are markedly reduced. Our data demonstrate that ezrin is a novel molecular regulator of B cell-associated lupus pathology.

Increased level of B cell differentiation factor in systemic lupus erythematosus patients

Most autoimmune disease are driven by a dysfunction in T and B cells, but B cells are still an interesting area of research, perturbations in their development are implicated in autoimmune diseases. B cell differentiating factor (BCDF) plays a part in the differentiation of B cells. The aim was To assess the levels of BCDF, IgM and IgG in SLE patients and whether they have any peculiarity in the clinical context of SLE. Thirty six patients with SLE and 24 healthy volunteers as control were enrolled in the study. BCDF was measured using Sandwich ELISA, total human IgM and IgG were measured by calorimetric methods. The mean concentrations of BCDF and IgM were significantly higher in patients with SLE as compared with controls (P < 0.001 and P < 0.0001 respectively). No significant difference was observed as regard IgG. We observed positive correlation between BCDF and IgM (r = 0.281, P = 0.03), and between IgG and IgM, duration of the disease (r = 0.468, P = 0.004, r = 0.337, P = 0.008 respectively). Moreover we observed lower IgM level in patients with discoid lesion (P = 0.009) and lower IgG level in those with hematologic manifestations (P = 0.02). ROC analysis revealed area under curve (AUC) 0.861 for BCDF and 0.902 for IgM, they can delineate SLE from controls at a cut-off value of 98.5 pg/ml, and 18 mg/dl IgM respectively.

Conclusion

BCDF and IgM are increased in SLE patients and are promissing diagnostic markers for SLE.

Peli1 negatively regulates noncanonical NF-κB signaling to restrain systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is characterized by uncontrolled secretion of autoantibodies by plasma cells. Although the functional importance of plasma cells and autoantibodies in SLE has been well established, the underlying molecular mechanisms of controlling autoantibody production remain poorly understood. Here we show that Peli1 has a B cell-intrinsic function to protect against lupus-like autoimmunity in mice. Peli1 deficiency in B cells induces autoantibody production via noncanonical NF-κB signaling. Mechanically, Peli1 functions as an E3 ligase to associate with NF-κB inducing kinase (NIK) and mediates NIK Lys48 ubiquitination and degradation. Overexpression of Peli1 inhibits noncanonical NF-κB activation and alleviates lupus-like disease. In humans, PELI1 levels negatively correlate with disease severity in SLE patients. Our findings establish Peli1 as a negative regulator of the noncanonical NF-κB pathway in the context of restraining the pathogenesis of lupus-like disease.

Trib1 Is Overexpressed in Systemic Lupus Erythematosus, While It Regulates Immunoglobulin Production in Murine B Cells

Systemic lupus erythematosus (SLE) is a severe and heterogeneous autoimmune disease with a complex genetic etiology, characterized by the production of various pathogenic autoantibodies, which participate in end-organ damages. The majority of human SLE occurs in adults as a polygenic disease, and clinical flares interspersed with silent phases of various lengths characterize the usual evolution of the disease in time. Trying to understand the mechanism of the different phenotypic traits of the disease, and considering the central role of B cells in SLE, we previously performed a detailed wide analysis of gene expression variation in B cells from quiescent SLE patients. This analysis pointed out an overexpression of TRIB1. TRIB1 is a pseudokinase that has been implicated in the development of leukemia and also metabolic disorders. It is hypothesized that Trib1 plays an adapter or scaffold function in signaling pathways, notably in MAPK pathways. Therefore, we planned to understand the functional significance of TRIB1 overexpression in B cells in SLE. We produced a new knock-in model with B-cell-specific overexpression of Trib1. We showed that overexpression of Trib1 specifically in B cells does not impact B cell development nor induce any development of SLE symptoms in the mice. By contrast, Trib1 has a negative regulatory function on the production of immunoglobulins, notably IgG1, but also on the production of autoantibodies in an induced model. We observed a decrease of Erk activation in BCR-stimulated Trib1 overexpressing B cells. Finally, we searched for Trib1 partners in B cells by proteomic analysis in order to explore the regulatory function of Trib1 in B cells. Interestingly, we find an interaction between Trib1 and CD72, a negative regulator of B cells whose deficiency in mice leads to the development of autoimmunity. In conclusion, the overexpression of Trib1 could be one of the molecular pathways implicated in the negative regulation of B cells during SLE.

