BAFF receptors and ligands create independent homeostatic niches for B cell subsets

B cell depletion with anti-CD20 promotes neuroprotection in a BAFF-dependent manner in mice and humans

Anti-CD20 therapy to deplete B cells is highly efficacious in preventing new white matter lesions in patients with relapsing-remitting multiple sclerosis (RRMS), but its protective capacity against gray matter injury and axonal damage is unclear. In a passive experimental autoimmune encephalomyelitis (EAE) model whereby TH17 cells promote brain leptomeningeal immune cell aggregates, we found that anti-CD20 treatment effectively spared myelin content and prevented myeloid cell activation, oxidative damage, and mitochondrial stress in the subpial gray matter. Anti-CD20 treatment increased B cell survival factor (BAFF) in the serum, cerebrospinal fluid, and leptomeninges of mice with EAE. Although anti-CD20 prevented gray matter demyelination, axonal loss, and neuronal atrophy, co-treatment with anti-BAFF abrogated these benefits. Consistent with the murine studies, we observed that elevated BAFF concentrations after anti-CD20 treatment in patients with RRMS were associated with better clinical outcomes. Moreover, BAFF promoted survival of human neurons in vitro. Together, our data demonstrate that BAFF exerts beneficial functions in MS and EAE in the context of anti-CD20 treatment.

Current Treatment Approach, Emerging Therapies and New Horizons in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE), the prototype of systemic autoimmune diseases is characterized by extreme heterogeneity with a variable clinical course. Renal involvement may be observed and affects the outcome. Hydroxychloroquine should be administered to every lupus patient irrespective of organ involvement. Conventional immunosuppressive therapy includes corticosteroids, methotrexate, cyclophosphamide, mycophenolate mofetil, azathioprine, cyclosporine and tacrolimus. However, despite conventional immunosuppressive treatment, flares occur and broad immunosuppression is accompanied by multiple side effects. Flare occurrence, target organ involvement, side effects of broad immunosuppression and increased knowledge of the pathogenetic mechanisms involved in SLE pathogenesis as well as the availability of biologic agents has led to the application of biologic agents in SLE management. Biologic agents targeting various pathogenetic paths have been applied. B cell targeting agents have been used successfully. Belimumab, a B cell targeting agent, has been approved for the treatment of SLE. Rituximab, an anti-CD20 targeting agent is also used in SLE. Anifrolumab, an interferon I receptor-targeting agent has beneficial effects on SLE. In conclusion, biologic treatment is applied in SLE and should be further evaluated with the aim of a good treatment response and a significant improvement in quality of life.

BAFF antagonism via the BAFF receptor 3 binding site attenuates BAFF 60-mer-induced classical NF-κB signaling and metabolic reprogramming of B cells

Human recombinant B cell activating factor (BAFF) is secreted as 3-mers, which can associate to form 60-mers in culture supernatants. However, the presence of BAFF multimers in humans is still debated and it is incompletely understood how BAFF multimers activate the B cells. Here, we demonstrate that BAFF can exist as 60-mers or higher order multimers in human plasma. In vitro, BAFF 60-mer strongly induced the transcriptome of B cells which was partly attenuated by antagonism using a soluble fragment of BAFF receptor 3. Furthermore, compared to BAFF 3-mer, BAFF 60-mer strongly induced a transient classical and prolonged alternate NF-κB signaling, glucose oxidation by both aerobic glycolysis and oxidative phosphorylation, and succinate utilization by mitochondria. BAFF antagonism selectively attenuated classical NF-κB signaling and glucose oxidation. Altogether, our results suggest critical roles of BAFF 60-mer and its BAFF receptor 3 binding site in hyperactivation of B cells.

Potential biomarkers for diagnosis and assessment of disease activity in systemic lupus erythematosus

BACKGROUND

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease involving multiple system functions. Our study aimed to screen out more effective new indicators that can assist clinical diagnosis and judge disease activity.

METHODS

We first screened serum levels of 45 cytokines of SLE patients (n = 3) and healthy controls (n = 3). Subsequently, we selected five elevated cytokines for verification with an expanded sample size. Then, the relationship between cytokines and laboratory parameters was also investigated. Finally, we used receiver operating characteristic (ROC) curves to assess the clinical value of these cytokines.

