Translational Mini-Review Series on B cell subsets in disease. Transitional B cells in systemic lupus erythematosus and Sjögren's syndrome: clinical implications and effects of B cell-targeted therapies

NF-kB's contribution to B cell fate decisions

NF-κB signaling is essential to an effective innate and adaptive immune response. Many immune-specific functional and developmental outcomes depend in large on NF-κB. The formidable task of sorting out the mechanisms behind the regulation and outcome of NF-κB signaling remains an important area of immunology research. Here we briefly discuss the role of NF-κB in regulating cell fate decisions at various times in the path of B cell development, activation, and the generation of long-term humoral immunity.

T Regulatory Cell-Associated Tolerance Induction by High-Dose Immunoglobulins in an HLA-Transgenic Mouse Model of Pemphigus

Pemphigus vulgaris (PV) is a potentially lethal autoimmune bullous skin disorder caused by IgG autoantibodies against desmoglein 3 (Dsg3) and Dsg1. During the last three decades, high-dose intravenous immunoglobulins (IVIgs) have been applied as an effective and relatively safe treatment regime in severe, therapy-refractory PV. This prompted us to study T- and B- cell polarization by IVIg in a human-Dsg3-dependent mouse model for PV. Using humanized mice transgenic for HLA-DRB1*04:02, which is a highly prevalent haplotype in PV, we employed IVIg in two different experimental approaches: in prevention and quasi-therapeutic settings. Our data show that intraperitoneally applied IVIg was systemically distributed for up to 42 days or longer. IVIg-treated Dsg3-immunized mice exhibited, in contrast to Dsg3-immunized mice without IVIg, significantly less Dsg3-specific IgG, and showed induction of T regulatory cells in lymphatic tissue. Ex vivo splenocyte analysis upon Dsg3-specific stimulation revealed an initial, temporarily reduced antigen-induced cell proliferation, as well as IFN-γ secretion that became less apparent over the course of time. Marginal-zone B cells were initially reduced in the preventive approach but re-expanded over time. In contrast, in the quasi-therapeutic approach, a robust down-regulation in both spleen and lymph nodes was observed. We found a significant down-regulation of the immature transitional 1 (T1) B cells in IVIg-treated mice in the quasi-therapeutic approach, while T2 and T3, representing a healthy stage of B-cell development, appeared to be up-regulated by IVIg. In summary, in two experimental settings employing an active PV mouse model, we demonstrate distinct alterations of T- and B-cell populations upon IVIg treatment, compatible with a tolerance-associated polarization in lymphatic tissue. Our data suggest that the clinical efficacy of IVIg is at least modulated by distinct alterations of T- and B-cell populations compatible with a tolerance-associated polarization in lymphatic tissue.

B cell-activating factor (BAFF) from dendritic cells, monocytes and neutrophils is required for B cell maturation and autoantibody production in SLE-like autoimmune disease

Purpose and methods

B cell-activating factor (BAFF) contributes to the pathogenesis of autoimmune diseases including systemic lupus erythematosus (SLE). Although several anti-BAFF Abs and derivatives have been developed for the treatment of SLE, the specific sources of BAFF that sustain autoantibody (auto-Ab) producing cells have not been definitively identified. Using BAFF-RFP reporter mice, we identified major changes in BAFF-producing cells in two mouse spontaneous lupus models (Tlr7 Tg mice and Sle1), and in a pristane-induced lupus (PIL) model.

Results

First, we confirmed that similar to their wildtype Tlr7 Tg and Sle1 mice counterparts, BAFF-RFP Tlr7 Tg mice and BAFF-RFP Sle1 mice had increased BAFF serum levels, which correlated with increases in plasma cells and auto-Ab production. Next, using the RFP reporter, we defined which cells had dysregulated BAFF production. BAFF-producing neutrophils (Nphs), monocytes (MOs), cDCs, T cells and B cells were all expanded in the spleens of BAFF-RFP Tlr7 Tg mice and BAFF-RFP Sle1 mice compared to controls. Furthermore, Ly6C^hi inflammatory MOs and T cells had significantly increased BAFF expression per cell in both spontaneous lupus models, while CD8^- DCs up-regulated BAFF expression only in the Tlr7 Tg mice. Similarly, pristane injection of BAFF-RFP mice induced increases in serum BAFF levels, auto-Abs, and the expansion of BAFF-producing Nphs, MOs, and DCs in both the spleen and peritoneal cavity. BAFF expression in MOs and DCs, in contrast to BAFF from Nphs, was required to maintain homeostatic and pristane-induced systemic BAFF levels and to sustain mature B cell pools in spleens and BMs. Although acting through different mechanisms, Nph, MO and DC sources of BAFF were each required for the development of auto-Abs in PIL mice.

Conclusions

Our findings underscore the importance of considering the relative roles of specific myeloid BAFF sources and B cell niches when developing treatments for SLE and other BAFF-associated autoimmune diseases.

