Constituent of the membrane attack complex (MAC) that plays a key role in the innate and adaptive immune response by forming pores in the plasma membrane of target cells. Heterotrimer of 3 chains: alpha, beta and gamma. The alpha and gamma chains are disulfide bonded. Component of the membrane attack complex (MAC). MAC assembly is initiated by proteolytic cleavage of C5 into C5a and C5b. C5b sequentially binds C6, C7, C8 and multiple copies of the pore-forming subunit C9 (By similarity). Belongs to the complement C6/C7/C8/C9 family.