Complement is a system of factors occurring in blood and tissue fluids that are activated characteristically by antibody-antigen interactions. The consequences of the activation of complement are the release of products which mediate a number of biologically significant events. In common with other major humoral effector systems, including the clotting, kinin and fibrinolytic systems, complement is composed of a series of discrete proteins present as precursor molecules. These, when activated by a variety of stimuli, result in a reaction sequence which proceeds in a predefined direction. Complement, like the other triggered enzyme systems, displays the inherent amplification kinetics of a chain reaction and each protein product becomes a catalyst for the next in sequence. The net result is a cascade phenomenon during which intermediate proteins and breakdown products possessing potent biological activity are produced. The whole system is under stringent internal control and regulation, but initial activation produces a rapid local inflammatory response at the activation site. The products of complement activation comprise all the major functions necessary for acute inflammation and their release in vasodilatation, increased capillary permeability, neutrophil chemotaxis and subsequent particle phagocytosis.
KeywordsSystemic Lupus Erythematosus Immune Complex Complement Activation Bullous Pemphigoid Classical Pathway
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