RESULTS

Through screening of 45 cytokines, 15 were found to be elevated in SLE patients. We chose five cytokines (IL-6, IL-10, IL-1RA, IP-10 and LIF) for further research and found elevated expression of all five cytokines in SLE patients. Serum levels of IL-10, IL-1RA and LIF were positively correlated with SLEDAI-2K score. Besides, the level of IL-10 was significantly positively correlated with serum IgG and erythrocyte sedimentation rate (ESR); IL-1RA was significantly negatively correlated with C3 and C4; and LIF was significantly positively correlated with serum IgG, C-reactive protein (CRP), and ESR. Furthermore, IL-1RA and LIF were strongly positively correlated with 24-hour urine protein levels. The ROC analysis showed that IL-1RA has good diagnostic value, and IL-10 and LIF levels can be utilized to discriminate between active and inactive SLE.

CONCLUSION

IL-1RA can be used as a biomarker for diagnosing SLE, while IL-10 and LIF can be indicators to discriminate between active and inactive SLE.

Differential expression of circulating miRNAs after alemtuzumab induction therapy in lung transplantation

Alemtuzumab is a monoclonal antibody targeting CD52, used as induction therapy after lung transplantation (LTx). Its engagement produces a long-lasting immunodepletion; however, the mechanisms driving cell reconstitution are poorly defined. We hypothesized that miRNAs are involved in this process. The expression of a set of miRNAs, cytokines and co-signaling molecules was measured with RT-qPCR and flow cytometry in prospectively collected serum samples of LTx recipients, after alemtuzumab or no induction therapy. Twenty-six LTx recipients who received alemtuzumab and twenty-seven matched LTx recipients without induction therapy were included in the analysis. One year after transplantation four miRNAs were differentially regulated: miR-23b (p = 0.05) miR-146 (p = 0.04), miR-155 (p < 0.001) and miR-486 (p < 0.001). Expression of 3 miRNAs changed within the alemtuzumab group: miR-146 (p < 0.001), miR-155 (p < 0.001) and miR-31 (p < 0.001). Levels of IL-13, IL-4, IFN-γ, BAFF, IL-5, IL-9, IL-17F, IL-17A and IL-22 were different one year after transplantation compared to baseline. In no-induction group, concentration of sCD27, sB7.2 and sPD-L1 increased overtime. Expression of miR-23b, miR-146, miR-486, miR-155 and miR-31 was different in LTx recipients who received alemtuzumab compared to recipients without induction therapy. The observed cytokine pattern suggested proliferation of specific B cell subsets in alemtuzumab group and co-stimulation of T-cells in no-induction group.

Osteopontin and malaria: no direct effect on parasite growth, but correlation with P. falciparum-specific B cells and BAFF in a malaria endemic area

Background

The dysregulation of B cell activation is prevalent during naturally acquired immunity against malaria. Osteopontin (OPN), a protein produced by various cells including B cells, is a phosphorylated glycoprotein that participates in immune regulation and has been suggested to be involved in the immune response against malaria. Here we studied the longitudinal concentrations of OPN in infants and their mothers living in Uganda, and how OPN concentrations correlated with B cell subsets specific for P. falciparum and B cell activating factor (BAFF). We also investigated the direct effect of OPN on P. falciparum in vitro.

Results

The OPN concentration was higher in the infants compared to the mothers, and OPN concentration in infants decreased from birth until 9 months. OPN concentration in infants during 9 months were independent of OPN concentrations in corresponding mothers. OPN concentrations in infants were inversely correlated with total atypical memory B cells (MBCs) as well as P. falciparum-specific atypical MBCs. There was a positive correlation between OPN and BAFF concentrations in both mothers and infants. When OPN was added to P. falciparum cultured in vitro, parasitemia was unaffected regardless of OPN concentration.

Conclusions

The concentrations of OPN in infants were higher and independent of the OPN concentrations in corresponding mothers. In vitro, OPN does not have a direct effect on P. falciparum growth. Our correlation analysis results suggest that OPN could have a role in the B cell immune response and acquisition of natural immunity against malaria.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02368-y.

