Study: Gut Bacteria of Healthy Human Infants Protect Mice Against Food Allergy

New research has found that bacteria in the feces of healthy human babies protect mice who are sensitized to cow’s milk against severe reactions to milk protein. In contrast, bacteria in the stools of human infants with cow’s milk allergy do not protect milk-sensitized mice from anaphylactic reaction to milk. Published in the journal Nature Medicine, these findings by scientists at the University of Chicago and the University of Naples Federico II might lay the groundwork for future therapies to prevent or treat food allergy by changing the human gut microbiome, the microorganisms that live in the human digestive tract.

Previous research has shown that the guts of healthy babies house different populations of microbes than the guts of babies allergic to cow’s milk, and that certain gut microbes are associated with a lower risk for food allergy. To find out whether some microbes might have a protective effect, researchers transplanted feces from eight human infants – four with milk allergy and four without – into groups of mice that were raised in a sterile environment and had no gut bacteria of their own. A third group of mice did not receive transplanted human feces and remained germ-free.

All of the mice were then sensitized to a protein found in cow’s milk, so that they made antibodies against the milk protein. When they were later fed milk protein, the germ-free mice and the mice who received microbes from milk-allergic babies had symptoms of anaphylaxis, a severe and potentially fatal allergic reaction. In contrast, the mice whose gut microbes came from healthy babies did not have severe reaction symptoms. Markers for allergic reaction were significantly lower in mice treated with feces from healthy babies than in mice whose germs came from babies with milk allergy.

This experiment, which was conducted using feces from formula-fed babies, was repeated using feces from breastfed healthy babies or breastfed babies with cow’s milk allergy. The results were similar: stool from healthy breastfed babies gave milk-sensitized mice significant protection against severe reactions, while stool from breastfed babies with milk allergy did not protect the mice against anaphylaxis.

As in previous research, the microbial populations of feces from healthy babies and babies with milk allergy differed in many ways. One of the bacterial species that was abundant in feces of healthy babies compared to feces of babies with milk allergy was Anaerostipes caccae. In a variation on the fecal transplant experiments, transfer of A. caccae to the guts of milk-sensitized mice provided protection against anaphylaxis to milk protein, similar to the protection provided by feces from healthy babies.

Searching for possible mechanisms for this protection, researchers found that in mice transplanted with stool from healthy babies, the surface cells of the small intestine expressed different genes than did cells lining the small intestine of mice transplanted with stool from babies allergic to milk. In other words, when different microbes were in contact with the lining of the mouse gut, the gut cells made different proteins and had different capabilities, some of which may relate to tolerance of food proteins. The researchers conclude that their study demonstrates an important role for gut microbes in preventing allergic responses to food and represents an important step in developing prevention and treatment strategies that modify the human gut’s microbial population.

FARE CEO Lisa Gable welcomes the new findings. “There is so much to learn about how the human gut and the microorganisms that live there might interact to prevent or promote food allergies,” notes Gable. “This study found that gut bacteria of healthy human babies have protective effects limiting allergic reactions to milk – at least in mice. More research is needed to understand the interplay between gut microorganisms, the immune system and food proteins, with the goal of finding new approaches to food allergy prevention and treatment.”