Immune response to traumatic brain injury

The immune system acts in two waves to repair damage resulting from mild traumatic brain injury, suggests a mouse study published online this week in Nature Immunology.

Mild traumatic brain injury (mTBI) is the most common form of brain injury. Roughly 50% of patients who have suffered mTBI experience damage within the brain meninges, the membranes that cover the surface of the brain, yet little is known about how these injuries heal, and no clinically approved treatment currently exists.

Dorian McGavern and colleagues use a mouse model to study immune cell responses to mTBI and identify a primary inflammatory response involving immune cells that scavenge dead cells within the wound site within the first four days after injury. They then observe a secondary wound-healing response involving other immune cells that gather at the wound’s perimeter before working their way inward, to promote the growth of new blood vessels and clear clotted material. This phase lasts between one week and three weeks. They also find that re-injury during the primary inflammatory phase disrupts the recovery process and can lead to persistent damage.

The authors speculate that the failure to repair meningeal blood vessels by interrupting this two-step process (via re-injury) might account for the post-concussive syndrome that develops in approximately 15% of patients after mTBI.