Decreased B cell activating factor receptor expression on peripheral lymphocytes associated with increased disease activity in primary Sjögren's syndrome and systemic lupus erythematosus

Self-reactive B cells are increased in all major stages of peripheral development in Sjögren's disease

Sjögren's disease (SjD) is a chronic autoimmune disorder characterized by increased circulating self-reactive B cells. While many of these self-reactive B cells emerge from the bone marrow, it is not known whether they are excluded from or enriched in specific developmental stages in the periphery. The aim of this study was to determine the immunophenotype of circulating self-reactive B cells in SjD to inform more precise therapeutic targeting. Five major B cell populations: transitional, mature naïve, switched memory, double negative and plasmablasts were single-cell sorted and cultured to produce IgG. Self-reactive IgG was identified by ELISA, flow cytometry of permeabilized HEK293 cells and HEp-2 indirect immunofluorescence. Immunoglobulin heavy chains were sequenced by Sanger and next-generation sequencing. Compared with healthy donor controls (HCs), SjD patients had higher frequencies of naïve and CD21low atypical memory B cell subsets, while antigen-experienced B cells expressed more Ki67 and CD86. B cells recognizing intracellular self-antigens were identified in all stages of peripheral B cell development for SjD and HCs, but frequencies of autoreactive B cells were up to 10-fold higher in SjD. Self-reactive transitional B cells expressed higher surface CD38 and lower surface IgM. An increase in self-reactive B cells throughout peripheral development in SjD compared with HCs suggests that counterselection of autoantibody-bearing B cells during central and peripheral tolerance checkpoints are reduced in SjD. Therapeutic strategies focused on depleting B cells based on B cell receptor specificity rather than the developmental stage would be more efficient to target self-reactive B cells in SjD.

Causal associations of BAFF-R on IgD+ CD24- B cell immune cell trait with hepatocellular carcinoma and the mediating role of phenylacetylglutamate levels: a Mendelian randomization study

We conducted a bi-directional two-sample Mendelian randomization (MR) analysis to investigate the causal associations between immune cell traits and hepatocellular carcinoma (HCC) and identified the mediating factor of metabolites. The exposure factors were immune cell traits, the mediators were metabolites, and the outcome variable was HCC. Inverse-variance weighted method (IVW) was the main method. Weighted median, MR-Egger regression, weighted mode, simple mode, and MR pleiotropy residual sum and outlier (MRPRESSO) methods were used as complementary methods. The results were tested by using the Bayesian weighted Mendelian randomization (BWMR) approach in our MR study. Subsequently, the potential mediating effect was investigated by conducting a two-step mediation analysis. We identified 26 traits with suggestive correlations between immune cell traits and HCC, with 4 immune cell traits among them having causal correlations with HCC. There were no causal correlations between HCC and immune cell traits in the reverse MR analysis. In the mediation analysis, we found a positive causal association between B cell-activating factor receptors (BAFF-R) on IgD+ CD24- B cell and HCC [IVW: odd ratio (OR), 0.845; 95% CI, 0.759-0.942; p = 0.002]. Phenylacetylglutamate (PAG) levels mediated 7.353% of the causal pathway from BAFF-R on IgD+ CD24- B cell and HCC. In conclusion, BAFF-R on IgD+ CD24- B cell lowers risk of HCC, with PAG levels playing a mediating role.

Features of BAFF and APRIL receptors on circulating B cells in antineutrophil cytoplasmic antibody-associated vasculitis

To investigate the features of circulating B cells, their expressing receptors, serum levels of B-cell activation factor of the TNF family (BAFF), and a proliferation-inducing ligand (APRIL) in antineutrophil cytoplasmic antibody-associated vasculitis (AAV). Blood samples from 24 patients with active AAV (a-AAV), 13 with inactive AAV (i-AAV), and 19 healthy controls (HC) were included in this study. The proportion of B cells and their expressing BAFF receptor (BAFF-R), transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI), and B-cell maturation antigen were analyzed via flow cytometry. Serum levels of BAFF, APRIL, and interleukin (IL)-4, IL-6, IL-10, and IL-13 were also evaluated using an enzyme-linked immunosorbent assay. The proportion of plasmablasts (PB)/plasma cells (PC) and serum levels of BAFF, APRIL, IL-4, and IL-6 were significantly higher in a-AAV than in HC. Higher serum levels of BAFF, APRIL, and IL-4 were observed in i-AAV than in HC. Lower expression of BAFF-R on memory B cells and higher expression of TACI on CD19+ cells, immature B cells, and PB/PC were demonstrated in a-AAV and i-AAV than in HC. The population of memory B cells was positively associated with serum APRIL levels and BAFF-R expression in a-AAV. In conclusion, decreased expression of BAFF-R on memory B cells and increased expression of TACI on CD19+ cells, immature B cells, and PB/PC, as well as increased serum levels of BAFF and APRIL, were sustained even in the remission phase of AAV. Persistent aberrant signaling of BAFF/APRIL may contribute to disease relapse.

Reemergence of pathogenic, autoantibody-producing B cell clones in myasthenia gravis following B cell depletion therapy

Myasthenia gravis (MG) is an autoantibody-mediated autoimmune disorder of the neuromuscular junction. A small subset of patients (<10%) with MG, have autoantibodies targeting muscle-specific tyrosine kinase (MuSK). MuSK MG patients respond well to CD20-mediated B cell depletion therapy (BCDT); most achieve complete stable remission. However, relapse often occurs. To further understand the immunomechanisms underlying relapse, we studied autoantibody-producing B cells over the course of BCDT. We developed a fluorescently labeled antigen to enrich for MuSK-specific B cells, which was validated with a novel Nalm6 cell line engineered to express a human MuSK-specific B cell receptor. B cells (≅ 2.6 million) from 12 different samples collected from nine MuSK MG patients were screened for MuSK specificity. We successfully isolated two MuSK-specific IgG4 subclass-expressing plasmablasts from two of these patients, who were experiencing a relapse after a BCDT-induced remission. Human recombinant MuSK mAbs were then generated to validate binding specificity and characterize their molecular properties. Both mAbs were strong MuSK binders, they recognized the Ig1-like domain of MuSK, and showed pathogenic capacity when tested in an acetylcholine receptor (AChR) clustering assay. The presence of persistent clonal relatives of these MuSK-specific B cell clones was investigated through B cell receptor repertoire tracing of 63,977 unique clones derived from longitudinal samples collected from these two patients. Clonal variants were detected at multiple timepoints spanning more than five years and reemerged after BCDT-mediated remission, predating disease relapse by several months. These findings demonstrate that a reservoir of rare pathogenic MuSK autoantibody-expressing B cell clones survive BCDT and reemerge into circulation prior to manifestation of clinical relapse. Overall, this study provides both a mechanistic understanding of MuSK MG relapse and a valuable candidate biomarker for relapse prediction.

Decreased BAFF Receptor Expression and Unaltered B Cell Receptor Signaling in Circulating B Cells from Primary Sjögren's Syndrome Patients at Diagnosis

Animal models of autoimmunity and human genetic association studies indicate that the dysregulation of B-cell receptor (BCR) signaling is an important driver of autoimmunity. We previously showed that in circulating B cells from primary Sjögren’s syndrome (pSS) patients with high systemic disease activity, protein expression of the BCR signaling molecule Bruton’s tyrosine kinase (BTK) was increased and correlated with T-cell infiltration in the target organ. We hypothesized that these alterations could be driven by increased B-cell activating factor (BAFF) levels in pSS. Here, we investigated whether altered BCR signaling was already present at diagnosis and distinguished pSS from non-SS sicca patients. Using (phospho-)flow cytometry, we quantified the phosphorylation of BCR signaling molecules, and investigated BTK and BAFF receptor (BAFFR) expression in circulating B cell subsets in an inception cohort of non-SS sicca and pSS patients, as well as healthy controls (HCs). We found that both BTK protein levels and BCR signaling activity were comparable among groups. Interestingly, BAFFR expression was significantly downregulated in pSS, but not in non-SS sicca patients, compared with HCs, and correlated with pSS-associated alterations in B cell subsets. These data indicate reduced BAFFR expression as a possible sign of early B cell involvement and a diagnostic marker for pSS.

