Scientists have discovered that the aging human brain may be far less isolated from the rest of the body than once believed. Stanford researchers found that large numbers of immune cells from the blood begin entering the brain as early as middle age, where they can transform into microglia, the brain’s specialized immune cells. The finding overturns a long-standing assumption that these cells remain largely separate from the body’s immune system throughout life.

Microglia are innate immune cells of the brain, very similar to the macrophages found elsewhere in the body outside the central nervous system. Both microglia and macrophages do…

Scientists have discovered that the aging human brain may be far less isolated from the rest of the body than once believed. Stanford researchers found that large numbers of…