Groundbreaking research from the National Institutes of Health shows that the brain has lymphatic vessels, allowing it to process “waste” that leaks out of the blood vessels. This finding sheds light on the relationship between the brain and the immune system.
The body’s lymphatic system depends on the lymphatic vessels to absorb, process, and return proteins and tissue fluid, that is, the fluid that surrounds the body’s tissue cells into the bloodstream. The fluid carried by the lymphatic vessels is called “lymph.”
There are three main functions of the lymphatic system: helping to keep blood volume and pressure constant, fighting external agents as part of the immune system, and absorbing fat and fat soluble vitamins.
Lymphatic vessels are distributed throughout our bodies, but thus far, there has been little evidence to suggest that the brain contains them as well .
A study on mice in 2015 showed that lymphatic vessels were present in the central nervous system of rodents, suggesting that the same could be true for humans and other primates.
Now, a team of researchers from the National Institutes of Health, led by scientist Daniel S. Reich, has confirmed that human brains also have lymphatic vessels; specifically, in the dura , or the thickest outer membrane that surrounds the brain.
“We literally saw how people’s brains drain fluids into these vessels. We hope that our results will add new insights to a variety of neurological disorders,” Reich says.
Thanks to MRI
The researchers used non-invasive methods to determine the presence of lymphatic vessels in the human brain.
They worked with five healthy volunteers and three marmosets whose brains were scanned using MRI, after injections with different types of contrast agents, which allows scientists to better visualize the blood vessels in the brain.
They first injected gadobutrol , the molecules of which are small enough to exit the blood vessels into the interstitial compartment of the brain. The MRI scan revealed thinner, more prominent lines, that is, the lymphatic vessels that had collected the contrast agent that had escaped from the blood vessels.
According to scientists, there are lymphatic vessels in the dura that collect fluid elements from the interstitial compartment of the brain.
“Now we can finally see that, like other organs in the body, brain fluid can drain through the lymphatic system,” Reich clarifies.
The authors of the study, which is published in the journal eLife, now hope to investigate what implications these findings have from a clinical perspective. For example, they would like to see how the lymphatic system works in people diagnosed with neuro-inflammatory diseases like multiple sclerosis.
“These results could fundamentally change the way we think about how the brain and the immune system are related,” the authors write.
Referencia: Martina Absinta et al. Human and nonhuman primate meninges harbor lymphatic vessels that can be visualized noninvasively by MRI, eLife (2017). DOI: 10.7554/eLife.29738
