Peanuts are one of the most common food allergens
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The microbiomes in our gut and mouth can determine whether people with a peanut allergy develop a life-threatening reaction. This may help explain why some people with allergies experience relatively mild reactions, while others develop severe or even fatal symptoms.
“There is a big question around why some patients are more prone to more severe reactions,” says Rodrigo Jiménez-Saiz of the Autonomous University of Madrid in Spain.
Peanut allergy occurs when the immune system mistakenly identifies proteins in the legume as a threat, causing it to produce large amounts of a specific type of antibody. This increases inflammation, leading to symptoms such as itching, swelling and vomiting. In extreme cases, peanut exposure causes anaphylaxis, a life-threatening reaction that usually involves difficulty breathing.
Jiménez-Saiz and his colleagues wondered whether the microbes that live on and in us play a role here, given the enormous influence that the body’s various microbiomes have on our immune system.
To find out, they put a small amount of peanut into the stomachs of three groups of mice without allergies. The first group was raised to develop no microbiome (known as germ-free mice), while the second had a minimally diverse microbiome, and the third had a microbiome 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 the germ-free and minimally microbial mice than in those with the most diverse microbiome.
Further analysis revealed that the latter group had the highest levels of a group of bacteria called Rothiaespecially the load Rothia R3which is involved in digesting and breaking down peanuts in the intestine.
To explore about Rothia R3 affects anaphylaxis risk, the researchers induced severe peanut allergies in a separate group of mice, which had a minimally diverse microbiome.
They then implanted Rothia R3 into some of their intestines, before delivering peanut paste directly into all the animals’ stomachs. Forty minutes later, all the mice had developed anaphylaxis, but the body temperature of those that did Rothia R3 had dropped by just 2 percent on average, compared to 3.5 percent for the 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 levels of an immune molecule called MMCP-1 in their blood, which usually rises during anaphylaxis, compared to the control mice. “The findings are compelling,” says Mohamed Shamji of Imperial College London. “If a similar immunological change occurred in humans, you would expect this to reduce the severity of anaphylaxis symptoms.”
In another experiment involving 19 people with peanut allergies, the team found that those with greater tolerance to peanuts had significantly higher levels of Rothia bacteria in the 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 anaphylaxis risk.
Rothia probiotics may one day reduce the severity of anaphylaxis that develops during a peanut allergy reaction, says Shamji. – The need for something like this is great, he says. In particular, it could alleviate fears surrounding 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 an allergen, he says.
The team hopes to demonstrate the potential of such a treatment in a clinical trial by giving people with peanut allergies either Rothia probiotics or placebo, before exposing them to low levels of peanuts, says Jiménez-Saiz.
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