Membranous nephropathy: recent travels and new roads ahead. Kidney Int. 2010;77:765-770. [PMID: 20182413 DOI: 10.1038/ki.2010.34]

Retinoids augment the expression of podocyte proteins by glomerular parietal epithelial cells in experimental glomerular disease

BACKGROUND/AIMS

A decrease in glomerular podocyte number in membranous nephropathy and focal segmental glomerulosclerosis (FSGS) ultimately underlines glomerulosclerosis and the decrease in kidney function. Recent studies have shown that in these diseases, glomerular parietal epithelial cells begin to express proteins considered unique to podocytes, and that these glomerular epithelial transition cells might serve as podocyte progenitors. Because retinoids improve many forms of experimental glomerular disease characterized by podocyte injury and loss, we asked if all-trans retinoic acid (ATRA) induces parietal epithelial cells to express podocyte proteins.

METHODS

ATRA or vehicle was administered to rats with experimental membranous nephropathy (passive Heymann nephritis model) and mice with experimental FSGS (anti-glomerular antibody model) following the onset of proteinuria. Immunohistochemistry staining of PAX2 (parietal epithelial cell marker), WT-1 (podocyte cell marker), and Ki-67 (proliferation marker) were performed on kidney tissues.

RESULTS

Compared to diseased animals receiving vehicle, ATRA statistically significantly increased the number of glomerular transition cells, defined as cells double-staining for PAX2 and WT-1, in membranous nephropathy at weeks 2, 5 and 16, and in FSGS at weeks 1 and 2. This was accompanied by an increase in the number of podocytes compared to diseased controls receiving vehicle.

CONCLUSION

ATRA increases the number of glomerular epithelial transition cells in experimental proteinuric glomerular diseases. Thus, ATRA may provide a useful pharmacologic approach to decipher the mechanisms underlying the possible progenitor role of parietal epithelial cells.

Treatment of idiopathic membranous nephropathy

Exciting progress recently has been made in our understanding of idiopathic membranous nephropathy, as well as treatment of this disease. Here, we review important advances regarding the pathogenesis of membranous nephropathy. We will also review the current approach to treatment and its limitations and will highlight new therapies that are currently being explored for this disease including Rituximab, mycophenolate mofetil, and adrenocorticotropic hormone, with an emphasis on results of the most recent clinical trials.

Glomerular disease: Predicting outcomes in idiopathic membranous nephropathy

Several immunosuppressive treatments have demonstrated their efficacy in idiopathic membranous nephropathy, but spontaneous remission does develop in more than 30% of patients. The availability of a validated biomarker that is easy to measure and able to accurately predict long-term outcomes would be very helpful for tailoring treatment of the disease to the individual.

IgG4-Related Disease Is Not Associated with Antibody to the Phospholipase A2 Receptor

Patients with IgG4-related disease (IgG4-RD) share histopathological characteristics that are similar across affected organs. The finding of infiltration with IgG4+ plasma cells in the proper clinical and histopathological contexts connects a large number of clinical entities that were viewed previously as separate conditions. The renal involvement in IgG4-RD is usually characterized by tubulointerstitial nephritis, but membranous nephropathy has also been reported to be one of the renal complications of IgG4-RD. The recent discovery that a high proportion of patients with idiopathic membranous nephropathy (IMN) have IgG4 autoantibodies to the M-type phospholipase A2 receptor (PLA2R) in the circulation and glomerular immune deposits, together with the profound IgG4 hypergammaglobulinemia and occasional reports of membranous nephropathy in IgG4-RD, raised the question of a common antigen. To assess the presence of anti-PLA2R antibody in patients with IgG4-RD, we screened sera from 28 IgG4-RD patients by immunoblot. None of the patients in this cohort had detectable circulating anti-PLA2R antibodies. This study suggests that despite some clinical and serological overlaps between IgG4-RD and IMN,anti-PLA2R antibodies do not play a role in the pathogenesis of IgG4-RD. Additional studies of IgG4-RD with evidence of membranous nephropathy are important to exclude any definite relationship.

Patterns of IgG subclass deposits in membranous glomerulonephritis in renal allografts

BACKGROUND

Membranous glomerulonephritis (MGN) may develop in the renal allograft either de novo or as a recurrence. These 2 forms of MGN may have different pathogenic mechanisms, with different IgG subclass profiles in the immune deposits. This study examined IgG subclass distributions in recurrent and de novo MGN in allograft kidneys.

METHODS

We identified allograft kidneys with MGN, including 7 with recurrent MGN, 2 with de novo MGN, and 2 atypical/indeterminate, and determined the relative intensity of IgG1, IgG2, IgG3, and IgG4 staining in capillary wall deposits by immunofluorescence microscopy.

