The BAFF/APRIL system: emerging functions beyond B cell biology and autoimmunity

The TNF Family of Ligands and Receptors: Communication Modules in the Immune System and Beyond

The tumor necrosis factor (TNF) and TNF receptor (TNFR) superfamilies (TNFSF/TNFRSF) include 19 ligands and 29 receptors that play important roles in the modulation of cellular functions. The communication pathways mediated by TNFSF/TNFRSF are essential for numerous developmental, homeostatic, and stimulus-responsive processes in vivo. TNFSF/TNFRSF members regulate cellular differentiation, survival, and programmed death, but their most critical functions pertain to the immune system. Both innate and adaptive immune cells are controlled by TNFSF/TNFRSF members in a manner that is crucial for the coordination of various mechanisms driving either co-stimulation or co-inhibition of the immune response. Dysregulation of these same signaling pathways has been implicated in inflammatory and autoimmune diseases, highlighting the importance of their tight regulation. Investigation of the control of TNFSF/TNFRSF activities has led to the development of therapeutics with the potential to reduce chronic inflammation or promote anti-tumor immunity. The study of TNFSF/TNFRSF proteins has exploded over the last 30 yr, but there remains a need to better understand the fundamental mechanisms underlying the molecular pathways they mediate to design more effective anti-inflammatory and anti-cancer therapies.

APRIL and sTACI could be predictors of multiorgan dysfunction syndrome in sepsis

Although the role of B cells in sepsis immunoregulation has become an interesting topic, there is lack of data on the role of B cell function regulators in prediction of multiorgan dysfunction syndrome (MODS). The aim of this study was to evaluate the prognostic value of A Proliferation Inducing Ligand (APRIL) and soluble Transmembrane Activator and CAML Interactor Protein (sTACI), the main B cell function regulators, in prediction of MODS development within the first 48 h after admission to intensive care unit, among septic patients. We included 112 patients with sepsis, treated at Clinic for Infectious Diseases and Emergency Center, Clinical Center of Vojvodina, Novi Sad, Serbia. Plasma concentrations of APRIL and sTACI were determined at the admission and potential development of MODS was confirmed in the first 48 h. Concentrations of APRIL (p = 0.003) and sTACI (p<0.001) were higher in patients who developed MODS (n = 30). ROC curve analysis showed that AUC for sTACI (AUC = 0.764) was greater than that for procalcitonin (AUC = 0.719) and APRIL (AUC = 0.673) in MODS development prediction. Multivariate regression analysis showed that sTACI, as an anti-inflammatory biomarker stimulating the apoptosis of B cells, was the only independent predictor of MODS, beside SOFA score. Elevated level of sTACI could be the alarm for the increased B cell apoptosis and development of immune paralysis. Including these biomarkers into predictive scores specific for septic patients may potentially improve their sensitivity and specificity. Measurement of their concentrations dynamics could contribute to better assessment of sepsis evolution and timely introduction of immunomodulatory therapy.

Differential regulation of IgA+ B cells in vitro by stromal cells from distinctive anatomical compartments

B cell development is regulated by stromal cells (SCs) that form a supportive microenvironment. These SCs along with other cell types produce cytokines, chemokines, and adhesion molecules that guide B cell commitment and differentiation. BM, spleen (Sp), and the gut lamina propria (LP) constitute distinctive anatomical compartments that support B cell differentiation. In order to characterize and compare the signals necessary to generate IgA⁺ B cells, we developed an in vitro system to co-culture gut LP, BM, or Sp-derived SCs with B lineage cells. Using this co-culture system, we found that gut LP SCs promote IgA⁺ B cell accumulation through the production of soluble stimulatory factors. In contrast to gut LP SCs, BM and splenic SCs were found to impair IgA⁺ B cell accumulation in vitro. Taken together, these observations provide new insights into how SCs derived from different anatomical locations shape IgA⁺ B cell responses.

Biological therapy of autoimmune blistering diseases

INTRODUCTION

Autoimmune blistering skin diseases are a group of disorders subdivided according to the location of blister formation: intraepidermal blistering in the pemphigus group and subepidermal in the pemphigoid group. These conditions are clinically heterogeneous and are treated with systemic corticosteroids and/or other forms of immunosuppression on the basis of clinical subtype and disease severity. These approaches may not be effective for the induction and maintenance of clinical response or need to be stopped because of intolerable side effects.

AREAS COVERED

Biological therapies can represent a valid alternative strategy in various autoimmune blistering disorders and this review article will address this issue with a special focus on pemphigus vulgaris and bullous pemphigoid. These biological approaches are designed to target B cells, autoantibodies, complement proteins, and several cytokines.

EXPERT OPINION

Innovative strategies for the treatment of autoimmune blistering conditions primarily depend on the use of drugs with a high degree of specificity targeting crucial steps in the immunopathology of these disorders. Novel biological agents offer treatment alternatives to patients with autoimmune blistering conditions by targeting B cells, pathogenic autoantibodies, complement and cytokines.

Mesenteric CD103+DCs Initiate Switched Coxsackievirus B3 VP1-Specific IgA Response to Intranasal Chitosan-DNA Vaccine Through Secreting BAFF/IL-6 and Promoting Th17/Tfh Differentiation

Intranasal chitosan-formulated DNA vaccination promotes IgA secretion in the intestine. However, the mechanism whereby chitosan-DNA skews IgA class switch recombination (CSR) of B cells in the Gut-associated lymph tissue (GALT) is not fully resolved. In this study, we investigated the effects of nasally administered chitosan-DNA (pcDNA3.1-VP1 plasmid encoding VP1 capsid protein of Coxsackievirus B3) on IgA production, DC activation and Tfh/Th17 response in the intestine. Compared to DNA immunization, intranasal chitosan-DNA vaccination induced antigen-specific IgA production in feces, a pronounced switching of antigen-specific IgA⁺ plasmablast B cells in the mesenteric lymph nodes (MLNs) and an enhanced expression of post-recombination Iα-CH transcripts/IgA germline transcript (αGT) as well as activation-induced cytidine deaminase (AID) in MLN B cells. MLN Tfh frequency was markedly enhanced by chitosan-DNA, and was associated with VP1-specific IgA titer. 24 h after immunization, intranasal chitosan-DNA induced a recruitment of CD103⁺DCs into the MLN that paralleled a selective loss of CD103⁺DCs in the lamina propria (LP). In vivo activated MLN-derived CD103⁺DCs produced high levels of IL-6 and BAFF in response to chitosan-DNA, which up-regulated transmembrane activator and CAML interactor (TACI) expression on MLN B cells. Upon co-culture with IgM⁺B in the presence of chitosan-DNA, MLN CD103⁺DCs induced IgA production in a T-dependent manner; and this IgA-promoting effect of CD103⁺DC was blocked by targeting TACI and, to a lower extent, by blocking IL-6. MLN CD103⁺DCs displayed an enhanced capacity to induce an enhanced CD4⁺Th17 response in vivo and in vitro, and IL-17A deficient mice had a pronounced reduction of specific intestinal IgA following immunization. Taken together, mesenteric CD103⁺DCs are indispensable for the adjuvant activity of chitosan in enhancing DNA vaccine-specific IgA switching in gut through activating BAFF-TACI and IL-6-IL-6R signaling, and through inducing Th17/Tfh differentiation in the MLN.

