Mild Traumatic Brain Injury and Subsequent Acute Pulmonary Inflammatory Response

The influence of moderate-to-severe traumatic brain injury (TBI) on acute pulmonary injury is well established, but the association between acute pulmonary injury and mild TBI has not been well studied. Here, we evaluated the histological changes and fluctuations in inflammatory markers in the lungs to determine whether an acute pulmonary inflammatory response occurred after mild TBI. Mouse models of mild TBI (n=24) were induced via open-head injuries using a stereotaxic impactor. The brain and lungs were examined 6 hours, 24 hours, and 72 hours after injury and compared to sham-operated controls (n=24). Fluoro-Jade B (FJB) staining and Astra blue and hematoxylin staining were performed to assess cerebral neuronal degeneration and pulmonary histological architecture. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis was done to measure inflammatory cytokines. Increased neuronal degeneration and the mRNA expression of IL-6, TNF-α, IL-10, and TGF-β were observed after mild TBI. The IL-6, TNF-α, and TGF-β levels in mice with mild TBI were significantly different compared to those of sham-operated mice 24 hours after injury, and this was more pronounced at 72 hours. Mild TBI induced acute pulmonary interstitial edema with cell infiltration and alveolar morphological changes. In particular, a significant infiltration of mast cells was observed. Among the inflammatory cytokines, TNF-α was significantly increased in the lungs at 6 hours, but there was no significant difference 24 and 72 hours after injury. Mild TBI induced acute pulmonary interstitial inflammation and alveolar structural changes, which are likely to worsen the patient's prognosis.