Features of the bronchial bacterial microbiome associated with atopy, asthma and responsiveness to inhaled corticosteroid treatment

It’s been known that asthmatic lungs are different from healthy lungs in many aspects, including housing different strains of bacteria.  So far, studies haven’t been able to tell whether these differences are due to asthma, associated allergies (atopy), or treatment with different drugs.  They also haven’t been able to determine how these differences affect the way asthma manifests itself and how asthma can be treated.  In this month’s issue of JACI, Durack and colleagues aim to answer these pressing questions (J Allergy Clin Immunol 2017; 140(1): 63-75).

Durack and other investigators looked at the bacterial communities in 84 individuals, split into three groups: (1) 42 atopic asthmatic subjects, (2) 21 atopic non-asthmatic subjects, and (3) 21 non-atopic non-asthmatic, otherwise healthy, subjects.  They also looked at inflammatory markers and changes in bronchial hyperresponsiveness after 6 weeks of treatment with fluticasone, an inhaled steroid commonly used for asthma treatment.

What they found is that the types of bacteria in each of the three groups were significantly different. This included the group with atopy without asthma, suggesting that atopy itself is associated with different patterns of bacterial colonization of the bronchi, but these patterns also differed from those in the subjects with atopic asthma.  The bacteria seen in the asthmatic patients expressed genes for different metabolic pathways that result in products previously linked to risks for asthma development.  And subjects with high levels of allergy/atopy-related inflammation markers in their bronchial epithelium (“T2-high asthma”) had overall lower amounts of bacteria.  Differences were also found in the asthmatic subjects who responded to fluticasone, in that their bronchial bacteria were less different from those in healthy subjects than were the bronchial bacteria in the non-responsive asthmatics.  

Overall these findings suggest that bacterial composition in the lungs is associated with various immunologic and clinical features of the disease.  It also suggests that targeting these bacteria may be a way to help prevent, or even treat, asthma in the future.