CD22 Controls Germinal Center B Cell Receptor Signaling, Which Influences Plasma Cell and Memory B Cell Output

Germinal center reactions are established during a thymus-dependent immune response. Germinal center (GC) B cells are rapidly proliferating and undergo somatic hypermutation in Ab genes. This results in the production of high-affinity Abs and establishment of long-lived memory cells. GC B cells show lower BCR-induced signaling when compared with naive B cells, but the functional relevance is not clear. CD22 is a member of the Siglec family and functions as an inhibitory coreceptor on B cells. Interestingly, GC B cells downregulate sialic acid forms that serve as high-affinity ligands for CD22, indicating a role for CD22 ligand binding during GC responses. We studied the role of CD22 in the GC with mixed bone marrow chimeric mice and found a disadvantage of CD22^-/- GC B cells during the GC reaction. Mechanistic investigations ruled out defects in dark zone/light zone distribution and affinity maturation. Rather, an increased rate of apoptosis in CD22^-/- GC B cells was responsible for the disadvantage, also leading to a lower GC output in plasma cells and memory B cells. CD22^-/- GC B cells showed a clearly increased calcium response upon BCR stimulation, which was almost absent in wild-type GC B cells. We conclude that the differential expression of the low-affinity cis CD22 ligands in the GC normally results in a strong attenuation of BCR signaling in GC B cells, probably due to higher CD22-BCR interactions. Therefore, attenuation of BCR signaling by CD22 is involved in GC output and B cell fate.

Function, occurrence and inhibition of different forms of BAFF

B cell activating factor (BAFF or BLyS), an important cytokine for B cell survival and humoral immune responses, is targeted in the clinic for the treatment of systemic lupus erythematosus. This review focuses on the structure, function and inhibition profiles of membrane-bound BAFF, soluble BAFF 3-mer and soluble BAFF 60-mer, all of which have distinct properties. BAFF contains a loop region not required for receptor binding but essential for receptor activation via promotion of BAFF-to-BAFF contacts. This loop region additionally allows formation of BAFF 60-mer, in which epitopes of the BAFF inhibitor belimumab are inaccessible. If 60-mer forms in humans, it is predicted to be short-lived and to act locally because adult serum contains a BAFF 60-mer dissociating activity. Cord blood contains elevated levels of BAFF, part of which displays attributes of 60-mer, suggesting a role for this form of BAFF in the development of foetal or neonate B cells.

A Detailed Analysis of Parameters Supporting the Engraftment and Growth of Chronic Lymphocytic Leukemia Cells in Immune-Deficient Mice

Patient-derived xenograft models of chronic lymphocytic leukemia (CLL) can be created using highly immunodeficient animals, allowing analysis of primary tumor cells in an in vivo setting. However, unlike many other tumors, CLL B lymphocytes do not reproducibly grow in xenografts without manipulation, proliferating only when there is concomitant expansion of T cells. Here we show that in vitro pre-activation of CLL-derived T lymphocytes allows for a reliable and robust system for primary CLL cell growth within a fully autologous system that uses small numbers of cells and does not require pre-conditioning. In this system, growth of normal T and leukemic B cells follows four distinct temporal phases, each with characteristic blood and tissue findings. Phase 1 constitutes a period during which resting CLL B cells predominate, with cells aggregating at perivascular areas most often in the spleen. In Phase 2, T cells expand and provide T-cell help to promote B-cell division and expansion. Growth of CLL B and T cells persists in Phase 3, although some leukemic B cells undergo differentiation to more mature B-lineage cells (plasmablasts and plasma cells). By Phase 4, CLL B cells are for the most part lost with only T cells remaining. The required B-T cell interactions are not dependent on other human hematopoietic cells nor on murine macrophages or follicular dendritic cells, which appear to be relatively excluded from the perivascular lymphoid aggregates. Notably, the growth kinetics and degree of anatomic localization of CLL B and T cells is significantly influenced by intravenous versus intraperitoneal administration. Importantly, B cells delivered intraperitoneally either remain within the peritoneal cavity in a quiescent state, despite the presence of dividing T cells, or migrate to lymphoid tissues where they actively divide; this dichotomy mimics the human condition in that cells in primary lymphoid tissues and the blood are predominately resting, whereas those in secondary lymphoid tissues proliferate. Finally, the utility of this approach is illustrated by documenting the effects of a bispecific antibody reactive with B and T cells. Collectively, this model represents a powerful tool to evaluate CLL biology and novel therapeutics in vivo.

