IgG subclasses and complement pathway in segmental and global membranous nephropathy

Mannose-Binding Lectin Deposition in Membranous Nephropathy and Differentiation of Primary from Secondary Forms

The differentiation between primary and secondary forms of membranous nephropathy (MN) is a cornerstone that is necessary for adequate decision making regarding the treatment options and behavior of each specific case. Kidney biopsy and antibody results can be controversial, and a unique biomarker has still not been found.

BACKGROUND AND OBJECTIVES

We investigated the lack of mannose-binding lectin (MBL) deposition in patients with secondary MNs (sMNs) with the presence of IgG4 deposition in relation to the presence of MBL deposition in patients with primary MNs (pMNs). We also established a connection between the stage of MN and MBL deposition.

MATERIALS AND METHODS

Materials from 72 renal biopsies with proven MN were used for immunohistochemistry staining (IHC) for the phospholipase A2 receptor (PLA2R), immunoglobulin subtype IgG4, and MBL. Patients were separated into one of the following three groups: primary MN (pMN), idiopathic MN (iMN), and secondary MN (sMN). Serum antibodies for PLA2R and thrombospondin type-I-domain-containing 7A (THSD7A) were also used for the precise evaluation of the type of MN, as well as for detecting positivity for PLA2R using IHC. Which stage of MN was present in relation to the deposition of MBL was evaluated.

RESULTS

In total, 50 patients were positive for IgG4, 34 with pMN, 12 with iMN, and 4 with sMN. A total of 20 patients were positive for MBL, 14 with pMN and 6 with iMN; no MBL deposits were found in patients with sMN. MBL positivity was predominantly present in the first two stages of MN, with a gradual reduction in the later stages.

CONCLUSIONS

The activation of the lectin-complement pathway occurs in the early stages of the disease and is associated with the deposition of IgG4; IgG4 deposition is present in sMN, but there is no MBL deposition. IgG4 cannot be used for the differentiation of primary from secondary MNs, but the lack of MBL can be used as a marker for sMN in the early stages of the disease.

The complement system in the pathogenesis and progression of kidney diseases: What doesn't kill you makes you older

The Complement System is an evolutionarily conserved component of immunity that plays a key role in host defense against infections and tissue homeostasis. However, the dysfunction of the Complement System can result in tissue damage and inflammation, thereby contributing to the development and progression of various renal diseases, ranging from atypical Hemolytic Uremic Syndrome to glomerulonephritis. Therapeutic interventions targeting the complement system have demonstrated promising results in both preclinical and clinical studies. Currently, several complement inhibitors are being developed for the treatment of complement-mediated renal diseases. This review aims to summarize the most recent insights into complement activation and therapeutic inhibition in renal diseases. Furthermore, it offers potential directions for the future rational use of complement inhibitor drugs in the context of renal diseases.

An Updated Review of Membranous Nephropathy

Membranous nephropathy (MN) is one of the most common causes of nephrotic syndrome in adults. The discovery of phospholipase A2 receptor (PLA2R) as a target antigen has led to a paradigm shift in the understanding and management of MN. At present, serum PLA2R antibodies are used for diagnosis, prognostication, and guiding treatment. Now, with the discovery of more than 20 novel target antigens, antigen mapping is almost complete. The clinical association of certain antigens provides clues for clinicians, such as the association of nerve epidermal growth factor-like 1 with malignancies and indigenous medicines. Serum antibodies are detected for most target antigens, except exostosin 1 and 2 and transforming growth factor-beta receptor 3, but their clinical utility is yet to be defined. Genome-wide association studies and studies investigating environmental factors, such as air pollution, shed more light on the underpinnings of MN. The standard therapy of MN diversified from cyclical cyclophosphamide and steroids to include rituximab and calcineurin inhibitors over the past decades. Here, we provide a cutting-edge review of MN, focusing on genetics, immune system and environmental factors, novel target antigens and their clinical characteristics, and currently available and emerging novel therapies in MN.

Complement activation and effector pathways in membranous nephropathy

Complement activation has long been recognized as a central feature of membranous nephropathy (MN). Evidence for its role has been derived from the detection of complement products in biopsy tissue and urine from patients with MN and from mechanistic studies primarily based on the passive Heymann nephritis model. Only recently, more detailed insights into the exact mechanisms of complement activation and effector pathways have been gained from patient data, animal models, and in vitro models based on specific target antigens relevant to the human disease. These data are of clinical relevance, as they parallel the recent development of numerous specific complement therapeutics for clinical use. Despite efficient B-cell depletion, many patients with MN achieve only partial remission of proteinuria, which may be explained by the persistence of subepithelial immune complexes and ongoing complement-mediated podocyte injury. Targeting complement, therefore, represents an attractive adjunct treatment for MN, but it will need to be tailored to the specific complement pathways relevant to MN. This review summarizes the different lines of evidence for a central role of complement in MN and for the relevance of distinct complement activation and effector pathways, with a focus on recent developments.

The Safety and Efficacy of Rituximab-Based Regimen in Atypical Membranous Nephropathy: A Single Center Retrospective Cohort Study

Purpose

There are increasing reports of atypical membranous nephropathy (AMN) cases with similar pathological characteristics to secondary membranous nephropathy (SMN) without definite underlying causes. Although rituximab has become a first-line option in treating idiopathic membranous nephropathy (IMN), the efficacy and safety of rituximab-based regimen for AMN is not clear.

Patients and Methods

This is a retrospective, single-center study. AMN patients who received rituximab-based therapy were included. IMN patients treated with rituximab during the same period were selected as the control group matched by gender, sex, baseline urinary protein and albumin levels. Baseline data and follow-up data were collected.

Results

A total of 20 AMN patients and 40 IMN patients were included. The baseline levels of urinary protein were comparable between the two groups [6.77 (IQR 3.34, 11.49) g/24 h vs 6.47 (IQR 3.4, 10.76) g/24 h, P=0.944]. The baseline levels of serum albumin were 26.15±6.71 g/L and 26.8±5.54 g/L (P=0.689) respectively. The cumulative remission rate for rituximab-based treatment at the 12th month was lower in AMN group than IMN group [13 (65%) vs 36 (90%), P=0.045]. In AMN group, non-responders showed a higher level of proteinuria and a worse renal function at baseline than those of responders. There was no significant difference in the overall adverse events or serious adverse events between the two groups.

Conclusion

In our study, AMN patients obtained proteinuria remission in a lower percentage compared with IMN patients. In general, rituximab-based therapy is effective in AMN patients with an acceptable safety profile.

