Prediction of membranous nephropathy recurrence after transplantation by monitoring of anti-PLA2R1 (M-type phospholipase A2 receptor) autoantibodies: a case series of 15 patients

Recurrence of membranous nephropathy after kidney transplantation: A multicenter retrospective cohort study

Membranous nephropathy (MN) is a leading cause of kidney failure worldwide and frequently recurs after transplant. Available data originated from small retrospective cohort studies or registry analyses; therefore, uncertainties remain on risk factors for MN recurrence and response to therapy. Within the Post-Transplant Glomerular Disease Consortium, we conducted a retrospective multicenter cohort study examining the MN recurrence rate, risk factors, and response to treatment. This study screened 22,921 patients across 3 continents and included 194 patients who underwent a kidney transplant due to biopsy-proven MN. The cumulative incidence of MN recurrence was 31% at 10 years posttransplant. Patients with a faster progression toward end-stage kidney disease were at higher risk of developing recurrent MN (hazard ratio [HR], 0.55 per decade; 95% confidence interval [CI], 0.35-0.88). Moreover, elevated pretransplant levels of anti-phospholipase A2 receptor (PLA2R) antibodies were strongly associated with recurrence (HR, 18.58; 95% CI, 5.37-64.27). Patients receiving rituximab for MN recurrence had a higher likelihood of achieving remission than patients receiving renin-angiotensin-aldosterone system inhibition alone. In sum, MN recurs in one-third of patients posttransplant, and measurement of serum anti-PLA2R antibody levels shortly before transplant could aid in risk-stratifying patients for MN recurrence. Moreover, patients receiving rituximab had a higher rate of treatment response.

High exposure to tacrolimus is associated with spontaneous remission of recurrent membranous nephropathy after kidney transplantation

Introduction

We aimed to characterize the incidence and clinical presentation of membranous nephropathy (MN) after kidney transplantation (KT), and to assess allograft outcomes according to proteinuria rates and immunosuppression management.

Methods

Multicenter retrospective cohort study including patients from six Spanish centers who received a KT between 1991-2019. Demographic, clinical, and histological data were collected from recipients with biopsy-proven MN as primary kidney disease (n = 71) or MN diagnosed de novo after KT (n = 4).

Results

Up to 25.4% of patients with biopsy-proven MN as primary kidney disease recurred after a median time of 18.1 months posttransplant, without a clear impact on graft survival. Proteinuria at 3-months post-KT was a predictor for MN recurrence (rMN, HR 4.28; P = 0.008). Patients who lost their grafts had higher proteinuria during follow-up [1.0 (0.5-2.5) vs 0.3 (0.1-0.5) g/24 h], but only eGFR after recurrence treatment predicted poorer graft survival (eGFR < 30 ml/min: RR = 6.8). We did not observe an association between maintenance immunosuppression and recurrence diagnosis. Spontaneous remission after rMN was associated with a higher exposure to tacrolimus before recurrence (trough concentration/dose ratio: 2.86 vs 1.18; P = 0.028). Up to 94.4% of KT recipients received one or several treatments after recurrence onset: 22.2% rituximab, 38.9% increased corticosteroid dose, and 66.7% ACEi/ARBs. Only 21 patients had proper antiPLA2R immunological monitoring.

Conclusions

One-fourth of patients with biopsy-proven MN as primary kidney disease recurred after KT, without a clear impact on graft survival. Spontaneous remission after rMN was associated with a higher exposure to tacrolimus before recurrence.

Prognostic prediction of idiopathic membranous nephropathy using interpretable machine learning

BACKGROUND

Established prognostic models of idiopathic membranous nephropathy (IMN) were limited to traditional modeling methods and did not comprehensively consider clinical and pathological patient data. Based on the electronic medical record (EMR) system, machine learning (ML) was used to construct a risk prediction model for the prognosis of IMN.

METHODS

Data from 418 patients with IMN were diagnosed by renal biopsy at the Fifth Clinical Medical College of Shanxi Medical University. Fifty-nine medical features of the patients could be obtained from EMR, and prediction models were established based on five ML algorithms. The area under the curve, recall rate, accuracy, and F1 were used to evaluate and compare the performances of the models. Shapley additive explanation (SHAP) was used to explain the results of the best-performing model.

RESULTS

One hundred and seventeen patients (28.0%) with IMN experienced adverse events, 28 of them had compound outcomes (ESRD or double serum creatinine (SCr)), and 89 had relapsed. The gradient boosting machine (LightGBM) model had the best performance, with the highest AUC (0.892 ± 0.052, 95% CI 0.840-0.945), accuracy (0.909 ± 0.016), recall (0.741 ± 0.092), precision (0.906 ± 0.027), and F1 (0.905 ± 0.020). Recursive feature elimination with random forest and SHAP plots based on LightGBM showed that anti-phospholipase A2 receptor (anti-PLA2R), immunohistochemical immunoglobulin G4 (IHC IgG4), D-dimer (D-DIMER), triglyceride (TG), serum albumin (ALB), aspartate transaminase (AST), β2-microglobulin (BMG), SCr, and fasting plasma glucose (FPG) were important risk factors for the prognosis of IMN. Increased risk of adverse events in IMN patients was correlated with high anti-PLA2R and low IHC IgG4.

CONCLUSIONS

This study established a risk prediction model for the prognosis of IMN using ML based on clinical and pathological patient data. The LightGBM model may become a tool for personalized management of IMN patients.

The expanding spectrum and utility of antigens in membranous nephropathy

PURPOSE OF REVIEW

Multiple antigenic targets were discovered in membranous nephropathy, representing distinct autoimmune diseases with a similar morphologic pattern of injury. An overview of recent developments, including antigen types, clinical associations, serologic monitoring, and advancements in understanding disease pathogenesis are provided.

RECENT FINDINGS

Several new antigenic targets have defined subtypes of membranous nephropathy, including Neural epidermal growth factor-like 1, protocadherin 7, HTRA1, FAT1, SEMA3B, NTNG1, NCAM1, exostosin 1/2, transforming growth factor beta receptor 3, CNTN1, proprotein convertase subtilisin/kexin type 6, and neuron-derived neurotrophic factor. Autoantigens in membranous nephropathy may demonstrate unique clinical associations, assisting the nephrologist to identify potential disease etiologies and triggers, such as autoimmune disease, cancer, medications, and infections.

SUMMARY

We are entering an exciting era for which an antigen-based approach will further define subtypes of membranous nephropathy, allow for development of noninvasive diagnostics, and improve care for patients.

