Following head injury, the protective lining that surrounds the brain may get a little help from its friends: immune cells that spring into action to assist with repairs. In a new study, scientists from the NIH watched in real-time as different immune cells took on carefully timed jobs to fix the damaged lining of the brain, also known as meninges, in mice. These results may help provide clues to the discovery that the meninges in humans may heal following mild TBI and why additional hits to the head can be so devastating. Within the first day of injury, immune cells from the blood called inflammatory monocytes entered the core of the injured meningeal tissue and started clearing away dead cells. These cells were assisted a few days later by a different type of blood monocyte that worked around the lesion edge to help rebuild damaged blood vessels, which were completely restored and fully functional within a week.
Dr. McGavern’s team found that while most patients had repaired their leaky blood vessels within 20 days, 17 percent of patients still showed leakage on their MRI scans three months after injury, indicating ongoing meningeal damage and incomplete recovery. The researchers also found that the timing of a second head injury has a significant impact on the repair process in mice. A second injury experienced within one day of the first TBI led to additional inflammation and the wound healing phase of repair, during which blood vessels are fixed, did not occur. However, if the re-injury occurred after a few days, once the wound healing phase had already begun, there was no effect on the meningeal repair process and blood vessels were rebuilt normally.