BUSINESS
Microbiome
UNDERSTANDING THE MICROBIOME:
THE GUT-LUNG AXIS Nutritionist Karen Jones, of Microbiome Labs, shares the latest thinking on the relationship between the gut microbiome and lung health… The last few years have witnessed a revolution
The pulmonary immune system is also
in our understanding of the microbiome and
impacted by the gut microbiota. Gut bacteria
particularly the micro-flora communities which
along with their metabolites, such as short chain
inhabit the gastrointestinal tract. This gut
fatty acids (SCFAs), and bacterial fragments,
microbiome assimilates many dietary nutrients
can translocate across the intestinal barrier and
indigestible by the human body, whose presence
enter systemic circulation through the mesenteric
and metabolites not only modulate GI immunity
lymphatic system to modulate the lung immune
but also impact the immune responses of distal
response. SCFAs act as signaling molecules in
organs, such as the liver, brain and lung.
the lungs on resident antigen presenting cells
Researchers are now beginning to understand that a healthy lung microbiota is essential in the maturation and homeostasis of lung immunity.
to help attenuate inflammatory and immune responses. There is clear evidence of a common mucosal
This is essential for reducing Th2-associated
immune system operating between the gut and
cytokine production after an allergen challenge
lung. T and B cells produced in the gut’s Peyer’s
and inducing regulatory cell production early
patches, migrate to intestinal and non-intestinal
in life. A healthy lung microbiota also helps to
sites, including the bronchial epithelium.
establish resident memory B cells, which are
Here, they transfer important immunological
important weapons against viruses such as
information through antibodies, particularly IgA.
influenza.
Innate lymphoid cells involved in tissue repair
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are also recruited to the lungs from the gut using inflammatory signals from IL-25. Commensal gut segmented filamentous bacteria (SFB) have been shown to regulate the CD4+ T-cell polarisation into the Th17 pathway. The over expression of these bacteria can exacerbate pulmonary fungal infections and autoimmune lung conditions. Dysbiosis usually manifests as the replacement of a complex and diverse community of anaerobes with a less diverse community and increased facultative anaerobes. This is driven by a poor diet, the use of broad-spectrum antibiotics, stress, alcohol or drug abuse, age and genetics, amongst other factors. Research has shown that microbiome imbalances are clearly implicated in asthma, CPOD and cystic fibrosis. For example, a reduction in Bifidobacteria and increase in Clostridia in the gut microbiome is associated with asthma in early life. Dysbiosis increases toll-like receptor (TLR) activation and the release of gut NF-κB, which is associated with an increased lung inflammatory response during influenza in mice. TLR activation is implicated in the cytokine storms recently seen in the most serious COVID-19 cases.
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