B Cell Dysregulation in Common Variable Immunodeficiency Interstitial Lung Disease

Common variable immunodeficiency (CVID) is the most frequently diagnosed primary antibody deficiency. About half of CVID patients develop chronic non-infectious complications thought to be due to intrinsic immune dysregulation, including autoimmunity, gastrointestinal disease, and interstitial lung disease (ILD). Multiple studies have found ILD to be a significant cause of morbidity and mortality in CVID. Yet, the precise mechanisms underlying this complication in CVID are poorly understood. CVID ILD is marked by profound pulmonary infiltration of both T and B cells as well as granulomatous inflammation in many cases. B cell depletive therapy, whether done as a monotherapy or in combination with another immunosuppressive agent, has become a standard of therapy for CVID ILD. However, CVID is a heterogeneous disorder, as is its lung pathology, and the precise patients that would benefit from B cell depletive therapy, when it should administered, and how long it should be repeated all remain gaps in our knowledge. Moreover, some have ILD recurrence after B cell depletive therapy and the relative importance of B cell biology remains incompletely defined. Developmental and functional abnormalities of B cell compartments observed in CVID ILD and related conditions suggest that imbalance of B cell signaling networks may promote lung disease. Included within these potential mechanisms of disease is B cell activating factor (BAFF), a cytokine that is upregulated by the interferon gamma (IFN-γ):STAT1 signaling axis to potently influence B cell activation and survival. B cell responses to BAFF are shaped by the divergent effects and expression patterns of its three receptors: BAFF receptor (BAFF-R), transmembrane activator and CAML interactor (TACI), and B cell maturation antigen (BCMA). Moreover, soluble forms of BAFF-R, TACI, and BCMA exist and may further influence the pathogenesis of ILD. Continued efforts to understand how dysregulated B cell biology promotes ILD development and progression will help close the gap in our understanding of how to best diagnose, define, and manage ILD in CVID.

New biomarkers in SLE: from bench to bedside

Biomarkers may have a diagnostic or monitoring value, or may predict response to therapy or disease course. The aim of this review is to discuss new serum and urinary biomarkers recently proposed for the diagnosis and management of SLE patients. Novel sensitive and specific assays have been proposed to evaluate complement proteins, ‘old’ biomarkers that are still a cornerstone in the management of this disease. Chemokines and lectins have been evaluated as surrogate biomarkers of IFN signature. Other cytokines like the B cell activating factor (BAFF) family cytokines are directly related to perturbations of the B cell compartment as key pathogenetic mechanism of the disease. A large number of urine biomarkers have been proposed, either related to the migration and homing of leukocytes to the kidney or to the local regulation of inflammatory circuits and the survival of renal intrinsic cells. The combination of traditional disease-specific biomarkers and novel serum or urine biomarkers may represent the best choice to correctly classify, stage and treat patients with SLE.

A longitudinal study of plasma BAFF levels in mothers and their infants in Uganda, and correlations with subsets of B cells

Malaria is a potentially life-threatening disease with approximately half of the world’s population at risk. Young children and pregnant women are hit hardest by the disease. B cells and antibodies are part of an adaptive immune response protecting individuals continuously exposed to the parasite. An infection with Plasmodium falciparum can cause dysregulation of B cell homeostasis, while antibodies are known to be key in controlling symptoms and parasitemia. BAFF is an instrumental cytokine for the development and maintenance of B cells. Pregnancy alters the immune status and renders previously clinically immune women at risk of severe malaria, potentially due to altered B cell responses associated with changes in BAFF levels. In this prospective study, we investigated the levels of BAFF in a malaria-endemic area in mothers and their infants from birth up to 9 months. We found that BAFF-levels are significantly higher in infants than in mothers. BAFF is highest in cord blood and then drops rapidly, but remains significantly higher in infants compared to mothers even at 9 months of age. We further correlated BAFF levels to P. falciparum-specific antibody levels and B cell frequencies and found a negative correlation between BAFF and both P. falciparum-specific and total proportions of IgG⁺ memory B cells, as well as CD27⁻ memory B cells, indicating that exposure to both malaria and other diseases affect the development of B-cell memory and that BAFF plays a part in this. In conclusion, we have provided new information on how natural immunity against malaria is formed.