Nanoparticle-mediated Delivery of IL-2 To T Follicular Helper Cells Protects BDF1 Mice from Lupus-like Disease

We recently reported that poly lactic-co-glycolic acid (PLGA) nanoparticles (NPs) loaded with interleukin (IL)-2 and targeted to T cells inhibited the development of lupus-like disease in BDF1 mice by inducing functional T regulatory cells (Tregs). Here we show that the protection from disease and the extended survival of BDF1 mice provided by IL-2-loaded NPs targeted to T cells is not only due to an induction of Tregs but also contributed by an inhibition of T follicular helper (T_FH) cells. These results identify a dual protective activity of IL-2 in the control of lupus autoimmunity, namely the inhibition of effector T_FH cells, in addition to the previously known induction of Tregs. This newly recognized activity of IL-2 delivered by NPs can help better explain the beneficial effects of low-dose IL-2 immunotherapy in systemic lupus erythematosus (SLE), and might be considered as a new strategy to slow disease progression and improve outcomes in lupus patients.

CD27-CD38+ B cells accumulated in early HIV infection exhibit transitional profile and promote HIV disease progression

Although peripheral B cell dysfunction in early HIV infection is established, how B cell subsets are altered by HIV infection is poorly understood. While investigating B cell subsets among individuals recently infected with HIV, we observe an accumulation of CD27^-CD38⁺ B cells and find that these cells can directly facilitate HIV infection of primary CD4⁺ T cells in vitro. Comprehensive analyses of the phenotype, function, and transcriptome of the CD27^-CD38⁺ B cell subset is conducted compared with memory and naive B cells. We find that the CD27^-CD38⁺ B cells exhibit a transitional B cell phenotype and an extremely high turnover rate. Importantly, individuals with higher proportions of CD27^-CD38⁺ B cells during early HIV infection tend to become rapid progressors in the chronic infection stage. In this study, we identify a peripheral transitional B cell subset that accumulates during early HIV infection and may contribute to disease progression.

CD21lo/-CD27-IgM- Double-Negative B Cells Accumulate in the Joints of Patients With Antinuclear Antibody-Positive Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis (JIA) encompasses a heterogeneous group of diseases. The appearance of antinuclear antibodies (ANAs) in almost half of the patients suggests B cell dysregulation as a distinct pathomechanism in these patients. Additionally, ANAs were considered potential biomarkers encompassing a clinically homogenous subgroup of JIA patients. However, in ANA+ JIA patients, the site of dysregulated B cell activation as well as the B cell subsets involved in this process is still unknown. Hence, in this cross-sectional study, we aimed in an explorative approach at characterizing potential divergences in B cell differentiation in ANA+ JIA patients by assessing the distribution of peripheral blood (PB) and synovial fluid (SF) B cell subpopulations using flow cytometry. The frequency of transitional as well as switched-memory B cells was higher in PB of JIA patients than in healthy controls. There were no differences in the distribution of B cell subsets between ANA- and ANA+ patients in PB. However, the composition of SF B cells was different between ANA- and ANA+ patients with increased frequencies of CD21^lo/-CD27^-IgM^- "double negative" (DN) B cells in the latter. DN B cells might be a characteristic subset expanding in the joints of ANA+ JIA patients and are potentially involved in the antinuclear immune response in these patients. The results of our explorative study might foster further research dissecting the pathogenesis of ANA+ JIA patients.

A novel BAFF antagonist, BAFF-Trap, effectively alleviates the disease progression of systemic lupus erythematosus in MRL/lpr mice

Abnormal B cells, which produce antibodies against self-antigens, play a key role in the pathogenesis of autoimmune diseases, such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). B-cell activating factor (BAFF) is closely associated with abnormal B cells and participates in B cell-mediated autoimmune diseases; thus, neutralizing BAFF is an effective method for treating these diseases. Our group designed a novel fusion protein, BAFF-Trap, that contains the BAFF-binding domains of two BAFF receptors (TACI and BAFF-R) and the Fc domain of human IgG1. In this study, we showed that BAFF-Trap significantly decreased the autoantibody levels, BAFF concentrations and B cells numbers in MRL/lpr mice. BAFF-Trap suppressed the expression of pro-inflammatory cytokines in the kidney and decreased the frequencies of T cell subsets and dendritic cells. Furthermore, BAFF-Trap reduced proteinuria and IgG deposition, relieved glomerular damage in the kidney, and markedly improved the survival rate of mice. These results indicated that BAFF-Trap may be a potential drug for the treatment of SLE.

Proportions of B-cell subsets are altered in incomplete systemic lupus erythematosus and correlate with interferon score and IgG levels

OBJECTIVES

Incomplete SLE (iSLE) patients display symptoms typical for SLE but have insufficient criteria to fulfil the diagnosis. Biomarkers are needed to identify iSLE patients that will progress to SLE. IFN type I activation, B-cell-activating factor (BAFF) and B-cell subset distortions play an important role in the pathogenesis of SLE. The aim of this cross-sectional study was to investigate whether B-cell subsets are altered in iSLE patients, and whether these alterations correlate with IFN scores and BAFF levels.

