Autoantibodies Targeting Nephrin in Podocytopathies.

BACKGROUND: Minimal change disease and primary focal segmental glomerulosclerosis in adults, along with idiopathic nephrotic syndrome in children, are immune-mediated podocytopathies that lead to nephrotic syndrome. Autoantibodies targeting nephrin have been found in patients with minimal change disease, but their clinical and pathophysiological roles are unclear. METHODS: We conducted a multicenter study to analyze antinephrin autoantibodies in adults with glomerular diseases, including minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, IgA nephropathy, antineutrophil cytoplasmic antibody-associated glomerulonephritis, and lupus nephritis, as well as in children with idiopathic nephrotic syndrome and in controls. We also created an experimental mouse model through active immunization with recombinant murine nephrin. RESULTS: The study included 539 patients (357 adults and 182 children) and 117 controls. Among the adults, antinephrin autoantibodies were found in 46 of the 105 patients (44%) with minimal change disease, 7 of 74 (9%) with primary focal segmental glomerulosclerosis, and only in rare cases among the patients with other conditions. Of the 182 children with idiopathic nephrotic syndrome, 94 (52%) had detectable antinephrin autoantibodies. In the subgroup of patients with active minimal change disease or idiopathic nephrotic syndrome who were not receiving immunosuppressive treatment, the prevalence of antinephrin autoantibodies was as high as 69% and 90%, respectively. At study inclusion and during follow-up, antinephrin autoantibody levels were correlated with disease activity. Experimental immunization induced a nephrotic syndrome, a minimal change disease-like phenotype, IgG localization to the podocyte slit diaphragm, nephrin phosphorylation, and severe cytoskeletal changes in mice. CONCLUSIONS: In this study, circulating antinephrin autoantibodies were common in patients with minimal change disease or idiopathic nephrotic syndrome and appeared to be markers of disease activity. Their binding at the slit diaphragm induced podocyte dysfunction and nephrotic syndrome, which highlights their pathophysiological significance. (Funded by Deutsche Forschungsgemeinschaft and others.).

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.

Podocyte expression of human phospholipase A2 receptor 1 causes immune-mediated membranous nephropathy in mice.

Antibody-mediated autoimmune pathologies like membranous nephropathy are difficult to model, particularly in the absence of local target antigen expression in model organisms such as mice and rats; as is the case for phospholipase A2 receptor 1 (PLA2R1), the major autoantigen in membranous nephropathy. Here, we generated a transgenic mouse line expressing the full-length human PLA2R1 in podocytes, which has no kidney impairment after birth. Beginning from the age of three weeks, these mice spontaneously developed anti-human PLA2R1 antibodies, a nephrotic syndrome with progressive albuminuria and hyperlipidemia, and the typical morphological signs of membranous nephropathy with granular glomerular deposition of murine IgG in immunofluorescence and subepithelial electron-dense deposits by electron microscopy. Importantly, human PLA2R1-expressing Rag2-/- mice, which lack mature and functioning B and T lymphocytes, developed neither anti-PLA2R1 antibodies nor proteinuria. Thus, our work demonstrates that podocyte expression of human PLA2R1 can induce membranous nephropathy with an underlying antibody-mediated pathogenesis in mice. Importantly, this antibody-mediated model enables proof-of-concept evaluations of antigen-specific treatment strategies, e.g., targeting autoantibodies or autoantibody-producing cells, and may further help understand the autoimmune pathogenesis of membranous nephropathy.

Glomerular Endothelial Cell-Derived microRNA-192 Regulates Nephronectin Expression in Idiopathic Membranous Glomerulonephritis.