Interleukin-33 Contributes Toward Loss of Tolerance by Promoting B-Cell-Activating Factor of the Tumor-Necrosis-Factor Family (BAFF)-Dependent Autoantibody Production

Breaking tolerance is a key event leading to autoimmunity, but the exact mechanisms responsible for this remain uncertain. Here we show that the alarmin IL-33 is able to drive the generation of autoantibodies through induction of the B cell survival factor BAFF. A temporary, short-term increase in IL-33 results in a primary (IgM) response to self-antigens. This transient DNA-specific autoantibody response was dependent on the induction of BAFF. Notably, radiation resistant cells and not myeloid cells, such as neutrophils or dendritic cells were the major source of BAFF and were critical in driving the autoantibody response. Chronic exposure to IL-33 elicited dramatic increases in BAFF levels and resulted in elevated numbers of B and T follicular helper cells as well as germinal center formation. We also observed class-switching from an IgM to an IgG DNA-specific autoantibody response. Collectively, the results provide novel insights into a potential mechanism for breaking immune-tolerance via IL-33-mediated induction of BAFF.

BAFF-R and TACI expression on CD3+ T cells: Interplay among BAFF, APRIL and T helper cytokines profile in systemic lupus erythematosus

BACKGROUND

Systemic lupus erythematosus (SLE) is the prototype of systemic autoimmune disease, characterized by loss of immune tolerance against self-antigens where autoantibody production is the hallmark of disease. B-cell-activating factor (BAFF) and A proliferation-inducing ligand (APRIL) are cytokines that promote autoreactive cell survival, immunoglobulin-class switching and autoantibody responses in human and mouse SLE models. BAFF and APRIL exert their functions through interactions with their receptors BAFF-R and TACI that are differentially expressed in B lymphocyte subsets, monocytes, dendritic cells and T lymphocytes. BAFF stimulation favors T lymphocyte activation and cytokine production through BAFF-R, which could contribute to the Th1, Th17 and/or Th2 response dysregulation observed in SLE patients.

OBJECTIVE

To evaluate the expression of the cytokines BAFF and APRIL and their association with the receptors BAFF-R and TACI on CD3+ T cells and to evaluate Th1/Th2/Th17 cytokine profile in patients with SLE.

METHODS

Fifteen healthy controls (HC) and 36 SLE patients were included, and their demographic and clinical data were assessed. The disease activity index (Mex-SLEDAI) and damage index (SLICC) were applied to the SLE patients. BAFF-R and TACI expression on CD3+ T cells were evaluated by flow cytometry. Serum BAFF and APRIL concentrations were measured by enzyme-linked immunosorbent assays (ELISA). Cytokine levels of Th1 (IL-12, IL-2, IFN-γ, TNF-α), Th2 (IL-4, IL-6, IL-10, IL-13) and Th17 (IL-1β e IL-17) were quantified with a multiplex assay (MAGPIX). Statistical analysis was performed using PASW Statistics v.20 and GraphPad Prism v.6 software.

RESULTS

No differences in BAFF-R or TACI expression on the CD3+ T cells of SLE and HC were observed. BAFF-R expression correlates inversely with disease activity (r = -0.538, p < 0.01), while TACI correlates with disease activity (r = 0.530, p < 0.05). Serum BAFF and APRIL levels were high in SLE patients and correlated with the disease activity index Mex-SLEDAI (r = 0.621, p < 0.01 and r = 0.416, p < 0.05). SLE patients were found to have significantly higher levels of IL-12, IFN-γ, TNF-α, IL-6, IL-10, IL-13, IL-1β and IL-17 compared to HC (p < 0.05). Cytokines IL-17 (r = 0.526) and TNF-α (r = 0.410) correlate with disease activity (p < 0.05), while APRIL (r = 0.477), IL-10 (r = 0.426) and IFN-γ (r = 0.440) levels were associated with organ damage (p < 0.01). Serum BAFF expression levels correlate with IL-4 (r = 0.424; p < 0.05), IL-6 (r = 0.420; p < 0.05) and IL-10 (r = 0.459; p < 0.01), whereas APRIL levels correlate with IL-2 (r = 0.666; p < 0.01), IL-12 (r = 0.611; p < 0.01) and TNF-α (r = 0.471; p < 0.05) cytokines. A subgroup of SLE patients with high serum BAFF levels (>2 ng/mL) also showed increased APRIL, IL-2, IL-6 and IL-10 levels (p < 0.05). Finally, BAFF, IL-4 and TNF-α serum levels were associated with high titers of antinuclear antibodies.

CONCLUSIONS

The study demonstrates an imbalance in the Th1/Th2 cytokine profile, with increased proinflammatory cytokines, as well as BAFF and APRIL serum levels. Associations of BAFF with Th2 profile cytokines and disease activity, as well as APRIL with Th1 profile cytokines and organ damage, suggest that BAFF and APRIL generated in the autoimmunity context could through still unknown mechanisms, modulate the microenvironment, and perpetuate the inflammatory response, autoantibody production and organ damage observed in SLE patients.

The role of B cells in multiple sclerosis: Current and future therapies

While it was long held that T cells were the primary mediators of multiple sclerosis (MS) pathogenesis, the beneficial effects observed in response to treatment with Rituximab (RTX), a monoclonal antibody (mAb) targeting CD20, shed light on a key contributor to MS that had been previously underappreciated: B cells. This has been reaffirmed by results from clinical trials testing the efficacy of subsequently developed B cell-depleting mAbs targeting CD20 as well as studies revisiting the effects of previous disease-modifying therapies (DMTs) on B cell subsets thought to modulate disease severity. In this review, we summarize current knowledge regarding the complex roles of B cells in MS pathogenesis and current and potential future B cell-directed therapies.

Urinary B-cell-activating factor of the tumour necrosis factor family (BAFF) in systemic lupus erythematosus

INTRODUCTION

We examined the clinical relevance of urinary concentrations of B-cell-activating factor of the tumour necrosis factor family (BAFF) and a proliferation-inducing ligand (APRIL) in systemic lupus erythematosus (SLE).

METHODS

We quantified urinary BAFF (uBAFF) by enzyme-linked immunosorbent assay in 85 SLE, 28 primary Sjögren syndrome (pSS), 40 immunoglobulin A nephropathy (IgAN) patients and 36 healthy controls (HCs). Urinary APRIL (uAPRIL) and monocyte chemoattractant protein 1 (uMCP-1) were also quantified. Overall and renal SLE disease activity were assessed using the Systemic Lupus Erythematosus Disease Activity Index 2000.

