Rogue immune cells can infiltrate old brains

Killer T cells may dampen new nerve cell production in aged mice

T cells

UNWELCOME GUESTS  In a brain region called the subventricular zone, stem cells (purple) create new nerve cells in mice’s brains. T cells (white), which are more common in older brains (right) than young brains (left), may interfere with this process.

Paloma Navarro

Immune cells can storm into the brains of older mice, where these normally helpful cells seem to be up to no good. The result, described July 3 in Nature, raises the possibility that immune cells may have a role in aging.

Anne Brunet of Stanford University School of Medicine and colleagues studied gene activity to identify all sorts of cells in a particular spot in mice brains — the subventricular zone, where new nerve cells are born. Compared with young mice, old mice had many more killer T cells in that area. These immune system fighters take out damaged or infected cells in the rest of the body, but aren’t usually expected to show up in the brain.

Experiments on postmortem human brain tissue suggest that a similar thing happens in old people. T cells were more abundant in tissue from people ages 79 to 93 than in tissue from people ages 20 to 44, the researchers found.

In the brains of mice, killer T cells churn out a compound called interferon-gamma. This molecule might be responsible for the falling birthrate of new nerve cells that comes with old age, experiments on mice’s stem cells in dishes suggest. 

The results come amid a debate over whether human brains continue to make new nerve cells as adults (SN Online: 3/8/18). If so, then therapies that shut T cells out of the brain might help keep nerve cell production rates high, even into old age — a renewal that might stave off some of the mental decline that comes with aging.

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