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C3, C4, and the terminal complement complex differ from C1q by binding predominantly to the antigenic part of solid
P Garred1, T E Michaelsen, A Aase
1Institute of Immunology and Rheumatology, National Hospital, University of Oslo, Norway.
Journal of Immunology (Baltimore, Md. : 1950)
|January 1, 1990
Summary
This study investigated complement system component binding to immune complexes. Complement components C1q, C4, C3, and the terminal complement complex (TCC) bind dose-dependently to immune complexes, with TCC showing increased binding with more antigen.
Area of Science:
- Immunology
- Complement System Biology
Background:
- Immune complexes are crucial in adaptive immunity and can activate the complement system.
- The terminal complement complex (TCC) plays a key role in complement-mediated cell lysis.
Purpose of the Study:
- To investigate the binding of complement components (C1q, C4, C3, TCC) and S protein to immune complexes.
- To analyze the impact of antigen (NIP-BSA) and soluble hapten (NIP) concentrations on complement component binding.
Main Methods:
- Immune complexes were formed using NIP-conjugated BSA and anti-NIP antibodies on polystyrene plates.
- Binding of complement components (C1q, C4, C3, TCC) and S protein was measured after serum addition.
- Alternative assays assessed TCC binding and C3 activation in fluid phase and solid phase.
Main Results:
- Dose-dependent binding of C1q, C4, C3, and TCC to immune complexes was observed.
- Increased NIP-BSA led to higher TCC binding and reduced S protein binding.
- C1q binding decreased with soluble NIP, while C4, C3, and TCC remained bound.
Conclusions:
- Complement components C1q, C4, C3, and TCC bind effectively to immune complexes.
- TCC binding to immune complexes is influenced by antigen availability.
- While C3 activates in fluid phase, TCC binding to solid phase immune complexes does not correlate with fluid phase TCC formation.