Membranous nephropathy

Membranous nephropathy is a glomerulopathy, which main affected target is the podocyte, and has consequences on the glomerular basement membrane. It is more common in adults, especially over 50 years of age. The clinical presentation is nephrotic syndrome, but many cases can evolve with asymptomatic non-nephrotic proteinuria. The mechanism consists of the deposition of immune complexes in the subepithelial space of the glomerular capillary loop with subsequent activation of the complement system. Great advances in the identification of potential target antigens have occurred in the last twenty years, and the main one is the protein "M-type phospholipase-A2 receptor" (PLA2R) with the circulating anti-PLA2R antibody, which makes it possible to evaluate the activity and prognosis of this nephropathy. This route of injury corresponds to approximately 70% to 80% of cases of membranous nephropathy characterized as primary. In the last 10 years, several other potential target antigens have been identified. This review proposes to present clinical, etiopathogenic and therapeutic aspects of membranous nephropathy in a didactic manner, including cases that occur during kidney transplantation.

How to maximize graft survival

PURPOSE OF REVIEW

Kidney transplant failure results in significant patient morbidity and mortality, increased financial burden and exacerbates the organ shortage faced by kidney transplant candidates. The different strategies to maximize graft survival in kidney transplant recipients is presented in this review.

RECENT FINDINGS

Maximizing kidney graft survival requires optimizing immunosuppression, preventing and managing recurrent disease and using general chronic kidney disease strategies to slow allograft injury. Herein, we review: 1) strategies to tailor immunosuppression to the individual patient to avoid over and underimmunosuppression, and avoid immunosuppression-related drug toxicities, 2) latest findings in the following recurrent diseases: focal segmental glomerulosclerosis, membranous nephropathy, complement-mediated kidney disease and monoclonal gammopathy of renal significance, and, 3) approaches to slow allograft injury including BP control, and the use of antiproteinuric agents and SGLT-2 inhibitors.

SUMMARY

The last two decades has seen significant improvement in allograft outcomes resulting from advances in immunosuppression. With the federal government's renewed focus on kidney disease and transplantation, and recent advances in biomarkers, genetic testing, big data analytics and machine learning, we hope to see further outcome improvements in the next decade.

Anti-phospholipase A2 Receptor Antibody in Differentiation and Prognostication of Membranous Nephropathy

Anti-M-type phospholipase A₂ receptor (anti-PLA₂R) antibody is believed to be associated with primary membranous nephropathy (pMN) and absent in secondary MN (sMN). There are few data regarding utility of anti-PLA₂R antibody as a prognosticator. Our study aimed to compare the incidence of positive serum anti-PLA₂R antibody titer in pMN versus sMN and correlation with clinical outcome. From August 2015 to July 2019, patients with biopsy-proven MN were evaluated for serum anti-PLA₂R antibody titers by the enzyme-linked immunosorbent assay. The subset of cases was repeated to monitor the clinical response in terms of 24 h proteinuria. A total of 169 patients, 65 pMN and 104 sMN were studied. Anti-PLA₂R antibody was found in 41 (63.08%) pMN with mean titer, 232.62 RU/mL, and 40 (38.46%) sMN with mean titer 253.59 RU/mL. Out of positive antiPLA₂R antibody titer in pMN cases, 15 were retested twice to 5 times with mean titers of 78.95, 36.27, 13.9, and 15.45 RU/mL, respectively. Out of positive anti-PLA₂R antibody in sMN cases, 11 were retested twice to five times with mean titers of 104.42, 122.49, 12.33, and 17.2 RU/mL, respectively. All patients with decreasing anti-PLA₂R antibody titer in both groups had clinical remission, with a decrease in mean 24 h proteinuria from 7.11 g to 3.36 g in pMN and 5.97 g to 3.41 g in sMN. Ten pMN and 11 sMN patients without remission showed persistent positive anti- PLA₂R antibody titer. Anti-PLA₂R antibody titer may be elevated in pMN/sMN. It can also be used as a noninvasive prognostic marker for MN.

The role of PLA2R antibody monitoring: what we know and what we don't know

For a long time, kidney biopsy was the only diagnostic mean for membranous nephropathy (MN), and proteinuria and serum creatinine the only markers of disease activity. The discovery of PLA2R antibody in 2009 has induced a paradigm shift in both the diagnostic and monitoring of patients. Two serological tests are routinely used: the ELISA which is quantitative and the immunofluorescence assay (IFA) which is more sensitive. In centers where the 2 assays are available, the recommendation is to use IFA for screening and diagnostic of immunological remission, and ELISA for monitoring effectiveness of therapy. In patients with positive PLA2R antibody serology, normal kidney function and no evidence for an underlying disease, a kidney biopsy is not mandatory given the almost 100% specificity of the assays. Because MN has different phases, one cannot base a clinical or therapeutic decision on a single measurement of PLA2R antibody at baseline. Risk evaluation of disease progression is a dynamic process that should be performed repeatedly to capture the trajectory of the disease based on both the traditional biomarkers (proteinuria, serum creatinine) and PLA2R antibody levels. Effectiveness of therapy is also evaluated on the PLA2R antibody trajectory, particularly during the first 6 months. Finally, PLA2R antibody monitoring has transformed the management of patients with a kidney allograft. Future studies are needed to develop more subtle immunological tests, including monitoring of antigen-specific memory B cells.

Recurrent Glomerular Disease after Kidney Transplantation: Diagnostic and Management Dilemmas

Recurrent glomerular disease after kidney transplant remains an important cause of allograft failure. Many of the different entities post-transplant still suffer from incomplete knowledge on pathophysiology, and therefore lack targeted and effective therapies. In this review, we focus on specific clinical dilemmas encountered by physicians in managing recurrent glomerular disease by highlighting new insights into the understanding and treatment of post-transplant focal segmental glomerulosclerosis, membranous nephropathy, atypical hemolytic uremic syndrome, C3 glomerulopathy, amyloid light-chain (AL) amyloidosis, and IgA nephropathy.

