The innate immune system identifies pathogens by recognizing known elements. This response ultimately leads to the production of proinflammatory substances and the activation of phagocytic neutrophils and macrophages. Activation of the complement system is an important initial even in the response against pathogens. This system includes some thirty different proteins that act together to form a complex. Three different pathways are known to activate the complement. The C3 complement plays a key role in all three pathways leading to the activation of the complement. Produced in the liver, C3 is the most abundant complement protein in the serum. It is composed of two polypeptides, an α and β chain. Cleavage of C3 leads to the production of C3b and C3a.