Corticosteroid Success Linked to Differences in Bronchial Microbiome

Individuals with atopic asthma were recently found to have a distinctive bronchial bacterial microbiome that not only differs from those without asthma, but between asthmatics with phenotypes responsive or resistant to inhaled corticosteroid treatment.

"Even in mild steroid-naive asthma subjects, differences in the bronchial microbiome are associated with immunologic and clinical features of the disease," indicated the investigators, led by author Juliana Durack, PhD, Department of Medicine, Division of Gastroenterology at University of California San Francisco. "The specific differences identified suggest possible microbiome targets for future approaches to asthma treatment or prevention."

Their comparison of compositional and functional differences in the bronchial bacterial microbiome examined individuals with atopic asthma, atopy without asthma, and healthy controls. They recruited 42 adult subjects with mild atopic asthma not previously treated with an inhaled corticosteroid to clarify whether the microbiome that has been associated with the asthmatic condition could reflect, in part, corticosteroid treatment in some subjects of previous studies.

The asthmatic condition was confirmed by airway hyper-responsiveness to methacholine challenge or improvement with albuterol. The asthmatic phenotype was distinguished as T2-high (Type2 helper T cell, associated with eosinophilic airway inflammation and responsiveness to corticosteroid treatment) or T2-low (corticosteroid-unresponsive type associated with neutrophilic or paucigranulocytic airway inflammation).

An additional question of whether the microbiome associated with asthma could instead reflect underlying atopy was investigated with the inclusion of 21 non-asthmatic adults with atopy, defined by serologic evidence of specific IgE reactivity to at least one of 12 aeroallergens. The study cohort was completed with a control group of 21 healthy adults

The investigators reported that the bronchial microbiome of asthmatic subjects was “uniquely enriched in members of the Haemophilus, Neisseria, Fusobacterium, Porphyromonas and Sphingomonodaceae” bacterial groups and “depleted in members of the Mogibacteriaceae and Lactobacillales.”

Among asthmatic subjects, those with corticosteroid responsive T2-high type were found to have a significantly lower bronchial bacterial burden than T2-low type. Although the relative bacterial burdens distinguished the two types, the particularly low burden in T2-high phenotype prevented the researchers from completing sufficient bacterial gene sequencing to compare profiles.

Durack and colleagues concluded that their work "expands the list of bacterial groups previously associated with asthma," "further supporting the idea that alterations in microbial composition from a healthy state, is a characteristic of asthma."

The research, “Features of the bronchial bacterial microbiome associated with atopy, asthma and responsiveness to inhaled corticosteroid treatment”, was published online November 10 in the Journal of Allergy-Clinical Immunology.

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