Discovery of seven novel putative antigens in membranous nephropathy and membranous lupus nephritis identified by mass spectrometry

Membranous nephropathy: pathogenesis and treatments

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

Identification and validation of anti-protein arginine methyltransferase 5 (PRMT5) antibody as a novel biomarker for systemic sclerosis (SSc)

OBJECTIVES

In the complex panorama of autoimmune diseases, the characterisation of pivotal contributing autoantibodies that are involved in disease progression remains challenging. This study aimed to employ a global antibody profiling strategy to identify novel antibodies and investigate their association with systemic sclerosis (SSc).

METHODS

We implemented this strategy by conducting immunoprecipitation (IP) following on-bead digestion with the sera of patients with SSc or healthy donors, using antigen pools derived from cell lysates. The enriched antigen-antibody complex was proceeded with mass spectrometry (MS)-based quantitative proteomics and over-represented by bioinformatics analysis. The candidate antibodies were then orthogonally validated in two independent groups of patients with SSc. Mice were immunised with the target antigen, which was subsequently evaluated by histological examination and RNA sequencing.

RESULTS

The IP-MS analysis, followed by validation in patients with SSc, revealed a significant elevation in anti-PRMT5 antibodies among patients with SSc. These antibodies exhibited robust diagnostic accuracy in distinguishing SSc from healthy controls and other autoimmune conditions, including systemic lupus erythematosus and Sjögren's syndrome, with an area under the curve ranging from 0.900 to 0.988. The elevation of anti-PRMT5 antibodies was verified in a subsequent independent group with SSc using an additional method, microarray. Notably, 31.11% of patients with SSc exhibited seropositivity for anti-PRMT5 antibodies. Furthermore, the titres of anti-PRMT5 antibodies demonstrated a correlation with the progression or regression trajectory in SSc. PRMT5 immunisation displayed significant inflammation and fibrosis in both the skin and lungs of mice. This was concomitant with the upregulation of multiple proinflammatory and profibrotic pathways, thereby underscoring a potentially pivotal role of anti-PRMT5 antibodies in SSc.

CONCLUSIONS

This study has identified anti-PRMT5 antibodies as a novel biomarker for SSc.

Membranous nephropathy-diagnosis and identification of target antigens

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

NELL1 membranous nephropathy: clinical associations provide mechanistic clues

Neural epidermal growth factor-like 1 (NELL1) membranous nephropathy (MN) is notable for its segmental deposit distribution, IgG1 dominant deposits, and comparatively high rate of spontaneous remission. It has been associated with a variety of exposures and secondary conditions, specifically use of thiol-containing medications - including lipoic acid, bucillamine, and tiopronin - as well as traditional indigenous medications (TIM) particularly those with high mercury content, and non-steroid anti-inflammatory drugs (NSAIDs). Malignancies, graft vs. host disease (GVHD), infection, and autoimmune conditions have also been associated with NELL1 MN. Herein, we provide a detailed summary of the clinicopathologic features of NELL1 and associations with underlying conditions, with a focus on treatment and outcomes. Rare cases of dual NELL1 and phospholipase A2 receptor (PLA2R) positive MN are reviewed. Genome-wide association study of NELL1, role of NELL1 in other physiologic and pathologic processes, and connection between NELL1 MN and malignancy with relevance of NELL1 tumor staining are examined. Finally, relationships and potential disease mechanisms of thiol- and mercury- associated NELL1 MN are discussed.

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.

Effectiveness of a novel rat model of off-target PLA2R1 knockout to renal impairment

Phospholipase A2 receptor 1 (PLA2R1) plays a crucial role in various diseases, including membranous nephropathy. However, the precise implications of PLA2R1 deficiency remain poorly understood. In this study, we created PLA2R1 knockout rats to explore potential consequences resulting from the loss of the PLA2R1 gene. Unexpectedly, our PLA2R1 knockout rats exhibited symptoms resembling those of chronic kidney disease after an 8-week observation period. Notably, several rats developed persistent proteinuria, a hallmark of renal dysfunction. Immunohistochemical and immunofluorescence analyses revealed insignificant glomerular fibrosis, reduced podocyte count, and augmented glomerular expression of complement C3 (C3) compared to immunoglobin A (IgA) and immunoglobin G(IgG) in the rat model. These findings suggest that the loss of PLA2R1 may contribute to the pathogenesis of membranous nephropathy and related conditions. Our knockout rat model provides a valuable tool for investigating the underlying pathology of PLA2R1-associated diseases, and may facilitate the development of targeted therapies for membranous nephropathy and other related disorders.