The classical pathway triggers pathogenic complement activation in membranous nephropathy

Membranous nephropathy (MN) is an antibody-mediated autoimmune disease characterized by glomerular immune complexes containing complement components. However, both the initiation pathways and the pathogenic significance of complement activation in MN are poorly understood. Here, we show that components from all three complement pathways (alternative, classical and lectin) are found in renal biopsies from patients with MN. Proximity ligation assays to directly visualize complement assembly in the tissue reveal dominant activation via the classical pathway, with a close correlation to the degree of glomerular C1q-binding IgG subclasses. In an antigen-specific autoimmune mouse model of MN, glomerular damage and proteinuria are reduced in complement-deficient mice compared with wild-type littermates. Severe disease with progressive ascites, accompanied by extensive loss of the integral podocyte slit diaphragm proteins, nephrin and neph1, only occur in wild-type animals. Finally, targeted silencing of C3 using RNA interference after the onset of proteinuria significantly attenuates disease. Our study shows that, in MN, complement is primarily activated via the classical pathway and targeting complement components such as C3 may represent a promising therapeutic strategy.

Lectin Complement Pathway Activation is Associated with Massive Proteinuria in PLA2R-Positive Membranous Nephropathy: A Retrospective Study

Introduction

Complement activation is highly involved in membranous nephropathy. Identifying the mechanism of the complement activation pathway carries crucial therapeutic implications yet remains controversial. This study explored lectin complement pathway activation in PLA2R-associated membranous nephropathy (MN).

Methods

One hundred and seventy-six patients with biopsy-proven PLA2R-associated MN were enrolled in the retrospective study and divided into the remission group (24-hour urine protein <0.75g and serum albumin >35 g/L) and the nephrotic syndrome group. The clinical manifestation and C3, C4d, C1q, MBL, and B factor in renal biopsy tissues and C3, C4, and immunoglobulins in serum were evaluated.

Results

Deposition of glomerular C3, C4d, and mannose-binding lectin (MBL) was significantly higher in the activated state than in the remission state in PLA2R-associated MN. MBL deposition was the risk factor for no remission. During follow-up, the persistent non-remission patients have significantly lower serum C3 levels.

Conclusion

Activation of the lectin complement pathway in PLA2R-associated MN may contribute to proteinuria progression and disease activity.

Factors affecting IgG4-mediated complement activation

Of the four human immunoglobulin G (IgG) subclasses, IgG4 is considered the least inflammatory, in part because it poorly activates the complement system. Regardless, in IgG4 related disease (IgG4-RD) and in autoimmune disorders with high levels of IgG4 autoantibodies, the presence of these antibodies has been linked to consumption and deposition of complement components. This apparent paradox suggests that conditions may exist, potentially reminiscent of in vivo deposits, that allow for complement activation by IgG4. Furthermore, it is currently unclear how variable glycosylation and Fab arm exchange may influence the ability of IgG4 to activate complement. Here, we used well-defined, glyco-engineered monoclonal preparations of IgG4 and determined their ability to activate complement in a controlled system. We show that IgG4 can activate complement only at high antigen and antibody concentrations, via the classical pathway. Moreover, elevated or reduced Fc galactosylation enhanced or diminished complement activation, respectively, with no apparent contribution from the lectin pathway. Fab glycans slightly reduced complement activation. Lastly, we show that bispecific, monovalent IgG4 resulting from Fab arm exchange is a less potent activator of complement than monospecific IgG4. Taken together, these results imply that involvement of IgG4-mediated complement activation in pathology is possible but unlikely.

Kidney diseases

Dysregulation and accelerated activation of the alternative pathway (AP) of complement is known to cause or accentuate several pathologic conditions in which kidney injury leads to the appearance of hematuria and proteinuria and ultimately to the development of chronic renal failure. Multiple genetic and acquired defects involving plasma- and membrane-associated proteins are probably necessary to impair the protection of host tissues and to confer a significant predisposition to AP-mediated kidney diseases. This review aims to explore how our current understanding will make it possible to identify the mechanisms that underlie AP-mediated kidney diseases and to discuss the available clinical evidence that supports complement-directed therapies. Although the value of limiting uncontrolled complement activation has long been recognized, incorporating complement-targeted treatments into clinical use has proved challenging. Availability of anti-complement therapy has dramatically transformed the outcome of atypical hemolytic uremic syndrome, one of the most severe kidney diseases. Innovative drugs that directly counteract AP dysregulation have also opened new perspectives for the management of other kidney diseases in which complement activation is involved. However, gained experience indicates that the choice of drug should be tailored to each patient's characteristics, including clinical, histologic, genetic, and biochemical parameters. Successfully treating patients requires further research in the field and close collaboration between clinicians and researchers who have special expertise in the complement system.

Clinical and pathologic features of primary membranous nephropathy in Turkey: a multicenter study by the Turkish Society of Nephrology Glomerular Diseases Working Group

Background

We aimed to evaluate the features of primary membranous nephropathy (MNP) in Turkish people.

Methods

This is a retrospective analysis of patients with biopsy-proven primary MNP. We obtained the data collected between 2009 and 2019 in the primary glomerulonephritis registry of the Turkish Society of Nephrology Glomerular Diseases Study Group (TSN-GOLD). Patients with a secondary cause for MNP were excluded. Clinical, demographic, laboratory, and histopathological findings were analyzed.

Results

A total of 995 patients with primary MNP were included in the analyses. Males constituted the majority (58.8%). The mean age was 48.4 ± 13.9 years. The most common presentation was the presence of nephrotic syndrome (81.7%) and sub nephrotic proteinuria (10.3%). Microscopic hematuria was detected in one-third of patients. The median estimated glomerular filtration rate (eGFR) was 100.6 mL/min/1.73 m² (IQR, 75.4–116.3), and median proteinuria was 6000 mg/d (IQR, 3656–9457). Serum C3 and C4 complement levels were decreased in 3.7 and 1.7% of patients, respectively. Twenty-four (2.4%) patients had glomerular crescents in their kidney biopsy samples. Basal membrane thickening was detected in 93.8% of cases under light microscopy. Mesangial proliferation and interstitial inflammation were evident in 32.8 and 55.9% of the patients, respectively. The most commonly detected depositions were IgG (93%), C3 complement (68.8%), and kappa and lambda immunoglobulin light chains (70%). Although renal functions were normal at presentation, vascular, interstitial, and glomerular findings were more prominent on biopsy in hypertensive patients. No significant effect of BMI on biopsy findings was observed.

Conclusions

Despite some atypical findings, the main features of primary MNP in Turkey were similar to the published literature. This is the largest MNP study to date conducted in Turkish people.

The role of the complement system in primary membranous nephropathy: A narrative review in the era of new therapeutic targets

Primary membranous nephropathy (MN) is an important cause of nephrotic syndrome and chronic kidney disease (CKD) in the adult population. Although the discovery of different autoantibodies against glomerular/podocytic antigens have highlighted the role of B cells in the pathogenesis of MN, suboptimal response or even resistance to B cell-directed therapies occurs, suggesting that other pathophysiological mechanisms are involved in mediating podocyte injury. The complement system plays an important role in the innate immune response to infection, and dysregulation of the complement system has been observed in various kidney diseases. There is compelling evidence of complement cascade activation in primary MN, with the mannose-binding lectin (MBL) and alternative pathways particularly implicated. With appropriate validation, assays of complements and associated activation products could hold promise as adjunctive tools for non-invasive disease monitoring and prognostication. While there is growing interest to target the complement system in MN, there is concern regarding the risk of infection due to encapsulated organisms and high treatment costs, highlighting the need for clinical trials to identify patients most likely to benefit from complement-directed therapies.