BACKGROUND: Autoantibodies binding to podocyte antigens cause idiopathic membranous glomerulonephritis (iMGN). However, it remains elusive how autoantibodies reach the subepithelial space because the glomerular filtration barrier (GFB) is size selective and almost impermeable for antibodies. METHODS: Kidney biopsies from patients with iMGN, cell culture, zebrafish, and mouse models were used to investigate the role of nephronectin (NPNT) regulating microRNAs (miRs) for the GFB. RESULTS: Glomerular endothelial cell (GEC)-derived miR-192-5p and podocyte-derived miR-378a-3p are upregulated in urine and glomeruli of patients with iMGN, whereas glomerular NPNT is reduced. Overexpression of miR-192-5p and morpholino-mediated npnt knockdown induced edema, proteinuria, and podocyte effacement similar to podocyte-derived miR-378a-3p in zebrafish. Structural changes of the glomerular basement membrane (GBM) with increased lucidity, splitting, and lamellation, especially of the lamina rara interna, similar to ultrastructural findings seen in advanced stages of iMGN, were found. IgG-size nanoparticles accumulated in lucidity areas of the lamina rara interna and lamina densa of the GBM in npnt-knockdown zebrafish models. Loss of slit diaphragm proteins and severe structural impairment of the GBM were further confirmed in podocyte-specific Npnt knockout mice. GECs downregulate podocyte NPNT by transfer of miR-192-5p-containing exosomes in a paracrine manner. CONCLUSIONS: Podocyte NPNT is important for proper glomerular filter function and GBM structure and is regulated by GEC-derived miR-192-5p and podocyte-derived miR-378a-3p. We hypothesize that loss of NPNT in the GBM is an important part of the initial pathophysiology of iMGN and enables autoantigenicity of podocyte antigens and subepithelial immune complex deposition in iMGN.

Clinical Relevance of Domain-Specific Phospholipase A2 Receptor 1 Antibody Levels in Patients with Membranous Nephropathy.

BACKGROUND: Antibodies against phospholipase A2 receptor 1 (PLA2R1) are found in 80% of patients with membranous nephropathy, and previous studies described three autoantibody-targeted PLA2R1 epitope regions. Although anti-PLA2R1 antibody levels are closely associated with treatment response and disease prognosis, the clinical role of epitope regions targeted by autoantibodies is unclear. METHODS: In a prospective cohort of 150 patients with newly diagnosed PLA2R1-associated membranous nephropathy, we investigated the clinical role of epitope-recognition patterns and domain-specific PLA2R1 antibody levels by western blot and ELISA. RESULTS: We identified a fourth epitope region in the CTLD8 domain of PLA2R1, which was recognized by anti-PLA2R1 antibodies in 24 (16.0%) patients. In all study patients, anti-PLA2R1 antibodies bound both the N-terminal (CysR-FnII-CTLD1) region and the C-terminal (CTLD7-CTLD8) region of PLA2R1 at study enrollment. The total anti-PLA2R1 antibody levels of patients determined detection of domain-specific PLA2R1 antibodies, and thereby epitope-recognition patterns. A remission of proteinuria occurred in 133 (89%) patients and was not dependent on the domain-recognition profiles. A newly developed ELISA showed that domain-specific PLA2R1 antibody levels targeting CysR, CTLD1, and CTLD7 strongly correlate with the total anti-PLA2R1 antibody level (Spearman's rho, 0.95, 0.64, and 0.40; P<0.001, P<0.001, and P=0.002, respectively) but do not predict disease outcome independently of total anti-PLA2R1 antibody levels. CONCLUSIONS: All patients with PLA2R1-associated membranous nephropathy recognize at least two epitope regions in the N- and C-terminals of PLA2R1 at diagnosis, contradicting the hypothesis that PLA2R1 "epitope spreading" determines the prognosis of membranous nephropathy. Total anti-PLA2R1 antibody levels, but not the epitope-recognition profiles at the time of diagnosis, are relevant for the clinical outcome of patients with this disease.

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.

T-lymphocyte-specific knockout of IKK-2 or NEMO induces Th17 cells in an experimental nephrotoxic nephritis mouse model.

