IMMUNOLOGY

Detailed explanation-1: -Once activated, the C1s enzyme acts on the next two components of the classical pathway, cleaving C4 and then C2 to generate two large fragments, C4b and C2b, which together form the C3 convertase of the classical pathway.

Detailed explanation-2: -Recent studies suggest broad C1 functions beyond the complement system. C1q binds to the Frizzled receptors to activate C1s, which cleaves lipoprotein receptor-related protein 6 to trigger aging-associated Wnt receptor signaling. C1q binds to apoptotic cells and the activated C1 proteases cleave nuclear antigens.

Detailed explanation-3: -The Classical Pathway of Complement Activation The classical pathway is initiated by the binding of the C1 complex (C1q, C1r and C1s) to bound antibody. C1r activates C1s which first cleaves C4 and then cleaves C2 leading to the formation of the classical pathway C3 convertase (C4bC2a).