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The microbial environment and its influence on asthma prevention in early life

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There is accumulating evidence to suggest that the environmental microbiome plays a significant role in asthma development. The very low prevalence of asthma in populations highly exposed to microbial environments (farm children and Amish populations) highlights its preventive potential. This microbial diversity might be necessary to instruct a well-adapted immune response and regulated inflammatory responses to other inhaled and ingested environmental elements, such as allergens, particles, and viruses. Like the internal gut microbiome, which is increasingly recognized as an important instructor of immune maturation, the external environmental microbiome might shape immune responses on the skin, airway mucosal surfaces, and potentially also the gut early in life. The diversity of the external microbial world will ensure that of the many maladapted pathways leading to asthma development, most, if not all, will be counterbalanced. Likewise, important contributors to asthma, such as allergen sensitization and allergic manifestations early in life, are being suppressed. Thus the facets of innate immunity targeted by microbes and their compounds and metabolites might be the master switch to asthma and allergy protection, which has been found in environments rich in microbial exposures.

Section snippets

The environmental microbial world

The fungal and bacterial composition inside and outside of more than 1100 homes across the United States was studied by using novel DNA fingerprinting techniques.1 Distinct microbial communities were found in indoor and outdoor dust samples, but these differences were larger for bacteria than for fungi.

It has been known that almost all indoor fungi originate from outdoors, except those associated with molds and water damage, wood degrading, and foods.1 Therefore it is not surprising that an

The lung microbiome

The new DNA-sequencing methods have shown not only that the indoor and outdoor air that we breathe daily contains thousands of microorganisms but also that these microbes actually enter and potentially colonize the lower airways. Hilty et al18 were among the first to demonstrate that in healthy children and adults bacteria are found in bronchoalveolar lavage fluid and airway brushings, respectively. The bacterial composition differed between healthy subjects and asthmatic patients in whom more

The gut microbiome

Bacterial colonization in the lower airways is more strongly constricted and regulated than in the gut, where microbes are found in much greater abundance. The microbial diversity is highest in the oral cavity and lowest in the stomach and increases again from the small intestine to the colon.28 Dominated by anaerobes, commensal bacteria are involved in the conversion of indigestible food components, production of essential vitamins and cofactors, regulation of epithelial development, and

The microbial environment and asthma development

The indoor bacterial microbiome is determined by its home occupants, their presence, and their activities, as outlined above. A number of studies have suggested an association between home occupants (ie, crowding, family size, day care, and pet keeping) on asthma development (Fig 1). Although it is suggestive to speculate that indoor bacterial composition accounts for these effects, few studies have investigated this question.

Summary

There is accumulating evidence to suggest that the environmental microbiome plays a significant role in asthma pathogenesis. The very low prevalence of asthma in Amish and highly exposed European farm children, which cannot be explained by genetic factors, highlights its preventive potential. The microbial diversity around us might be necessary to instruct a well-adapted immune response and regulated inflammatory responses to other inhaled and ingested environmental elements, such as allergens,

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    Disclosure of potential conflict of interest: E. von Mutius has served as an Associate Editor for the Journal of Allergy and Clinical Immunology; is on the editorial board for the New England Journal of Medicine; has consultant arrangements with GlaxoSmithKline, Novartis, ALK-Abelló, Astellas Pharma Europe, and Vifor Pharma; has provided expert testimony on behalf of the European Research Council, the UK Research Excellence Framework, and AUKCAR; and has received grants from FrieslandCampina.

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