Modern view on the complement system role in membranous nephropathy

Membranous nephropathy (MN), an immune-mediated glomerular disease, is the most common cause of adult nephrotic syndrome. In MN, proteinuria is developed by podocyte damage due to the complement system activation in response to the subepithelial deposition of immune complexes containing various auto- and exogenous antigens. Membrane-attacking complex (MAC) is the terminal product of any complement pathways activation (classical, lectin or alternative) and plays the leading role in the complement-mediated podocytic damage. Thus far, the main pathway of complement activation leading to the formation of MAC in MN has not been established. The review highlights current evidence of various complement pathways activation in the development of MN, as well as recently established new molecular mechanisms of complement-mediated podocyte damage.

Classical complement pathway factor alterations in narcolepsy

OBJECTIVE

Narcolepsy is a chronic sleep disorder long hypothesised to be an autoimmune disease. Complement-mediated immune mechanisms have not been investigated in detail in narcolepsy. Our aim was to establish the significance of classical pathway activation in narcolepsy.

METHODS

Sera of 42 narcolepsy patients and 26 healthy controls were screened with ELISA to determine the levels of C1q, C3a, C4d and complement component 4 binding protein (C4BP). A home-made ELISA method was developed to detect antibodies to C4BP-alpha (anti-C4BPA). The correlation between complement levels and clinical findings was examined.

RESULTS

C1q levels were significantly higher in narcolepsy patients while C4d and C4BP levels were significantly lower compared to healthy controls. C3a levels were comparable among patients and controls. Eleven narcolepsy patients showed serum anti-C4BPA levels. Total rapid eye movements (REM) time, sleep onset latency, REM sleep latency, sleep activity, percentage of wakefulness after sleep onset and Epworth sleepiness scale scores were correlated with levels of different complement factors.

CONCLUSION

Complement-mediated immune mechanisms might partake in narcolepsy pathogenesis. The precise role of autoantibodies on complement level alterations needs to be investigated. Levels of complement factors and degradation products may potentially be utilised as biomarkers to predict the clinical severity of narcolepsy.

IgG4 Autoantibodies in Organ-Specific Autoimmunopathies: Reviewing Class Switching, Antibody-Producing Cells, and Specific Immunotherapies

Organ-specific autoimmunity is often characterized by autoantibodies targeting proteins expressed in the affected tissue. A subgroup of autoimmunopathies has recently emerged that is characterized by predominant autoantibodies of the IgG4 subclass (IgG4-autoimmune diseases; IgG4-AID). This group includes pemphigus vulgaris, thrombotic thrombocytopenic purpura, subtypes of autoimmune encephalitis, inflammatory neuropathies, myasthenia gravis and membranous nephropathy. Although the associated autoantibodies target specific antigens in different organs and thus cause diverse syndromes and diseases, they share surprising similarities in genetic predisposition, disease mechanisms, clinical course and response to therapies. IgG4-AID appear to be distinct from another group of rare immune diseases associated with IgG4, which are the IgG4-related diseases (IgG4-RLD), such as IgG4-related which have distinct clinical and serological properties and are not characterized by antigen-specific IgG4. Importantly, IgG4-AID differ significantly from diseases associated with IgG1 autoantibodies targeting the same organ. This may be due to the unique functional characteristics of IgG4 autoantibodies (e.g. anti-inflammatory and functionally monovalent) that affect how the antibodies cause disease, and the differential response to immunotherapies of the IgG4 producing B cells/plasmablasts. These clinical and pathophysiological clues give important insight in the immunopathogenesis of IgG4-AID. Understanding IgG4 immunobiology is a key step towards the development of novel, IgG4 specific treatments. In this review we therefore summarize current knowledge on IgG4 regulation, the relevance of class switching in the context of health and disease, describe the cellular mechanisms involved in IgG4 production and provide an overview of treatment responses in IgG4-AID.

New Insights into the Treatment of Glomerular Diseases: When Mechanisms Become Vivid

Treatment for glomerular diseases has been extrapolated from the experience of other autoimmune disorders while the underlying pathogenic mechanisms were still not well understood. As the classification of glomerular diseases was based on patterns of juries instead of mechanisms, treatments were typically the art of try and error. With the advancement of molecular biology, the role of the immune agent in glomerular diseases is becoming more evident. The four-hit theory based on the discovery of gd-IgA1 gives a more transparent outline of the pathogenesis of IgA nephropathy (IgAN), and dysregulation of Treg plays a crucial role in the pathogenesis of minimal change disease (MCD). An epoch-making breakthrough is the discovery of PLA2R antibodies in the primary membranous nephropathy (pMN). This is the first biomarker applied for precision medicine in kidney disease. Understanding the immune system's role in glomerular diseases allows the use of various immunosuppressants or other novel treatments, such as complement inhibitors, to treat glomerular diseases more reasonable. In this era of advocating personalized medicine, it is inevitable to develop precision medicine with mechanism-based novel biomarkers and novel therapies in kidney disease.

Comparison of Complement Pathway Activation in Autoimmune Glomerulonephritis

Introduction

Methods

Results

Conclusion

The diagnostic value of immunohistochemical staining of the interstitial vascular C4d complement in membranous nephropathy

Membranous glomerulonephritis (MGN) is the most common cause of adulthood nephrotic syndrome. Diagnosis of membranous nephritis is based on light electron immunofluorescence microscopy and clinical signs. Immune complex deposition against podocyte antigens such as phospholipase A2 receptor (PLA2R) activates the complement system. Of this, complement Component C4d (C4d) is involved in the classical and lectin pathways. This marker may be used by immunohistochemistry to diagnose MGN when other methods are not available. In this work, C4d expression was monitored by immunohistochemical analysis in the glomerular capillaries of patients with primary MGN (study group, N=33) versus patients with minimal change disease (MCD, control group, N=20) in a cross-sectional evaluation performed based on the diagnosis confirmed by light microscopy and immunofluorescence. There was no significant demographic difference between the two groups except for age (P=0.002). C4d immune-expression was positive in glomerular capillary (2+ to 4+) in most of the MGN patients, while it was negative in the MCD group. The sensitivity and specificity of C4d immunostaining were 95% and 100%, respectively. The Pearson correlation coefficient was 0.74 between C4d (immunohistochemistry) and immunoglobulins (IgG; immunofluorescence) and 0.65 between C4d (immunohistochemistry) and the C3 complement product (immunofluorescence). Immunohistochemical evaluation of C4d is, therefore, a sensitive and specific method that has a high correlation with IgG immunofluorescence.

