Target antigens and nephritogenic antibodies in membranous nephropathy: of rats and men

Determination of Anti-Phospholipase A2 and Anti-Thrombospondin Type 1 Domain-Containing Protein 7A in Latin Patients with Membranous Nephropathy

Primary membranous nephropathy (MN) is caused by antibodies against podocyte antigens, especially the type M receptor of phospholipase A2 (PLA2R) and thrombospondin type-1 domain containing 7 A (THSD7A). This study's aim was the determination of anti-PLA2R, anti-THSD7A serum antibodies, and anti-PLA2R renal tissue staining prevalence in a Latin population with MN, as well as evaluating their role as biomarkers for disease activity. The performance of the two anti-PLA2R serum diagnostic methods-ELISA and indirect immunofluorescence (IFI)-was evaluated for the diagnosis of MN. Fifty-nine patients, including 29 with MN, 18 with lupus membranous nephropathy (LMN) and 12 with focal and segmental glomerulosclerosis (FSGS), were evaluated for serum antibodies. Renal biopsies were also evaluated for the presence of anti-PLA2R staining. Twenty-one patients with MN were followed for 1 year. Patients with LMN and FSGS were negative for both antibodies. All 29 MN patients were negative for anti-THSD7A; 16 MN patients were positive for anti-PLA2R by ELISA and/or IFI, and 3 MN patients were positive for anti-PLA2R only by IFI. Thus, the anti-PLA2R ELISA test demonstrated 45% sensitivity and 97% specificity, while the IFI test showed, respectively, 55% and 100% in our MN patients. Among the 28 MN renal biopsies, 20 presented anti-PLA2R positive staining, corresponding to a 72% sensitivity. Positive correlations were observed between the anti-PLA2R ELISA titer and proteinuria. In conclusion, determination of anti-PLA2R antibodies in the MN Latin population showed similar rates to those reported for other populations. The anti-PLA2R serum levels correlated with MN disease activity.

Transforming Growth Factor Beta Receptor 3 (TGFBR3)-Associated Membranous Nephropathy

Background

Membranous lupus nephritis (MLN) comprises 10%-15% of lupus nephritis and increases morbidity and mortality of patients with SLE through complications of nephrotic syndrome and chronic kidney failure. Identification of the target antigens in MLN may enable noninvasive monitoring of disease activity, inform treatment decisions, and aid in prognostication, as is now possible for idiopathic MN caused by antibodies against the phospholipase A2 receptor. Here, we show evidence for type III TGF-β receptor (TGFBR3) as a novel biomarker expressed in a subset of patients with MLN.

Methods

Mass spectrometry was used for protein discovery through enrichment of glomerular proteins by laser capture microdissection and through elution of immune complexes within MLN biopsy specimens. Colocalization with IgG within glomerular immune deposits from patients and disease controls was evaluated by confocal microscopy. Immunostaining of consecutive case series was used to determine the overall frequency in MN and MLN.

Results

TGFBR3 was found to be enriched in glomeruli and coimmunoprecipitated with IgG within a subset of MLN biopsy specimens by mass spectrometry. Staining of consecutive MN cases without clinical evidence of SLE did not show TGFBR3 expression (zero of 104), but showed a 6% prevalence in MLN (11 of 199 cases). TGFBR3 colocalized with IgG along the glomerular basement membranes in TGFBR3-associated MN, but not in controls.

Conclusions

Positive staining for TGFBR3 within glomerular immune deposits represents a distinct form of MN, substantially enriched in MLN. A diagnosis of TGFBR3-associated MN can alert the clinician to search for an underlying autoimmune disease.

Role of Podocyte Injury in Glomerulosclerosis

Finding new therapeutic targets of glomerulosclerosis treatment is an ongoing quest. Due to a living environment of various stresses and pathological stimuli, podocytes are prone to injuries; moreover, as a cell without proliferative potential, loss of podocytes is vital in the pathogenesis of glomerulosclerosis. Thus, sufficient understanding of factors and underlying mechanisms of podocyte injury facilitates the advancement of treating and prevention of glomerulosclerosis. The clinical symptom of podocyte injury is proteinuria, sometimes with loss of kidney functions progressing to glomerulosclerosis. Injury-induced changes in podocyte physiology and function are actually not a simple passive process, but a complex interaction of proteins that comprise the anatomical structure of podocytes at molecular levels. This chapter lists several aspects of podocyte injuries along with potential mechanisms, including glucose and lipid metabolism disorder, hypertension, RAS activation, micro-inflammation, immune disorder, and other factors. These aspects are not technically separated items, but intertwined with each other in the pathogenesis of podocyte injuries.

