Circulating plasmablasts and high level of BAFF are hallmarks of minimal change nephrotic syndrome in adults

Serum BAFF levels are associated with the prognosis of idiopathic membranous nephropathy

OBJECTIVE

High serum levels of B-cell activation factor (BAFF) and a proliferation-inducing ligand (APRIL) have been observed in patients with idiopathic membranous nephropathy (iMN); however, their relationships with disease severity and progression remain unclear.

METHODS

Patients with iMN diagnosed via renal biopsy were enrolled in this study. The concentrations of BAFF and APRIL were determined using ELISA kits. Proteinuria remission, including complete remission (CR) and partial remission (PR), and renal function deterioration were defined as clinical events. The Cox proportional hazards method was used to analyze the relationship between cytokine levels and disease progression.

RESULTS

Seventy iMN patients were enrolled in this study, with a median follow-up time of 24 months (range 6-72 months). The serum levels of BAFF and APRIL were higher in iMN patients than in healthy controls but lower than those in minimal change disease (MCD) patients. The serum BAFF level was positively correlated with the serum APRIL level, serum anti-phospholipase A2 receptor (anti-PLA2R) antibody level, and 24-h proteinuria and negatively correlated with the serum albumin (ALB) level. However, no significant correlation was observed between the serum APRIL level and clinical parameters. According to the multivariate Cox proportional hazards regression model adjusted for sex, age, systolic blood pressure (SBP), estimated glomerular filtration rate (eGFR), immunosuppressive agent use, 24-h proteinuria, APRIL level, and anti-PLA2R antibody, only the serum BAFF level was identified as an independent predictor of PR (HR, 0.613; 95% CI, 0.405-0.927; p = 0.021) and CR of proteinuria (HR, 0.362; 95% CI, 0.202-0.648; p < 0.001).

CONCLUSIONS

A high serum BAFF level is associated with severe clinical manifestations and poor disease progression in patients with iMN.

B cell dysregulation and depletion therapy in primary membranous nephropathy: Prospects and potential challenges

B cells are crucial to the humoral immune response, originating in the bone marrow and maturing in the spleen and lymph nodes. They primarily function to protect against a wide range of infections through the secretion of antibodies. The role of B cells in primary membranous nephropathy (PMN) has gained significant attention, especially following the discovery of various autoantibodies that target podocyte antigens and the observed positive outcomes from B cell depletion therapy. Increasing evidence points to the presence of abnormal B cell subsets and functions in MN. B cells have varied roles during the different stages of disease onset, progression, and relapse. Initially, B cells facilitate self-antigen presentation, activate effector T cells, and initiate cellular immunity. Subsequently, the disruption of both central and peripheral immune tolerance results in the emergence of autoreactive B cells, with strong germinal center responses as a major source of MN autoantibodies. Additionally, critical B cell subsets, including Bregs, memory B cells, and plasma cells, play roles in the immune dysregulation observed in MN, assisting in predicting disease recurrence and guiding management strategies for MN. This review offers a detailed overview of research advancements on B cells and elucidates their pathological roles in MN.

Overview of Immunological Response in Urological Membranous Nephropathy: Focus on Cytokine and Treatment Options

Membranous nephropathy (MN) is an autoimmune disease that is caused by the production of autoantibody against glomerular podocyte antigens by immune cells due to the lack of self-tolerance mechanisms. Similar to many autoimmune diseases, the pathogenesis of MN is still vague and many experiments are being conducted to detect the antigens and genetic reasons for MN illness. Recently, new antigens, such as exotosin 1/exotosin 2, neural EGF-like-1, semaphorin 3B, and protocadherin 7 have been identified in MN patients who did not have presence of antiphospholipase A2 receptor antigen. What is more, cytokines, which are molecules that regulate immune responses, have been found to have harmful effects in various autoimmune diseases, including multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus, and MN. The role of cytokines and treatment strategies in MN patients is discussed in this article. As the understanding of the disease improves, targeted therapies that focus on specific antigens or cytokines may be developed to effectively manage MN.

Role of the Innate Immune Response in Glomerular Disease Pathogenesis: Focus on Podocytes

Accumulating evidence indicates that inflammatory and immunologic processes play a significant role in the development and progression of glomerular diseases. Podocytes, the terminally differentiated epithelial cells, are crucial for maintaining the integrity of the glomerular filtration barrier. Once injured, podocytes cannot regenerate, leading to progressive proteinuric glomerular diseases. However, emerging evidence suggests that podocytes not only maintain the glomerular filtration barrier and are important targets of immune responses but also exhibit many features of immune-like cells, where they are involved in the modulation of the activity of innate and adaptive immunity. This dual role of podocytes may lead to the discovery and development of new therapeutic targets for treating glomerular diseases. This review aims to provide an overview of the innate immunity mechanisms involved in podocyte injury and the progression of proteinuric glomerular diseases.

