Mayo Clinic consensus report on membranous nephropathy: proposal for a novel classification

How to Choose Treatment Regimens for Idiopathic Membranous Nephropathy Patients with PLA2R-Negative: A Single-Center Retrospective Cohort Study

Background

Cyclophosphamide, tacrolimus, and rituximab (RTX) are first-line treatments for idiopathic membranous nephropathy (IMN), regardless of PLA2R status. While the efficacy of RTX in IMN patients with PLA2R-positive has been well-documented, its effectiveness in IMN patients with PLA2R-negative remains understudied. This study aimed to evaluate the efficacy and adverse events of these three treatment regimens in IMN patients with PLA2R-negative.

Methods

This study included 46 PLA2R-negative IMN patients confirmed by renal biopsy and immunofluorescence from the Department of Nephrology, the Second Affiliated Hospital of Nanchang University between September 2021 and October 2023. We compared clinical remission rates, and side effects at 3, 6, and 12 months follow-up in 14 patients who received prednisolone combined with cyclophosphamide (cyclophosphamide group), in 11 patients who treated with prednisolone combined with tacrolimus (tacrolimus group), and 21 patients who treated with rituximab (RTX group).

Results

Baseline characteristics were similar among the three groups. At the 12-month follow-up, the complete response rate was significantly higher in the cyclophosphamide and tacrolimus groups compared to the RTX group (p = 0.029). However, there were no significant differences in cumulative complete remission rates or cumulative composite remission rates among the three groups during the follow-up period (p = 0.192, p = 0.212). Severe adverse events occurred in all groups, but the differences were not statistically significant (p > 0.05).

Conclusion

Cyclophosphamide and tacrolimus appear to offer long-term benefits for PLA2R-negative IMN patients, with tacrolimus demonstrating superior efficacy among the treatment options evaluated. These insights offer important guidance for clinical decision-making in the management of PLA2R-negative IMN. However, further large-scale, multicenter studies with long-term follow-up are necessary to confirm these findings.

Malignancies and glomerulonephritis: when to suspect and when to screen?

Glomerular diseases may occur secondary to malignancies. Age-specific cancer screening is recommended for patients with glomerular diseases and may be extended based on the specific risk associated with the detected histopathologic pattern. Membranous nephropathy is the prototype of cancer-associated glomerulonephritis, with 10% of cases presenting with malignancy within a year from diagnosis. Among antigens that are expressed in patients with membranous nephropathy thrombospondin type 1 domain-containing 7A and neural epidermal growth factor-like-1 are often reported in patients with underlying malignancies. However, the risk of having a concurrent malignancy does not exceed 25%-30% when these antigens are expressed. While less frequent in other glomerulonephritides, co-occurrence of malignancy is reported in a substantial proportion of glomerular diseases including IgA nephropathy, podocytopathies with prominent podocyte foot process effacement such as minimal change disease as glomerular lesion pattern, amyloidosis, C3 glomerulopathy, monoclonal immunoglobulin deposition disease, or immune-complex-mediated glomerulonephritis. Treatment of malignancy-associated glomerulonephritis is usually directed toward treatment of the underlying malignancy with combinations of surgery, chemotherapy, and/or radiotherapy. Moreover, relapse of the malignancy may result in recurrence of glomerulonephritis. Refractoriness of glomerulonephritis to initial therapy may be due to an occult primary malignancy that was not diagnosed during initial cancer screening. In such a scenario a step-up diagnostic approach is recommended. In addition, re-screening may be sensible for relapsing patients who carry higher risks for cancer including patients of older age and those with a smoking history. This review focuses on the description of malignancies in the context of glomerular diseases and provides practical guidance on screening.

Designing clinical trials for the treatment of membranous nephropathy in the anti-PLA2R era: results of a Nephcure membranous nephropathy workshop

Primary membranous nephropathy is a common cause of adult-onset nephrotic syndrome, with an overall incidence of 12 cases per million per year. Primary membranous nephropathy is an autoimmune kidney disease; however, primary membranous nephropathy autoantigens remained elusive until 2009 when the M-type phospholipase A2 receptor 1 (PLA2R) was identified as a disease autoantigen. This was followed relatively rapidly by identification of several other autoantigens. Autoantibodies against PLA2R are detectable in ≈75% of patients with primary membranous nephropathy. The discovery of circulating and deposited autoantibodies against PLA2R offers an opportunity in nephrology to personalize disease management. On January 14, 2023, Nephcure Kidney International convened a scientific workshop in Arlington, Virginia, to discuss the state of the science on autoantibodies against PLA2R and considerations related to the incorporation of autoantibodies against PLA2R in drug development programs for membranous nephropathy. The present report captures the discussion that occurred at the Membranous Nephropathy Scientific Workshop.

Risk factors and predictive model for renal outcomes in autoimmune membranous nephropathy with and without acute kidney injury: a retrospective cohort study

Objective

This study aimed to delineate the risk factors affecting renal outcomes in autoimmune membranous nephropathy (aMN) with or without acute kidney injury (AKI) and develop a predictive model.

Methods

This retrospective cohort study included 441 patients with biopsy-confirmed aMN from the First Affiliated Hospital of Fujian Medical University (January 2010 to March 2023). Patients were grouped based on the presence of AKI and followed up until a renal endpoint event (progression to end-stage renal disease, initiation of dialysis, or either a >40% decline in estimated glomerular filtration rate from baseline or a doubling of serum creatinine levels from baseline, both sustained for ≥3 months) or study endpoint (March 2024). Clinicopathological and renal outcomes were collected and analyzed. Risk factors for renal endpoints were identified via Cox regression analyses, and a nomogram was constructed. Model performance was evaluated using the C-index, time-dependent receiver operating characteristic (Time-ROC) curves, calibration curves, and decision curve analysis (DCA). Kaplan-Meier survival curves compared renal survival between AKI subgroups.

