Pathogenesis of Infectious Diseases and Mechanisms of Immunity

The sequence of steps in the disease process caused by pathogenic microbes is known as pathogenesis. Pathogenesis encompasses the entire host-pathogen interaction and requires an understanding of the pathogen and pathogen-associated factors that contribute to the disease process as well as host responses that can be protective, circumvented, or contribute to disease pathology. During this process, microbes must evade innate and/or adaptive host defenses and often have developed molecular strategies to subvert host defenses including secretion of toxins that kill host cells or enzymes that degrade immune effectors, such as antibodies, or involve secretion of effector proteins that engage in molecular interactions with host cell targets in order to modulate cellular processes/immune responses that favor survival of the pathogen. In some cases, the damage to the host involves over-reactive response to the microbe that leads to tissue damage, such as overproduction of inflammatory cytokines as occurs in sepsis. Vaccines often do not prevent infection, but vaccine-induced antibodies can block attachment of the microbe to the host, prevent invasion, neutralize a secreted toxin, or enhance microbial killing. This chapter defines pathogenesis with respect to infectious diseases and exploresfeatures of pathogenesis and how vaccines and vaccine-induced immune mechanisms interrupt disease pathogenesis.