Species-Specific Microbes May Be Key to a Healthy Immune System

and so do we. These microorganisms help both mice and us break down dinner. As we are finding, these bugs also help to regulate the immune system. But we are just starting to learn how these tiny organisms influence us and how changing their composition changes us.

In an attempt to find out, postdoctoral researcher Hachung Chung and her colleagues at Dennis Kasper's Lab at Harvard Medical School tried raising mice with exclusively human gut microbiota.

The human microbes did pretty well in the mice guts (the researchers could tell by culturing fecal pellets from these mice). Interestingly, though, the mice with these microbes did not: their immune systems remained underdeveloped. Even when researchers gave rat microbiota to mice, the mice's immune systems failed to mature. The results were published in the June 22 issue of Science.

The findings are "perhaps the most definitive that I've seen," says Eugene Chang, a professor of medicine at the University of Chicago, who was not involved in the new study. They show "the critical and specific relationship between host and gut microbes, which is needed for proper development of the host immune response," he says.

The results support the thinking that we humans have coevolved with our microbes

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