GUT BACTERIA MAY PROTECT AGAINST FOOD ALLERGY GUT BACTERIA MAY PROTECT AGAINST FOOD ALLERGY
NATIONAL INSTITUTE OF ALLERGY AND INFECTIOUS DISEASES

Food Allergy Gut Bacteria May Protect Against Food Allergy Gut bacteria isolated from a stool sample.
Credit: CDC/Lois S. Wiggs

Researchers have found that certain naturally occurring gut bacteria may protect against food allergen sensitization—a key step in the development of food allergy. Using a mouse model of peanut allergy, the scientists showed that altering the bacterial communities in the gut could change the animals’ immune responses to peanut allergen, suggesting potential new strategies for food allergy treatment and prevention. The study, funded in part by NIAID, appears in Proceedings of the National Academy of Sciences.

Background

Food allergy among children in the United States rose 18 percent from 1997 to 2007, according to the Centers for Disease Control and Prevention. Reasons for this increase remain unclear, but recent studies have suggested that environmental factors play an important role by changing the composition of the commensal bacteria that colonize the intestinal tract. These trillions of bacteria, collectively known as the intestinal microbiota, are vital for health and immune system development. The rise in antibiotic use during childhood has been linked to an increased risk of allergic diseases, suggesting that in addition to destroying infectious bacteria, these drugs also can alter the composition of the microbiota.

Results of Study

To examine how changes in the microbiota influence allergic responses to food, researchers led by Cathryn Nagler, Ph.D., of the University of Chicago exposed different groups of mice to peanut allergen. Germ-free mice—those born and raised with no microbes—and mice treated with antibiotics as newborns produced higher levels of peanut-specific antibodies than mice with normal gut bacteria.

The scientists found that introducing specific types of bacteria into the animals’ guts could influence immune responses to peanut allergen exposure. Germ-free and antibiotic-treated mice given a mixture of Clostridia, a class of bacteria normally found in the intestinal microbiota, were protected against peanut sensitization. However, introducing Bacteroides, another major group of gut bacteria, did not have a similar effect, suggesting that Clostridia play a unique role in protecting against allergen sensitization.

Analysis of immune cell and protein levels before and after colonization with Clostridia revealed significant differences. Clostridia stimulated immune cells to produce high levels of a molecule called interleukin 22 (IL-22), which reduced the permeability of the intestinal lining, preventing the allergen from entering the bloodstream. The scientists also found that the bacteria altered the levels of cells involved in immune regulation and levels of immunoglobulin A, the major protective antibody found in mucosal tissues such as the intestine.

Significance

These findings in a mouse model of food allergy suggest that the intestinal microbiota play an important role in determining immune responses to food allergens and also provide insight into the molecular changes that result.

Next Steps

Future research will focus on gaining a more complete understanding of how Clostridia enables the immune system to protect against allergen sensitization and most importantly on determining whether the bacteria have a similar effect in humans. Ultimately, scientists may investigate strategies to prevent and treat food allergy by modifying the bacterial communities in the gut.