Immune cells flood into the aging brain, Stanford scientists discover

For decades, scientists have generally viewed the brain's immune system as largely separate from the immune defenses operating throughout the rest of the body. The brain has its own specialized immune cells, along with the blood-brain barrier, which restricts many substances and cells from entering brain tissue.

New research from Stanford is challenging that picture. Scientists found that large numbers of immune cells from elsewhere in the body enter the human brain as people age. The discovery could reshape scientists' understanding of brain aging and may eventually create new possibilities for treating neurological diseases. The work, supported in part by the Knight Initiative for Brain Resilience at the Wu Tsai Neurosciences Institute, was published recently in the journal Nature.

"We usually think of the brain as a closed system," said Julia Belk, a postdoctoral scholar in pathology at Stanford Medicine and first author on the new study. "What we found is that actually a lot of immune cells enter the human brain during aging."

Belk's interest in neuroscience began while she was a graduate student in the Department of Computer Science at Stanford Humanities and Sciences. During that time, she also trained through Sarafan ChEM-H's Chemistry/Biology Interface Predoctoral Training Program. She has described that experience as important in shaping an interdisciplinary approach that combines basic science, computer science, and medicine.