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Insights from experimental studies have been recently translated into substantial advances in understanding the pathogenesis of human membranous nephropathy (MN). These include identification of neutral endopeptidase (NEP) as the target antigen in alloimmune MN resulting from fetomaternal immunization in NEP-deficient mothers, and our demonstration that a high proportion of patients with idiopathic MN (IMN) have circulating antibodies to the M-type phospholipase A2 receptor (PLA2R), a transmembrane protein located on podocytes. Here we highlight the studies that led to these discoveries and our current knowledge about the possible role of anti-PLA2R autoantibodies in the pathogenesis of IMN. Given that the sensitivity and specificity of anti-PLA2R for IMN are >75 and 100%, respectively, we foresee that a widely available assay for anti-PLA2R will prove to be valuable for diagnosing IMN, distinguishing it from secondary MN, and evaluating response to therapy. We suggest reasons why 25% of patients with IMN have tested negative for anti-PLA2R, and propose possible explanations for the presence of complement deposits in IMN despite the fact that immunoglobulin G4 (IgG4), the predominant anti-PLA2R IgG subclass, is incapable of activating the classical complement pathway. Finally, we point out avenues to be explored, including the events that induce production of anti-PLA2R, their ability to cause podocyte injury, the role of complement, and the nature of the antibodies in secondary forms of MN.
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PMID:Membranous nephropathy: recent travels and new roads ahead. 2018 13

Membranous nephropathy, a disease characterized by an accumulation of immune deposits on the outer aspect of the glomerular basement membrane, is the most common cause of idiopathic nephrotic syndrome in Caucasian adults. In the rat model described by Heymann in 1959, the target antigen of antibodies is megalin, a multiligand receptor expressed in the rat glomerulus but absent from the human glomerulus. In the past few years, two major antigens have been identified in human membranous nephropathy. The first is neutral endopeptidase, the alloantigen involved in neonatal cases of membranous nephropathy that occur in newborns from neutral endopeptidase-deficient mothers. The second is the type-M phospholipase A2 receptor (PLA(2)R), the first autoantigen identified in idiopathic membranous nephropathy in the adult. Megalin, neutral endopeptidase, and PLA(2)R are all expressed on the podocyte surface where they serve as targets for circulating antibodies, which lead to in situ immune complex formation, complement activation, and proteinuria. The recent discovery of neutral endopeptidase and PLA(2)R provides new tools for monitoring human disease activity and should be of value in designing new antigen-driven therapeutic strategies.
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PMID:Antigen identification in membranous nephropathy moves toward targeted monitoring and new therapy. 2018 38

1. embranous nephropathy is characterized by an accumulation of immune deposits on the outer aspect of the glomerular basement membrane. 2. In the rat model described by Heymann in 1959, the target antigen of antibodies is megalin, a multiligand receptor expressed in the rat glomerulus but absent from the human glomerulus. 3. In recent years, two major antigens have been identified in human membranous nephropathy (MN). The first is neutral endopeptidase (NEP), the alloantigen involved in neonatal cases of MN that occur in newborns from NEP-deficient mothers. The second is the M-type phospholipase A(2) receptor (PLA(2) R), the first autoantigen identified in idiopathic MN in the adult. Megalin, NEP and PLA(2) R are all expressed on the podocyte surface, where they can serve as targets for circulating antibodies, leading to in situ immune complex formation, complement activation and proteinuria. 4. In addition to podocyte antigens, we recently showed that some patients with childhood MN had both circulating cationic bovine serum albumin (BSA) and anti-BSA antibodies, with BSA being present in immune deposits. This suggests that food antigens may be involved in MN through charge-dependent binding to the anionic glomerular capillary wall and in situ formation of immune complexes.
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PMID:Advances in membranous nephropathy: success stories of a long journey. 2138 32

