Stanford researchers have discovered that as humans age, large numbers of immune cells from the bloodstream begin entering the brain. Once there, these cells can transform into microglia — the brain’s specialized immune cells. This finding challenges the long-held assumption that the brain is a largely isolated system from the body’s immune system throughout life. The study, published in Nature, suggests that cells originating in the bone marrow can travel to the brain and take on the role of microglia. Interestingly, this process does not appear to occur in other species like mice or non-human primates. The discovery could reshape scientists’ understanding of brain aging and potentially open new avenues for treating neurological diseases. It also highlights that the life history of blood stem cells could influence the risk of brain disorders by altering the microglia.
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