Experimental nephrotoxic serum nephritis (NTN) is a model for T-cell-mediated human rapid progressive glomerulonephritis. T-cell receptor stimulation involves intracellular signaling events that ultimately lead to the activation of transcription factors, such as NF-κB. We explored the involvement of the NF-κB components IKK-2 and NEMO in NTN, by using cell-specific knockouts of IKK-2 and NEMO in CD4+ T lymphocytes. Our results demonstrate that although the course of disease was not grossly altered in CD4xIKK2Δ and CD4xNEMOΔ animals, renal regulatory T cells were significantly reduced and T helper (Th)1 and Th17 cells significantly increased in both knockout mouse groups. The expression of the renal cytokines and chemokines IL-1ß, CCL-2, and CCL-20 was also significantly altered in both knockout mice. Lymphocyte transcriptome analysis confirmed the increased expression of Th17-related cytokines in spleen CD4+ T cells. Moreover, our array data demonstrate an interrupted canonical NF-κB pathway and an increased expression of noncanonical NF-κB pathway-related genes in nephritic CD4xNEMOΔ mice, highlighting different downstream effects of deletion of IKK-2 or NEMO in T lymphocytes. We propose that better understanding of the role of IKK-2 and NEMO in nephritis is essential for the clinical application of kinase inhibitors in patients with glomerulonephritis.-Guo, L., Huang, J., Chen, M., Piotrowski, E., Song, N., Zahner, G., Paust, H.-J., Alawi, M., Geffers, R., Thaiss, F. T-lymphocyte-specific knockout of IKK-2 or NEMO induces Th17 cells in an experimental nephrotoxic nephritis mouse model.

The Most N-Terminal Region of THSD7A Is the Predominant Target for Autoimmunity in THSD7A-Associated Membranous Nephropathy.

Background Thrombospondin type 1 domain-containing 7A (THSD7A) has been identified as a pathogenic autoantigen in membranous nephropathy (MN). However, the THSD7A epitopes targeted by patient autoantibodies are unknown.Methods We performed an in silico analysis of the THSD7A multidomain structure, expressed the folded domains in HEK293 cells, and tested for domain reactivity with 31 serum samples from patients with THSD7A-associated MN using Western and native blotting. Immunogenicity of the antigen domains was further investigated by cDNA immunization of rabbits and mice.Results We characterized the extracellular topology of THSD7A as a tandem string of 21 thrombospondin type 1 domains. Overall, 28 serum samples (90%) recognized multiple epitope domains along the molecule. Detailed epitope mapping revealed that the complex consisting of the first and second N-terminal domains (amino acids 48-192) was recognized by 27 of 31 patient serum samples (87%). Serum recognizing one or two epitope domains showed lower anti-THSD7A antibody levels than serum recognizing three or more epitope domains. During follow-up, a loss of epitope recognition was observed in seven of 16 patients, and it was accompanied by decreasing antibody levels and remission of proteinuria. In four of 16 patients, epitope recognition patterns changed during follow-up. Notably, immunization experiments in rabbits and mice revealed that induced antibodies, like patient autoantibodies, preferentially bound to the most N-terminal domains of THSD7A.Conclusions Our data show that the immune response in THSD7A-associated MN is polyreactive and that autoantibodies predominantly target the most N-terminal part of THSD7A.

A Heterologous Model of Thrombospondin Type 1 Domain-Containing 7A-Associated Membranous Nephropathy.

