The Role of the Microbiome in Asthma: The Gut⁻Lung Axis

Abstract

Asthma is one of the most common chronic respiratory diseases worldwide. It affects all ages but frequently begins in childhood. Initiation and exacerbations may depend on individual susceptibility, viral infections, allergen exposure, tobacco smoke exposure, and outdoor air pollution. The aim of this review was to analyze the role of the gut⁻lung axis in asthma development, considering all asthma phenotypes, and to evaluate whether microbe-based therapies may be used for asthma prevention. Several studies have confirmed the role of microbiota in the regulation of immune function and the development of atopy and asthma. These clinical conditions have apparent roots in an insufficiency of early life exposure to the diverse environmental microbiota necessary to ensure colonization of the gastrointestinal and/or respiratory tracts. Commensal microbes are necessary for the induction of a balanced, tolerogenic immune system. The identification of commensal bacteria in both the gastroenteric and respiratory tracts could be an innovative and important issue. In conclusion, the function of microbiota in healthy immune response is generally acknowledged, and gut dysbacteriosis might result in chronic inflammatory respiratory disorders, particularly asthma. Further investigations are needed to improve our understanding of the role of the microbiome in inflammation and its influence on important risk factors for asthma, including tobacco smoke and host genetic features.

Keywords: asthma; atopy; gut microbiota; immunity; lung microbiota; microbiome.

Figure 1

Differences in the lung bacterial microbiota between asthmatic and healthy children. In the upper section, the names and the image of pathogens that can influence asthma development are represented. In the lower section, on the left it is shown the respiratory tract of an asthmatic child with an increase in interleukin (IL)-4, IL-5, and IL-13; on the right is shown the respiratory tract of a healthy child with normal values of IL-4, IL-5, and IL-13.