[Idiopathic membranous nephropathy: Evolution in understanding the problem]

The review highlights the evolution of ideas on the. mechanisms responsible for the 'development of membranous nephropathy(MN), glomerulopathy that is the most common cause of nephrotic syndrome in adults. Primary emphasis is placed on the primary form of MN. The important step to understanding the nature of this clinical and morphological form of glomerulonephritis is to create its animal model (Heymann nephritis), then to decipher the mechanisms of immune complex damage (complement activation,a role of cellular immunity), and to identify autoantigens responsible for the development of idiopathic MN in man (podocyteneutral endopeptidase, transmembrane M-type phospholipase A2 receptor, thrombospondin type-1 domain-containing 7A. The findings constituted the basis for developing current methods for the diagnosis and treatment of MN, including the pathogenetically sound inhibition of autoantibody production, as well as a molecular orientation effect on podocyte dysfunction.

Anti-Phospholipase A2 Receptor Autoantibody: A New Biomarker for Primary Membranous Nephropathy

Primary membranous nephropathy (also known as idiopathic membranous nephropathy, IMN) is an organ specific autoimmune kidney disease characterized by the development of immune complex deposits in the sub-epithelial spaces, podocyte effacement and glomerular capillary wall thickening in the later stages. Clinical studies have demonstrated that over 70% of patients with IMN possess circulating autoimmune antibodies specifically targeting the phospholipase A₂ receptor (PLA₂R) on the surface of podocytes. The autoantibodies only bind to the extracellular portion of PLA₂R under the non-reducing condition, indicating that the epitope in PLA₂R is conformational requiring specific disulfide bonds to maintain its structure. We recently have successfully located the dominant epitope in PLA₂R to the extreme N-terminus of the receptor. This finding has opened a new direction for understanding the pathogenesis of anti-PLA₂R autoantibody induced IMN and offered a strong basis for developing sensitive clinical assays for IMN diagnosis and prognosis, and potentially, new therapeutic approaches for IMN treatment.

Identification of the immunodominant epitope region in phospholipase A2 receptor-mediating autoantibody binding in idiopathic membranous nephropathy

Membranous nephropathy (MN) is a common cause of nephrotic syndrome in adults. Recent clinical studies established that >70% of patients with idiopathic (also called primary) MN (IMN) possess circulating autoantibodies targeting the M-type phospholipase A2 receptor-1 (PLA2R) on the surface of glomerular visceral epithelial cells (podocytes). In situ, these autoantibodies trigger the formation of immune complexes, which are hypothesized to cause enhanced glomerular permeability to plasma proteins. Indeed, the level of autoantibody in circulation correlates with the severity of proteinuria in patients. The autoantibody only recognizes the nonreduced form of PLA2R, suggesting that disulfide bonds determine the antigenic epitope conformation. Here, we identified the immunodominant epitope region in PLA2R by probing isolated truncated PLA2R extracellular domains with sera from patients with IMN that contain anti-PLA2R autoantibodies. Patient sera specifically recognized a protein complex consisting of the cysteine-rich (CysR), fibronectin-like type II (FnII), and C-type lectin-like domain 1 (CTLD1) domains of PLA2R only under nonreducing conditions. Moreover, absence of either the CysR or CTLD1 domain prevented autoantibody recognition of the remaining domains. Additional analysis suggested that this three-domain complex contains at least one disulfide bond required for conformational configuration and autoantibody binding. Notably, the three-domain complex completely blocked the reactivity of autoantibodies from patient sera with the full-length PLA2R, and the reactivity of patient sera with the three-domain complex on immunoblots equaled the reactivity with full-length PLA2R. These results indicate that the immunodominant epitope in PLA2R is exclusively located in the CysR-FnII-CTLD1 region.

Membranous nephropathy: not just a disease for adults

Membranous nephropathy (MN) is an immune complex-mediated cause of the nephrotic syndrome that can occur in all age groups, from infants to the elderly. While systemic disorders such as hepatitis B infection or lupus may more frequently cause secondary MN in the younger population, primary or "idiopathic" MN has generally been considered a disease of adults. Recent progress in our understanding of primary disease was recently made when the target antigen in primary MN was identified as the M-type phospholipase A2 receptor (PLA2R). Circulating anti-PLA2R antibodies may serve both as a diagnostic tool for distinguishing primary from secondary disease and as a biomarker for monitoring the immunologic activity of this organ-specific autoimmune disease during treatment. Whereas definitive therapy for secondary forms of MN should be targeted at the underlying cause, immunosuppressive therapy is often necessary for primary disease. Alkylating agents in combination with corticosteroids, as well as calcineurin inhibitors (± steroids), are first line agents due to randomized controlled trials in an adult population with relatively long durations of follow-up. However, rituximab, mycophenolate and adrenocorticotropic hormone have shown promise in smaller and/or observational studies. The optimal therapy for children and adolescents with MN is less well defined.