Nanomedicines in B cell-targeting therapies

B cells play multiple roles in immune responses related to autoimmune diseases as well as different types of cancers. As such, strategies focused on B cell targeting attracted wide interest and developed intensively. There are several common mechanisms various B cell targeting therapies have relied on, including direct B cell depletion, modulation of B cell antigen receptor (BCR) signaling, targeting B cell survival factors, targeting the B cell and T cell costimulation, and immune checkpoint blockade. Nanocarriers, used as drug delivery vehicles, possess numerous advantages to low molecular weight drugs, reducing drug toxicity, enhancing blood circulation time, as well as augmenting targeting efficacy and improving therapeutic effect. Herein, we review the commonly used targets involved in B cell targeting approaches and the utilization of various nanocarriers as B cell-targeted delivery vehicles. STATEMENT OF SIGNIFICANCE: As B cells are engaged significantly in the development of many kinds of diseases, utilization of nanomedicines in B cell depletion therapies have been rapidly developed. Although numerous studies focused on B cell targeting have already been done, there are still various potential receptors awaiting further investigation. This review summarizes the most relevant studies that utilized nanotechnologies associated with different B cell depletion approaches, providing a useful tool for selection of receptors, agents and/or nanocarriers matching specific diseases. Along with uncovering new targets in the function map of B cells, there will be a growing number of candidates that can benefit from nanoscale drug delivery.

B Lineage Cells in ANCA-Associated Vasculitis

Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is a systemic autoimmune disease that affects small sized blood vessels and can lead to serious complications in the lungs and kidneys. The prominent presence of ANCA autoantibodies in this disease implicates B cells in its pathogenesis, as these are the precursors of the ANCA-producing plasma cells (PCs). Further evidence supporting the potential role of B lineage cells in vasculitis are the increased B cell cytokine levels and the dysregulated B cell populations in patients. Confirmation of the contribution of B cells to pathology arose from the beneficial effect of anti-CD20 therapy (i.e., rituximab) in AAV patients. These anti-CD20 antibodies deplete circulating B cells, which results in amelioration of disease. However, not all patients respond completely, and this treatment does not target PCs, which can maintain ANCA production. Hence, it is important to develop more specific therapies for AAV patients. Intracellular signalling pathways may be potential therapeutic targets as they can show (disease-specific) alterations in certain B lineage cells, including pathogenic B cells, and contribute to differentiation and survival of PCs. Preliminary data on the inhibition of certain signalling molecules downstream of receptors specific for B lineage cells show promising therapeutic effects. In this narrative review, B cell specific receptors and their downstream signalling molecules that may contribute to pathology in AAV are discussed, including the potential to therapeutically target these pathways.

Dysregulated translational factors and epigenetic regulations orchestrate in B cells contributing to autoimmune diseases

B cells play a crucial role in antigen presentation, antibody production and pro-/anti-inflammatory cytokine secretion in adaptive immunity. Several translational factors including transcription factors and cytokines participate in the regulation of B cell development, with the cooperation of epigenetic regulations. Autoimmune diseases are generally characterized with autoreactive B cells and high-level pathogenic autoantibodies. The success of B cell depletion therapy in mouse model and clinical trials has proven the role of B cells in pathogenesis of autoimmune diseases. The failure of B cell tolerance in immune checkpoints results in accumulated autoreactive naïve B (B_N) cells with aberrant B cell receptor signaling and dysregulated B cell response, contributing to self-antibody-mediated autoimmune reaction. Dysregulation of translational factors and epigenetic alterations in B cells has been demonstrated to correlate with aberrant B cell compartment in autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, primary Sjögren's syndrome, multiple sclerosis, diabetes mellitus and pemphigus. This review is intended to summarize the interaction of translational factors and epigenetic regulations that are involved with development and differentiation of B cells, and the mechanism of dysregulation in the pathogenesis of autoimmune diseases.

Skewed peripheral B- and T-cell compartments in patients with ANCA-associated vasculitis

OBJECTIVES

To characterize lymphocytes dysregulation in patients with granulomatosis with polyangiitis (GPA) and microscopic polyangiitis (MPA).

METHODS

Using flow cytometry, we analysed B- and T-cell subsets in peripheral blood from 37 untreated patients with active disease (29 GPA and 8 MPA) and 22 healthy controls (HCs).

RESULTS

GPA patients had increased Th2 (1.8 vs 1.0%, P = 0.02), Th9 (1.1 vs 0.2%, P = 0.0007) and Th17 (1.4 vs 0.9%, P = 0.03) cells compared with HC. Patients with MPO-ANCAs had significantly more CD21- B cells than HC or PR3-ANCA patients (6.9 vs 3.3% and 4.4%, P = 0.01). CD69 expressing B cells were significantly higher in GPA and MPA (3.0 and 5.9 vs 1.4%, P = 0.02 and P = 0.03, respectively) compared with HC, whereas B-cell activating factor-receptor expression was decreased in GPA and MPA (median fluorescence intensity ratio 11.8 and 13.7 vs 45.1 in HC, P < 0.0001 and P = 0.003, respectively). Finally, IL-6-producing B cells were increased in GPA vs HC (25.8 vs 14.9%, P < 0.0001) and decreased in MPA vs HC (4.6 vs 14.9%, P = 0.005), whereas TNF-α-producing B cells were lower in both GPA and MPA patients compared with controls (15 and 8.4 vs 30%, P = 0.01 and P = 0.006, respectively).

CONCLUSION

Skewed T-cell polarization towards Th2, Th9 and Th17 responses characterizes GPA, whereas B-cell populations are dysregulated in both GPA and MPA with an activated phenotype and a decreased B-cell activating factor-receptor expression. Finally, inflammatory B cells producing IL-6 are dramatically increased in GPA, providing an additional mechanism by which rituximab could be effective.

Pathogenetic Mechanisms Implicated in Sjögren's Syndrome Lymphomagenesis: A Review of the Literature

Sjögren's Syndrome (SS) is a chronic autoimmune disorder characterized by focal mononuclear cell infiltrates that surround the ducts of the exocrine glands, impairing the function of their secretory units. Compared to other autoimmune disorders, SS is associated with a notably high incidence of non-Hodgkin lymphoma (NHL) and more frequently mucosa associated lymphoid tissue (MALT) lymphoma, leading to increased morbidity and mortality rates. High risk features of lymphoma development include systemic extraepithelial manifestations, low serum levels of complement component C4 and mixed type II cryoglobulinemia. The discrimination between reactive and neoplastic lymphoepithelial lesion (LEL) is challenging, probably reflecting a continuum in the evolution from purely inflammatory lymphoid infiltration to the clonal neoplastic evolution. Early lesions display a predominance of activated T cells, while B cells prevail in severe histologic lesions. This strong B cell infiltration is not only a morphologic phenomenon, but it is also progressively associated with the presence of ectopic germinal centers (GCs). Ectopic formation of GCs in SS represents a complex process regulated by an array of cytokines, adhesion molecules and chemokines. Chronic antigenic stimulation is the major driver of specific B cell proliferation and increases the frequency of their transformation in the ectopic GCs and marginal zone (MZ) equivalents. B cells expressing cell surface rheumatoid factor (RF) are frequently detected in the salivary glands, suggesting that clonal expansion might arise from antigen selection of RF-expressing B cells. Abnormal stimulation and incomplete control mechanisms within ectopic lymphoid structures predispose RF MZ like cells to lymphoma development. Immunoglobulin recombination, somatic mutation and isotype switching during B cell development are events that may increase the translocation of oncogenes to immunoglobulin loci or tumor suppressor gene inactivation, leading to monoclonal B cell proliferation and lymphoma development. Concerning chronic antigenic stimulation, conclusive data is so far lacking. However immune complexes containing DNA or RNA are the most likely candidates. Whether additional molecular oncogenic events contribute to the malignant overgrowth remains to be proved.

