Co-localization of IgG with nephrin in immune-mediated idiopathic nephrotic syndrome

Abstract Background Increased serum anti-nephrin antibody titers and co-localization of nephrin and IgG in kidney tissues have been reported in minimal change disease (MCD) and post-transplant recurrent focal segmental glomerulosclerosis (FSGS). These results indicate an association of anti-nephrin antibodies with nephrotic syndrome (NS); however, the exact relationship remains unclear. Herein, we evaluated nephrin/IgG co-localization in the glomeruli of patients with various kidney diseases, including monogenic NS, to clarify the association between idiopathic nephrotic syndrome (INS) and anti-nephrin antibodies. Methods IgG and nephrin co-localization was investigated in 52 kidney tissue biopsy samples, comprising INS in the active phase ( n = 26; MCD, n = 19; FSGS, n = 7) and remission ( n = 6), monogenic NS ( n = 3), and other kidney diseases ( n = 17). Double-immunofluorescence staining for nephrin/IgG was performed in unfixed frozen sections for 2 h at room temperature with Alexa Fluor-labeled nephrin/IgG cocktail antibodies. Nephrin/IgG co-localization was assessed using optical sectioning under a fluorescence microscope. Results Nephrin/IgG co-localization was observed in 81% (21/26, children: 15/17, adults: 6/9) of active INS cases, 84% (16/19) of MCD cases, and 71% (5/7) of FSGS cases. No co-localization was observed in NS with monogenic variants or other kidney diseases. Conclusion Nephrin/IgG co-localization in the kidney tissue is finding observed in active INS , strongly indicating an association between anti-nephrin antibodies and INS onset. The nephrin/IgG cocktail antibody is a rapid and effective approach for investigating INS pathogenesis that facilitates the differential diagnosis of immune-mediated NS from other kidney diseases, including monogenic NS.