A Stanford Medicine team led by postdoctoral researcher Julia Belk and senior author Siddhartha Jaiswal has found that circulating immune cells can cross the blood-brain barrier and develop into functional microglia in the aging human brain. Using naturally occurring somatic mutations to trace cell lineages in matched blood and postmortem brain samples, researchers found that this process begins around middle age and continues with aging.

The discovery challenges the long-standing belief that microglia are derived exclusively from embryonic cells. Notably, the same phenomenon was not observed in mice or non-human primates, suggesting it may be a human-specific feature of aging.

The findings could provide new insight into the relationship between clonal hematopoiesis of indeterminate potential (CHIP) and Alzheimer's disease. Blood stem-cell clones carrying specific mutations may produce immune cells that enter the brain and influence its immune environment after developing microglia-like characteristics.

The discovery also raises potential therapeutic possibilities. Researchers suggest that blood-derived immune cells could potentially be engineered to perform beneficial functions in the brain, such as helping clear pathological proteins including amyloid and tau. However, further research is needed to determine how this process is regulated and whether it can be safely targeted to treat neurodegenerative diseases.

Source: https://allsci.com/news/research/immune-cells-aging-brain-stanford-researchers/