Results

Among 441 patients, 109 (24.72%) experienced AKI. Renal endpoint events occurred in 40.4% of the AKI group and 4.5% of the non-AKI group. Multivariate Cox regression identified AKI (HR = 7.298, P < 0.001), triglycerides (HR = 1.140, P = 0.002), serum creatinine (HR = 1.008, P = 0.012), hematuria (HR = 2.246, P = 0.040), and kidney anti-M-type phospholipase A2 receptor staining 4+ (HR = 2.473, P = 0.003) as independent risk factors, while serum C3 (HR = 0.082, P < 0.001) was an independent protective factor. The nomogram had a C-index of 0.845 (P < 0.001), with Time-ROC AUCs of 0.92, 0.81, 0.83, and 0.87 for 3 to 6 years, respectively. Calibration plots revealed good consistency between the predicted and actual probabilities. DCA indicated that the nomogram had potential clinical utility. Kaplan-Meier analysis showed lower cumulative renal survival in patients with AKI (P < 0.001).

Conclusions

The risk factor model suggests that renal outcomes in patients with aMN can be predicted. Early assessment and management targeting these identified risk factors could help delay renal function decline in these patients.

Drug-Induced Membranous Nephropathy: Piecing Together Clues to Understand Disease Mechanisms

There is a resurgence of interest in drug-induced membranous nephropathy because of the widespread availability of recently discovered culprit medications, such as lipoic acid supplements, mercury in skin-lightening creams, and nonsteroidal anti-inflammatory drugs, and the relationship between these drugs and newly described target antigens. The clinical syndromes associated with drug-induced membranous nephropathy are similar in that proteinuria ranges from low grade to nephrotic range and generally remits within months of drug cessation. Histology is notable for subepithelial deposits that are IgG1 subclass predominant, sometimes with a unique segmental distribution. The two antigens associated with drug-induced membranous nephropathy are neural epidermal growth factor-like 1 and proprotein convertase subtilisin/kexin type 6. Notably, several of the culprit drugs contain one or more sulfhydryl groups that may have potential mechanistic relevance. In this review, we explore past research investigations into mechanisms of membranous nephropathy associated with gold salts, penicillamine, and mercury and use these historical studies as the basis for formulating new hypotheses on how drugs might promote immune dysregulation and, ultimately, membranous nephropathy.

Pembrolizumab-Mediated Complete Remission of a PLA2R-Positive Paraneoplastic Membranous Nephropathy: A Case Report

Management of paraneoplastic membranous nephropathy (MN) is directed toward the underlying malignancy, and prescriptions of immune checkpoint inhibitors (ICIs) are skyrocketing in the field of oncology. However, this drug category is usually discouraged for patients with autoimmune disorders (AIDs) because it might trigger immune-related adverse events (irAEs) in the form of flare-ups or even genesis of AID. Yet, nothing is known about the efficacy and safety of ICIs for cancers associated with paraneoplastic MN. Here, we report a rare case of PLA2R-positive MN related to a PDL1-positive locally advanced lung adenocarcinoma. Antineoplastic treatment with the anti-PD1 pembrolizumab as a first-line, single-drug therapy allowed for both cancer and nephropathy remissions. To date, to our knowledge, this is the first description of a (PLA2R-positive) paraneoplastic MN that was put into remission via an ICI monotherapy successfully targeting the associated neoplasia only, without additional immunosuppressive agents.

Mass Spectrometry With Data-Independent Acquisition for the Identification of Target Antigens in Membranous Nephropathy

RATIONALE & OBJECTIVE

In recent years, the strategy of using laser capture microdissection and mass spectrometry (LCM/MS) has expanded the landscape of antigens associated with membranous nephropathy (MN). Specific associations with phenotypes, diseases, and sometimes reversible triggers led to an antigen-based classification of MN, informing precision medicine and highlighting the potential value of routine use of proteomics in classifying MN. This study reproduces and further improves the original LCM/MS for antigen detection in MN.

STUDY DESIGN

Retrospective cohort study using residual material from kidney biopsies.

SETTING & PARTICIPANTS

We applied LCM/MS to kidney biopsy specimens from 64 individuals, including 31 healthy controls; 5 with M-type phospholipase A2 receptor (PLA2R)-associated MN; 23 with PLA2R-negative MN; and 5 individuals with other glomerular diseases.

PREDICTOR

Proteomic analysis of microdissected glomeruli.

OUTCOME

Protein abundance and C3 fragments in PLA2R-MN specimens versus controls; identification of target antigens in PLA2R-negative MN.

ANALYTICAL APPROACH

The technique of LCM/MS was expanded by integrating a data-independent acquisition (DIA) approach to enable the identification and quantification of peptides of varying abundance.

RESULTS

We observed significant enrichment in PLA2R, IgG4, and complement proteins, providing molecular evidence for complement activation in glomeruli from patients with PLA2R-MN. Compared with conventional data-dependent acquisition (DDA), DIA increased the number of glomerular proteins (∼3,800 vs ∼1,200) identified in healthy glomeruli, allowed the detection of all known antigens except NELL1 in normal glomeruli, and increased the detection rate of antigens from 46% to 83% in PLA2R-negative MN.

LIMITATIONS

Retrospective design; sample size; no identification of novel antigens.

CONCLUSIONS

An integrative approach combining LCM/MS and DIA enabled identification of more target antigens than LCM/MS with DDA, potentially informing our understanding of disease mechanisms in MN.

