https://doi.org/10.1351/goldbook.13033
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.