# Stanford Study Finds Blood Immune Cells Flood Into the Aging Human Brain

*2026-08-18 10:00 UTC · Science · 1 min read*

> Stanford researchers found that blood-borne immune cells enter the human brain starting in middle age and convert into microglia, a process unique to humans that could reshape treatment of neurodegenerative disease.

Stanford Medicine researchers have found that immune cells from the bloodstream cross into the human brain as early as middle age, challenging the long-standing assumption that the brain's immune system is sealed off from the rest of the body. The peripheral cells appear to transform into microglia, the brain's resident immune defenders.

The team, led by postdoctoral scholar Julia Belk with senior authors Siddhartha Jaiswal and Howard Chang, compared DNA from matched blood and brain tissue samples from the Stanford Rapid Autopsy Center and the University of Washington's Alzheimer's Disease Sequencing Project. Shared genetic mutations let them trace which microglia originated in the brain and which arrived from circulating blood. The migration pattern does not appear to occur in mice or non-human primates, making it a distinctly human trait.

"We usually think of the brain as a closed system," said Belk. "What we found is that actually a lot of immune cells enter the human brain during aging." The team says the finding, published in Nature, could open a new route for treating neurodegenerative disease: engineering these incoming peripheral cells to clear harmful protein buildup before it damages neurons.

## Sources

- [sciencedaily.com](https://www.sciencedaily.com/releases/2026/08/260814011033.htm)
- [news.stanford.edu](https://news.stanford.edu/stories/2026/08/aging-brain-immune-system-research)

---
TechTools News · https://techtools.cz/tools/news/article/2210-stanford-study-finds-blood-immune-cells-flood-into-the-aging-human-brain
Česká verze: https://techtools.cz/tools/news/clanek/2283-studie-stanfordovy-univerzity-do-starnouciho-lidskeho-mozku-proudi-imunitni