The presence of a common gut microbe called Clostridia protects mice against peanut sensitization by keeping the allergens from entering their bloodstream, according to findings published in Proceedings of the National Academy of Sciences this week.

In the U.S., food allergy rates among children rose about 50 percent between 1997 and 2011. We don’t know what causes food allergies, though numerous studies hint that recent changes in diet and hygiene (and the use of antibiotics and antimicrobial this and that) have altered the natural community of microorganisms in our gastrointestinal tracts -- increasing our susceptibility to food allergies.

To see how altered microbiota affect immune responses to food, a team led by Cathryn Nagler from the University of Chicago exposed three groups of mice to peanut allergens: germ-free mice without any resident bacteria, mice given antibiotics as newborns to reduce their GI bacteria, and control mice with a normal cohort of GI bacteria.

Germ-free and antibiotic-treated mice showed strong immunological responses, producing higher levels of antibodies against peanuts allergens -- compared to mice with normal gut bacteria, which seem to provide some degree of protection against food allergies.

This peanut sensitization (the rodent model of human allergy) can be reversed. When Clostridia bacteria were reintroduced into the intestines of germ-free and antibiotic-treated mice, they were no longer sensitive to peanuts. Introducing another type of common GI bacteria, called Bacteroides, failed to alleviate sensitization, further suggesting that Clostridia bacteria are the ones mediating the protection.

To identify the protective mechanism, the team looked at the immune responses on a cellular and molecular level. A gene expression analysis revealed that Clostridia induced an immune response -- the production of molecules called cytokine interleukin-22 (IL-22) -- which reduces the permeability of the lining of mouse intestines. This results in less allergen reaching the bloodstream. “The bacteria are maintaining the integrity of the [intestinal] barrier,” Nagler tells Science.

Finally, the team gave antibiotic-treated mice either IL-22 or Clostridia. When exposed to peanut allergens, mice in both conditions showed reduced allergen levels in their blood, compared to controls. Accordingly, allergen levels increased when mice were given antibodies that neutralized IL-22.

“The first step in getting sensitized to a food allergen is for it to get into your blood and be presented to your immune system,” Nagler says in a news release. “The presence of these bacteria regulates that process." Her team is working to develop and test compositions that could be used for probiotic therapy.

Image: U.S. Department of Agriculture’s Flickr CC BY 2.0