After the activation of which component do all three complement activation pathways become identical?

The complement system consists of a series of proteins that work together to cascade immune responses. There are three primary pathways for activating the complement system: the classical pathway, the lectin pathway, and the alternative pathway. Each pathway is initiated by different triggers but ultimately converges at a specific point.

After the activation of C3, all three pathways become identical. Once C3 is activated (C3 convertase cleaves C3 into C3a and C3b), it leads to the attachment of C3b to pathogens, marking them for destruction. Subsequently, C3b initiates the formation of the C5 convertase, which is crucial for proceeding to the terminal complement pathway, leading to the assembly of the membrane attack complex (MAC), which can lyse pathogens.

The activation of C2, C4, and C5 serves specific roles in the complement cascade but does not serve as the point of convergence for the pathways. C2 and C4 are primarily involved in the classical and lectin pathways and are required earlier in the complement activation process. C5 is part of the terminal pathway, but it is only after C3 is activated that all pathways lead to the same outcomes in terms of immune response.