The brain undergoes a quiet but important change in its immune cells starting around age 50 — a shift that may help explain why aging is the biggest risk factor for dementia.
Researchers at UC San Diego, the New York Genome Center and partners analyzed postmortem hippocampus tissue — a memory hub — from 40 neurologically healthy people aged 20 to 95, using single-cell genomics and 3D genome mapping. They found that microglia, the brain’s resident immune cells, gradually decline between ages 50 and 75 and are replaced by cells with stronger inflammatory signals that resemble immune cells from the bloodstream. The work was published in Science in 2026.
What else changed
The team also saw age-related decline in cells that support the blood-brain barrier, along with widespread reorganization of how the genome is packaged and how genes are regulated — a broad remodeling of the aging brain’s cellular landscape.
Why it matters
This immune remodeling “may help explain how aging contributes to the long-lasting brain inflammation often seen in neurodegenerative diseases,” the researchers said, particularly Alzheimer’s. “Aging is the single largest risk factor for dementia, but our understanding of how it drives disease is still incomplete,” noted the NIH’s Richard Hodes. Mapping when and how the brain changes is a step toward intervening earlier.