Gut microbes may prevent, reverse, food allergy

The national epidemic of food allergy may be caused by the absence of certain beneficial bacteria in the human gut, according to a new study by scientists at Boston Children's Hospital and Brigham and Women's Hospital in Massachusetts and published in the journal Nature Medicine.

The number of Americans who suffer from food allergy has risen sharply over the last decade to as many as 32 million, according to Food Allergy Research and Education. One hypothesis is that certain Western lifestyle factors are disrupting the normal microbial balance in the gut, depriving babies of the "good" bacteria that prepare the immune system to recognize food as harmless, researchers said.

Rima Rachid, MD, assistant director of the Food Allergy Program in Boston Children's Division of Immunology, began testing this hypothesis by studying gut bacteria in babies with and without food allergies. Her team collected stool samples from 56 food-allergic patients and 98 matched controls.

Next, Georg Gerber, MD, PhD, first co-author of the study, and his colleagues at Brigham and Women's Hospital analyzed the samples for changes in bacterial content. The work revealed that the bacteria in the feces of babies with food allergies were different from those of controls. Researchers found mice that had been given fecal bacteria from food-allergic babies went into the life-threatening reaction called anaphylaxis. 

To find out which bacteria might be offering that protection, Lynn Bry, MD, PhD, senior author from Brigham and Women's Hospital, provided a mix of six bacterial species from the order Clostridiales, which previous studies had suggested might protect against food allergy. When these bacteria were given to the mice, the animals were protected from food allergy to chicken egg protein, whereas mice given other common bacteria were not. 

Bry then provided a second mix of unrelated bacteria from the order Bacteroidales, which was also protective. When the team treated mice that already had food allergy with the Clostridiales or Bacteroidales mixes, they found those therapies completely suppressed the animals' allergic reactions.

According to Talal Chatila, MD, director of the Food Allergy Program at Boston Children's and a senior author on the paper, the study could prove that the loss of protective gut bacteria is a critical factor in food allergy.

“At the very least it is a fundamental mechanism,” he said. “And more likely, in my mind, it is the fundamental mechanism on which other things can be layered.”

While previous studies have suggested that certain bacteria can protect against food allergies, the new study goes a step further, describing the specific immunological pathway by which the bacteria act in mice. It begins with a protein, known as MyD88, that serves as a "microbial sensor" in the immune system's regulatory T cells.

The researchers believe their findings will eventually lead to new treatments that prevent the development of food allergies in newborns at risk. The treatments might take the form of probiotics, mixes of beneficial bacteria, or drugs that prime the immune system in the same way, they said.

And for the millions who already suffer from food allergies, the same treatments may be able to reverse their disease, according to Chatila. In adult mice that had become food-allergic, researchers could suppress their disease by introducing the good bacteria, which means there is the potential to treat somebody with established food allergy and reset their immune system in favor of tolerance.

Ultimately, the promising results in mice will have to be duplicated in humans, Chatila said. This may happen soon. Researchers are already working on a clinical trial at Boston Children’s Hospital to test the safety and efficacy of fecal transplants in adults with peanut allergy. Chatila notes that several companies are already preparing bacterial mixes for clinical trials. 

“If the race continues with the same intensity, or accelerates,” he said, “I think you'll see a product on the market within five years.”