At least 100 trillion bacteria live in the mammalian gut and are crucial helpers for food digestion and energy production. But this poses a paradox: How can we carry all those organisms and not get sick?
As it turns out, bacteria are physically separated from the intestinal lining, which prevents them from activating their host’s immune system. According to a new study of the mouse small intestine, a molecule called MyD88 signals the presence of the bacteria, activating production of an antibacterial protein that kills any bacteria within a 50-micrometer radius – about the size of a speck of dust. The loss of this protective barrier—what the researchers cheekily call the ‘demilitarized zone,’ or DMZ—could be involved in inflammatory bowel disease or other diseases characterized by an inflamed intestine, the researchers say.
“Good fences make good neighbors,” says HHMI investigator Lora V. Hooper, quoting poet Robert Frost. Hooper led the new study, published October 14, 2011 in Science. “Trillions of friendly bacteria inhabit our guts, and we want them there, but they have to be kept at arm’s length.”
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