RESULTS

uBAFF was detected in 12% (10/85) of SLE patients, but was undetectable in HCs, IgAN and pSS patients. uBAFF was detectable in 28% (5/18) of SLE patients with active nephritis vs 5/67 (7%) of those without ( p = 0.03), and uBAFF was significantly higher in active renal patients ( p = 0.02) and more likely to be detected in patients with persistently active renal disease. In comparison, uAPRIL and uMCP-1 were detected in 32% (25/77) and 46% (22/48) of SLE patients, respectively. While no difference in proportion of samples with detectable uAPRIL was observed between SLE, HCs and IgAN patients, both uAPRIL and uMCP-1 were significantly detectable in higher proportions of patients with active renal disease.

CONCLUSIONS

uBAFF was detectable in a small but a significant proportion of SLE patients but not in other groups tested, and was higher in SLE patients with active renal disease.

Belimumab restores Treg/Th17 balance in patients with refractory systemic lupus erythematosus

Belimumab, a specific inhibitor of the soluble B lymphocyte stimulator (BlyS), is the first biological drug approved by the United States Food and Drug Administration for the treatment of patients with active systemic lupus erythematosus (SLE) refractory to standard therapy. Given that an imbalance between regulatory T cells (Treg) and interleukin (IL)-17A-secreting T cells (Th17) has been reported in various autoimmune disorders, we assessed the frequency of both Treg and Th17 peripheral blood populations before and after belimumab administration in 20 patients with active SLE refractory to standard therapy. After six months of treatment, the mean SELENA-SLEDAI score as well as the mean anti-double-stranded DNA antibody titers were significantly decreased. In addition, we observed a significant increase in Treg percentages and a parallel, significant decrease in Th17 percentages, accompanied by significantly reduced serum levels of IL-21. In vitro studies showed that Treg purified from belimumab-treated patients were fully functional and displayed a suppressor function similar to that of Treg purified from healthy donors. Belimumab can restore Treg/Th17 balance in SLE patients with uncontrolled disease activity, and this results in decreased flare rate and reduced glucocorticoid dosage.

The role of TNF-α superfamily members in immunopathogenesis of sepsis

BACKGROUND

Members of TNFα superfamily, A proliferation inducing ligand (APRIL), B-cell activating factor (BAFF) and Transmembrane activator and calcium cyclophylin interactor (TACI) are main regulators of B-cell function. The aim of this study was to evaluate concentrations of APRIL, BAFF and soluble TACI (sTACI) receptor in septic patients compared to healthy controls and compare concentrations of these biomarkers depending on sepsis severity and outcome.

MATERIALS AND METHODS

A total of 115 septic patients and 30 healthy volunteers were included and concentrations of APRIL, BAFF and sTACI were determined in all subjects at the admission (ELISA R&D Systems tests). Concentrations of these biomarkers in function of sepsis severity (sepsis n = 94 and septic shock n = 21) and outcome (lethal n = 40, recovery n = 75) were tested, as well as correlations with APACHE II and SOFA scores, immunoglobulins, complement, PCT and CRP concentrations.

RESULTS

Concentrations of all three biomarkers were significantly increased in septic patients compared to controls (AUC_APRIL = 0.982, AUC_BAFF = 0.873, AUC_sTACI = 0.683). Higher concentrations of APRIL and sTACI (p = 0.033, p = 0.037), and lower concentrations of BAFF (p = 0.005) were observed in patients with septic shock compared to sepsis. BAFF concentrations correlated positively with IgM, C3 and C4 levels. sTACI and APRIL were shown to be predictors of lethal outcome (p = 0.003, p = 0.049).

CONCLUSIONS

Concentrations of observedTNFα superfamily members are significantly increased in septic patients, confirming their role in sepsis pathogenesis.Higher concentrations of anti-inflammatory sTACI receptor correlated with severity of sepsis and poorer prognosis, thus potentially indicating domination of anti-inflammatory response in septic patients with worse outcome.

Recent advances in the management of systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease presenting highly heterogeneous clinical manifestations and multi-systemic involvement. Patients are susceptible to relapse- and remission, thus making management challenging. Moreover, a considerable number of side effects may occur with conventional therapies; therefore, there is clearly a need for new therapeutic strategies. Since the pathogenesis of SLE is highly complex, it is far from being fully understood. However, greater understanding of the pathways and of the cellular and molecular mediators involved in SLE is being achieved. Emerging evidence has allowed the development of new biological therapeutic options targeting crucial molecular mediators involved in the pathogenesis of SLE. This literature review analyzes the availability of biological and target-directed treatments, phase II and III trials, and new therapies that are being developed for the treatment of SLE.

The soluble form of LOTUS inhibits Nogo receptor type 1-mediated signaling induced by B lymphocyte stimulator and chondroitin sulfate proteoglycans

There are global efforts in developing therapeutic strategies for central nervous system (CNS) injuries using multimodal approaches. Nogo receptor type 1 (NgR1) has been known as a primary molecule limiting neuronal regeneration in the adult CNS. We identified lateral olfactory tract usher substance (LOTUS) as an endogenous NgR1 antagonist. Membrane-bound LOTUS interacts with NgR1 and inhibits its function by blocking its ligand binding. Five molecules including Nogo, myelin-associated glycoprotein (MAG), oligodendrocyte myelin glycoprotein (OMgp), B lymphocyte stimulator (BLyS) and chondroitin sulfate proteoglycans (CSPGs) have been identified as NgR1 ligands. These ligands bind to NgR1 and activate NgR1 signaling, leading to axon growth inhibition such as growth cone collapse and neurite outgrowth inhibition. We have recently reported that the soluble form of LOTUS (s-LOTUS) also suppressed NgR1-mediated signaling induced by myelin axonal inhibitors (MAIs) including Nogo, MAG and OMgp by binding with both NgR1 and its co-receptor p75 neurotrophin receptor (p75^NTR). Though s-LOTUS has been reported to suppress MAIs, whether s-LOTUS also suppresses NgR1 signaling induced by BLyS and CSPGs remains to be elucidated. Here, we show that s-LOTUS inhibits NgR1-mediated signaling induced by BLyS and CSPGs. Although treatment with s-LOTUS did not suppress BLyS-NgR1 interaction, s-LOTUS inhibited growth cone collapse and neurite outgrowth inhibition induced by BLyS and CSPGs in chick dorsal root ganglion (DRG) neurons. Furthermore, s-LOTUS compensated for the suppressive function of endogenous LOTUS in NgR1-mediated signaling in olfactory bulb neurons of lotus-knockout mice. These findings suggest that s-LOTUS is a potent therapeutic agent for neuronal regeneration in the CNS injuries.

Novel Insights on the Regulation of B Cell Functionality by Members of the Tumor Necrosis Factor Superfamily in Jawed Fish

Most ligands and receptors from the tumor necrosis factor (TNF) superfamily play very important roles in the immune system. In particular, many of these molecules are essential in the regulation of B cell biology and B cell-mediated immune responses. Hence, in mammals, it is known that many TNF family members play a key role on B cell development, maturation, homeostasis, activation, and differentiation, also influencing the ability of B cells to present antigens or act as regulators of immune responses. Evolutionarily, jawed fish (including cartilaginous and bony fish) constitute the first animal group in which an adaptive immune response based on B cells and immunoglobulins is present. However, until recently, not much was known about the expression of TNF ligands and receptors in these species. The sequences of many members of the TNF superfamily have been recently identified in different species of jawed fish, thus allowing posterior analysis on the role that these ligands and receptors have on B cell functionality. In this review, we summarize the current knowledge on the impact that the TNF family members have in different aspects of B cell functionality in fish, also providing an in depth comparison with functional aspects of TNF members in mammals, that will permit a further understanding of how B cell functionality is regulated in these distant animal groups.