Novel Antigens and Clinical Updates in Membranous Nephropathy

Membranous nephropathy (MN), an autoimmune kidney disease and leading cause of nephrotic syndrome, leads to kidney failure in up to one-third of affected individuals. Most MN cases are due to an autoimmune reaction against the phospholipase A2 receptor (PLA2R) located on kidney podocytes. Serum PLA2R antibody quantification is now part of routine clinical practice because antibody titers correlate with disease activity and treatment response. Recent advances in target antigen detection have led to the discovery of more than 20 other podocyte antigens, yet the clinical impact of additional antigen detection remains unknown and is under active investigation. Here we review recent findings and hypothesize how current research will inform future care of patients with MN.

C3aR-initiated signaling is a critical mechanism of podocyte injury in membranous nephropathy

The deposition of antipodocyte autoantibodies in the glomerular subepithelial space induces primary membranous nephropathy (MN), the leading cause of nephrotic syndrome worldwide. Taking advantage of the glomerulus-on-a-chip system, we modeled human primary MN induced by anti-PLA2R antibodies. Here we show that exposure of primary human podocytes expressing PLA2R to MN serum results in IgG deposition and complement activation on their surface, leading to loss of the chip permselectivity to albumin. C3a receptor (C3aR) antagonists as well as C3AR gene silencing in podocytes reduced oxidative stress induced by MN serum and prevented albumin leakage. In contrast, inhibition of the formation of the membrane-attack-complex (MAC), previously thought to play a major role in MN pathogenesis, did not affect permselectivity to albumin. In addition, treatment with a C3aR antagonist effectively prevented proteinuria in a mouse model of MN, substantiating the chip findings. In conclusion, using a combination of pathophysiologically relevant in vitro and in vivo models, we established that C3a/C3aR signaling plays a critical role in complement-mediated MN pathogenesis, indicating an alternative therapeutic target for MN.

Prognostic factors affecting long-term outcomes in patients with concurrent IgA nephropathy and membranous nephropathy

Background

The incidence of concurrent immunoglobulin A nephropathy and membranous nephropathy (cIgAN/MN) is low and rarely reported, and the prognosis of patients with cIgAN/MN remains unclear. This study was designed to compare the clinical and prognostic characteristics of cIgAN/MN with IgAN and MN and to identify crucial factors influencing the outcomes of patients with cIgAN/MN.

Methods

We included biopsy-proven cIgAN/MN patients between December 2012 and December 2020 at Xijing Hospital. In the same period, propensity score matching was employed to select an equal number of IgAN and MN patients according to the following criteria: age, sex, and follow-up time. The primary endpoint was defined as a composite of eGFR decline ≥30 %, end-stage renal disease, or death. The patient survival rate was examined using Kaplan-Meier survival curves. Univariate and multivariate Cox regression analysis models were utilized to identify the risk factors affecting renal prognosis.

Results

A total of 135 patients were finally included in this study and 35 (25.9 %) reached the primary endpoint. The median follow-up time of cIgAN/MN was 45.9 (24.0, 72.0) months. Compared to the IgAN group, the cIgAN/MN group exhibited a lower cumulative incidence rate of composite renal endpoints (P = 0.044), while no significant difference was found between MN and cIgAN/MN patients (P = 0.211). Univariate Cox analysis revealed that mean arterial pressure, serum potassium, blood urea nitrogen, serum IgA, segmental glomerulosclerosis (S1), and MN staging were associated with an increased risk of renal composite endpoints. The multivariate Cox regression analysis of clinical variables plus histological lesion scoring demonstrated that potassium (HR = 14.350, 95 % CI 2.637-78.090, P = 0.002), serum IgA (HR = 1.870, 95 % CI 1.109-3.153, P = 0.019), and S1 (HR = 11.965, 95 % CI 2.166-66.105, P = 0.004) were independent risk factors influencing renal outcomes in cIgAN/MN patients.

Conclusion

The prognosis of cIgAN/MN patients may exhibit an intermediate pattern between IgAN and MN, leaning towards being more similar to MN in certain aspects. Within the cIgAN/MN cohort, potassium, and serum IgA may be more predictive of rapid progression of renal endpoints, and S1 may indicate a more aggressive disease course.

