Complement components C3a, C5a, and C5b-9 membrane attack complex (C3a/C5a/MAC)

The complement system is a critical component of the innate immune response, consisting of a cascade of proteins that facilitate the clearance of pathogens and damaged cells (StatPearls: Complement System). The components C3a, C5a, and the C5b-9 membrane attack complex (MAC) are the primary effector molecules generated during this cascade (UniProt: P01024, P01031). C3a and C5a are small peptide fragments known as anaphylatoxins that mediate potent inflammatory responses, including the recruitment of immune cells and increased vascular permeability, by binding to specific G protein-coupled receptors (Nature Reviews Drug Discovery, 2018). The C5b-9 complex, or MAC, is a multi-protein assembly that inserts into the membranes of target cells, creating pores that cause osmotic lysis and cell death (StatPearls: Complement System). Dysregulation of these effectors is central to the pathology of several rare and severe diseases, such as paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS) (Seminars in Immunology, 2019). Therapeutic strategies targeting these components include monoclonal antibodies that prevent the cleavage of C5, direct inhibitors of C5a, and receptor antagonists, all of which aim to reduce complement-mediated tissue damage while requiring careful management of infection risks (FDA Labels: Soliris, Tavneos).

Other names

Anaphylatoxins and Membrane Attack ComplexTerminal Complement ComplexTCCMACC5b-9

Inhibition of C5 cleavage to prevent C5a and C5b-9 formation; antagonism of the C5a receptor (C5aR1); direct neutralization of C5a; inhibition of C3 cleavage to prevent C3a and downstream C5 activation; inhibition of alternative pathway factors (Factor B, Factor D) to reduce terminal pathway activation.