Complement

The complement system is a biochemical pathway involved in both innate and adaptive immune responses. There are four main functions of the complement system; lysis of microorganisms, promotion of phagocytosis, triggering inflammation and immune clearance.

There are three pathways that can activate the complement system; the classical complement pathway (in response to IgG- or IgM-antigen complexes), the alternative complement pathway (spontaneous activation) and the mannose-binding lectin pathway (in response to lectin residues on pathogen cell surface membranes). All three pathway generate variants of C3 convertase, which cleaves C3 into C3a and C3b. C3a and C3b activate a series of further cleavage events that activates the complement cascade. This leads to immune defence responses such as degranulation of mast cells, increasing vascular permeability and initiation of the membrane attack pathway.

Deregulation of the complement system would be extremely damaging to the host, so it is tightly regulated by complement control proteins. These regulatory proteins are found in much higher concentrations that complement proteins themselves and prevent complement system activation in 'self' tissues. The complement system has been implicated in many autoimmune disorders, including systemic lupus erythematosus, multiple sclerosis and arthritis, and more recently has been suggested to have a pathophysiological role in Alzheimer's and other neurodegenerative disorders.

Complement Gene Data