Thrombospondin type 1 domain-containing 7A (THSD7A) is a target for autoimmunity in patients with membranous nephropathy (MN). Circulating autoantibodies from patients with THSD7A-associated MN have been demonstrated to cause MN in mice. However, THSD7A-associated MN is a rare disease, preventing the use of patient antibodies for larger experimental procedures. Therefore, we generated antibodies against the human and mouse orthologs of THSD7A in rabbits by coimmunization with the respective cDNAs. Injection of these anti-THSD7A antibodies into mice induced a severe nephrotic syndrome with proteinuria, weight gain, and hyperlipidemia. Immunofluorescence analyses revealed granular antigen-antibody complexes in a subepithelial location along the glomerular filtration barrier 14 days after antibody injection, and immunohistochemistry for rabbit IgG and THSD7A as well as ultrastructural analyses showed the typical characteristics of human MN. Mice injected with purified IgG from rabbit serum that was taken before immunization failed to develop any of these changes. Notably, MN developed in the absence of detectable complement activation, and disease was strain dependent. In vitro, anti-THSD7A antibodies caused cytoskeletal rearrangement and activation of focal adhesion signaling. Knockdown of the THSD7A ortholog, thsd7aa, in zebrafish larvae resulted in altered podocyte differentiation and impaired glomerular filtration barrier function, with development of pericardial edema, suggesting an important role of THSD7A in glomerular filtration barrier integrity. In summary, our study introduces a heterologous mouse model that allows further investigation of the molecular events that underlie MN.

An Indirect Immunofluorescence Method Facilitates Detection of Thrombospondin Type 1 Domain-Containing 7A-Specific Antibodies in Membranous Nephropathy.

Thrombospondin type 1 domain-containing 7A (THSD7A) is a target antigen identified in adult membranous nephropathy (MN) along with the major antigen phospholipase A2 receptor 1 (PLA2R1). The prevalence of THSD7A-Ab-positive patients is unknown, and it is unclear whether the clinical presentation differs between patients positive for PLA2R1-Ab or THSD7A-Ab. We screened serum samples of 1276 patients with MN from three different cohorts for the presence of THSD7A-Ab by Western blot analysis and a newly developed indirect immunofluorescence test (IFT). Compared with Western blot analysis, the IFT had a 92% sensitivity and a 100% specificity. The prevalence of THSD7A-associated MN in a prospective cohort of 345 patients with MN was 2.6%, and most were women. In this cohort, the percentage of patients with THSD7A-associated MN and malignant disease significantly exceeded that of patients with PLA2R1-associated MN and malignant disease. In all cohorts, we identified 40 patients with THSD7A-associated MN, eight of whom developed a malignancy within a median time of 3 months from diagnosis of MN. In one patient with THSD7A-associated MN and metastases of an endometrial carcinoma, immunohistochemistry showed THSD7A expression on the metastatic cells and within follicular dendritic cells of the metastasis-infiltrated lymph node. We conclude that the IFT allows sensitive and specific measurement of circulating THSD7A-Ab in patients with MN. Patients with THSD7A-associated MN differ in their clinical characteristics from patients with PLA2R1-associated MN, and more intensive screening for the presence of malignancies may be warranted in those with THSD7A-associated MN.

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

BACKGROUND: Idiopathic membranous nephropathy is an autoimmune disease. In approximately 70% of patients, it is associated with autoantibodies against the phospholipase A2 receptor 1 (PLA2R1). Antigenic targets in the remaining patients are unknown. METHODS: Using Western blotting, we screened serum samples from patients with idiopathic membranous nephropathy, patients with other glomerular diseases, and healthy controls for antibodies against human native glomerular proteins. We partially purified a putative new antigen, identified this protein by means of mass spectrometry of digested peptides, and validated the results by analysis of recombinant protein expression, immunoprecipitation, and immunohistochemical analysis. RESULTS: Serum samples from 6 of 44 patients in a European cohort and 9 of 110 patients in a Boston cohort with anti-PLA2R1-negative idiopathic membranous nephropathy recognized a glomerular protein that was 250 kD in size. None of the serum samples from the 74 patients with idiopathic membranous nephropathy who were seropositive for anti-PLA2R1 antibodies, from the 76 patients with other glomerular diseases, and from the 44 healthy controls reacted against this antigen. Although this newly identified antigen is clearly different from PLA2R1, it shares some biochemical features, such as N-glycosylation, membranous location, and reactivity with serum only under nonreducing conditions. Mass spectrometry identified this antigen as thrombospondin type-1 domain-containing 7A (THSD7A). All reactive serum samples recognized recombinant THSD7A and immunoprecipitated THSD7A from glomerular lysates. Moreover, immunohistochemical analyses of biopsy samples from patients revealed localization of THSD7A to podocytes, and IgG eluted from one of these samples was specific for THSD7A. CONCLUSIONS: In our cohort, 15 of 154 patients with idiopathic membranous nephropathy had circulating autoantibodies to THSD7A but not to PLA2R1, a finding that suggests a distinct subgroup of patients with this condition. (Funded by the French National Center for Scientific Research and others.).