Peripheral B-Cell Subset Distribution in Primary Antiphospholipid Syndrome

Background: B-cell differentiation and B-cell tolerance checkpoints may be different in antiphospholipid syndrome (APS) from systemic lupus erythematosus (SLE) and can help to understand differences between them. Our aim was to define alterations of B-cell subsets in patients with primary APS (pAPS) and to compare them with SLE patients and healthy controls (HC). Methods: Cross-sectional study including three study groups: 37 patients with pAPS, 11 SLE patients, and 21 age- and gender-matched HC. We determined the frequencies of different B-cell subsets in peripheral blood naïve and memory compartments. In addition, we measured serum B cell-activating factor (BAFF) levels and circulating pro-inflammatory cytokines, such as IL-6, by commercial ELISA and CBA, respectively. Results: Patients with pAPS showed a lower percentage of immature and naïve B cells than patients with SLE (p = 0.013 and p = 0.010, respectively) and a higher percentage of non-switched memory B cells than patients with SLE (p = 0.001). No differences either in the percentage of switched memory cells or plasma cells were found among the different groups. Serum BAFF levels were higher in SLE patients than in healthy controls and pAPS patients (p = 0.001 and p = 0.017, respectively). A significant increase in the serum BAFF levels was also observed in pAPS patients compared to HC (p = 0.047). Circulating IL-6 levels were higher in SLE and pAPS patients than HC (p = 0.036 and p = 0.048, respectively). A positive correlation was found between serum BAFF and IL-6 levels in patients with SLE but not in pAPS (p = 0.011). Conclusions: Our characterization of peripheral blood B-cell phenotypes in pAPS demonstrates different frequencies of circulating B cells at different stages of differentiation. These differences in the naïve B-cell repertoire could explain the higher number and variety of autoantibodies in SLE patients in comparison to pAPS patients, especially in those with obstetric complications.

Monoclonal Antibody Therapies for Hematological Malignancies: Not Just Lineage-Specific Targets

Today, monoclonal antibodies (mAbs) are a widespread and necessary tool for biomedical science. In the hematological cancer field, since rituximab became the first mAb approved by the Food and Drug Administration for the treatment of B-cell malignancies, a number of effective mAbs targeting lineage-specific antigens (LSAs) have been successfully developed. Non-LSAs (NLSAs) are molecules that are not restricted to specific leukocyte subsets or tissues but play relevant pathogenic roles in blood cancers including the development, proliferation, survival, and refractoriness to therapy of tumor cells. In consequence, efforts to target NLSAs have resulted in a plethora of mAbs-marketed or in development-to achieve different goals like neutralizing oncogenic pathways, blocking tumor-related chemotactic pathways, mobilizing malignant cells from tumor microenvironment to peripheral blood, modulating immune-checkpoints, or delivering cytotoxic drugs into tumor cells. Here, we extensively review several novel mAbs directed against NLSAs undergoing clinical evaluation for treating hematological malignancies. The review focuses on the structure of these antibodies, proposed mechanisms of action, efficacy and safety profile in clinical studies, and their potential applications in the treatment of hematological malignancies.

Correlation of APRIL with production of inflammatory cytokines during acute malaria in the Brazilian Amazon

INTRODUCTION

A proliferation-inducing ligand (APRIL) and B cell activation factor (BAFF) are known to play a significant role in the pathogenesis of several diseases, including BAFF in malaria. The aim of this study was to investigate whether APRIL and BAFF plasma concentrations could be part of inflammatory responses associated with P. vivax and P. falciparum malaria in patients from the Brazilian Amazon.

METHODS

Blood samples were obtained from P. vivax and P. falciparum malaria patients (n = 52) resident in Porto Velho before and 15 days after the beginning of treatment and from uninfected individuals (n = 12). We investigated APRIL and BAFF circulating levels and their association with parasitaemia, WBC counts, and cytokine/chemokine plasma levels. The expression levels of transmembrane activator and calcium-modulating cyclophilin ligand interactor (TACI) on PBMC from a subset of 5 P. vivax-infected patients were analyzed by flow cytometry.

RESULTS

APRIL plasma levels were transiently increased during acute P. vivax and P. falciparum infections whereas BAFF levels were only increased during acute P. falciparum malaria. Although P. vivax and P. falciparum malaria patients have similar cytokine profiles during infection, in P. vivax acute phase malaria, APRIL but not BAFF levels correlated positively with IL-1, IL-2, IL-4, IL-6, and IL-13 levels. We did not find any association between P. vivax parasitaemia and APRIL levels, while an inverse correlation was found between P. falciparum parasitaemia and APRIL levels. The percentage of TACI positive CD4+ and CD8+ T cells were increased in the acute phase P. vivax malaria.

CONCLUSION

These findings suggest that the APRIL and BAFF inductions reflect different host strategies for controlling infection with each malaria species.

Toward Small-Molecule Inhibition of Protein-Protein Interactions: General Aspects and Recent Progress in Targeting Costimulatory and Coinhibitory (Immune Checkpoint) Interactions

Protein-Protein Interactions (PPIs) that are part of the costimulatory and coinhibitory (immune checkpoint) signaling are critical for adequate T cell response and are important therapeutic targets for immunomodulation. Biologics targeting them have already achieved considerable clinical success in the treatment of autoimmune diseases or transplant recipients (e.g., abatacept, belatacept, and belimumab) as well as cancer (e.g., ipilimumab, nivolumab, pembrolizumab, atezolizumab, durvalumab, and avelumab). In view of such progress, there have been only relatively limited efforts toward developing small-molecule PPI inhibitors (SMPPIIs) targeting these cosignaling interactions, possibly because they, as all other PPIs, are difficult to target by small molecules and were not considered druggable. Nevertheless, substantial progress has been achieved during the last decade. SMPPIIs proving the feasibility of such approaches have been identified through various strategies for a number of cosignaling interactions including CD40-CD40L, OX40-OX40L, BAFFR-BAFF, CD80-CD28, and PD-1-PD-L1s. Here, after an overview of the general aspects and challenges of SMPPII-focused drug discovery, we review them briefly together with relevant structural, immune-signaling, physicochemical, and medicinal chemistry aspects. While so far only a few of these SMPPIIs have shown activity in animal models (DRI-C21045 for CD40-D40L, KR33426 for BAFFR-BAFF) or reached clinical development (RhuDex for CD80-CD28, CA-170 for PD-1-PD-L1), there is proof-of-principle evidence for the feasibility of such approaches in immunomodulation. They can result in products that are easier to develop/ manufacture and are less likely to be immunogenic or encounter postmarket safety events than corresponding biologics, and, contrary to them, can even become orally bioavailable.

