The complement system plays important roles in both innate and adaptive immune response and can produce an inflammatory and protective reaction to challenges from pathogens.
Complement C5 is a central molecule in all three pathways and after cleavage by its convertases, it initiates the terminal pathway in order to generate the cytolytic MAC.C5 is mainly synthesised in the liver as a single polypeptide chain and is present in serum in a concentration of 50-80 μm/ml. Besides, local synthesis of C5 is also supported by other cell types including monocytes/macrophages, neutrophils, fibroblasts, and astrocytes. Before secretion the molecule is glycosylated and secreted into plasma as a 190 kDa glycoprotein consisting of a disulphide linked alpha-chain (111 kDa) and beta-chain (75 kDa).