METHODS

iSLE patients (n = 34), SLE patients (n = 41) with quiescent disease (SLEDAI ≤4) and healthy controls (n = 22) were included. Proportions of B-cell subsets were measured with flow cytometry, IFN scores with RT-PCR and BAFF levels with ELISA.

RESULTS

Proportions of age-associated B-cells were elevated in iSLE patients compared with healthy controls and correlated with IgG levels. In iSLE patients, IFN scores and BAFF levels were significantly increased compared with healthy controls. Also, IFN scores correlated with proportions of switched memory B-cells, plasma cells and IgG levels, and correlated negatively with complement levels in iSLE patients.

CONCLUSION

In this cross-sectional study, distortions in B-cell subsets were observed in iSLE patients and were correlated with IFN scores and IgG levels. Since these factors play an important role in the pathogenesis of SLE, iSLE patients with these distortions, high IFN scores, and high levels of IgG and BAFF may be at risk for progression to SLE.

Alterations in peripheral blood B cells in systemic lupus erythematosus patients with renal insufficiency

OBJECTIVE

Systemic lupus erythematosus (SLE) is one of the autoimmune diseases, believed to be closely related to hyperactivity of B cells, overproduction of autoantibodies and immune complex formation and deposition in affected tissue. The autoreactive inflammation leads to multiorgan damage with kidney dysfunction in the forefront. Studies on lupus nephritis (LN), affecting the majority of SLE patients, are mainly focused on cells causing local inflammation. The aim of our work was to detect alterations in more accessible peripheral blood B cells in the course of SLE focusing on the influence of renal insufficiency (RI) on those parameters.

METHODS

We performed a comprehensive flow cytometry analysis of B cell subpopulations, analyzed gene expression patterns with qPCR, and examined serum cytokine levels with multiplex cytokine/chemokine assay.

RESULTS

We discovered distribution of specific B cell subsets, especially CD38⁺ cells, plasmablasts, associated with the presence and severity of the disease. Changes in expression of MBD2, DNMT1 and APRIL genes were not only associated with activity of SLE but also were significantly changed in patients with RI.

CONCLUSIONS

All these results shed new light on the role of circulating B cells, their subpopulations, function, and activity in the SLE with kidney manifestation.

Impacts of GFP-FoxP3+ regulatory T cells on lupus hallmarks differ by genetic background and type of GFP knock-in

FoxP3 reporter mice expressing green fluorescence protein (GFP) have been used as a very convenient tool to investigate the impact of regulatory T (Treg) cells on pathogenesis in autoimmune diseases. Here, we found that GFP-FoxP3⁺ knock-in (KI) mice showed alterations in the production of anti-nuclear autoantibodies (ANAs) and nephritis with different extent, depending on the presence or absence of lupus susceptibility gene locus 1 (Sle1) and KI method: contrasting with B6.Sle1.fGFP-FoxP3 mice, expressing GFP via N-terminal insertion, B6.Sle1.iGFP-FoxP3, expressing GFP via bicistronic internal ribosome entry site-driven promotion, exhibited significantly lower penetrance of serum ANA, comparing to control B6.Sle1 mice. Moreover, B6.Sle1.GFP-FoxP3⁺ mice reduced the Sle1-induced splenomegaly and B-cell expansion independently of the KI method employed, mainly by reducing the numbers of transitional 1 (T1) B cells and CD21^-CD23^- B cells, including plasmablasts and plasma cells. The absolute numbers of both splenic CD4⁺ T cells and Treg cells from B6.Sle1.GFP-FoxP3 KI mice were significantly reduced but their proportion was not changed, compared to B6.Sle1 mice. Although the glomerular basement membranes were thickened in both B6.Sle1 and B6.Sle1.iGFP-FoxP3 mice, they were thinner in B6.Sle1.fGFP-FoxP3 mice. The latter mice expressed more nephrophilic autoantibodies and deposited more complement component 3 in glomeruli compared to B6.iGFP-FoxP3 mice. FoxP3⁺ Treg cells may modulate B-cell tolerance in lupus-prone B6.Sle1 mice, presumably by modulating pathogenic, nephrophilic autoantibody production and nephritis.

Association Between Changes in BLyS Levels and the Composition of B and T Cell Compartments in Patients With Refractory Systemic Lupus Erythematosus Treated With Belimumab

Introduction: Belimumab is a monoclonal antibody against soluble BLyS used for treatment of refractory Systemic Lupus Erythematosus (SLE). Although B cells are the main target of this therapy, a BLyS-dependent T cell activation pathway has also been demonstrated. The aim of the study is to analyze B and T cells phenotype modifications in a cohort of SLE patients treated with belimumab in correlation with serum BLyS levels.

Materials and Methods: Fourteen SLE patients were enrolled in the study. Lymphocyte immunophenotyping by flow cytometry and determination of serum BLyS levels by high sensitivity ELISA were performed before the first infusion of belimumab, after 6 and 12 months of treatment. Sex and age-matched healthy controls were enrolled for the comparisons.

