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C1 subcomponent complexes: basic and clinical aspects
1Department of Clinical Immunology, University of Lund, Sweden.
Insights
Studies reveal complement C1 subcomponent complexes in serum, offering insights into disease mechanisms. Specific complexes like C1 inhibitor-C1r-C1s-C1 inhibitor may indicate classical pathway activation.
Area of Science:
- Immunology
- Biochemistry
Background:
- Complement system C1 subcomponents form complexes detectable in serum.
- Aberrations in these complexes may reflect in vivo interactions and influence complement function.
- Studying C1 subcomponent complexes can provide insights into disease pathogenetic mechanisms.
Purpose of the Study:
- To investigate the formation and clinical significance of C1 subcomponent complexes.
- To identify specific complexes as potential biomarkers for complement activation and disease states.
Main Methods:
- Analysis of C1 subcomponent complexes in normal and pathological sera.
- Characterization of complexes formed through C1 inhibitor (C1Inh)-dependent dissociation.
- Detection of free C1q and zymogen (C1r-C1s)2 in pathological samples.
Main Results:
- C1 inhibitor (C1Inh)-dependent dissociation of C1q(C1r-C1s)2 yields C1Inh-C1r-C1s or C1Inh-C1r-C1s-C1Inh complexes.
- Increased C1Inh-C1r-C1s suggests prevention of C1 activation.
- C1Inh-C1r-C1s-C1Inh serves as a marker for efficient classical pathway activation.
- "Free" C1q in pathological sera and joint fluids may result from C1Inh-dependent dissociation.
- Circulating zymogen (C1r-C1s)2 can be found in conditions with low C1q or due to interactions with C1q's collagenous region.
Conclusions:
- C1 subcomponent complexes are valuable indicators of complement system activity.
- Specific complexes, such as C1Inh-C1r-C1s-C1Inh, are clinically useful markers for classical pathway activation.
- Understanding these complexes aids in elucidating pathogenetic mechanisms in various diseases.
Abstract:
C1 subcomponents form a variety of complexes that can be detected in normal and pathological sera. Since aberrations of C1 subcomponents in disease could reflect in vivo interactions with influence on complement function, studies of C1 subcomponent complexes might provide insight into pathogenetic mechanisms. C1 inhibitor (C1Inh)-dependent dissociation of the C1q(C1r-C1s)2 complex gives rise to C1Inh-C1r-C1s or C1Inh-C1r-C1s-C1Inh complexes. Increased concentrations of C1Inh-C1r-C1s probably signify prevention of C1 activation, while C1Inh-C1r-C1s-C1Inh appears to be a clinically useful marker of efficient classical pathway activation. "Free" C1q as found in some pathological sera, and in joint fluids of patients with rheumatoid arthritis could be a result of C1Inh-dependent dissociation of C1q(C1r-C1s)2. The presence in serum of zymogen (C1r-C1s)2 is an expected finding in various conditions with low C1q concentrations without evidence of C1 activation. It is not excluded that circulating (C1r-C1s)2 might sometimes be acquired due to factors capable of interacting with the collagenous part of the C1q molecule.