From Patterns to Proteins: Mass Spectrometry Comes of Age in Glomerular Disease

Laser capture microdissection and mass spectrometry (LCM/MS) is a technique that involves dissection of glomeruli from paraffin-embedded biopsy tissue, followed by digestion of the dissected glomerular proteins by trypsin, and subsequently mass spectrometry to identify and semiquantitate the glomerular proteins. LCM/MS has played a crucial role in the identification of novel types of amyloidosis, biomarker discovery in fibrillary GN, and more recently discovery of novel target antigens in membranous nephropathy (MN). In addition, LCM/MS has also confirmed the role for complement proteins in glomerular diseases, including C3 glomerulopathy. LCM/MS is now widely used as a clinical test and considered the gold standard for diagnosis and typing amyloidosis. For the remaining glomerular diseases, LCM/MS has remained a research tool. In this review, we discuss the usefulness of LCM/MS in other glomerular diseases, particularly MN, deposition diseases, and diseases of complement pathways, and advocate more routine use of LCM/MS at the present time in at least certain diseases, such as MN, for target antigen detection. We also discuss the limitations of LCM/MS, particularly the difficulties faced from moving from a research-based technique to a clinical test. Nonetheless, the role of LCM/MS in glomerular diseases is expanding. Currently, LCM/MS may be used to identify the etiology in certain glomerular diseases, but in the future, LCM/MS can play a valuable role in determining pathways of complement activation, inflammation, and fibrosis.

Novel biomarkers and pathophysiology of membranous nephropathy: PLA2R and beyond

Research on membranous nephropathy truly exploded in the last 15 years. This happened because of the application of new techniques (laser capture microdissection, mass spectrometry, protein G immunoprecipitation, arrays) to the study of its pathogenesis. After the discovery of PLA2R as the major target antigen, many other antigens were identified and others are probably ongoing. Clinical and pathophysiology rebounds of new discoveries are relevant in terms of diagnosis and prognosis and it is time to make a first assessment of the innovative issues. In terms of classification, target antigens can be divided into: 'membrane antigens' and 'second wave' antigens. The first group consists of antigens constitutionally expressed on the podocyte membrane (as PLA2R) that may become a target of an autoimmune process because of perturbation of immune-tolerance. 'Second wave' antigens are antigens neo-expressed by the podocyte or by infiltrating cells after a stressing event: this allows the immune system to produce antibodies against them that intensify and maintain glomerular damage. With this abundance of target antigens it is not possible, at the moment, to test all antibodies at the bedside. In the absence of this possibility, the role of histological evaluation is still irreplaceable.

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

Membranous nephropathy (MN) is a pattern of injury caused by autoantibodies binding to specific target antigens, with accumulation of immune complexes along the subepithelial region of glomerular basement membranes. The past 20 years have brought revolutionary advances in the understanding of MN, particularly via the discovery of novel target antigens and their respective autoantibodies. These discoveries have challenged the traditional classification of MN into primary and secondary forms. At least 14 target antigens have been identified, accounting for 80%-90% of cases of MN. Many of the forms of MN associated with these novel MN target antigens have distinctive clinical and pathologic phenotypes. The Mayo Clinic consensus report on MN proposes a 2-step classification of MN. The first step, when possible, is identification of the target antigen, based on a multistep algorithm and using a combination of serology, staining of the kidney biopsy tissue by immunofluorescence or immunohistochemistry, and/or mass spectrometry methodology. The second step is the search for a potential underlying disease or associated condition, which is particularly relevant when knowledge of the target antigen is available to direct it. The meeting acknowledges that the resources and equipment required to perform the proposed testing may not be generally available. However, the meeting consensus was that the time has come to adopt an antigen-based classification of MN because this approach will allow for accurate and specific MN diagnosis, with significant implications for patient management and targeted treatment.

Introduction of a novel chimeric active immunization mouse model of PLA2R1-associated membranous nephropathy

The phospholipase A2 receptor 1 (PLA2R1) is the major target antigen in patients with membranous nephropathy (MN), an antibody-mediated autoimmune glomerular disease. Investigation of MN pathogenesis has been hampered by the lack of reliable animal models. Here, we overcome this issue by generating a transgenic mouse line expressing a chimeric PLA2R1 (chPLA2R1) consisting of three human PLA2R1 domains (cysteine-rich, fibronectin type-II and CTLD1) and seven murine PLA2R1 domains (CTLD2-8) specifically in podocytes. Mice expressing the chPLA2R1 were healthy at birth and showed no major glomerular alterations when compared to mice with a wild-type PLA2R1 status. Upon active immunization with human PLA2R1 (hPLA2R1), chPLA2R1-positive mice developed anti-hPLA2R1 antibodies, a nephrotic syndrome, and all major histological features of MN, including granular deposition of mouse IgG and complement components in immunofluorescence and subepithelial electron-dense deposits and podocyte foot process effacement in electron microscopy. In order to investigate the role of the complement system in this model, we further crossed chPLA2R1-positive mice with mice lacking the central complement component C3 (C3-/- mice). Upon immunization with hPLA2R1, chPLA2R1-positive C3-/- mice had substantially less severe albuminuria and nephrotic syndrome when compared to chPLA2R1-positive mice with a wild-type C3 status. In conclusion, we introduce a novel active immunization model of PLA2R1-associated MN and demonstrate a pathogenic role of the complement system in this model.