B-Cell Activating Factor Secreted by Neutrophils Is a Critical Player in Lung Inflammation to Cigarette Smoke Exposure

Cigarette smoke (CS) is the major cause of chronic lung injuries, such as chronic obstructive pulmonary disease (COPD). In patients with severe COPD, tertiary lymphoid follicles containing B lymphocytes and B cell-activating factor (BAFF) overexpression are associated with disease severity. In addition, BAFF promotes adaptive immunity in smokers and mice chronically exposed to CS. However, the role of BAFF in the early phase of innate immunity has never been investigated. We acutely exposed C57BL/6J mice to CS and show early BAFF expression in the bronchoalveolar space and lung tissue that correlates to airway neutrophil and macrophage influx. Immunostaining analysis revealed that neutrophils are the major source of BAFF. We confirmed in vitro that neutrophils secrete BAFF in response to cigarette smoke extract (CSE) stimulation. Antibody-mediated neutrophil depletion significantly dampens lung inflammation to CS exposure but only partially decreases BAFF expression in lung tissue and bronchoalveolar space suggesting additional sources of BAFF. Importantly, BAFF deficient mice displayed decreased airway neutrophil recruiting chemokines and neutrophil influx while the addition of exogenous BAFF significantly enhanced this CS-induced neutrophilic inflammation. This demonstrates that BAFF is a key proinflammatory cytokine and that innate immune cells in particular neutrophils, are an unconsidered source of BAFF in early stages of CS-induced innate immunity.

Expression of BAFF and BAFF receptors in primary Sjögren's syndrome patients with ectopic germinal center-like structures

B cell-activating factor (BAFF) is an essential cytokine in primary Sjögren's syndrome (pSS) physiopathology. It has been reported that pSS patients develop germinal center-like (GC-like) structures in their minor salivary glands (MSGs). BAFF, BAFF-R, TACI, and BCMA expression was analyzed in MSGs from 29 subjects (nonspecific chronic sialadenitis and focal lymphocytic sialadenitis with the presence [pSS-GC(+)] or absence [pSS-GC(-)] of GC-like structures). Twenty-four percent of patients showed ectopic GC-like structures and a high focus score [p < 0.001 vs pSS-GC(-)]. BAFF serum levels (sBAFF) were high in pSS patients (p = 0.025 vs healthy subjects). However, the pSS-GC(-) group showed higher sBAFF levels than pSS-GC(+) patients. BAFF and BAFF-R glandular expression levels were higher in pSS-GC(+) patients, without significant differences compared to pSS-GC(-) patients. Soluble levels of BAFF correlated with anti-La/SSB antibodies and disease duration. Our results showed that BAFF could contribute to focal lymphocytic infiltration. The role of BAFF-binding receptors in MSGs is proposed as a mechanism for the possible establishment of ectopic GC-like structures and disease progression in some patients. In conclusion, this study supports previous evidence that considers the active BAFF system role in the pathogenesis of pSS and the need for strong biomarkers in this disease.

Combined proinflammatory cytokine and cognate activation of invariant natural killer T cells enhances anti-DNA antibody responses

iNKT cells can both provide help and inhibit B cell responses. Our data show that when iNKT cells are activated with the glycolipid agonist αGalCer together with the inflammatory cytokine IL-18, they switch from regulating autoreactive B cells to promoting their expansion. As a consequence, autoreactive B cell responses remain unchecked by iNKT cells. The glycolipid αGalCer has been shown to have promising effects when administered as an adjuvant to achieve a better response to vaccines, as an antitumor agent, as well as in the regulation of autoimmunity. Our results highlight a facet of αGalCer-mediated iNKT cell activation in the context of inflammation and have broad implications for understanding the regulation of autoimmunity and use of αGalCer in therapy.

Invariant natural killer T (iNKT) cells serve as early rapid responders in the innate immune response to self-derived autoantigens and pathogen-derived danger signals and antigens. iNKT cells can serve both as helpers for effector B cells and negatively regulate autoreactive B cells. Specifically, iNKT cells drive B cell proliferation, class switch, and antibody production to induce primary antigen-specific immune responses. On the other hand, inflammasome-mediated activation drives accumulation of neutrophils, which license iNKT cells to negatively regulate autoreactive B cells via Fas ligand (FasL). This positions iNKT cells at an apex to support or inhibit B cell responses in inflammation. However, it is unknown which effector mechanism dominates in the face of cognate glycolipid activation during chronic inflammation, as might result from glycolipid vaccination or infection during chronic autoimmune disease. We stimulated iNKT cells by cognate glycolipid antigen α-galactosylceramide (αGalCer) and measured B cell activation during interleukin 18 (IL-18)-induced chronic inflammation. Moreover, glycolipid-activated iNKT cells increased the serum concentration of autoantibodies, frequency of germinal center (GC) B cells, and antigen-specific plasma cells induced during chronic IL-18–mediated inflammation, as compared with IL-18 alone. Further, activation of iNKT cells via cognate glycolipid during IL-18–mediated inflammation overrides the licensing function of neutrophils, instead inducing iNKT follicular helper (iNKTfh) cells that in turn promote autoimmunity. Thus, our data demonstrate that glycolipids which engage iNKT cells support antigen-specific B cell help during inflammasome-mediated inflammation.

