Title: complement system
Long Title: IUPAC Gold Book - complement system
DOI: 10.1351/goldbook.13033
Status: current

Definition
Group of serum proteins with the capacity to interact with each other when activated in a chain reaction which results in formation of a lytic complex and the release of several biologically active peptides of low relative molecular mass (anaphylatoxins).

Note
The system can be activated by antigen–antibody complexes (classical pathway) and by other components, e.g., bacteria (alternative pathway). As an effector mechanism of the humoral immune response, the activated complement system facilitates opsonization, phagocytosis, and lysis of cellular antigens.

Related Terms
- alternative pathway: https://goldbook.iupac.org/terms/view/12866
- anaphylatoxins: https://goldbook.iupac.org/terms/view/12873
- classical pathway: https://goldbook.iupac.org/terms/view/13011
- humoral immune response: https://goldbook.iupac.org/terms/view/13235
- opsonization: https://goldbook.iupac.org/terms/view/13526
- phagocytosis: https://goldbook.iupac.org/terms/view/13562

Source
- PAC, 2012, 84, 1113. 'IUPAC glossary of terms used in immunotoxicology (IUPAC Recommendations 2012)' on page 1147 (https://doi.org/10.1351/PAC-REC-11-06-03)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/13033/html
- json: https://goldbook.iupac.org/terms/view/13033/json
- xml: https://goldbook.iupac.org/terms/view/13033/xml

Citation: Citation: 'complement system' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.13033
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Accessed: 2026-06-30T22:59:42+00:00