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C6 depletion reduces proteinuria in experimental nephropathy induced by a nonglomerular antigen
W G Couser1, R F Ochi, P J Baker
1Department of Medicine, University of Washington, Seattle 98195.
Insights
Complement component C6 depletion prevents membrane attack complex formation, significantly reducing glomerular injury in experimental nephritis. This highlights the C5b-9 complex
Area of Science:
- Nephrology
- Immunology
- Complement System
Background:
- The complement membrane attack complex (C5b-9) is implicated in glomerular injury in membranous nephropathy.
- Previous studies focused on endogenous antigens, leaving the role of C5b-9 in nephritis induced by exogenous antigens less clear.
Purpose of the Study:
- To investigate the effect of selective C6 depletion, preventing C5b-9 formation, on glomerular injury in a rat model of in situ subepithelial immune complex nephritis.
- To assess the impact of C5b-9 inhibition on proteinuria and morphologic changes.
Main Methods:
- Induction of nephritis using cationized human IgG and rabbit anti-human IgG in rats.
- Selective C6 depletion using goat anti-rat C6 antibody.
- Generalized complement depletion with cobra venom factor and leukocyte depletion with irradiation served as controls.
- Quantification of glomerular antigen-antibody deposition and proteinuria.
Main Results:
- Selective C6 depletion successfully reduced C6 levels to <3% without affecting glomerular deposition of antigen and antibody at 4 hours.
- Glomerular C3 deposition and circulating C3 levels were similar between C6-depleted and control groups.
- Proteinuria and morphologic damage were significantly reduced in C6-depleted rats (data not shown in abstract).
Conclusions:
- Selective depletion of C6 effectively inhibits C5b-9 formation.
- The C5b-9 complex plays a crucial role in mediating glomerular injury in this model of nephritis induced by exogenous antigens.
- Targeting C5b-9 formation represents a potential therapeutic strategy for immune complex-mediated kidney diseases.
Abstract:
The role of the complement membrane attack complex, C5b-9, in mediating glomerular injury has been well defined in models of membranous nephropathy induced by antibody to endogenous glomerular epithelial cell membrane antigens. The effect of selective C6 depletion (to prevent C5b-9 formation) on morphologic characteristics and proteinuria in a model of in situ subepithelial immune complex nephritis induced by an exogenous cationized antigen (human immunoglobulin G (IgG)) followed by rabbit antibody to human IgG was studied. Selective C6 depletion was achieved by repeated administration of a goat antibody to rat C6. Other groups were treated with cobra venom factor to induce generalized complement depletion and with sublethal irradiation to deplete circulating leukocytes. In C6-depleted rats, C6 levels were reduced to less than 3% of baseline throughout the 2 days of the study compared with over 100% in controls. At 4 h after disease induction, glomerular deposition of antigen and antibody were similar in C6D and control groups by immunofluorescence and by direct measurement of glomerular deposition of radiolabeled antigen and antibody (cationized 131I human IgG, 9.1 +/- 0.1 micrograms/38,000 glomeruli in C6D versus 9.8 +/- 0.9 in controls; P = was not significant; rabbit 125I-labeled anti-human IgG, 104 +/- 10 ng in C6D versus 80 +/- 9 ng in controls; P = was not significant). Circulating C3 levels and glomerular C3 deposition were also similar in C6D and control groups.(ABSTRACT TRUNCATED AT 250 WORDS)