Assessing Autophagy in Mouse Models and Patients with Systemic Autoimmune Diseases

Autophagy is a tightly regulated mechanism that allows cells to renew themselves through the lysosomal degradation of proteins, which are misfolded or produced in excess, and of damaged organelles. In the context of immunity, recent research has specially attempted to clarify its roles in infection, inflammation and autoimmunity. Autophagy has emerged as a spotlight in several molecular pathways and trafficking events that participate to innate and adaptive immunity. Deregulation of autophagy has been associated to several autoimmune diseases, in particular to systemic lupus erythematosus. Nowadays, however, experimental data on the implication of autophagy in animal models of autoimmunity or patients remain limited. In our investigations, we use Murphy Roths Large (MRL)/lymphoproliferation (lpr) lupus-prone mice as a mouse model for lupus and secondary Sjögren's syndrome, and, herein, we describe methods applied routinely to analyze different autophagic pathways in different lymphoid organs and tissues (spleen, lymph nodes, salivary glands). We also depict some techniques used to analyze autophagy in lupus patient's blood samples. These methods can be adapted to the analysis of autophagy in other mouse models of autoinflammatory diseases. The understanding of autophagy implication in autoimmune diseases could prove to be very useful for developing novel immunomodulatory strategies. Our attention should be focused on the fact that autophagy processes are interconnected and that distinct pathways can be independently hyper-activated or downregulated in distinct organs and tissues of the same individual.

Expression of CCR6 on B cells in systemic lupus erythematosus patients

B cells are known to play a dominant pathogenic role in autoimmune conditions such as systemic lupus erythematosus (SLE) and rheumatoid arthritis. In recent times, the chemokine receptor CCR6 and its cognate ligand CCL20 have been shown to play a role in the fundamental kinetics of germinal centres and B cell responses. As CCR6 is found on B cells and is upregulated after activation, we investigated the expression of CCR6 on naive, pre-germinal centre (GC), GC/plasma cell and memory B cells in peripheral B cells of SLE patients and healthy controls using flow cytometry. Pre-germinal centre B cells are found in lower proportions and the expression of CCR6 is increased on B cells of SLE patients, suggesting a role for the chemokine pair in the pathogenesis of the disease. Further studies are needed to explore these preliminary results.

Targeted B cell therapies in the treatment of adult and pediatric systemic lupus erythematosus

Belimumab (Benlysta) is a fully-humanized monoclonal antibody that inhibits B-lymphocyte stimulator (also known as B cell activating factor) and was approved by the U.S. Federal Drug Administration and European Medicines Evaluation Agency for treatment in adults with autoantibody-positive systemic lupus erythematosus (SLE). Rituximab (Rituxan) is a chimeric anti-CD20 monoclonal antibody targeting B lymphocytes. This review discusses the key findings of the phase III trials in adults with SLE and of real-world use of belimumab and rituximab in the care of both adult and pediatric SLE patients. It highlights the safety profile of belimumab and rituximab and gives insight into the consideration of these therapies for specific SLE disease states. It concludes with a discussion of the current clinical trials investigating B cell therapies in specific SLE disease states and a look to the future, with ongoing clinical trials.

Chromatin landscapes and genetic risk in systemic lupus

BACKGROUND

Systemic lupus erythematosus (SLE) is a multi-system, complex disease in which the environment interacts with inherited genes to produce broad phenotypes with inter-individual variability. Of 46 single nucleotide polymorphisms (SNPs) shown to confer genetic risk for SLE in recent genome-wide association studies, 30 lie within noncoding regions of the human genome. We therefore sought to identify and describe the functional elements (aside from genes) located within these regions of interest.

METHODS

We used chromatin immunoprecipitation followed by sequencing to identify epigenetic marks associated with enhancer function in adult neutrophils to determine whether enhancer-associated histone marks were enriched within the linkage disequilibrium (LD) blocks encompassing the 46 SNPs of interest. We also interrogated available data in Roadmap Epigenomics for CD4+ T cells and CD19+ B cells to identify these same elements in lymphoid cells.

RESULTS

All three cell types demonstrated enrichment of enhancer-associated histone marks compared with genomic background within LD blocks encoded by SLE-associated SNPs. In addition, within the promoter regions of these LD blocks, all three cell types demonstrated enrichment for transcription factor binding sites above genomic background. In CD19+ B cells, all but one of the LD blocks of interest were also enriched for enhancer-associated histone marks.

CONCLUSIONS

Much of the genetic risk for SLE lies within or near genomic regions of disease-relevant cells that are enriched for epigenetic marks associated with enhancer function. Elucidating the specific roles of these noncoding elements within these cell-type-specific genomes will be crucial to our understanding of SLE pathogenesis.