Pretransplant serum BAFF levels are associated with pretransplant HLA immunization and renal allograft survival

BACKGROUND

The essential function of B cell-activating factor (BAFF) is regulating the survival and differentiation of B cells. The link between pretransplant BAFF levels and pretransplant alloimmunization and its value to predict subsequent acute antibody-mediated rejection (AMR) and outcome after renal transplantation is not fully understood.

METHODS

Objective of our retrospective single-center study was to determine, by ELISA analysis of pretransplant serum BAFF levels in 249 patients undergoing renal transplantation, association between preformed anti-human leukocyte antigen (HLA) antibodies, occurrence of acute antibody mediated rejection (AMR) and renal allograft survival.

RESULTS

Pretransplant serum BAFF levels were significantly higher in presensitized recipients with anti-HLA antibodies (3262±2796pg/ml) than in recipients without occurrence of anti-HLA antibodies (2252±1425pg/ml; p<0.0001). In addition, pretransplant BAFF levels correlated with cumulative MFI values of anti-HLA antibodies (r=0.2966, p=0.0025). Patients with high pretransplant BAFF levels (≥2137pg/ml) experienced significantly lower allograft survival rates compared to low pretransplant BAFF levels (80% vs. 91%; p=0.01). Coexistence of high pretransplant BAFF levels and posttransplant AMR was associated with the worst allograft survival rates (56%). Relative risk (RR) for allograft loss was associated with high serum BAFF levels (RR 2.3; p=0.02), presence of anti-HLA antibodies (RR 2.5; p=0.007) or anti-HLA -donor-specific antibodies (DSAs) (RR 2.6; p=0.003) before transplant and AMR post transplant (RR 2.5; p=0.007). AMR was the strongest independent risk factor for allograft failure (RR 2.6; p=0.03).

CONCLUSION

Elevated pretransplant serum BAFF levels negatively affect renal allograft survival and represent a risk factor for allosensitization and subsequent AMR.

Replacing mouse BAFF with human BAFF does not improve B-cell maturation in hematopoietic humanized mice

Hematopoietic humanized mice (hu-mice) have been developed to study the human immune system in an experimental in vivo model, and experiments to improve its performance are ongoing. Previous studies have suggested that the impaired maturation of human B cells observed in hu-mice might be in part due to inefficient interaction of the human B-cell-activating factor (hBAFF) receptor with mouse B-cell-activating factor (mBAFF), as this cytokine is an important homeostatic and differentiation factor for B lymphocytes both in mice and humans. To investigate this hypothesis, we created a genetically engineered mouse strain in which a complementary DNA (cDNA) encoding full-length hBAFF replaces the mBAFF-encoding gene. Expression of hBAFF in the endogenous mouse locus did not lead to higher numbers of mature and effector human B cells in hu-mice. Instead, B cells from hBAFF knock-in (hBAFFKI) hu-mice were in proportion more immature than those of hu-mice expressing mBAFF. Memory B cells, plasmablasts, and plasma cells were also significantly reduced, a phenotype that associated with diminished levels of immunoglobulin G and T-cell-independent antibody responses. Although the reasons for these findings are still unclear, our data suggest that the inefficient B-cell maturation in hu-mice is not due to suboptimal bioactivity of mBAFF on human B cells.

BP180 Is Critical in the Autoimmunity of Bullous Pemphigoid

Bullous pemphigoid (BP) is by far the most common autoimmune blistering dermatosis that mainly occurs in the elderly. The BP180 is a transmembrane glycoprotein, which is highly immunodominant in BP. The structure and location of BP180 indicate that it is a significant autoantigen and plays a key role in blister formation. Autoantibodies from BP patients react with BP180, which leads to its degradation and this has been regarded as the central event in BP pathogenesis. The consequent blister formation involves the activation of complement-dependent or -independent signals, as well as inflammatory pathways induced by BP180/anti-BP180 autoantibody interaction. As a multi-epitope molecule, BP180 can cause dermal-epidermal separation via combining each epitope with specific immunoglobulin, which also facilitates blister formation. In addition, some inflammatory factors can directly deplete BP180, thereby leading to fragility of the dermal-epidermal junction and blister formation. This review summarizes recent investigations on the role of BP180 in BP pathogenesis to determine the potential targets for the treatment of patients with BP.

BAFF is involved in macrophage-induced bortezomib resistance in myeloma

We aimed to characterize the role of B-cell activating factor (BAFF) in macrophage-mediated resistance of multiple myeloma (MM) cells to bortezomib (bort), and to further understand the molecular mechanisms involved in the process. First, we detected BAFF and its three receptors on myeloma cells and macrophages using the quantitative reverse transcriptase-polymerase chain reaction and flow cytometry. The secretion of BAFF was tested in patients with MM, MM cell lines, and macrophages. The ability of macrophages to protect MM cells from bort-induced apoptosis was significantly attenuated using BAFF-neutralizing antibody in the co-culture system or knocking down the expression of BAFF in macrophages with small interfering RNA. We also showed that the MM–macrophage interaction through BAFF and its receptors was primarily mediated by the activation of Src, Erk1/2, Akt, and nuclear factor kappa B signaling and the suppression of caspase activation induced by bort. Our data demonstrated that BAFF played a functional role in the macrophage-mediated resistance of MM cells to bort, suggesting that targeting BAFF may provide a basis for the molecular- and immune-targeted therapeutic approach.

BAFF augments IgA2 and IL-10 production by TLR7/8 stimulated total peripheral blood B cells

Class‐switching of B cells to IgA can be induced via both T‐cell‐dependent and T‐cell‐independent mechanisms. IgA is most predominantly produced mucosally and is important for combating infections and allergies. In contrast to mice, humans have two forms of IgA; IgA1 and IgA2 with diverse tissue distribution. In early life, IgA levels might be sub‐optimal especially during the fall season when bacterial and viral infections are more common. Therefore, we investigated using human B cells whether T‐cell‐independent factors ‐promoting cell survival, class switching and immunoglobulin secretion‐ BAFF, APRIL, IL‐10 and retinoic acid can boost IgA production in the context of viral or bacterial infection. To this end total and naive peripheral blood B cells were stimulated with these factors for 6 days in the presence or absence of TLR7/8 agonist R848 (mimicking viral infection) or TLR9 agonist CpG‐ODN (mimicking bacterial infection). We show that BAFF significantly augments IgA2 production in TLR7/8 stimulated mature, but not naïve B cells. In addition, BAFF augments IL‐10 production and viability in TLR7/8 and TLR9 stimulated mature B cells. These data warrant further investigation of its role in immune regulation both in the periphery and mucosal tissues in early life or during disease.