2DE maps in the discovery of human autoimmune kidney diseases: the case of membranous glomerulonephritis

The identification of antigens in the autoimmune diseases is a primary point to elucidate the pathogenesis of disease. Here, we propose an "in vivo" proteomics approach to identify the antigens of auto-antibodies in membranous glomerulonephritis. In this approach, podocyte proteins resolved by two-dimensional electrophoresis were semidry blotted to nitrocellulose membrane. Then the antibodies eluted from microdissected glomeruli and serum samples were used as a probe for the detection of podocyte antigens and characterized by means of mass spectrometry. These combined methods allowed us to identify six new antigens in membranous glomerulonephritis.

The Effects of Helicobacter pylori Eradication on Proteinuria in Patients with Primary Glomerulonephritis

Background. Membranous nephropathy (MN) is a common cause of nephrotic syndrome. In most cases it is idiopathic, while it may also be secondary to many diseases. In this study, prevalence of H. pylori infection and the effects of H. pylori eradication on proteinuria levels were investigated. Methods. Thirty five patients with MN (19 male), 12 patients with IgA nephropathy (4 male) and 12 patients with focal segmental glomerulosclerosis (FSGS) (8 male) were studied. The presence of H. pylori antigen was investigated in renal tissues obtained by biopsy, and the effects of H. pylori eradication on proteinuria levels were investigated. Results. Immunohistochemistry with H. pylori antigen revealed no positive staining in the glomeruli of all patients. 19 patients (54%) with MN, 10 (83%) with IgA nephropathy and 4 (33%) with FSGS were positive for H. pylori stool antigen test (P = 0.045). Patients with H. pylori infection were administered eradication therapy (lansoprazole, 30 mg twice daily, plus amoxicillin, 0.75 g twice daily, plus clarithromycin, 250 mg twice daily, for 14 days). Before the eradication therapy the mean proteinuria of patients with MN, IgA nephropathy and FSGS were 2.42 ± 3.24 g/day, 2.12 ± 1.63 g/day and 1.80 ± 1.32 g/day, respectively. Three months after eradication, baseline proteinuria levels of patients with MN significantly decreased to 1.26 ± 1.73 g/day (P = 0.031). In all three groups there were no significant differences with regard to serum creatinine, albumin and C-reactive protein levels before and after eradication therapy. Conclusions. The eradication of H. pylori infection may be effective to reduce proteinuria in patients with MN, while spontaneous remission of MN could not be excluded in this patient cohort. This trial is registered with NCT00983034.

Detection of anti-PLA2R autoantibodies and IgG subclasses in post-allogeneic hematopoietic stem cell transplantation membranous nephropathy

BACKGROUND

Membranous nephropathy (MN) is the most common glomerular disease of post-allogeneic hematopoietic stem cell transplantation (HSCT). Although this condition is now considered a renal complication of chronic graft-versus-host disease (cGVHD), the pathogenesis of this disease is not well established.

METHODS

Five patients with post-HSCT MN diagnosed by renal biopsy were selected for this study. The clinical and renal pathological data of these patients were analyzed, and anti-PLA2R (M-type phospholipase A2 receptor) autoantibodies and IgG subclasses were detected in the serum samples from the patients.

RESULTS

None of the 5 patients had a history of kidney disease. All the patients had a combination of cGVHD and proteinuria, which was in remission after an effective anti-graft-versus-host disease treatment. The immunofluorescent detection showed that IgG4 was the predominant IgG subclass, and the distribution of IgG4 was the same as that of nephrin. The anti-PLA2R autoantibodies were negative in 4 patients and positive in 1 patient. The levels of IgG2, IgG3 and IgG4 increased in the majority of the patients.

CONCLUSIONS

Our data showed that the clinical course of post-HSCT MN patients was closely related to that of cGVHD. Although the renal pathology was similar to idiopathic MN, the negative result for the anti-PLA2R autoantibodies in the majority of the patients suggested that the formation of an immune complex occurs differently between these 2 diseases.

