Learning to Tolerate Our Microbial Self

[n2doc]

ScienceDaily (Apr. 22, 2011) — The human gut is filled with 100 trillion symbiotic bacteria -- ten times more microbial cells than our own cells -- representing close to one thousand different species. "And yet, if you were to eat a piece of chicken with just a few Salmonella, your immune system would mount a potent inflammatory response," says Sarkis K. Mazmanian, assistant professor of biology at the California Institute of Technology (Caltech).

Salmonella and its pathogenic bacterial kin don't look that much different from the legion of bacteria in our gut that we blissfully ignore, which raises the question: What decides whether we react or don't? Researchers have pondered this paradox for decades.

In the case of a common "friendly" gut bacterium, Bacteroides fragilis, Mazmanian and his colleagues have figured out the surprising answer: "The decision is not made by us," he says. "It's made by the bacteria. Since we are their home, they hold the key to our immune system."

What's more, the bacteria enforce their "decision" by hijacking cells of the immune system, say Mazmanian and his colleagues, who have figured out the mechanism by which the bacteria accomplish this feat -- and revealed an explanation for how the immune system distinguishes between beneficial and pathogenic organisms.

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http://www.sciencedaily.com/releases/2011/04/110421141632.htm