Mechanism of formation of subepithelial electron-dense deposits in active in situ immune complex glomerulonephritis.

The influences of the epitope density on cationic antigens on the fate of immune reactants and the formation of subepithelial electron dense deposits (EDD) were studied in a model of active in situ immune complex glomerulonephritis (ICGN), using a hapten-carrier system. Three weeks after immunization with trinitrophenol conjugated bovine serum albumin (TNP17.3-BSA), the left kidneys of rats were perfused with 500 micrograms of TNP6.2-cationized human immunoglobulin G (C-HIgG) or TNP31.3-C-HIgG. The renal tissues were then examined at intervals by light, immunofluorescence, and electron microscopies. The perfused kidneys of rats given high-valency antigens (TNP31.3) showed marked subepithelial EDDs with foot process retraction associated with proteinuria. In contrast, those of rats given low-valency antigens (TNP6.2) showed only small subepithelial EDDs beneath the slit membrane, which consisted of apparently normal epithelial cells, and did not develop proteinuria. Kinetic studies on immunofluorescence showed that glomerular depositions of immune reactants (TNP-carrier conjugate, rat IgG, and C3) were present longer in rats treated with high-valency antigens than in those treated with low-valency antigens. We conclude that the epitope density on cationic antigens strongly influences the retention of immune reactants and the formation of subepithelial EDDs, as well as development of glomerular injury.