Membranous nephropathy

Membranous nephropathy (MN) is a glomerular disease that can occur at all ages. In adults, it is the most frequent cause of nephrotic syndrome. In ~80% of patients, there is no underlying cause of MN (primary MN) and the remaining cases are associated with medications or other diseases such as systemic lupus erythematosus, hepatitis virus infection or malignancies. MN is an autoimmune disease characterized by a thickening of the glomerular capillary walls due to immune complex deposition. Identification of the phospholipase A2 receptor (PLA2R) as the major antigen in adults in 2009 induced a paradigm shift in disease diagnosis and monitoring and several other antigens have since been characterized. Disease outcome is difficult to predict and around one-third of patients will undergo spontaneous remission. In those at high risk of progression, immunosuppressive therapy with cyclophosphamide plus corticosteroids has substantially reduced the need for kidney replacement therapy. Owing to carcinogenic risk, other treatments (calcineurin inhibitors and CD20-targeted B cell depletion therapy (rituximab)) have been developed. However, disease relapses are frequent when calcineurin inhibitors are stopped and the remission rate with rituximab is lower than with cyclophosphamide, particularly in patients with high PLA2R antibody titres. Other new drugs are already available and antigen-specific immunotherapies are being developed.

Primary membranous nephropathy in the era of autoantibodies and biological therapies

Primary membranous nephropathy is an autoimmune kidney disease and the most common cause of nephrotic syndrome in adults. About 70%-80% of cases are caused by anti-PLA2R antibodies. Its association with anti-THSD7A antibodies and other autoantibodies has also been described. Recent pilot studies and clinical trials have shown that several biological agents targeting autoantibody-producing cells are effective in controlling the disease with an acceptable safety profile. In this narrative review, we update key concepts about the pathogenesis, autoantibody-based diagnosis, and kidney biopsy findings in primary membranous nephropathy. In addition, we propose a diagnostic and therapeutic algorithm, including guidance on monitoring the response to therapy. We compare the efficacy and safety of currently available treatments, including rituximab and new biological agents, and identify unmet clinical needs.

Seropositive PLA2R-associated membranous nephropathy but biopsy-negative PLA2R staining

BACKGROUND

Serum phospholipase A2 receptor (PLA2R) antibody (SAb) and glomerular deposits of PLA2R antigen (GAg) have been tested widely in idiopathic membranous nephropathy (MN). Recently, we noticed a special form of PLA2R-associated MN with positive circulating PLA2R antibody but negative PLA2R deposits in the glomeruli by immunofluorescence on frozen tissue (IF-F). The significance of this form of PLA2R-associated MN is yet to be elucidated. This study aimed to explore the clinicopathological features of these PLA2R-associated MN patients.

METHODS

This study enrolled 229 biopsy-proven PLA2R-associated MN patients with SAb+. SAb was measured by enzyme-linked immunosorbent assay, and GAg was detected by IF-F. These patients were divided into SAb+/GAg+ and SAb+/GAg- groups. Clinicopathological characteristics of SAb+/GAg+ and SAb+/GAg- PLA2R-associated MN patients were compared. PLA2R antigens of 19 SAb+/GAg- PLA2R-associated MN patients were verified by immunohistochemistry on paraffin tissue (IHC-P).

RESULTS

Among 229 SAb+ PLA2R-associated MN patients, 210 (91.70%) were GAg+ and 19 (8.3%) were GAg-. These 19 SAb+/GAg- PLA2R-associated MN patients presented positive PLA2R deposits by IHC-P. Compared with SAb+/GAg+ PLA2R-associated MN patients, SAb+/GAg- PLA2R-associated MN patients had higher levels of serum PLA2R antibody (P = 0.004), increased proteinuria (P = 0.008), lower serum albumin (P = 0.019), more prominent chronic pathological lesions in terms of glomerulosclerosis score (P = 0.025), interstitial fibrosis score (P = 0.016), tubular atrophy score (P = 0.010) and total renal chronicity score (P = 0.010), and were more likely to be accompanied by focal segmental glomerulosclerosis (P = 0.014). Higher SAb level was associated with the total renal chronicity score (odds ratio per 100 RU/mL, 1.16; 95% confidence interval 1.01-1.33; P = 0.033).

CONCLUSIONS

PLA2R-associated MN patients with seropositive PLA2R antibody but negative PLA2R deposits in the glomeruli by IF-F have higher levels of SAb and worse clinicopathological manifestations compared with their double-positive counterparts. IHC-P can be an alternative technique to reveal PLA2R glomerular deposits.

The association of anti-PLA2R with clinical manifestations and outcomes in idiopathic membranous nephropathy: a meta-analysis

PURPOSE

The meta-analysis aims to investigate the relationship between anti-phospholipase A2 receptor autoantibody (anti-PLA2R) and clinical characteristics and adverse outcomes of idiopathic membranous nephropathy (IMN).

METHODS

Related studies published before February 2020 were systematically retrieved from foreign and domestic databases, RevMan5.3 software was used for meta-analysis and subgroup analysis, and STATA 15.0 statistical software was used for its heterogeneity and testing publication bias.

RESULTS

Twenty studies were included, involving 2224 patients with IMN. Our results showed that a significant correlation existed between the expression of serum anti-PLA2R and age (MD = 2.91, 95% CI = 2.15-3.67, P < 0.00001), total serum cholesterol (MD = 35.52, 95% CI = 9.52-61.52, P = 0.007), urine protein by creatinine ratio (UPCR) (MD = 2.15, 95% CI = 1.86-2.44, P<0.00001), serum albumin (MD = -0.40, 95% CI = -0.56 to -0.23, P < 0.00001), eGFR (MD = -10.44, 95% CI = -12.19 to -8.68, P < 0.00001), unremission rate (RR = 1.76, 95% CI = 1.37-2.27, P < 0.0001). In addition, the high titer in seropositive group was closely correlated with serum albumin (MD = -0.40, 95% CI = -0.74 to -0.05, P = 0.03), eGFR (MD = -12.40, 95% CI = -16.29 to -8.52, P < 0.00001) and unremission rate (RR = 2.52, 95% CI = 1.79-3.55, P < 0.00001). No significant correlation was found between glomerular anti-PLA2R and clinical manifestations except for serum cholesterol (MD = 0.81, 95% CI = 0.21-1.41, P = 0.008). However, in terms of prognosis, glomerular anti-PLA2R showed a significant relevance to recurrence rate (RR = 2.25, 95% CI = 1.07-4.72, P = 0.03).

CONCLUSION

Compared with glomerular anti-PLA2R, serum anti-PLA2R may better reflect the activities of IMN disease, while the glomerular anti-PLA2R might be connected with the recurrence of the disease.

