Three steps 1. Recognition(C1 activation The components involved Clg, clr, cls Ag+Ab→IC→ bind o1q→C1r→C1s→C1 2. Activation The components involved C4, C2 and c3 (1C4 and C2 activation, generation of C3 convertase (2 generation of C5 convertase 3. Attack(terminal pathway) The components involved C5, C6, C7, C8, C9 the membrane attack complex MAC C5b6789Three steps 1. Recognition ( C1 activation ) The components involved：C1q, C1r, C1s Ag + Ab→IC→bind C1q→C1r→C1s →C1 2. Activation The components involved: C4, C2 and C3 (1) C4 and C2 activation, generation of C3 convertase (2) generation of C5 convertase 3. Attack (terminal pathway) The components involved: C5, C6, C7, C8, C9 the membrane attack complex (MAC): C5b6789