Upregulation of c-mip is closely related to podocyte dysfunction in membranous nephropathy

Membranous nephropathy is a glomerular disease typified by a nephrotic syndrome without infiltration of inflammatory cells or proliferation of resident cells. Although the cause of the disease is unknown, the primary pathology involves the generation of autoantibodies against antigen targets on the surface of podocytes. The mechanisms of nephrotic proteinuria, which reflect a profound podocyte dysfunction, remain unclear. We previously found a new gene, c-mip (c-maf-inducing protein), that was associated with the pathophysiology of idiopathic nephrotic syndrome. Here we found that c-mip was not detected in the glomeruli of rats with passive-type Heymann nephritis given a single dose of anti-megalin polyclonal antibody, yet immune complexes were readily present, but without triggering of proteinuria. Rats reinjected with anti-megalin develop heavy proteinuria a few days later, concomitant with c-mip overproduction in podocytes. This overexpression was associated with the downregulation of synaptopodin in patients with membranous nephropathy, rats with passive Heymann nephritis, and c-mip transgenic mice, while the abundance of death-associated protein kinase and integrin-linked kinase was increased. Cyclosporine treatment significantly reduced proteinuria in rats with passive Heymann nephritis, concomitant with downregulation of c-mip in podocytes. Thus, c-mip has an active role in the podocyte disorders of membranous nephropathy.

Anti-neutral endopeptidase, natriuretic peptides disarrangement, and proteinuria onset in membranous nephropathy

Neutral endopeptidase (NEP) is the first podocytic antigen responsible for human membranous nephropathy (MN). Besides the prevailing pathogenetic mechanism of immune complex, NEP is also involved in the metabolism of natriuretic peptides (NP). The identification of anti-NEP antibodies in human MN suggests that the decreased circulating NEP may down-regulate the NP catabolism. In this context, we hypothesize that NP disarrangement secondary to anti-NEP antibodies may account, in part, for the onset of proteinuria in MN. Whereas the pathways for the onset of proteinuria caused by elevated NP level are still obscure. The data presented in this review focus on those which support this hypothesis with regards to evidence from the glomerular haemodynamic changes, endothelial permeability, glomerular basement membrane disruption, and podocyte detachment.

An overview of molecular mechanism of nephrotic syndrome

Podocytopathies (minimal change disease (MCD) and focal segmental glomerulosclerosis (FSGS)) together with membranous nephropathy are the main causes of nephrotic syndrome. Some changes on the expression of nephrin, podocin, TGF-β, and slit diaphragm components as well as transcription factors and transmembrane proteins have been demonstrated in podocytopathies. Considering the pathogenesis of proteinuria, some elucidations have been directed towards the involvement of epithelial-mesenchymal transition. Moreover, the usefulness of some markers such as TGF-β1, nephrin, synaptopodin, dystroglycans, and malondialdehyde have been determined in the differentiation between MCD and FSGS. Experimental models and human samples indicated an essential role of autoantibodies in membranous glomerulonephritis, kidney damage, and proteinuria events. Megalin and phospholipase-A2-receptor have been described as antigens responsible for the formation of the subepithelial immune complexes and renal disease occurrence. In addition, the complement system seems to play a key role in basal membrane damage and in the development of proteinuria in membranous nephropathy. This paper focuses on the common molecular changes involved in the development of nephrotic proteinuria.

Basic and translational concepts of immune-mediated glomerular diseases

Genetically modified immune responses to infections and self-antigens initiate most forms of GN by generating pathogen- and danger-associated molecular patterns that stimulate Toll-like receptors and complement. These innate immune responses activate circulating monocytes and resident glomerular cells to release inflammatory mediators and initiate adaptive, antigen-specific immune responses that collectively damage glomerular structures. CD4 T cells are needed for B cell-driven antibody production that leads to immune complex formation in glomeruli, complement activation, and injury induced by both circulating inflammatory and resident glomerular effector cells. Th17 cells can also induce glomerular injury directly. In this review, information derived from studies in vitro, well characterized experimental models, and humans summarize and update likely pathogenic mechanisms involved in human diseases presenting as nephritis (postinfectious GN, IgA nephropathy, antiglomerular basement membrane and antineutrophil cytoplasmic antibody-mediated crescentic GN, lupus nephritis, type I membranoproliferative GN), and nephrotic syndrome (minimal change/FSGS, membranous nephropathy, and C3 glomerulopathies). Advances in understanding the immunopathogenesis of each of these entities offer many opportunities for future therapeutic interventions.