RESULTS

IgG4 was the dominant or codominant IgG subclass in capillary loop deposits in all 7 cases of recurrent MGN. IgG1 staining was dominant in 3 of 4 de novo or atypical MGN cases and codominant with IgG4 in the fourth.

CONCLUSIONS

Although pretransplantation kidney biopsies were not available for comparisons, these findings suggest that all allograft recurrences represent idiopathic MGN and that de novo MGN cases had a different pathogenic mechanism.

Coexistence of ANCA-associated glomerulonephritis and anti-phospholipase A(2) receptor antibody-positive membranous nephropathy

Antibodies to myeloperoxidase (MPO) and proteinase 3 (PR3) have been demonstrated to mediate anti-neutrophil cytoplasmic antibody (ANCA)-associated disease. For membranous nephropathy, antibodies to the podocyte-expressed phospholipase A₂ receptor (anti-PLA₂R) are highly associated with disease activity and have been reported in at least 70% of patients with idiopathic membranous nephropathy (IMN). We present a case of a 56-year-old male with a 1 year history of hypertension, leg edema, and proteinuria, who presented with advanced renal failure and was found to have both ANCA-associated glomerulonephritis (GN) and IMN on kidney biopsy. Consistent with the idea that this is due to the chance occurrence of two independent diseases, we found both anti-MPO and anti-PLA₂R antibodies in the patient's sera. Treatment with methylprednisolone, plasmapheresis, and cyclophosphamide resulted in improvement in kidney function and proteinuria, together with the simultaneous decrease in both autoantibodies. This is the first demonstration of two pathogenic antibodies giving rise to ANCA-associated GN and IMN in the same patient. It confirms the importance of classifying disease based upon the underlying mechanism, in addition to renal histopathology, to both optimize therapy and predict prognosis.

Coexistence of ANCA-associated glomerulonephritis and anti-phospholipase A(2) receptor antibody-positive membranous nephropathy

Antibodies to myeloperoxidase (MPO) and proteinase 3 (PR3) have been demonstrated to mediate anti-neutrophil cytoplasmic antibody (ANCA)-associated disease. For membranous nephropathy, antibodies to the podocyte-expressed phospholipase A(2) receptor (anti-PLA(2)R) are highly associated with disease activity and have been reported in at least 70% of patients with idiopathic membranous nephropathy (IMN). We present a case of a 56-year-old male with a 1 year history of hypertension, leg edema, and proteinuria, who presented with advanced renal failure and was found to have both ANCA-associated glomerulonephritis (GN) and IMN on kidney biopsy. Consistent with the idea that this is due to the chance occurrence of two independent diseases, we found both anti-MPO and anti-PLA(2)R antibodies in the patient's sera. Treatment with methylprednisolone, plasmapheresis, and cyclophosphamide resulted in improvement in kidney function and proteinuria, together with the simultaneous decrease in both autoantibodies. This is the first demonstration of two pathogenic antibodies giving rise to ANCA-associated GN and IMN in the same patient. It confirms the importance of classifying disease based upon the underlying mechanism, in addition to renal histopathology, to both optimize therapy and predict prognosis.

Recent advances and prognosis in idiopathic membranous nephropathy

Idiopathic membranous nephropathy (MN) is one of the most common causes of nephrotic syndrome. Recently, progress has been made in understanding the pathogenesis of idiopathic MN with the finding of M-type phospholipase A2 receptor (PLA2R) antibodies in the serum and immune complexes of glomeruli in the majority of adult idiopathic MN patients. In the future, the detection of M-type PLA2R antibodies may help distinguish patients with primary MN who require aggressive immunosuppressive therapy from those with secondary disease. Levels of circulating antibody to this receptor may help in monitoring disease activity and in gauging response to therapy, as changes in antibody levels may precede changes in proteinuria. The degree of renal dysfunction or change in renal function over time and the level of persistent proteinuria are key prognostic factors in the decision to initiate therapy in idiopathic MN patients. Although spontaneous remissions occur in ~30% of patients, partial and complete remissions help to define the clinical course of an individual patient.

Lipids, blood pressure, kidney - what was new in 2011?

The year 2011 was very interesting regarding new studies, trials and guidelines in the field of lipidology, hypertensiology and nephrology. Suffice it to mention the new European Society of Cardiology (ESC)/European Atherosclerosis Society (EAS) guidelines on the management of dyslipidaemias, American College of Cardiology Foundation (ACCF)/American Heart Association (AHA) guidelines on hypertension in the elderly, and many important trials presented among others during the American Society of Nephrology (ASN) Annual Congress in Philadelphia and the AHA Annual Congress in Orlando. The paper is an attempt to summarize the most important events and reports in the mentioned areas in the passing year.

