Indicators
A protein complex composed of 18 complement component 1q (C1q) subcomponent chains: six C1qA, six C1qB and six C1qC. The C1q complex is part of the complement component C1 complex (C1 complex) and undergoes confirmational rearrangement following binding of pentraxins or antigen-antibody complexes that include either immunoglobulin M (IgM) or several IgG molecules. These confirmational changes activate the C1r chains of the C1 complex, which, in turn, cleaves C1s chains of the C1 complex. Following C1s cleavage, the C1 complex can proteolytically activate C2 and C4 and promotes formation of C3-convertase, which cleaves C3 and activates the classical complement pathway.
Indicators
Complement component-4 (1744 aa, ~193 kDa) is part of the complement cascade, which mediates the innate immune response to infection. The full length protein is a precursor that is secreted as a trimeric molecule containing an alpha, beta and gamma chain. When the complement cascade is initiated, the protein is cleaved. This proteolysis releases both the alpha chain, C4 anaphylatoxin, which stimulates inflammation, and a dimer of the beta and gamma chains, which mediates the interaction between the antigen-antibody complex and other complement components.
Article
Research record from Clin Microbiol Infect, 2026-03-27. PMID 41905558.
Glossary Term
Problem associated with the degree to which an antibody or antigen participates in cross reactions.
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Tests
The determination of the Cryptococcus antigen present in a sample.
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Tests
The determination of the amount of antigen from any member of the genus Cryptosporidium present in a sample.
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Tests
The determination of the cytomegalovirus antigen present in a sample.
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Tests
A measurement of the Dermatophagoides farinae antigen IgE antibody in a biological specimen.
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Tests
The determination of the amount of Dermatophagoides pteronyssinus antigen IgG4 antibody present in a sample.
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Article
Research record from Bioanalysis, 2026-10-29. PMID 42953976.
Article
Research record from Sci Rep, 2026-06-01. PMID 42225882.
Article
Research record from ACS Sens, 2026-10-13. PMID 42867157.