Therapeutic Blockade of Immune Complex-Mediated Glomerulonephritis by Highly Selective Inhibition of Bruton's Tyrosine Kinase

Lupus nephritis (LN) is a potentially dangerous end organ pathology that affects upwards of 60% of lupus patients. Bruton’s tyrosine kinase (BTK) is important for B cell development, Fc receptor signaling, and macrophage polarization. In this study, we investigated the effects of a novel, highly selective and potent BTK inhibitor, BI-BTK-1, in an inducible model of LN in which mice receive nephrotoxic serum (NTS) containing anti-glomerular antibodies. Mice were treated once daily with vehicle alone or BI-BTK-1, either prophylactically or therapeutically. When compared with control treated mice, NTS-challenged mice treated prophylactically with BI-BTK-1 exhibited significantly attenuated kidney disease, which was dose dependent. BI-BTK-1 treatment resulted in decreased infiltrating IBA-1+ cells, as well as C3 deposition within the kidney. RT-PCR on whole kidney RNA and serum profiling indicated that BTK inhibition significantly decreased levels of LN-relevant inflammatory cytokines and chemokines. Renal RNA expression profiling by RNA-seq revealed that BI-BTK-1 dramatically modulated pathways related to inflammation and glomerular injury. Importantly, when administered therapeutically, BI-BTK-1 reversed established proteinuria and improved renal histopathology. Our results highlight the important role for BTK in the pathogenesis of immune complex-mediated nephritis, and BTK inhibition as a promising therapeutic target for LN.

Recent advances and current state of immunotherapy in systemic lupus erythematosus

INTRODUCTION

Systemic lupus erythematosus (SLE) is an autoimmune syndrome that poses significant challenges in diagnosis and treatment. Dysregulated innate and adaptive immune systems are involved in its pathogenesis. A plethora of novel immunotherapies have been developed for the treatment of SLE but many have failed early clinical trials.

AREAS COVERED

This review summarizes immunotherapies under recent development with relevance to the targeted cellular or soluble factors involved in the pathogenesis of SLE.

EXPERT OPINION

SLE is a complicated disease with much heterogeneity. Novel immunotherapies with different mechanisms of action that are currently under development include biologic agents targeting co-stimulatory molecules, cytokines or their receptors and signaling molecules and B cells, cell-based therapy and peptide therapy. Together with good scientific rationale and advanced biological engineering techniques, optimization of clinical trial design, patient selection and disease outcome measures are essential to demonstrate the clinical efficacy and safety of these agents.

Antibodies as Mediators of Brain Pathology

The brain is normally sequestered from antibody exposure by the blood brain barrier. However, antibodies can access the brain during fetal development before the barrier achieves full integrity, and in disease states when barrier integrity is compromised. Recent studies suggest that antibodies contribute to brain pathology associated with autoimmune diseases such as systemic lupus erythematosus and neuromyelitis optica, and can lead to transient or permanent behavioral or cognitive abnormalities. We review these findings here and examine the circumstances associated with antibody entry into the brain, the routes of access and the mechanisms that then effect pathology. Understanding these processes and the nature and specificity of neuronal autoantibodies may reveal therapeutic strategies toward alleviating or preventing the neurological pathologies and behavioral abnormalities associated with autoimmune disease.

Belimumab in systemic lupus erythematosus: a perspective review

Belimumab (Benlysta(®)) is a fully humanized monoclonal antibody that inhibits B-lymphocyte stimulator (also known as B cell activating factor of the tumor necrosis factor family) and was approved by the US Food and Drug Administration and the European Medicines Evaluation Agency for treatment of autoantibody-positive systemic lupus erythematosus (SLE) in adults. This review discusses the key findings of the phase III trials, post hoc analyses, and real-world postmarketing use of belimumab in the routine care of SLE patients. It also highlights the safety profile of belimumab and gives insight into its potential use to treat childhood-onset SLE. It concludes with a discussion of the current clinical trials investigating belimumab in specific SLE disease states and a look to the future with novel targeted B-cell therapies.

Post-marketing experiences with belimumab in the treatment of SLE patients

Belimumab (Benlysta) is a human recombinant monoclonal antibody that targets and inhibits soluble B-lymphocyte stimulator, also known as B-cell activating factor, a proliferation and survival factor for B cells. The published clinical trials data showed that in patients with active systemic lupus erythematosus (SLE), belimumab effectively reduced peripheral B-cell levels and improved disease activity. This article reviews the belimumab clinical trials and the post-marketing experience with belimumab in the treatment of those lupus patients with persistent active disease despite current standard of care (SOC) therapy.

