What is the Origin of Complement C3?

The term Complement refers to the system's ability to "complement" or enhance the action of antibodies and phagocytic cells in fighting infection. C3 simply denotes the third component of this complex cascade to be historically identified and characterized. This protein is a foundational element of innate immunity, acting as a crucial bridge to the more specific adaptive immune response.

What is the Mechanism of Complement C3?

C3 can be activated through the classical, alternative, or lectin pathways, all converging on its enzymatic cleavage. The resulting C3b fragment covalently binds to the surface of a pathogen or abnormal host cell, a process called opsonization, which tags the target for efficient engulfment by phagocytes. Concurrently, the smaller C3a fragment acts as a potent anaphylatoxin, triggering mast cell degranulation and promoting localized inflammatory responses to recruit other immune cells.

Complement C3 ∞ Area

Complement C3

Meaning

Complement C3 is a highly abundant, central protein component of the innate immune system’s complement cascade, which is essential for host defense against pathogens and the clearance of damaged cells. Upon activation, this protein is rapidly cleaved into powerful fragments, C3a and C3b, which are responsible for mediating inflammation, marking targets for destruction, and facilitating the direct lysis of foreign cells. Measuring its level is a key clinical marker of active immune system engagement and inflammatory status.