The discovery was made possible by 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 there they were. The impossible existed. “Live imaging of these vessels was crucial to demonstrate their function, and it would not be possible without collaboration with Tajie Harris,” Kipnis noted. Harris is an assistant professor of neuroscience and a member of the Center for Brain Immunology and Glia. Kipnis also saluted the “phenomenal” surgical skills of Igor Smirnov, a research associate in the Kipnis lab whose work was critical to the imaging success of the study.

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. For example, take Alzheimer’s disease. “In Alzheimer’s, there are accumulations of big protein chunks in the brain,” Kipnis said. “We think they may be accumulating in the brain because they’re not being efficiently removed by these vessels.” He noted that the vessels look different with age, so the role they play in aging is another avenue to explore. And there’s an enormous array of other neurological diseases, from autism to multiple sclerosis, that must be reconsidered in light of the presence of something science insisted did not exist.