Results: Baseline number of total B cells, especially switched memory B cells, were lower in SLE patients compared to control subjects. After 6 months of treatment, the total number of B cells, particularly, naive and transitional B cells, was significantly reduced in correlation with the reduction of BLyS levels. No significant association was found between baseline counts of B cells and reduction of SLEDAI-2K over time. In terms of response prediction, a significant association between SLEDAI-2K improvement at 12 months and the decrease of total number of B cells within the first 6 months of therapy was observed. Concerning the T cell compartment, the baseline percentage number of CD8+ effector memory was associated with SLEDAI-2K at baseline and with its improvement after 12 months of therapy. Furthermore, T cell lymphopenia and low number of circulating recent thymic emigrants were also observed compared to control subjects measured at baseline.

Discussion: The effects of belimumab on B cell subpopulations could be explained by the direct blockage of soluble BLyS, while the mild effects on T cells might be explained indirectly by the reduction of disease activity by means of therapy. B cell immunophenotyping during belimumab might be useful for monitoring the response to treatment.

The role of surface molecule CD229 in Multiple Myeloma

The outcome of Multiple Myeloma (MM) patients has dramatically improved, however, most patients will still succumb to their disease. Additional therapeutic options are urgently needed and novel immunotherapies are enormously promising in the therapeutic armamentarium against MM. The first step in the development of any immunotherapy needs to be the identification of an appropriate target structure. In this review we present the current knowledge on surface molecule CD229, a member of the Signaling Lymphocyte Activation (SLAM) family of immune receptors. We believe that based on its characteristics, including (1) strong and homogenous expression on all myeloma cells, (2) expression on myeloma precursors, (3) absence from most normal tissues, (4) a central function in the biology of MM, CD229 (SLAMF3) represents a promising target for anti-MM immunotherapies. The introduction of novel anti-CD229 approaches into the clinic will hopefully lead to more durable responses, or maybe even cures, in MM.

The aetiology of B-cell lymphoid malignancies with a focus on chronic inflammation and infections

B-cell malignancies are a heterogeneous group of lymphoproliferative disorders with different molecular characteristics and clinical course. It is increasingly recognized that the group displays considerable heterogeneity also regarding aetiologic factors. Here, we summarize the latest developments in the aetiology of B-cell lymphoid malignancy subtypes focusing on immune perturbation. Severe immune suppression constitutes a strong and well-established risk factor for aggressive subtypes (e.g. diffuse large B-cell and Burkitt lymphoma), but appears unrelated to risk of common low-grade subtypes (e.g. follicular and mantle cell lymphoma). Inflammation and infections are known co-factors amongst the immunosuppressed; however, immune stimulation is now recognized as a crucial determinant of lymphomagenesis also amongst immunocompetent individuals. This is best exemplified in marginal zone lymphomas where local chronic inflammation and infection in the stomach, ocular adnexa and salivary glands have been directly linked with the development of oligoclonal and monoclonal malignant B-cell populations. Aggressive subtypes (e.g. diffuse large B-cell lymphoma) are increasingly linked with features of systemic immune stimulation including autoimmune/inflammatory disease and subclinical cytokine elevations. Lifestyle factors (e.g. high body mass index, cigarette smoking) are associated with risk of diffuse large B-cell and follicular lymphoma, respectively, possibly mediated through inflammation. Recent genome-wide association studies further underline the importance of immune function by linking several subtypes to variations in the human leucocyte antigen (HLA) class genes. In the future, improved knowledge of mechanistic pathways of inflammation/infections in lymphoma development may translate to active measures of prevention or treatment, as is already the case for some low-grade lymphoma subtypes.

High resolution IgH repertoire analysis reveals fetal liver as the likely origin of life-long, innate B lymphopoiesis in humans

The ontogeny of the natural, public IgM repertoire remains incompletely explored. Here, high-resolution immunogenetic analysis of B cells from (unrelated) fetal, child, and adult samples, shows that although fetal liver (FL) and bone marrow (FBM) IgM repertoires are equally diversified, FL is the main source of IgM natural immunity during the 2nd trimester. Strikingly, 0.25% of all prenatal clonotypes, comprising 18.7% of the expressed repertoire, are shared with the postnatal samples, consistent with persisting fetal IgM + B cells being a source of natural IgM repertoire in adult life. Further, the origins of specific stereotypic IgM + B cell receptors associated with chronic lymphocytic leukemia, can be traced back to fetal B cell lymphopoiesis, suggesting that persisting fetal B cells can be subject to malignant transformation late in life. Overall, these novel data provide unique insights into the ontogeny of physiological and malignant B lymphopoiesis that spans the human lifetime.

