Subepithelial Immune Deposits Research Articles

Complement activation products in the circulation and urine of primary membranous nephropathy

BackgroundComplement activation plays a substantial role in the pathogenesis of primary membranous nephropathy (pMN). C5b-9, C3c, MBL, and factor B have been documented in the subepithelial immune deposits. However, the changing of complement activation products in circulation and urine is not clear.MethodsWe measured the circulating and urinary levels of C1q, MBL, C4d, Bb, properdin, C3a, C5a, and sC5b-9, in 134 patients with biopsy-proven pMN, by enzyme-linked immunosorbent assay. All the plasma values were corrected by eGFR and all the urinary values were corrected by urinary creatinine and urinary protein excretion. Anti-PLA2R antibodies were measured in all patients.ResultsThe plasma complement activation products were elevated both in the patients with and without anti-PLA2R antibodies. C3a levels were remarkably increased in the circulation and urine, much higher than the elevated levels of C5a. C5b-9 was in normal range in plasma, but significantly higher in urine. The urinary C5a had a positive correlation with anti-PLA2R antibody levels and urinary protein. The plasma level of C4d was elevated, but C1q and MBL were comparable to healthy controls. Positive correlations were observed between plasma C4d/MBL and urinary protein, only in the patients with positive anti-PLA2R antibodies but not in those without. The plasma level of Bb was elevated and had positive correlation with urinary protein only in the patients without anti-PLA2R antibodies.ConclusionComplement activation products were remarkable increased in pMN and may serve as sensitive biomarkers of disease activity. The complement may be activated through lectin pathway with the existence of anti-PLA2R antibodies, while through alternative pathway in the absence of antibody.

Membranous nephropathy succeeding autologous hematopoietic stem cell transplant: a case report

BackgroundMembranous nephropathy (MN), the leading cause of nephrotic syndrome in adults, is characterized by the deposition of subepithelial immune deposits. Most of the cases are primary, while only approximately 25% of the cases are secondary to some known diseases. Recently, MN has been considered to be a possible presentation of chronic graft-versus-host disease (GVHD) of the kidney in allogeneic hematopoietic stem cell transplantation (HSCT) patients. In autologous HSCT populations, there have been scarce reports of associated MN, as a result of immune dysregulation leading to systemic autoimmunity and miming chronic GVHD.Case presentationWe report an exceptional case of MN associated to an acute renal failure occurring within days following an autologous HSCT indicated by multiple myeloma. There was no evidence of GVHD or myeloma relapse. A complete remission of nephrotic syndrome with normalization of renal function were rapidly obtained by corticosteroid therapy.ConclusionThis is the first published case of acute renal failure due to MN occurring in the acute phase of an autologous HSCT. These findings support the antibodymediated autoimmune glomerular disease.

A Comprehensive Narrative Review of Diagnostic Biomarkers in Human Primary Membranous Nephropathy

Membranous nephropathy (MN) is relatively major cause of nephrotic syndrome in adults which is recognized as an organ-specific autoimmune disease. The etiology of most cases is idiopathic, whereas the secondary MN is caused by systemic autoimmune diseases, infections, medications and malignancies. The idiopathic disease is developed by the formation of sub-epithelial immune complex deposits most likely due to binding the circulating auto-antibodies to intrinsic antigen on podocytes. The major auto antibody is the anti-phospholipase A2 receptor(anti-PLA2R), however, it is not enough sensitive. Several attempts for diagnostic biomarker identification by modern analytical technologies have been devoted recently. This article reviews the biomarker candidates for primary type of MN that are detected by different approaches on human subjects.

Membranous Nephropathy: A Journey From Bench to Bedside.

