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Glomerular CR1 express in situ cofactor activity for degradation of C3b
C A Vedeler1, R Matre, B M Iversen
1Broegelmann Research Laboratory for Microbiology, Gade Institute, Norway.
Insights
Sheep erythrocytes sensitized with complement protein C3b adhered to human kidney C3b/C4b receptors (CR1). Factor I triggered C3b degradation, releasing C3c and detaching cells, indicating CR1
Area of Science:
- Immunology
- Renal Pathology
- Complement System
Background:
- The complement system plays a crucial role in immune responses and inflammation.
- Complement receptor 1 (CR1) is expressed on various immune cells and renal cells.
- Understanding CR1's function in the kidney is vital for comprehending renal diseases.
Purpose of the Study:
- To investigate the adherence of complement-opsonized erythrocytes to human renal glomeruli.
- To determine the role of complement receptor 1 (CR1) in the interaction between erythrocytes and glomerular structures.
- To elucidate the mechanism of C3b degradation on glomerular CR1.
Main Methods:
- Sheep erythrocytes sensitized with IgM antibodies and C3b (EAC3b) were used as indicator cells.
- The closed chamber technique was employed to study EAC3b adherence to cryostat sections of human renal glomeruli.
- Factor I and protease inhibitors were used to assess C3b degradation and cell detachment.
Main Results:
- EAC3b showed stable adherence to glomerular CR1 for at least 3 hours at 37°C.
- In the presence of Factor I, EAC3b detached from the glomeruli within 30 minutes.
- Detached cells showed degradation of C3b to C3d, with C3c released, indicating Factor I-mediated cleavage.
- CR1 in renal glomeruli acted as a cofactor for Factor I-mediated C3b degradation.
Conclusions:
- Human renal glomerular CR1 possesses cofactor activity for Factor I-mediated degradation of C3b.
- This interaction leads to the cleavage of C3b into C3d and C3c, facilitating the detachment of opsonized cells.
- The findings highlight a novel function of glomerular CR1 in regulating complement activation within the kidney.
Abstract:
Adherence of sheep erythrocytes (E) sensitized with IgM antibodies (A) and C3b (EAC3b) to C3b/C4b receptors (CR1) in cryostat sections of human renal glomeruli was studied using the closed chamber technique. The adsorption was stable for at least 3 h at 37 degrees C. In the presence of purified factor I, the indicator cells, however, detached from the sections after 30 min at 37 degrees C. Factor H was not required. The release was not due to loss of CR1 activity in the tissue. The detached indicator cells were negative in the immune adherence test and were agglutinated by antibody to C3d, but not by antibody to C3c. Western blot of the detached indicator cells revealed the presence of C3d and C3c was found in the chamber fluid. Accordingly, detachment of the indicator cells was due to degradation of C3b to C3d with the release of C3c into the chamber fluid. Protease inhibitors did not prevent the detachment of the indicator cells. EAC3b incubated with sections of renal glomeruli preincubated with anti-CR1 antibody were not degraded. The results therefore indicate that CR1 in situ in renal glomeruli can provide the necessary cofactor activity for factor I-mediated degradation of C3b to C3d and C3c.