Clinical and Histopathologic Characteristics of Pediatric Patients With Primary Membranous Nephropathy

Introduction

Primary membranous nephropathy (PMN) is uncommon in children. Therefore, data on the clinical course of affected children are scarce. In recent years, several novel antigens have been implicated in the pathogenesis of PMN. However, the histopathologic characteristics of pediatric patients with PMN remain poorly represented in the literature.

Methods

We have retrospectively analyzed the clinical presentation and outcomes data of 21 children with PMN from 3 centers in the United States. In addition, we have identified novel antigens in biopsy specimens from these patients and correlated their presence or absence to clinical outcomes. Finally, we compared the results of the novel antigen staining from our clinical cohort to a validation cohort of 127 biopsy specimens from children with PMN at Arkana Laboratories.

Results

The data from the 2 cohorts demonstrated similar overall antigen positivity rates of 62% to 63%, with phospholipase A2 receptor (PLA2R) and exostosin 1 (EXT1) being the most commonly found antigens. Results from the clinical cohort showed that overall, the kidney prognosis for children with PMN was good, with 17 of 21 patients entering a complete or partial remission. Children who were positive for PLA2R or EXT1 were significantly more likely to enter remission than those in the antigen negative group.

Conclusion

Approximately 60% of pediatric membranous cases are positive for a novel antigen on kidney biopsy and the clinical prognosis is generally favorable. More studies are needed to understand the clinical implications of each specific novel antigen.

Mayo Clinic Consensus Report on Membranous Nephropathy: Proposal for a Novel Classification

Membranous nephropathy (MN) is a pattern of injury caused by autoantibodies binding to specific target antigens, with accumulation of immune complexes along the subepithelial region of glomerular basement membranes. The past 20 years have brought revolutionary advances in the understanding of MN, particularly via the discovery of novel target antigens and their respective autoantibodies. These discoveries have challenged the traditional classification of MN into primary and secondary forms. At least 14 target antigens have been identified, accounting for 80%-90% of cases of MN. Many of the forms of MN associated with these novel MN target antigens have distinctive clinical and pathologic phenotypes. The Mayo Clinic consensus report on MN proposes a 2-step classification of MN. The first step, when possible, is identification of the target antigen, based on a multistep algorithm and using a combination of serology, staining of the kidney biopsy tissue by immunofluorescence or immunohistochemistry, and/or mass spectrometry methodology. The second step is the search for a potential underlying disease or associated condition, which is particularly relevant when knowledge of the target antigen is available to direct it. The meeting acknowledges that the resources and equipment required to perform the proposed testing may not be generally available. However, the meeting consensus was that the time has come to adopt an antigen-based classification of MN because this approach will allow for accurate and specific MN diagnosis, with significant implications for patient management and targeted treatment.

THSD7A as a Promising Biomarker for Membranous Nephrosis

Membranous nephropathy (MN) is an autoimmune disease of the kidney glomerulus and one of the leading causes of nephrotic syndrome. The disease exhibits heterogeneous outcomes with approximately 30% of cases progressing to end-stage renal disease. Traditionally, the standard approach of diagnosing MN involves performing a kidney biopsy. Nevertheless, kidney biopsy is an invasive procedure that poses risks for the patient including bleeding and pain, and bears greater costs for the health system. The clinical management of MN has steadily advanced owing to the identification of autoantibodies to the phospholipase A2 receptor (PLA2R) in 2009 and thrombospondin domain-containing 7A (THSD7A) in 2014 on the podocyte surface. At present, serum anti-PLA2R antibody detection and glomerular PLA2R antigen staining have been used for clinical diagnosis and prognosis, but the related detection of THSD7A has not been widely used in clinical practice. Here, we summarized the emerging knowledge regarding the roles THSD7A plays in MN and its clinical implications as diagnostic, prognostic, and therapeutic response as well as Methods for detecting serum THSD7A antibodies.