Single-cell repertoire tracing identifies rituximab-resistant B cells during myasthenia gravis relapses

Rituximab, a B cell-depleting therapy, is indicated for treating a growing number of autoantibody-mediated autoimmune disorders. However, relapses can occur after treatment, and autoantibody-producing B cell subsets may be found during relapses. It is not understood whether these autoantibody-producing B cell subsets emerge from the failed depletion of preexisting B cells or are generated de novo. To further define the mechanisms that cause postrituximab relapse, we studied patients with autoantibody-mediated muscle-specific kinase (MuSK) myasthenia gravis (MG) who relapsed after treatment. We carried out single-cell transcriptional and B cell receptor profiling on longitudinal B cell samples. We identified clones present before therapy that persisted during relapse. Persistent B cell clones included both antibody-secreting cells and memory B cells characterized by gene expression signatures associated with B cell survival. A subset of persistent antibody-secreting cells and memory B cells were specific for the MuSK autoantigen. These results demonstrate that rituximab is not fully effective at eliminating autoantibody-producing B cells and provide a mechanistic understanding of postrituximab relapse in MuSK MG.

B-cell profile, B-cell activating factor concentration and IgG levels in human cutaneous and mucosal leishmaniasis

AIMS

The aim of this study was to evaluate characteristics of B cells in human tegumentary leismaniasis (TL) analysing cutaneous leishmaniasis (CL), most prevalent form and mucosal leishmaniasis (ML), aggressive form characterized by the destruction of the oral-nasal-pharyngeal cavities.

METHODS AND RESULTS

By flow cytometry analysis, we found decreased percentages of non-class-switched memory B cells in TL with the degree of the loss related to clinical severity. Using commercial ELISA, we reported high levels of B-cell activating factor (BAFF) and IgG preferentially in aggressive CL and markedly in ML together with decreased BAFF receptors in the latter. We also found lower levels of BAFF after clinical recovery suggesting a relation between BAFF and disease activity. Mucosal leishmaniasis history of therapeutic failure presented high levels of BAFF accompanied by detectable concentrations of IFN-γ and IL-6 (assayed by commercial ELISA and cytometric bead arrays respectively), cytokines involved in exaggerated inflammatory responses and tissue damage in TL.

CONCLUSION

We demonstrate B-cell disturbances in TL with the degree of the alterations related to clinical severity. We suggest a relation between excess of BAFF and disease activity and point towards a possible implication of BAFF in the inflammatory phenomenon of ML.

Decreased of BAFF-R expression and B cells maturation in patients with hepatitis B virus-related hepatocellular carcinoma

BACKGROUND

Recent evidence has indicated the role of B cells and B cell-activating factor (BAFF) in the development of hepatocellular carcinoma (HCC).

AIM

To characterize circulating BAFF receptor expression and B cell subpopulations in patients with hepatitis B virus (HBV)-related HCC.

METHODS

Peripheral blood samples collected from 41 patients with chronic HBV infection (25 patients without HCC and 16 patients with HCC) and 9 healthy controls were assessed for BAFF receptors [BAFF-R(B cell-activating factor receptor), transmembrane activator and cyclophilin ligand interactor, B-cell maturation antigen] and B cell subpopulations by multicolor flow cytometry.

RESULTS

The frequency of BAFF-R expressing B cells to total B cells was significantly lower in patients with HCC (3.39% ± 2.12%) compared with the non-HCC group (5.37% ± 1.90%) and healthy controls (6.23% ± 2.32%), whereas there was no difference in transmembrane activator and cyclophilin ligand interactor and B-cell maturation antigen. The frequencies of CD27⁺IgD⁺ memory B cells, CD27⁺IgD^- class-switched memory B cells and plasmablasts were significantly lower in the patients with HCC compared to patients without HCC (1.23 ± 1.17 vs 3.09 ± 1.55, P = 0.001, 0.60 ± 0.44 vs 1.69 ± 0.86, P < 0.0001 and 0.16 ± 0.12 vs 0.37 ± 0.30, P = 0.014, respectively). However, the ratio of naïve and transitional B cell did not differ significantly between the three groups. In addition, decreased BAFF-R expression on B cells was significantly correlated with large tumor size and advanced tumor stage.

CONCLUSION

Our data demonstrated BAFF-R expression was reduced in B cells that involved with the frequencies of B cells maturation in patients with HCC. The depletion of BAFF-R might play an important role in the development of HCC in patients with chronic HBV infection.

Comprehensive B Cell Phenotyping Profile for Chronic Graft-versus-Host Disease Diagnosis

Previous studies have reported single B cell-related chronic graft-versus-host disease diagnostic (cGVHD) biomarkers, such as B cell-activating factor (BAFF), CD21^low, and immature B cells, but research on the performance of biomarker combinations and the covariate effect of steroids is lacking. The primary objective of this study was to determine the most accurate combination of B cell populations using cell surface staining flow cytometry in an independent cohort of patients with cGVHD. Secondary objectives included assessing the effect of corticosteroid use at sample collection on the makeup and accuracy of the diagnostic panel and identifying the mechanism underlying low surface expression of BAFF receptor (BAFF-R) on B cells in cGVHD. Flow cytometry analysis was performed in an adult cohort of post-HCT patients with cGVHD onset (n = 44) and time-matched recipients without cGVHD (n = 63). We confirmed that the onset of cGVHD was associated with higher soluble BAFF (sBAFF) levels, elevated CD27^-CD10^-CD21^low CD19⁺ B cell and classical switched memory B cell counts, and reduced transitional and naïve B cell counts. The highest single B cell population area under the receiver operating characteristic (ROC) curve (AUC) was .72 for transitional type 1 CD21^low B cells. We also showed a significant inverse relationship between sBAFF and surface BAFF-R expression caused by sBAFF modulation of BAFF-R. Steroid use at sample collection influenced the significance of the sBAFF:B cell ratio, naïve and marginal zone-like B cells. The optimal combination of B cell subsets most significantly associated with cGVHD onset with or without concurrent corticosteroid use resulted in ROC AUCs of .87 and .84, respectively. Transitional and CD21^low B cells were the only populations present in both panels; however, analyzing only these populations resulted in ROC AUCs of .79 and .78, respectively. This suggests that the inclusion of other populations and use of different panels depending on steroid use is necessary to achieve better accuracy. sBAFF was not a component of either panel. These novel B cell profiles could be tested prospectively in patients post-HSCT and could lead to focused mechanistic studies.

Delayed onset of autoreactive antibody production and M2-skewed macrophages contribute to improved survival of TACI deficient MRL-Fas/Lpr mouse

Anti-B cell activating factor belonging to TNF-family (BAFF) antibody therapy is indicated for the treatment of patients with active systemic lupus erythematosus (SLE). We hypothesized that the BAFF receptor, transmembrane activator and calcium-modulator and cyclophilin interactor (TACI) may be responsible for the generation of antibody secreting plasma cells in SLE. To test this hypothesis, we generated TACI deficient MRL-Fas/Lpr (LPR-TACI−/−) mouse. TACI deficiency resulted in improved survival of MRL-Fas/Lpr mice and delayed production of anti-dsDNA and anti-SAM/RNP antibodies. There was also a delay in the onset of proteinuria and the accumulation of IgG and inflammatory macrophages (Mϕs) in the glomeruli of young LPR-TACI−/− mice compared to wild-type mice. Underscoring the role of TACI in influencing Mϕ phenotype, the transfer of Mϕs from 12-week-old LPR-TACI−/− mice to age-matched sick wild-type animals led to a decrease in proteinuria and improvement in kidney pathology. The fact that, in LPR-TACI−/− mouse a more pronounced delay was in IgM and IgG3 autoreactive antibody isotypes and the kinetics of follicular helper T (Tfh) cell-development was comparable between the littermates suggest a role for TACI in T cell-independent autoantibody production in MRL-Fas/Lpr mouse prior to the onset of T cell-dependent antibody production.

