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C1q and C4b bind simultaneously to CR1 and additively support erythrocyte adhesion
S W Tas1, L B Klickstein, S F Barbashov
1Department of Medicine, Harvard Medical School, Charles A. Dana Research Institute, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
Journal of Immunology (Baltimore, Md. : 1950)
|October 21, 1999
Summary
Complement receptor 1 (CR1) binds C1q, supporting red blood cell adhesion and immune complex clearance. This study confirms CR1 as the sole receptor for complement opsonins, highlighting C1q
Area of Science:
- Immunology
- Complement System
- Cellular Adhesion
Background:
- Soluble C1q was previously shown to bind specifically to complement receptor 1 (CR1) on transfected cells.
- The CR1-C1q interaction's role in immune complex clearance suggested it should support red blood cell (E) adhesion.
Purpose of the Study:
- To investigate the CR1-C1q interaction's role in immune adherence and clearance.
- To determine if CR1 is the single receptor for all complement opsonins.
- To identify the binding site of C1q on CR1.
Main Methods:
- Tip plate adhesion assay to measure E adhesion to immobilized C1q.
- Inhibition studies using anti-CR1 Fab fragments.
- BIAcore instrument analysis to study binding kinetics of C1q, C4b, and C3b to CR1.
Main Results:
- Immobilized C1q mediated human E adhesion, specifically inhibited by anti-CR1 antibodies.
- C1q, C4b, and C3b binding to CR1 were independent events.
- C1q-dependent binding of immune complexes and heat-aggregated IgG to E was observed.
Conclusions:
- CR1 is the single receptor for all complement opsonins (C1q, C4b, C3b).
- Evidence suggests a single C1q binding site on the LHR-D domain of CR1.
- C1q likely participates in immune complex clearance via CR1-mediated adhesion.