Complement C3, C4, and membrane attack complex components (C3/C4/MAC)

The complement system is a critical component of the innate immune system, consisting of a series of plasma proteins that act in a cascade to eliminate pathogens and damaged cells (StatPearls, Complement System). Complement C3 and C4 are central to this process; C3 is the most abundant complement protein and the point where all activation pathways converge (UniProt P01024), while C4 is a key mediator of the classical and lectin pathways (UniProt P0C0L4). The activation of these proteins ultimately leads to the formation of the membrane attack complex (MAC), a pore-forming structure composed of C5b, C6, C7, C8, and C9 that causes direct osmotic lysis of target cells (UniProt P01031, P02748). Dysregulation of these components is a primary driver in diseases such as paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS), where uncontrolled complement activity leads to host cell destruction. Therapeutic agents like eculizumab and pegcetacoplan target specific components of this pathway to prevent tissue damage, though they necessitate precautions against infections by encapsulated bacteria (FDA, Soliris Label; FDA, Empaveli Label).

Other names

Complement systemC3C4Membrane attack complexC5b-9 complexTerminal complement complexTCC

Inhibition of the complement cascade by targeting C3 or C5 to prevent the formation of the membrane attack complex and the release of pro-inflammatory anaphylatoxins.