Système du complément

Complement system, a major part of the innate immunity, is a cascade of soluble plasma proteins and membrane expressed receptors and regulators. Complement system operates in plasma, in tissues, on cell surface, and even within the cell. Complement system plays a key role in host homeostasis, inflammation, and in the defense against pathogens. Complement system can be activated through three main pathways: the classical pathway (CP), the lectin pathway (LP), and the alternative pathway (AP). These pathways depend on different molecules for their initiation, but they converge to generate the same set of terminal effector molecules: anaphylatoxins (C4a/C3a/C5a), the membrane attack complex (MAC), and opsonins (e.g., C3b). Complement system plays a key role in defense against pathogens and in host homeostasis.