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

Circulating antibodies to \u03b1-enolase and phospholipase A2 receptor and composition of glomerular deposits in Japanese patients with primary or secondary membranous nephropathy

BackgroundPhospholipase A2 receptor (PLA2R) is recognized as a target antigen in primary membranous nephropathy (MN); Anti-α-enolase antibody in primary and secondary MN has been proposed, however, little is known about the potential contribution of α-enolase to the pathogenesis of MN.MethodsWe evaluated circulating antibodies to α-enolase by a dot blotting system and PLA2R by indirect immunofluorescence, and glomerular deposition of these proteins in 25 patients with primary MN, 20 patients with secondary MN, 44 patients with collagen disease or severe infection, 60 patients with nephritis (each ten patients of IgA nephropathy, focal segmental gloemrulosclerosis, minimal change nephrotic syndrome, membranoproliferative glomeurlonephritis, diabetic glomerulosclerosis, and tubulointerstitial nephritis) as disease control, and 20 healthy subjects.ResultsIn primary MN, 18 of 25 sera (72 %) showed anti-α-enolase antibody (IgG1 and IgG4, 11 pts; IgG4 alone, six pts; IgG1 alone, one pt). In secondary MN, 15 of 20 sera (75 %) contained anti-α-enolase antibody (IgG1 and IgG3, 13 pts; IgG3 alone, two pts). No circulating anti-α-enolase antibody was found in 44 collagen diseases or septic patients, 60 nephritis without MN, and 20 healthy subjects. Twelve of 25 sera (48 %) from patients with primary MN were positive for anti-PLA2R antibody, whereas all patients with secondary MN were negative. Eight of the 12 PLA2R-positive patients (67 %) with primary MN also had anti α-enolase antibody. Although PLA2R antigen was present in a subepithelial pattern in 10 of 19 (52 %) patients with primary MN, α-enolase was never detected in glomerular deposits in 19 and ten patients with primary and secondary MN, respectively.ConclusionsCirculating anti-α-enolase antibodies are highly present in both primary and secondary MN (about 70 %, respectively), while anti-PLA2R antibodies are specific for primary MN (48 %) with a prevalence apparently lower in the Japanese population than in Chinese and Caucasian populations. The absence of α-enolase from subepithelial immune deposits suggests that anti-α-enolase antibodies do not contribute directly to immune-deposit formation, although they may have other pathogenic effects.

Immunology of membranous nephropathy: from animal models to humans.

Membranous nephropathy (MN), the leading cause of nephrotic syndrome in adults, is characterized by the deposition of subepithelial immune deposits that consist mainly of immunoglobulin (Ig)G and complement. Most of the cases are primary or idiopathic (iMN), while only approximately 25% of the cases are secondary to some known disease such as systemic lupus erythematosus, hepatitis B, drugs and malignancies. Most of our knowledge on the pathogenesis of iMN has relied upon old experimental models (i.e. Heymann nephritis) that have shown that immune deposits are formed in situ by the reaction of autoantibodies against the respective podocyte antigen. Recent findings indicate that podocyte proteins also act as an autoantigen in human iMN. The M-type phospholipase A2 receptor (PLA2R) has been identified as the main target antigen, as it can be found in approximately 70% of iMN patients but only rarely in other glomerulonephritides. Podocytes damage in the experimental model of Heymann nephritis is complement-mediated. In humans, the presence of complement within the subepithelial deposits is well established, but IgG4, which does not activate complement by classical or alternative pathways, represents the predominant subclass of IgG anti-PLA2R. Some evidence suggests that IgG4 anti-PLA2R autoantibodies can bind mannan-binding lectin (MBL) and activate the lectin complement pathway. A genetic background for iMN has been demonstrated by genome-wide association studies that have shown highly significant associations of the PLA2R1 and the human leucocyte antigen (HLA)-DQA1 loci with iMN. In addition to their diagnostic value, anti-PLA2R antibodies may be useful to monitor disease activity and predict response to treatment.

An unusual association between focal segmental sclerosis and lupus nephritis: a distinct concept from lupus podocytopathy?