Anti-PLA2R1 Antibodies Containing Sera Induce In Vitro Cytotoxicity Mediated by Complement Activation

The phospholipase A2 receptor (PLA2R1) is the major autoantigen in idiopathic membranous nephropathy (MN). However, the pathogenic role of anti-PLA2R1 autoantibodies is unclear. Our aim was to evaluate the in vitro cytotoxicity of anti-PLA2R1 antibodies mediated by complement. Forty-eight patients with PLA2R1-related MN from the prospective cohort SOURIS were included. Anti-PLA2R1 titer, epitope profile, and anti-PLA2R1 IgG subclasses were characterized by ELISA. Cell cytotoxicity was evaluated by immunofluorescence in HEK293 cells overexpressing PLA2R1 incubated with patient or healthy donor sera in the presence or absence of rabbit complement or complement inhibitors. Mean cytotoxicity of anti-PLA2R1 sera for HEK293 cells overexpressing PLA2R1 was 2 ± 2%, which increased to 24 ± 6% after addition of rabbit complement (p < 0.001) (n = 48). GVB-EDTA, which inhibits all complement activation pathways, completely blocked cell cytotoxicity, whereas Mg-EGTA, which only inhibits the classical and lectin pathways, highly decreased suggesting a limited role of the alternative pathway. A higher diversity of IgG subclasses beyond IgG4 and high titer of total IgG anti-PLA2R1 were associated with increased cytotoxicity (p = 0.01 and p = 0.03 respectively). In a cohort of 37 patients treated with rituximab, high level of complement-mediated cytotoxicity was associated with less and delayed remission at month 6 after rituximab therapy (5/12 vs. 20/25 (p = 0.03) in 8.5 months ± 4.4 vs. 4.8 ± 4.0 (p = 0.02)). Kaplan-Meier analysis demonstrated that high level of cytotoxicity (≥40%) (p = 0.005), epitope spreading (defined by immunization beyond the immunodominant CysR domain) (p = 0.002), and high titer of anti-PLA2R1 total IgG (p = 0.01) were factors of poor renal prognosis. Anti-PLA2R1 antibodies containing sera can induce in vitro cytotoxicity mediated by complement activation, and the level of cytotoxicity increases with the diversity and the titer of anti-PLA2R1 IgG subclasses. These patients with high level of complement-mediated cytotoxicity could benefit from adjuvant therapy using complement inhibitor associated with rituximab to induce earlier remission and less podocyte injury.

Membranous Nephropathy Posttransplantation: An Update of the Pathophysiology and Management

Membranous nephropathy (MN) is a common cause of nephrotic syndrome after transplantation and is associated with an increased risk of allograft loss. MN may occur either as a recurrent or as a de novo disease. As in native kidneys, the pathophysiology of the MN recurrence is in most cases associated with antiphospholipid A2 receptor antibodies. However, the posttransplant course has some distinct features when compared with primary MN, including a lower chance of spontaneous remission and a greater requirement for adjuvant immunosuppressive therapy to induce complete remission. Although the efficacy of rituximab in primary MN is now well established, no randomized studies have assessed its effectiveness in MN after transplant, and there are no specific recommendations for the management of these patients. This review aims to synthesize and update the pathophysiology of posttransplant MN, as well as to address unsolved issues specific to transplantation, including the prognostic value of antiphospholipid A2 receptor, the risk of living-related donation, the link between de novo MN and rejection, and different therapeutic strategies so far deployed in posttransplant MN. Lastly, we propose a management algorithm for patients with MN who are planning to receive a kidney transplant, including pretransplant considerations, posttransplant monitoring, and the clinical approach after the diagnosis of recurrence.

Membranous Nephropathy (MN) Recurrence After Renal Transplantation

Primary membranous nephropathy (MN) is a frequent cause of NS in adults. In native kidneys the disease may progress to ESRD in the long term, in some 40–50% of untreated patients. The identification of the pathogenic role of anti-podocyte autoantibodies and the development of new therapeutic options has achieved an amelioration in the prognosis of this disease. MN may also develop in renal allograft as a recurrent or a de novo disease. Since the de novo MN may have some different pathogenetic and morphologic features compared to recurrent MN, in the present paper we will deal only with the recurrent disease. The true incidence of the recurrent form is difficult to assess. This is mainly due to the variable graft biopsy policies in kidney transplantation, among the different transplant centers. Anti-phospholipase A2 receptor (PLA2R) autoantibodies are detected in 70–80% of patients. The knowledge of anti-PLA2R status before transplant is useful in predicting the risk of recurrence. In addition, the serial survey of the anti-PLA2R titers is important to assess the rate of disease progression and the response to treatment. Currently, there are no established guidelines for prevention and treatment of recurrent MN. Symptomatic therapy may help to reduce the signs and symptoms related to the nephrotic syndrome. Anecdotal cases of response to cyclical therapy with steroids and cyclophosphamide have been published. Promising results have been reported with rituximab in both prophylaxis and treatment of recurrence. However, these results are based on observational data, and prospective controlled trials are still missing.

Clinical Presentation, Outcomes, and Treatment of Membranous Nephropathy after Transplantation

There are scarce data about clinical presentation and outcomes of posttransplant membranous nephropathy (MN), and few reports include a large number of patients. This was a retrospective cohort including adult patients with posttransplant MN transplanted between 1983 and 2015 in a single center (n=41). Only patients with histological diagnosis of MN in kidney grafts were included. Clinical and laboratory presentation, histological findings, treatment, and outcomes were detailed. Patients were predominantly male (58.5%), with a mean age of 49.4 ± 13.2 years; 15 were considered as recurrent primary MN; 3 were class V lupus nephritis; 14 were considered as de novo cases, 7 secondary and 7 primary MN; and 9 cases were considered primary but it was not possible to distinguish between de novo MN and recurrence. Main clinical presentations were proteinuria (75.6%) and graft dysfunction (34.1%). Most patients with primary recurrent and de novo primary MN were submitted to changes in maintenance immunosuppressive regimen, but no standard strategy was identified; 31 patients presented partial or complete remission, and glomerulopathy appeared not to impact graft and patient survival.

