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Special immune cells protect your brain by sweeping away dead or dysfunctional cells. Now, scientists have discovered that they have another role, as targeted assassins of sick cells.

Here’s what lead researcher Greg Lemke of the Salk Institute said about the research on mouse brains, published in Nature.

How does the brain clear out dead cells?

In these areas of the brain where you’re giving rise to new neurons, it was known that during that process a large number of the newly born cells die. In the hippocampus, this is about 80 percent. Those cells have to be cleared away, and the cells that do that are called microglia. Those microglia cells use two specific receptors to recognize the dead cells and then start the process of eating them.


What else did you see the microglia do?

[We saw] it was highly likely that a significant amount of death that you see in neurogenesis is not because the cells themselves die intrinsically. It’s that they’re actually killed by microglia. They’re eaten alive. Some of these cells aren’t healthy, and they may be expressing the “eat me” signals that are normally expressed by dead cells. It must be a mechanism, we guess, for selecting the healthiest and fittest cells.