Preprint Club
A cross-institutional Journal Club Initiative

Keywords

• food allergy

• microbiota

• anaphylaxis

Main Findings

The role of the gut microbiota in shaping food allergy outcomes has long been of interest, as bacteria could influence allergen availability or create a pro-inflammatory environment licensing a Th2 response. In this preprint by Sánchez-Martínez et al., the authors explore a novel connection between microbial metabolism and its ability to modulate anaphylaxis — a life-threatening complication and the most severe manifestation of food allergy triggered by accidental allergen exposure. The study focuses on peanut allergy, one of the most severe and persistent food allergies, with a rising global incidence. In their initial experiments, the authors demonstrate that the gut microbiota is able to degrade peanut protein, Enterococcus species appears to be primarily responsible in specific pathogen-free (SPF) mice.

Using a C3H-HeN SPF mouse model, which is susceptible to Th2-driven allergic inflammation, the authors show that the gut microbiota plays a protective role in peanut allergy - induced anaphylaxis. Specifically, mice with diverse microbiota exhibit lower serum levels of mucosal mast cell protease-1 (mMCP-1) and reduced body temperature drop — both indicators of less anaphylactic severity. Bridging their findings to human relevance, the authors examined the oral microbiota of healthy volunteers for peanut-degrading capabilities. They identified Staphylococcus and Rothiaspecies as the most efficient peanut degraders ex vivo. Subsequent in vitro experiments revealed that peanut extracts pre-digested by these bacteria has less Ara h 1 and Ara h 2 proteins (key peanut allergens) as seen via SDS-PAGE. The digested extract also reduced mast cell activation in the presence of allergen-specific IgE in vitro. A central finding of the preprint shows that colonizing C3H-HeN mice with three Rothia strains (R1, R2, and R3), which were previously identified in humans, has a mild protective effect upon allergenic challenge, as evidenced by lower serum mMCP-1 levels compared to the non-colonized control. Adding further clinical relevance, the study reports that peanut-allergic individuals with higher tolerance thresholds (able to consume more than 40 mg of peanut protein) have a greater abundance of Ara h 2-degrading bacteria in their oral microbiota.

In summary, this study presents an intriguing mechanism by which microbial metabolism can modulate allergen bioavailability, potentially reducing the severity of allergic reactions such as anaphylaxis.

Limitations & Suggestions

• How long does it take the bacteria to degrade the peanut proteins? Would be interesting to better understand timing of peanut digestion, and how physiologically relevant it would be in the end. Can chewing peanut longer reduce chances of anaphylaxis, if there is a “proper” peanut-degrading bacterial community in the oral cavity?

• It would be very interesting to understand what metabolism pathway in bacteria is responsible for peanut degradation, and how common it is.

• The key figure on Rothia colonization would benefit from showing temperature changes in mouse anaphylaxis.

• The Fig. 2 should include Fig. S3 on body temperature reduction upon anaphylaxis, and that mice with microbiota are protected from that.

• Bacterial digestion of peanut protein by Rothia and Staphylococcus could be moved to the supplementary, and experiments with in vitro stimulation of mast cells with degraded peanut extract + IgE would benefit from flow cytometry analysis and a figure to visualize the experimental design.

• In Fig. 7H, there is no correlation of peanut threshold tolerance and Ara h 2 levels, but overall, with a larger sample size that would be expected; people with severe peanut allergy cannot tolerate even low doses of peanut.

• Technical point: indicate how many replicates of mouse experiments were performed, and plot data points on bar charts.

• In general, and perhaps outside of the scope of this preprint, to have a more ecological understanding how microbial community regulates peanut digestion. This will also help to understand how it can be improved / designed into a therapeutic.

Significance/Novelty

This preprint presents a novel mechanism that may influence anaphylaxis outcomes in humans. However, important questions remain regarding its physiological relevance in humans. Nevertheless, the study inspires future investigations into potential dietary or therapeutic interventions. One of potential application is, for example, combination of specific probiotic with an oral immunotherapy to achieve tolerance to food.

Credit

Reviewed by anonymous as part of a cross-institutional journal club between the Max-Delbrück Center Berlin, the Ragon Institute Boston (Mass General, MIT, Harvard), the University of Virginia, the Medical University of Vienna and other life science institutes in Vienna.

The author declares no conflict of interests in relation to their involvement in the review.