C3aR-initiated signaling is a critical mechanism of podocyte injury in membranous nephropathy.

The deposition of antipodocyte autoantibodies in the glomerular subepithelial space induces primary membranous nephropathy (MN), the leading cause of nephrotic syndrome worldwide. Taking advantage of the glomerulus-on-a-chip system, we modeled human primary MN induced by anti-PLA2R antibodies. Here we show that exposure of primary human podocytes expressing PLA2R to MN serum results in IgG deposition and complement activation on their surface, leading to loss of the chip permselectivity to albumin. C3a receptor (C3aR) antagonists as well as C3AR gene silencing in podocytes reduced oxidative stress induced by MN serum and prevented albumin leakage. In contrast, inhibition of the formation of the membrane-attack-complex (MAC), previously thought to play a major role in MN pathogenesis, did not affect permselectivity to albumin. In addition, treatment with a C3aR antagonist effectively prevented proteinuria in a mouse model of MN, substantiating the chip findings. In conclusion, using a combination of pathophysiologically relevant in vitro and in vivo models, we established that C3a/C3aR signaling plays a critical role in complement-mediated MN pathogenesis, indicating an alternative therapeutic target for MN.

Antibody-Guided Therapy in Phospholipase A2 Receptor-Associated Membranous Nephropathy.

Introduction: A 6-month course of cyclophosphamide (CP) and steroids is effective in primary membranous nephropathy (MN), but unappealing because of long-term side effects. We evaluated efficacy of an "antibody-guided" treatment schedule. Methods: Patients with phospholipase A2 receptor (PLA2R)-related MN and high risk of progression were treated with CP 1.5 mg/kg/d and steroids in cycles of 8 weeks. Anti-PLA2R antibodies were measured by indirect immunofluorescence (IIFT) at 8, 16, and 24 weeks, and a negative test resulted in withdrawal of CP, and rapid tapering of prednisone. In patients with persistent anti-PLA2R antibodies at 24 weeks, CP was switched to mycophenolate mofetil. Treatment was repeated in patients with a relapse. Results: Our analysis included 65 patients (48 males, 17 females), age 61 ± 12 years, estimated glomerular filtration rate (eGFR) 46 ml/min per 1.73 m2 (35-68), urine protein-to-creatinine ratio 7.7 grams/10 mmol creatinine (5.4-11.1) and serum albumin 20 g/l (16-26). Immunologic remission rate was 71% after 8 weeks, 86% after 16 weeks, 88% after 24 weeks, and 94% after 3 years. Twenty-seven patients (42%) had persistent clinical remission after only 8 weeks of therapy. Sixteen patients needed a second course of therapy because of immunologic or clinical relapse. Follow-up was 37 (26-58) months. Overall partial remission rate was 92%. One patient developed end-stage kidney disease. Antibody-guided therapy (ABG) was as effective as the standard 6-month course, whereas providing a lower cumulative dose of CP (11.1 [8.0-18.5] vs. 18.9 [14.2-23.6] grams). Conclusion: ABG is effective, and allows individualized therapy, with many patients responding to 8 weeks of CP-based therapy.

Anti-PLA2R1 Antibodies as Prognostic Biomarker in Membranous Nephropathy.

INTRODUCTION: Personalized treatment for patients with membranous nephropathy requires accurate prediction of the disease course at an early stage. In this study, we evaluated the value of baseline anti-phospholipase A2 receptor (PLA2R1) antibody titer as a prognostic biomarker in patients with PLA2R1-associated membranous nephropathy. METHODS: In this cohort study, we included 168 patients (118 men, 50 women) referred to our nephrology center between February 1995 and November 2016. Mean age was 52 ± 13 years. There were 156 patients with new-onset disease and 12 patients with a relapse (n = 10) or recent use of immunosuppressive therapy (n = 2). We measured anti-PLA2R1 titer at baseline and analyzed progression to severe disease (30% increase of serum creatinine or start of immunosuppressive therapy) as a primary study endpoint over 60 months. RESULTS: There was a clear association between anti-PLA2R1 antibody titer and severity of the nephrotic syndrome. In univariate analysis, anti-PLA2R1 antibody titer was also associated with disease progression. However, in Cox proportional hazard models that included proteinuria and serum creatinine, anti-PLA2R1 antibody titer was no longer associated with clinical outcome. Results were similar when limiting the analysis to the patients with new-onset disease. CONCLUSION: Our study questions the relevance of single measurement of anti-PLA2R1 antibodies at baseline as a prognostic biomarker in membranous nephropathy. Future studies are needed to determine the possible role of sequential measurements of anti-PLA2R1 antibodies as a prognostic biomarker of disease progression.

The bias between different albumin assays may affect clinical decision-making.

Differences between laboratory assays can have important clinical implications. For creatinine assays this became apparent soon after the introduction of the Modification of Diet in Renal Disease formula and resulted in international efforts towards standardization. Albumin in blood is measured by different assays, either chromogenic using Bromocresol green (BCG) or Bromocresol purple (BCP), or by an immunoassay. Since differences between these assays have received limited attention we evaluated bias and imprecision of BCG and BCP assays in comparison to the immunoassay using blood samples from patients with membranous nephropathy and nephrotic syndrome. For the BCG assay, the mean bias was high (6.2 g/l, with a standard deviation of 2.4 g/l) compared to a bias of 0.3 g/l (standard deviation 1.5 g/l) for the BCP assay. Importantly, we questioned clinical relevance by evaluating the accuracy of the decision toward the use of prophylactic anticoagulant therapy. Notably, nephrologists may reach inappropriate treatment decisions using the BGC assay in up to 59% of patients. Thus, our study should stimulate efforts towards standardization of the albumin assays.