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Second trimester human fetal liver and fetal bone marrow B-cells have IgM repertoires that are equally diversified

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Human fetal liver B-cells are the main source of innate, natural IgM responses

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CLL-associated, stereotypic B cell receptors are detected in fetal IgM repertoire

Emerging Role of the Spleen in the Pharmacokinetics of Monoclonal Antibodies, Nanoparticles and Exosomes

After being absorbed, drugs distribute in the body in part to reach target tissues, in part to be disposed in tissues where they do not exert clinically-relevant effects. Therapeutically-relevant effects are usually terminated by drug metabolism and/or elimination. The role that has been traditionally ascribed to the spleen in these fundamental pharmacokinetic processes was definitely marginal. However, due to its high blood flow and to the characteristics of its microcirculation, this organ would be expected to be significantly exposed to large, new generation drugs that can hardly penetrate in other tissues with tight endothelial barriers. In the present review, we examine the involvement of the spleen in the disposition of monoclonal antibodies, nanoparticles and exosomes and the possible implications for their therapeutic efficacy and toxicity. The data that we will review lead to the conclusion that a new role is emerging for the spleen in the pharmacokinetics of new generation drugs, hence suggesting that this small, neglected organ will certainly deserve stronger attention by pharmacologists in the future.

Central role for marginal zone B cells in an animal model of Sjogren's syndrome

Patients with Sjogren's syndrome (SS) have been shown to have abnormal B cell function and increased numbers of marginal zone B cells (MZB and MZB precursors. The current studies utilized the Interleukin 14 alpha transgenic mouse model (IL14aTG) for SS to investigate the roles of marginal zone B cells (MZB) of the innate immune system in the pathophysiology of the disease. Eliminating MZB from IL14aTG mice by B cell specific deletion of RBP-J resulted in complete elimination of all disease manifestations of SS. Mice had normal salivary gland secretions, negative autoantibodies and normal histology of the salivary and lacrimal glands compared to IL14aTG mice at the same time points. In contrast, eliminating B1 cells by deleting btk did not ameliorate the disease. Therefore, MZB are critical for the development of SS.

Immunologic profiles of multiple sclerosis treatments reveal shared early B cell alterations

Objective:

We undertook a systems immunology approach of the adaptive immune system in multiple sclerosis (MS), overcoming tradeoffs between scale and level of detail, in order to identify the immunologic signature of MS and the changes wrought by current immunomodulatory treatments.

Methods:

We developed a comprehensive flow cytometry platform measuring 38 immunologic cell types in the peripheral blood of 245 individuals in a routine clinical setting. These include patients with MS, untreated or receiving any of 4 current immunomodulatory treatments (interferon-β, glatiramer acetate, natalizumab, or fingolimod), patients with autoimmune thyroid disease, and healthy controls.

Results:

An increase in memory CD8⁺ T cells and B cells was observed in untreated patients with MS. Interferon-β and fingolimod induce significant changes upon multiple aspects of the peripheral immune system, with an unexpectedly prominent alteration of B cells. Overall, both treatments push the immune system in different directions, with only 2 significant effects shared across these treatments—an increase in transitional B cells and a decrease in class-switched B cells. We further identified heightened B cell-activating factor (BAFF) levels as regulating this shared B cell pathway.

Conclusions:

A systems immunology approach established different immunologic profiles induced by current immunomodulatory MS treatments, offering perspectives for personalized medicine. Pathways shared between the immunologic architecture of existing efficacious treatments identify targets for future treatment design.

B Cell Activating Factor (BAFF) and BAFF Receptor Expression in Autoimmune and Nonautoimmune Thyroid Diseases

BACKGROUND

The B cell activating factor (BAFF) is a member of the tumor necrosis factor family, which controls the survival/proliferation of B cells and is involved in the pathogenesis of a number of autoimmune diseases. The objective of the present study was to investigate the expression of BAFF and BAFF receptor (BAFF-R) in the thyroid tissue of patients affected with autoimmune thyroid disorders (AITD) or multinodular goiter (MNG) compared with those with normal thyroids.

METHODS

Immunohistochemistry was performed using a panel of antibodies against BAFF, BAFF-R, CD3, CD4, CD8, CD20, CD34, CD79a, CD1a, CD68, and CD163 on the thyroid sections of 27 patients affected with Graves' disease (GD), 23 with Hashimoto's thyroiditis (HT), 16 with nontoxic nodular goiter (NTG), and 15 with toxic nodular goiter (TG), submitted to total thyroidectomy between 2000 and 2011.

RESULTS

The overall BAFF-R expression in thyrocytes was weak and not different in AITD and MNG. Conversely, a stronger BAFF expression was observed in MNG compared with AITD. BAFF and BAFF-R expression in the infiltrating lymphocytes was higher in AITD compared with MNG. Interestingly, in lymphocytes of follicular-like structures observed in HT, BAFF and BAFF-R were localized in the germinal center or in the mantle, respectively.

CONCLUSIONS

This study shows that BAFF and BAFF-R are expressed in the thyrocytes derived from patients with either AITD or MNG, in addition to the expected expression of BAFF and its receptor in the infiltrating immune cells of GD and HT. These findings suggest a possible involvement of BAFF and its receptors in the pathophysiology of AITD.