Down-regulating humoral immune responses: implications for organ transplantation

Alloantibody can be a major barrier to successful organ transplantation; however, therapy to control antibody production or to alter its impact on the allograft remains limited. The goal of this review is to examine the regulatory steps that are involved in the generation of alloreactive B cells, with a specific emphasis on how known mechanisms relate to clinical situations in transplant recipients. Thus, we will examine the process of activation of mature, naïve B cells and how this relates to de novo antibody production. The role of long-lived plasma cells in persistent antibody production and the factors regulating their longevity will be explored. The regulation of memory B cells and their possible roles in alloimmunity also will be assessed. Finally, we will review current therapeutic approaches aimed at controlling alloantibody and assess their efficacy. By examining the pathways to antibody production mechanistically, we hope to identify important gaps in our current knowledge and gain insight into possible new therapeutic approaches to overcoming antibody in transplant patients.

B-cell-targeted therapies in systemic lupus erythematosus and ANCA-associated vasculitis: current progress

B cells play a central role in the pathogenesis of systemic lupus erythematosus and anti-neutrophil cytoplasmic antibody-associated vasculitis. There are various strategies for targeting B cells including depletion, inhibition of survival factors, activation and inhibition of co-stimulatory molecules. Controlled trials in systemic lupus erythematosus have shown positive results for belimumab, promising results for epratuzumab and negative results for rituximab. The failure of rituximab in controlled trials has been attributed to trial design, sample size and outcome measures rather than true inefficacy. In anti-neutrophil cytoplasmic antibody-associated vasculitis, rituximab is effective for remission induction and in relapsing disease. However, the optimal long-term re-treatment strategy remains to be determined. Over the next 5 years, evidence will be available regarding the clinical efficacy of these novel therapies, biomarkers and their long-term safety.

Suppression of glomerulonephritis in lupus-prone NZB × NZW mice by RN486, a selective inhibitor of Bruton's tyrosine kinase

OBJECTIVE

Bruton's tyrosine kinase (BTK) plays a critical role in B cell development and function. We recently described a selective BTK inhibitor, RN486, that blocks B cell receptor (BCR) and Fcγ receptor signaling and is efficacious in animal models of arthritis. The aim of this study was to examine the potential efficacy of BTK in systemic lupus erythematosus (SLE), using an NZB × NZW mouse model of spontaneous SLE.

METHODS

Mice received RN486 or its vehicle (administered in chow) at a final concentration of 30 mg/kg for 8 weeks, starting at 32 weeks of age.

RESULTS

The administration of RN486 completely stopped disease progression, as determined by histologic and functional analyses of glomerular nephritis. The efficacy was associated with striking inhibition of B cell activation, as demonstrated by a significant reduction in CD69 expression in response to BCR crosslinking. RN486 markedly reduced the secretion of IgG anti-double-stranded DNA (anti-dsDNA) secretion, as determined by enzyme-linked immunosorbent and enzyme-linked immunospot assays. Flow cytometric analysis demonstrated depletion of CD138(high) B220(low) plasma cells in the spleen. RN486 inhibited secretion of IgG anti-dsDNA but not IgM anti-dsDNA, suggesting that pharmacologic blockade of BTK resembles the reported transgenic expression of low levels of endogenous BTK in B cells. In addition, RN486 may also impact the effector function of autoantibodies, as evidenced by a significant reduction in immune complex-mediated activation of human monocytes in vitro and down-regulation of the expression of macrophage-related and interferon-inducible genes in both the kidneys and spleens of treated mice.

CONCLUSION

Collectively, our data suggest that BTK inhibitors may simultaneously target autoantibody-producing and effector cells in SLE, thus constituting a promising therapeutic alternative for this disease.

