Allergic rhinitis: get out the tissues and follow the dysbiosis

Spring goes hand in hand with... sneezing! Itching, tingling, a runny nose, watery eyes... every year, the arrival of spring and high concentrations of pollen bring hay fever back with a bang. Allergic rhinitis—commonly known as hay fever—and its succession of symptoms plague the lives of 40% of the world’s population (sidenote: Cheng L, Chen J, Fu Q, et al. Chinese Society of Allergy Guidelines for Diagnosis and Treatment of Allergic Rhinitis. Allergy Asthma Immunol Res (2018) 10(4):300–53.  Eifan AO, Durham SR. Pathogenesis of Rhinitis. Clin Exp Allergy (2016) 46 (9):1139–51. ) . This complex condition results from a combination of genetic and environmental factors, including an interaction between a respiratory microbiota imbalance and an abnormal and excessive immune system response. But what are the effects of this dysbiosis? And which microorganisms are involved?

An unbalanced respiratory microbiota

To find out, a Chinese team compared respiratory microbiota in nasal samples taken from 28 people suffering from acute episodes of seasonal allergic rhinitis with those of 15 non-allergic subjects. They found no difference between the two groups in terms of microorganism diversity and abundance, but important disparities in their composition. The bacterial genera Moraxella, Haemophilus, Streptococcus and Flavobacterium, predominant in the respiratory microbiota of healthy individuals, had been replaced in allergic individuals by the genera Klebsiella, Prevotella and Staphylococcus. In total, the researchers identified 10 bacterial genera that were over-represented in the latter.

A disturbed metabolism 

The scientists then applied serum metabolomics, a technique that consists in analyzing the concentration of metabolites (sidenote: Metabolites Small molecules produced during cellular or bacterial metabolism. For example, short-chain fatty acids are metabolites produced by intestinal microbiota during fermentation of non-digestible complex carbohydrates (fibers, etc.). Silva YP, Bernardi A, Frozza RL. The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication. Front Endocrinol (Lausanne). 2020;11:25.  Lamichhane S, Sen P, Dickens AM, et al An overview of metabolomics data analysis: current tools and future perspectives. Comprehensive analytical chemistry. 2018 ; 82: 387-413 ) in serum. This revealed the presence of 26 different metabolites in allergic people compared to healthy people. They also discovered the presence of 16 altered metabolic pathways, including those of arachidonic acids, already known to produce inflammatory mediators involved in some inflammatory diseases, such as allergic asthma.

Hope for individualized treatments?

The combined results of these two approaches confirm the hypothesis that inflammatory reactions of allergic origin influence the balance of respiratory microbiota. More importantly, they provide important candidate biomarkers of potential use in the diagnosis of allergic rhinitis. The authors therefore suggest continuing this work to refine the identification of different subtypes of allergic rhinitis (seasonal/perennial, intermittent/persistent, mild/moderate/severe), which may pave the way for the development of individualized treatments... and an end to the ordeal of thousands of people.