B-cell survival factors in autoimmune rheumatic disorders

Autoimmune rheumatic disorders have complex etiopathogenetic mechanisms in which B cells play a central role. The importance of factors stimulating B cells, notably the B-cell activating factor (BAFF) and A proliferation inducing ligand (APRIL) axis is now recognized. BAFF and APRIL are cytokines essential for B-cell proliferation and survival from the immature stages to the development of plasma cells. Their levels are increased in some subsets of patients with autoimmune disorders. Several recent biologic drugs have been developed to block this axis, namely belimumab [already licensed for systemic lupus erythematosus (SLE) treatment], tabalumab, atacicept and blisibimod. Many clinical trials to evaluate the safety and efficacy of these drugs in several autoimmune disorders are ongoing, or have been completed recently. This review updates the information on the use of biologic agents blocking BAFF/APRIL for patients with SLE, rheumatoid arthritis, Sjögren's syndrome and myositis.

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.

Lymphoma development in patients with autoimmune and inflammatory disorders--what are the driving forces?

For decades, it has been known that patients with certain autoimmune and inflammatory disorders, such as rheumatoid arthritis (RA) and primary Sjögren's syndrome (pSS), have an increased risk of developing malignant lymphoma. Although the clinico-biological reasons for this association remain largely unknown, our knowledge has improved and new insights have been obtained. First, the direct link between autoimmunity and lymphomagenesis has been strengthened by large epidemiological studies showing a consistent risk increase of lymphoma associated with certain autoimmune/inflammatory conditions in independent cohorts from different countries. Second, a number of local and systemic disease-related risk factors in these diseases have been repeatedly linked to lymphoma development, with the prime examples being disease severity and the degree of inflammatory activity. Considering the key role of B- and T-cell activation in the pathogenesis of both autoimmunity and lymphoma, it is perhaps not surprising that longstanding chronic inflammation and/or antigen stimulation have emerged as major predisposing factors of lymphoma in patients with active autoimmune disease. Finally, increasing evidence suggests that lymphomas associated with autoimmunity constitute a different spectrum of entities compared to lymphomas arising in patients without any known autoimmune or inflammatory conditions, pointing to a different pathobiology. In this review, we summarize the recent literature that supports a direct or indirect link between immune-mediated disease and lymphoma and describe the characteristics of lymphomas developing in the different diseases. We also discuss molecular, genetic and microenvironmental factors that may come into play in the pathobiology of these disorders.

Overexpression of TLR7 promotes cell-intrinsic expansion and autoantibody production by transitional T1 B cells

Transgenic expression of TLR7 results in the expansion and hyperactivation of T1 B cells in response to endogenous RNA complexes, leading to increased autoantibody production.

Toll-like receptor (TLR), a ligand for single-stranded RNA, has been implicated in the development of pathogenic anti-RNA autoantibodies both in systemic lupus erythematous (SLE) patients and in murine models of lupus. It is still unclear, however, where and how TLR7-mediated interactions affect the development of autoreactive B cells. We found that overexpression of TLR7 in transgenic mice (TLR7.1Tg) leads to marked alterations of transitional (T1) B cells, associated with their expansion and proliferation within the splenic red pulp (RP). This phenotype was intrinsic to the T1 subset of B cells and occurred independently of type 1 IFN signals. Overexpression of RNase in TLR7.1Tg mice significantly limited the expansion and proliferation of T1 cells, indicating that endogenous RNA complexes are driving their activation. TLR7.1Tg T1 cells were hyper-responsive to anti-IgM and TLR7 ligand stimulation in vitro and produced high concentrations of class-switched IgG2b and IgG2c, including anti-RNA antibodies. Our results demonstrate that initial TLR7 stimulation of B cells occurs at the T1 stage of differentiation in the splenic RP and suggest that dysregulation of TLR7 expression in T1 cells can result in production of autoantibodies.

From immunosuppression to immunomodulation: current principles and future strategies

Over the last few decades, tremendous progress has been made in understanding the mechanisms of immune responses. This progress has also led to a more detailed knowledge of the processes leading to the loss of self-tolerance and the destruction of self-tissue in the case of autoimmune diseases, the effector mechanism involved in transplant allograft rejection as well as the driving factors in exacerbated inflammatory disorders. Despite this progress, the challenge still remains to selectively interfere with immune responses responsible for autoimmunity or transplant rejection while keeping an intact response to infectious agents. To date, such a selective interference is still difficult to achieve, as highlighted by the fact that an overall increased risk for infections and malignancy continues to be the most frequent side effect of the currently used immunosuppressive principles. Nevertheless, although discovered several decades ago, many of the 'first-generation' immunosuppressive principles such as steroids, methotrexate and cyclosporin A are still in clinical use, demonstrating the therapeutic value of these drugs for the patients that are in need. In this review, the author describes the mode of action of the currently most used immunosuppressive agents (not attempting to cover all principles that are available) and expands on recent activities in the discovery and development of novel immunomodulatory principles.

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.

