The immune cells that patrol the brain's memory center appear to be replaced during midlife by cells carrying the molecular signatures of immune cells from the bloodstream, according to an analysis of human hippocampal tissue spanning the adult lifespan.
Between roughly ages 50 and 75, microglia that formed during embryonic development declined sharply, and in their place researchers found cells whose profiles resembled circulating monocytes. Those replacement cells carried elevated inflammatory signatures.
