Immune cells may heal bleeding brain after strokes

Credit: Courtesy of Aronowski lab, University of Texas Health Science Center, Houston.

While immune cells called neutrophils are known to act as infantry in the body’s war on germs, a National Institutes of Health-funded study suggests they can act as medics as well. By studying rodents, researchers showed that instead of attacking germs, some neutrophils may help heal the brain after an intracerebral hemorrhage, a form of stroke caused by ruptured blood vessels. The study suggests that two neutrophil-related proteins may play critical roles in protecting the brain from stroke-induced damage and could be used as treatments for intracerebral hemorrhage.

“Intracerebral hemorrhage is a damaging and often fatal form of stroke for which there are no effective medicines,” said Jaroslaw Aronowski, M.D., Ph.D., professor, department of neurology, at the University of Texas Health Science Center at Houston, and senior author of the study published in Nature Communications. “Our results are a hopeful first step towards developing a treatment for this devastating form of stroke.”
Accounting for 10 to 15 percent of all strokes, intracerebral hemorrhages happen when blood vessels rupture and leak blood into the brain, often leading to death or long-term disability. Chronic high blood pressure is the leading risk factor for these types of strokes. The initial phase of damage appears to be caused by the pressure of blood leaking into the brain. Over time, further damage may be caused by the accumulation of toxic levels of blood products, infiltrating immune cells, and swelling.

Decades of research suggest that neutrophils are some of the earliest immune cells to respond to a hemorrhage, and that they may both harm and heal the brain. In this study, the researchers found that interleukin-27 (IL-27), a protein that controls the activity of immune cells, may shift the role of neutrophils from harming the brain to helping with recovery.
Injections of IL-27 after a hemorrhage helped mice recover. Days after the strokes, the treated mice had better mobility, including walking, limb stretching and navigating holes in a floor. In contrast, injections of an antibody that blocked natural IL-27 activity slowed recovery. The brains of the mice treated with IL-27 also showed less damage. They had less swelling around the hemorrhages and lower levels of iron and the blood protein hemoglobin, both of which are toxic at high
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