In a discovery that overturns decades of textbook teaching, researchers have found that the brain is directly linked to the immune system by vessels previously thought not to exist. The discovery could have profound implications for diseases from autism to Alzheimer's to multiple sclerosis, researchers said.

"Instead of asking, 'How do we study the immune response of the brain?' now we can approach this mechanistically," said Jonathan Kipnis, professor in the University of Virginia Department of Neuroscience and director of UVA's Center for Brain Immunology and Glia.

"It changes entirely the way we perceive the neuro-immune interaction. We always perceived it before as esoteric that can't be studied. But now we can ask mechanistic questions," he said.

The discovery made with the work of Antoine Louveau, a postdoctoral fellow in Kipnis' lab. The vessels were detected after Louveau developed a method to mount a mouse's meninges - the membranes covering the brain - on a single slide so that they could be examined as a whole. After noticing vessel-like patterns in the distribution of immune cells on his slides, he tested for lymphatic vessels and found them.

As to how the brain's lymphatic vessels managed to escape notice all this time, Kipnis described them as "very well hidden" and noted that they follow a major blood vessel down into the sinuses, an area difficult to image.

"It's so close to the blood vessel, you just miss it. If you don't know what you're after, you just miss it," he said. The unexpected presence of the lymphatic vessels raises a tremendous number of questions that now need answers, both about the workings of the brain and the diseases that plague it, researchers said.