Antibodies to neutral endopeptidase, a podocyte protein, are responsible for rare alloimmune neonatal membranous nephropathy that develops in children from neutral endopeptidase-deficient mothers. Neutral endopeptidase was the first podocyte antigen described in human membranous nephropathy. PLA2R1, the type-M receptor of soluble phospholipase A2, is a major target antigen in so-called idiopathic membranous nephropathy in adults. Antibodies to PLA2R1 are detected in 60 to 80% of patients before immunosuppressive treatment, and are only occasionally found in secondary membranous nephropathy. To date, they have not been detected in other pathological conditions and in healthy individuals. PLA2R1 and HLA-DQA1 gene variants defined by single nucleotide polymorphisms are strongly associated with idiopathic membranous nephropathy in patients of white ancestry, and can thus be considered as predisposing genes. In addition to their diagnostic value, anti-PLA2R1 antibodies can be used to monitor treatment. Immunization against cationic bovine serum albumin is a cause of early childhood membranous nephropathy. This finding points to a possible role of food and environmental antigens in membranous nephropathy. The newly identified antigen-antibody systems should be considered as molecular signatures challenging the uniform histological definition and having a major impact on patient care in a near future.
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PMID:[Idiopathic and secondary membranous nephropathies]. 2220 61

Over the past few years, considerable advances have been made in our understanding of the molecular pathomechanisms of human membranous nephropathy, inspired by studies of Heymann nephritis, a faithful experimental model of this disease. This research led to the identification of neutral endopeptidase, the M-type receptor for secretory phospholipase A(2) (PLA(2)R1) and cationic bovine serum albumin as target antigens of circulating and deposited antibodies in alloimmune neonatal, adult 'idiopathic' and early-childhood membranous nephropathy, respectively. A genome-wide association study has provided further evidence for a highly significant association between PLA2R1 and HLA-DQA1 loci and idiopathic membranous nephropathy in patients of white ancestry. Additional antibody specificities for cytoplasmic antigens have also been identified, but their pathogenic role is uncertain. The time has come to revisit the spectrum of membranous nephropathies based on the newly identified antigen-antibody systems that should be considered as molecular signatures of the disease and that challenge the uniform histological definition. These signatures will soon have a major impact on patient care.
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PMID:Pathogenesis of membranous nephropathy: recent advances and future challenges. 2237 Dec 47

Membranous glomerulonephritis is one of the leading causes of nephrotic syndrome in adults. It may have very variable course, with some patients slowly progressing to renal failure and some entering spontaneous remission. The aim of this article is to review recent advances in the pathogenesis and treatment of the disease in recent years. In recent years, first human podocyte autoantigens, responsible for autoantibodies and in situ immune complexes formation, were discovered: neutral endopeptidase, m-type phospholipase A2 receptor, superoxide-dismutase 2, aldose-reductase, alpha-enolase. It is postulated that these discoveries will help in differentiation between primary and secondary membranous glomerulonephritis, in predicting remission and/or relapse and also in determining more specific therapy. There have been also some pilot studies recently, in which new drugs have been introduced in the treatment of membranous glomerulonephritis: ACTH, rituximab and tacrolimus.
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PMID:[Membranous glomerulonephritis--recent advances in pathogenesis and treatment]. 2340 79

Membranous nephropathy (MN) is a kidney disease characterized by deposition of immune complexes and complement on the outer aspect of the glomerular capillary wall. It is responsible for a loss of serum proteins in the urine and kidney failure. During the last ten years, considerable progress has occurred in the understanding of the molecular bases of the disease with the description of three distinct mechanisms in humans. In the neonatal allo-immune form, antibodies are directed against neutral endopeptidase (NEP), a podocyte antigen absent in the mothers who become immunized against this antigen expressed by placenta cells during pregnancy. NEP was the first podocyte antigen to be identified in MN. Most adult forms of MN are autoimmune diseases without identified etiology (primary MN), linked to the production of antibodies raised against another podocyte antigen, the type-M phospholipase A2 receptor (PLA2R1). Anti-PLA2R1 antibodies are detected in 70 to 80% of patients before any immunosuppressive treatment, and only occasionally in secondary forms of MN, variants of PLAR1 and HLA-DQA1 genes are very significantly associated with occurrence of primary MN in Caucasians. The third mechanism is characterized by immunization against a foreign protein, cationic bovine serum albumin (BSA), which is involved in rare forms of MN during early childhood. This finding points to a possible role of food and environmental antigens in membranous nephropathy.
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PMID:[Pathophysiology of extramembranous glomerulopathies. Fifty years of progress, from laboratory to patient]. 2459 73