[Membranous nephropathy: Pathophysiology and natural history]

Membranous nephropathy is a major cause of nephrotic syndrome in adults, with various etiologies and outcomes. One third of patients enter spontaneous remission with blockade of the renin-angiotensin system, one third develop a persistent nephrotic syndrome, while another third of patients develop end-stage kidney disease and 40% of them relapse after kidney transplantation. Treatment of membranous nephropathy remains controversial. Immunosuppressive therapy is only recommended in case of renal function deterioration or persistent nephrotic syndrome after 6months of renin-angiotensin system blockade. Therefore, delayed immunosuppressive treatments may lead to significant and potentially irreversible complications. For long, no biological markers could predict clinical outcome and guide therapy. The discovery of autoantibodies to the phospholipase A2 receptor (PLA2R1) in 2009, and to the thrombospondin type 1 domain containing 7A (THSD7A) in 2014 in respectively 70 and 5% of patients with membranous nephropathy were major breakthroughs. The passive infusion of human anti-THSD7A antibodies in mouse induces proteinuria and membranous nephropathy. The identification of these antigens has allowed developing diagnostic and prognostic tests. High anti-PLA2R1 titers at time of diagnosis predict a poor renal outcome. Anti-PLA2R1 antibodies can bind at least three different domains of PLA2R1. Epitope spreading with binding of two or three of these antigenic domains is associated with active membranous nephropathy and poor renal survival. These new tools could help us to monitor disease severity and to predict renal prognosis for a better selection of patients that should benefit of early immunosuppressive therapy.

Recurrence of primary glomerulonephritis: Review of the current evidence

In view of the availability of new immunosuppression strategies, the recurrence of allograft glomerulonephritis (GN) are reported to be increasing with time post transplantation. Recent advances in understanding the pathogenesis of the GN recurrent disease provided a better chance to develop new strategies to deal with the GN recurrence. Recurrent GN diseases manifest with a variable course, stubborn behavior, and poor response to therapy. Some types of GN lead to rapid decline of kidney function resulting in a frustrating return to maintenance dialysis. This subgroup of aggressive diseases actually requires intensive efforts to ascertain their pathogenesis so that strategy could be implemented for better allograft survival. Epidemiology of native glomerulonephritis as the cause of end-stage renal failure and subsequent recurrence of individual glomerulonephritis after renal transplantation was evaluated using data from various registries, and pathogenesis of individual glomerulonephritis is discussed. The following review is aimed to define current protocols of the recurrent primary glomerulonephritis therapy.

The utility of phospholipase A2 receptor autoantibody in membranous nephropathy after kidney transplantation

Membranous nephropathy (MN) is estimated to cause end-stage renal disease in ∼ 5% of patients, in whom renal transplantation is the therapy of choice. Among patients receiving a transplant for MN, the disease will recur in the graft in 30–50%; among these, graft loss will occur in 50% within 10 years. Several studies have suggested that phospholipase A2 receptor autoantibody (aPLA2R) levels before transplantation might be useful in predicting recurrence, and their titration after transplantation is clinically relevant to assess the risk of recurrence and progression, to guide treatment indications and to monitor treatment response. In this review we describe the evolving role of aPLA2R as a biomarker in primary MN and its current usefulness in predicting recurrence of this autoimmune podocytopathy after renal transplantation.

Phospholipase A2 Receptor 1 Epitope Spreading at Baseline Predicts Reduced Likelihood of Remission of Membranous Nephropathy

The phospholipase A2 receptor (PLA2R1) is the major autoantigen in primary membranous nephropathy. Several PLA2R1 epitopes have been characterized, and a retrospective study identified PLA2R1 epitope spreading as a potential indicator of poor prognosis. Here, we analyzed the predictive value of anti-PLA2R1 antibody (PLA2R1-Ab) titers and epitope spreading in a prospective cohort of 58 patients positive for PLA2R1-Ab randomly allocated to rituximab (n=29) or antiproteinuric therapy alone (n=29). At baseline, the epitope profile (CysR, CysRC1, CysRC7, or CysRC1C7) did not correlate with age, sex, time from diagnosis, proteinuria, or serum albumin, but epitope spreading strongly correlated with PLA2R1-Ab titer (P<0.001). Ten (58.8%) of the 17 patients who had epitope spreading at baseline and were treated with rituximab showed reversal of epitope spreading at month 6. In adjusted analysis, epitope spreading at baseline was associated with a decreased remission rate at month 6 (odds ratio, 0.16; 95% confidence interval, 0.04 to 0.72; P=0.02) and last follow-up (median, 23 months; odds ratio, 0.14; 95% confidence interval, 0.03 to 0.64; P=0.01), independently from age, sex, baseline PLA2R1-Ab level, and treatment group. We propose that epitope spreading at baseline be considered in the decision for early therapeutic intervention in patients with primary membranous nephropathy.

Recent Progress in Deciphering the Etiopathogenesis of Primary Membranous Nephropathy

Primary membranous nephropathy (MN) is the leading cause of nephrotic syndrome in adults. Discovery of several antibodies has contributed to an increased understanding of MN. Antibodies against the M-type phospholipase A2 receptor (PLA2R) are present in 50-100% with primary MN and are associated with a lower frequency of spontaneous remission. High levels are linked with a higher probability of treatment resistance, higher proteinuria, and impaired renal function, as well as a more rapid decline of kidney function during follow-up. Immunologic remission precedes reduction of proteinuria by months. Pretransplant evaluation of PLA2R antibodies is warranted to predict recurrence of disease following renal transplantation. Several risk alleles related to the PLA2R1 gene and within the HLA loci have been identified, whereas epitope spreading of PLA2R may predict treatment response. More recently, thrombospondin type 1 domain-containing 7A (THSD7A) antibodies have been discovered in primary MN. Several other rare antigens have been described, including antibodies against neutral endopeptidase as a cause of antenatal MN and circulating cationic bovine serum albumin as an antigen with implications in childhood MN. This review focuses on the progress with a special focus on diagnostic accuracy, predictive value, and treatment implications of the established and proposed antigens.

A Proposal for a Serology-Based Approach to Membranous Nephropathy

Primary membranous nephropathy (MN) is an autoimmune disease mainly caused by autoantibodies against the recently discovered podocyte antigens: the M-type phospholipase A2 receptor 1 (PLA2R) and thrombospondin type 1 domain-containing 7A (THSD7A). Assays for quantitative assessment of anti-PLA2R antibodies are commercially available, but a semiquantitative test to detect anti-THSD7A antibodies has been only recently developed. The presence or absence of anti-PLA2R and anti-THSD7A antibodies adds important information to clinical and immunopathologic data in discriminating between primary and secondary MN. Levels of anti-PLA2R antibodies and possibly, anti-THSD7A antibodies tightly correlate with disease activity. Low baseline and decreasing anti-PLA2R antibody levels strongly predict spontaneous remission, thus favoring conservative therapy. Conversely, high baseline or increasing anti-PLA2R antibody levels associate with nephrotic syndrome and progressive loss of kidney function, thereby encouraging prompt initiation of immunosuppressive therapy. Serum anti-PLA2R antibody profiles reliably predict response to therapy, and levels at completion of therapy may forecast long-term outcome. Re-emergence of or increase in antibody titers precedes a clinical relapse. Persistence or reappearance of anti-PLA2R antibodies after kidney transplant predicts development of recurrent disease. We propose that an individualized serology-based approach to MN, used to complement and refine the traditional proteinuria-driven approach, will improve the outcome in this disease.

