Glomerular epithelial-cell endocytosis of horseradish peroxidase-polylysine conjugate in immune-complex...

Glomerulonephritis was induced in rats by daily intravenous cationised bovine serum albumin. The conjugate of horseradish peroxidase with poly-L-lysine was injected as a tracer of endocytosis by glomerular epithelial cells. The rats were sacrificed serially from 1 min to 24 h after the injection of the conjugate. The cytochemical localisation of peroxidase was observed by light- and electron-microscopy. Peroxidase was detectable in the GBM and immune deposits from 1 min after the injection but was cleared by 2 h. Cellular membrane staining by the conjugate and the membrane invaginations containing concentrated peroxidase were prominent adjacent to the subepithelial immune deposits. Peroxidase was initially localised intracellularly in membrane-bound vesicles adjacent to the subepithelial deposits. They subsequently moved towards the cell centre and became larger, some having the characteristics of lysosomes. Peroxidase activity significantly diminished within the cells by 16 h. The results show that glomerular epithelial-cell endocytosis in immune-complex glomerulonephritis is similar to that observed in the normal, but cellular membrane binding and invagination are more prominent adjacent to immune deposits. The trapping of the tracer in the deposits did not seem to alter its property of being taken up by the epithelial cells.