Decreased circulating terminal complement component concentration Decreased circulating complement C6 concentration 2020-07-25T08:40:27Z Formation of the MAC is triggered by cleavage of C5 by a C5 convertase, which is followed by sequential interaction of C5b with C6, C7, C8, and C9. Assembly of the MAC on a cellular membrane results in its gradual insertion into the lipid bilayer and the formation of a transmembrane channel, which can kill susceptible cells or transmit activation or apoptotic signals. Concentration of the complement component C6 in the blood circulation below the lower limit of normal.