The team at the University of Virginia School of Medicine found the brain – like every other tissue – is connected to the immune system through lymphatic vessels, although these had never been detected despite a thorough mapping of the body.
“I really did not believe there are structures in the body that we are not aware of. I thought the body was mapped,” said Jonathan Kipnis, a neuroscience professor and director of the university’s Center for Brain Immunology and Glia. “I thought that these discoveries ended somewhere around the middle of the last century — but apparently they have not.”
The vessels are “well hidden” along a major blood vessel that travels down into the sinuses, the researchers said, and were discovered only after devising a new way to examine the membrane covering the brain on a single microscope slide.
Antoine Louveau, one of the researchers, noticed vessel-like patterns in the immune cells on his slides, and tests revealed they were lymphatic vessels.
“The first time these guys showed me the basic result, I just said one sentence: ‘They’ll have to change the textbooks,’” said Kevin Lee, chair of the university’s neuroscience department.
The discovery could radically alter the study and treatment of neurological diseases because brain diseases can now be understood mechanically instead of abstractly, researchers said.
“It changes entirely the way we perceive the neuro-immune interaction,” Kipnis said. “We always perceived it before as something esoteric that can’t be studied – but now we can ask mechanistic questions.”
For example, Kipnis said scientists already understand that Alzheimer’s disease is the result of protein accumulations in the brain, but the discovery suggests the lymphatic vessels – which change with age – simply don’t remove them efficiently enough.
The findings have been published in the journal Nature, and the researchers said they could radically alter the way scientists understand the central nervous system’s relationship with the immune system.