B cell phenotypes in patients with rheumatoid arthritis relapsing after rituximab: expression of B cell-activating factor-binding receptors on B cell subsets

Serum levels of B cell-activating factor (BAFF) rise following rituximab (RTX) therapy in patients with rheumatoid arthritis (RA). Initiation of naive B cell return to the periphery and autoreactive B cell expansion leading to relapse after RTX may therefore be linked to interactions between BAFF and BAFF-binding receptors (BBR). Relationships between serum BAFF and BBR expression [(BAFFR, calcium signal modulating cyclophilic ligand interactor (TACI) and B cell maturation antigen (BCMA)] were determined on B cell subsets, defined using immunoglobulin (Ig)D/CD38. Twenty pre-RTX and 18 RA patients relapsing after B cell depletion were included. Results were analysed with respect to timing of relapse up to 7 months after peripheral B cell return (≥ 5 B cells/μl) and to serum BAFF levels. After B cell return, B cell populations from relapsing patients had significantly lower BAFFR⁺ expression compared to HC and pre-RTX patients. The percentage of BAFFR⁺ B cells increased with time after B cell return and was correlated inversely with serum BAFF levels. BAFFR expression remained reduced. The percentage of TACI⁺ memory B cells were lower in RA patients after RTX compared with healthy controls (HC). BCMA expression (% and expression) did not differ between patients and HC. Relapse following B cell return appeared largely independent of the percentage of BAFFR⁺ or percentage of BCMA⁺ B cells or serum BAFF levels. The lower percentage of TACI⁺ memory B cells may reduce inhibitory signalling for B cell differentiation. In patients relapsing at longer periods after B cell return, recovery of the B cell pool was more complete, suggesting that selection or expansion of autoreactive B cells may be needed to precipitate relapse.

Direct-Acting Antiviral Therapy Restores Immune Tolerance to Patients With Hepatitis C Virus-Induced Cryoglobulinemia Vasculitis

BACKGROUND & AIMS

Interferon-free direct-acting antiviral (DAA) therapies are effective in patients with hepatitis C virus-induced cryoglobulinemia vasculitis (HCV-CV). We analyzed blood samples from patients with HCV-CV before and after DAA therapy to determine mechanisms of these drugs and their effects on cellular immunity.

METHODS

We performed a prospective study of 27 consecutive patients with HCV-CV (median age, 59 y) treated with DAA therapy (21 patients received sofosbuvir plus ribavirin for 24 weeks, 4 patients received sofosbuvir plus daclatasvir for 12 weeks, and 2 patients received sofosbuvir plus simeprevir for 12 weeks) in Paris, France. Blood samples were collected from these patients before and after DAA therapy, and also from 12 healthy donors and 12 individuals with HCV infection without CV. HCV load, cryoglobulins, and cytokines were quantified by flow cytometry, cytokine multiplex assays, and enzyme-linked immunosorbent assay.

RESULTS

Twenty-four patients (88.9%) had a complete clinical response of CV to DAA therapy at week 24, defined by improvement of all the affected organs and the absence of relapse. Compared with healthy donors and patients with HCV infection without CV, patients with HCV-CV, before DAA therapy, had a lower percentage of CD4+CD25hiFoxP3+ regulatory T cells (P < .01), but higher proportions of IgM+CD21-/low memory B cells (P < .05), CD4+IFNγ+ cells (P < .01), CD4+IL17A+ cells (P < .01), and CD4+CXCR5+interleukin 21+ follicular T-helper (Tfh) cells (P < .01). In patients with HCV-CV, there was a negative correlation between numbers of IgM+CD21-/low memory B cells and T-regulatory cells (P = .03), and positive correlations with numbers of Tfh cells (P = .03) and serum levels of cryoglobulin (P = .01). DAA therapy increased patients' numbers of T-regulatory cells (1.5% ± 0.18% before therapy vs 2.1% ± 0.18% after therapy), decreased percentages of IgM+CD21-/low memory B cells (35.7% ± 6.1% before therapy vs 14.9% ± 3.8% after therapy), and decreased numbers of Tfh cells (12% ± 1.3% before therapy vs 8% ± 0.9% after therapy). Expression levels of B lymphocyte stimulator receptor 3 and programmed cell death 1 on B cells increased in patients with HCV-CV after DAA-based therapy (mean fluorescence units, 37 ± 2.4 before therapy vs 47 ± 2.6 after therapy, P < .01; and 29 ± 7.3 before therapy vs 48 ± 9.3 after therapy, P < .05, respectively).

CONCLUSIONS

In a prospective clinical trial of patients with HCV-CV, DAA-based therapy restored disturbances in peripheral B- and T-cell homeostasis.

MRL Strains Have a BAFFR Mutation without Functional Consequence

It has been shown that B cell activating factor receptor (BAFFR) is critical for B cell development and survival. In this study, we sought to evaluate the expression and function of BAFFR across multiple stains of mice that vary in their potential to develop systemic autoimmune disease. The inability of a commercial antibody to bind to BAFFR in the autoimmune prone mouse strains, MRL and MRL/Lpr led to the discovery of a mutation in TNFRSF13C gene (encoding BAFFR) that resulted in a Pro44Ser substitution in the N-terminus near the BAFF binding site in these strains. To define the biological consequences of mutant BAFFR, we compared the expression and activity of BAFFR in MRL and MRL/Lpr mice to BALB/c, which express the consensus version of TNFRSF13C. B cells from MRL and MRL/Lpr mice expressed mutant BAFFR on surface and were capable of responding to BAFF as exhibited by BAFF-mediated reduction in apoptosis and NF-κB2 activation. Signaling through MAPK ERK1/2 was not significantly induced by BAFF in MRL/Lpr mice; however, MAPK ERK1/2 signaling was intact in MRL mice. The inability of MRL/Lpr B cells to significantly activate ERK1/2 in response to BAFF was due to the high basal activity of the signaling pathway in these cells. In fact, basal activity of ERK1/2 in B cells correlated with the degree of autoimmune susceptibility exhibited by each strain. In addition, aged MRL/Lpr mice with severe autoimmune disease had high BAFF levels, low surface BAFFR, and high basal NF-κB2 activation, a pattern which is attributed to the high frequency of antibody secreting cells. We conclude that P44S BAFFR mutation does not hinder BAFFR function or enhance B cell activity in MRL/Lpr and MRL mice and that other susceptibility loci on the MRL background contributed to the hyperactivity of these cells.

Increase of Intracellular BAFF in B Cells of Sjögren's Patients Is Not Affected by Decrease of BAFFR

The presence of a broad spectrum of autoantibodies in Sjögren's syndrome (SjS) patients is the result of abnormal B-cell regulation that can be at least partially explained by abnormal BAFF/BAFFR regulation. The objective of this study was to determine both membrane and intracellular expression of BAFF/BAFFR in monocytes and B-cells in peripheral blood of 19 primary Sjögren's syndrome patients and 20 healthy controls using flow cytometry. We also measured sBAFF in serum. Compared to healthy controls, both surface and intracellular expression of BAFF was significantly increased in monocytes and B-cells of SjS patients. Also serum sBAFF level was elevated. Expression of BAFFR on B-cells of SjS patients was surprisingly decreased, but there was no clear increase or decrease within monocytes. Our results indicate that activated monocytes communicate with B-cells via BAFF and BAFFR, so that B-cells are stimulated, but BAFF is also produced to stimulate cells in autocrine way. The decrease of BAFFR expression in SjS patients suggests that there is the mechanism that attempts to take over in order to balance the high level of BAFF.

Association of BAFF, APRIL serum levels, BAFF-R, TACI and BCMA expression on peripheral B-cell subsets with clinical manifestations in systemic lupus erythematosus

Objective

B-cell-activating factor (BAFF) and a proliferation-inducing ligand (APRIL) signaling pathways regulate B-cell survival through interactions with their receptors BAFF-R, TACI and BCMA. We evaluated the association of these ligands/receptors on B-cell subsets according to clinical manifestations of systemic lupus erythematosus (SLE).

