The cells that line the blood vessels in our brains are highly selective. By deciding which molecules are allowed in and out of our most important organ, the barrier these cells form is critical for keeping us alive. But how the brain chooses what passes beyond this barrier has been difficult to decipher.

Now, a team led by Janelia Research Campus Group Leader Jiefu Li has developed a new method to examine the proteins lining the inside surface of blood vessels. The technique enables them to uncover two proteins and pathways that play a role in opening and closing the blood-brain barrier—a first step in starting to understand how this important interface works. The study is published in the journal Science.

Uncovering how the blood-brain barrier functions could help scientists figure out what happens when it goes awry, contributing to conditions like multiple sclerosis, encephalitis, and dementia. It could also help researchers develop better ways to deliver medicines that treat neurodegenerative diseases like Alzheimer’s and Parkinson’s, which are often blocked from entering the brain.