Neutrophil priming and activation in the pathogenesis of postinjury multiple organ failure.

The continuing study of multiple organ failure (MOF) has led to the development of inflammatory models of tissue injury in contrast to earlier infectious models. This change of focus is in response to more recent clinical observations suggesting that postinjury MOF frequently occurs in the absence of infection. In the alternative "two-hit" inflammatory model that has been proposed, the initial traumatic insult "primes" the inflammatory response such that a delayed, otherwise innocuous, inflammatory insult triggers an exaggerated response. The neutrophil (PMN), being uniquely equipped to cause oxidative tissue injury via the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase system, has been implicated as an early pivotal player in this model of postinjury MOF. Similar to the "two-hit" inflammatory model, circulating PMNs respond to proinflammatory mediators by becoming primed for enhanced superoxide anion (O2.) production and by increasing adherence to endothelium of organs that are susceptible to PMN-mediated injury. Subsequent proinflammatory insults promote further neutrophil sequestration and activate them for enhanced release of O2.-. The resulting tissue injury can be perpetuated and lead to eventual end-organ damage and failure. In terms of the NADPH oxidase system, PMN priming and activation by various agonists have been well documented in vitro and lead to increased endothelial damage. PMN priming and activation are also operable in an in vivo model of gut ischemia/reperfusion, a surrogate of shock and trauma resuscitation, leading to distant organ damage. Finally, in clinical studies of severely injured trauma patients, PMN priming and activation sequences identify patients at risk for developing MOF with its associated high mortality. Further characterization of the mechanisms that regulate PMN priming and activation in the trauma patient is necessary for the development of new therapeutic interventions designed to block deleterious PMN responses which lead to MOF while not compromising beneficial PMN functions of host defense and tissue repair.