PLAIN-LANGUAGE SUMMARY

Membranous nephropathy is an autoimmune kidney disease characterized by circulating autoantibodies that recognize antigens in podocytes or in the glomerular basement membrane. To date, more than 10 different antigens have been identified, with specific associations with various etiologies and potential impact on management. In this study, proteomic analyses were implemented on glomeruli microdissected from kidney biopsies in patients with membranous nephropathy and appropriate controls. The original technique of proteomic analysis developed by Sethi and coworkers was expanded by applying a specific and more sensitive mass spectrometry method (data-independent acquisition) combined with bioinformatics analysis. We showed that this approach is a powerful tool to detect target antigens, and it may provide insights into disease mechanisms, with the potential to inform clinical diagnosis and classification of membranous nephropathy.

Bucillamine-induced membranous nephropathy versus primary membranous nephropathy: comparing pathological features and kidney prognosis

To evaluate the pathological and clinical course differences between bucillamine‑induced membranous nephropathy (BCL-MN) and primary membranous nephropathy (p-MN). This retrospective cohort study included 29 BCL-MN patients and 98 p-MN patients at two hospitals from 2000 to 2019. We compared the kidney biopsy findings and clinical course between the BCL-MN and p-MN groups, focusing on pathological differences, proteinuria relapse rates, and 30% or greater decrease in the eGFR. While kidney function and proteinuria levels were similar, histopathological differences were observed. BCL-MN group showed less spike formation in LM and more stage I cases. IgG1 was predominant in BCL-MN group, contrasting with IgG4 in p-MN group. BCL-MN group had significantly higher prevalence of segmental subepithelial deposits (66.7% vs. 24.7%, p < 0.001) and para-mesangial deposits (61.5% vs. 18.1%, p < 0.001). Notably, foot process effacement in areas without dense deposits was more common in BCL-MN (96.3% vs. 4.6%, p < 0.001). Clinically, the majority of patients in the BCL-MN group experienced proteinuria resolution after 1 year of drug discontinuation alone, and there was no progression of renal function decline. BCL-MN differs from p-MN both histologically and clinically, which may be related to the mechanism induced by BCL.

Immune Imbalance in Primary Membranous Nephropathy at Single-cell Resolution

BACKGROUND

Primary membranous nephropathy (pMN) often progresses to end-stage renal disease (ESRD) in the absence of immunosuppressive therapy. The immunological mechanisms driving pMN progression remain insufficiently understood.

METHODS

We developed a single-cell transcriptomic profile of peripheral blood mononuclear cells (PBMCs) from 11 newly-diagnosed pMN patients and 5 healthy donors. Through correlation analysis, we identified potential biomarkers for disease stratification and poor prognosis.

RESULTS

Expression levels of several proinflammatory factors were significantly increased in patients compared to healthy donors, such as interleukins (IL1B, IL8, and IL15) and interferon G (IFNG). Multiple pattern recognition receptors involved in proinflammatory signaling were also upregulated in patients, including NOD-like receptors (NLRs) (NLRP1, NLRP3, and NLRC5), RNA helicases (DDX58, IFIH1, DHX9, and DHX36), cGAS (cyclic GMP-AMP synthase) and IFI16 (interferon gamma inducible protein 16). Additionally, human leukocyte antigen molecules HLA-DQA1 and HLA-DRB1 enriched in memory B cells were upregulated in patients. More importantly, we found that the genes for antiviral defense response were significantly elevated in high-risk patients relative to the low-risk group. More than twenty genes were negatively correlated with estimated glomerular filtration rate (eGFR), such as BST2 (bone marrow stromal cell antigen 2) and SLC35F1 (solute carrier family 35 member F1). Their predicted values were confirmed in a larger population with nephrotic syndrome or other chronic kidney diseases from a public database. Furthermore, we developed a series of scoring systems for distinguishing high-risk patients from low- and moderate-risk individuals.

CONCLUSIONS

Our study provides insight into the immunological mechanism of pMN and identifies numerous biomarkers and signaling pathways as potential therapeutic targets for managing the progression of high-risk pMN.

Membranous Nephropathy Target Antigens Display Podocyte-Specific and Non-Specific Expression in Healthy Kidneys

BACKGROUND/OBJECTIVES

Autoimmunity towards podocyte antigens causes membranous nephropathy (MN). Numerous MN target antigens (MNTAgs) have been reported, including PLA2R1, THSD7A, NTNG1, TGFBR3, HTRA1, NDNF, SEMA3B, FAT1, EXT1, CNTN1, NELL1, PCDH7, EXT2, PCSK6, and NCAM1, but their podocyte expression has not been thoroughly studied.

METHODS

We screened CZ CELLxGene single-cell RNA (scRNA) sequence datasets for those of adult, fetal, and mouse kidneys and analyzed the above MNTAgs' expression.

RESULTS

In adult kidneys, most MNTAgs are present in podocytes, except PCSK6 and NCAM1. PLA2R1 is expressed significantly more than other MNTAgs in podocytes and is a major podocyte marker, consistent with PLA2R1 as the dominant MNTAg. Additionally, PLA2R1 is a top-upregulated gene in the podocytes of chronic kidney disease, acute kidney injury, and diabetic nephropathy, indicating its general role in causing podocyte injury. PLA2R1, NTNG1, HTRA1, and NDNF display podocyte-enriched expression along with elevated chromatin accessibility in podocytes, suggesting transcription initiation contributing to their preference expression in podocytes. In the fetal kidney, most MNTAgs are expressed in podocytes. While PLA2R1 is weakly present in podocytes, SEMA3B is abundantly expressed in immature and mature podocytes, supporting SEMA3B as a childhood MNTAg. In mouse kidneys, Thsd7a is the only MNTAg with a prominent level and podocyte-specific expression. Conclusions: Most MNTAgs are present in podocytes in adults and during renal development. In adults, PLA2R1 expression is highly enriched in podocytes and significantly upregulated in multiple kidney diseases accompanied by proteinuria. In mouse kidneys, Thsd7a is specifically expressed in podocytes at an elevated level.