Structural modulation of gut microbiota during alleviation of experimental passive Heymann nephritis in rats by a traditional Chinese herbal formula

BACKGROUND

Jianpi-Qushi-Heluo formula (JQHF) has been used to treat idiopathic membranous nephropathy (IMN) in hospitals for many years.

PURPOSE

Elucidating the protective effect and exploring the potential mechanism of JQHF against IMN.

METHODS

Passive Heymann nephritis (PHN) was induced in rats by a single tail vein injection of anti-Fx1A antiserum. Then, the animals were treated with JQHF at 16.2 g/kg or 32.4 g/kg, with benzepril (10 mg/kg) as a positive control. Renal function was evaluated by biochemical measurements and pathological testing. Fecal samples were collected before and after treatment to analyze the gut microbiota composition by shotgun whole metagenome sequencing.

RESULTS

JQHF exhibited potent efficacy in ameliorating PHN at both doses, as revealed by decreasing the deposition of IgG and C5b-9, relieving podocyte injury, and reducing glomerular and tubular cell apoptosis. The lower dose was corresponding to the clinical dosage and showed better therapeutic effects than the higher dose. Metagenomic analysis showed that gavage with 16.2 g/kg of JQHF shifted the structure of the gut microbiota in PHN rats and significantly increased the relative abundances of Prevotella copri, Lactobacillus vaginalis and Subdoligranulum variabile. Particularly, S. variabile was strongly negatively correlated with serum levels of TC and TG, the deposition of IgG and C5b-9, and apoptosis of glomerular cells.

CONCLUSIONS

The JQHF is an effective agent for the treatment of experimental PHN. The PHN-allevating effect of JQHF is associated with specific alternation of gut microbiota.

Renal diseases and the role of complement: Linking complement to immune effector pathways and therapeutics

The complement system is an ancient and phylogenetically conserved key danger sensing system that is critical for host defense against pathogens. Activation of the complement system is a vital component of innate immunity required for the detection and removal of pathogens. It is also a central orchestrator of adaptive immune responses and a constituent of normal tissue homeostasis. Once complement activation occurs, this system deposits indiscriminately on any cell surface in the vicinity and has the potential to cause unwanted and excessive tissue injury. Deposition of complement components is recognized as a hallmark of a variety of kidney diseases, where it is indeed associated with damage to the self. The provenance and the pathophysiological role(s) played by complement in each kidney disease is not fully understood. However, in recent years there has been a renaissance in the study of complement, with greater appreciation of its intracellular roles as a cell-intrinsic system and its interplay with immune effector pathways. This has been paired with a profusion of novel therapeutic agents antagonizing complement components, including approved inhibitors against complement components (C)1, C3, C5 and C5aR1. A number of clinical trials have investigated the use of these more targeted approaches for the management of kidney diseases. In this review we present and summarize the evidence for the roles of complement in kidney diseases and discuss the available clinical evidence for complement inhibition.

Immune-mediated membranous nephropathy: Long term fluconazole usage caused podocyte autophagy

The primary consequences of membranous nephropathy (MN) are the development of nephrotic syndrome including hypogammaglobulinemia, the increased infectious risk, the loss of protein-bound vitamin D, and, above all, an elevated thromboembolic incidence of up to 50% in severe proteinuria patients. Membrane nephropathy may be either idiopathic or primary, not recognized (70%-80%) or secondary (20%-30%) to pathological sicknesses such as hepatitis B, systemic lupus erythematosus, malignancies, and side-effects of medicines. The immunological responses in MN involve multiple components: immunoglobulin G (IgG), long-escaped antigens, and the membrane attachment complex, formed by the supplement to form C5b-9. In general, IgG4 is the most significant IgG subclass deposited in idiopathic membranous nephropathic disease but fluctuating IgG1 levels also are linked with immunological deposits. In contrast, IgG1, IgG2, and IgG3 deposition are greater than IgG4 deposition in secondary nephropathy. Fluconazole is a synthetic antifungal triazole that is often used. It is well tolerated in general and has never been identified as a cause of nephropathies. We report on the development of MN caused by fluconazole therapy that could potentiate podocyte autophagy.

Contactin-1 is a novel target antigen in membranous nephropathy associated with chronic inflammatory demyelinating polyneuropathy

Primary membranous nephropathy (MN) is an autoimmune glomerular disease in which autoantibodies are directed against podocyte proteins. In about 80% of cases the main targeted antigen is the phospholipase A2 receptor 1 (PLA2R1). Anti-PLA2R1 antibodies are mainly immunoglobulin G type 4 (IgG4). However, the antigenic target remains to be defined in 20% of cases. MN can be associated with chronic inflammatory demyelinating polyneuropathy, an autoimmune disease of the peripheral nervous system where a common antigenic target has yet to be identified. To ascertain a possible novel target antigen, we analyzed kidney biopsies from five patients positive for anti-contactin 1 antibodies and presenting with MN combined with chronic inflammatory demyelinating polyneuropathy. Eluted IgG from biopsy sections against contactin 1 and nerve tissue were screened. Western blot revealed contactin 1 expression in normal kidney glomeruli. Confocal microscopic analysis showed the presence and colocalization of contactin 1 and IgG4 on the glomerular basement membrane of these patients. Glomerular contactin 1 was absent in patients with anti-PLA2R1-associated MN or membranous lupus nephritis or a healthy control. The eluted IgG from contactin 1-positive biopsy sections but not the IgG eluted from patients with PLA2R1 MN bound contactin 1 with the main eluted subclass IgG4. Eluted IgG could bind paranodal tissue (myelinated axon) and colocalized with commercial anti-contactin 1 antibody. Thus, contactin 1 is a novel common antigenic target in MN associated with chronic inflammatory demyelinating polyneuropathy. However, the precise pathophysiology remains to be elucidated.

Short- and Long-Lived Autoantibody-Secreting Cells in Autoimmune Neurological Disorders

As B cells differentiate into antibody-secreting cells (ASCs), short-lived plasmablasts (SLPBs) are produced by a primary extrafollicular response, followed by the generation of memory B cells and long-lived plasma cells (LLPCs) in germinal centers (GCs). Generation of IgG4 antibodies is T helper type 2 (Th2) and IL-4, -13, and -10-driven and can occur parallel to IgE, in response to chronic stimulation by allergens and helminths. Although IgG4 antibodies are non-crosslinking and have limited ability to mobilize complement and cellular cytotoxicity, when self-tolerance is lost, they can disrupt ligand-receptor binding and cause a wide range of autoimmune disorders including neurological autoimmunity. In myasthenia gravis with predominantly IgG4 autoantibodies against muscle-specific kinase (MuSK), it has been observed that one-time CD20⁺ B cell depletion with rituximab commonly leads to long-term remission and a marked reduction in autoantibody titer, pointing to a short-lived nature of autoantibody-secreting cells. This is also observed in other predominantly IgG4 autoantibody-mediated neurological disorders, such as chronic inflammatory demyelinating polyneuropathy and autoimmune encephalitis with autoantibodies against the Ranvier paranode and juxtaparanode, respectively, and extends beyond neurological autoimmunity as well. Although IgG1 autoantibody-mediated neurological disorders can also respond well to rituximab induction therapy in combination with an autoantibody titer drop, remission tends to be less long-lasting and cases where titers are refractory tend to occur more often than in IgG4 autoimmunity. Moreover, presence of GC-like structures in the thymus of myasthenic patients with predominantly IgG1 autoantibodies against the acetylcholine receptor and in ovarian teratomas of autoimmune encephalitis patients with predominantly IgG1 autoantibodies against the N‐methyl‐d‐aspartate receptor (NMDAR) confers increased the ability to generate LLPCs. Here, we review available information on the short-and long-lived nature of ASCs in IgG1 and IgG4 autoantibody-mediated neurological disorders and highlight common mechanisms as well as differences, all of which can inform therapeutic strategies and personalized medical approaches.