Rituximab treatment for membranous nephropathy: a French clinical and serological retrospective study of 28 patients

The development of well-tolerated and effective therapies that target the pathogenesis of membranous nephropathy (MN) would be useful. Our objective was to evaluate the efficacy of rituximab in MN. We analyzed the outcome of 28 patients treated with rituximab for idiopathic MN. Anti-PLA₂R antibodies in serum and PLA₂R antigen in kidney biopsy were assessed in 10 and 9 patients, respectively. Proteinuria was significantly decreased by 56, 62 and 87% at 3, 6 and 12 months, respectively. At 6 months, 2 patients achieved complete remission (CR) and 12 partial remission (PR; overall renal response, 50%). At 12 months (n = 23), CR was achieved in 6 patients and PR in 13 patients (overall renal response, 82.6%). Three patients suffered a relapse of nephrotic proteinuria 27–50 months after treatment. Univariate analysis suggested that the degree of renal failure (MDRD estimated glomerular filtration rate <45/ml/min/1.73 m²) is an independent factor that predicts lack of response to rituximab. Anti-PLA₂R antibodies were detected in the serum of 10 patients, and PLA₂R antigen in immune deposits in 8 of 9 patients. Antibodies became negative in all 5 responsive patients with available follow-up sera. In this retrospective study, a high rate of remission was achieved 12 months after treatment.

Production of heterologous IgG antibody against Heymann nephritis antigen by injections of immune complexes

Heterologous IgG antibody (ab) can be produced against Heymann nephritis (HN) antigen (ag) in rabbits by administering it in Freund's complete adjuvant. The developing abs reacted at high titre with rat kidney brush border (BB) regions of the renal proximal tubules in an indirect fluorescence ab test. A single IV injection of the heterologous ab into a susceptible strain of rat resulted in the localization of IgG ab to glomerular fixed ags, producing immune complex glomerular nephritis. The injected ab also reacted with the BB region of the renal proximal tubules. The aim of this experiment was to find out whether heterologous IgG ab against the HN ag can also be produced in recipient rabbits by injecting immune complexes (ICs) composed of a rat kidney tubular preparation [rat kidney fraction 3 (rKF3)] and donor rabbit-derived rabbit anti-rKF3 IgG ab. We found that anti-rKF3 IgG ab--against the BB region of the renal proximal tubules--could be induced in rabbits injected with ICs, and the resulting ab was able to initiate passive HN in rats. This was the first time a pathogenic IgG ab was produced against HN ag in rabbits without the use of adjuvant. Ab responses in recipient rabbits were achieved by ab information transfer. Recipient rabbits injected with the IC produced the same class of immunoglobulin with the same specificity against the target ag rKF3, as was present in the innoculum, namely rabbit anti-rKF3 IgG ab.

Rituximab-induced depletion of anti-PLA2R autoantibodies predicts response in membranous nephropathy

Autoantibodies to the M-type phospholipase A(2) receptor (PLA(2)R) are sensitive and specific for idiopathic membranous nephropathy. The anti-B cell agent rituximab is a promising therapy for this disease, but biomarkers of early response to treatment currently do not exist. Here, we investigated whether levels of anti-PLA(2)R correlate with the immunological activity of membranous nephropathy, potentially exhibiting a more rapid response to treatment than clinical parameters such as proteinuria. We measured the amount of anti-PLA(2)R using Western blot immunoassay in serial serum samples from a total of 35 patients treated with rituximab for membranous nephropathy in two distinct cohorts. Pretreatment samples from 25 of 35 (71%) patients contained anti-PLA(2)R, and these autoantibodies declined or disappeared in 17 (68%) of these patients within 12 months after rituximab. Those who demonstrated this immunologic response fared better clinically: 59% and 88% attained complete or partial remission by 12 and 24 months, respectively, compared with 0% and 33% among those with persistent anti-PLA(2)R levels. Changes in antibody levels preceded changes in proteinuria. One subject who relapsed during follow-up had a concomitant return of anti-PLA(2)R. In summary, measuring anti-PLA(2)R levels by immunoassay may be a method to follow and predict response to treatment with rituximab in membranous nephropathy.

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.