Dynein light chain regulates adaptive and innate B cell development by distinctive genetic mechanisms

Mechanistic differences in the development and function of adaptive, high-affinity antibody-producing B-2 cells and innate-like, “natural” antibody-producing B-1a cells remain poorly understood. Here we show that the multi-functional dynein light chain (DYNLL1/LC8) plays important roles in the establishment of B-1a cells in the peritoneal cavity and in the ongoing development of B-2 lymphoid cells in the bone marrow of mice. Epistasis analyses indicate that Dynll1 regulates B-1a and early B-2 cell development in a single, linear pathway with its direct transcriptional activator ASCIZ (ATMIN/ZNF822), and that the two genes also have complementary functions during late B-2 cell development. The B-2 cell defects caused by loss of DYNLL1 were associated with lower levels of the anti-apoptotic protein BCL-2, and could be supressed by deletion of pro-apoptotic BIM which is negatively regulated by both DYNLL1 and BCL-2. Defects in B cell development caused by loss of DYNLL1 could also be partially suppressed by a pre-arranged SW_HELIgm-B cell receptor transgene. In contrast to the rescue of B-2 cell numbers, the B-1a cell deficiency in Dynll1-deleted mice could not be suppressed by the loss of Bim, and was further compounded by the SW_HEL transgene. Conversely, oncogenic MYC expression, which is synthetic lethal with Dynll1 deletion in B-2 cells, did not further reduce B-1a cell numbers in Dynll1-defcient mice. Finally, we found that the ASCIZ-DYNLL1 axis was also required for the early-juvenile development of aggressive MYC-driven and p53-deficient B cell lymphomas. These results identify ASCIZ and DYNLL1 as the core of a transcriptional circuit that differentially regulates the development of the B-1a and B-2 B lymphoid cell lineages and plays a critical role in lymphomagenesis.

Antibody-producing B cells can be segregated into two major populations: The better known conventional B-2 cells typically produce high-affinity and mono-specific antibodies, but only after they encounter a particular pathogen or in response to vaccines. In contrast, the B-1a cells constitutively produce lower-affinity broad-specificity “natural” antibodies that serve as a preemptive defense against a wide range of microbes. Here we reveal that the transcription factor ASCIZ and its target DYNLL1 are essential for mice to have a normally sized pool of B-1a cells in place shortly after birth. We show that these two factors function in a single linear pathway during the development of B-1a cells. This interaction represents a rare example where the activity of a transcription factor, in this case ASCIZ, can be explained by the effects of a single target gene, in this case Dynll1. While ASCIZ and DYNLL1 are also required for producing normal numbers of B-2 cells, we discovered that they regulate B-1a cells and B-2 cells by distinct genetic mechanisms. Finally, we found that ASCIZ also contributes to the early onset of B-1a B cell-derived lymphoid cancers in juvenile mice. The results provide insight into the development of an important cell population of the immune system.

Aiolos Overexpression in Systemic Lupus Erythematosus B Cell Subtypes and BAFF-Induced Memory B Cell Differentiation Are Reduced by CC-220 Modulation of Cereblon Activity

BAFF is a B cell survival and maturation factor implicated in the pathogenesis of systemic lupus erythematosus (SLE). In this in vitro study, we describe that soluble BAFF in combination with IL-2 and IL-21 is a T cell contact-independent inducer of human B cell proliferation, plasmablast differentiation, and IgG secretion from circulating CD27⁺ memory and memory-like CD27^-IgD^- double-negative (DN) B cells, but not CD27^-IgD⁺ naive B cells. In contrast, soluble CD40L in combination with IL-2 and IL-21 induces these activities in both memory and naive B cells. Blood from healthy donors and SLE patients have similar circulating levels of IL-2, whereas SLE patients exhibit elevated BAFF and DN B cells and reduced IL-21. B cell differentiation transcription factors in memory, DN, and naive B cells in SLE show elevated levels of Aiolos, whereas Ikaros levels are unchanged. Treatment with CC-220, a modulator of the cullin ring ligase 4-cereblon E3 ubiquitin ligase complex, reduces Aiolos and Ikaros protein levels and BAFF- and CD40L-induced proliferation, plasmablast differentiation, and IgG secretion. The observation that the soluble factors BAFF, IL-2, and IL-21 induce memory and DN B cell activation and differentiation has implications for extrafollicular plasmablast development within inflamed tissue. Inhibition of B cell plasmablast differentiation by reduction of Aiolos and Ikaros may have utility in the treatment of SLE, where elevated levels of BAFF and Aiolos may prime CD27⁺ memory and DN memory-like B cells to become Ab-producing plasmablasts in the presence of BAFF and proinflammatory cytokines.

Lupus nephritis and B-cell targeting therapy

INTRODUCTION

Lupus Nephritis (LN) is a severe manifestation of Systemic Lupus Erythematosus (SLE) with a significant prognostic impact. Over a prolonged course, an exhaustion of treatment alternatives may occur and further therapeutic options are needed. B cells play a pivotal role in disease pathogenesis and represent an attractive therapeutic target. Areas covered: This review provides an update regarding targeting B cells in LN. The rational for this approach, as well as currently available and future targets are discussed. Expert commentary: Despite its wide clinical use and the encouraging results from retrospective studies, a role of rituximab in LN has not been prospectively confirmed. Trial design methodologies as well as intrinsic limitations of this approach may be responsible and rituximab use is currently limited as a rescue treatment or in settings where a strong steroid sparing effect is warranted. Despite belimumab now being licensed for use in SLE, the evidence in LN is weak although prospective trials are on-going. The combination of different targeted approaches as well as a focus on new clinical end-points may be strategies to identify new therapeutic options.

Evaluation of Antigen-Specific IgM and IgG Production during an In Vitro Peripheral Blood Mononuclear Cell Culture Assay

The recent attention given to diseases associated with memory B-cell (mBC)-produced antibodies (Abs) suggests the need for a similar in vitro assay to evaluate the functions of mBCs. Here, we cultured peripheral blood mononuclear cells (PBMCs) with the intent to collect mBC-derived Abs in vitro and maintain their cell–cell contact-dependent interactions with helper T-cells. PBMCs were cultured with interleukin (IL)-21, CpG-oligodeoxynucleotides (ODN), phorbol myristate acetate (PMA), and phytohemagglutinin/leucoagglutinin (PHA-L) in 24-well flat-bottom plates (5 × 10⁵ cells/well). A culture supernatant analysis of PBMCs from healthy donors (n = 10) indicated that antigen-specific IgM Ab levels in a PBMC culture supernatant might be better able to demonstrate the antigen sensitization status in a smaller peripheral blood sample, compared to IgG because Epstein–Barr virus-specific IgM mBCs circulate peripherally at a significantly higher frequency once antiviral humoral immunity has stabilized. Thus, our in vitro assay demonstrated the potential significance of antigen-specific IgM Ab production in the culture supernatants. Furthermore, an analysis of cultured PBMCs from allograft kidney recipients (n = 16) sensitized with de novo donor-specific human leukocyte antigen (HLA)-specific Abs (DSAs) showed that IgM-type HLA-specific Abs were detected mainly from the culture supernatants from PBMCs of patients with stable graft function, whereas IgG isotype HLA Abs were detectable only from patients with biopsy-proven antibody-mediated rejection. In other words, these IgG isotype Abs also represented an activated humoral immune response in vivo. Additionally, IgM- and IgG-expressing mBCs from healthy donors (n = 5) were cultured with IL-21, CpG-ODN, and a supernatant produced by stimulating CD19⁺ B-cell-depleted PBMCs with PHA-L and PMA in 24-well flat-bottom plates (1 × 10⁵ cells/well), and the resulting in vitro analysis provided some information regarding the biological processes of IgG and IgM mBCs in peripheral blood. Taken together, our findings suggest that antigen-specific Ab subtype analyses of supernatants from cultured PBMCs might more effectively and accurately reflect a patient’s Ab-associated pathological condition vs. than serum IgG and IgM levels.

