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Injuries to the brain can disrupt the blood/brain membrane, allowing for inflammation-promoting molecules to enter the bloodstream. If the brain detects these molecules, it will produce more, causing a feedback loop leading to increased pain sensitivity.

Those who have had a traumatic brain injury (TBI) often live with pain and sickness in other parts of the body. Now, Arizona research has connected how a single TBI may suppress a person’s whole immune system and give them pain long after their injury.

Following TBI, researchers found more inflammation-promoting molecules, which increase pain sensitivity while the body suppressed the activity of T-cells, which control immune system response. This correlation fits with TBI patients reporting increased neuropathic pain caused by damage or disease to the nervous system.

Primary experiments on mice were done by Rachel Rowe of Phoenix Children’s Hospital, along with University of Arizona College of Medicine - Phoenix and the University of Kentucky.

“With these mice, we’re pricking them in the foot with really fine filament," said Rowe. "And so, you start off and it doesn’t cause pain and then after the brain injury, the same exact prick causes pain. So it would be, in a human, they have a brain injury and they normally sit at their desk all day and it’s not painful, but now, they have back pain.”

Rowe said the researchers want to learn how long it takes the body to regain T-cells after TBI and if injecting more can help jump-start immune system response.