C3 and neoplasm: Each of these mechanisms converges at the point of complement alternative 3 (C3) convertase with cleavage into its active subunits C3a and C3b, the defining step in complement activation.39 The alternative pathway can directly induce opsonization of nanoparticles as well as contributing to protein corona formation (discussed next), which activates the classical and lectin pathways for greater complement effect, modifying the nanoparticle surface further.[qv: 35b] Activation of the complement system can result in inflammation,40 immune cell activation,41 and potentially even tumor growth.42