The role of neuroinflammation in traumatic brain injury

In industrialized countries, traumatic brain injury (TBI) still represents the leading cause of death and persisting neurologic impairment among young individuals < 45 years of age. Patients who survive the initial injury are susceptible to sustaining secondary cerebral insults which are initiated by the release of neurotoxic and inflammatory endogenous mediators by resident cells of the central nervous system (CNS). The presence of hypoxia and hypotension in the early resuscitative period further aggravates the inflammatory response due to ischemia/reperfusion-mediated injuries. These are induced by the intrathecal generation of free radicals and activation of the complement cascade. Posttraumatic neuroinflammation is further exacerbated by the subsequent intracranial recruitment of blood-derived immunocompetent cells, leading to secondary cerebral edema and increased intracranial pressure. The profound endogenous neuroinflammatory response after TBI, which is phylogenetically aimed at defending the CNS from invading pathogens and repairing lesioned tissue, is, in large part, responsible for the development of secondary brain damage and adverse outcome. However, aside from these deleterious effects, posttraumatic inflammation mediates neuroreparative mechanisms after TBI as well. This "dual effect" of neuroinflammation has been the focus of extensive experimental and clinical research in the past years and has led to an expanded basic knowledge on the cellular and molecular mechanisms which regulate the intracranial inflammatory response after trauma. The present article provides an up-to-date overview on the pathophysiological mechanisms of neuroinflammation after TBI. New potential therapeutic strategies for reducing the extent of secondary brain damage after neurotrauma are discussed.