Alterations of B-Cell subsets in Peripheral Blood from Adult Patients with Idiopathic Membranous Nephropathy

OBJECTIVES

Idiopathic membranous nephropathy (MN) is an autoimmune disease characterized by specific antibodies. However, the underlying mechanisms by which lymphocytes promote the development of MN remain poorly understood. This study aims to determine the changes of B-cell subsets and their clinical significance in MN patients.

METHODS

We included a cohort of 21 idiopathic MN patients with new onset or a relapse, 19 healthy controls (HCs) and 10 patients with minimal change disease (MCD). Immunohistochemistry and flow cytometry were performed to assess the B-cell infiltration in renal biopsy tissues and peripheral blood, respectively.

RESULTS

Idiopathic MN patients (including new-onset and relapse groups) had lower percentages of marginal-zone B (MZB) and non-switched memory B cells, and higher percentages of plasmablasts than HCs (P < 0.01). Particularly, the new-onset group had lower percentages of switched memory B cells and MZB cells, and higher percentages of Naïve B cells than HCs (P<0.05). Interestingly, the percentage of plasmablasts was significantly correlated with urine protein to creatinine ratio, serum albumin, IgG, anti-M-type phospholipase A2 receptor antibody level and age in MN patients (P < 0.05). MN with Ehrenreich-Churg stage Ⅱ-Ⅳ had a lower median percentage of MZB and non-switched memory B cells, while a higher median percentage of plasmablasts than those in MN patients with stage Ehrenreich-Churg I (P < 0.05).

CONCLUSION

Idiopathic MN patients had specific changes in B-cell subsets proportions in peripheral blood. Further studies are needed to precisely determine the roles of B-cell subsets in MN.

Understanding the podocyte immune responses in proteinuric kidney diseases: from pathogenesis to therapy

The glomerular filtration barrier, comprising the inner layer of capillary fenestrated endothelial cells, outermost podocytes, and the glomerular basement membrane between them, plays a pivotal role in kidney function. Podocytes, terminally differentiated epithelial cells, are challenging to regenerate once injured. They are essential for maintaining the integrity of the glomerular filtration barrier. Damage to podocytes, resulting from intrinsic or extrinsic factors, leads to proteinuria in the early stages and eventually progresses to chronic kidney disease (CKD). Immune-mediated podocyte injury is a primary pathogenic mechanism in proteinuric glomerular diseases, including minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, and lupus nephritis with podocyte involvement. An extensive body of evidence indicates that podocytes not only contribute significantly to the maintenance of the glomerular filtration barrier and serve as targets of immune responses but also exhibit immune cell-like characteristics, participating in both innate and adaptive immunity. They play a pivotal role in mediating glomerular injury and represent potential therapeutic targets for CKD. This review aims to systematically elucidate the mechanisms of podocyte immune injury in various podocyte lesions and provide an overview of recent advances in podocyte immunotherapy. It offers valuable insights for a deeper understanding of the role of podocytes in proteinuric glomerular diseases, and the identification of new therapeutic targets, and has significant implications for the future clinical diagnosis and treatment of podocyte-related disorders.

The extrafollicular B cell response is a hallmark of childhood idiopathic nephrotic syndrome

The efficacy of the B cell-targeting drug rituximab (RTX) in childhood idiopathic nephrotic syndrome (INS) suggests that B cells may be implicated in disease pathogenesis. However, B cell characterization in children with INS remains limited. Here, using single-cell RNA sequencing, we demonstrate that a B cell transcriptional program poised for effector functions represents the major immune perturbation in blood samples from children with active INS. This transcriptional profile was associated with an extrafollicular B cell response marked by the expansion of atypical B cells (atBCs), marginal zone-like B cells, and antibody-secreting cells (ASCs). Flow cytometry of blood from 13 children with active INS and 24 healthy donors confirmed the presence of an extrafollicular B cell response denoted by the expansion of proliferating RTX-sensitive extrafollicular (CXCR5-) CD21low T-bet+ CD11c+ atBCs and short-lived T-bet+ ASCs in INS. Together, our study provides evidence for an extrafollicular origin for humoral immunity in active INS.

