Complement is involved in host defence against infection, through: (1) opsonisation of pathogens by C3b, iC3b, C3d, and C4b fragments that are covalently bound to target surfaces to boost phagocytosis [8,10,11,12]; (2) chemotaxis and the activation of leucocytes through the production of potent proinflammatory molecules (the anaphylatoxins C3a and C5a); and (3) direct lysis of bacteria or infected self-cells through the terminal membrane attack complex (MAC, C5b-9) [10]. This evidence concerns the gene C3 and infection.