What should I think about when I think about the immune system? For starters, you shouldn’t think about some kind of battle between good and evil. Microbes in your body dial the immune system up and down (so you don’t get all infected or go all auto-immune); they cause certain cells to get made; they train it to differentiate good guys from bad guys. “I think it’s more accurate to see the immune system as a team of rangers in charge of a national park—as ecosystem managers,” writes Yong. “They must carefully control the numbers of resident species, and expel problematic invaders.” Because the immune system isn’t a standing army. “The immune system isn’t just a means of controlling microbes. It is at least partly controlled by microbes.” They are kind of the boss of you. You need to update your mental metaphor. - http://www.wired.com/2016/07/germs-magic-things-learned-ed-yongs-new-book/