Current understanding of the molecular mechanisms of circulating permeability factor in focal segmental glomerulosclerosis

The pathogenetic mechanisms underlying the onset and the post-transplant recurrence of primary focal segmental glomerulosclerosis (FSGS) are complex and remain yet to be fully elucidated. However, a growing body of evidence emphasizes the pivotal role of the immune system in both initiating and perpetuating the disease. Extensive investigations, encompassing both experimental models and patient studies, have implicated T cells, B cells, and complement as crucial actors in the pathogenesis of primary FSGS, with various molecules being proposed as potential "circulating factors" contributing to the disease and its recurrence post kidney-transplantation. In this review, we critically assessed the existing literature to identify essential pathways for a comprehensive characterization of the pathogenesis of FSGS. Recent discoveries have shed further light on the intricate interplay between these mechanisms. We present an overview of the current understanding of the engagement of distinct molecules and immune cells in FSGS pathogenesis while highlighting critical knowledge gaps that require attention. A thorough characterization of these intricate immune mechanisms holds the potential to identify noninvasive biomarkers that can accurately identify patients at high risk of post-transplant recurrence. Such knowledge can pave the way for the development of targeted and personalized therapeutic approaches in the management of FSGS.

Age and memory B cells at baseline are associated with risk of relapse and memory B-cell reappearance following anti-CD20 treatment in pediatric frequently-relapsing/steroid-dependent nephrotic syndrome

B-cell depleting anti-CD20 monoclonal antibodies, such as rituximab, have proven efficacy in children with frequently-relapsing/steroid-dependent nephrotic syndrome (FR/SDNS). However, drug-free remission is variable and specific baseline markers predictive of relapse after anti-CD20 treatment are still being defined. To clarify these, we performed a bicentric observational study in a large cohort of 102 children and young adults with FR/SDNS treated with anti-CD20 monoclonal antibodies (rituximab and ofatumumab). Sixty-two patients (60.8%) relapsed during a 24-month period (median [interquartile range] relapse-free survival, 14.4 months [7.9-24.0]). A lower risk of relapse was significantly associated with an older age (over 9.8 years, hazard ratio, 0.44; 95% confidence interval, 0.26-0.74) and a higher risk of relapse was significantly associated with higher circulating levels of memory B cells (1.14; 1.09-1.32) at time of anti-CD20 infusion, independent of time elapsed from onset, previous anti-CD20 treatment, type of administered anti-CD20 monoclonal antibodies, and previous or maintenance oral immunosuppression. Patients younger than 9.8 years at anti-CD20 infusion had a subsequent higher recovery of total, transitional, mature-naïve and memory B-cell subsets independent of previous anti-CD20 treatment and maintenance immunosuppression. Significantly, younger age and higher circulating levels of memory B cells at time of anti-CD20 infusion were also independently associated with the recovery of memory B cells by linear mixed-effects modelling. Thus, both younger age and higher circulating levels of memory B cells at time of infusion are independently associated with a higher risk of relapse and an earlier recovery of memory B cells following anti-CD20 treatment in children with FR/SDNS.

Immunophenotypic Alterations in Adult Patients with Steroid-Dependent and Frequently Relapsing Nephrotic Syndrome

Immune dysregulation plays a key role in the pathogenesis of steroid-dependent/frequently relapsing nephrotic syndrome (SDNS/FRNS). However, in contrast with evidence from the pediatric series, no major B- or T-cell alterations have been described for adults. In these patients, treatment with rituximab allows safe discontinuation of steroids, but long-term efficacy is variable, and some patients experience NS relapses after B cell reconstitution. In this study, we aimed to determine disease-associated changes in the B and T cell phenotype of adult patients with SDND/FRNS after steroid-induced remission. We also investigated whether any of these changes in immune cell subsets could discriminate between patients who developed NS relapses after steroid-sparing treatment with rituximab from those who did not. Lymphocyte subsets in SDNS/FRNS patients (n = 18) were compared to those from patients with steroid-resistant NS (SRNS, n = 7) and healthy volunteers (HV, n = 15). Before rituximab, SDND/FRNS patients showed increased frequencies of total and memory B cells, mainly with a CD38-negative phenotype. Within the T-cell compartment, significantly lower levels of FOXP3⁺ regulatory T cells (Tregs) were found, mostly due to a reduction in CD45RO⁺ memory Tregs compared to both SRNS and HV. The levels of CD45RO⁺ Tregs were significantly lower at baseline in patients who relapsed after rituximab (n = 9) compared to patients who did not (n = 9). In conclusion, patients with SDND/FRNS displayed expansion of memory B cells and reduced memory Tregs. Treg levels at baseline may help identify patients who will achieve sustained remission following rituximab infusion from those who will experience NS relapses.

