Complement Cascade System

The complement cascade system is a crucial component of the innate immune response, consisting of more than 20 small proteins (primarily produced by the liver) that circulate in blood and tissue fluids in an inactive form. Upon activation by specific triggers—such as pathogens or injury—these proteins undergo a series of proteolytic cleavages in a highly regulated sequence called a cascade. This process amplifies the immune response and helps eliminate microbes and damaged cells. The main functions of the complement cascade include opsonization, chemotaxis, cell lysis, and agglutination. There are three primary pathways for activating the complement system: classical, lectin, and alternative. Because uncontrolled activation can damage host tissues, several regulatory mechanisms exist. Deficiencies or dysregulation in any part of this system can lead to increased susceptibility to infections or autoimmune diseases. Overactivation may contribute to inflammatory disorders or tissue damage.