Complement factor D is a component of the alternative pathway of the complement system and part of the innate immune system, playing a vital role in the initiation and amplification of complement activation, in order to defend against infection (Barratt and Weitz). A serine protease belonging to the S1 peptidase family, complement factor D is secreted by adipocytes into circulating blood, and is also expressed by macrophages and monocytes (White et al.). In the initiation phase of the complement pathway, complement factor D cleaves complement factor B (bound to component C3) to produce a complex known as C3 convertase. During the amplification phase, complement factor D cleaves complement factor B (bound to component C3b) to produce the C3bBb convertase, and is involved in the propagation of complement activation. In addition to its immunological role, complement factor D is involved in other physiological processes, such as the efficient clearing of damaged cell debris by phagocytes following acute liver injury (Cresci et al.). Complement factor D deficiency is associated with an increased susceptibility to pathogens like Neisseria meningitidis (Biesma et al.). This protein contains a His-residue tag at the carboxyl end of the polypeptide chain. For consistency and reproducibility across your applications, complement factor D from STEMCELL comes lyophilized with ≥ 94% purity, and is verified by LAL analysis to ensure endotoxin levels are ≤ 1.0 EU/μg protein.