Methods

BAFF and APRIL serum concentrations were measured in 30 SLE patients by enzyme-linked immunosorbent assay. The BAFF-R, TACI and BCMA expression was analyzed on each B cell subset (CD19 + CD27-CD38–/ + naïve; CD19 + CD27 + CD38–/ + memory; CD19 + CD27-CD38 + + immature and CD19 + CD27 + CD38 + + plasma cells) by flow cytometry, and compared among patients with different clinical manifestations as well as healthy controls (HCs).

Results

Serum BAFF and APRIL levels were high in SLE patients and correlated with the Mex-SLEDAI disease activity index ( r = 0.584; p = 0.001 and r = 0.456; p = 0.011, respectively). The SLE patients showed an increased proportion of memory and plasma B cells ( p < 0.05). BAFF-R, TACI and BCMA expression in SLE patients was decreased in almost all B cell subsets compared to HCs ( p < 0.05). A lower BCMA expression was associated with severe disease activity, glomerulonephritis, serositis and hemolytic anemia ( p < 0.01). BCMA expression showed a negative correlation with Mex-SLEDAI score ( r = –0.494, p = 0.006).

Conclusions

Decreased BCMA expression on peripheral B cells according to severe disease activity suggests that BCMA plays an important regulating role in B-cell hyperactivity and immune tolerance homeostasis in SLE patients.

Control of Viremia Enables Acquisition of Resting Memory B Cells with Age and Normalization of Activated B Cell Phenotypes in HIV-Infected Children

HIV affects the function of all lymphocyte populations, including B cells. Phenotypic and functional defects of B cells in HIV-infected adults have been well characterized, but defects in children have not been studied to the same extent. We determined the proportion of B cell subsets and frequencies of Ag-specific memory B cells in peripheral blood from HIV-infected children and healthy controls, using flow cytometry and B cell ELISPOT, respectively. In addition, we measured the quantities and avidities of plasma Abs against various Ags by ELISA. We also determined plasma levels of BAFF and expression of BAFF receptors on B cells. Children with high HIV viremia had increased proportions of activated mature B cells, tissue-like memory B cells and plasmablasts, and low proportions of naive B cells when compared with community controls and children with low HIV viremia, similar to adults infected with HIV. HIV-infected groups had lower proportions of resting memory B cells than did community controls. Notably, high HIV viremia prevented the age-dependent accumulation of class-switched resting memory B cells. HIV-infected children, regardless of the level of viremia, showed lower quantities and avidities of IgG and lower frequencies of memory B cells against Expanded Program on Immunization vaccines. The HIV-infected children had an altered BAFF profile that could have affected their B cell compartment. Therefore, B cell defects in HIV-infected children are similar to those seen in HIV-infected adults. However, control of HIV viremia is associated with normalization of activated B cell subsets and allows age-dependent accumulation of resting memory B cells.

Treatment with belimumab restores B cell subsets and their expression of B cell activating factor receptor in patients with primary Sjogren's syndrome

OBJECTIVE

The aim of this study was to investigate the biological effects of belimumab on B cells in the first phase II open-label trial with belimumab in patients with primary SS (pSS) (BELISS).

METHODS

Peripheral blood B cell subsets and their B cell activating factor-receptor (BAFF-R) expression were analysed by multicolour flow cytometry in 10 pSS patients either before or after 24 and 52 weeks of therapy with belimumab. Serum BAFF levels were analysed by ELISA.

RESULTS

At baseline, pSS patients showed a significant increase in circulating B cells compared with healthy donors matched for age and sex, with a predominant expansion of transitional and naive B cell subsets. pSS patients also showed higher serum BAFF levels and lower B cell BAFF-R expression. Therapy with belimumab in pSS patients induced a significant reduction in transitional and naive B cell subsets to levels similar to those observed in healthy donors. Furthermore, belimumab normalized BAFF-R expression in all B subsets comprised within the memory compartment. The restoration of B cell frequency and subset composition in response to belimumab was also associated with a decrease in serum levels of Ig, RF, ANAs, and with an increase in the C4 complement fraction. All of these belimumab-mediated effects were observed after 24 weeks of therapy and maintained until the end of the therapeutic protocol.

CONCLUSION

Taken together, our findings show that targeting BAFF with belimumab is successful in normalizing B cell frequency, phenotype and functions in pSS.

TRIAL REGISTRATION

clinicaltrials.gov; https://clinicaltrials.gov/; NCT01008982.

The strength of the antibody response to the nematode Ascaris lumbricoides inversely correlates with levels of B-Cell Activating Factor (BAFF)

Background

B-Cell Activating Factor (BAFF) is a cytokine regulating antibody production. Polymorphisms in the gene encoding BAFF were associated with the antibody response to Ascaris but not to mite allergens. In the present study we evaluated the relationship between BAFF and specific antibodies against Ascaris and mites in 448 controls and 448 asthmatics. Soluble BAFF was measured by ELISA and BAFF mRNA by qPCR. Surface expression of BAFF and its receptor (BAFF-R) was analyzed by flow cytometry.

Results

Individuals with specific IgE levels to Ascaris >75th percentile had lower levels of soluble BAFF; those with specific IgG levels to Ascaris >75th percentile had reduced BAFF mRNA. Total IgE and specific IgE to mites were not related to BAFF levels. There were no differences in soluble BAFF or mRNA levels between asthmatics and controls. There was an inverse relationship between the cell-surface expression of BAFF-R on CD19⁺ B cells and BAFF levels at the transcriptional and protein level.

Conclusions

These findings suggest that differences in BAFF levels are related to the strength of the antibody response to Ascaris.

B cell subsets and dysfunction of regulatory B cells in IgG4-related diseases and primary Sjögren's syndrome: the similarities and differences

Introduction

IgG4-related disease (IgG4-RD) is a multisystem-involved autoimmune disease. Abnormally activated and differentiated B cells may play important roles. Regulatory B cells (Breg) are newly defined B cell subgroups with immunosuppressive functions. In this study, we investigated the differences of B cell subsets, the expressions of co-stimulatory molecules on B cells, and the function of Breg cells in patients with IgG4-RD, primary Sjögren’s syndrome (pSS) as well as in healthy controls (HC).

Methods

Newly diagnosed IgG4-RD patients (n = 48) were enrolled, 38 untreated pSS patients and 30 healthy volunteers were recruited as disease and healthy controls. To analyze B cell subsets and B cell activity, PBMCs were surface stained and detected by flow cytometry. The function of Breg cells was tested by coculturing isolated CD19 + CD24^hiCD38^hi Breg cells with purified CD4 + CD25- T cells. Serum cytokines were measured by ELISA and cytometric bead array. Relationship between clinical data and laboratory findings were analyzed as well.

Results

Compared with pSS patients and HC, IgG4-RD patients had a lower frequency of peripheral Breg cells. Interestingly, CD19 + CD24-CD38^hi B cell subsets were significantly higher in peripheral B cells from IgG4-RD patients than in pSS patients and HC, which correlated with serum IgG4 levels. The expression of BAFF-R and CD40 on B cells was significantly lower in IgG4-RD patients compared with those in pSS patients and HC. Unlike HC, Breg cells from pSS patients lacked suppressive functions.

Conclusions

B cells in patients with IgG4-RD and pSS display a variety of abnormalities, including disturbed B cell subpopulations, abnormal expression of key signaling molecules, co-stimulatory molecules, and inflammatory cytokines. In addition, a significantly increased B cell subset, CD19 + CD24-CD38^hi B cells, may play an important role in the pathogenesis of IgG4-RD.

