Most of the time, our immune system protects us – though there are times when it overreacts and harms us further. The same can happen with our brains. Science writer Donna Jackson Nakazawa joins Krys Boyd to talk about microglia, cells that act as the brain’s housekeeper but can sometimes be unreliable. Her new book is “The Angel and the Assassin: The Tiny Brain Cell That Changed the Course of Medicine.”