The immune system in traumatic brain injury

•TBI is the main cause of death and disability in children and young adults.•Secondary brain injury may occur for month and years after injury.•Cognitive decline after TBI may have an inflammatory component.•Peripheral leukocytes are detrimental while microglia promote regeneration.•Future therapeutic strategies should be aware of the dual aspect of inflammation.

Traumatic brain injury (TBI) is the major cause of death in children and young adults and one of the major reasons for long-term disability worldwide, however, no specific clinical treatment option could be established so far. This is surprising since it is well known that following the initial mechanical damage to the brain a plethora of delayed processes are activated which ultimately result in additional brain damage. Among these secondary mechanisms, acute and chronic activation of the innate and adaptive immune system is increasingly believed to play an important role for the pathogenesis of TBI. Understanding these processes may results in new, clinically applicable therapeutic options for TBI patients.