Your microbiome can determine your risk of a severe allergic reaction

The microbiomes in our guts and mouths can determine whether people with peanut allergies develop a life-threatening reaction. This could help explain why some people with allergies experience relatively mild reactions, while others develop severe or even fatal symptoms.

“There is a big question as to why some patients are more prone to more severe reactions,” he says Rodrigo Jimenez-Saiz at the Autonomous University of Madrid, Spain.

A peanut allergy occurs when the immune system mistakenly identifies the protein in the legume as a threat, causing it to produce an excess of a certain type of antibody. This increases inflammation, leading to symptoms such as itching, swelling and vomiting. In extreme cases, exposure to peanuts causes anaphylaxis, a life-threatening reaction that usually involves difficulty breathing.

Jiménez-Saiz and his colleagues wondered if the microbes that live in and on us play a role, given the enormous influence that our body’s various microbiomes have on our immune system.

To find out, they put small amounts of peanuts into the stomachs of three groups of mice without any allergies. The first group was bred to develop no microbiome (known as germ-free mice), while the second had a minimally different microbiome, and the third had a microbiome that is typical of a healthy mouse.

Forty minutes later, the team found higher levels of two proteins that play a major role in peanut allergy, known as Ara h 1 and Ara h 2, in the small intestine of mice with no microbes and mice with a minimal microbiome than in mice with the most diverse microbiome.

Further analysis revealed that the second group carried the highest levels of a group of bacteria called Rothiaespecially voltage Rothia R3which is involved in the digestion and degradation of peanuts in the intestines.

Explore whether Rothia R3 affects the risk of anaphylaxis, the researchers induced severe peanut allergies in a separate group of mice that had a minimally different microbiome.

Then they implanted Rothia R3 into some of their guts before the peanut paste goes straight into the stomachs of all the animals. Forty minutes later, all mice developed anaphylaxis, but the body temperature of those who received Rothia R3 it dropped an average of just 2 percent, compared to 3.5 percent in mice that didn’t get it. Anaphylaxis usually causes a drop in body temperature, which can lead to hypothermia and organ failure.

The Rothia-implanted mice also had about half the blood levels of an immune molecule called MMCP-1, which usually rises during anaphylaxis, compared to control mice. “The findings are compelling,” he says Mohammed Shamji at Imperial College London. “If a similar immunological change occurred in humans, you would expect it to reduce the severity of anaphylaxis symptoms.”

In another experiment involving 19 people with peanut allergies, the team found that those with greater peanut tolerance had significantly higher levels of Rothia bacteria in their saliva than those with more severe allergies. This suggests that the presence of these bacteria in people’s mouths, as well as in their guts, affects their risk of anaphylaxis.

Rothia probiotics could one day reduce the severity of anaphylaxis that develops during an allergic reaction to peanuts, Shamji says. “The need for something like this is huge,” he says. In particular, it could ease fear of accidental exposure to peanuts and reduce the risk of adverse reactions during oral immunotherapy, which aims to treat allergies by gradually exposing people to increasing doses of the allergen, he says.

The team hopes to demonstrate the potential of such a treatment in a clinical trial by giving it to people with peanut allergies Rothia probiotics or a placebo before exposing them to low levels of peanuts, says Jiménez-Saiz.

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