The spectrum and prognosis of Sjögren's syndrome with membranous nephropathy

Background

This study aims to investigate the spectrum and prognosis of membranous nephropathy (MN) in patients with Sjögren's syndrome (SS).

Methods

SS patients with biopsy-proven kidney involvement who were diagnosed at our center between April 2007 and February 2024 were retrospectively reviewed and analyzed.

Results

A total of 290 SS patients with kidney involvement were enrolled. The frequency of MN increased from 16.28% during the 2007-2010 period to 44.05% during the 2021-2024 period. After 2016, MN became the most common renal pathologic type, surpassing tubulointerstitial nephritis. PLA2R antibody or antigen was detected in 74 SS-MN patients, in whom 37 (50%) showed a negative result. Within the PLA2R-negative group, five out of 15 showed positivity for EXT1/EXT2 antigen and one out of eight for THSD7A antigen. Sixty-one SS patients with MN were followed up for >6 months, and 44 (72.13%) of them achieved renal complete remission (CR). Compared with PLA2R-negative patients, PLA2R-positive patients spent a longer time to achieve CR (1.46 ± 1.16 vs. 0.74 ± 0.47 years, P = .015) and had a higher rate of progression to the renal endpoint (8/32 vs. 1/29, P = .028). After adjusting for age, proteinuria, and eGFR, Cox regression analysis showed that PLA2R positivity remained a risk factor for CR [HR = 0.511, 95% CI (0.262 to 0.998), P = .049].

Conclusions

MN has become the predominant renal pathologic type in SS. PLA2R-positivity testing followed by EXT1/EXT2 and THSD7A testing is recommended for SS-MN patients. Although most patients can achieve renal CR, the prognosis is usually poor in PLA2R-positive SS-MN patients.

Kidney immunology from pathophysiology to clinical translation

Kidney diseases are widespread and represent a considerable medical, social and economic burden. However, there has been marked progress in understanding the immunological aspects of kidney disease. This includes the identification of distinct intrarenal immunological niches and characterization of kidney disease endotypes according to the underlying molecular immunopathology, as well as a better understanding of the pathological roles for T cells, mononuclear phagocytes and B cells and the renal elements they target. These insights have improved the diagnosis of kidney disease. Here, we discuss new developments in our understanding of kidney immunology, focusing on immune mechanisms of disease and their translational implications for the diagnosis and treatment of kidney disease. We also describe the immune-mediated crosstalk between the kidney and other organs that influences kidney disease and extrarenal inflammation.

Global and national public awareness and interest in glomerular diseases from 2004 to 2024

Background

Glomerular diseases significantly impact global health. This study investigated public interest in five common glomerular diseases.

Methods

Google Trends™ were used to analyze search activity from January 2004 to December 2024 for IgA nephropathy (IgAN), membranous glomerulonephritis (MN), focal segmental glomerulosclerosis (FSGS), lupus nephritis (LN), and diabetic nephropathy (DN). Data were retrieved both globally and in English-speaking countries, including the United States. Monthly and yearly relative search activity were assessed and compared.

Results

Globally, IgAN had the highest average relative search activity, followed by DN, FSGS, LN, and MN. Both IgAN and FSGS exhibited declining trends, while LN showed an upward pattern. MN and DN experienced a modest decline before 2016, preceded by a slight increase. Among English-speaking countries, search interest was predominantly concentrated in five countries, primarily including the United States, United Kingdom, Canada, and Australia, with the United States consistently ranking as the leading country. For IgAN, LN, and MN, the trends observed in the United States appeared to align with global data. In contrast, search interest for FSGS exceeded global levels, while interest in DN was slightly lower than global activity. In the United States, IgAN, FSGS, and LN were most prominent in North Dakota, Massachusetts, and Delaware, respectively, while DN and MN saw peak activity in West Virginia.

Conclusion

Public engagement with glomerular diseases has not uniformly grown, at least in English-speaking countries, emphasizing the need for enhanced awareness efforts. Future analysis should prioritize search terms in the predominant language of each country.

Updated diagnostic and therapeutic management for membranous nephropathy

PURPOSE OF REVIEW

Pioneering contributions in membranous nephropathy over the last decade have greatly enhanced our comprehension of its pathogenesis, diagnosis, and treatments, igniting renewed interest in this entity. This review provides an updated perspective on the diagnosis and therapeutic management of membranous nephropathy.

RECENT FINDINGS

The identification of antiphospholipase A2 receptor (PLA2R) antibodies in 50-80% of membranous nephropathy patients was a key breakthrough. High or increasing PLA2R antibody levels are linked to persistent nephrotic syndrome and the need for targeted treatment. Given the high specificity of PLA2R antibodies, a kidney biopsy may not be required for pure nephrotic syndrome cases with no comorbidities. Over the years, various target antigens and associated conditions have been identified in membranous nephropathy patients, leading to a reclassification of membranous nephropathy. Treatment approaches vary based on baseline characteristics and changes in proteinuria and PLA2R titers. Rituximab has emerged as the first-line therapy for most patients without severe risk factors, with other emerging therapies under development.

SUMMARY

Advances in the diagnosis and treatment of membranous nephropathy have moved the management towards a more precision-based approach, though further studies and new therapies are needed for a comprehensive management strategy.

Diagnostic Immunostaining of Renal Biopsies: An Overview of Markers for Glomerular Diseases

Background

The analysis of a renal biopsy is made complex by multifactorial etiologies involving different renal compartments. Recent proteomic data, pattern-based classification, and a better understanding of various glomerular renal diseases have underscored the importance of immunohistology as an integral part of the diagnostic evaluation of renal biopsies. These include immunofluorescence on formalin-fixed paraffin-embedded renal tissue (IF-P), IgG subclass staining, typing of amyloid, and other organized deposits, classification of membranous nephropathy, etc.

