The membrane attack complex (MAC) is the cytolytic end product of the complement cascade, composed of one C5:C6:C7:C8 complex and 12 to 15 C9 molecules (Podack et al. 1982, Biesecker et al. 1993). 12 C9 molecules are represented in this reaction. C9 peptides polymerize to form a ring-shaped transmembrane channel, which causes osmotic lysis of the target cell (Kondos et al. 2010). While formation of a pore is typically associated with necrotic cell death, there is evidence of membrane permeabilization from MACs containing one C9 molecule per C5b–8 complex (Sims et al. 1983).