C1s, Human, mAb M81

Monoclonal antibody M81 reacts with an epitope on human C protein activated C1s, a subcomponent of the first component of C (C1). Activated C1s is a glycosylated single-polypeptide zymogen, MW 85 kD. Activation of the proenzyme C1s occurs through cleavage by the active form of C1r. The activated protease, activated C1s, consists of a disulfide-linked H chain and a L chain. Activated C1s is a serine protease and its catalytic site is located in the L chain. Activation of the classical C pathway is triggered by activated C1s which cleaves C4 and C2 to form the C3 convertase, C4bC2a. The epitope recognised by the antibody M81 is domain IV and/or V of the gamma-domain of activated C1s. Monoclonal antibody M81 blocks C4 activation and C4 binding to activated C1s. The antibody reacts around the binding site of C1s and reacts with both active and inactive C1s.