Anti-phospholipase A₂ receptor antibodies correlate with clinical status in idiopathic membranous nephropathy

BACKGROUND AND OBJECTIVES

Circulating autoantibodies against the M-type phospholipase A(2) receptor (anti-PLA(2)R) were recently identified in the majority of patients in the United States with idiopathic membranous nephropathy (iMN). The objectives of this study were to assess the prevalence of anti-PLA(2)R in a separate, European cohort of iMN patients and to correlate the presence of anti-PLA(2)R with clinical parameters reflective of disease activity.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Anti-PLA(2)R levels were blindly assessed by a Western blot immunoassay in 54 serum samples from 18 patients with iMN collected in various stages of clinical disease. Anti-PLA(2)R levels were correlated with other clinical parameters.

RESULTS

77.8% of iMN patients in our cohort had antibodies reactive with human PLA(2)R. The antibody levels in these patients correlated strongly with both clinical status and proteinuria (r = 0.73, P < 0.01).

CONCLUSIONS

The role of PLA(2)R as a major antigen in iMN was confirmed in an independent, European patient cohort, and levels of circulating anti-PLA(2)R revealed a strong correlation with clinical disease activity. We propose that detection and measurement of these autoantibodies may provide a tool for monitoring of disease activity and treatment efficacy.

Risk HLA-DQA1 and PLA(2)R1 alleles in idiopathic membranous nephropathy

BACKGROUND

Idiopathic membranous nephropathy is a major cause of the nephrotic syndrome in adults, but its etiologic basis is not fully understood. We investigated the genetic basis of biopsy-proven cases of idiopathic membranous nephropathy in a white population.

METHODS

We performed independent genomewide association studies of single-nucleotide polymorphisms (SNPs) in patients with idiopathic membranous nephropathy from three populations of white ancestry (75 French, 146 Dutch, and 335 British patients). The patients were compared with racially matched control subjects; population stratification and quality controls were carried out according to standard criteria. Associations were calculated by means of a chi-square basic allele test; the threshold for significance was adjusted for multiple comparisons (with the Bonferroni method).

RESULTS

In a joint analysis of data from the 556 patients studied (398 men), we identified significant alleles at two genomic loci associated with idiopathic membranous nephropathy. Chromosome 2q24 contains the gene encoding M-type phospholipase A(2) receptor (PLA(2)R1) (SNP rs4664308, P=8.6×10(-29)), previously shown to be the target of an autoimmune response. Chromosome 6p21 contains the gene encoding HLA complex class II HLA-DQ alpha chain 1 (HLA-DQA1) (SNP rs2187668, P=8.0×10(-93)). The association with HLA-DQA1 was significant in all three populations (P=1.8×10(-9), P=5.6×10(-27), and P=5.2×10(-36) in the French, Dutch, and British groups, respectively). The odds ratio for idiopathic membranous nephropathy with homozygosity for both risk alleles was 78.5 (95% confidence interval, 34.6 to 178.2).

CONCLUSIONS

An HLA-DQA1 allele on chromosome 6p21 is most closely associated with idiopathic membranous nephropathy in persons of white ancestry. This allele may facilitate an autoimmune response against targets such as variants of PLA2R1. Our findings suggest a basis for understanding this disease and illuminate how adaptive immunity is regulated by HLA.

Correlation between B Lymphocyte Abnormality and Disease Activity in Patients with Idiopathic Membranous Nephropathy

This study investigated the relationship between peripheral blood B lymphocytes, regulatory T-cells and T lymphocyte subsets, the distribution of B lymphocytes in the kidney, and the pathogenesis of idiopathic membranous nephropathy (IMN). Lymphocyte subsets were measured using flow cytometry in 66 patients with clinically-confirmed IMN and in 40 healthy control subjects. Compared with healthy subjects, the number of peripheral blood B lymphocytes was significantly increased in IMN patients and that of regulatory T-cells was significantly decreased, accompanied by an increased CD4+/CD8+ T-cell ratio. There was no relationship between the number of peripheral blood B lymphocytes and markers of kidney function. Although the number of infiltrating B lymphocytes in the kidney of IMN patients was higher, there was no relationship with the number of peripheral blood B lymphocytes. In conclusion, there was no relationship between peripheral blood B lymphocytes and disease activity, suggesting that peripheral blood B lymphocytes are not a biomarker of disease activity and therapeutic efficacy in IMN.

A case of membranous nephropathy with primary biliary cirrhosis and cyclosporine-induced remission

We report a case of membranous nephropathy with primary biliary cirrhosis (PBC). A 76-year-old Japanese man had been treated for PBC and was referred to our department because of acute severe proteinuria (10 g/day). Renal biopsy was performed and was compatible with a diagnosis of membranous nephropathy. The patient was treated with cyclosporine A (CsA; Neoral®), which was followed by normalization of liver function and partial remission of proteinuria (0.68 g/day) within six months without any significant side effects. This case suggests that CsA monotherapy is effective for the treatment of both liver dysfunction and membranous nephropathy associated with PBC.