Non-classical monocytes mediate secondary injury neurocognitive outcome and neutrophil infiltration after Traumatic Brain Injury

摘要

Traumatic brain injury (TBI) results in rapid recruitment of leukocytes into the injured brain. Monocytes constitute a significant proportion of the initial infiltrate and have the potential to propagate secondary brain injury or generate an environment of repair and regeneration. Monocytes are a diverse population of cells (classical, intermediate and non-classical), with distinct functions, however, the recruitment order of these subpopulations to the injured brain is largely remains unknown. Thus, we examined which monocyte subpopulations are required for the generation of early inflammatory infiltrate within the injured brain, and whether their depletion attenuates secondary injury or neurocognitive outcome. Global monocyte depletion correlated with significant improvements in brain edema, motor coordination, and working memory, and abrogated neutrophil infiltration into the injured brain. However, targeted depletion of classical monocytes alone had no effect on neutrophil recruitment to the site of injury, implicating the non-classical monocyte in this process. In contrast, mice that have markedly reduced numbers of non-classical monocytes (CX3CR1^−/−) exhibited a significant reduction in neutrophil infiltration into the brain after TBI as compared to control mice. Our data suggest a critical role for non-classical monocytes in the pathology of TBI in mice, including important clinical outcomes associated with mortality in this injury process.