Stanford study: aging human brain receives immune-cell reinforcements from the blood
A new Stanford study published in Nature finds that immune cells from the blood cross into the human brain during aging and transform into microglia, the brain's own defense cells. The finding overturns the long-standing assumption that the brain's immune system stays sealed off from the rest of the body.
For decades, scientists believed the brain's immune system operated independently, protected by the blood-brain barrier, with its specialized cells called microglia self-renewing from birth. A new Stanford study published in Nature shows that immune cells from the blood begin crossing into the human brain as early as middle age and transform into microglia themselves. Researchers led by Julia Belk traced the migration by comparing shared DNA mutations between blood and brain immune cells, using samples from the Stanford Rapid Autopsy Center and the University of Washington's Alzheimer's Disease Sequencing Project. The process does not appear to occur in mice or other primates, suggesting it may be a distinctly human feature of aging. The team's earlier work had linked certain blood stem cell mutations to lower Alzheimer's risk. Scientists say the discovery could open the door to engineering peripheral immune cells to target amyloid and tau buildup linked to neurodegenerative disease.