Groundbreaking Study Reveals Major Shift in Brain’s Immune System

A team of researchers from the University of California, San Diego, the New York Genome Center, and the University of California, Irvine, have made a groundbreaking discovery about the human brain’s immune system. The study, funded by the National Institutes of Health (NIH), has uncovered a previously hidden overhaul of the brain’s immune environment, which begins around the age of 50.

The researchers used advanced single-cell methods to study postmortem hippocampal tissue from 40 neurologically healthy adults between the ages of 20 and 95. Their analysis found that microglia, the brain’s main immune cells, gradually decline from about age 50 to age 75. At the same time, they appear to be replaced by cells with stronger inflammatory signals and other traits similar to immune cells that originate in peripheral blood.

This discovery challenges a long-standing assumption about microglia, which first develop during embryonic growth and were believed to remain in the brain and continually renew themselves throughout a person’s life. However, the study found that the brain’s immune system undergoes a significant transformation as people age, which may help explain how aging contributes to long-lasting brain inflammation often seen in neurodegenerative diseases.