Asthma: what are the links between phenotypes and respiratory tract microbiota?

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Neutrophilic asthma is associated with changes in the bronchial microbiota. This observation could lead to better management of the pathology and improved prediction of attacks.

 

Stratification of asthma patients, by the level of respiratory tract inflammation, is crucial for phenotype identification1. An Australian team examined respiratory tract microbiota to see if it varied based on asthma phenotype and whether it would allow for personalized treatment. 167 patients (84 eosinophilic, 14 neutrophilic, 60 paucigranulocytic and 9 mixed) suffering from severe, but stable, asthma were enrolled in the study.

Variable interactions according to phenotype

Microbial populations were analyzed by genome amplification and sequencing of 16S ribosomal RNA using samples collected via induced sputum. Results demonstrated loss of diversity and greater heterogeneity in neutrophilic asthma compared with other phenotypes, in particular eosinophilic asthma, which to date is the best documented phenotype.

Neutrophilia and pathogen abundance

The changes in the bronchial microbiota in neutrophilic asthma present as an abundance of pathogenic bacteria, particularly the genera Haemophilus and Moraxella. Conversely, a significant reduction is observed in commensal bacterial populations, be they Gemella, Porphyromonas or Streptococcus genera. This dysbiosis could explain the types of inflammatory symptoms found in this form of asthma, although no causal link has been demonstrated to date.

A route to personalized treatment?

The researchers consider that these initial results warrant further work to clarify the links between inflammatory phenotype and microbiota. This could lead to the possible personalization of anti-asthma treatments according to phenotype and composition of the bronchial microbiota. Another benefit: monitoring changes in bacterial populations could also help to predict an acute attack.

 

1. There are four broad asthma phenotypes, linked to serum levels of the different circulating granulocytes: eosinophilic, neutrophilic, paucigranulocytic and mixed (eosinophilic-neutrophilic). Each is associated with different pathophysiological mechanisms, symptoms, course and treatment.  

 

Sources: 

S. Taylor, L. Leong, J. Choo, et al. : Inflammatory phenotypes in patients with severe asthma are associated with distinct airway. J Allergy Clin Immunol, volume 141, number 1, january 2018.