B cell phenotype, activity, and function in idiopathic nephrotic syndrome

Idiopathic nephrotic syndrome (INS) is the most frequent glomerular disease in childhood. However, its underlying etiology mechanism lacks thorough understanding. Previous studies have described INS as a T cell functional disorder resulting in increased plasma lymphocyte-derived permeability factors. In children with frequent relapses of nephrotic syndrome, the mechanism underlying the therapeutic efficacy of CD20 monoclonal antibodies in depleting B cells may provide additional evidence in exploring the critical role of B lymphocytes in INS pathogenesis. Previous studies have proposed that RTX bound to CD20 through antibody-dependent and complement-dependent cytotoxicity and led to lytic clearance of B cells. Additionally, RTX exerted an effect by blocking the interaction between B and T cells or regulating homeostasis and functions of T cell subsets. Recent studies on the development, differentiation, and activation of B-lymphocytes in glomerular diseases have suggested that the B-lymphocytes participate in the INS pathogenesis through interaction with T cells, secretion of antibodies, or production of cytokines. In this study, we aimed to provide a detailed description of the current knowledge on the development, differentiation, activity, functions, and related regulating factors of B cells involved in INS. Thus, further understanding of the immunopathogenesis of INS may offer some opportunities in precisely targeting B cells during therapeutic interventions. IMPACT: The topic "B cells play a role in glomerular disease" is a novel point, which is not completely described previously. We described interactions between T and B cells and immunoglobulin, IgG, IgM, IgE, etc. as well in glomerular disease. The research of regulatory factors associated with B cell's function, like BAFF, is a hot topic in other diseases; however, it is rare in glomerular disease.

Circulating plasmablasts in children with steroid-sensitive nephrotic syndrome

BACKGROUND

The therapeutic efficacy of B cell-depleting anti-CD20 treatment in both pediatric and adult steroid-sensitive nephrotic syndromes (SSNS) suggests that B cells play a pathogenic role in the disease. In adults with minimal change disease (MCD), only circulating plasmablasts are increased during the active phase of the disease, among B cell subsets. These cells have not been studied yet in children with SSNS.

METHODS

We retrospectively quantified by flow cytometry analysis circulating plasmablasts in 107 pediatric patients with SSNS (51 at disease onset, 27 during relapse, and 29 in remission). Data were compared with an equal number of age- and sex-matched healthy donors (HD).

RESULTS

Circulating plasmablast levels, expressed as percentage of total CD19⁺ B cells or as percentage of total lymphocytes, were normal in all SSNS subgroups, compared to HD. Patients in remission had significantly fewer circulating plasmablasts compared to patients at disease onset. No significant correlation was observed between plasmablast levels and proteinuria or serum proteins, at onset. Treatment with prednisone and mycophenolate mofetil significantly reduced circulating levels of plasmablasts, unlike treatment with prednisone and calcineurin inhibitors.

CONCLUSIONS

The B cell phenotype of children with SSNS differs from that of adults with MCD. This may justify different therapeutic approaches.

B-Cell Dysregulation in Idiopathic Nephrotic Syndrome: What We Know and What We Need to Discover

The therapeutic efficacy of B-cell depletion by anti-CD20 treatment in pediatric and, more recently, in adult idiopathic nephrotic syndrome patients suggests a key role of B cells in the pathogenesis of the disease. However, their exact role is still unclear. B cells are able to secrete a large variety of antibodies that can protect against infections. However, B-cell dysregulation is well-established in a variety of autoimmune diseases. In parallel with their ability to produce antibodies, pathogenic B cells display altered effector functions by expressing activating surface molecules, which can strongly modify the immune homeostasis, or by producing specific cytokines, which can directly affect either podocyte structure and functions or modulate T-cell homeostasis. Herein, we report the most relevant clinical and experimental evidences of a pathogenic role of B cells in idiopathic nephrotic syndrome. We further highlight similarities and differences between children and adults affected by non-genetic forms of the disease and discuss what needs to be investigated in order to define the exact mechanisms underlying the pathogenic role of B cells and to identify more tailored therapeutic approaches.

