C1s

The complement system is a well-known effector mechanism of the immune response, providing not only protection against pathogens and other harmful agents but also recovery from injury. The complement pathway comprises a number of proteins that typically exist in the body in an inactive form. The classical complement pathway is triggered by activation of the first component of complement, referred to as the CI complex, which consists of Clq, Clr, and Cls proteins. Upon binding of CI to an immune complex or other activator, the Cls component, a diisopropyl fluorophosphate (DFP)-sensitive serine protease, cleaves complement components C4 and C2 to initiate activation of the classical complement pathway. The classical complement pathway appears to play a role in many diseases and disorders.