Diagnostic and prognostic significance of extent of subepithelial electron dense deposits in membranous glomerulonephritis

There are limited data concerning the range and diagnostic significance of the extent of subepithelial electron dense deposits (SEEDD) in membranous glomerulonephritis (MGN). We described the range, and assessed the diagnostic and prognostic significance of extent of SEEDD, particularly in patients with sparse SEEDD, where diagnostic difficulty can arise. Adult renal biopsies with a confident or suspected histological diagnosis of MGN between 2013 and 2020 were included. Patients were classified based on extent of SEEDD as having either global MGN (GMGN, >75% SEEDD), segmental MGN (SMGN, 25%-75% SEEDD), or sparse-SEEDD (<25% SEEDD). Clinical and other features were compared. One hundred and eleven (74%) patients had GMGN; 23 (15%) had SMGN; and 16 (11%) had sparse-SEEDD. Patients with sparse-SEEDD had a significantly shorter duration of nephrotic syndrome prior to biopsy. 53% of patients with GMGN and 14% with SMGN had serum anti-phospholipase A2 receptor (PLA2r) antibodies. Patients with sparse-SEEDD did not have anti-PLA2r antibodies. Urine protein:creatinine ratio was significantly lower in sparse-SEEDD patients after 3, 6, 9, and 12 months. The proportion of sparse-SEEDD patients in complete remission from nephrotic range proteinuria at 6 and 12 months was significantly higher than that of GMGN patients. Analysis of a subgroup suggested sparse-SEEDD patients responded more rapidly to steroid containing immunosuppression than GMGN patients. There is a wide range of extent of SEEDD in patients with MGN. Sparse-SEEDD appears distinct from SMGN and GMGN and may be either an early form of MGN, or an epiphenomenon associated with another primary disease process, particularly minimal change disease.

Perspectives in membranous nephropathy

The identification of the phospholipase A2 receptor 1 (PLA2R) and thrombospondin type-1 domain-containing protein 7A (THSD7A) as podocyte antigens in adult patients with membranous nephropathy (MN) has strongly impacted both experimental and clinical research on this disease. Evidence has been furnished that podocyte-directed autoantibodies can cause MN, and novel PLA2R- and THSD7A-specific animal models have been developed. Today, measurement of serum autoantibody levels and staining of kidney biopsies for the target antigens guides MN diagnosis and treatment worldwide. Additionally, anti-PLA2R antibodies have been proven to be valuable prognostic biomarkers in MN. Despite these impressive advances, a variety of questions regarding the disease pathomechanisms, clinical use of antibody measurement, and future treatments remain unanswered. In this review, we will outline recent advances made in the field of MN and discuss open questions and perspectives with a focus on novel antigen identification, mechanisms of podocyte injury, clinical use of antibody measurement to guide diagnosis and treatment, and the potential of innovative, pathogenesis-based treatment strategies.

Segmental membranous nephropathy

Most cases of membranous nephropathy (MGN) present with global and diffuse distribution of subepithelial deposits. However, segmental MGN, in which there is focal or diffuse segmental subepithelial deposits, are occasionally encountered. The clinical and pathologic significance of segmental MGN is not well understood and thought to be more likely due to either early or resolving phase of the global form of MGN. Several case reports and literature available suggest that it may be a manifestation of secondary causes based on pathologic features such as presence of C1q and mesangial deposits, extra-glomerular deposits involving tubular basement membranes, absence of PLA2R and THSD7A, IgG1 and IgG3 subclass dominance, and the presence of other co-existing renal disease. Other reports, however, suggest that some of these cases may be a variant of the primary form of MGN. In this review, we integrate what is known about segmental MGN in order to better direct interpretation of renal biopsies in which it is identified.

Altered glycosylation of IgG4 promotes lectin complement pathway activation in anti-PLA2R1-associated membranous nephropathy

Primary membranous nephropathy (pMN) is a leading cause of nephrotic syndrome in adults. In most cases, this autoimmune kidney disease is associated with autoantibodies against the M-type phospholipase A2 receptor (PLA2R1) expressed on kidney podocytes, but the mechanisms leading to glomerular damage remain elusive. Here, we developed a cell culture model using human podocytes and found that anti-PLA2R1-positive pMN patient sera or isolated IgG4, but not IgG4-depleted sera, induced proteolysis of the 2 essential podocyte proteins synaptopodin and NEPH1 in the presence of complement, resulting in perturbations of the podocyte cytoskeleton. Specific blockade of the lectin pathway prevented degradation of synaptopodin and NEPH1. Anti-PLA2R1 IgG4 directly bound mannose-binding lectin in a glycosylation-dependent manner. In a cohort of pMN patients, we identified increased levels of galactose-deficient IgG4, which correlated with anti-PLA2R1 titers and podocyte damage induced by patient sera. Assembly of the terminal C5b-9 complement complex and activation of the complement receptors C3aR1 or C5aR1 were required to induce proteolysis of synaptopodin and NEPH1 by 2 distinct proteolytic pathways mediated by cysteine and aspartic proteinases, respectively. Together, these results demonstrated a mechanism by which aberrantly glycosylated IgG4 activated the lectin pathway and induced podocyte injury in primary membranous nephropathy.

Deposition of the Membrane Attack Complex in Healthy and Diseased Human Kidneys

The membrane attack complex-also known as C5b-9-is the end-product of the classical, lectin, and alternative complement pathways. It is thought to play an important role in the pathogenesis of various kidney diseases by causing cellular injury and tissue inflammation, resulting in sclerosis and fibrosis. These deleterious effects are, consequently, targeted in the development of novel therapies that inhibit the formation of C5b-9, such as eculizumab. To clarify how C5b-9 contributes to kidney disease and to predict which patients benefit from such therapy, knowledge on deposition of C5b-9 in the kidney is essential. Because immunohistochemical staining of C5b-9 has not been routinely conducted and never been compared across studies, we provide a review of studies on deposition of C5b-9 in healthy and diseased human kidneys. We describe techniques to stain deposits and compare the occurrence of deposits in healthy kidneys and in a wide spectrum of kidney diseases, including hypertensive nephropathy, diabetic nephropathy, membranous nephropathy, IgA nephropathy, lupus nephritis, C3 glomerulopathy, and thrombotic microangiopathies such as the atypical hemolytic uremic syndrome, vasculitis, interstitial nephritis, acute tubular necrosis, kidney tumors, and rejection of kidney transplants. We summarize how these deposits are related with other histological lesions and clinical characteristics. We evaluate the prognostic relevance of these deposits in the light of possible treatment with complement inhibitors.

