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Bacteria in the gut can help protect mice against peanut food allergies, according to a new study. The findings suggest that probiotics might help treat or prevent these potentially lethal food allergies in people, researchers say.
Food allergies, which are sometimes deadly immune system reactions to certain foods, currently affect about 15 million people in the United States. Food allergy rates among children rose by about 50 percent between 1997 and 2011.
"We've seen a generational change in the prevalence of food allergies," said senior study author Cathryn Nagler, an immunologist at the University of Chicago. "When I was in elementary school, my brothers and I ate peanut butter and jelly for lunch every day. Now, my children's classrooms are peanut free — it's estimated that, in the U.S., there are now two children in every classroom with potentially life-threatening allergic responses to food."
Previous studies have suggested that modern changes in diet, hygiene and the increased use of antimicrobials might disturb the body's microbiota, the population of bacteria that naturally live in and on people. This change, in turn, might increase people's susceptibility to food allergies, researchers say.
To see how changes in the microbiota of the intestines might influence allergic responses to food, Nagler and her colleagues experimented with germ-free mice, which were born and raised in sterile conditions to possess no microbes inside them, and mice treated with antibiotics as newborns, which have significantly reduced gut bacteria levels compared with normal mice. The researchers exposed these rodents to allergens — the substances that cause allergic reactions — from peanuts. Both groups of mice experienced strong immune responses, generating significantly higher levels of antibodies against the peanut allergens than mice with normal gut bacteria.
The scientists then investigated which types of gut bacteria, if any, could be given to mice to prevent them from developing peanut allergies. They found that when a class of bacteria called Clostridia was implanted into the mice's intestines, it could both prevent these mice from developing a peanut allergy and reverse any sensitivity they had to peanut allergens.
Clostridia are a highly diverse class of bacteria, and are also common in humans. There are toxic Clostridia, such as Clostridium difficile, but the types of Clostridia used in the new study did not include the toxic kind, Nagler said.
The scientists analyzed the genetic activity of intestinal cells in mice that possessed Clostridia. They found that Clostridia spurred the cells of the outermost layers of the mice intestines to generate high levels of a molecule known as interleukin-22, which reduced how permeable the intestines were to food allergens. When the intestines were less permeable, fewer allergens reached the bloodstream, where they could have otherwise triggered allergic reactions.
Other recent findings have made it increasingly clear that gut microbes have many important functions within the body. For instance, they help make some essential vitamins and break down otherwise indigestible dietary fiber. They also release signals that help the immune system function.
"We have co-evolved with our microbiota for millennia," Nagler said. "It seems that a consequence of some of our 21st-century lifestyle habits has been the disruption of our relationship with the communities of commensal (friendly) bacteria that reside on our skin and mucosal surfaces, and particularly in the gut."
The researchers have filed a patent to develop ways to prevent food allergies, and they plan to work with biotechnology companies to engineer such probiotic therapies.
The researchers suggested that other commensal bacteria may also help to regulate the body's tolerance of food allergens. "We still have a lot to learn about the commensal microbiota," Nagler said.
Nagler and her colleagues detailed their findings online Aug. 25 in the journal Proceedings of the National Academy of Sciences.
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