Serum B-Cell Maturation Antigen (BCMA) Levels Differentiate Primary Antibody Deficiencies

BACKGROUND

Primary antibody deficiencies (PADs) are the most prevalent primary immunodeficiencies. More severe forms of PADs-common variable immunodeficiency (CVID) and X-linked agammaglobulinemia (XLA)-require immunoglobulin replacement therapy (IRT) and may have serious complications. Differentiating severe PAD from milder hypogammaglobulinemia not requiring IRT can involve prolonged evaluations and treatment discontinuation. Severe PAD is defined by plasma cell deficiency, but this requires a biopsy to establish. Serum B-cell maturation antigen (sBCMA) is elevated in multiple myeloma, but levels are reduced among patients with myeloma in remission who have hypogammaglobulinemia.

OBJECTIVE

To measure the sBCMA level in 165 subjects to determine whether it differentiates severe PAD-CVID and XLA-from less severe forms not requiring IRT and those without PAD.

METHODS

sBCMA, B cells, and tissue plasma cells were measured among subjects with and without PAD, and correlated to clinical and laboratory data.

RESULTS

Subjects with an IgG level of less than 600 mg/dL had reduced sBCMA levels compared with subjects with PAD with IgG levels of greater than or equal to 600 mg/dL and controls without PAD. sBCMA level was lower in patients with CVID and XLA compared with patients with IgA or IgG deficiency and controls. sBCMA level correlated with gastrointestinal plasma cells. sBCMA level of less than 15 ng/mL had 97% positive predictive value for CVID or XLA, whereas 25 ng/mL or more had an 88% negative predictive value.

CONCLUSIONS

sBCMA level is profoundly reduced in patients with severe PAD, including those with CVID and XLA and those with IgG levels of less than 600 mg/dL. sBCMA level measurement has potential to augment clinical evaluation of PAD. Prospective studies are needed to evaluate sBCMA for new PAD diagnosis and determine the necessity of IRT.

BAFF-driven B cell hyperplasia underlies lung disease in common variable immunodeficiency

BACKGROUND

Common variable immunodeficiency (CVID) is the most common symptomatic primary immunodeficiency and is frequently complicated by interstitial lung disease (ILD) for which etiology is unknown and therapy inadequate.

METHODS

Medical record review implicated B cell dysregulation in CVID ILD progression. This was further studied in blood and lung samples using culture, cytometry, ELISA, and histology. Eleven CVID ILD patients were treated with rituximab and followed for 18 months.

RESULTS

Serum IgM increased in conjunction with ILD progression, a finding that reflected the extent of IgM production within B cell follicles in lung parenchyma. Targeting these pulmonary B cell follicles with rituximab ameliorated CVID ILD, but disease recurred in association with IgM elevation. Searching for a stimulus of this pulmonary B cell hyperplasia, we found B cell-activating factor (BAFF) increased in blood and lungs of progressive and post-rituximab CVID ILD patients and detected elevation of BAFF-producing monocytes in progressive ILD. This elevated BAFF interacts with naive B cells, as they are the predominant subset in progressive CVID ILD, expressing BAFF receptor (BAFF-R) within pulmonary B cell follicles and blood to promote Bcl-2 expression. Antiapoptotic Bcl-2 was linked with exclusion of apoptosis from B cell follicles in CVID ILD and increased survival of naive CVID B cells cultured with BAFF.

CONCLUSION

CVID ILD is driven by pulmonary B cell hyperplasia that is reflected by serum IgM elevation, ameliorated by rituximab, and bolstered by elevated BAFF-mediated apoptosis resistance via BAFF-R.

FUNDING

NIH, Primary Immune Deficiency Treatment Consortium, and Rare Disease Foundation.

