The complement system is an important mediator of tissue inflammation and injury. It is a family of more than 20 serum and cell-surface proteins and they operate as a cascade of reactions. The IgG immune complexes bind to complement factor C1q and activate the C1 complex, leading to the formation of C3 convertase and the enzymatic cleavage of the central complement component C3. C3 then releases the chemotactic factor C3a and the covalent C3b attaches to the host cells, which is an important step for continued activation of the terminal membrane attack complex, C5b-9, and for the amplification through the alternative pathway. C5b-9 is thought to be.
