The Microbiome and Epidemiology
The respiratory microbiome: an underappreciated player in the human response to inhaled pollutants?

https://doi.org/10.1016/j.annepidem.2016.03.010Get rights and content

Abstract

Purpose

Microbial communities in or on the body (i.e., the microbiome) are highly physiologically active and influence human health. Although environmental scientists are increasingly aware of the gut microbiome, the respiratory microbiome's role in the human response to inhaled pollutants is largely unknown.

Methods

We reviewed the literature and present mechanisms by which the microbiome might mediate or modify human responses to inhaled pollutants.

Results

The respiratory microbiome has been shown to influence chronic lung disease exacerbations, and increasing evidence indicates a role in disease development. Research also suggests that the respiratory microbiome could plausibly metabolize inhaled pollutants or modulate host inflammatory responses to exposure. Because these responses depend on the microbes present, defining the composition of the resident microbiome and how microbial communities shift with exposure may help to explain variations in susceptibility to inhaled pollutants. Although more research is needed, significant measurement challenges remain for large epidemiologic studies of the respiratory microbiome.

Conclusions

The respiratory microbiome is likely an underexplored intermediate and potential cause of individual susceptibility to inhaled irritants/toxicants. Characterizing the microbiome's role in the human response to inhaled exposures could improve our understanding of the casual agents of exposure and suggest novel public health interventions.

Section snippets

What do we know about the respiratory microbiome?

For over 100 years, traditional wisdom was that in those without lung diseases, microbial communities resided only in the upper (i.e., mouth and nose) but not the lower (i.e., lungs) airways. More recently, however, the use of culture-independent, sequence-based techniques has clearly shown that the lungs are not sterile [13], [14]. A summary of the current state of the science can be found in several excellent review articles [15], [16], [17], [18] with brief highlights in the following

How might the respiratory microbiome influence the human response to inhaled irritants/toxicants?

There is a growing understanding that our microbiota plays a critical role in the development and mediation of many human processes. As some of the first cells in the body encountering inhaled environmental toxicants, it is likely that the respiratory microbiome is both affected by these exposures and affects these exposures (Fig. 1). In the ideal world, the microbiome would serve as a protective shield for human host. However, it is also likely that the human host gets caught in the

What evidence is there of a respiratory microbiome response to environmental pollutants?

An extremely small literature on smoking supports the hypothesis that inhaled air irritants/toxicants may impact the respiratory microbiome. Most such research, however, is short term and from the subgingival environment. In this environment, lower abundances of health-promoting microbes and higher abundances of pathogens have been reported with smoking exposures [52]. Interestingly, smoking appears to have a rapid impact on the oral microbiome with changes in bacterial colonization reported

What challenges do we face in studying the role of the respiratory microbiome?

One of the key challenges to clinical and epidemiologic research on environmental exposures and the respiratory microbiome relates to existing measurement techniques. Approaches to study microbial communities of the lungs have traditionally included bronchoalveolar lavage and induced sputum [17]. Although previous concerns about the potential for contamination during the bronchoscopic process have been allayed based on results of protected specimen brushing [20], [23], both bronchoalveolar

Summary and implications

There is a growing understanding that the human responsiveness to external assaults can be shaped by our microbiome. In this article, we presented evidence that the respiratory microbiome is an active player in human health and proposed mechanisms by which the microbiome might plausibly mediate or modify the human health response to inhaled irritants/toxicants. Such a role would have several important implications for our understanding of how inhaled irritants/toxicants impact health and who is

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    The authors have no conflicts of interest to disclose.

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