Molecular Mechanisms of Proteinuria in Minimal Change Disease

Minimal change disease (MCD) is the most common type of idiopathic nephrotic syndrome in childhood and represents about 15% cases in adults. It is characterized by massive proteinuria, edema, hypoalbuminemia, and podocyte foot process effacement on electron microscopy. Clinical and experimental studies have shown an association between MCD and immune dysregulation. Given the lack of inflammatory changes or immunocomplex deposits in the kidney tissue, MCD has been traditionally thought to be mediated by an unknown circulating factor(s), probably released by T cells that directly target podocytes leading to podocyte ultrastructural changes and proteinuria. Not surprisingly, research efforts have focused on the role of T cells and podocytes in the disease process. Nevertheless, the pathogenesis of the disease remains a mystery. More recently, B cells have been postulated as an important player in the disease either by activating T cells or by releasing circulating autoantibodies against podocyte targets. There are also few reports of endothelial injury in MCD, but whether glomerular endothelial cells play a role in the disease remains unexplored. Genome-wide association studies are providing insights into the genetic susceptibility to develop the disease and found a link between MCD and certain human haplotype antigen variants. Altogether, these findings emphasize the complex interplay between the immune system, glomerular cells, and the genome, raising the possibility of distinct underlying triggers and/or mechanisms of proteinuria among patients with MCD. The heterogeneity of the disease and the lack of good animal models of MCD remain major obstacles in the understanding of MCD. In this study, we will review the most relevant candidate mediators and mechanisms of proteinuria involved in MCD and the current models of MCD-like injury.

Involvement of Hemopexin in the Pathogenesis of Proteinuria in Children with Idiopathic Nephrotic Syndrome

Hemopexin (Hpx) is considered a factor in the pathogenesis of idiopathic nephrotic syndrome (INS). The aim of the study was to evaluate the serum and urine values of Hpx (sHpx and uHpx) in children with INS, analyze the role of Hpx, and assess its usefulness as a marker of the disease course. 51 children with INS and 18 age-matched controls were examined. Patients were divided into subgroups depending on the number of relapses (group IA-the first episode of INS, group IB-with relapses) and according to method of treatment (group IIA treated with gluco-corticosteroids (GCS), group IIB treated with GCS and other immunosuppressants). Hpx concentrations were determined by enzyme-linked immunosorbent assay (ELISA). sHpx and uHpx values in relapse were elevated in the whole INS group versus controls (p < 0.000). In remission their levels decreased, but still remained higher than in the control group (p < 0.000). In group IB uHpx levels were increased during remission as compared to group IA (p < 0.006). No significant impact of immuno-suppressants on sHpx was observed, but uHpx excretion in group IIA was higher in relapse (p < 0.026) and lower in remission (p < 0.0017) as compared to group IIB. The results suggest the role of Hpx in the pathogenesis of INS. Hpx may be a useful indicator for continuation of treatment, but it requires confirmation by further controlled studies.

B Lymphocyte Subsets in Children With Steroid-Sensitive Nephrotic Syndrome: A Longitudinal Study

Background: B-cell subsets may be involved in the pathogenesis of childhood steroid-sensitive nephrotic syndrome (SSNS). Horizontal control studies have shown that homeostasis of B-cell subsets changes at different stages of the SSNS. However, there is a lack of longitudinal studies that have investigated dynamic changes in B cell subpopulations. Methods: Blood samples were collected at the following time points from 15 children with SSNS treated at our hospital: before administration of steroid and after 3 days, 1 week, and 3, 6, 9, and 12 months. The proportions of circulating total B cells (CD19⁺), transitional B cells (CD19⁺CD24^highCD38^high), mature B cells (CD19⁺CD24^lowCD38^intermediate), and memory B cells (CD19⁺CD24^highCD38^-) were monitored by flow cytometry. Results: The proportion of CD19+ B cells before steroid administration was significantly higher than that observed at any other time point or in the healthy control (HC) group (p < 0.001). However, this proportion was significantly lower than that in the HC group at 12 months (p = 0.031). Transitional B cells before (%BL 9.5 ± 4.4) and 3 days after steroid administration (%BL 10.6 ± 5.1) were significantly higher than at any other time point or in the HC group (p < 0.001). Although these cells declined after the 3rd day the percentage was still significantly lower than that of the HC group at 12 months (p = 0.029). Memory B cells increased gradually after steroid administration and decreased to the normal range after 9 months. Conclusions: B cell subpopulations show dynamic changes in children with SSNS, suggesting that they are involved in the pathogenesis of the disorder. Further studies are required to determine whether this change can guide individualized treatment.