Evidence of dynamically dysregulated gene expression pathways in hyperresponsive B cells from African American lupus patients

Recent application of gene expression profiling to the immune system has shown a great potential for characterization of complex regulatory processes. It is becoming increasingly important to characterize functional systems through multigene interactions to provide valuable insights into differences between healthy controls and autoimmune patients. Here we apply an original systematic approach to the analysis of changes in regulatory gene interconnections between in Epstein-Barr virus transformed hyperresponsive B cells from SLE patients and normal control B cells. Both traditional analysis of differential gene expression and analysis of the dynamics of gene expression variations were performed in combination to establish model networks of functional gene expression. This Pathway Dysregulation Analysis identified known transcription factors and transcriptional regulators activated uniquely in stimulated B cells from SLE patients.

Ly9 (CD229) Cell-Surface Receptor is Crucial for the Development of Spontaneous Autoantibody Production to Nuclear Antigens

The Signaling Lymphocyte Activation Molecule Family (SLAMF) genes, which encode cell-surface receptors that modulate innate and adaptive immune responses, lay within a genomic region of human and mouse chromosome 1 that confers a predisposition for the development of systemic lupus erythematosus (SLE). Herein, we demonstrate that the SLAMF member Ly9 arises as a novel receptor contributing to the reinforcement of tolerance. Specifically, Ly9-deficient mice spontaneously developed features of systemic autoimmunity such as the production of anti-nuclear antibodies (ANA), -dsDNA, and -nucleosome autoantibodies, independently of genetic background [(B6.129) or (BALB/c.129)]. In aged (10- to 12-month-old) Ly9^−/− mice key cell subsets implicated in autoimmunity were expanded, e.g., T follicular helper (Tfh) as well as germinal center (GC) B cells. More importantly, in vitro functional experiments showed that Ly9 acts as an inhibitory receptor of IFN-γ producing CD4⁺ T cells. Taken together, our findings reveal that the Ly9 receptor triggers cell intrinsic safeguarding mechanisms to prevent a breach of tolerance, emerging as a new non-redundant inhibitory cell-surface receptor capable of disabling autoantibody responses.

Prolactin rescues and primes autoreactive B cells directly and indirectly through dendritic cells in B6.Sle3 mice

The lupus susceptibility interval Sle3/5 confers responsiveness to prolactin in C57BL/6 (B6) mice and hyperprolactinaemia induces a lupus-like phenotype in B6.Sel3/5 mice. In this study, the immunostimulatory effects of prolactin in B6 mice containing the Sle3 portion of the Sel3/5 interval (B6.Sle3 mice) were dissected. Because of the Sle3 interval's involvement in activation of myeloid cells, the effect of dendritic cells (DCs) from prolactin-treated B6.Sle3 mice on the phenotype of B6 mice was also evaluated. B cells from prolactin-treated B6 and B6.Sle3 mice and from B6 recipients of prolactin-modulated DCs from B6.Sle3 mice were tested for DNA-reactivity and resistance to B cell receptor (BCR)-mediated apoptosis. The expression of co-stimulatory molecules on lymphocytes and myeloid cells was also evaluated. In prolactin-treated B6.Sle3 mice, transitional type 2 B cells increased while type 1 B cells decreased as a consequence of prolactin-induced resistance to BCR-mediated apoptosis leading to the survival of DNA-reactive B cells. Follicular B cells from prolactin-treated mice expressed increased levels of CD40, B7·2 and IA(b), and DCs and monocytes had higher levels of CD44 and B7·2 than placebo-treated mice. Adoptive transfer of DCs from prolactin-treated B6.Sle3 mice to B6 recipients demonstrated the intrinsic ability of prolactin-modulated DCs to induce a development of lupus-like characteristics in B6 mice. Based on these results, prolactin accelerates the breakdown of immune tolerance in B6.Sle3 mice by promoting the survival, maturation and activation of autoreactive B cells, DCs and macrophages.

Aberrant B cell selection and activation in systemic lupus erythematosus

The detrimental role of B lymphocytes in systemic lupus erythematosus (SLE) is evident from the high levels of pathogenic antinuclear autoantibodies (ANAs) found in SLE patients. Affirming this causative role, additional antibody-independent roles of B cells in SLE were appreciated. In recent years, many defects in B cell selection and activation have been identified in murine lupus models and SLE patients that explain the increased emergence and persistence of autoreactive B cells and their lowered activation threshold. Therefore, clinical trials with B cell depletion regimens in SLE patients were initiated but disappointingly the efficacy of B cell depleting agents proved to be limited. Remarkably however, a major breakthrough in SLE therapy was accomplished by blocking B cell survival factors rather then eliminating B cells. This surprising finding indicates that although SLE is a B cell-driven disease, the amplifying crosstalk between B cells and other cells of the immune system likely evokes the observed tolerance breakdown in B cells. Moreover, this implies that intelligent interception of pro-inflammatory loops rather then selectively silencing B cells will be key to the development of new SLE therapies. In this review, we will not only highlight the intrinsic B cell defects that facilitate the persistence of autoreactive B cells and their activation, but in addition we will focus on B cell extrinsic signals derived from T cells and innate immune cells that lower the activation threshold for B cells.