Renal tubular epithelial cell-derived BAFF expression mediates kidney damage and correlates with activity of proliferative lupus nephritis in mouse and men

B-cell activating factor of the tumour necrosis factor family (BAFF) is a cytokine, mainly produced by hematopoietic cells (e.g. monocytes/macrophages, dendritic cells), indispensable for B-cell maturation. The BLISS studies have demonstrated that blocking BAFF by the human monoclonal antibody belimumab is a valuable therapeutic approach in patients with clinically and serologically active systemic lupus erythematosus (SLE). However, the defined sources of BAFF, which contributes to SLE, are still unclear. Recent findings show that BAFF expression is not restricted to myeloid cells. Since lupus nephritis is the main cause of morbidity and mortality for SLE patients, the aim of this study was to investigate whether renal tubular epithelial cells (TEC) are an important source of BAFF and thus may contribute to the pathogenesis and progression of SLE. We found BAFF expression both in cultured murine and human TEC. These results could be verified with in situ data from the kidney. Moreover, BAFF expression in the kidneys of lupus-prone MRL- Fas^lpr mice correlated with disease activity, and BAFF expression on TEC in biopsies of patients with diffuse proliferative lupus nephritis showed a correlation with the histopathological activity index. In vitro functional assays revealed an autocrine loop of BAFF with its binding receptors on TEC, resulting in a strong induction of colony stimulating factor-1. Finally, we identified divergent effects of BAFF on TEC depending on the surrounding milieu ('inflammatory versus non-inflammatory'). Taken together, our findings indicate that renal-derived BAFF may play an important role in the pathophysiology of the systemic autoimmune disease SLE.

Autoantibodies against BAFF, APRIL or IL21 - an alternative pathogenesis for antibody-deficiencies?

BACKGROUND

The ability of anti-cytokine antibodies to play a disease-causing role in the pathogenesis of immunodeficiencies is widely accepted. The aim of this study was to investigate whether autoantibodies against BAFF (important B cell survival signal), APRIL (important plasma cell survival signal), or Interleukin-21 (important cytokine for immunoglobulin class switch) present an alternative mechanism for the development of the following primary antibody deficiencies (PADs): common variable immune deficiency (CVID) or selective IgA deficiency (sIgAD).

RESULTS

Two hundred thirty-two sera from patients with PADs were screened for autoantibodies against cytokines by ELISA. Statistical data analysis yielded a significant difference (p < 0.01) between the healthy donor sera and both PAD cohorts. The analysis was deepened by subdividing the patient collective into groups with distinct B cell phenotypes but no significant differences were found. For selected sera with notable high ELISA-read outs functional analysis ensued. Anti-BAFF and anti-APRIL antibodies were further examined by a B cell survival assay, whilst the functional relevance of putative anti-IL-21 autoantibodies was investigated by means of a STAT3 phosphorylation assay. However, the results of these experiments revealed no discernible functional effect.

CONCLUSION

Whilst statistical analysis of ELISA results showed significant differences between patients and healthy controls, in our set of patients functional tests yielded no evidence for an involvement of autoantibodies against BAFF, APRIL, or IL-21 in the pathogenesis of CVID or sIgAD.

Comparative efficacy and safety of intravenous or subcutaneous belimumab in combination with standard therapy in patients with active systemic lupus erythematosus: a Bayesian network meta-analysis of randomized controlled trials

Objective In this study, we aimed to assess the relative efficacy and safety of intravenous (IV) or subcutaneous (SC) belimumab compared with those of placebo in patients with active systemic lupus erythematosus (SLE). Methods We performed a Bayesian network meta-analysis to combine the direct and indirect evidence from randomized controlled trials (RCTs) examining the efficacy and safety of belimumab 1 mg/kg and 10 mg/kg IV administration, and belimumab 200 mg SC injection, and placebo in patients with active SLE despite having received standard therapy. Results Five RCTs (3460 patients) met the inclusion criteria. The SLE Responder Index (SRI) response rate at week 52 was significantly higher in the belimumab 10 mg/kg group than in the placebo group (OR 2.63, 95% CrI 2.14-3.23). Similarly, the SRI response rates were significantly higher in the belimumab 1 mg/kg, and belimumab 200 mg SC groups than in the placebo group (OR 2.42, 95% CrI 1.90-3.09; OR 1.71, 95% CrI 1.27-2.29). Ranking probability based on surface under the cumulative ranking curve (SUCRA) indicated that belimumab 10 mg/kg had the highest probability of being the best treatment for achieving the SRI response (SUCRA = 0.9174), followed by belimumab 1 mg/kg (SUCRA = 0.7338), belimumab 200 mg SC (SUCRA = 0.3487), and placebo (SUCRA = 0.0000). However, a sensitivity test by omitting one outlier study showing low SRI response rate compared with the other three studies (11% vs. 33%, 40%, 48%) showed that belimumab 200 mg SC and belimumab 10 mg/kg had the highest probability of being the best treatment for achieving the SRI response (SUCRA = 0.7903, SUCRA = 0.7456), followed by belimumab 1 mg/kg, and placebo. The number of serious adverse events (SAEs) did not differ significantly among the four treatment options. Conclusions Belimumab at 1 and 10 mg/kg IV and belimumab 200 mg SC in combination with standard therapy was an efficacious intervention for active SLE, and was not associated with a significant risk of SAEs.

Crosstalk Between T and B Cells in the Germinal Center After Transplantation

Crosstalk between B and T cells in transplantation is increasingly recognized as being important in the alloimmune response. T cell activation of B cells occurs by a 3-stage pathway, culminating with costimulation signals. We review the distinct T cell subtypes required for B-cell activation and discuss the formation of the germinal center (GC) after transplantation, with particular reference to the repopulation of the GC after depletional induction, and the subsequent effect of immunosuppressive manipulation of T cell-B cell interactions. In addition, ectopic GCs are seen in transplantation, but their role is not fully understood. Therapeutic options to target T cell-B cell interactions are of considerable interest, both as immunosuppressive tools, and to aid in the further understanding of these important alloimmune mechanisms.

Recurrent respiratory tract infections (RRTI) in the elderly: A late onset mild immunodeficiency?

Elderly with late-onset recurrent respiratory tract infections (RRTI) often have specific anti-polysaccharide antibody deficiency (SPAD). We hypothesized that late-onset RRTI is caused by mild immunodeficiencies, such as SPAD, that remain hidden through adult life. We analyzed seventeen elderly RRTI patients and matched controls. We determined lymphocyte subsets, expression of BAFF receptors, serum immunoglobulins, complement pathways, Pneumovax-23 vaccination response and genetic variations in BAFFR and MBL2. Twelve patients (71%) and ten controls (59%) had SPAD. IgA was lower in patients than in controls, but other parameters did not differ. However, a high percentage of both patients (53%) and controls (65%) were MBL deficient, much more than in the general population. Often, MBL2 secretor genotypes did not match functional deficiency, suggesting that functional MBL deficiency can be an acquired condition. In conclusion, we found SPAD and MBL deficiency in many elderly, and conjecture that at least the latter arises with age.

