Influence of the gut and airway microbiome on asthma development and disease

Abstract

There are ample data to suggest that early‐life dysbiosis of both the gut and/or airway microbiome can predispose a child to develop along a trajectory toward asthma. Although individual studies show clear associations between dysbiosis and asthma development, it is less clear what (collection of) bacterial species is mechanistically responsible for the observed effects. This is partly due to issues related to the asthma diagnosis and the broad spectrum of anatomical sites, sample techniques, and analysis protocols that are used in different studies. Moreover, there is limited attention for potential differences in the genetics of individuals that would affect the outcome of the interaction between the environment and that individual. Despite these challenges, the first bacterial components were identified that are able to affect the transcriptional state of human cells, ergo the immune system. Such molecules could in the future be the basis for intervention studies that are now (necessarily) restricted to a limited number of bacterial species. For this transition, it might be prudent to develop an ex vivo human model of a local mucosal immune system to better and safer explore the impact of such molecules. With this approach, we might move beyond association toward understanding of causality.

The Role of Biodiversity in the Development of Asthma and Allergic Sensitization: A State-of-the-Science Review

“…Our comprehensive review included also evidence from longitudinal studies on biodiversity and respiratory outcomes, 13 – 21 which allowed assessment of the time-dependent effects related to outer and inner layer biodiversity on the development of asthma, wheezing, and allergic sensitization. The different exposure assessment, sampling methods applied, and different types of samples (including stool and airway samples) may also complicate the comparison of different studies For example, the multitude of locations (nasal cavity; naso-, oro-, and hypopharynx; trachea; and/or bronchi) and diverse sampling techniques (brush, swab, nasal wash, induced sputum, or bronchial alveolar lavage) used to assess the airway microbiome may introduce differences in the characterization of the microbiome composition 22 and limit comparison between different studies. Another challenge in comparing studies may be the temporal variation in biodiversity, namely, the human microbiome.…”

“…Another challenge in comparing studies may be the temporal variation in biodiversity, namely, the human microbiome. 22 Previous studies indicate that human microbiome exhibits high variability in early life, 22 throughout seasons, and in response to respiratory tract infections (i.e., the airway microbiome) 15 , 17 , 23 and is also influenced by interactions between the environment 24 and host- and microbiome-associated factors. 25 – 28 Moreover, the different metrics used for diversity throughout different studies (e.g., Shannon diversity index, Simpson index, phylogenetic diversity, Chao1) may also complicate comparison between studies.…”