Nephritogenic mAb 5-1-6 is directed art the extracellular domain of rat nephrin

mAb 5-1-6 identifies an antigen on rat podocyte slit-diaphragms and induces severe proteinuria when injected into rats. Nephrin, an Ig-like transmembr ane protein that is mutated in congenital nephrotic syndrome of the Finnish type, has been localized to the slit-diaphragm on human podocytes. Here we document that the mAb 5-1-6 antigen is rat nephrin. After incubation of ra t glomeruli with this mAb, the antibody/antigen complex was chemically cros s-linked, extracted, and immunoprecipitated, prior to Western analysis. By mass spectrometry and 2D gel electrophoresis, we identified several peptide s with complete identity to human nephrin. In addition, the 185-kDa protein immunoprecipitated by mAb 5-1-6 from rat glomerular extracts reacts with a rabbit anti-mouse nephrin antibody. Finally, nephrin and the mAb 5-1-6 ant igen have identical glomerular localization patterns on immunofluorescence of rat kidney. These results demonstrate that the nephritogenic mAb 5-1-6 i dentifies the extracellular domain of nephrin, thereby documenting the impo rtance of the slit-diaphragm and its component, nephrin, in the regulation of glomerular permselectivity.