Anti-nephrin, anti-podocin and anti-Kirrel1 antibodies: Biological challenges and clinical implications.

The discovery of circulating autoantibodies targeting slit diaphragm proteins-particularly nephrin, podocin, and Kirrel1-has redefined the pathogenic framework of nephrotic syndrome (NS), shifting the focus from empirical, morphology-based classification to a mechanistic, biomarker-driven model. This evolution holds promise for earlier, non-invasive diagnosis, individualized risk stratification, and tailored immunomodulatory therapy. However, the translation of these insights into clinical practice requires reliable serum assays but biological complexity and technical variability remain challenging. In this review we identify five hurdles to unlock the full diagnostic and therapeutic utility of anti-slit diaphragm autoantibodies. First, the low or transient serum levels of anti-nephrin antibodies reflect their rapid onset of NS and autoantibody loss into the urine, making timing of sample collection essential. Second, antibody levels closely mirror immunological activity and proteinuria levels-rising during relapse and falling in remission-rendering detection highly phase-dependent. Third, autoimmune NS are various, which complicates diagnosis. Up to 25% of pediatric and adult NS are negative for anti-nephrin IgG but positive for anti-podocin IgG, and anti-Kirrel1 autoimmunity, though rare, also occurs. Overlapping profiles and epitope spreading underscore the limitations of single-target assays. Fourth, assay performance is influenced by antigen fragment selection, expression system, and post-translational modifications-especially for nephrin, which is structurally complex and heavily glycosylated. Finally, combined serological and tissue-based strategies-particularly those integrating ELISA with super-resolution microscopy are a gold standard needed to determine sensitivity and specificity of serum ELISA and reliably inform therapeutic decision-making. Here we will discuss a roadmap for the clinical implementation of anti-nephrin, anti-podocin and anti-Kirrel1 (anti-slit diaphragm) antibody testing lays the foundation for precision diagnostics and personalized treatment in autoimmune podocytopathies.