Complement system activation product

Complement system activation products are protein fragments generated upon the cascade activation of the complement system, a central part of innate immunity[1][3][5]. These fragments mediate multiple immune responses—such as opsonization (coating pathogens for phagocytosis), chemotaxis (attracting immune cells), inflammation induction (via anaphylatoxins C3a, C5a), direct lysis of pathogens (MAC), and modulation of coagulation and tissue repair[4][5]. Dysregulation or overproduction of these fragments is implicated in a wide range of diseases, including autoimmune conditions, sepsis, and thrombotic disorders. Therapeutic interventions often target specific complement products (like C5a or C5) to modulate the immune response in various diseases. The term "complement system activation products" refers to a group of molecules rather than a discrete molecular entity, and thus is not optimal as a canonical drug target[3][5][6].

Other names

Complement activation fragmentsAnaphylatoxins (subset: C3a, C5a)Opsonins (C3b, C4b)

Mechanisms of action for drugs targeting complement activation products include inhibition of complement cleavage or activation (e.g., Eculizumab prevents C5 cleavage to C5a/C5b), competitive inhibition at the receptor level (e.g., C5aR antagonism), and enhancement of regulatory protein activity (e.g., C1-inhibitor).