What is the definition or description of: complement?

Immune protein: Complement is a component of the immune system. It is one of the back bones of the immune system that helps fight infections. Complement deficiencies can lead to infections and some complement deficiencies can even led to a disease involving life threatening swelling reactions.

Complement System: The complement system is an important effector mechanism of both humoral and innate immunity. Its functions are to promote phagocytosis of microbes, to stimulate inflammation, and to induce lysis of these organisms. The system is highly complex and comprised of over 50 effector and regulatory molecules. It is activated via one of three pathways: antibody, lectin, or by natural "tick-over" of C3.