It’s the largest security force in the world. A teeming network of first responders that live on nearly every surface of your body, inside and out. They’re not part of the body, like your immune system — they’re immigrants — but they’re still naturalized citizens, and without them your world couldn’t function. Since the Human Microbiome Project began in 2008, biologists have begun to uncover just how closely your body relies on these semiautonomous partners in securing your well-being. From the skin to the lining of the intestine, the trillions of bacteria and viruses that make up your own personal microbiome keep you safe from invading diseases. Someday soon, scientists hope to train them for new roles, like fighting cancer and providing early warning of infections. The body cells in our immune system do a great job of protecting us on the inside, but they provide little to no protection for surfaces like skin and the lining of the intestine. That job is outsourced to the microbiome. The billions of bacteria in the microbiome act like a security force that bars vagrant disease-causing microbes from hanging out in dark alleys. They also alert the immune system when they encounter a threat they aren’t equipped to handle.
Unlike security patrols, these public servants don’t move around independently. Instead, during a security breach they clone themselves on the spot to form a tight line of newly born, fully armed adult protectors.
Good Cop, Bad Cop
But not every threat comes from the outside. Sometimes, some of these micro-protectors get a little overzealous. They accidentally multiply too much and block absorption of food in the intestine or gum up pores in our skin. At other times, good bacteria go rogue.