Increased CD3 Immunoreactive Cells Persist Chronically in the Brain Parenchyma in Association with Focal Cortical Contusion following Experimental TBI

While a history of TBI is associated with an increased risk of neurodegenerative disease, associated mechanisms remain largely unknown. Neuroinflammation is commonly implicated as playing a role in progressive neurodegeneration in general, yet little is known about the adaptive response of neuroinflammation in TBI or how it may contribute to progressive pathologies. To parse out components of the adaptive response, we assessed for intraparenchymal T-cell infiltration in two different translational large animal (swine) models of TBI, inertial injury and focal contusion. We characterized the extent and distribution of T cells post-injury and their association with blood-brain barrier disruption and axonal pathology. T-cell infiltration following focal TBI followed a spatiotemporal progression from gray matter at 72 hours to both gray and white matter at 6 months post-injury, consistent with recruitment into the parenchyma and then white matter. Inertial injury did not lead to substantial T-cell infiltration despite BBB breakdown and axonal pathology. We did not find a spatial correlation between blood-brain barrier breakdown or axonal pathology and T-cell infiltration in focal TBI. These data suggest that there is an active adaptive response to TBI, particularly in tissue proximal to contusions. A large animal model that reproducibly demonstrates chronic T-cell infiltration may allow for examination of the downstream effects of the adaptive response to TBI, and whether targeting this adaptive response may reduce chronic inflammation and improve recovery.