Bacteria that live in our mouths and intestines can 'disarm' the proteins that trigger allergic reactions to peanuts, a new study has found.
Giving people with severe peanut allergies a hefty boost of these microbes could potentially help them cope better with exposure – but that's still a long way off.
A team led by scientists from the Autonomous University of Madrid in Spain and McMaster University in Canada has identified two microbes – Rothia and Staphylococcus – with this unique ability.
These bacteria, which occur naturally in human saliva and the small intestine, can break down the proteins in peanuts that trigger life-threatening anaphylaxis.
This serious allergic reaction is the reason schools elect to outlaw peanuts: while up to 2 percent of people in Europe and the US have peanut allergies, rates are much higher among children, for whom the risk of death is far greater, too.
Allergic reactions happen when our bodies identify a threat, but anaphylaxis to peanuts is something of an overreaction, a glitch in the immune system.
The danger a peanut actually poses to the body (mainly, that our own digestive enzymes can't break it down properly) pales in comparison to the danger of an anaphylactic response.
People with severe peanut allergies produce large amounts of immunoglobulin E (IgE) antibodies when exposed to peanut proteins, including two called Ara h 1 and 2. This leads to an inflammation response strong enough to cause their throat to swell shut and blood pressure to drop, in a reaction called anaphylactic shock.
In a clinical study, the researchers found that people with peanut allergies can tolerate exposure to the legumes much better when they have a higher abundance of those bacteria that can break down some of these proteins before the immune system has time to react.
The study was designed around 19 children with peanut allergies, ages 1-14, who had already signed up for oral immunotherapy (an experimental treatment aimed at carefully desensitizing patients to peanut allergens).
Before treatment began, the researchers took a swab of saliva to profile each child's oral microbiome. Then, the children underwent a routine test to assess the severity of their reactions to peanut proteins.
Blood tests following peanut exposure showed that patients with more of the peanut-protein-munching microbes in their oral and intestinal microbiomes had a higher tolerance to the allergen and a less severe allergic response.
Conversely, patients with a low threshold for peanut exposure had lower levels of Micrococcales bacteria – a taxon that includes Rothia and Micrococcus, which are both adept at breaking down peanut proteins.
"These findings suggest that the oral microbiota could serve as a predictive marker of threshold reactivity to peanuts, highlighting the potential importance of microbial allergen metabolism in IgE-mediated reactions," the researchers note.
Experiments on mice revealed how Rothia and Staphylococcus can break down Ara h 1 and 2, potentially reducing the volume of triggers the immune system has to react to.
Using a strain of lab mice prone to peanut anaphylaxis, the researchers found that deliberately tweaking the microbiome could offer similarly protective effects.
Rothia had already shown a particularly strong appetite for the two main allergenic peanut proteins in petri dish experiments. When the researchers gave mice a substantial dose of this bacterium, their anaphylactic reactions were greatly reduced.
Together, these findings suggest microbes could be important players in the future of managing peanut allergies, taking the edge off a potentially fatal reaction, and helping to identify which patients should avoid oral immunotherapy, which carries serious risks for people with more severe allergies.
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More clinical testing will be needed to determine whether probiotics, for instance, could be a safe and effective route for allergy treatment. At the moment, the findings in humans are only observational.
"Identifying the microbes involved in peanut metabolism in humans and characterizing the related microbially mediated IgE-specific immune responses could have implications for reducing the severity of allergic reactions," the researchers write.
"Our results underscore the role of the human microbiota in dictating the severity of IgE-mediated reactions through allergen metabolism and highlight the therapeutic potential of harnessing bacterial allergen-degrading capabilities for managing food allergies."
The research was published in Cell Host & Microbe.