Summary

We describe the recent immunohistological markers on immunofluorescence (IF) and immunohistochemistry (IHC) on fresh and formalin-fixed paraffin-embedded renal native biopsies for proper evaluation and classification of glomerular diseases. The article also provides information on the diagnostic utility, interpretation, and established antibody clones described in the literature for various glomerular diseases. The indications of IF-P in renal biopsies are also outlined.

Key Messages

Immunohistology has become integral to diagnosing and classifying various glomerular renal diseases. A specific protein or antigen-based classification has prognostic and therapeutic implications. Additionally, it provides clue for screening the patient for an underlying etiology.

Designing Clinical Trials for the Treatment of Membranous Nephropathy in the Anti-Phospholipase A2 Receptor 1 Era: Results of a NephCure Membranous Nephropathy Workshop

Primary membranous nephropathy is a common cause of adult-onset nephrotic syndrome, with an overall incidence of 12 cases per million per year. Primary membranous nephropathy is an autoimmune kidney disease; however, primary membranous nephropathy autoantigens remained elusive until 2009, when the M-type phospholipase A2 receptor 1 (PLA2R) was identified as a disease autoantigen. This was followed relatively rapidly by the identification of several other autoantigens. Autoantibodies against PLA2R are detectable in ≈75% of patients with primary membranous nephropathy. The discovery of circulating and deposited autoantibodies against PLA2R offers an opportunity in nephrology to personalize disease management. On January 14, 2023, NephCure Kidney International convened a scientific workshop in Arlington, Virginia, to discuss the state of the science on autoantibodies against PLA2R and considerations related to the incorporation of autoantibodies against PLA2R in drug development programs for membranous nephropathy. The present report captures the discussion that occurred at the Membranous Nephropathy Scientific Workshop.

Post-transplant glomerular diseases: update on pathophysiology, risk factors and management strategies

In recent years, advancements in immunosuppressive medications and post-transplant management have led to a significant decrease in acute rejection rates in renal allografts and consequent improvement in short-term graft survival. In contrast, recent data have shown an increased incidence of post-transplant glomerular diseases, which currently represent a leading cause of allograft loss. Although pathogenesis is not fully understood, growing evidence supports the role of inherited and immunological factors and has identified potential pre- and post-transplant predictors. In this review, we illustrate recent advancements in the pathogenesis of post-transplant glomerular disease and the role of risk factors and immunological triggers. In addition, we discuss potential prevention and management strategies.

Anti Phospholipase A2 Receptor 1 Antibodies and Membranous Nephropathy Recurrence After Kidney Transplantation

Introduction

Membranous nephropathy can lead to end-stage kidney disease, for which kidney transplantation is the preferred therapy. However, the disease often relapses, which can impact allograft survival.

Methods

We conducted a prospective multicenter study in France involving 72 patients with membranous nephropathy who were awaiting and then underwent kidney transplantation. In addition, we established a retrospective validation cohort of 65 patients. The primary objective was to evaluate the prognostic significance of pretransplant anti phospholipase A2 receptor 1 (PLA2R1) antibodies on the recurrence of membranous nephropathy. The study also assessed the incidence rate, time to onset, and risk factors for recurrence, as well as allograft outcome.

Results

The prospective cohort showed a 26% cumulative incidence of membranous nephropathy recurrence after a median follow-up of 23.5 months. This was confirmed by a 28% cumulative incidence after a median follow-up of 67 months in the retrospective cohort. A strong association was found between the presence of anti-PLA2R1 antibodies prior to transplantation and the risk of disease recurrence (risk ratio = 5.9; 95% confidence interval [CI]: 2.3-15.7; P < 0.0001). These results were confirmed in the retrospective cohort. Monitoring of anti-PLA2R1 antibodies in the immediate posttransplant period is of limited value, because recurrence occurred early in the first 6 months (median delay of 5 [3-14] months) after transplantation despite decreasing antibody levels.

Conclusion

The presence of anti-PLA2R1 antibodies prior to transplantation was a strong predictor of recurrence of allograft membranous nephropathy. An individualized immunomonitoring and management strategy for kidney transplant candidates with anti-PLA2R1-associated membranous nephropathy should be considered.

SARS-CoV-2 Protein Deposition Enhances Renal Complement Activation and Aggravates Kidney Injury in Membranous Nephropathy After COVID-19

Introduction

COVID-19 has been reported to be associated with the occurrence and recurrence of membranous nephropathy (MN). The clinicopathological characteristics and complement system activation of MN after COVID-19 are unclear.

Methods

A total of 38 patients with biopsy-proven MN who developed new-onset proteinuria after COVID-19 were enrolled in this study. One hundred patients with primary MN diagnosed before the COVID-19 pandemic were the control. Renal immunohistochemical staining for SARS-CoV-2 nucleocapsid protein was performed in 38 patients with MN after COVID-19. Serum membrane attack complex (MAC) was detected by enzyme-linked immunosorbent assay. Glomerular staining for the complement proteins in different pathways were detected by immunohistochemistry.

Results

Thirteen of 38 patients had positive staining for SARS-CoV-2 nucleocapsid protein. Compared with the control patients, the clinical manifestations were more severe in patients after COVID-19. Patients with positive SARS-CoV-2 staining had a higher proportion of nephrotic syndrome, lower level of serum albumin, and greater severity of renal interstitial fibrosis than those of patients with negative SARS-CoV-2 staining. Serum MAC level and renal MAC staining intensity of MN after COVID-19 were significantly higher than those of the control patients. MAC expression in MN patients with positive SARS-CoV-2 staining was stronger than that in both control patients and MN after COVID-19 with negative SARS-CoV-2 staining. The expression trend of factor H was consistent with that of MAC.

