Eosinophilic airway inflammation in asthmatic patients is associated with an altered airway microbiome

Until a few years ago, it was thought that microbes don’t live in the lung’s passages.  But now we know that there is a diverse range of microbiota that lives there.  In this month’s issue of JACI, Sverrild and colleagues examine the relationship between these microbes and patterns of airway inflammation in healthy patients and in asthmatics who have not taken steroids (J Allergy Clin Immunol 2017; 140(2): 407-417).  In order to do so, they took 10 healthy participants and 23 nonsmoking steroid-free asthmatics and had them undergo bronchoscopy so that they could get fluid from the lower passageways.  They then sequenced bacterial DNA and looked at the number and type of immune cells.  The 33 participants also had their asthma better characterized through other standardized measures of disease severity like airway hyperresponsiveness to mannitol and fraction of exhaled nitric oxide.

They found that patients with eosinophilic asthma and those with hyperresponsiveness to mannitol, had  changes in microbial composition.  This was in contrast to patients with neutrophilic asthma.  Those asthmatics with the lowest numbers of eosinophils also had differences compared to healthy controls; they had more Neisseria, Bacteroides, and Rothia species while having less Sphingomonas, Halomonas, and Aeribacillus species.  These results suggest that the level of eosinophilic inflammation correlates with variations in bacterial composition.  This may point the way to newer diagnostic tools and therapies to help better identify and control asthma.

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