Complement component 1 complex (C1)

The **Complement component 1 complex (C1)** is a multiprotein assembly initiating the classical complement pathway, comprising C1q (recognition molecule), and two serine proteases C1r and C1s, forming the C1qC1r2C1s2 structure[1][2][5]. Activation occurs when C1q binds antigen–antibody complexes or other ligands, leading to proteolytic activation of C1r and then C1s. Activated C1s cleaves complement proteins C4 and C2, driving downstream immune responses and inflammation. Beyond complement activation, C1 complex is involved in cell debris clearance, modulation of immune and cellular functions, and interacts with diverse molecules including cell surface receptors and apoptotic cells, illustrating its role as a versatile node in immunity and cellular biology[2][3][4]. Pathological dysregulation of C1 or its subunits is linked to a range of diseases including autoimmunity and chronic inflammatory conditions, making C1 a critical biomarker and therapeutic target[4].

Other names

Complement C1C1 complexC1qC1r2C1s2C1qr2s2C1qC1rC1s

Inhibition of C1 activation (blockade of subunit interactions, often targeting the protease activity of C1r or C1s, or the recognition by C1q); Prevention of complement cascade initiation