Lupus nephritis (LN) is usually associated with immune deposition in the glomerular capillary wall. On the other hand, focal segmental glomerulosclerosis (FSGS) is not typically associated with immune deposition, and its pathogenesis includes podocyte damage and loss. The definition of lupus podocytopathy (LP) excludes patients with electron-dense glomerular basement membrane deposits. Here, we report the case of an LN patient with nephrotic proteinuria. Renal pathology demonstrated focal endocapillary hypercellularity superimposed on foam cells. Immunofluorescence revealed diffuse global subepithelial immune deposits, and electron microscopy showed electron-dense glomerular basement membrane deposits and diffuse foot process effacement. Treatment with steroid and cyclosporine improved her proteinuria. Post-treatment renal re-biopsy revealed focal segmental sclerotic lesions closely resembling FSGS. These results indicate that the pathogenesis of this case may involve an FSGS-like condition or podocytopathic change. It is possible that careful examination would reveal podocytopathic changes other than LP in patients previously diagnosed as LN class III + V. Further investigations are needed to understand FSGS-like pathological changes accompanied with capillary immune deposits in LN.

Phosphotriesterase-related protein sensed albuminuria and conferred renal tubular cell activation in membranous nephropathy.

BackgroundMembranous nephropathy (MN) is a common cause of nephrotic syndrome that may progress to end-stage renal disease (ESRD). The formation of MN involves the in situ formation of subepithelial immune deposits and leads to albuminuria; however, the underlying mechanism of how MN leads to ESRD remains unclear. The aim of this study was to investigate the expression and biological functions of phosphotriesterase-related protein (PTER) in MN.ResultsIn the progression of MN, the expression of PTER increased significantly and was mainly expressed in the renal tubular cells. Both mRNA and protein expression levels of PTER were increased in a concentration- and time-dependent manner in the in vitro albuminuria tubular cell model. Silencing the expression of PTER by RNA interference diminished albuminuria-induced inflammatory and pro-fibrotic cytokines production.ConclusionsOur findings reveal that PTER may sense albuminuria in the progression of MN, induce tubular cell activation and lead to ESRD.

The Role of Complement in Membranous Nephropathy

Membranous nephropathy (MN) describes a histopathologic pattern of injury marked by glomerular subepithelial immune deposits and collectively represents one of the most common causes of adult nephrotic syndrome. Studies in Heymann nephritis, an experimental model of MN, have established a paradigm in which these deposits locally activate complement to cause podocyte injury, culminating in cytoskeletal reorganization, loss of slit diaphragms, and proteinuria. There is much circumstantial evidence for a prominent role of complement in human MN because C3 and C5b-9 are found consistently within immune deposits. Secondary MN often shows the additional presence of C1q, implicating the classic pathway of complement activation. Primary MN, however, is IgG4-predominant and IgG4 is considered incapable of binding C1q and activating the complement pathway. Recent studies have identified the M-type phospholipase A2 receptor (PLA2R) as the major target antigen in primary MN. Early evidence hints that IgG4 anti-PLA2R autoantibodies can bind mannan-binding lectin and activate the lectin complement pathway. The identification of anti-PLA2R antibodies as likely participants in the pathogenesis of disease will allow focused investigation into the role of complement in MN. Definitive therapy for MN is immunosuppression, although future therapeutic agents that specifically target complement activation may represent an effective temporizing measure to forestall further glomerular injury.

Idiopathic membranous nephropathy and anti-phospholipase A2 receptor antibodies.

Implication for health policy/practice/research/medical education: Membranous nephropathy (MN) is a glomerular disease due to subepithelial immune deposits and local complement activation resulting in podocyte injury and proteinuria. Patients with idiopathic (but not secondary) MN had circulating autoantibodies, predominantly of the IgG4 subclass, directed against M-type phospholipase A2 receptor (PLA2R) located on podocytes. It is also possible that the binding of anti-PLA2R antibodies to PLA2R on podocytes could alter receptor function resulting in podocyte dysfunction. Please cite this paper as:Nayer A, Asif A. Idiopathic membranous nephropathy and anti-phospholipase A2 receptor antibodies. J Nephropathology. 2013; 2(4): 214-216, DOI: 10.5812/nephropathol.11627