Bone marrow T-cell infiltration during acute GVHD is associated with delayed B-cell recovery and function after HSCT

B-cell immune dysfunction contributes to the risk of severe infections after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Delayed B-cell regeneration is found in patients with systemic graft-versus-host disease (GVHD) and is often accompanied by bone marrow (BM) suppression. Little is known about human BM GVHD. We analyzed the reconstitution kinetics of B-cell subsets in adult leukemic patients within 6 months after allo-HSCT. B-cell deficiency already existed before transplant and was aggravated after transplant. Onset of B-cell reconstitution characterized by transitional B-cell recovery occurred either early (months 2-3) or late (from month 6 on) and correlated highly positively with reverse transcription-polymerase chain reaction quantified numbers of κ-deleting recombination excision circles (KRECs). Delayed recovery was associated with systemic acute GVHD and full-intensity conditioning therapy. Histological analysis of BM trephines revealed increased T-cell infiltration in late recovering patients, which was associated with reduced numbers of osteoblasts. Functionally, late recovering patients displayed less pneumococcal polysaccharide-specific immunoglobin M-producing B cells on ex vivo B-cell activation than early recovering patients. Our results provide evidence for acute BM GVHD in allo-HSCT patients with infiltrating donor T cells and osteoblast destruction. This is associated with delayed B-cell reconstitution and impaired antibody response. Herein, KREC appears suitable to monitor BM B-cell output after transplant.

Reduced BAFF-R and increased TACI expression in common variable immunodeficiency

PURPOSE

B-cell survival and differentiation critically depend on the interaction of BAFF-R and TACI with their ligands, BAFF and APRIL. Mature B-cell defects lead to Common Variable Immunodeficiency (CVID), which is associated with elevated serum levels of BAFF and APRIL. Nevertheless, BAFF-R and TACI expression in CVID and their relationship with ligand availability remain poorly understood.

METHODS AND RESULTS

We found that BAFF-R expression was dramatically reduced on B cells of CVID patients, relative to controls. BAFF-R levels inversely correlated with serum BAFF concentration both in CVID and healthy subjects. We also found that recombinant BAFF stimulation reduced BAFF-R expression on B cells without decreasing transcript levels. On the other hand, CVID subjects had increased TACI expression on B cells in direct association with serum BAFF but not APRIL levels. Moreover, splenomegaly was associated with higher TACI expression, suggesting that perturbations of TACI function may underlie lymphoproliferation in CVID.

CONCLUSIONS

Our results indicate that availability of BAFF determines BAFF-R and TACI expression on B cells, and that BAFF-R expression is controlled by BAFF binding. Identification of the factors governing BAFF-R and TACI is crucial to understanding CVID pathogenesis, and B-cell biology in general, as well as to explore their potential as therapeutic targets.

BAFF and BAFF receptor levels correlate with B cell subset activation and redistribution in controlled human malaria infection

Characteristic features of Plasmodium falciparum malaria are polyclonal B cell activation and an altered composition of the blood B cell compartment, including expansion of CD21(-)CD27(-) atypical memory B cells. BAFF is a key cytokine in B cell homeostasis, but its potential contribution to the modulation of the blood B cell pool during malaria remains elusive. In the controlled human malaria model (CHMI) in malaria-naive Dutch volunteers, we therefore examined the dynamics of BAFF induction and B cell subset activation and composition, to investigate whether these changes are linked to malaria-induced immune activation and, in particular, induction of BAFF. Alterations in B cell composition after CHMI closely resembled those observed in endemic areas. We further found distinct kinetics of proliferation for individual B cell subsets across all developmental stages. Proliferation peaked either immediately after blood-stage infection or at convalescence, and for most subsets was directly associated with the peak parasitemia. Concomitantly, plasma BAFF levels during CHMI were increased and correlated with membrane-expressed BAFF on monocytes and dendritic cells, as well as blood-stage parasitemia and parasite-induced IFN-γ. Correlating with increased plasma BAFF and IFN-γ levels, IgD(-)CD38(low)CD21(-)CD27(-) atypical B cells showed the strongest proliferative response of all memory B cell subsets. This provides unique evidence for a link between malaria-induced immune activation and temporary expansion of this B cell subset. Finally, baseline BAFF-R levels before CHMI were predictive of subsequent changes in proportions of individual B cell subsets. These findings suggest an important role of BAFF in facilitating B cell subset proliferation and redistribution as a consequence of malaria-induced immune activation.

A higher frequency of peripheral blood activated B cells in patients with non-traumatic osteonecrosis of the femoral head

OBJECTIVES

B cells play important roles in inflammatory diseases. This study was aimed at examining the frequency of different subsets of B cells in patients with non-traumatic osteonecrosis of the femoral head (NONFH).

METHODS

The percentages of the different subsets of circulating B cells in 28 patients with steroid-related, alcohol-related, or idiopathic NONFH and 10 healthy controls (HC) were examined by flow cytometry. The concentrations of serum C-reactive protein (CRP), fibrinogen (FIB), immunoglobulins, cytokines and blood erythrocyte sedimentation rate (ESR) were measured.

RESULTS

In comparison with those in the HC, significantly higher percentages of CD27-, CD86+, CD95+, and CD27+CD95+CD19+ but lower CD27+CD19+ B cells were detected in the patients. The percentages of CD86+, CD95+, and CD27+CD95+CD19+ B cells in each group of the patients were significantly higher than those in the HC. The levels of serum IL-17A and IFN-γ in steroid group and serum TNF-α in alcoholic group were significantly higher than those in the HC. The percentages of CD86+CD19+ B cells were positively associated with the degrees of femoral head collapse in both steroid and alcoholic groups of patients and the levels of serum TNF-α were positively associated with the degrees of femoral head collapse in the alcoholic NONFH patients.

CONCLUSIONS

These data suggest a higher frequency of CD86+CD19+ activated B cells and elevated levels of serum TNF-α may be associated with the development of NONFH.

B-cell activating factor (BAFF) is elevated in chronic granulomatous disease

Chronic Granulomatous Disease (CGD) is an inherited defect in superoxide production leading to life-threatening infections, granulomas, and, possibly, abnormal immunoglobulin concentrations. We investigated whether factors controlling antibody production, such as B-cell activating factor (BAFF), were altered in CGD. CGD subjects had significantly increased mean (2.3-fold, p < 0.0001) plasma concentrations of BAFF compared to healthy donors. Patients on IFN-γ treatment had significantly higher BAFF concentrations compared with CGD patients not taking IFN-γ (1.6-fold, p < 0.005). Leukocytes from CGD subjects produced normal amounts of BAFF in response to IFN-γ or G-CSF in vitro. Expression of BAFF-R and TACI was significantly reduced on CGD B cells. Elevated BAFF in CGD correlated with CRP (R = 0.44), ESR (R = 0.49), and IgM (R = 0.47) and increased rapidly in healthy subjects following intravenous endotoxin administration. These findings suggest that elevated BAFF in CGD subjects and healthy donors is a consequence of acute and chronic inflammation.

BAFF and TACI gene expression are increased in patients with untreated very early rheumatoid arthritis

OBJECTIVE

B cells play important roles in rheumatoid arthritis (RA). Given the beneficial effect of B cell depletion therapy in RA as well as the observed alterations in B cell subpopulations in this disease, we evaluated whether changes in the expression of genes related to B cell survival and activation were already present in patients with untreated very early RA (VERA; < 6 weeks of disease duration).

METHODS

The expression of a group of B cell-related activation and survival genes was quantified in peripheral blood mononuclear cells from patients with VERA by real-time PCR and compared with untreated early RA (< 1 year), established treated RA, and other untreated early arthritis conditions. Serum B cell-activating factor belonging to the tumor necrosis factor family (BAFF) was quantified by ELISA.

RESULTS

BAFF gene expression and serum levels were highest in patients with VERA. The expression of BAFF receptor (BAFF-R) increased with disease progression, while transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) was elevated since the first weeks of RA onset. Paired box 5 gene expression was also increased at all RA stages. Chemokine (C-X-C motif) receptor 5 was elevated only in established RA. No differences were observed in B cell maturation antigen, activation-induced cytidine deaminase, B lymphocyte-induced maturation protein, and B cell lymphoma 2 expression.

