By scanning the brains of healthy volunteers, researchers have found long-sought evidence that our brains may drain out some waste through lymphatic vessels, the body’s sewer system. The research team discovered lymphatic vessels in the dura, the leathery outer coating of the brain.
The results, published online in the journal eLife, further suggest that the vessels could act as a pipeline between the brain and the immune system. “We literally watched people’s brains drain fluid into these vessels,” said Daniel Reich, senior investigator at the National Institute of Neurological Disorders and Stroke (NINDS), part of the US National Institutes of Health.
“We hope that our results provide new insights to a variety of neurological disorders,” Reich said. Lymphatic vessels are part of the body’s circulatory system. In most of the body they run alongside blood vessels. They transport lymph, a colourless fluid containing immune cells and waste, to the lymph nodes.
Blood vessels deliver white blood cells to an organ and the lymphatic system removes the cells and recirculates them through the body. The process helps the immune system detect whether an organ is under attack from bacteria or viruses or has been injured. Until very recently, researchers in the modern era found no evidence of a lymphatic system in the brain, leaving some puzzled about how the brain drains waste, and others to conclude that the brain is an exceptional organ.
Brain scans and autopsy studies of brains from non-human primates confirmed the results seen in humans, suggesting the lymphatic system is a common feature of mammalian brains. “These results could fundamentally change the way we think about how the brain and immune system inter-relate,” said Walter Koroshetz, Director, NINDS. The researchers said they plan 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,” Reich said.