There is a fine line between help and harm. The trillions of gut bacteria that are important for our health are prevented from escaping to cause havoc in other tissues by special immune cells.
A team led by David Artis at the University of Pennsylvania School of Medicine in Philadelphia has demonstrated, using mice, that the immune cells ? innate lymphoid cells ? confine bacteria to the gut by barricading the lining of the gut and neighbouring tissues. Keeping the microbes in check seems to be important: other research has shown that they are abnormally abundant in the blood of people with Crohn's disease.
When the team eliminated the innate lymphoid cells from mice, the bacteria escaped to other parts of the body. The immune cells work by secreting a chemical called interleukin-22. Treatment with IL-22 provided an effective alternative to the immune cells.
It is possible that the immune system has evolved several subsets of cells to shepherd specific groups of gut bacteria. "It may be that the immune system is more sophisticated in controlling these bacteria than we thought," says Artis.
The discovery opens up new ways to treat diseases aggravated by bugs that escape from the gut, says Lora Hooper of the University of Texas Southwestern Medical Center in Dallas.
"This work has uncovered some truly exciting new insights into the role of innate lymphoid cells in the gut, showing that they function like border collies that keep intestinal bacteria from escaping to other parts of the body," she says.
Journal reference: Science, DOI: 10.1126/science.1222551
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