Recent advances in our understanding of recurrent primary glomerulonephritis after kidney transplantation

Recurrent glomerulonephritis (GN) is an important cause of kidney allograft failure, particularly in younger recipients. Approximately 15% of death-censored graft failures are due to recurrent GN, but this incidence is likely an underestimation of the magnitude of the problem. Overall, 18% to 22% of kidney allografts are lost due to GN, either recurrent or presumed de novo. The impact of recurrent GN on allograft survival was recognized from the earliest times in kidney transplantation. However, progress in this area has been slow, and our understanding of GN recurrence remains limited, in large part due to incomplete understanding of the pathogenesis of these diseases. This review focuses on recent advances in our general understanding of the pathophysiology of primary GN, the risk of recurrence in the allograft, and the consequences for kidney graft survival. We focus specifically on the most common forms of primary GN, including focal segmental glomerulosclerosis, membranous nephropathy, membranoproliferative glomerulonephritis, and IgA nephropathy. New understanding of the pathogenesis of these diseases has had direct clinical implications for transplantation, allowing better identification of candidates at high risk of recurrence and earlier diagnoses, and it is expected to lead to significance improvements in the therapy and perhaps even prevention of GN recurrence. More than ever, it is essential to fully characterize GN before transplantation as this information will direct our management posttransplantation. Further, the relative rarity of recurrent GN dictates the need for multicenter studies in order to evaluate, test, and validate recent advances and therapies.

Membranous Nephropathy: A Journey From Bench to Bedside

Lessons from an animal model that faithfully resembles human membranous nephropathy (MN) have informed our understanding of the pathogenesis of this organ-specific autoimmune disease and common cause of nephrotic syndrome. After it was established that the subepithelial immune deposits that characterize experimental MN form in situ when circulating antibodies bind to an intrinsic podocyte antigen, it was merely a matter of time before the human antigen was identified. The M-type phospholipase A2 receptor 1 (PLA2R) represents the major target antigen in primary MN, and thrombospondin type 1 domain-containing 7A (THSD7A) was more recently identified as a minor antigen. Serologic tests for anti-PLA2R and kidney biopsy specimen staining for PLA2R show >90% specificity and 70% to 80% sensitivity for the diagnosis of primary MN in most populations. The assays distinguish most cases of primary MN from MN associated with other systemic diseases, and sequential anti-PLA2R titers are useful to monitor treatment response. A positive pretransplantation test result for anti-PLA2R is also helpful for predicting the risk for posttransplantation recurrence. Identification of target epitopes within PLA2R and the genetic association of primary MN with class II major histocompatibility and PLA2R1 variants are 2 additional examples of our evolving understanding of this disease.

Autoantibodies against thrombospondin type 1 domain-containing 7A induce membranous nephropathy

Membranous nephropathy (MN) is the most common cause of nephrotic syndrome in adults, and one-third of patients develop end-stage renal disease (ESRD). Circulating autoantibodies against the podocyte surface antigens phospholipase A2 receptor 1 (PLA2R1) and the recently identified thrombospondin type 1 domain-containing 7A (THSD7A) are assumed to cause the disease in the majority of patients. The pathogenicity of these antibodies, however, has not been directly proven. Here, we have reported the analysis and characterization of a male patient with THSD7A-associated MN who progressed to ESRD and subsequently underwent renal transplantation. MN rapidly recurred after transplantation. Enhanced staining for THSD7A was observed in the kidney allograft, and detectable anti-THSD7A antibodies were present in the serum before and after transplantation, suggesting that these antibodies induced a recurrence of MN in the renal transplant. In contrast to PLA2R1, THSD7A was expressed on both human and murine podocytes, enabling the evaluation of whether anti-THSD7A antibodies cause MN in mice. We demonstrated that human anti-THSD7A antibodies specifically bind to murine THSD7A on podocyte foot processes, induce proteinuria, and initiate a histopathological pattern that is typical of MN. Furthermore, anti-THSD7A antibodies induced marked cytoskeletal rearrangement in primary murine glomerular epithelial cells as well as in human embryonic kidney 293 cells. Our findings support a causative role of anti-THSD7A antibodies in the development of MN.

Acute and Chronic Allograft Dysfunction in Kidney Transplant Recipients

Allograft dysfunction after a kidney transplant is often clinically asymptomatic and is usually detected as an increase in serum creatinine level with corresponding decrease in glomerular filtration rate. The diagnostic evaluation may include blood tests, urinalysis, transplant ultrasonography, radionuclide imaging, and allograft biopsy. Whether it occurs early or later after transplant, allograft dysfunction requires prompt evaluation to determine its cause and subsequent management. Acute rejection, medication toxicity from calcineurin inhibitors, and BK virus nephropathy can occur early or later. Other later causes include transplant glomerulopathy, recurrent glomerulonephritis, and renal artery stenosis.

Pre-transplant phospholipase A2 receptor autoantibody concentration is associated with clinically significant recurrence of membranous nephropathy post-kidney transplantation

Previous studies that have assessed the association of pre-transplant antiphospholipase A2 receptor autoantibody (PLA2R-Ab) concentration with a recurrence of membranous nephropathy (rMN) post-kidney transplant have yielded variable results. We tested 16 consecutive transplant patients with a history of iMN for pre-transplant PLA2R-Ab. Enzyme-linked immunosorbent assay titers (Euroimmun, NJ, USA) >14 RU/mL were considered positive. A receiver operating characteristic (ROC) analysis was performed after combining data from Quintana et al. (n = 21; Transplantation February 2015) to determine a PLA2R-Ab concentration which could predict rMN. Six of 16 (37%) patients had biopsy-proven rMN at a median of 3.2 yr post-transplant. Of these, five of six (83%) had a positive PLA2R-Ab pre-transplant with a median of 82 RU/mL (range = 31-1500). The only patient who had rMN with negative PLA2R-Ab was later diagnosed with B-cell lymphoma. One hundred percent (n = 10) of patients with no evidence of rMN (median follow-up = five yr) had negative pre-transplant PLA2R-Ab. In a combined ROC analysis (n = 37), a pre-transplant PLA2R-Ab > 29 RU/mL predicted rMN with a sensitivity of 85% and a specificity of 92%. Pre-transplant PLA2R-Ab could be a useful tool for the prediction of rMN. Patients with rMN in the absence of PLA2R-Ab should be screened for occult malignancy and/or alternate antigens.

