Activation of the complement cascade by the classical or alternative pathway leads to the cleavage of complement fragments and the formation of biologically active complexes. The C5b fragment aggregates with complement proteins C6, C7, C8 and C9, resulting in the polymerization of the membrane attack complex (MAC). MAC lyses cells by inseing into the lipid bilayer, forming a pore and destroying the permeability barrier of the plasma membrane. Kallikrein and kinins are formed following tissue trauma and mediate pain transmission.