How Inflammation Spreads Through the Brain

After a traumatic brain injury, inflammation can spread throughout the brain and cause long-lasting damage. Now, in a new study done in mice, researchers have identified a way that this inflammation can spread.

It turns out that inflammation is spread by the release of tiny sacks filled with inflammatory chemicals from immune cells in the brain.

These sacks — called microparticles — can spread throughout the brain, causing inflammation in locations far from the original site of the injury, according to the study, which was published today (March 8) in the Journal of Neuroinflammation.

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The study was a proof-of-concept study, and more research is needed to understand the role of these microparticles in the brain, as well as to determine if they have the same effect in humans. [10 Things You Didn't Know About the Brain]

Studies in humans that used brain scans, however, have shown that inflammation can spread through the brain following an injury, even to locations far from where the injury occurred, said senior study author Dr. Alan Faden, a neurologist and professor of anesthesiology at the University of Maryland School of Medicine.

And other studies, done during autopsies, have found that patients who had head injuries but died of other causes many years later showed chronic inflammation throughout their brains, Faden told Live Science.

The question was, "How did [the inflammation] get there?" Faden said. The new study could explain it, he said.

In the study, Faden and his team looked at microparticles in mice.

They began by showing that microparticle levels increased in the blood of mice after they had traumatic brain injuries, the researchers found. All microparticles have "fingerprints" that show what type of cell they came from; in this case, the microparticles came from immune cells in the brain.

Next, the researchers looked at the effects of microparticles on these immune cells in the brain, called microglia.

In a lab experiment, the researchers took microparticles from mice with brain injuries and added them to a petri dish with normal microglial cells. The microparticles activated the microglia, and prompted them to release their own microparticles, the researchers found.

Finally, the researchers injected microparticles into the brains of healthy mice, and found that they caused inflammation in the brain, both near the site of the injection and elsewhere in the brain.

Taken together, the experiments suggest that microparticles are released from the microglial cells after a brain injury, and these microparticles can travel throughout the brain, activating more microglia along the way.

The research looks at "a different way of how inflammation propagates in the brain…after various injuries or disease," Faden said.

And the findings could have major implications for future research.

For example, scientists could collect microparticles from people's blood at different points after a head injury and see if they could be used as a biomarker to assess the severity of the injury, Faden said. "Microparticles are small enough that they can go through the blood-brain barrier, so they can go from blood to brain and brain to blood," he said.

In addition, the microparticles could be drug targets, Faden said. One thing to look at is whether you can target them, and prevent them from activating other immune cells, he said.

Originally published on Live Science.