Novel targets for immunotherapy in glomerulonephritis

Glomerulonephritis is a common cause of chronic kidney disease and end stage renal failure. Current therapy relies on variably effective, nonspecific and toxic immunosuppression. Recent insights into underlying biology and disease pathogenesis in human glomerulonephritis combined with advances in the fields of inflammation and autoimmunity promise a cadre of novel targeted interventions. This review highlights the therapeutic potential of two antigens, alpha3 (IV)NC1 collagen and podocyte neutral endopeptidase, and two cell signaling and effector molecules, IgG Fc receptors and complement, judged to be particularly amenable to therapeutic manipulation in man. It is anticipated that continued dissection of pathogenesis in the diverse disorders that comprise the glomerulonephritides will provide the basis for individualized disease-specific therapy.

Induction of podocyte-derived VEGF ameliorates podocyte injury and subsequent abnormal glomerular development caused by puromycin aminonucleoside

Our previous studies using puromycin aminonucleoside (PAN) established that podocyte damage leads to glomerular growth arrest during development and glomerulosclerosis later in life. This study examined the potential benefit of maintaining podocyte-derived VEGF in podocyte defense and survival after PAN injury using conditional transgenic podocytes and mice, in which human VEGF-A (hVEGF) transgene expression is controlled by tetracycline responsive element (TRE) promoter and reverse tetracycline transactivator (rtTA) in podocytes. In vitro experiments used primary cultured podocytes harvested from mice carrying podocin-rtTA and TRE-hVEGF transgenes, in which hVEGF can be induced selectively. Induction of VEGF in PAN-exposed podocytes resulted in preservation of intrinsic VEGF, α-actinin-4 and synaptopodin, antiapoptotic marker Bcl-xL/Bax, as well as attenuation in apoptotic marker cleaved/total caspase-3. In vivo, compared with genotype controls, PAN-sensitive neonatal mice with physiologically relevant levels of podocyte-derived VEGF showed significantly larger glomeruli. Furthermore, PAN-induced up-regulation of desmin, down-regulation of synaptopodin and nephrin, and disruption of glomerular morphology were significantly attenuated in VEGF-induced transgenic mice. Our data indicate that podocyte-derived VEGF provides self-preservation functions, which can rescue the cell after injury and preempt subsequent deterioration of the glomerulus in developing mice.

Anti-phospholipase A2 receptor antibody in membranous nephropathy

The M-type phospholipase A2 receptor (PLA2R) is a target autoantigen in adult idiopathic membranous nephropathy (MN), but the prevalence of autoantibodies against PLA2R is unknown among Chinese patients with MN. Here, we measured anti-PLA2R antibody in the serum of 60 patients with idiopathic MN, 20 with lupus-associated MN, 16 with hepatitis B (HBV)-associated MN, and 10 with tumor-associated MN. Among patients with idiopathic MN, 49 (82%) had detectable anti-PLA2R autoantibodies using a Western blot assay; an assay with greater sensitivity detected very low titers of anti-PLA2R in 10 of the remaining 11 patients. Using the standard assay, we detected anti-PLA2R antibody in only 1 patient with lupus, 1 with HBV, and 3 with cancer, producing an overall specificity of 89% in this cohort limited to patients with secondary MN. The enhanced assay detected low titers of anti-PLA2R in only 2 additional samples of HBV-associated MN. In summary, these results suggest that PLA2R is a major target antigen in Chinese idiopathic MN and that detection of anti-PLA2R is a sensitive test for idiopathic MN.

Immunohistochemical evaluation of podocalyxin expression in glomerulopathies associated with nephrotic syndrome

It is now well established that morphological change of podocytes is closely correlated to the development of proteinuria. The aim of this study was to investigate the role of podocalyxin, a major podocyte protein, in the pathogenesis of glomerulopathies primarily associated with the nephrotic syndrome. Immunohistochemical expression of podocalyxin has been evaluated in 51 renal samples, including healthy controls, patients with podocytopathies (minimal change disease [MCD], focal segmental glomerulosclerosis [FSGS]) and membranous glomerulopathy (MG). A computerized image analysis program has been used. Statistical analysis was performed using analysis of variance and Bonferroni tests. Immunohistochemical expression of podocalyxin has been observed within the podocytes of healthy controls. In MCD, podocalyxin expression was globally reduced despite the normal appearance of the glomeruli. In FSGS, podocalyxin loss was observed in both the segmental sclerotic and the nonsclerotic areas being significantly more prominent in the former. Reduction of podocalyxin in MG was demonstrated for the first time immunohistochemically. The percentage of the stained area was statistical significantly higher in the controls than in each pathologic group. However, among pathologic groups (FSGS, MCD, MG), there was no statistically significant difference. This is one of the few studies investigating podocalyxin immunohistochemical expression in glomerulopathies associated with nephrotic syndrome. The observed reduction in podocalyxin expression suggests that it constitutes a target molecule in nephrotic syndrome pathogenesis regardless of the underlying cause.

