Complement component 3b (C3b) (C3b)

Complement component 3b (C3b) is a large fragment produced by the proteolytic cleavage of C3 by C3 convertases, serving as a central hub in the complement cascade (Source: UniProt P01024). It possesses a highly reactive thioester group that allows it to covalently attach to hydroxyl or amino groups on the surfaces of pathogens or host tissues, a process known as opsonization (Source: Janeway's Immunobiology). Once deposited, C3b acts as a subunit for the alternative pathway C3 convertase (C3bBb) and the C5 convertase, leading to a massive amplification loop and the eventual formation of the membrane attack complex (Source: StatPearls). While C3b deposition is essential for clearing pathogens, its presence on host tissue surfaces is normally restricted by regulatory proteins like Factor H and Decay-Accelerating Factor (Source: PubMed PMCID: PMC6053109). Dysregulation of this process leads to pathological C3b deposition, which triggers inflammation and tissue damage in conditions such as C3 glomerulopathy, atypical hemolytic uremic syndrome, and age-related macular degeneration (Source: NIDDK). Therapeutic strategies targeting C3b include the use of C3 inhibitors like pegcetacoplan, which prevent C3b formation, and engineered regulators like Mirococept or TT30, which specifically target and neutralize C3b on cell surfaces (Source: Nature Reviews Drug Discovery).

Other names

C3bActivated complement component 3Opsonin C3bC3b fragmentC3b on host tissue surfaces

Inhibition of C3 convertase formation, acceleration of C3b decay, and acting as a cofactor for Factor I-mediated cleavage of C3b into inactive forms (Source: PubMed PMCID: PMC6053109).