By scanning the brains of healthy volunteers, researchers at the National Institutes of Health saw the first, long-sought evidence that our brains may drain some waste out through lymphatic vessels, the body’s waste system. The results further suggest the vessels could act as a pipeline between the brain and the immune system.
Daniel S. Reich, M.D., Ph.D., senior investigator at the NIH’s National Institute of Neurological Disorders and Stroke (NINDS) and the senior author of the study published online in eLife. “We hope that our results provide new insights to a variety of neurological disorders.”
Researchers use primarily magnetic resonance imaging (MRI) to investigate multiple sclerosis and other neurological disorders which are thought to involve the immune system. Led by post-doctoral fellows, Martina Absinta, Ph.D. and Seung-Kwon Ha, Ph.D., along with researchers from the National Cancer Institute, the team discovered lymphatic vessels in the dura, the leathery outer coating of the brain.
In 2015, two studies of mice found evidence of the brain’s lymphatic system in the dura. Coincidentally, that year, Dr. Reich saw a presentation by Jonathan Kipnis, Ph.D., a professor at the University of Virginia and an author of one of the mouse studies.
“I was completely surprised. In medical school, we were taught that the brain has no lymphatic system,” said Dr. Reich. “After Dr. Kipnis’ talk, I thought, maybe we could find it in human brains?”
To look for the vessels, Dr. Reich’s team used MRI to scan the brains of five healthy volunteers who had been injected with gadobutrol, a magnetic dye typically used to visualize brain blood vessels damaged by diseases, such as multiple sclerosis or cancer. The dye molecules are small enough to leak out of blood vessels in the dura but too big to pass through the blood-brain barrier and enter other parts of the brain.
“These results could fundamentally change the way we think about how the brain and immune system inter-relate,” said Walter J. Koroshetz, M.D., NINDS director.
Dr. Reich’s team plans to investigate whether the lymphatic system works differently in patients who have multiple sclerosis or other neuroinflammatory disorders.
“For years we knew how fluid entered the brain. Now we may finally see that, like other organs in the body, brain fluid can drain out through the lymphatic system,” said Dr. Reich.