The respiratory microbiome in childhood asthma.

Asthma is the most prevalent noncommunicable disease in childhood, characterized by reversible airway constriction and inflammation of the lower airways. The respiratory tract consists of the upper and lower airways, which are lined with a diverse community of microbes. The composition and density of the respiratory microbiome differs across the respiratory tract, with microbes adapting to the gradually changing physiology of the environment. Over the past decade, both the upper and lower respiratory microbiomes have been implicated in the etiology and disease course of asthma, as well as in its severity and phenotype. We have reviewed the literature on the role of the respiratory microbiome in asthma, making a careful distinction between the relationship of the microbiome with development of childhood asthma and its relationship with the disease course, while accounting for age and the microbial niches studied. Furthermore, we have assessed the literature regarding the underlying asthma endotypes and the impact of the microbiome on the host immune response. We have identified distinct microbial signatures across the respiratory tract associated with asthma development, stability, and severity. These data suggest that the respiratory microbiome may be important for asthma development and severity and may therefore be a potential target for future microbiome-based preventive and treatment strategies.