INTRODUCTION:Autoantibodies against the podocyte protein nephrin were recently identified in a pediatric cohort primarily comprising steroid-sensitive (SSNS) and steroid-dependent (SDNS) nephrotic syndrome (NS). However, their prevalence across all NS subtypes, particularly in steroid-resistant nephrotic syndrome (SRNS), and their relation to therapy response need to be determined to advance pathophysiological understanding and refine treatment strategies. METHODS:A multicenter cohort study measuring anti-nephrin autoantibodies in samples from children with SSNS, SDNS, nongenetic and genetic SRNS was conducted. RESULTS:Sixty-nine of 101 (68%) patients with SSNS, 19 of 67 (28%) patients with SDNS, 14 of 103 patients (14%) with non-genetic SRNS, and 1 of 62 patients (2%) with genetic SRNS were positive for anti-nephrin autoantibodies. The prevalence of anti-nephrin autoantibodies increased with presence of active disease in cases of SSNS and SDNS. Within the group of non-genetic SRNS patients with active disease, anti-nephrin positivity was found in 13 of 74 (18%) patients responding to intensified immunosuppression compared to none of 17 patients with multidrug-resistant SRNS. CONCLUSIONS:The prevalence of anti-nephrin antibodies is substantially higher in children with steroid responsive NS than in those with SRNS, suggesting that anti-nephrin antibodies primarily drive SSNS/SDNS. In contrast, NS due to podocyte gene mutations is primarily genotype-caused. Anti-nephrin autoantibodies may serve as a positive prognostic marker in pediatric NS, indicating a favorable response to immunosuppressive therapy.

Chronic kidney disease (CKD) affects over 850 million individuals worldwide, often progressing to stages requiring dialysis or kidney transplants. Central to kidney function is the glomerular filtration barrier (GFB), which selectively filters waste while retaining essential proteins. Traditional models, including animal studies and 2D cell cultures, fail to fully replicate the GFB's complexity, limiting CKD research. Recent developments in microphysiological systems (MPS), particularly microphysiological glomerular filtration barriers (MPGFB), provide more accurate in vitro models for studying kidney diseases and evaluating therapies. MPGFB systems use organ-on-chip technology to integrate podocytes and glomerular endothelial cells within confined microfluidic environments, closely mimicking GFB's dynamic in vivo conditions. This setup enables detailed permeability analysis, aiding in research on disease mechanisms and drug toxicity. Furthermore, using human-induced pluripotent stem cells in MPGFB platforms allows patient-specific studies, enhancing insights into genetic kidney disorders. This review first examines the GFB's structure and function, focusing on its cellular and extracellular matrix components. It then discusses biological and engineering approaches to MPGFB fabrication, covering materials, 3D design, and flow control. The review concludes with MPGFB applications in disease modeling and drug testing, and addresses improvements needed for refining MPGFB as a key tool in kidney disease research and treatment.

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.) Antinephrin autoantibodies occur in adults with minimal change disease and children with idiopathic nephrotic syndrome and appear to be disease activity markers. Their binding at slit diaphragms may induce podocyte dysfunction.

Membranous nephropathy (MN) is a glomerular disease that can occur at all ages. In adults, it is the most frequent cause of nephrotic syndrome. In ~80% of patients, there is no underlying cause of MN (primary MN) and the remaining cases are associated with medications or other diseases such as systemic lupus erythematosus, hepatitis virus infection or malignancies. MN is an autoimmune disease characterized by a thickening of the glomerular capillary walls due to immune complex deposition. Identification of the phospholipase A2 receptor (PLA2R) as the major antigen in adults in 2009 induced a paradigm shift in disease diagnosis and monitoring and several other antigens have since been characterized. Disease outcome is difficult to predict and around one-third of patients will undergo spontaneous remission. In those at high risk of progression, immunosuppressive therapy with cyclophosphamide plus corticosteroids has substantially reduced the need for kidney replacement therapy. Owing to carcinogenic risk, other treatments (calcineurin inhibitors and CD20-targeted B cell depletion therapy (rituximab)) have been developed. However, disease relapses are frequent when calcineurin inhibitors are stopped and the remission rate with rituximab is lower than with cyclophosphamide, particularly in patients with high PLA2R antibody titres. Other new drugs are already available and antigen-specific immunotherapies are being developed.

Membranous nephropathy (MN) is a glomerular disease that can occur at all ages. In adults, it is the most frequent cause of nephrotic syndrome. In ~80% of patients, there is no underlying cause of MN (primary MN) and the remaining cases are associated with medications or other diseases such as systemic lupus erythematosus, hepatitis virus infection or malignancies. MN is an autoimmune disease characterized by a thickening of the glomerular capillary walls due to immune complex deposition. Identification of the phospholipase A2 receptor (PLA2R) as the major antigen in adults in 2009 induced a paradigm shift in disease diagnosis and monitoring and several other antigens have since been characterized. Disease outcome is difficult to predict and around one-third of patients will undergo spontaneous remission. In those at high risk of progression, immunosuppressive therapy with cyclophosphamide plus corticosteroids has substantially reduced the need for kidney replacement therapy. Owing to carcinogenic risk, other treatments (calcineurin inhibitors and CD20-targeted B cell depletion therapy (rituximab)) have been developed. However, disease relapses are frequent when calcineurin inhibitors are stopped and the remission rate with rituximab is lower than with cyclophosphamide, particularly in patients with high PLA2R antibody titres. Other new drugs are already available and antigen-specific immunotherapies are being developed. Membranous nephropathy is a glomerular disease that is the most frequent cause of nephrotic syndrome in adults. This Primer reviews the epidemiology, pathophysiology, diagnosis and management of this disease and discusses how to improve long-term renal prognosis and quality of life.