ABSTRACT

Complement is a complex system of enzymes, regulatory proteins, and cell surface receptors that are involved in host defense, infl ammation, and modulation of immune responses. The system provides a fast-acting mechanism for the identifi cation and removal of foreign substances, providing protection before the adaptive immune system can come into play. It is also involved in a wide variety of homeostatic processes including the clearance of immune complexes, effete cells, and cellular debris from damaged tissues. Complement system contributes to infl ammation by inducing local changes in blood fl ow and the infl ux of infl ammatory cells into the affected area. The fragments of complement also induce the release of additional mediators, cytokines, and enzymes from cells near the site of activation. It is a tightly regulated system designed to produce minimum “collateral damage” that might result in tissue damage and loss of function. The pathology that accompanies uncontrolled activation or incomplete performance of complement’s functions is often the result of a defi ciency or impairment of one of the components.