The role of B lymphocyte stimulator in B cell biology: implications for the treatment of lupus

B lymphocyte stimulator (BLyS; also known as B cell activating factor (BAFF)) plays a key role in peripheral B cell tolerance. Mounting evidence indicates that B cell tolerance can be either broken or modulated by deliberately manipulating BLyS levels, and belimumab, a BLyS-neutralizing antibody, was recently approved for the treatment of systemic lupus erythematosus (SLE). Thus, intense investigation has focused on understanding how therapeutics targeting BLyS may work, and accumulating evidence suggests multiple points of action. BLyS signaling, in conjunction with B cell receptor (BCR) signaling, determines the size and quality of the mature primary B cell compartment. Moreover, BLyS family members play roles in antigen-experienced B cell selection and differentiation. Together, these findings have implications for the continued development of novel therapeutics that target BLyS.

n-3 PUFAs enhance the frequency of murine B-cell subsets and restore the impairment of antibody production to a T-independent antigen in obesity

The role of n-3 polyunsaturated fatty acids (PUFA) on in vivo B-cell immunity is unknown. We first investigated how n-3 PUFAs impacted in vivo B-cell phenotypes and antibody production in the absence and presence of antigen compared with a control diet. Lean mice consuming n-3 PUFAs for 4 weeks displayed increased percentage and frequency of splenic transitional 1 B cells. Upon stimulation with trinitrophenylated-lipopolysaccharide, n-3 PUFAs increased the number of splenic transitional 1/2, follicular, premarginal, and marginal zone B cells. n-3 PUFAs also increased surface, but not circulating, IgM. We next tested the effects of n-3 PUFAs in a model of obesity that is associated with suppressed humoral immunity. An obesogenic diet after ten weeks of feeding, relative to a lean control, had no effect on the frequency of B cells but lowered circulating IgM upon antigen stimulation. Administration of n-3 PUFAs to lean and obese mice increased the percentage and/or frequency of transitional 1 and marginal zone B cells. Furthermore, n-3 PUFAs in lean and obese mice increased circulating IgM relative to controls. Altogether, the data show n-3 PUFAs enhance B cell-mediated immunity in vivo, which has implications for immunocompromised populations, such as the obese.

Expression of CXCL12 receptors in B cells from Mexican Mestizos patients with systemic Lupus erythematosus

BACKGROUND

Systemic Lupus Erythematosus (SLE) is a chronic autoimmune disease characterized by B-cell hyper-reactivity and the production of pathogenic anti-nuclear-directed auto-antibodies (Abs). B-cell ontogeny is partly dependent on the CXCL12/CXCR4 axis for which the contribution to SLE pathogenesis remains unclear. CXCR7, the novel receptor for CXCL12, is differentially expressed among memory B-cell subsets. However, its biological role in SLE remains to be explored.

METHODS

Relative CXCR4 and CXCR7 expression levels were compared by quantitative PCR in leukocytes from blood samples of 41 Mexican Mestizos patients with SLE and 45 ethnicity-matched healthy subjects. Intracellular and membrane expression of both receptors was analyzed by flow cytometry in naive and Ab-secreting B cells. B-cell responsiveness to CXCL12 was investigated using Transwell-based chemotaxis assays. Data were analyzed using the Kruskal-Wallis test for comparisons of values amongst healthy controls and patients with inactive or active SLE, and non-parametrically using the Mann-Whitney U-test for multiple comparisons and unpaired samples. Correlations were determined by Spearman's ranking.

RESULT

SLE leukocytes displayed reduced levels of CXCR4 and CXCR7 transcripts. In SLE patients, a significant defect in CXCR4 expression was detected at the surface of naive and Ab-secreting B cells, associated with an abnormal intracellular localization of the receptor. CXCR7 predominantly localized in cytosolic compartments of B cells from healthy and SLE individuals. Disease activity did not impact on these expression patterns. Altered receptor compartmentalization correlated with an impaired CXCL12-promoted migration of SLE B cells.

CONCLUSIONS

Our data highlight a down-regulation of CXCL12 receptors on circulating B cells from SLE patients that likely influences their migratory behavior and distribution.

Belimumab and the clinical data

Benlysta (belimumab) is a fully human recombinant monoclonal IgG antibody that neutralizes soluble B-lymphocyte stimulator and inhibits its biologic activity. Benlysta was recently approved by the US Food and Drug Administration to treat systemic lupus erythematosus (SLE). The current review discusses the data from the belimumab clinical trials and the role of this new medication in the treatment of SLE. We propose that Benlysta should be used in antinuclear antibody-positive patients with active disease in whom the goal of therapy is to decrease SLE activity, reduce flares, and help lower background medications. With this being the first drug approved for treatment of SLE in 50 years, patients have more treatment options, while researchers have a greater understanding of SLE and clinical trial design in such a heterogeneous disease.

