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Fungal and bacterial microbiota in asthmatic airways

Published online: July 3, 2019

Asthma is a complex, heterogenous disease characterized by airway inflammation, airflow obstruction, and bronchial hyperresponsiveness. The relationship between asthma, atopy, and underlying type-2 (T2) airway inflammation is complex. Two types of asthma, defined by atopy markers and type 2 (T2) inflammation, have different molecular pathways and treatment responsiveness. While aspects of the asthma microbiome have been characterized recently, the relationship of both the bacterial and fungal microbiome to T2 inflammation is still uncertain.

In an article recently published in The Journal of Allergy & Clinical Immunology (JACI), Sharma and colleagues investigated both fungal and bacterial diversity with associated atopy and type-2 inflammation in patients with mild to severe asthma. They collected bronchoalveolar lavages (BAL) and endobronchial brushings (EB) samples from 39 asthmatic subjects and 19 healthy control subjects. The authors compared the fungal and bacterial microbiota between (1) asthmatic subjects with atopy (AA) and without atopy (ANA) to control subjects with (CA) and without atopy (CNA), and (2) among asthmatics, between T2-High and T2 Low inflammatory phenotypes as defined by the number of blood eosinophils.

The researchers found that subjects with asthma and the T2-High phenotype had lower fungal diversity compared to T2-Low patients; key fungal genera enriched in the T2-High group included Cladosporium, Fusarium, and Aspergillus. Correlative analyses identified significant positive associations between specific fungal genera and key clinical variables in the asthma cohort, including forced expiratory volume in 1 second (FEV1), BAL-lymphocytes, and BAL-eosinophils. The authors also identified distinct interkingdom (bacterial and fungal) co-occurrence patterns between asthmatic subjects and healthy controls. Compositional analyses led to identification of precise bacterial and fungal microbiome signatures associated with these asthma endotypes.

In summary, this study demonstrates 1) bacterial and fungal biomarkers of inflammatory phenotypes in asthma, 2) significant co-association between bacterial and fungal genera, and 3) correlation between predicted bacterial functional gene abundances and clinical parameters. These findings provide potential new biomarkers that may be useful, particularly when combined with other clinical and biological markers, to distinguish asthma endotypes.

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