Membranous Nephropathy and Nonsteroidal Anti-inflammatory Agents

Membranous nephropathy presents clinically as nephrotic syndrome, with subepithelial immune complex deposits seen on biopsy. Historically, in about three-quarters of membranous cases, no obvious etiologic agent or condition can be identified. More recently, serum antibodies to the phospholipase A2 receptor have been discovered in many patients with primary/idiopathic membranous nephropathy. About one-quarter of patients have membranous nephropathy as a manifestation of another systemic disorder, such as autoimmune conditions, infection, malignancy, toxin exposure, or drugs (classically gold or penicillamine). In this report, we present a case of recurrent nephrotic syndrome with biopsy-proven membranous nephropathy closely associated with use of the nonsteroidal anti-inflammatory drugs (NSAIDs) naproxen and piroxicam. Characterization of the immunoglobulin G (IgG) subclass profile of the deposits showed abundant IgG1, weak IgG4, and positive staining for phospholipase A2 receptor. This case serves to highlight membranous nephropathy as an under-recognized renal complication of NSAID use. Other kidney effects of NSAIDs, such as hemodynamic compromise, interstitial nephritis, and minimal change disease, are more broadly recognized.

Membranous nephropathy

Primary membranous nephropathy is a common glomerular disease characterized by sub-epithelial immune deposits that has become the prototype of an autoimmune glomerular disease. The purpose of this review is to highlight recent advances regarding the pathogenesis of membranous nephropathy as well as potential new therapies. The discovery of two major podocyte antigens, neutral endopeptidase (NEP), involved in rare cases of neonatal membranous nephropathy, and the M-type phospholipase A2 receptor 1 (PLA2R1), the first antigen discovered in adults, have been major 'breakthroughs' in our understanding of the pathogenesis of human membranous nephropathy. Anti-PLA2R antibodies appear to predict activity of the disease as well as response to therapy. Pediatric and adult cases of membranous nephropathy occurring in the presence of circulating cationic bovine serum album (BSA) and anti-BSA antibodies have also been described, raising the possibility that food antigens may be involved in the development of membranous nephropathy. Moreover, the results of genetic susceptibility have become available. Exciting progress has also been made in the treatment of this disease including therapy with adrenocorticotropic hormone and rituximab. Understanding disease pathogenesis is crucial in guiding patient evaluation and designing appropriate therapy. Recent discoveries have helped to elucidate the pathophysiology of membranous nephropathy and may facilitate a more patient-specific treatment approach in these patients.

Renal-limited 'lupus-like' nephritis

In the setting of an IgG-dominant immune complex-mediated glomerulonephritis, there are multiple pathological findings that strongly suggest the diagnosis of lupus nephritis (LN) including (i) 'full-house' immunofluorescence staining for IgG, IgM, IgA, C3 and C1; (ii) extraglomerular immune deposits; (iii) combined mesangial, subendothelial and subepithelial immune deposits and (iv) the presence of endothelial tubuloreticular inclusions. We report four female adult patients with renal biopsy findings which are highly suggestive of LN but without extrarenal signs, symptoms or serologies of systemic lupus erythematosus at the time of biopsy or over a mean follow-up period of 3 years. Despite aggressive therapy, outcomes were poor in this small cohort. We refer to these cases as renal-limited 'lupus-like' nephritis.