Lymphocyte-specific deletion of IKK2 or NEMO mediates an increase in intrarenal Th17 cells and accelerates renal damage in an ischemia-reperfusion injury mouse model.

Acute kidney injury (AKI) is associated with poor patient outcome and a global burden for end-stage renal disease. Ischemia-reperfusion injury (IRI) is one of the major causes of AKI, and experimental work has revealed many details of the inflammatory response in the kidney, such as activation of the NF-κB pathway. Here, we investigated whether deletion of the NF-κB kinases IKK2 or NEMO in lymphocytes or systemic inhibition of IKK2 would cause different kidney inflammatory responses after IRI induction. Serum creatinine, blood urea nitrogen (BUN) level, and renal tubular injury score were significantly increased in CD4creIKK2f/f (CD4xIKK2Δ) and CD4creNEMOf/f (CD4xNEMOΔ) mice compared with CD4cre mice after IRI induction. The frequency of Th17 cells infiltrating the kidneys of CD4xIKK2Δ or CD4xNEMOΔ mice was also significantly increased at all time points. CCL20, an important chemokine in Th17 cell recruitment, was significantly increased at early time points after the induction of IRI. IL-1ß, TNF-α, and CCL2 were also significantly increased in different patterns. A specific IKK2 inhibitor, KINK-1, reduced BUN and serum creatinine compared with nontreated mice after IRI induction, but the frequency of kidney Th17 cells was also significantly increased. In conclusion, although systemic IKK2 inhibition improved kidney function, lymphocyte-specific deletion of IKK2 or NEMO aggravated kidney injury after IRI, and, in both conditions, the percentage of Th17 cells was increased. Our findings demonstrate the critical role of the NF-κB pathway in Th17 activation, which advises caution when using systemic IKK2 inhibitors in patients with kidney injury, since they might impair the T cell response and aggravate renal disease.

Phospholipase A2 receptor autoantibodies and clinical outcome in patients with primary membranous nephropathy.

Membranous nephropathy (MN) is the most common cause of nephrotic syndrome in adults, with an uncertain clinical outcome. The characterization of the phospholipase A2 receptor (PLA2R) as the major target antigen in primary MN and the detection of circulating autoantibodies in these patients is a major advance in understanding this disease. To test whether PLA2R antibody levels reflect disease activity or clinical outcome, we performed a prospective multicenter study of 133 adult patients with primary MN and detectable serum PLA2R antibodies who had not received immunosuppressive therapy. Patients were followed ≤24 months. PLA2R antibody levels associated with clinical disease activity (proteinuria) in patients with immunosuppressive therapy (n=101) or supportive care (n=32). Within 3 months, immunosuppressive therapy led to a sustained 81% reduction in PLA2R antibody levels paralleled by a 39% reduction in proteinuria. Patients who experienced remission of proteinuria after 12 months had significantly lower PLA2R antibody levels at the time of study inclusion compared with patients with no remission. Patients with high PLA2R antibody levels achieved remission of proteinuria significantly later than patients with low PLA2R antibody levels. PLA2R antibody levels fell over time in patients with spontaneous remission but remained elevated in patients who did not show a reduction in proteinuria. Multivariable Cox regression analysis confirmed PLA2R antibody level as an independent risk factor for not achieving remission of proteinuria. We conclude that a decrease in PLA2R antibody level is associated with a decrease of proteinuria in patients with primary MN.