Conclusion

Excessive activation of the complement system aggravated symptoms in MN after COVID-19. Therapeutic strategy targeting the complement system may need to be considered.

A reliable clinical test for detection of membranous nephropathy antigens using laser microdissection and mass spectrometry

Membranous nephropathy (MN) results from accumulation of antigen-antibody immune complexes along the subepithelial region of the glomerular basement membranes. Over the last years, 13 target antigens have been discovered and include PLA2R, THSD7A, EXT1 and EXT2, NELL1, SEMA3B, NCAM1, CNTN1, HTRA1, FAT1, PCDH7, NTNG1, PCSK6 and NDNF, accounting for 80-90% of MN antigens. MN associated with many of these antigens have distinctive clinicopathologic findings. It is important to accurately identify the antigen in MN. Immunohistochemical (IHC) and/or immunofluorescence (IF) methods are currently used to detect PLA2R, THSD7A, NELL1, SEMA3B and EXT1/EXT2. However, for the remaining antigens, IHC/IF methods do not exist and are not practical for detection. Here, we developed laser microdissection-based mass spectrometry methodology (LMD/MS) as a one-stop clinical test for the detection of MN antigens using paraffin-embedded kidney biopsy tissue. The LMD/MS test was validated in two steps. LMD/MS was used to detect the antigen in 75 cases of MN with known antigens and correctly identified the antigen in all these cases. Next, LMD/MS was used to identify the antigen in 61 MN cases where the antigen was unknown and identified one of the known antigens in 40 of 61 cases including many of the less common antigens. This lower-than-expected detection rate is explained by intentional enrichment of the cohort with PLA2R-negative MN. Overall, PLA2R was identified in 16.4%, one of the other antigens detected in 49.1%, and in the remaining 34.5% of cases, none of the above antigens was detected. Thus, LMD/MS is an extremely useful and reliable method for the detection of known MN antigens and possibly indicating an unknown MN antigen for eventual discovery.

An Updated Comprehensive Review on Diseases Associated with Nephrotic Syndromes

There have been exciting advances in our knowledge of primary glomerular diseases and nephrotic syndromes in recent years. Beyond the histological pattern from renal biopsy, more precise phenotyping of the diseases and the use of modern nephrogenetics helps to improve treatment decisions and sometimes also avoid unnecessary exposure to potentially toxic immunosuppression. New biomarkers have led to easier and more accurate diagnoses and more targeted therapeutic decisions. The treatment landscape is becoming wider with a pipeline of promising new therapeutic agents with more sophisticated approaches. This review focuses on all aspects of entities that are associated with nephrotic syndromes with updated information on recent advances in each field. This includes podocytopathies (focal segmental glomerulosclerosis and minimal-change disease), membranous nephropathy, membranoproliferative glomerulonephritis, IgA nephropathy, fibrillary glomerulonephritis, amyloidosis, and monoclonal gammopathy of renal significance in the context of the nephrotic syndrome, but also renal involvement in systemic diseases, diabetic nephropathy, and drugs that are associated with nephrotic syndromes.

The role of kidney biopsy in the diagnosis of membranous nephropathy

The discovery of the target antigen M-type phospholipase A2 receptor (PLA2R) with the possibility to detect anti-PLA2R antibodies in serum as well as the identification of several other antigens, overall accounting for almost all cases of membranous nephropathy, paved the way to a revolutionary change in the classification of membranous nephropathy. Serum anti-PLA2R autoantibody titers have been found to be highly specific diagnostic and prognostic biomarkers. Therefore, a positive test for anti-PLA2R serology in patients who present with nephrotic syndrome, normal kidney function, and no evidence of another process to account for proteinuria is believed to suffice to make a diagnosis of primary membranous nephropathy, thus removing the need for a renal biopsy. While technological advances will likely allow this proposal to prevail in the near future, the reasons why renal biopsy could still remain a critical tool for the management of membranous nephropathy in real life are discussed.

Therapeutic targets in membranous nephropathy: plasma cells and complement

Membranous nephropathy (MN) is an antibody-mediated autoimmune disease and the most common cause of nephrotic syndrome in adults. The discovery of phospholipase A2 receptor 1 (PLA2R1) as the first target antigen in patients with MN 15 years ago has led to a paradigm shift in the pathobiological understanding of this disease. Autoantibodies against PLA2R1 as well as thrombospondin type-1 domain-containing 7A, the second identified antigen in adults, were shown to be disease-causing and act through local activation of the complement system, primarily via the classical and lectin pathways. These findings indicate that both plasma cells, the main source of antibodies and autoantibodies, as well as the complement system, the main pathogenic effector mechanism in MN, are rational and pathogenesis-based treatment targets in MN. This review summarizes pathomechanistic and clinical evidence for and against plasma cell- and complement-targeted treatments in MN.

Anti-Neuron-Derived Neurotrophic Factor Antibodies in Secondary Membranous Nephropathy Caused by Syphilis: A Case Report

We present the case of a 61-year-old man who developed nephrotic syndrome as a result of syphilis-associated secondary membranous nephropathy (MN). The patient showed nephrotic syndrome remission following antibiotic treatment for syphilis alone. Pathologically, the target antigen of immune complexes accumulated on glomerular basement membranes (GBM) in secondary MN caused by syphilis has been reported to be neuron-derived neurotrophic factor (NDNF). His renal histopathology was consistent with secondary MN caused by syphilis, with a full-house pattern on immunofluorescence microscopy, in addition to NDNF deposits that colocalized with IgG deposits granularly on the GBM. However, to date, there is no serological evidence for the involvement of NDNF in the GBM. In the present study, we found that anti-NDNF autoantibodies in the acute-phase serum disappeared in the convalescent-phase serum of a patient who recovered from syphilis and nephrotic syndrome after antibiotic therapy alone. This result supports the hypothesis that treatment of syphilis with antibiotics suppresses NDNF's antigenicity. In summary, we found new serological evidence emphasizing that NDNF is an etiological antigen in secondary MN caused by syphilis.