Membranous nephropathy: recent travels and new roads ahead

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.

Autoimmunity in membranous nephropathy targets aldose reductase and SOD2

Glomerular targets of autoimmunity in human membranous nephropathy are poorly understood. Here, we used a combined proteomic approach to identify specific antibodies against podocyte proteins in both serum and glomeruli of patients with membranous nephropathy (MN). We detected specific anti-aldose reductase (AR) and anti-manganese superoxide dismutase (SOD2) IgG(4) in sera of patients with MN. We also eluted high titers of anti-AR and anti-SOD2 IgG(4) from microdissected glomeruli of three biopsies of MN kidneys but not from biopsies of other glomerulonephritides characterized by IgG deposition (five lupus nephritis and two membranoproliferative glomerulonephritis). We identified both antigens in MN biopsies but not in other renal pathologies or normal kidney. Confocal and immunoelectron microscopy (IEM) showed co-localization of anti-AR and anti-SOD2 with IgG(4) and C5b-9 in electron-dense podocyte immune deposits. Preliminary in vitro experiments showed an increase of SOD2 expression on podocyte plasma membrane after treatment with hydrogen peroxide. In conclusion, our data support AR and SOD2 as renal antigens of human MN and suggest that oxidative stress may drive glomerular SOD2 expression.

Controversies in the treatment of idiopathic membranous nephropathy

Optimum treatment of idiopathic membranous nephropathy is both controversial and challenging. The most extensively studied and frequently used immunosuppressive regimens for this disease comprise alkylating agents plus corticosteroids or ciclosporin. All of these treatment options have inherent problems: they are not effective in all patients, partial-rather than complete-remissions are common, adverse effects are worrisome, and relapses after treatment cessation remain problematic. Alternative immunosuppressive agents have been tested in an effort to overcome these unresolved issues. This paper reviews the available evidence regarding both established and new agents for the treatment of patients with idiopathic membranous nephropathy, with an emphasis on the results of the most recent clinical trials.

Inducible rodent models of acquired podocyte diseases

Glomerular diseases remain the leading cause of chronic and end-stage kidney disease. Significant advances in our understanding of human glomerular diseases have been enabled by the development and better characterization of animal models. Diseases of the glomerular epithelial cells (podocytes) account for the majority of proteinuric diseases. Rodents have been extensively used experimentally to better define mechanisms of disease induction and progression, as well as to identify potential targets and therapies. The development of podocyte-specific genetically modified mice has energized the research field to better understand which animal models are appropriate to study acquired podocyte diseases. In this review we discuss inducible experimental models of acquired nondiabetic podocyte diseases in rodents, namely, passive Heymann nephritis, puromycin aminonucleoside nephrosis, adriamycin nephrosis, liopolysaccharide, crescentic glomerulonephritis, and protein overload nephropathy models. Details are given on the model backgrounds, how to induce each model, the interpretations of the data, and the benefits and shortcomings of each. Genetic rodent models of podocyte injury are excluded.

Pathophysiological lessons from rare associations of immunological disorders

Rare associations of immunological disorders can often tell more than mice and rats about the pathogenesis of immunologically mediated human kidney disease. Cases of glomerular disease with thyroiditis and Graves' disease and of minimal change disease with lymphoepithelioma-like thymic carcinoma and lymphomatoid papulosis were recently reported in Pediatric Nephrology. These rare associations can contribute to the unraveling of the pathogenesis of membranous nephropathy (MN) and minimal change disease (MCD) and lead to the testing of novel research hypotheses. In MN, the target antigen may be thyroglobulin or another thyroid-released antigen that becomes planted in the glomerulus, but other scenarios can be envisaged, including epitope spreading, polyreactivity of pathogenic antibodies, and dysregulation of T regulatory cells, leading to the production of a variety of auto-antibodies with different specificities [immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX syndrome)]. The occurrence of MCD with hemopathies supports the role of T cells in the pathogenesis of proteinuria, although the characteristics of those T cells remain to be established and the glomerular permeability factor(s) identified.