Category:Complement activation

Complement is a collection of circulating soluble proteins mostly produced by the liver. Complement can be activated the presence of pathogens or Ab (or Ab-like MBL or CRP).

The final outcome is the killing of pathogen (either directly via MAC or enhanced phagocytosis) and the induction of the inflammatory response.

There are 3 pathways of complement activation. All include the key step of the formation of C3 convertase, which cleaves C3 → C3a + C3b. The binding of C3b to the pathogen surface targets it for phagocytosis or the assembly of the C5 convertase. C3a and C5a are mediators of inflammation. C5a is a chemoattractant for neutrophils.
 * Alternative = spontaneous breakdown of C3
 * Lectin
 * Classical