IgG4-related disease complicated by PLA2R-associated membranous nephropathy: A case report

IgG4-related tubulointerstitial nephritis (IgG4-related TIN) is the prevalent clinical manifestation of IgG4-related diseases (IgG4-RD). However, there are limited cases of IgG4-RD occurring with membranous nephropathy (MN) in the absence of phospholipase A2 receptor (PLA2R). There have been no indications of treatment using Tripterygium wilfordii. This study reported a rare case of IgG4-RD with PLA2R-associated MN without any of the distinct IgG4-related TIN. The patient was treated effectively with T. wilfordii. A 71-year-old patient was admitted to the medical facility after presenting with a 1 month history of edema and 8 months of albuminuria. The renal biopsy tissue examination confirmed the presence of MN (phase II) in the absence of pathological manifestations of IgG4-related TIN. Immunohistochemistry identified PLA2R++ (granular capillaries). The serum PLA2R antibody titer was 1:180 (1:20). The patient met the diagnosis with IgG4-RD. Over 8 years of follow-up, the patient was effectively treated with low-dose hormones and T. wilfordii, without any adverse effects. This MN is considered a unique form of IgG4-RD, regardless of whether PLA2R antibodies are present or not. Research suggests that T. wilfordii could be a promising option for elderly people with IgG4-related MN, as it has been found to have fewer adverse effects.

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.

Paraneoplastic Glomerular Diseases

Paraneoplastic glomerular disease (PGD) develops from tumor cell products, leading to renal dysfunction. Unlike direct tumor effects, PGD illustrates the complex association between cancer and diverse clinical presentations and outcomes. Initially detected in a Hodgkin's disease patient, current research has defined diagnostic criteria based on PGD symptoms and cancer progression. PGDs, although rare (found in <1% of adult cancer patients with overt renal manifestations), are crucial, as they can signal cancer onset and frequently resist standard glomerulonephritis treatments. The emerging field of onconephrology studies this relationship between kidney disorders and cancers. The exact cause of many PGD cases remains unknown. This review examines PGDs, their clinicopathological features, related cancers, and mechanisms, emphasizing the need for early diagnosis and tailored treatment for kidney disease and linked cancer.

[The complement cascade in renal pathology]

The complement cascade comprises a variety of soluble and cell surface proteins and is an important component of the innate immune system. When the cascade is triggered by any of the three activation pathways, the complement system rapidly produces large amounts of protein fragments that are potent mediators of inflammatory, vasoactive, and metabolic responses. All activation pathways lead to the terminal complement cascade with the formation of the membrane attack complex, which lyses cells by forming membrane pores. Although the complement system is essential for pathogen defense and homeostasis, excessive or uncontrolled activation can lead to tissue damage. Recent research shows that the complement system is activated in almost all kidney diseases, even those not traditionally considered immune-mediated. In directly complement-mediated kidney diseases, complement factors or regulators are defective, afunctional or inactivated by antibodies. In many other renal diseases, the complement system is activated secondarily as a result of renal damage and is therefore involved in the pathogenesis of the disease, but is not the trigger. The detection of complement deposits is also used to diagnose kidney disease. This review describes the structure of the complement system and the effects of its dysregulation as a cause and modulator of renal disease.

Membranous Nephropathy: Updates on Management

Membranous nephropathy is a major etiology of nephrotic syndrome in adults and less frequently in children. Circulating antibodies to intrinsic podocyte antigens, such as M-type phospholipase A2 receptor, or to extrinsic proteins accumulate beneath the podocyte to cause damage via complement activation and/or other mechanisms. The availability of clinical testing for autoantibodies to M-type phospholipase A2 receptor has allowed noninvasive diagnosis of this form of membranous nephropathy and a means to monitor immunologic activity to guide immunosuppressive therapy. Treatment of membranous nephropathy includes optimal supportive care with renin-angiotensin-system blockers, lipid-lowering agents, diuretics, lifestyle changes, and additional immunosuppressive therapy in patients with an increased risk of progression to kidney failure. Rituximab has been recognized as a first-line immunosuppressive therapy for most membranous nephropathy patients with an increased risk of progressive disease, except those with life-threatening nephrotic syndrome or rapidly deteriorating kidney function from membranous nephropathy. This article discusses the major and minor antigens described in membranous nephropathy, the natural history of the disease, and guidelines for clinical management and immunosuppressive treatment.

Membranous nephropathy: pathogenesis and treatments

Membranous nephropathy (MN), an autoimmune disease, can manifest at any age and is among the most common causes of nephrotic syndrome in adults. In 80% of cases, the specific etiology of MN remains unknown, while the remaining cases are linked to drug use or underlying conditions like systemic lupus erythematosus, hepatitis B virus, or malignancy. Although about one-third of patients may achieve spontaneous complete or partial remission with conservative management, another third face an elevated risk of disease progression, potentially leading to end-stage renal disease within 10 years. The identification of phospholipase A2 receptor as the primary target antigen in MN has brought about a significant shift in disease management and monitoring. This review explores recent advancements in the pathophysiology of MN, encompassing pathogenesis, clinical presentations, diagnostic criteria, treatment options, and prognosis, with a focus on emerging developments in pathogenesis and therapeutic strategies aimed at halting disease progression. By synthesizing the latest research findings and clinical insights, this review seeks to contribute to the ongoing efforts to enhance our understanding and management of this challenging autoimmune disorder.

