Trapping of circulating proteins in immune deposits of Heymann nephritis

The renal distribution of autologous and heterologous albumin and IgG was studied by electron microscopy using peroxidase-labeled conjugates in rats with Heymann nephritis. In addition, the renal distribution of autologous and heterologous antiperoxidase IgG and their F(ab')2 and Fab fragments was detected using peroxidase alone. All of these proteins crossed the glomerular lamina densa and passed into the urinary space by an extracellular pathway through the epithelial slits and the sites of epithelial detachment. The proteins were trapped in subepithelial immune deposits irrespective of the degree of proteinuria and regardless of the molecular weight, the autologous or heterologous origin, and the electric charges of the protein studied. The trapping was transient and easily reversed. These findings suggest that circulating proteins are able to modify the composition of immune deposits, thereby altering the course of immune complex disease.