Activation
Chapter: 2
This is a concept that can be applied either to cells or to plasma proteins. The inflammatory process is potentially dangerous, because it can produce indiscriminate damage to tissues. To minimize this danger, cells and plasma proteins that are potentially the source of injury normally exist in a quiescent, non-active state. Until they are needed, they are harmless. The inflammatory process is designed to marshal its forces locally, i.e., at the site of an inciting stimulus, rather than systemically. This is achieved, in part, through the phenomenon of local activation of inflammatory cells and plasma proteins that can produce proinflammatory mediators. Thus, for example, increased vascular permeability allows plasma proteins that are precursors of inflammatory mediators to leak out into the tissues, where they become activated locally by proteolytic cleavage. Loss of such localization can lead to exceptionally dangerous systemic processes, such as disseminated intravascular coagulation. By the same token, leukocytes are quiescent until they encounter mediators at a site of inflammation that then prime and/or activate them for a variety of functions, such as enhanced phagocytic activity and killing.