Properdin or Factor P is the only known positive regulator of complement activation that stabilizes the alternative pathway convertases. It is found in the blood serum of more complex animals. Properdin is a gamma globulin protein composed of multiple identical protein subunits with a separate ligand-binding site. It is known that it participates in some specific immune responses. It plays a part in tissue inflammation as well as the engulfing of pathogens by phagocytes. In addition it is known to help to neutralize some viruses.