Beyond the Immune System: How Bacteria in the Mouth Dictate Peanut Allergy Severity

A groundbreaking study published in Cell Host & Microbe suggests that the severity of peanut allergies may be influenced not only by the immune system but also by the bacteria living in a person’s mouth and gut. Researchers from McMaster University and the Autonomous University of Madrid discovered that certain microbes can break down the peanut proteins that trigger allergic reactions. By degrading these allergens before they interact with the immune system, these beneficial bacteria may influence how strongly someone reacts to peanut exposure.

The research team identified two types of bacteria—Rothia and Staphylococcus—that have the ability to metabolize major peanut allergens known as Ara h 1 and Ara h 2. These microbes occur naturally in human saliva and the small intestine. “Microbes in the mouth and gut play an important role in digestion,” explained co-senior author Alberto Caminero Fernandez, an associate professor at McMaster University. “In our study, we found evidence that some of these microbes may help break down peanut components in ways that could influence allergic responses.”

One of the study’s most intriguing findings may help explain why people with similar levels of peanut-specific antibodies can experience very different reactions when exposed to peanuts. Researchers analyzed saliva samples from 19 children with peanut allergies and compared those results with an external dataset of 120 participants. Children with higher levels of Rothia species were able to tolerate significantly larger amounts of peanut protein before experiencing symptoms, while those with lower levels appeared more prone to immediate reactions.

To better understand how these microbes function in a living system, the scientists also conducted experiments in laboratory mice prone to peanut anaphylaxis. When the mice were given Rothia, their allergic responses were significantly reduced. The bacteria appeared to break down peanut proteins before they could interact with IgE-bearing immune cells, effectively reducing the amount of allergen capable of triggering a reaction.

“Peanut allergies can cause serious reactions like difficulty breathing and, in some cases, can even be life-threatening,” noted Liam Rondeau, a postdoctoral fellow at McMaster’s Farncombe Family Digestive Health Research Institute. Rondeau explained that while some people can tolerate small amounts of peanuts, others cannot, prompting the researchers to investigate whether the oral microbiome might help explain those differences. “We were curious about why this happens, and we discovered the answer while studying the microbes in our mouth.”

The findings suggest that the oral microbiota could potentially serve as a biomarker to help doctors identify which patients may be at higher risk for severe reactions. The research may also eventually help improve the safety of treatments such as oral immunotherapy, which involves gradually exposing patients to small amounts of an allergen to build tolerance. Understanding a patient’s microbial profile could one day help clinicians tailor treatment approaches or develop microbiome-based therapies.

While more clinical research will be required before these discoveries lead to probiotic-based treatments, the study highlights a promising new pathway for understanding and managing food allergies. The researchers concluded that their findings “underscore the role of the human microbiota in dictating the severity of IgE-mediated reactions” and point toward the therapeutic potential of harnessing bacteria capable of degrading allergens. For families living with the constant risk of accidental peanut exposure, the discovery offers a hopeful glimpse into how the microbiome may one day play a role in reducing allergic reactions.