Idiopathic Membranous Nephropathy: An Autoimmune Disease

For more than 50 years researchers have debated the evidence for an autoimmune basis of human idiopathic membranous nephritis (MN). Work published in the past 2 years has substantially strengthened the belief that MN is indeed an autoimmune disease of the kidney. Autoantibodies of the IgG4 subclass to at least three podocyte membrane proteins including phospholipase A(2)-receptor, aldose reductase, and manganese superoxide dismutase have been detected by immunoblotting in sera as well as in acid eluates prepared from renal biopsy tissue of patients with this disease, using either whole tissue or microdissected glomeruli from frozen sections. In each case the podocyte antigen has been shown to co-localize with the subepithelial glomerular immune deposits in renal tissue of the same patients. It is not certain if any of these podocyte proteins is an inciting/primary autoantigen or whether they are secondary antigens recruited by intermolecular epitope-spreading, initiating from a yet-to-be-discovered autoantigen. Although it is clear that autoantibodies to podocyte membrane proteins are elicited in idiopathic MN and contribute to the formation of the subepithelial deposits, many questions remain concerning the triggers for their development and their contribution toward proteinuria and progression of the disease.

Complement Factor H Deficiency Accelerates Development of Lupus Nephritis

Complement factor H (CfH) is a key regulator of the alternative pathway, and its presence on mouse platelets and podocytes allows the processing of immune complexes. Because of the role of immune complexes in the pathophysiology of lupus nephritis, we studied the role of CfH in the development of nephritis in MRL-lpr mice, an animal model of lupus. At 12 weeks, CfH-deficient MRL-lpr mice had significantly more albuminuria and higher BUN levels than MRL-lpr controls. Cfh-deficient MRL-lpr mice also experienced earlier mortality: at 14 weeks, 6 of 9 CfH-deficient MRL-lpr mice had died of renal failure, whereas all 11 littermate CfH-sufficient MRL-lpr mice were alive (P ≤ 0.001). Histologically, CfH-deficient MRL-lpr mice developed severe diffuse lupus nephritis by 12 weeks (glomerulonephritis scores of 2.6 ± 0.4 versus 0.4 ± 0.2 in littermate controls, P = 0.001). Similar to other CfH-deficient mouse models on nonautoimmune backgrounds, immunofluorescence staining showed extensive linear C3 staining along glomerular capillary walls. IgG was present in the mesangium and peripheral capillary walls along with excessive infiltration of macrophages and neutrophils. Ultrastructurally, there were subendothelial and subepithelial immune deposits and extensive podocyte foot process effacement. In summary, the loss of CfH accelerates the development of lupus nephritis and recapitulates the functional and structural features of the human disease. This illustrates the critical role of complement regulation and metabolism of immune complexes in the pathogenesis of lupus nephritis.

Membranous nephropathy: From mechanisms to therapies

AbstractMembranous nephropathy (MN) is an important glomerular disease characterized by podocyte injury and protein‐uria. The understanding of cellular and molecular mechanisms involved in the pathogenesis of MN has come from studies in the Heymann nephritis model of MN in the rat. MN involves the in situ formation of subepithelial immune deposits of antibodies reactive to podocyte antigens, activation of complement, and assembly of C5b‐9 on podo‐cyte plasma membranes. The podocyte responds to C5b‐9 attack by activating protein kinases, phospholipases, oxidants, transcription factors, growth factors, stress pathways, proteinases, and other mediators. These signals impact on metabolic pathways, structure/function of lipids, proteins in the cytoskeleton and slit diaphragm, and turnover of extracellular matrix components. Some effects of C5b‐9 affect podocyte functions adversely, while other effects may limit injury or promote recovery. Increased understanding of pathogenic antigens, complement activation, and changes in podocyte biology induced by C5b‐9 is an opportunity for new diagnostic and concept‐driven therapeutic approaches to this disease.

Light Microscopic Features of Membranous Nephropathy With Unusual Changes of the Podocytes and Glomerular Basement Membrane in a Patient With Sudden Onset of Nephrotic Syndrome

Membranous nephropathy (MN) is a pathologic entity characterized by a spectrum of changes in the glomerular basement membrane (GBM). Diagnostic features include subepithelial immune deposits and thickening of the GBM.1 In 1968, Ehrenreich and Churg2 proposed a morphologic classification of MN using electron microscopic findings. This classification was based on immune deposits in the GBM, GBM reaction to the deposits, and resolution of glomerular injury with resorption of the deposits. However, some biopsy specimens with features of MN also show spherical microparticles and podocyte microvillous entrapment in thickened GBM on electron microscopy.

