During the complement pathways, complement proteins such as C3a, C3b, C4a, C4b, and C5a are produces. These all play a role in inflammation and phagocytosis. C5a, C3a, and C4a stimulate mast cells to release histamine and other vasoactive agents to promote inflammation and diapedesis. C5a also functions as a chemoattractant for phagocytes. Most C3b and C4b binds to antigens on the microbial surface.The phagocytes are then able to bind to the C3b attached to the surface of the microorganism allowing for opsonization (enhanced attachment).