Belimumab promotes negative selection of activated autoreactive B cells in systemic lupus erythematosus patients

Belimumab has therapeutic benefit in active systemic lupus erythematosus (SLE), especially in patients with high-titer anti-dsDNA antibodies. We asked whether the profound B cell loss in belimumab-treated SLE patients is accompanied by shifts in the immunoglobulin repertoire. We enrolled 15 patients who had been continuously treated with belimumab for more than 7 years, 17 matched controls, and 5 patients who were studied before and after drug initiation. VH genes of sort-purified mature B cells and plasmablasts were subjected to next-generation sequencing. We found that B cell-activating factor (BAFF) regulates the transitional B cell checkpoint, with conservation of transitional 1 (T1) cells and approximately 90% loss of T3 and naive B cells after chronic belimumab treatment. Class-switched memory B cells, B1 B cells, and plasmablasts were also substantially depleted. Next-generation sequencing revealed no redistribution of VH, DH, or JH family usage and no effect of belimumab on representation of the autoreactive VH4-34 gene or CDR3 composition in unmutated IgM sequences, suggesting a minimal effect on selection of the naive B cell repertoire. Interestingly, a significantly greater loss of VH4-34 was observed among mutated IgM and plasmablast sequences in chronic belimumab-treated subjects than in controls, suggesting that belimumab promotes negative selection of activated autoreactive B cells.

B Cell Activating Factor, Renal Allograft Antibody-Mediated Rejection, and Long-Term Outcome

Antibody-mediated rejection (ABMR) of renal allograft lacks typical phenotypes and clinical manifestations, always resulting in delayed diagnosis and treatment. It has been considered to be an elemental factor influencing the improvement of the long-term outcome of renal allograft. The B cell activating factor (BAFF) signal plays a fundamental function in the process of antibody-mediated immune response. Data from recipients and the nonhuman primate ABMR model suggest that the BAFF signal participates in the ABMR of renal allograft, while there are objections. The challenges in the diagnosis of ABMR, different study population, and details of research may explain the discrepancy. Large quantities of dynamic, credible data of BAFF ligands and their association with renal allograft pathological characteristics would constitute a direct proof of the role of BAFF in the progression of renal allograft ABMR.

Testosterone is an endogenous regulator of BAFF and splenic B cell number

Testosterone deficiency in men is associated with increased risk for autoimmunity and increased B cell numbers through unknown mechanisms. Here we show that testosterone regulates the cytokine BAFF, an essential survival factor for B cells. Male mice lacking the androgen receptor have increased splenic B cell numbers, serum BAFF levels and splenic Baff mRNA. Testosterone deficiency by castration causes expansion of BAFF-producing fibroblastic reticular cells (FRCs) in spleen, which may be coupled to lower splenic noradrenaline levels in castrated males, as an α-adrenergic agonist decreases splenic FRC number in vitro. Antibody-mediated blockade of the BAFF receptor or treatment with the neurotoxin 6-hydroxydopamine revert the increased splenic B cell numbers induced by castration. Among healthy men, serum BAFF levels are higher in men with low testosterone. Our study uncovers a previously unrecognized regulation of BAFF by testosterone and raises important questions about BAFF in testosterone-mediated protection against autoimmunity.

Testosterone deficiency is associated with autoimmunity and increased B cell numbers, but the underlying mechanism is unclear. Here the authors show that testosterone may modulate the production of B cell survival factor BAFF by fibroblastic reticular cells via regulation of splenic neurotransmitter levels.

Increased B cell activating factor is associated with B cell class switching in patients with tuberculous pleural effusion

B cell activating factor (BAFF), a member of the tumor necrosis factor family, is a key cytokine for B cell survival, a function that is essential for B cell maturation and memory. The expression levels of BAFF and its potential contribution to B cell maturation remain elusive in patients with tuberculous pleural effusion (TPE). The present study enrolled 40 healthy controls (HC) and 45 TPE patients, and investigated the levels of BAFF in the plasma and pleural effusion. Concomitantly, B cell subsets including naïve B cell (CD19+IgD+CD27‑), unswitched B cell (CD19+IgD+CD27+), switched B cell (CD19+IgD‑CD27+), total memory B cell (CD19+CD27+), plasma B cell (CD19+IgD‑CD38+CD27+) and transitional B cell (CD19+IgDdim CD38+) in peripheral blood mononuclear cells (PBMCs) and pleural fluid mononuclear cells (PFMCs) were assessed using multicolor flow cytometry. Finally, the associations between BAFF and each sub‑group of B cells in TPE patients were analyzed. Compared with HC cases, an increased BAFF level and elevated frequency of switched B cell were observed in the blood and pleural effusion from patients with TPE. The proportions of naïve B cell, plasma B cell and transitional B cell were lower in the PFMCs of TPE patients. Furthermore, a significant correlation was observed between the level of BAFF, and the proportion of switched B cell in the peripheral blood and pleural effusion of TPE patients. These findings indicated that the B cell profile may be different in the pleural effusion, and BAFF may activate switched B cells to enhance the humoral immune responses in patients with TPE. Further studies are required to elucidate the underlying mechanisms and determine the potential immunotherapy of the BAFF‑switched B cell axis.