B-cell targeted therapy in systemic lupus erythematosus: potential of rituximab

Systemic lupus erythematosus (SLE) is a complex autoimmune disease of unknown etiology, and the limited available therapeutic options for this disease, are frustrating to both clinicians and patients. However, recent advances in the understanding of disease mechanisms have given rise to numerous studies on specific approaches to SLE treatment. Rituximab, the first chimeric, mouse-human monoclonal antibody which is directed against CD20, seems to be a new therapeutic option. The purpose of this review is to explain the current clinical evidence on the therapeutic use of rituximab in adult SLE patients. Two randomized clinical trials with rituximab (the EXPLORER and LUNAR studies) failed to prove efficacy of this drug on SLE. Ongoing data analysis continues to explain the reasons behind why this treatment fails to work. However data from open source and observational studies contrast with clinical trials results. The global analysis of this data supports the off-label use of rituximab in subsets of SLE that are refractory to standard treatment.

Cyclin-dependent kinase inhibitor Cdkn2c deficiency promotes B1a cell expansion and autoimmunity in a mouse model of lupus

The lupus-prone NZM2410 mice present an expanded B1a cell population that we have mapped to the Sle2c1 lupus susceptibility locus. The expression of Cdkn2c, a gene encoding for cyclin-dependent kinase inhibitor p18(Ink4c) and located within Sle2c1, is significantly lower in B6.Sle2c1 B cells than in B6 B cells. To test the hypothesis that the B1a cell expansion in B6.Sle2c1 mice was due to a defective p18 expression, we analyzed the B1a cell phenotypes of p18-deficient C57BL/6 mice. We found a dose-dependent negative correlation between the number of B1a cells and p18 expression in B cells, with p18-deficient mice showing an early expansion of the peritoneal B1a cell pool. p18 deficiency enhanced the homeostatic expansion of B1a cells but not of splenic conventional B cells, and the elevated number of B6.Sle2c1 B1a cells was normalized by cyclin D2 deficiency. These data demonstrated that p18 is a key regulator of the size of the B1a cell pool. B6.p18(-/-) mice produced significant amounts of anti-DNA IgM and IgG, indicating that p18 deficiency contributes to humoral autoimmunity. Finally, we have shown that Sle2c1 increases lpr-associated lymphadenopathy and T cell-mediated pathology. B6.p18(-/-).lpr mice showed a greater lymphadenopathy than B6.Sle2c1.lpr mice, but their renal pathology was intermediate between that of B6.lpr and B6.Sle2c1.lpr mice. This indicated that p18-deficiency synergizes, at least partially, with lpr-mediated pathology. These results show that Cdkn2c contributes to lupus susceptibility by regulating the size of the B1a cell compartment and hence their contribution to autoimmunity.

Fcγ receptor IIB (FcγRIIB) maintains humoral tolerance in the human immune system in vivo

Maintenance of immunological tolerance is crucial to prevent development of autoimmune disease. The production of autoantibodies is a hallmark of many autoimmune diseases and studies in mouse model systems suggest that inhibitory signaling molecules may be important checkpoints of humoral tolerance. By generating humanized mice with normal and functionally impaired Fcγ receptor IIB (FcγRIIB) variants, we show that the inhibitory Fcγ-receptor is a checkpoint of humoral tolerance in the human immune system in vivo. Impaired human FcγRIIB function resulted in the generation of higher levels of serum immunoglobulins, the production of different autoantibody specificities, and a higher proportion of human plasmablasts and plasma cells in vivo. Our results suggest that the inhibitory FcγRIIB may be an important checkpoint of humoral tolerance in the human immune system.

More to come: humoral immune responses in MS

Interest in the role of B-cells in multiple sclerosis (MS) pathogenesis has increased, and a number of B-cell targeted therapies are currently in clinical trials. B-cells are key mediators of the humoral immune response, with roles including antibody production and acting as antigen presenting cells. Whilst previously, the presence of B-cells within MS plaques has been thought to be secondary to T-cell dysregulation, it is now becoming clear that B-cells play an independent role in disease. In this review we will discuss the potential role of B-cells in MS, how this influences our understanding of the disease, and potential therapeutic implications.

BAFF and selection of autoreactive B cells

B cell activating factor (BAFF) is a crucial survival factor for transitional and mature B cells, and is a promising therapeutic target for systemic lupus erythematosus (SLE). A BAFF inhibitor, belimumab, is the first new drug in 50 years to be approved for the treatment of SLE. However, the mechanism of action of this drug is not entirely clear. In this review we will focus on the role of the BAFF-APRIL signaling pathway in the selection of autoreactive B cells, and discuss whether altered selection is the mechanism for the therapeutic efficacy of BAFF inhibition in SLE.