Complement Activation

**Semantic type:** Molecular Function

**Definition:** Any physiologic process in which a protease directs the cleavage of complement components C4, C2, or factor B which then form the C3 and C5 convertases for the classical and lectin pathways, respectively. This process is involved in direct lysis of target cells, immune adherence and phagocytosis of pathogens, and recruitment and activation of immunocompetent cells.