The complement system can be activated through three pathways: the classical pathway, the lectin pathway, and the alternative pathway. These pathways converge on the activation of C3, a central component of the complement system. Activation of C3 leads to the formation of the C5 convertase, which cleaves C5 into C5a and C5b. C5b initiates the assembly of the membrane attack complex (MAC), which can lyse pathogenic cells.
