Inflammation seen in the brain after a stroke, which was till now seen as a negative consequence, may actually help the organ to self-repair by attracting immune cells to the damaged area, scientists have found for the first time.
The findings may lead to new ways of treating stroke in the future, researchers said.
Until now, it was thought that inflammation after a stroke needs to be abolished as soon as possible, researchers said.
"This is in total contrast to our previous beliefs," said Professor Zaal Kokaia from Lund University in Sweden.
When stroke occurs, the nerve cells in the damaged area of the brain die, causing an inflammation that attracts cells from the immune system. Among them are found monocytes - a type of white blood cells produced in the bone marrow.
The monocytes travel to the inflamed area, and here they develop into macrophages that clear out any dead tissue. However, they also secrete substances that help the brain repair the damage, researchers said.
Most stroke patients recover at least partly over time. This spontaneous improvement is well known, but not its exact cause. The researchers now believe that the improvement is partly due to the substances released by the immune cells.
In animal model of stroke, researchers were able to ablate monocytes from the blood.
Mice with decreased number of circulating monocytes were much less successful in their recovery from stroke than mice whose immune system was functioning as normal.
Today's treatment against stroke primarily involves dissolving or removing the blood clot that caused the stroke.
However, such treatments must be performed in the very early phase, which means that most stroke patients are too late to receive it.
A future treatment method could start at some point within the first few weeks, rather than within the first few hours after a stroke.
The researchers have focused on what happens in the brain during this later stage. They were the first to show that, after a stroke, the brain produces new nerve cells from its own stem cells.
They now want to proceed with animal experiments to see if the self-healing can be improved by adding more monocytes to the brain, or by stimulating the production of monocytes in bone marrow.
"This is no less than a paradigm shift within research, as inflammation has in many instances been seen as a purely negative phenomenon that should be combated using any means available," said Professor Olle Lindvall from Lund University.
The study was published in the Journal of Neuroscience.