Recurrent Membranous Nephropathy After Kidney Transplantation: Treatment and Long-Term Implications

BACKGROUND

Membranous nephropathy (MN) can recur in kidney allografts leading to graft dysfunction and failure. The aims of these analyses were to assess MN recurrence, clinical and histologic progression, and response to anti-CD20 therapy.

METHODS

Included were 63 kidney allograft recipients with biopsy proven primary MN followed up for 77.0 (39-113) months (median, interquartile range). Disease recurrence was diagnosed by biopsy (protocol or clinical), and follow-up was monitored by laboratory parameters and protocol biopsies.

RESULTS

Thirty of 63 patients (48%) had histologic recurrence often during the first year. In 53% of the cases, recurrence was diagnosed by protocol biopsy. Recurrence risk was higher in patients with higher proteinuria pretransplant [hazard ratio = 1.869 (95% confidence interval, 1.164-3.001) per gram, P = 0.010] and those with anti-phospholipase A2 receptor antibodies [hazard ratio = 3.761 (1.635-8.652), P = 0.002]. Thirteen patients with recurrence had no clinical progression, and in 2, MN resolved histologically. Seventeen of 63 patients (27%) had progressive proteinuria and were treated with anti-CD20 antibodies, resulting in complete response in 9 (53%), partial response in 5 (29%), and no response in 3 (18%). Posttreatment biopsies were obtained in 15 patients and showed histologic resolution in 6 (40%). Disease recurrence did not correlate with graft survival. However, 5 of 11 (45.4%) graft losses were due to recurrent MN. Death-censored graft survival in MN did not differ from that of 273 control recipients with autosomal dominant polycystic kidney disease.

CONCLUSIONS

Membranous nephropathy recurs in 48% of cases threatening the allograft. Treatment of early but progressive recurrence with anti-CD20 antibodies is quite effective achieving clinical remission and histologic resolution of MN.

Epitope Spreading of Autoantibody Response to PLA2R Associates with Poor Prognosis in Membranous Nephropathy

The phospholipase A2 receptor (PLA2R1) is the major autoantigen in idiopathic membranous nephropathy. However, the value of anti-PLA2R1 antibody titers in predicting patient outcomes is unknown. Here, we screened serum samples from 50 patients positive for PLA2R1 for immunoreactivity against a series of PLA2R1 deletion mutants covering the extracellular domains. We identified reactive epitopes in the cysteine-rich (CysR), C-type lectin domain 1 (CTLD1), and C-type lectin domain 7 (CTLD7) domains and confirmed the reactivity with soluble forms of each domain. We then used ELISAs to stratify 69 patients positive for PLA2R1 by serum reactivity to one or more of these domains: CysR (n=23), CysRC1 (n=14), and CysRC1C7 (n=32). Median ELISA titers measured using the full-length PLA2R1 antigens were not statistically different between subgroups. Patients with anti-CysR-restricted activity were younger (P=0.008), had less nephrotic range proteinuria (P=0.02), and exhibited a higher rate of spontaneous remission (P=0.03) and lower rates of renal failure progression (P=0.002) and ESRD (P=0.01) during follow-up. Overall, 31 of 69 patients had poor renal prognosis (urinary protein/creatinine ratio >4 g/g or eGFR<45 ml/min per 1.73 m(2) at end of follow-up). High anti-PLA2R1 activity and epitope spreading beyond the CysR epitope were independent risk factors of poor renal prognosis in multivariable Cox regression analysis. Epitope spreading during follow-up associated with disease worsening (n=3), whereas reverse spreading from a CysRC1C7 profile back to a CysR profile associated with favorable outcome (n=1). We conclude that analysis of the PLA2R1 epitope profile and spreading is a powerful tool for monitoring disease severity and stratifying patients by renal prognosis.

Pathophysiological advances in membranous nephropathy: time for a shift in patient's care

Membranous nephropathy is a major cause of nephrotic syndrome of non-diabetic origin in adults. It is the second or third leading cause of end-stage renal disease in patients with primary glomerulonephritis, and is the leading glomerulopathy that recurs after kidney transplantation (occurring in about 40% of patients). Treatment with costly and potentially toxic drugs remains controversial and challenging, partly because of insufficient insight into the pathogenesis of the disease and absence of sensitive biomarkers of disease activity. The disease is caused by the formation of immune deposits on the outer aspect of the glomerular basement membrane, which contain podocyte or planted antigens and circulating antibodies specific to those antigens, resulting in complement activation. In 2002, podocyte neutral endopeptidase was identified as an antigenic target of circulating antibodies in alloimmune neonatal nephropathy, and in 2009, podocyte phospholipase A2 receptor (PLA2R) was reported as an antigenic target in autoimmune adult membranous nephropathy. These major breakthroughs were translated to clinical practice very quickly. Measurement of anti-PLA2R antibodies in serum and detection of PLA2R antigen in glomerular deposits can now be done routinely. Anti-PLA2R antibodies have high specificity (close to 100%), sensitivity (70-80%), and predictive value. PLA2R detection in immune deposits allows for retrospective diagnosis of PLA2R-related membranous nephropathy in archival kidney biopsies. These tests already have a major effect on diagnosis and monitoring of treatment, including after transplantation.

Autoantibodies in renal diseases - clinical significance and recent developments in serological detection

Autoimmune dysfunctions are the "bête noire" in a range of debilitating nephropathies. Autoimmune-mediated damage to the kidneys can be triggered by autoantibodies directed against specific proteins or renal structures, for example, the phospholipase A2 receptor or the glomerular basement membrane, resulting in glomerular diseases such as primary membranous nephropathy or Goodpasture's disease. Moreover, secondary damage to the kidney can be part of the wide-reaching effects of systemic autoimmune diseases such as vasculitis or systemic lupus erythematosus (SLE) - the latter counts lupus nephritis among its most severe manifestations. Systemic autoimmune diseases are characterized by non-organ-specific autoantibodies, directed for example against neutrophil cytoplasmic antigens in systemic vasculitis and against double-stranded DNA and nucleosomes in SLE. A large variety of innovative and highly specific and sensitive autoantibody tests have been developed in the last years that are available to identify autoimmune kidney diseases at an early stage. Thus, serological in vitro diagnostics allow for appropriate interventional therapy in order to prevent disease progression often resulting in need of dialysis and transplantation.

