Ultrastructural alterations of glomerular anionic sites in idiopathic membranous glomerulonephritis

The relation of ultrastructural alterations of glomerular anionic sites to morphological changes of the glomerular basement membrane (GBM) was studied in biopsy specimens from patients with idiopathic membranous glomerulonephritis (MGN) using polyethyleneimine (PEI) as a cationic probe. The subepithelial deposits did not fix PEI, and only a very few anionic sites were found between subepithelial deposits and adjacent epithelial cells. Thus, anionic sites of the lamina rara externa (LRE) were markedly decreased in number and interrupted by subepithelial deposits in the earlier stages (stage I and II). As the deposits were incorporated into the GBM in the later stage (stage III), the anionic sites of the LRE were restored on the epithelial cell surface coat (ESC) covering the deposits, but foot process effacement persisted during the course of the disease. The anionic sites of the lamina rara interna (LRI) appeared much less altered in all stages of MGN. These findings suggest that subepithelial deposition of immune reactants is associated with focal loss and disorganization of anionic sites on the GBM, resulting in a defect of glomerular-barrier function.