Since the early 2000s, considerable advances have been achieved in the understanding of molecular pathomechanisms of human membranous nephropathy (MN), inspired by studies of Heymann nephritis, a faithful experimental model. These studies led to the identification of neutral endopeptidase, the type-M phospholipase A2 receptor (PLA2R), and cationic bovine serum albumin as target antigens of circulating and deposited antibodies in neonatal alloimmune, adult 'idiopathic', and early childhood MN, respectively. A genome-wide association study further showed a highly significant association of the PLA2R1 and the HLA-DQA1 loci with idiopathic MN in patients of white ancestry. The time has come to revisit the spectrum of MN based on the newly identified antigen-antibody systems which should be considered as molecular signatures of the disease, challenging the uniform histological definition. Although some uncertainties remain as to the pathogenic effects of anti-PLA2R antibodies because of the lack of an appropriate experimental model, the value of these antibodies as biomarkers for diagnosis and disease activity is increasingly being recognized. It is not exaggerated to state that they have induced a paradigm shift in the monitoring of patients with MN, thus opening a new era of personalized medicine.
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PMID:Anti-phospholipase A2 receptor antibodies and the pathogenesis of membranous nephropathy. 2540 74

Alloimmune antenatal membranous nephropathy (MN) during pregnancy results from antibodies produced by a neutral endopeptidase (NEP)-deficient mother. Here we report two recent cases that provide clues to the severity of renal disease. Mothers of the two children had circulating antibodies against NEP showing the characteristic species-dependent pattern by immunofluorescence on kidney slices. A German mother produced predominantly anti-NEP IgG4 accompanied by a low amount of IgG1. Her child recovered renal function within a few weeks. In sharp contrast, an Italian mother mainly produced complement-fixing anti-NEP IgG1, which also inhibits NEP enzymatic activity, whereas anti-NEP IgG4 has a weak inhibitory potency. Her child was dialyzed for several weeks. A kidney biopsy performed at 12 days of age showed MN, ischemic glomeruli, and arteriolar and tubular lesions. A second biopsy performed at 12 weeks of age showed aggravation with an increased number of collapsed capillary tufts. Both mothers were homozygous for the truncating deletion mutation 466delC and were thus NEP deficient. The 466delC mutation, identified in three previously described families, suggests a founder effect. Because of the potential severity of alloimmune antenatal MN, it is essential to identify families at risk by the detection of anti-NEP antibodies and NEP antigen in urine. On the basis of the five families identified to date, we propose an algorithm for the diagnosis of the disease and the prevention of complications.
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PMID:Genetic homogeneity but IgG subclass-dependent clinical variability of alloimmune membranous nephropathy with anti-neutral endopeptidase antibodies. 2572 31

Fetomaternal alloimmunization against neutral endopeptidase (NEP) is a rare cause of antenatal membranous nephropathy, yet lessons from such cases continue to elucidate important pathophysiologic points. Vivarelli and colleagues describe two recent cases of this disease and demonstrate that despite a common genetic cause, differences in maternal anti-NEP IgG subclass modulate disease severity through such mechanisms as complement activation and enzyme inhibition.
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PMID:Lessons from a rare disease: IgG subclass and disease severity in alloimmune antenatal membranous nephropathy. 2556 8


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