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Transcellular transport and membrane insertion of the C5b-9 membrane attack complex of complement by glomerular
D Kerjaschki1, M Schulze, S Binder
1Institute of Pathological Anatomy, University of Vienna, Austria.
Abstract:
Deposition of the C5b-9 complex of C in glomeruli of rats with experimental membranous nephropathy (MN) is essential for the development of proteinuria. In this investigation C5b-9 was localized in the passive Heymann nephritis (PHN) by immunoelectron microscopy with a mAb specific for C5b-9(m) neoantigen. Its distribution was compared with that in another model of MN induced by successive injections of cationic human IgG and rabbit anti-human IgG into rats. In PHN C5b-9 was found: 1) in the immune deposits (ID), and on the cell membranes of foot processes close to the ID; 2) in clathrin-coated pits of the glomerular epithelial cells (GEC) close to the ID and in membrane vesicles in the cytoplasm, separated from sheep IgG and the gp330 Ag; 3) in high concentration in multivesicular bodies of GEC; and 4) in association with membrane vesicles in the urinary space which presumably are the exocytosed content of membrane vesicular bodies. By contrast, in the cationic IgG-MN model C5b-9 was found mostly in ID, but rarely within the GEC. By freeze-fracture electron microscopy we have further identified 200- to 250-A intramembrane particles in PHN in the cell membranes of the "soles" of the foot processes which resemble membrane inserted human C5b-9(m). Degradation products of C5b-9 were further detected by immunoblotting of a 100,000 x g pellet of PHN rat urine. These results indicate that, in PHN, C5b-9 is inserted into the cell membranes of GEC, and that it is selectively endocytosed and transported across GEC by a cellular mechanism which apparently protects the cell from accumulation of membrane-inserted C5b-9.
Insights
The C5b-9 complex is crucial for membranous nephropathy (MN) and proteinuria. In passive Heymann nephritis (PHN), C5b-9 inserts into glomerular epithelial cells (GEC) and is endocytosed, protecting GEC from damage.
Area of Science:
- Nephrology
- Immunology
- Cell Biology
Background:
- Deposition of the C5b-9 complement complex in glomeruli is essential for proteinuria development in experimental membranous nephropathy (MN).
- Understanding the precise localization and cellular handling of C5b-9 in MN is critical for developing targeted therapies.
Purpose of the Study:
- To investigate the distribution and cellular fate of the C5b-9 complex in passive Heymann nephritis (PHN), a model of MN.
- To compare C5b-9 localization in PHN with another MN model induced by cationic human IgG.
Main Methods:
- Immunoelectron microscopy using a mAb specific for the C5b-9(m) neoantigen.
- Freeze-fracture electron microscopy to identify intramembrane particles.
- Immunoblotting of rat urine to detect C5b-9 degradation products.
Main Results:
- In PHN, C5b-9 was found in immune deposits and on glomerular epithelial cell (GEC) membranes, particularly in clathrin-coated pits and vesicles.
- C5b-9 was concentrated in multivesicular bodies within GEC and associated with urinary vesicles, suggesting exocytosis.
- In contrast, C5b-9 was primarily in immune deposits in the cationic IgG-MN model, with rare intracellular localization in GEC.
- Freeze-fracture revealed particles resembling membrane-inserted C5b-9(m) in GEC foot process membranes in PHN.
- Degradation products of C5b-9 were detected in PHN rat urine.
Conclusions:
- In PHN, C5b-9 is inserted into GEC membranes.
- GEC selectively endocytose and transport membrane-inserted C5b-9 via a vesicular mechanism.
- This cellular transport protects GEC from the accumulation of membrane-inserted C5b-9, mitigating cellular damage.