The immune system consists of integrated innate and adaptive responses that together form the basis of host defense. The innate immune system is an evolutionarily conserved network against invading microorganisms. It nonspecifically destroys pathogens through activation of the complement system, inflammation, phagocytosis and cellular responses that further activate specific adaptive immune responses. In contrast, the adaptive immune responses are highly antigen-specific processes that neutralize pathogens. The adaptive immune system is activated by the innate immune system and provides a stronger attack by recognizing and “remembering” specific pathogens.