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C1q--how many functions? How many receptors?
P Eggleton1, K B Reid, A J Tenner
1Dept of Biochemistry, University of Oxford, UK. eggleton@bioch.ox.ac.uk
Insights
The complement component C1q has functions beyond activating complement, potentially mediated by newly found binding proteins. These proteins may act as cell-surface receptors or soluble modulators, influencing C1q
Area of Science:
- Immunology
- Molecular Biology
Background:
- C1q is the initial component of the classical complement activation pathway.
- Its primary role involves binding aggregated IgG to initiate complement cascade.
- Emerging evidence suggests C1q possesses non-complement functions.
Purpose of the Study:
- To explore the diverse biological activities of C1q.
- To investigate the role of C1q-binding proteins in modulating C1q functions.
- To discuss the influence of cell-surface and soluble binding proteins on C1q.
Main Methods:
- Literature review of C1q functions and binding proteins.
- Analysis of studies on C1q-mediated non-complement activities.
- Examination of evidence for C1q-binding protein interactions.
Main Results:
- C1q exhibits various functions independent of classical complement activation.
- Recently identified binding proteins interact with C1q.
- These interactions can occur via cell-surface receptors or soluble modulators.
Conclusions:
- C1q has multifaceted roles extending beyond complement.
- C1q-binding proteins are key regulators of these diverse functions.
- Understanding these interactions is crucial for deciphering C1q's broader biological significance.
Abstract:
C1, the first component of the classical pathway of complement activation is a complex of three proteins called C1q, C1r and C1s. Normally, C1q binding to aggregated IgG molecules results in activation of the classical pathway of complement. However, C1q has a number of other observed functions, not directly related to complement, that could be mediated by recently identified binding proteins acting as cell-surface receptors or soluble modulators of C1q-mediated functions. This article discusses the various activities of C1q and the evidence that these functions might be influenced by both membrane-bound and soluble C1q-binding proteins.