Anti-phospholipase A₂ receptor antibodies in recurrent membranous nephropathy

About 70% of patients with primary membranous nephropathy (MN) have circulating anti-phospholipase A2 receptor (PLA2R) antibodies that correlate with disease activity, but their predictive value in post-transplant (Tx) recurrent MN is uncertain. We evaluated 26 patients, 18 with recurrent MN and 8 without recurrence, with serial post-Tx serum samples and renal biopsies to determine if patients with pre-Tx anti-PLA2R are at increased risk of recurrence as compared to seronegative patients and to determine if post-Tx changes in anti-PLA2R correspond to the clinical course. In the recurrent group, 10/17 patients had anti-PLA2R at the time of Tx versus 2/7 patients in the nonrecurrent group. The positive predictive value of pre-Tx anti-PLA2R for recurrence was 83%, while the negative predictive value was 42%. Persistence or reappearance of post-Tx anti-PLA2R was associated with increasing proteinuria and resistant disease in 6/18 cases; little or no proteinuria occurred in cases with pre-Tx anti-PLA2R and biopsy evidence of recurrence in which the antibodies resolved with standard immunosuppression. Some cases with positive pre-Tx anti-PLA2R were seronegative at the time of recurrence. In conclusion, patients with positive pre-Tx anti-PLA2R should be monitored closely for recurrent MN. Persistence or reappearance of antibody post-Tx may indicate a more resistant disease.

Translational nephrology: what translational research is and a bird's-eye view on translational research in nephrology

The ultimate aim of biomedical research is to preserve health and improve patient outcomes. However, by a variety of measures, preservation of kidney health and patient outcomes in kidney disease are suboptimal. Severe acute kidney injury has been treated solely by renal replacement therapy for over 50 years and mortality still hovers at around 50%. Worldwide deaths from chronic kidney disease (CKD) increased by 80% in 20 years--one of the greatest increases among major causes of death. This dramatic data concur with huge advances in the cellular and molecular pathophysiology of kidney disease and its consequences. The gap appears to be the result of sequential roadblocks that impede an adequate flow from basic research to clinical development [translational research type 1 (T1), bench-to-bed and back] and from clinical development to clinical practice and widespread implementation (translational research T2) that supported by healthcare policy-making reaches all levels of society throughout the globe (sometimes called translational research T3). Thus, it is more than 10 years since the introduction of the last new-concept drug for CKD patients, cinacalcet; and 30 years since the introduction of reninangiotensin system (RAS) blockade, the current mainstay to prevent progression of CKD, illustrating the basic science-clinical practice disconnect. Roadblocks from clinical advances to widespread implementation, together with lag time-to-benefit may underlie the 20 years since the description of the antiproteinuric effect of RAS blockade to the observation of decreased age-adjusted incidence of endstage renal disease due to diabetic kidney disease. Only a correct understanding of the roadblocks in translational medicine and a full embracement of a translational research culture will spread the benefits of the biomedical revolution to its ultimate destinatary, the society.

Thrombospondin type-1 domain-containing 7A in idiopathic membranous nephropathy

BACKGROUND

Idiopathic membranous nephropathy is an autoimmune disease. In approximately 70% of patients, it is associated with autoantibodies against the phospholipase A2 receptor 1 (PLA2R1). Antigenic targets in the remaining patients are unknown.

METHODS

Using Western blotting, we screened serum samples from patients with idiopathic membranous nephropathy, patients with other glomerular diseases, and healthy controls for antibodies against human native glomerular proteins. We partially purified a putative new antigen, identified this protein by means of mass spectrometry of digested peptides, and validated the results by analysis of recombinant protein expression, immunoprecipitation, and immunohistochemical analysis.

RESULTS

Serum samples from 6 of 44 patients in a European cohort and 9 of 110 patients in a Boston cohort with anti-PLA2R1-negative idiopathic membranous nephropathy recognized a glomerular protein that was 250 kD in size. None of the serum samples from the 74 patients with idiopathic membranous nephropathy who were seropositive for anti-PLA2R1 antibodies, from the 76 patients with other glomerular diseases, and from the 44 healthy controls reacted against this antigen. Although this newly identified antigen is clearly different from PLA2R1, it shares some biochemical features, such as N-glycosylation, membranous location, and reactivity with serum only under nonreducing conditions. Mass spectrometry identified this antigen as thrombospondin type-1 domain-containing 7A (THSD7A). All reactive serum samples recognized recombinant THSD7A and immunoprecipitated THSD7A from glomerular lysates. Moreover, immunohistochemical analyses of biopsy samples from patients revealed localization of THSD7A to podocytes, and IgG eluted from one of these samples was specific for THSD7A.

CONCLUSIONS

In our cohort, 15 of 154 patients with idiopathic membranous nephropathy had circulating autoantibodies to THSD7A but not to PLA2R1, a finding that suggests a distinct subgroup of patients with this condition. (Funded by the French National Center for Scientific Research and others.).

Anti-phospholipase A2 receptor antibodies and the pathogenesis of membranous nephropathy

Since the early 2000s, considerable advances have been achieved in the understanding of molecular pathomechanisms of human membranous nephropathy (MN), inspired by studies of Heymann nephritis, a faithful experimental model. These studies led to the identification of neutral endopeptidase, the type-M phospholipase A2 receptor (PLA2R), and cationic bovine serum albumin as target antigens of circulating and deposited antibodies in neonatal alloimmune, adult 'idiopathic', and early childhood MN, respectively. A genome-wide association study further showed a highly significant association of the PLA2R1 and the HLA-DQA1 loci with idiopathic MN in patients of white ancestry. The time has come to revisit the spectrum of MN based on the newly identified antigen-antibody systems which should be considered as molecular signatures of the disease, challenging the uniform histological definition. Although some uncertainties remain as to the pathogenic effects of anti-PLA2R antibodies because of the lack of an appropriate experimental model, the value of these antibodies as biomarkers for diagnosis and disease activity is increasingly being recognized. It is not exaggerated to state that they have induced a paradigm shift in the monitoring of patients with MN, thus opening a new era of personalized medicine.