Membranous glomerulonephritis in a patient with ankylosing spondylitis: a rare association

Ankylosing spondylitis is a chronic inflammatory disease of the vertebral joints and soft tissues. Renal involvement, apart from amyloidosis, is rare in this disorder. Of the various glomerulonephritides reported in association with ankylosing spondylitis, IgA nephropathy is the most common. Membranous glomerulonephritis occurs very rarely in patients with ankylosing spondylitis, and only four such cases have been reported in the available English literature. Due to the rarity of this association, membranous glomerulonephritis may not initially be considered in patients with ankylosing spondylitis and proteinuria. We report the case of a 29-year-old man with ankylosing spondylitis who presented with pedal edema and was detected to have nephrotic syndrome. A percutaneous renal biopsy showed features of membranous glomerulonephritis with capillary wall granular deposits of IgG and C3 on immunofluorescence and subepithelial immune complex deposits on electron microscopy. No other secondary cause of membranous glomerulopathy was found on extensive investigations. Membranous glomerulonephritis is extremely rare in association with ankylosing spondylitis, the present case being the fifth such report. The exact relationship of these two entities (etiological or coincidental) still needs to be elucidated. The occurrence of this rare association needs to be recognized and differentiated from other more common causes of renal involvement in ankylosing spondylitis.

Microarray and Bioinformatics Analysis of Gene Expression in Experimental Membranous Nephropathy

Background: Passive Heymann nephritis (PHN), the best characterized animal model of experimental membranous nephropathy, is characterized by subepithelial immune deposits, podocyte foot processes effacement and massive proteinuria beginning 4 days following disease induction. Although single genes involved in PHN have been studied, no whole genome-wide expression analysis of kidney tissue has been performed. Methods: Microarray analysis was performed to identify gene expression changes in PHN rat kidneys during the onset of proteinuria. Results: Our results showed that 234 transcripts were differentially expressed in diseased animals compared to controls. Genes exclusively upregulated in diseased animals were mainly required for cell structure and motility, immunity and defense, cell cycle, and developmental processes. The single most increased gene was transgelin (Tagln) showing a 70-fold upregulation in animals with PHN. Protein-protein interaction analysis revealed the following four processes of major relevance in disease manifestation: (i) DNA damage and repair; (ii) changes in the extracellular matrix; (iii) deregulation of cytokines and growth factors, as well as (iv) rearrangements of the cytoskeleton. Conclusion: We show for the first time the complex interplay between multiple different genes in experimental membranous nephropathy, supporting a role for genomic approaches to better understanding and defining specific disease processes.

Glomerular subendothelial and subepithelial immune complexes, containing the same antigen, are removed at different rates

To examine the persistence of immune deposits in the subendothelial and subepithelial areas of the glomerular basement membrane in rats, immune deposits were formed by injection of radiolabelled, cationized human serum albumin (HSA) as antigen, followed by rabbit antibodies to HSA. The disappearance of the radiolabelled antigen from immune deposits in glomeruli was described by a curve consisting of two exponential components. By electron microscopy, subendothelial and subepithelial immune deposits were initially present in glomeruli. At later time-points, only subepithelial immune deposits were present. The fast component of disappearance, attributed to subendothelial deposits, had a half-life of 3.89 +/- 0.32 h. The slow component of disappearance from glomeruli, attributed to subepithelial deposits, had a half-life of 85.5 +/- 3.1 h. Since some of the injected, radiolabelled antigen was sequestered in other compartments of the body, the possibility was raised that antigen from these sites might be released and contribute to the persistence of deposits in glomeruli. This possibility, however, was excluded when transplantation of kidneys with immune deposits to untreated recipients revealed no difference in the amount of antigen persisting in nontransplanted and transplanted kidneys.