CONCLUSION

Disturbances in the expression of B cell-related activation and survival genes, particularly BAFF and TACI, occur from the onset of RA and precede changes in BAFF-R. These alterations can lead to the development of autoreactive B cells from the first weeks of RA onset.

Serum levels of beta2-microglobulin and free light chains of immunoglobulins are associated with systemic disease activity in primary Sjögren's syndrome. Data at enrollment in the prospective ASSESS cohort

Objectives

To analyze the clinical and immunological characteristics at enrollment in a large prospective cohort of patients with primary Sjögren's syndrome (pSS) and to investigate the association between serum BAFF, beta2-microglobulin and free light chains of immunoglobulins and systemic disease activity at enrollment.

Methods

Three hundred and ninety five patients with pSS according to American-European Consensus Criteria were included from fifteen centers of Rheumatology and Internal Medicine in the “Assessment of Systemic Signs and Evolution of Sjögren's Syndrome” (ASSESS) 5-year prospective cohort. At enrollment, serum markers were assessed as well as activity of the disease measured with the EULAR Sjögren's Syndrome Disease Activity Index (ESSDAI).

Results

Patient median age was 58 (25^th–75^th: 51–67) and median disease duration was 5 (2–9) years. Median ESSDAI at enrollment was 2 (0–7) with 30.9% of patients having features of systemic involvement. Patients with elevated BAFF, beta2-microglobulin and kappa, lambda FLCS had higher ESSDAI scores at enrollment (4 [2]–[11] vs 2 [0–7], P = 0.03; 4 [1]–[11] vs 2 [0–7], P< 0.0001); 4 [2]–[10] vs 2 [0–6.6], P< 0.0001 and 4 [2–8.2] vs 2 [0–7.0], P = 0.02, respectively). In multivariate analysis, increased beta2-microglobulin, kappa and lambda FLCs were associated with a higher ESSDAI score. Median BAFF and beta2-microglobulin were higher in the 16 patients with history of lymphoma (1173.3(873.1–3665.5) vs 898.9 (715.9–1187.2) pg/ml, P = 0.01 and 2.6 (2.2–2.9) vs 2.1 (1.8–2.6) mg/l, P = 0.04, respectively).

Conclusion

In pSS, higher levels of beta2-microglobulin and free light chains of immunoglobulins are associated with increased systemic disease activity.

The effect of BLyS on the activity of peripheral B lymphocytes mediated by BLyS receptors in patients with systemic lupus erythematosus

The study was promoted to probe into the effect of BLyS on the activity of peripheral B lymphocytes mediated by BLyS receptors in patients with systemic lupus erythematosus (SLE). Thirty new-onset patients having fulfilled the American College of Rheumatology (ACR) revised criteria for the diagnosis of SLE. Twenty age-matched healthy volunteers were recruited for this study. Peripheral blood samples were used to analyze the expression of BLyS protein and related receptors (BR3, TACI), to detect peripheral B cell subpopulations of different phases. Clinical disease activity was evaluated according to the systemic lupus erythematosus disease activity index (SLEDAI-2000). The percentage of CD19(+)CD5(+), CD19(+)CD27(+), CD19(+)CD38(+) and total CD19(+) in the peripheral blood is significantly higher in SLE patients than that in healthy controls (p < 0.01). BLyS concentrations and TACI expression are up-regulated in SLE patients (p < 0.01) while BR3 showed no differences between the two groups (p > 0.05). BLyS concentrations and TACI MFI both showed positive correlation with SLEDAI (r(2) = 0.391, p < 0.001, r(2) = 0.339, p = 0.001), whereas BR3 expression showed no relationship with SLEDAI. The disorders of peripheral B cell subsets maybe reflect the effect of BLyS on the activity of peripheral B lymphocytes mediated by BLyS receptors. The significant up-regulation of BLyS and its receptors, especially TACI may serve as a target for the treatment of SLE.

BAFF and BAFF-R levels are associated with risk of long-term kidney graft dysfunction and development of donor-specific antibodies

There are lines of evidence that B cells may play a role in transplantation. B cell activating factor, BAFF, is a homotrimer that has been shown to play a role in B cell survival, maturation and activation. To date, little is known of the role of BAFF and its receptors in transplantation. We analyzed the level of BAFF mRNA and its soluble protein, as well as transcripts coding for its receptors, BAFF-R, TACI and BCMA, in the blood of 143 patients with stable kidney transplant function 5 years or more posttransplantation. Three endpoints were analyzed: the time to renal dysfunction, the time to appearance of anti-HLA antibodies and the time to development of donor-specific antibodies. We established threshold values for BAFF and BAFF-R and showed that (1) stable patients with high BAFF-R levels had a higher risk of developing graft dysfunction, (2) patients with lower levels of BAFF transcripts or a higher level of soluble BAFF had a significantly higher risk of developing donor-specific antibodies. These data suggest that BAFF constitutes a risk factor for renal graft dysfunction and development of donor-specific antibodies. They also suggest that agents targeting BAFF-R interactions may offer new therapeutic opportunities in transplantation.

How does BAFF activate B cells in patients with autoimmune diseases?

In a study in a recent issue of Arthritis Research & Therapy, Yoshimoto and colleagues demonstrate that peripheral monocytes from patients with Sjögren's syndrome (SS) produce significantly higher amounts of B cell-activating factor (BAFF) and interleukin-6 (IL-6) in comparison with normal monocytes. This difference exists at baseline and is amplified after stimulation with interferon-gamma. Increased IL-6 secretion is partially suppressed by an anti-BAFF antibody, suggesting that signal transduction pathways mediated by BAFF are implicated in the regulation of IL-6 production by monocytes. The origin and pathways involved in this higher susceptibility to BAFF-driven IL-6 induction by monocytes of patients with SS are still unknown.

Blood memory B cells are disturbed and predict the response to rituximab in patients with rheumatoid arthritis

OBJECTIVE

To examine blood B cell subsets in patients with rheumatoid arthritis (RA) prior to B cell depletion therapy and to assess their potential as predictors of clinical response to rituximab (RTX).

METHODS

Blood B cell subsets were assessed by flow cytometry in 208 RA patients included in an RTX retreatment study (assessed prior to RTX treatment) and in 47 age-matched controls. Expression of BAFF receptor (BAFF-R) on B cells and serum B cell biomarkers was also measured. B cell subsets and BAFF-R expression were compared between RA patient and control populations. Univariate and multivariate analyses were performed to identify baseline factors associated with a European League Against Rheumatism response 24 weeks after 1 cycle of RTX.

RESULTS

Mean ± SD counts of both CD27- naive and CD27+ memory B cells were decreased in RA patients (188.6 ± 121.4/mm(3)) compared with controls (257.3 ± 154.1/mm(3)) (P = 0.001) and were partially restored in patients treated with methotrexate (MTX) plus anti-tumor necrosis factor compared with patients treated with MTX alone. Within the CD27+ memory B cells, the CD27+IgD- switched memory subtype was selectively decreased, irrespective of treatment. The frequency of CD27+ memory B cells correlated inversely with levels of several B cell activation biomarkers in RA. Serum BAFF level and BAFF-R expression was comparable in RA patients and controls. A low baseline CD27+ memory B cell frequency was associated with a greater clinical response to RTX (odds ratio 0.97 [95% confidence interval 0.95-0.99], P = 0.0015).

CONCLUSION

In B cell depletion therapy-naive RA patients, a low frequency of CD27+ memory B cells correlated with levels of serum B cell activation biomarkers and may predict response to RTX. These results suggest that low memory B cell frequency may be indicative of a B cell-driven RA subtype that is more sensitive to B cell depletion therapy.

