Corticosteroids, airflow obstruction, and the airway microbiome

Published Online: November 25, 2015

The lung has a diverse microbiome that, while modest in biomass compared to other body sites, may be an important component of the pathogenesis of airways diseases such as asthma. Greater diversity of bacterial and environmental exposures in early childhood reduce the subse-quent risk of asthma while the presence of select bacteria such as Hemophilus in the upper air-ways may increase the risk of asthma in later life. Several reports suggest that the lower airway microbiome may be different in adults with chronic asthma compared to subjects without lung disease; these differences may correlate with clinical measures of asthma control such as bron-chial hyperresponsiveness and corticosteroid use.

In this study recently published in The Journal of Allergy and Clinical Immunology (JACI), Denner et al. examined the relation of the lower airway microbiome, sampling both in the central airways using endobronchial brushes and in the peripheral airways using bronchoalveolar lavage, to asthma severity. They examined a group of 39 adults with asthma ranging in severity from mild to se-vere disease, as well as a separate group of 19 control subjects without lung disease. Two key measures of severity were evaluated: first, severity of airflow obstruction as assessed by FEV1, and second, requirement for corticosteroid therapy, particularly, oral therapy. As the technology to assess the microbiome has evolved, the authors used the latest MiSeq platform that permitted a more in-depth analysis of samples. All samples were collected at a time when asthma patients were clinically stable.

The diversity of the microbiome of asthmatic central airways was decreased in asthmatic sub-jects versus that of the controls. In the peripheral airways using BAL, genera such as Rickettsia and Staphylococcus were enriched in asthmatics compared to controls. In the central airways using brush samples, the genus Pseudomonas was significantly more abundant in asthmatics compared to controls, while Actinomyces and Prevotella were significantly less abundant in asthmatic samples. In these central airways samples, Streptococcus, Prevotella, Gemella and Veillonella were significantly reduced from asthmatic patients with the lowest FEV1. When ex-amined by oral corticosteroid use, there was decreased relative abundance of Prevotella and a significant increased abundance of Pseudomonas. Diversity indices in these asthmatic central airways samples were decreased from that seen in controls and correlated with a FEV1 in the lowest quartile, oral corticosteroid use, European ancestry, and BAL eosinophil proportion in the highest quartile.

The Denner study demonstrates clear differences in the airway microbiome recovered from en-dobronchial brushes and bronchoalveolar lavage in both asthmatic and control subjects. Asth-matic subjects differ in their central airways microbiome based on oral corticosteroid use and degree of airflow obstruction. These point prevalence data set the stage for needed future trials in which the influence of corticosteroids and other asthma medications, antibiotics, and disease progression can be examined over time. Understanding the role of the microbiome in asthmatic airways may in the future lead to novel, targeted therapies that improve clinical asthma control.

The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.

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