A new NIH‑funded study found that the immune environment inside the hippocampus – the brain area that helps us learn and remember – changes in midlife. This shift may explain why older brains often have long‑lasting inflammation.
Immune Cells Start to Transform Around Age 50
Researchers examined hippocampus samples from 40 healthy adults aged 20 to 95. They used cutting‑edge single‑cell techniques to look at each cell’s activity.
They saw that microglia, the brain’s main immune cells, slowly decrease from about age 50 to 75. At the same time, other immune‑like cells that carry stronger inflammation signals appear to take their place.
For a long time scientists thought microglia were born before birth and stayed in the brain forever, renewing themselves. This new evidence suggests they are partly replaced by cells that come from the blood.
How the Researchers Got a Clearer Picture
The team combined classic gene‑activity measurements with newer tools that map the 3‑dimensional shape of DNA and its chemical tags (the epigenome). By looking at both, they could spot changes in cell identity that would have been missed by older methods.
The Blood‑Brain Barrier Also Ages
They also found that cells that help keep the blood‑brain barrier – the filter that protects the brain – become weaker with age. Across many brain cell types, the overall organization of DNA also shifts as people get older.
What This Might Mean for Alzheimer’s
Future work will test why resident microglia disappear and whether the new inflammatory cells directly contribute to Alzheimer’s disease or other age‑related brain problems.
This research was supported by several NIH grants and is part of a larger effort to understand how the 3‑D genome influences development, aging, and disease.