Epstein-Barr virus in systemic lupus erythematosus, rheumatoid arthritis and multiple sclerosis—association and causation

Epidemiological data suggest that the Epstein-Barr virus (EBV) is associated with several autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis and multiple sclerosis. However, it is not clear whether EBV plays a role in the pathogenesis of these diseases, and if so, by which mechanisms the virus may contribute. In this review, we discuss possible viral and immunological mechanisms that might explain associations between EBV and autoimmune diseases and whether these associations represent causes or effects of inflammation and autoimmunity.

Acquired C1-inhibitor deficiency and lymphoproliferative disorders: a tight relationship

Angioedema due to the acquired deficiency of C1-inhibitor is a rare disease known as acquired angioedema (AAE), which was first described in a patient with high-grade lymphoma and is frequently associated with lymphoproliferative diseases, including expansion of B cell clones producing anti-C1-INH autoantibodies, monoclonal gammopathy of uncertain significance (MGUS) and non-Hodgkin lymphoma (NHL). AAE is clinically similar to hereditary angioedema (HAE), and is characterized by recurrent episodes of sub-cutaneous and sub-mucosal edema. It may affect the face, tongue, extremities, trunk and genitals. The involvement of the gastrointestinal tract causes bowel sub-occlusion with severe pain, vomiting and diarrhea, whereas laryngeal edema can be life-threatening. Unlike those with HAE, AAE patients usually have late-onset symptoms, do not have a family history of angioedema and present variable response to treatment due to the hyper-catabolism of C1-inhibitor. Reduced C1-inhibitor function leads to activation of the classic complement pathway with its consumption and activation of the contact system leading to the generation of the vasoactive peptide bradykinin, which increases vascular permeability and induces angioedema. Lymphoprolipherative diseases and AAE are tightly linked with either angioedema or limphoprolyferation being the first symptom. Experimental data indicate that neoplastic tissue and/or anti-C1-inhibitor antibodies induce C1-inhibitor consumption, and this is further supported by the observation that cytotoxic treatment of the lymphoproliferative diseases associated with AAE variably reverses the complement impairment and leads to a clinical improvement in angioedema symptoms.

To B or not to B cells-mediate a healthy start to life

Maternal immune responses during pregnancy are critical in programming the future health of a newborn. The maternal immune system is required to accommodate fetal immune tolerance as well as to provide a protective defence against infections for the immunocompromised mother and her baby during gestation and lactation. Natural immunity and antibody production by maternal B cells play a significant role in providing such immunoprotection. However, aberrations in the B cell compartment as a consequence of maternal autoimmunity can pose serious risks to both the mother and her baby. Despite their potential implication in shaping pregnancy outcomes, the role of B cells in human pregnancy has been poorly studied. This review focuses on the role of B cells and the implications of B cell depletion therapy in pregnancy. It highlights the evidence of an association between aberrant B cell compartment and obstetric conditions. It also alludes to the potential mechanisms that amplify these B cell aberrances and thereby contribute to exacerbation of some maternal autoimmune conditions and poor neonatal outcomes. Clinical and experimental evidence suggests strongly that maternal autoantibodies contribute directly to the pathologies of obstetric and neonatal conditions that have significant implications for the lifelong health of a newborn. The evidence for clinical benefit and safety of B cell depletion therapies in pregnancy is reviewed, and an argument is mounted for further clinical evaluation of B cell-targeted therapies in high-risk pregnancy, with an emphasis on improving neonatal outcomes and prevention of neonatal conditions such as congenital heart block and fetal/neonatal alloimmune thrombocytopenia.

B-cell selection and the development of autoantibodies

The clearest evidence that B cells play an important role in human autoimmunity is that immunotherapies that deplete B cells are very effective treatments for many autoimmune diseases. All people, healthy or ill, have autoreactive B cells, but not at the same frequency. A number of genes influence the level of these autoreactive B cells and whether they are eliminated or not during development at a central checkpoint in the bone marrow (BM) or at a later checkpoint in peripheral lymphoid tissues. These genes include those encoding proteins that regulate signaling through the B-cell receptor complex such as Btk and PTPN22, proteins that regulate innate signaling via Toll-like receptors (TLRs) such as MyD88 and interleukin-1 receptor-associated kinase 4, as well as the gene encoding the activation-induced deaminase (AID) essential for B cells to undergo class switch recombination and somatic hypermutation. Recent studies have revealed that TLR signaling elements and AID function not only in peripheral B cells to help mediate effective antibody responses to foreign antigens, but also in the BM to help remove autoreactive B-lineage cells at a very early point in B-cell development. Newly arising B cells that leave the BM and enter the blood and splenic red pulp can express both AID and TLR signaling elements like TLR7, and thus are fully equipped to respond rapidly to antigens (including autoantigens), to isotype class switch, and to undergo somatic hypermutation. These red pulp B cells may thus be an important source of autoantibody-producing cells arising particularly in extrafollicular sites, and indeed may be as significant a source of autoantibody-producing cells as B cells arising from germinal centers.