A Review of the Current Practice of Diagnosis and Treatment of Idiopathic Membranous Nephropathy in China

Idiopathic membranous nephropathy (IMN), a common pathological type of nephrotic syndrome, is one of the main causes of kidney failure. With an increasing prevalence, IMN has received considerable attention in China. Based on recent studies, we discuss advances in the diagnosis of IMN and the understanding of its genetic background. Although the pathogenesis of IMN remains unclear, our understanding has been substantially enhanced by the discovery of new antigens such as phospholipase A₂ receptor, thrombospondin type-1 domain-containing 7A, exostosin1/exostosin2, neural epidermal growth factor-like 1 protein, neural cell adhesion molecule 1, semaphorin 3B, and factor H autoantibody. However, due to ethnic, environmental, economic, and lifestyle differences and other factors, a consensus has not yet been reached regarding IMN treatment. In view of the differences between Eastern and Western populations, in-depth clinical evaluations of biomarkers for IMN diagnosis are necessary. This review details the current treatment strategies for IMN in China, including renin-angiotensin system inhibitors, corticosteroid monotherapy, cyclophosphamide, calcineurin inhibitors, mycophenolate mofetil, adrenocorticotropic hormone, and traditional Chinese medicine, as well as biological preparations such as rituximab. In terms of management, the 2012 Kidney Disease Improving Global Outcomes (KDIGO) clinical practice guidelines do not fully consider the characteristics of the Chinese population. Therefore, this review aims to present the current status of IMN diagnosis and treatment in Chinese patients, and includes a discussion of new approaches and remaining clinical challenges.

Clinical significance of glomerular C3 deposition in primary membranous nephropathy

BACKGROUND

We aimed to investigate the effects of glomerular C3 deposition on clinical, histopathological features, and outcomes of patients with primary membranous nephropathy (MN).

METHODS

A total of 261 patients with biopsy-proven primary MN, who were on follow up for at least 6 months, were included in the study. The patients were grouped according to their C3 immunostaining in kidney biopsy samples at the time of diagnosis: Low intensity [LI; (C3 1 +)] and high intensity [HI; (C3 2 + or C3 3 +)]. The primary outcome was the development of kidney failure. Complete (CR) or partial remission (PR) was defined as secondary outcome.

RESULTS

Sixteen patients reached the primary outcome after a median follow-up of 33.8 months. Patients in the high intensity group (119 cases) had lower eGFR and higher proteinuria at admission and last follow-up compared to patients in the low intensity group (142 cases). Also, more patients in the high intensity group reached the primary outcome compared to patients in the low intensity group: twelve patients (10.1%) in the high intensity group and four patients (2.8%) in the low intensity group reached the primary outcome (p = 0.015). Kaplan-Meier analysis demonstrated that patients in the high intensity group had a higher risk for kidney failure (p = 0.02). In multivariate logistic regression analysis, high intensity C3 deposition and initial estimated glomerular filtration rate (eGFR) indepenently predicted primary outcome.

CONCLUSION

Extensive glomerular C3 deposition is a predictor of kidney failure in patients with MN.

Is primary membranous nephropathy a complement mediated disease?

Membranous nephropathy (MN) is an immune complex mediated disease. Although limited to the kidney, in up to 20% of patients MN is associated with other autoimmune, infectious or malignant diseases. The initial pathogenetic event in what is still considered "primary" MN is the binding of circulating autoantibodies to proteins (autoantigens) expressed in glomerular podocytes. This antibody binding leads to the formation of immune complexes in the glomerular basement membrane. There is clinical and experimental evidence that these immune deposits lead to the activation of the complement system. Experimental studies in the MN model of Heymann's nephritis show that the terminal membrane attack complex (MAC) of the complement system induces a disturbance of the glomerular filtration barrier and leads to proteinuria, the clinical hallmark of MN. After the discovery of the phospholipase A₂ receptor 1 and thrombospondin type 1 domain containing protein 7A as endogenous antigens, it is assumed that IgG4 antibodies directed against these proteins induce MN in over 85% of patients with primary MN. As a result, the role of complement in the pathogenesis of MN needs to be defined in light of these developments. In this review we describe the current knowledge on the function of the complement system in primary MN and discuss the open questions, which have to be solved for a better understanding of the potential role of complement in the pathophysiology of primary MN.

Update on IgG4-mediated autoimmune diseases: New insights and new family members

Antibodies of IgG4 subclass are exceptional players of the immune system, as they are considered to be immunologically inert and functionally monovalent, and as such may be part of classical tolerance mechanisms. IgG4 antibodies are found in a range of different diseases, including IgG4-related diseases, allergy, cancer, rheumatoid arthritis, helminth infection and IgG4 autoimmune diseases, where they may be pathogenic or protective. IgG4 autoimmune diseases are an emerging new group of diseases that are characterized by pathogenic, antigen-specific autoantibodies of IgG4 subclass, such as MuSK myasthenia gravis, pemphigus vulgaris and thrombotic thrombocytopenic purpura. The list of IgG4 autoantigens is rapidly growing and to date contains 29 candidate antigens. Interestingly, IgG4 autoimmune diseases are restricted to four distinct organs: 1) the central and peripheral nervous system, 2) the kidney, 3) the skin and mucous membranes and 4) the vascular system and soluble antigens in the blood circulation. The pathogenicity of IgG4 can be validated using our classification system, and is usually excerted by functional blocking of protein-protein interaction.

