Fig. 1

Timeline of cellular response after TBI. a Upon TBI, cellular damage results in the rapid release of damage-associated molecular patterns (DAMPs) that prompt resident cells to release cytokines and chemokines. These signals quickly recruit neutrophils, which aid in the containment of the injury site and promote the removal of debris and damaged cells. As neutrophil numbers begin to decline after days, infiltrating monocytes and activated microglia and astrocytes begin to accumulate around the site of injury to perform reparative functions. Depending on the severity of the brain injury, T and B cells can also be recruited to sites of brain pathology at later time points in the response (5-7 days post-injury). Severity of the brain damage (red dashed) depends on the secondary injury mainly caused by the fluctuating microglia especially the M1-type (neurotoxic) microglia as shown by green dashed lines. b Schematic representation to highlight the behaviour of cells after TBI