Orbital fibroblasts of Graves' orbitopathy stimulated with proinflammatory cytokines promote B cell survival by secreting BAFF

The success of rituximab for the treatment of active Graves' orbitopathy (GO) suggests that B cells play a critical role in intraorbital inflammation. B cell activating factor (BAFF) and its homolog a proliferation-inducing ligand (APRIL) are critical for B cell survival. However, the contribution of BAFF/APRIL to GO remains unclear. We sought to determine the role of BAFF/APRIL in the orbits of GO, and found that BAFF was markedly upregulated, while APRIL was not. Additionally, cultured GO orbital fibroblasts (GO-OFs)² expressing BAFF were induced to produce a large amount of BAFF. In contrast, a weak APRIL expression was detected in the OFs, and they exhibited a slight response to stimulation. Notably, pretreated GO-OFs promoted B cell survival, and this effect was significantly inhibited by a BAFF-R neutralizing antibody. This study indicates that OFs from GO can express BAFF and mediate the intraorbital survival of B cells via BAFF mechanism.

The BAFF / APRIL axis plays an important role in virus-induced peritoneal responses in rainbow trout

IgM⁺ B cells have been recently demonstrated to be key regulators of peritoneal inflammation in teleost, as a large number of them occupy the peritoneal cavity after 48 h of antigenic stimulation. Despite this, the number of studies addressing the mechanism through which this cell population expands and differentiates in response to stimuli has been scarcely addressed. Because the BAFF/APRIL axis is known to play a major role in B cell survival and differentiation in mammals, we hypothesized that it could be affected in the peritoneal cavity in response to an inflammatory stimulus. To verify this hypothesis, we studied how BAFF, APRIL and the fish-specific related cytokine BALM as well as their putative receptors are regulated in rainbow trout after intraperitoneal (i.p.) injection of viral hemorrhagic septicemia virus (VHSV). When the transcriptional analysis was performed in total cells from the peritoneum, we observed that VHSV provoked an up-regulation of both BAFF and BAFF receptor (BAFF-R) mRNA levels. However, when we examined how isolated peritoneal IgM⁺ B cells were transcriptionally affected by VHSV i.p. injection, we found that APRIL, BALM and the transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) were also up-regulated in response to the virus. IgM^- cells, on the other hand, only up-regulated BALM transcription in response to VHSV. Finally, to gain further insight on the role that these cytokines play in the peritoneum, we have studied their effect on the survival of peritoneal IgM⁺ B cells. This work demonstrates a key role for the BAFF/APRIL axis in the peritoneal inflammatory response and contributes to further understanding how IgM⁺ B cells are regulated at this specific peripheral site.

Monoclonal Antibodies for Relapsing Multiple Sclerosis: A Review of Recently Marketed and Late-Stage Agents

Treatment of multiple sclerosis (MS) has improved considerably over the last decade because of new insights into MS pathology and biotechnological advances. This has led to the development of new potent pharmaceutical compounds targeting different processes in the complex autoimmune pathology leading to chronic central nervous system (CNS) demyelination, neural loss, and, finally, neurological disability. Although a number of disease-modifying treatments are available for the treatment of the inflammatory phase of MS, there is still a need for highly efficacious therapies with an acceptable safety profile in order to gain therapeutic control early in the disease course. Monoclonal antibodies have proven to be some of the most efficacious disease-modifying therapies in the field of MS, and recent developments in clinical research hold promise for new compounds fulfilling the need for improved safety and high efficacy. We review recent developments in the field of therapeutic monoclonal antibodies used for the treatment of MS and current information on the mode of action, efficacy, and safety of existing and emerging therapeutic monoclonal antibodies as well as their place within the context of different treatment strategies. Finally, we consider the most important future developments.

Serum 25-Hydroxyvitamin D3 and BAFF Levels Are Associated with Disease Activity in Primary Sjogren's Syndrome

The study investigated the association between disease activity and serum 25-hydroxyvitamin D3 (25(OH)-D3), B cell activation of the tumor necrosis factor family (BAFF), or β₂ microglobulin in patients with primary Sjogren's syndrome (SS). Sixty-nine primary SS patients and 22 sicca control patients were included in the study. Disease activity was measured with EULAR Sjogren's syndrome disease activity index (ESSDAI). Serum levels of 25(OH)-D3 and β₂ microglobulin were measured by radioimmunoassay and BAFF was measured by an enzyme-linked immunosorbent assay. Serum levels of 25(OH)-D3 were significantly lower in SS patients compared to the sicca controls (p = 0.036). Serum levels of BAFF tended to be higher (p = 0.225) and those of β₂ microglobulin were significantly higher in patients with SS than in sicca controls (p = 0.023). In univariate regression analyses, ESSDAI was significantly associated with serum levels of 25(OH)-D3, BAFF, and β₂ microglobulin. After stepwise backward multivariate linear regression analyses including age and acute phase reactants, ESSDAI was associated with 25(OH)-D3 (β = −0.042, p = 0.015) and BAFF (β = 0.001, p = 0.015) in SS patients. In SS patients, ESSDAI is negatively associated with serum levels of 25(OH)-D3 and positively associated with BAFF.

B Cell-Activating Factor (BAFF)-Targeted B Cell Therapies in Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBD) involve dysregulated immune responses to gut antigens in genetically predisposed individuals. While a better elucidation of IBD pathophysiology has considerably increased the number of treatment options, the need for more effective therapeutic strategies remains a pressing priority. Defects of both non-hematopoietic (epithelial and stromal) and hematopoietic (lymphoid and myeloid) cells have been described in patients with IBD. Within the lymphoid system, alterations of the T cell compartment are viewed as essential in the pathogenesis of IBD. However, growing evidence points to the additional perturbations of the B cell compartment. Indeed, the intestinal lamina propria from IBD patients shows an increased presence of antibody-secreting plasma cells, which correlates with enhanced pro-inflammatory immunoglobulin G production and changes in the quality of non-inflammatory IgA responses. These B cell abnormalities are compounded by the emergence of systemic antibody responses to various autologous and microbial antigens, which predates the clinical diagnosis of IBD and identifies patients with complicated disease. It is presently unclear whether such antibody responses play a pathogenetic role, as B cell depletion with the CD20-targeting monoclonal antibody rituximab did not ameliorate ulcerative colitis in a clinical trial. However, it must be noted that unresponsiveness to rituximab is also observed also in some patients with autoimmune disorders usually responsive to B cell-depleting therapies. In this review, we discussed mechanistic aspects of B cell-based therapies and their potential role in IBD with a special interest on BAFF and BAFF-targeting therapies buoyed by the success of anti-BAFF treatments in rheumatologic disorders.