Complement component (C)

The complement component system consists of a complex cascade of more than 30 plasma and cell-surface proteins that play a critical role in the innate immune system (StatPearls, PMID: 30020619). These proteins work through three main pathways—the classical, lectin, and alternative pathways—to promote opsonization, trigger inflammation via anaphylatoxins like C3a and C5a, and directly lyse pathogens through the formation of the membrane attack complex (MAC) (PubMed, PMID: 28438089). Dysregulation or overactivation of specific complement components is linked to various autoimmune and inflammatory diseases, including paroxysmal nocturnal hemoglobinuria (PNH), atypical hemolytic uremic syndrome (aHUS), and generalized myasthenia gravis (UniProt, P01031). Consequently, specific proteins within this system, most notably Complement component 5 (C5) and Complement component 3 (C3), have become high-value therapeutic targets for monoclonal antibodies and small molecules (NIH/NCBI, PMC7138379). Pharmacological intervention typically involves inhibiting protease activity or blocking receptor binding to prevent downstream tissue damage and chronic inflammation. However, because the system is vital for defense against certain bacteria, therapeutic inhibition carries a significant safety concern regarding life-threatening infections by encapsulated organisms such as Neisseria meningitidis (FDA Label, Soliris).

Other names

Complement system proteinsComplement cascadeComplement factorsComplement proteins

Inhibition of C5 cleavage to prevent MAC formation; C3 inhibition to block all activation pathways; Factor D or Factor B inhibition to block the alternative pathway; C5a receptor (C5aR1) antagonism to reduce inflammation.