Stanford researchers have discovered that the human brain is not the closed system scientists once believed. A new study published in Nature reveals that immune cells from the body migrate into the brain as people age. This influx of cells challenges long-standing assumptions about how the brain maintains its defense systems over time.
Previously, experts thought that brain-specific immune cells, known as microglia, remained constant from birth. However, by tracking genetic mutations that occur in blood stem cells over decades, the research team identified that peripheral immune cells eventually move into the brain and adapt to function like local microglia. This process appears to be a unique feature of human aging.
The findings offer potential for new medical treatments. If peripheral immune cells can travel into the brain, scientists may be able to engineer these cells to combat protein buildup linked to neurodegenerative conditions such as Alzheimer’s disease. This approach suggests that the health of bone marrow and blood-forming stem cells plays a larger role in cognitive resilience than previously understood.
This study relied on genetic data from thousands of participants and post-mortem tissue analysis provided by the Stanford Rapid Autopsy Center. By mapping the lineage of immune cells through shared DNA mutations, researchers proved that the brain receives reinforcements from the body throughout a person’s adult life. These insights provide a path toward preventative strategies that target the body to support long-term brain health.