BAFF and CD4+ T cells are major survival factors for long-lived splenic plasma cells in a B-cell–depletion context

Modification of the splenic microenvironment induced by B-cell depletion creates a dependence of PCs on BAFF and CD4+ T cells. Combining anti-CD20 and anti-BAFF reduces the number of splenic PCs, opening therapeutic perspectives for antibody-mediated cytopenia.

Defining B Cell Chromatin: Lessons from EBF1

Hematopoiesis is regulated by signals from the microenvironment, transcription factor networks, and changes of the epigenetic landscape. Transcription factors interact with and shape chromatin to allow for lineage- and cell type-specific changes in gene expression. During B lymphopoiesis, epigenetic regulation is observed in multilineage progenitors in which a specific chromatin context is established, at the onset of the B cell differentiation when early B cell factor 1 (EBF1) induces lineage-specific changes in chromatin, during V(D)J recombination and after antigen-driven activation of B cells and terminal differentiation. In this review, we discuss the epigenetic changes underlying B cell differentiation, focusing on the role of transcription factor EBF1 in B cell lineage priming.

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.

Signalling for B cell survival

The number of mature B cells is carefully controlled by signalling from receptors that support B cell survival. The best studied of these are the B cell antigen receptor (BCR) and BAFFR. Recent work has shown that signalling from these receptors is closely linked, involves the CD19 co-receptor, and leads to activation of canonical and non-canonical NF-κB pathways, ERK1, ERK2 and ERK5 MAP kinases, and PI-3 kinases. Importantly, studies show that investigation of the importance of signalling molecules in cell survival requires the use of inducible gene deletions within mature B cells. This overcomes the limitations of many earlier studies using constitutive gene deletions which were unable to distinguish between requirements for a protein in development versus survival.

Research and therapeutics-traditional and emerging therapies in systemic lupus erythematosus

This review summarizes traditional and emerging therapies for SLE. Evidence suggests that the heterogeneity of SLE is a crucial aspect contributing to the failure of large clinical trials for new targeted therapies. A clearer understanding of the mechanisms driving disease pathogenesis combined with recent advances in medical science are predicted to enable accelerated progress towards improved SLE diagnosis and personalized approaches to treatment.

B cells are required for sunlight protection of mice from a CNS-targeted autoimmune attack

The ultraviolet (UV) radiation contained in sunlight is a powerful immune suppressant. While exposure to UV is associated with protection from the development of autoimmune diseases, particularly multiple sclerosis, the precise mechanism by which UV achieves this protection is not currently well understood. Regulatory B cells play an important role in preventing autoimmunity and activation of B cells is a major way in which UV suppresses adaptive immune responses. Whether UV-protection from autoimmunity is mediated by the activation of regulatory B cells has never been considered before. When C57BL/6 mice were exposed to low, physiologically relevant doses of UV, a unique population of B cells was activated in the skin draining lymph nodes. As determined by flow cytometry, CD1d(low)CD5(-)MHC-II(hi)B220(hi) UV-activated B cells expressed significantly higher levels of CD19, CD21/35, CD25, CD210 and CD268 as well as the co-stimulatory molecules CD80, CD86, CD274 and CD275. Experimental autoimmune encephalomyelitis (EAE) in mice immunized with MOG/CFA was reduced by exposure to UV. UV significantly inhibited demyelination and infiltration of inflammatory cells into the spinal cord. Consequently, UV-exposed groups showed elevated IL-10 levels in secondary lymphoid organs, delayed EAE onset, reduced peak EAE score and significantly suppressed overall disease incidence and burden. Importantly, protection from EAE could be adoptively transferred using B cells isolated from UV-exposed, but not unirradiated hosts. Indeed, UV-protection from EAE was dependent on UV activation of lymph node B cells because UV could not protect mice from EAE who were pharmacologically depleted of B cells using antibodies. Thus, UV maintenance of a pool of unique regulatory B cells in peripheral lymph nodes appears to be essential to prevent an autoimmune attack on the central nervous system.