Ten tips on immunosuppression in primary membranous nephropathy

Membranous nephropathy (MN) management poses challenges, particularly in selecting appropriate immunosuppressive treatments (IST) and monitoring disease progression and complications. This article highlights 10 key tips for the management of primary MN based on current evidence and clinical experience. First, we advise against prescribing IST to patients without nephrotic syndrome (NS), emphasizing the need for close monitoring of disease progression. Second, we recommend initiating IST in patients with persistent NS or declining kidney function. Third, we suggest prescribing rituximab (RTX) or RTX combined with calcineurin inhibitors in medium-risk patients. Fourth, we propose cyclophosphamide-based immunosuppression for high-risk patients. Fifth, we discourage the use of glucocorticoid monotherapy or mycophenolate mofetil as initial treatments. Sixth, we underscore the importance of preventing infectious complications in patients receiving IST. Seventh, we emphasize the need for personalized monitoring of IST by closely measuring kidney function, proteinuria, serum albumin and anti-M-type phospholipase A2 receptor levels. Eighth, we recommend a stepwise approach in the treatment of resistant disease. Ninth, we advise adjusting treatment for relapses based on individual risk profiles. Finally, we caution about the potential recurrence of MN after kidney transplantation and suggest appropriate monitoring and treatment strategies for post-transplantation MN. These tips provide comprehensive guidance for clinicians managing MN, aiming to optimize patient outcomes and minimize complications.

The Prevalence, Characteristics, and Putative Mechanisms of Dual Antigen-Positive Membranous Nephropathy: The Underestimated Condition

Following the discovery of podocyte phospholipase A2 receptor and thrombospondin type-1 domain-containing 7A, various potential target antigens for membranous nephropathy (MN) have been reported one after another. MN target antigens have now been identified in a significant proportion of patients, and a new classification framework classifies patients with MN based on the detected antigen and associated disease phenotype. A serology-based approach that does not require a histological diagnosis for patients suspected of having MN has also been proposed. However, there have been cases in which dual positivity for MN antigens and/or corresponding antibodies has been shown. Importantly, some of them showed a transition of the affected patient's immune responses to MN antigens, suggesting that serological diagnosis changes depending on the timing of the analysis. In this review, we provide detailed information on these cases and present an overview of our recent understanding of their putative mechanisms involved in these cases. Greater awareness is required to adequately recognize and develop appropriate therapeutic strategies for this condition.

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.

Membranous nephropathy-diagnosis and identification of target antigens

Membranous nephropathy (MN) is a common cause of nephrotic syndrome in adults. MN is characterized by subepithelial accumulation of immune complexes along the glomerular basement membrane. The immune complexes are composed of immunoglobulin G and a target antigen. PLA2R is the target antigen in approximately 60% of MN cases, and MN is traditionally classified as PLA2R-positive or PLA2R-negative MN. Over the last 7 years, additional target antigens have been identified, which have specific disease associations, distinctive clinical and pathologic findings, and therapeutic implications. The newly discovered target antigens include NELL1, EXT1/EXT2, NCAM1, SEMA3B, PCDH7, FAT1, CNTN1, NTNG1, PCSK6 and NDNF. To group all these antigens into a generic 'PLA2R-negative' MN group is imprecise and un-informative. We propose a logical approach for detection of the target antigen which includes (i) currently available serology-based testing to detect anti-PLA2R and anti-THSD7A antibodies; and (ii) kidney biopsy testing to detect the target antigens. Determination of the antigen on kidney biopsy can be done by immunohistochemistry or immunofluorescence studies. Alternatively, laser capture microdissection (LCM) of glomeruli followed by mass spectrometry (MS) can be used to identify a target antigen. LCM/MS has the advantage of being a one-stop test and is particularly useful for detection of rare target antigens. At the current time, while it is possible to detect the newer antigens by immunohistochemistry/immunofluorescence/LCM/MS, serology-based tests to detect serum antibodies to the new antigens are not yet available. It is critical that serology-based tests should be developed not just for accurate diagnosis, but as a guide for treatment. We review the current methodology and propose an algorithm for diagnosis and detection of target antigens in MN that may shape the current practice in the future. Membranous nephropathy (MN) results from accumulation of subepithelial immune complexes along the glomerular basement membrane.PLA2R is the most common target antigen, but newly discovered target antigens have filled the void of PLA2R-negative MN.MN associated with the newly discovered target antigens have distinctive clinical and pathologic findings, treatment and prognostic implications. These include NELL1, EXT1/EXT2, NCAM1, PCDH7, SEMA3B, CNTN1, FAT1, NDNF and PCSK6.Immunohistochemistry/immunofluorescence methodology is currently in use for detecting target antigens in kidney biopsy tissue, although we anticipate laser capture microdissection of glomeruli followed by mass spectrometry will become available soon.Serologic testing is currently available for only detecting antibodies to PLA2R and THSD7A. It is critical that serologic tests become available for detecting antibodies to the newly discovered antigens.

Membranous nephropathy treatment standard

Membranous nephropathy (MN) is characterized by deposition of immune complexes leading to thickening of glomerular basement membranes. Over time, the understanding of MN has evolved, with the identification of specific autoantibodies against novel podocyte antigens and the unraveling of intricate pathogenic pathways. Although the anti-CD20 monoclonal antibody rituximab is favored as part of the initial therapy in MN, a subgroup of MN patients may be resistant to rituximab necessitating the use of alternative agents such as cytotoxic therapies. In addition, newer agents such as novel anti-CD20 monoclonal antibodies, therapies targeting the CD38-positive plasma cells and anti-complement therapy are being studied in patients who are resistant to traditional treatment strategies. This manuscript furnishes a review of the novel developments in the pathophysiology of MN including the identification of target antigens and current treatment standards for MN, concentrating on evidenced-based interventions designed to attain remission and to prevent disease progression.

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.