Immunodeficiency and autoimmunity: lessons from systemic lupus erythematosus

Recent evidence suggests that systemic autoimmunity and immunodeficiency are not separate entities, but rather are interconnected processes. Immunodeficiency results from distinct defects of the immune response and primarily presents as infections but also frequently with autoimmune features. Systemic autoimmunity is the combined effect of multiple genetic variations and infectious and immunoregulatory factors that result in dominant autoimmune manifestations, in addition to frequent and opportunistic infections. The overlap in disease manifestations and symptoms suggests that immunodeficiency should be considered in the presence of autoimmunity, and vice versa. In this review, we present the shared or similar aspects of immunodeficiency and autoimmunity using systemic lupus erythematosus as a paradigm and discuss the implications for clinical care.

The plasma concentration of the B cell activating factor is increased in children with acute malaria

Malaria-specific antibody responses in children often appear to be short-lived but the mechanisms underlying this phenomenon are not well understood. In this study, we investigated the relationship between the B-cell activating factor (BAFF) and its receptors expressed on B cells with antibody responses during and after acute malaria in children. Our results demonstrate that BAFF plasma levels increased during acute malarial disease and reflected disease severity. The expression profiles for BAFF receptors on B cells agreed with rapid activation and differentiation of a proportion of B cells to plasma cells. However, BAFF receptor (BAFF-R) expression was reduced on all peripheral blood B cells during acute infection, but those children with the highest level of BAFF-R expression on B cells maintained schizont-specific immunoglobin G (IgG) over a period of 4 months, indicating that dysregulation of BAFF-R expression on B cells may contribute to short-lived antibody responses to malarial antigens in children. In summary, this study suggests a potential role for BAFF during malaria disease, both as a marker for disease severity and in shaping the differentiation pattern of antigen-specific B cells.

p52 Activation in monomorphic B-cell posttransplant lymphoproliferative disorder/diffuse large B-cell lymphoma without BAFF-R expression

Posttransplantation lymphoproliferative disorders (PTLD) are associated with Epstein-Barr virus (EBV) and activate the NF-κB pathway. B-cell activating factor (BAFF) modulates cell growth and survival in non-Hodgkin's lymphomas. However, there are few studies of EBV, BAFF/BAFF-R signaling, and NF-κB1 and NF-κB2 pathway activation in PTLD. Diffuse large B-cell lymphomas (DLBCL) in two different clinical contexts, immunocompetent patients (DLBCL/IC; n = 30) or posttransplantation solid-organ recipients (DLBCL/PTLD; n = 21), were characterized histogenically as germinal center (GC) or non-germinal center (NGC). Expression of BAFF, BAFF-R, and NF-κB proteins p50 and p52 and the presence or absence of EBV were compared in these clinical contexts. Regardless of the GC or NGC pattern of DLBCL, BAFF-R was expressed in 37% of DLBCL/IC but in only 4.8% of DLBCL/PTLD. p52 was expressed in DLBCL/PTLD/NGC (12 of 19 cases) as compared with DLBCL/IC/NGC (0 of 18 cases). This pattern might be related to the presence of EBV and latent membrane protein 1 because p52 expression was observed primarily in EBV-positive DLBCL/PTLD cases expressing latent membrane protein 1. Thus, the activation profile or NGC pattern of DLBCL/PTLD was not associated with BAFF/BAFF-R expression, whereas nuclear p52 related to NF-κB2 pathway activation might be linked to EBV.

Pathway of Toll-like receptor 7/B cell activating factor/B cell activating factor receptor plays a role in immune thrombocytopenia in vivo

Immune thrombocytopenia (ITP) is an autoimmune disorder characterized by anti-platelet autoantibody-mediated platelet destruction. Antigen-presenting cell (APC) dysfunction is considered to play crucial roles in ITP. However, how APC affects autoreactive B cells in ITP is still unknown. Using a mouse model of immune thrombocytopenia, we demonstrated an increase in levels of TLR7 in splenic mononuclear cells (SMCs). Using both TLR7 agonist and TLR7 silencing lentivirus, we found stimulation of TLR7 decreased platelet counts and increased levels of platelet-associated IgG (PAIgG) in ITP mice, which correlates TLR7 with platelet destruction by autoantibodies. Levels of serum BAFF increased significantly in ITP mice and stimulation of TLR7 promoted secretion of BAFF. Among the three BAFF receptors, only BAFF receptor (BAFF-R) increased in ITP mice. However, activation of TLR7 showed no effect on the expression of BAFF receptors. These findings indicate that upregulation of TLR7 may augment BAFF secretion by APC and through ligation of BAFF-R promote autoreactive B cell survival and thus anti-platelet autoantibody production. The pathway of TLR7/BAFF/BAFF-R provides us with an explanation of how activation of APC affects autoantibody production by B cells in ITP and thus might provide a reasonable therapeutic strategy for ITP.

Anti-M(3) muscarinic cholinergic autoantibodies from patients with primary Sjögren's syndrome trigger production of matrix metalloproteinase-3 (MMP-3) and prostaglandin E(2) (PGE(2)) from the submandibular glands

BACKGROUND

We demonstrated that serum immunoglobulin G (IgG) from patients with primary Sjögren's syndrome (pSS), interacting with the second extracellular loop of human glandular M(3) muscarinic acetylcholine receptors (M(3) mAChR), trigger the production of matrix metalloproteinase-3 (MMP-3) and prostaglandin E(2) (PGE(2)).

METHODS

Enzyme-linked immunosorbent assays (ELISAs) were performed in the presence of M(3) mAChR synthetic peptide as antigen to detect in serum the autoantibodies. Further, MMP-3 and PGE(2) production were determined in the presence of anti-M(3) mAChR autoantibodies.

RESULTS

An association was observed between serum and anti-M(3) mAChR autoantibodies and serum levels of MMP-3 and PGE(2) in pSS patients. Thus, we established that serum anti-M(3) mAChR autoantibodies, MMP-3 and PGE(2) may be considered to be early markers of pSS associated with inflammation. Affinity-purified anti-M(3) mAChR peptide IgG from pSS patients, whilst stimulating salivary-gland M(3) mAChR, causes an increase in the level of MMP-3 and PGE(2) as a result of the activation of phospholipase A(2) (PLA(2)) and cyclooxygenase-2 (COX-2) (but not COX-1).

CONCLUSIONS

These results provide a novel insight into the role that cholinoceptor antibodies play in the development of glandular inflammation. This is the first report showing that an antibody interacting with glandular mAChR can induce the production of pro-inflammatory mediators (MMP-3/PGE(2)).

Expressions of BAFF/BAFF receptors and their correlation with disease activity in Chinese SLE patients

B-cell activating factor belonging to tumour necrosis factor family (BAFF) is essential for B-cell survival and function through interaction with its receptors BAFF receptor 3 (BR3), B-cell maturation antigen (BCMA) and/or transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI), though BCMA and/or TACI can also bind to a proliferation-inducing ligand (APRIL). We evaluate the correlation of the expressions of these ligands/receptors with different clinical manifestations of systemic lupus erythematosus (SLE). Levels of BAFF and APRIL in plasma from 73 SLE patients were determined by enzyme-linked immunosorbent assay. Expressions of BR3, TACI and BCMA on CD19+ B cells were detected by flow cytometry. Clinical data were collected and disease activity was evaluated using SLEDAI-2000. SLE patients had elevated BAFF and APRIL levels in their plasma. BAFF levels correlated positively with SLEDAI while negatively with the BR3 protein expression on CD19+ B cells (p < .05). The detected BR3 protein expression in SLE patients was reduced on CD19+IgD+CD27-, CD19+IgD+CD27+ as well as CD19+IgD-CD27+ B cells compared to the counterparts of healthy controls (p < .001), whereas SLE patients did not differ from healthy controls in BR3 mRNA levels. In untreated new-onset patients, the expression rate of BR3 on CD19+ B cells correlated negatively with SLEDAI (p < .05). Elevation of BAFF and reduction of BR3 on CD19+ B cells were more obvious in those with lupus nephritis (LN, p < .05). TACI expression on CD19+ B cells was up-regulated only in those subjects with LN (p < .05). Elevated plasma BAFF and reduced BR3 protein expression on peripheral B cells could act as biomarkers for active disease in SLE patients. High expression of TACI may indicate the occurrence of LN.