Complement component 3 (C3) and Complement component 4 (C4) (C3 and C4)

Complement components C3 and C4 are essential proteins of the innate immune system that play a central role in the complement cascade. C3 serves as the convergence point for the classical, lectin, and alternative pathways, where its activation leads to opsonization, inflammation, and the eventual formation of the membrane attack complex. C4 is a key component of the classical and lectin pathways, contributing to the formation of the C3 convertase enzyme complex. These proteins are critical for the defense against pathogens but can also drive tissue damage in autoimmune and inflammatory diseases such as systemic lupus erythematosus (SLE) and paroxysmal nocturnal hemoglobinuria (PNH). Clinically, C3 and C4 levels serve as vital biomarkers for monitoring disease activity and treatment efficacy in immune complex-mediated disorders. Therapeutic strategies targeting these components, particularly C3, aim to suppress pathological complement activation in conditions like geographic atrophy and PNH. However, such interventions carry a significant risk of serious infections, particularly from encapsulated bacteria, necessitating careful patient management and vaccination.

Other names

Complement C3Complement C4C3C4CPAMD1CPAMD2CPAMD3Complement component 3Complement component 4

Inhibition of C3 and C4 cleavage by convertases, preventing the activation and amplification of the complement cascade and the formation of downstream effectors like C3a, C5a, and the membrane attack complex.