ABSTRACT
During evolution, an extremely complex system of anti-infectious defenses has emerged. Innate immunity includes anti-infectious defenses that preexist before exposure to an infectious agent. In contrast, adaptive immunity is triggered by the recognition of non-self components, is specific for the inducing agent, and takes several days to develop. The chapter discusses in detail the innate immune mechanisms, with special emphasis on the role of toll-like receptors on phagocytic cells, natural killer cells, and natural antibodies. The humoral immune response is revisited, emphasizing the mechanism involved in the elimination of pathogens. The anti-infectious role of cell-mediated immunity and the related effector molecules are described. The last section of the chapter deals with the microbial mechanism of evasion from the immune response and with abnormal consequences of the antimicrobial immune response.