Management of Lupus Nephritis: New Treatments and Updated Guidelines

Management of lupus nephritis has evolved considerably over the past years. Here, we provide a comprehensive review of clinical trials that form the basis for the Kidney Disease: Improving Global Outcomes and EULAR/ERA-EDTA updated guidelines and present day trials that will change the landscape of lupus nephritis therapy in years to come. In addition, we highlight the issues related to cost of therapy, resistant disease, and downstream adverse effects of specific therapies.

From systemic lupus erythematosus to lupus nephritis: The evolving road to targeted therapies

Systemic lupus erythematosus is a chronic autoimmune disease characterized by loss of tolerance against nuclear and cytoplasmic self-antigens, induction of immunity and tissue inflammation. Lupus nephritis (LN), the most important predictor of morbidity in SLE, develops in almost 30% of SLE patients at disease onset and in up to 50-60% within the first 10 years. Firstly, in this review, we put the pathogenic mechanisms of the disease into a conceptual frame, giving emphasis to the role of the innate immune system in this loss of self-tolerance and the induction of the adaptive immune response. In this aspect, many mechanisms have been described such as dysregulation and acceleration of cell-death pathways, an aberrant clearance and overload of immunogenic acid-nucleic-containing debris and IC, and the involvement of antigen-presenting cells and other innate immune cells in the induction of this adaptive immune response. This result in a clonal expansion of autoreactive lymphocytes with generation of effector T-cells, memory B-cells and plasma cells that produce autoantibodies that will cause kidney damage. Secondly, we review the immunological pathways of damage in the kidney parenchyma, initiated by autoantibody binding and immune complex deposition, and followed by complement-mediated microvascular injury, activation of kidney stromal cells and the recruitment of leukocytes. Finally, we summarize the rationale for the treatment of LN, from conventional to new targeted therapies, focusing on their systemic immunologic effects and the minimization of podocytary damage.

One antigen closer to understanding membranous nephropathy

Membranous nephropathy is an immune-mediated kidney disease characterized by subepithelial immune deposits. Through the utilization of advanced proteomic techniques, multiple target antigens have been identified, including those associated with primary and secondary etiologies. Nonsteroidal anti-inflammatory drugs represent an important secondary cause of membranous nephropathy. In this study by Sethi et al., advanced proteomic techniques identify proprotein convertase subtilisin/kexin type 6 as a target antigen in nonsteroidal anti-inflammatory drug-associated membranous nephropathy.

Towards the Definition of the Molecular Hallmarks of Idiopathic Membranous Nephropathy in Serum Proteome: A DIA-PASEF Approach

Idiopathic membranous nephropathy (IMN) is a pathologically defined disorder of the glomerulus, primarily responsible for nephrotic syndromes (NS) in nondiabetic adults. The underlying molecular mechanisms are still not completely clarified. To explore possible molecular and functional signatures, an optimised mass spectrometry (MS) method based on next-generation data-independent acquisition combined with ion-mobility was applied to serum of patients affected by IMN (n = 15) or by other glomerulopathies (PN) (n = 15). The statistical comparison highlighted a panel of 57 de-regulated proteins with a significant increase in lipoprotein-related proteins (APOC1, APOB, APOA1, APOL1 and LCAT) and a substantial quantitative alteration of key serpins (including A4, D1, A7, A6, F2, F1 and 1) possibly associated with IMN or NS and podocyte stress. A critical dysregulation in metabolisms of lipids (e.g., VLDL assembly and clearance) likely to be related to known hyperlipidemia in IMN, along with involvement of non-classical complement pathways and a putative enrolment of ficolin-2 in sustaining the activation of the lectin-mediated complement system have been pinpointed. Moreover, mannose receptor CD206 (MRC1-down in IMN) and biotinidase (BTD-up in IMN) are able alone to accurately distinguish IMN vs. PN. To conclude, our work provides key proteomic insights into the IMN complexity, opening the way to an efficient stratification of MN 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.

Mapping antigens of membranous nephropathy: almost there

Membranous nephropathy (MN) is characterized by subepithelial accumulation of immune complexes along the glomerular basement membranes. The immune complexes compromise IgG and the corresponding target antigen. Recent advances have led to the discovery of novel target MN antigens. In this study, by Caza et al., 7 novel "putative" antigens are proposed. Target antigens can now be identified in approximately 90% of cases of MN. In addition to describing another 10 novel putative antigens, we propose a working algorithm for evaluating the target antigens in MN.