Ultrastructural change of the glomerular basement membrane in rats with Heymann nephritis revealed by ultrahigh resolution scanning electron microscopy.

To assess the relationship between the glomerular injury induced by immune complex deposition and proteinuria, ultrastructural changes of the glomerular basement membrane (GBM) were investigated in Heymann nephritis. Active Heymann nephritis was induced in rats by injecting them with tubular brush border antigen, known as Fx1A, emulsified in complete Freund's adjuvant (CFA). Measurement of urinary protein excretion and histological examinations were carried out for up to 15 weeks after immunization. Proteinuria developed in rats within 10 weeks of immunization and coincided with the development of subepithelial deposits with minimal spike-like basement membrane protrusion. Acellular glomeruli were prepared by detergent treatment and were subjected to tannic acid-osmium conductive staining prior to examination with an ultrahigh resolution scanning electron microscope (HSEM). HSEM of the acellular GBM prepared from control rats injected with CFA alone revealed a meshwork structure, with pores of about 9 nm in diameter. Proteinuric rats immunized with Fx1A showed a loosened meshwork structure, with pores of about 15 nm in the acellular GBM adjacent to the deposits. The newly formed GBM overlying the deposit consisted of a meshwork structure associated with unorganized thin fibrils. Ultrastructural changes were never seen in GBM devoid of deposits. These findings indicate that subepithelial deposits are closely involved in the development of proteinuria by injuring the size selectivity of the GBM.