Old friends, microbes, and allergic diseases

Soil intake modifies the gut microbiota and alleviates Th2-type immune response in an ovalbumin-induced asthma mouse model

Background

A low-clean living environment (LCLE) can increase gut microbial diversity and prevent allergic diseases, whereas gut microbial dysbiosis is closely related to the pathogenesis of asthma. Our previous studies suggested that soil in the LCLE is a key factor in shaping intestinal microbiota. We aimed to explore whether sterilized soil intake as a prebiotic while being incubated with microbes in the air can attenuate mouse asthma inflammation by modifying gut microbiota.

Methods

16S rRNA gene sequencing was used to analyze the gut microbial composition, in combination with immune parameters measured in the lung and serum samples.

Results

16S rRNA gene sequencing results showed significant differences in the fecal microbiota composition between the test and control mice, with a higher abundance of Allobaculum, Alistipes, and Lachnospiraceae_UCG-001, which produce short-chain fatty acids and are beneficial for health in the test mice. Soil intake significantly downregulated the concentrations of IL-4 and IL-9 in serum and increased the expression of IFN-γ, which regulated the Th1/Th2 balance in the lung by polarizing the immune system toward Th1, alleviating ovalbumin-induced asthma inflammation. The effect of sensitization on gut microbiota was greater than that of air microbes and age together but weaker than that of soil.

Conclusions

Soil intake effectively reduced the expression of inflammatory cytokines in asthmatic mice, possibly by promoting the growth of multiple beneficial bacteria. The results indicated that the development of soil-based prebiotic products might be used for allergic asthma management, and our study provides further evidence for the hygiene hypothesis.

Reconciling Hygiene and Cleanliness: A New Perspective from Human Microbiome

The term hygiene is deeply rooted with the concept of maintaining sound health and alertness towards cleanliness, while "hygiene hypothesis" depicts the protective role of microbial community exposure in development of early immunity and initial allergic and aesthetic reactions. The tug-of-war has now been pushed toward the literal term "hygiene" over the "hygiene hypothesis" and has continued with disinfection of all microbial loads from the related environments to avoid infections in humans. With the advancement in the microbiome studies, it became clear that humans possess warm, and significant relationships with diverse microbial community. With this opinion article, we have emphasized on the importance of hygiene hypothesis in immunological responses. We also propose the individual/targeted hygiene instead of application of unanimous hygiene hypothesis. This review also elaborates the common practices that should be employed to maintain hygiene along with the balanced microbiome.