The clinicopathologic spectrum of segmental membranous glomerulopathy

Membranous glomerulopathy (MGN) is characterized by global subepithelial immune deposits that stain most intensely by immunofluorescence for IgG. Here we describe the clinical and pathologic findings in a cohort of patients with MGN in which, by definition, only segmental immune deposits are present. This rare variant, termed segmental MGN (sMGN), is poorly characterized. We retrospectively identified all patients with sMGN diagnosed at Columbia University from January 2010 to October 2018, excluding those with systemic lupus erythematosus. Data on presenting features, pathologic findings, and outcomes were collected. Fifty cases of sMGN were identified, representing 2.5% of MGN. In 21 of 50 biopsies, there was an alternative, predominant disease process. The remaining 29 patients with isolated sMGN had a median creatinine of 0.97 mg/dl, median 24-hour urine protein 3.1 g/day, and 32% had nephrotic syndrome. Staining for NELL-1 (a protein kinase C binding protein) was positive in five of 17 cases. Staining for PLA2R, THSD7A, and exostosin 1 (autoantigens in primary MGN) was negative in all biopsies evaluated. Ultrastructural evaluation revealed predominantly early stage sMGN (stage 1 or 1-2 in 14/29). Follow-up was available for 21 of the 29 patients with isolated sMGN (median 12 months), including seven who received immunosuppression (primarily glucocorticoids). During follow-up, 86% had stable/improved kidney function and 45% achieved complete while 15% achieved partial remission. Among the 15 patients with isolated sMGN without full nephrotic syndrome, only two received immunosuppression; nonetheless, 50% achieved complete while 21% achieved partial remission. Thus, sMGN is a rare PLA2R-negative variant of MGN with 29% NELL-1 positivity and favorable prognosis, even in the absence of immunosuppressive treatment.

Renal hypoplasia can be the cause of membranous nephropathy-like lesions

BACKGROUND

Renal hypoplasia (RH) is the most common cause of chronic kidney disease in children. In cases of RH, proteinuria is often induced by glomerular hypertrophy and hyperfiltration that is commonly associated with focal segmental glomerulosclerosis. This study reports the first case series of a possible association between RH and membranous nephropathy (MN).

METHODS

Of the 168 children with RH who visited our department between 1999 and 2017, five with overt proteinuria (≥ 1 g/gCr) underwent renal biopsy. We retrospectively reviewed the medical charts and analyzed biopsy specimens using light microscopy (LM), immunofluorescence (IF), and electron microscopy.

RESULTS

The five children (four boys and one girl) had a median age of 5.5 years at the time of renal biopsy. The median proteinuria was 4.23 g/gCr (range 1.46-14.25), median serum albumin, 2.9 g/dL (range 2.3-3.7), and median estimated glomerular filtration rate, 59.7 mL/min/1.73 m² (range 36.7-103.6). LM showed segmental spike formation and mesangial hypercellularity and IF study showed segmental granular immunoglobulin G (IgG) staining (IgG1 and IgG3 dominant) along the capillary loops in all five patients. Electron-dense deposits were observed in the subepithelial and mesangial areas. Thus, the pathological studies showed MN-like lesions in all patients.

CONCLUSION

Our study suggests that RH can be the cause of MN-like lesions.

New Ways of Understanding Membranous Nephropathy

BACKGROUND

In the last decade, great advances have been made in the field of membranous nephropathy (MN). The autoimmune nature of the disease has been confirmed with the description of diverse antigens, and few but very important prospective trials regarding treatment alternatives have been published, changing profoundly the way we understand this entity. Nowadays, an individualized therapeutic scheme based on clinical and serologic data appears to be the most appropriate method to manage patients with MN. Although there is still a long way to go, it is expected that future scientific progress will enable a patient-centered medicine based on concept-driven therapies.

SUMMARY

MN is the most common cause of nephrotic syndrome (NS) in white adults. Approximately one-third of patients achieve spontaneous remission, one-third remain stable, and one-third have an aggressive course with persistent NS and deterioration of renal function. About 80% of patients have circulating autoantibodies to phospholipase A2 receptor 1. Numerous therapies have been described including alkylating agents, rituximab, and calcineurin inhibitors, but new drugs are currently being explored. Here, we review the most important aspects regarding MN with an emphasis on results of the most recent clinical trials and pathophysiologic advances. Key Messages: 1. Evolving pathophysiologic concepts and recently published clinical trials have deeply changed our view of MN. 2. Most patients with MN present autoantibodies against diverse glomerular antigens. 3. Currently, an individual patient-centered management based on clinical and serologic markers is the most adequate approach to treat patients with MN.

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.

A novel mouse model of phospholipase A2 receptor 1-associated membranous nephropathy mimics podocyte injury in patients

The phospholipase A2 receptor 1 (PLA2R1) is the major autoantigen in patients suffering from membranous nephropathy. To date, the lack of endogenous glomerular expression of PLA2R1 in mice and rats has impeded the establishment of PLA2R1-dependent animal models of this disease. Here, we generated a transgenic mouse line expressing murine full-length PLA2R1 in podocytes. Furthermore, expression of murine PLA2R1 did not result in any morphological disturbance as high-resolution confocal microscopy demonstrated an intact nephrin distribution with normal foot processes. Transfer of rabbit anti-mPLA2R1 antibodies to these mice induced nephrotic range proteinuria, hypercholesterolemia, and histomorphological signs of membranous nephropathy. Immunohistochemical and immunofluorescence analyses revealed enhanced staining for murine PLA2R1 in the presence of unaffected staining for murine thrombospondin type-1 domain-containing 7A in the diseased mice, resembling what is classically found in patients with PLA2R1-associated membranous nephropathy Thus, our mouse model of membranous nephropathy will allow investigation of PLA2R1-specific pathomechanisms and may help to develop and assess antigen-specific treatments in vivo.

Molecular Pathogenesis of Membranous Nephropathy

Membranous nephropathy is a noninflammatory autoimmune disease of the kidney glomerulus, characterized by the formation of immune deposits, complement-mediated proteinuria, and risk of renal failure. Considerable advances in understanding the molecular pathogenesis have occurred with the identification of several antigens [neutral endopeptidase, phospholipase A2 receptor (PLA₂R), thrombospondin domain-containing 7A (THSD7A)] in cases arising from the neonatal period to adulthood and the characterization of antibody-binding domains (that is, epitopes). Immunization against PLA2R occurs in 70% to 80% of adult cases. The development of highly specific and sensitive assays of circulating antibodies has induced a paradigm shift in diagnosis and treatment monitoring. In addition, several interacting loci in HLA-DQ, HLA-DR, and PLA2R1, as well as classical human leukocyte antigen (HLA)-D alleles have been identified as being risk factors, depending on a patient's ethnicity. Additionally, mechanisms of antibody pathogenicity and pathways of complement activation are now better understood. Further research is mandatory for designing new therapeutic strategies, including the identifying triggering events, the molecular bases of remission and progression, and the T cell epitopes involved.

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.

The anti-PLA2R antibody in membranous nephropathy: what we know and what remains a decade after its discovery

The discovery in 2009 of the M-type phospholipase A2 receptor (PLA2R) as the primary target in membranous nephropathy (MN) greatly advanced basic and clinical research. Primary MN is now considered a renal-limited autoimmune disease, with antibodies against PLA2R (aPLA2Rab) identified in 70-80 % of patients of various ethnic groups. Although the use of aPLA2Rab as a diagnostic and prognostic biomarker is now widely accepted, many questions related to the development of the auto-immune response, the role of IgG subclasses and antigenic epitopes, and the pathways to podocyte injury remain unresolved. PLA2R-associated MN most likely develops governed by factors such as genetic susceptibility, loss of tolerance, alterations in antigen expression with a role for environmental factors like air pollution, smoking, and infections. More detailed knowledge of genetic factors, the relevant B- and T-cell epitopes, and the mechanisms of podocyte injury is needed to identify patients at risk for disease progression and to develop optimized, targeted treatment strategies. In this review we highlight unresolved issues, addressing initiation of antibody formation, the timeline of antibody production, the role of IgG subclass, and the pathogenicity of the antibodies in concert with complement to produce glomerular pathology and proteinuria.

