<P> The alternative pathway of the complement system is an innate component of the immune system's natural defense against infections . </P> <P> The alternative pathway is one of three complement pathways that opsonize and kill pathogens . The pathway is triggered when the C3b protein directly binds a microbe . It can also be triggered by foreign materials and damaged tissues . </P> <P> It is initiated by the spontaneous hydrolysis of C3, which is abundant in the blood plasma . "Tickover" occurs through the spontaneous cleavage of the thioester bond in C3 to form C3 (H O). </P>

Alternative pathway of complement activation is initiated by