Leukocyte-derived MMP9 is crucial for the recruitment of proinflammatory macrophages in experimental glomerulonephritis.

Matrix metalloproteinase 9 (MMP9) is a conditionally expressed enzyme and is upregulated in glomerulonephritis. Its function in these diseases, however, remains to be fully elucidated. The induction of nephrotoxic serum nephritis (NTN) in wild-type mice resulted in an upregulation of MMP9, followed by leukocyte infiltration, albuminuria, and subsequent renal failure. MMP9 deficiency ameliorated the course of NTN as indicated by reduced histological injury and reduced infiltration of proinflammatory macrophages. The chemotaxis of MMP9-deficient macrophages in vitro was impaired. Intrarenal macrophages isolated from the kidneys of nephritic MMP9 knockout mice still displayed the typical features of a proinflammatory phenotype and were indistinguishable from wild type-derived cells. Bone marrow transplantation restored renal tissue injury and macrophage recruitment when wild type-derived donor cells were transplanted onto MMP9-deficient mice prior to the induction of NTN. Thus, leukocyte-derived MMP9 mediates the recruitment of proinflammatory macrophages into kidneys during experimental crescentic glomerulonephritis.

Non-functional ubiquitin C-terminal hydrolase L1 drives podocyte injury through impairing proteasomes in autoimmune glomerulonephritis.

Little is known about the mechanistic significance of the ubiquitin proteasome system (UPS) in a kidney autoimmune environment. In membranous nephropathy (MN), autoantibodies target podocytes of the glomerular filter resulting in proteinuria. Converging biochemical, structural, mouse pathomechanistic, and clinical information we report that the deubiquitinase Ubiquitin C-terminal hydrolase L1 (UCH-L1) is induced by oxidative stress in podocytes and is directly involved in proteasome substrate accumulation. Mechanistically, this toxic gain-of-function is mediated by non-functional UCH-L1, which interacts with and thereby impairs proteasomes. In experimental MN, UCH-L1 becomes non-functional and MN patients with poor outcome exhibit autoantibodies with preferential reactivity to non-functional UCH-L1. Podocyte-specific deletion of UCH-L1 protects from experimental MN, whereas overexpression of non-functional UCH-L1 impairs podocyte proteostasis and drives injury in mice. In conclusion, the UPS is pathomechanistically linked to podocyte disease by aberrant proteasomal interactions of non-functional UCH-L1.

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.

Enhanced expression of the M-type phospholipase A2 receptor in glomeruli correlates with serum receptor antibodies in primary membranous nephropathy.

The M-type phospholipase A2 receptor (PLA2R) is the major target antigen in idiopathic membranous nephropathy with detectable autoantibodies in the serum of up to 70% of patients. In retrospective studies, the PLA2R-autoantibody titer in the serum was sometimes negative indicating their measurement alone may be inconclusive. In order to better differentiate between primary and secondary membranous nephropathy, we conducted a prospective study that included 88 patients with a histologic diagnosis of membranous nephropathy. Immunohistochemical analysis for PLA2R was faintly positive in kidneys from normal individuals and patients with various other glomerular injuries. In 61 of the 88 patients, PLA2R expression was strongly positive in glomeruli, and in 60 of these patients PLA2R autoantibodies were also detected in the serum. The 27 patients negative for serum PLA2R autoantibodies were faintly positive for PLA2R staining in glomeruli and in 15 of these patients a secondary cause was found. The remaining 12 patients have a yet undetected secondary cause of membranous nephropathy or have different glomerular antigens other than PLA2R. Thus, increased staining for PLA2R in glomeruli of renal biopsies tightly correlates with the presence of PLA2R autoantibodies in the serum and this may help discriminate between primary and secondary membranous nephropathy.