Differential expression study of circular RNAs in exosomes from serum and urine in patients with idiopathic membranous nephropathy

INTRODUCTION

The aim of the study was to further explore the pathogenesis of idiopathic membranous nephropathy (IMN), gene-sequencing was used to analyze the differentially expressed circRNAs in exosomes of patients with IMN, which may lay the foundation for the research of circRNAs as a new class of exosome-based IMN diagnosis biomarkers.

MATERIAL AND METHODS

Ten patients with IMN and ten normal controls were recruited as experimental subjects in our study. The exosomes were extracted from the collected serum and urine. Then, pure circRNAs were extracted from the exosomes with a series of enzymatic reactions. Afterwards, the significantly differentially expressed circRNAs were chosen by the method of gene-sequencing.

RESULTS

Compared with normal controls, the circRNAs were reduced in the exosomes from serum of patients with IMN, which mostly originated from intron gene regions. Meanwhile, a total of 89 circRNAs were significantly differentially expressed, which were also mostly derived from intron gene regions, including 49 up-regulated and 40 down-regulated genes. However, the species were increased in the exosomes from the urine of patients with IMN compared to normal controls, and they mainly originated from exon gene regions. Simultaneously, 60 circRNAs were significantly differentially expressed, which primarily belonged to intron gene regions, including 54 up-regulated and 6 down-regulated regions.

CONCLUSIONS

The significant differential and specific expression of circRNAs in the exosomes from patients with IMN were observed. For example, MUC3A, which originated from chr7:100550808|100551062, could be considered a potential diagnostic biomarker of IMN. Furthermore, these figures may be used as a reference or supplement in the research of the pathogenesis of IMN.

Low serum C3 level, high neutrophil-lymphocyte-ratio, and high platelet-lymphocyte-ratio all predicted poor long-term renal survivals in biopsy-confirmed idiopathic membranous nephropathy

Idiopathic membranous nephropathy (iMN) is the major cause of end-stage renal disease (ESRD). Recent guidelines suggest limiting immunosuppressants only to high risk patients for ESRD. The present study is aimed at identifying new predictors for the renal outcome of iMN patients. We conducted a retrospective cohort study covering a period from January 2003 to December 2013. We enrolled participants who had received their first renal biopsy at our medical center in Taiwan with the diagnosis of iMN. Clinical, pathological and laboratory data were collected from medical records. Analyses with Mann-Whitney U test was used for continuous variables and Chi-square test for categorical variables. The Kaplan-Meier curve was used for the analyses of patient survival and renal survival. Youden index was used for evaluating the performance of a dichotomous diagnostic test for renal and patient outcomes. Cox proportional hazard regression was used to determine factors affecting renal survival.A total of 99 patients with renal biopsy-confirmed idiopathic iMNs were enrolled. C3 level ≤114 mg/dl predicted patient outcome (p < 0.001) with good predictive power (AUC = 0.736). The univariate analysis showed that risk factors for poor renal outcome were older age (HR = 1.04, p = 0.002), high BUN (HR = 1.03, p < 0.001), poor baseline renal function (HR = 1.30 and p < 0.001 for higher serum creatinine; HR = 0.97 and p < 0.001 for higher eGFR; HR = 1.06 and p < 0.001 for urine PCR), C3 ≤ 93.4 mg/dl (HR = 2.15, p = 0.017), NLR > 3.34 (HR = 3.30, p < 0.001) and PLR > 14.48 (HR = 2.54, p = 0.003). Stage of iMN did not fully account for the risk of ESRD. This is the first evidence that serum levels of C3 ≤ 93.4 mg/dl predicted poor renal outcomes with good predictive power. Easily obtained markers, NLR > 3.34 also predicted poor renal outcomes.

Developments in anti-complement therapy; from disease to clinical trial

The complement system is well known for its role in innate immunity and in maintenance of tissue homeostasis, providing a first line of defence against infection and playing a key role in flagging apoptotic cells and debris for disposal. Unfortunately complement also contributes to pathogenesis of a number of diseases; in some cases driving pathology, and in others amplifying or exacerbating the inflammatory and damaging impact of non-complement disease triggers. The role of complement in pathogenesis of an expanding number of diseases has driven industry and academia alike to develop an impressive arsenal of anti-complement drugs which target different proteins and functions of the complement cascade. Evidence from genetic and biochemical analyses, combined with improved identification of complement biomarkers and supportive data from sophisticated animal models of disease, has driven a drug development landscape in which the indications selected for clinical trial cluster in three 'target' tissues: the kidney, eye and vasculature. While the disease triggers may differ, complement activation and amplification is a common feature in many diseases which affect these three tissues. An abundance of drugs are in clinical development, some show favourable progression whereas others experience significant challenges. However, these hurdles in themselves drive an ever-evolving portfolio of 'next-generation' drugs with improved pharmacokinetic and pharmacodynamics properties. In this review we discuss the indications which are in the drug development 'spotlight' and review the relevant indication validation criteria. We present current progress in clinical trials, highlighting successes and difficulties, and look forward to approval of a wide selection of drugs for use in man which give clinicians choice in mechanistic target, modality and route of delivery.

Alternative Pathway Is Essential for Glomerular Complement Activation and Proteinuria in a Mouse Model of Membranous Nephropathy

Membranous nephropathy is an immune kidney disease caused by IgG antibodies that form glomerular subepithelial immune complexes. Proteinuria is mediated by complement activation, as a result of podocyte injury by C5b-9, but the role of specific complement pathways is not known. Autoantibodies-mediating primary membranous nephropathy are predominantly of IgG4 subclass, which cannot activate the classical pathway. Histologic evidence from kidney biopsies suggests that the lectin and the alternative pathways may be activated in membranous nephropathy, but the pathogenic relevance of these pathways remains unclear. In this study, we evaluated the role of the alternative pathway in a mouse model of membranous nephropathy. After inducing the formation of subepithelial immune complexes, we found similar glomerular IgG deposition in wild-type mice and in factor B-null mice, which lack a functional alternative pathway. Unlike wild-type mice, mice lacking factor B did not develop albuminuria nor exhibit glomerular deposition of C3c and C5b-9. Albuminuria was also reduced but not completely abolished in C5-deficient mice. Our results provide the first direct evidence that the alternative pathway is necessary for pathogenic complement activation by glomerular subepithelial immune complexes and is, therefore, a key mediator of proteinuria in experimental membranous nephropathy. This knowledge is important for the rational design of new therapies for membranous nephropathy.