The link between the gut microbiota and airway inflammation

Anh-Vu Nguyen

Introduction. Inflammation associated airway diseases (IAADs), which include asthma and chronic obstructive pulmonary disease (COPD), affect millions of Americans every year. COPD, for example, is the 3rd leading cause of death in the U.S. Despite this, there are no cures for IAADs at this time. Currently, treatment for IAADs is supportive and includes technique such as oxygen therapy and smoking cessation to manage the patient’s symptoms. Recent studies have linked the gut flora, which are microbes that line our digest tract, to systemic and respiratory immunity. This study aims to identify novel treatments for IAADs based on the manipulation and supplementation of these microbes. Methods. Humans, mice, and rats were used in various studies to correlate gut flora composition to the incidence and severity of inflammation and various IAADs. Identification of treatments for IAADs focused on probiotic supplementation, fecal oral transplantation, and dietary changes. Results. Probiotic supplementation were shown to alter local microflora and regulate gut Toll-like receptors; consequently, suppressing the Th2 response in allergic disease and decreasing lung inflammation1. Additionally, probiotics were shown to decrease the incidence of upper respiratory tract infection in human athletes by limiting exercise-induced drops in tryptophan levels2. Fecal transplantation also showed promise in IAAD treatment. Fecal transplantation was shown to normalize concentrations of the inflammatory cytokines TNFa and IL-10 in mice 6-hours following a pneumococcal infection3. Administration of Clostridium buyrate was additionally shown to enhance the effects of SIT therapy – the only available effective treatment that targets allergic diseases, such as asthma, rather than the symptoms4. Conversely, germ-free mice with low-diversity microbiota were had elevated serum IgE in early life, which is associated with the development of asthma5. Similarly, mice with depleted gut flora had increased bacterial dissemination and inflammation following pneumococcal pneumonia infection when compared to controls3. Finally, dietary supplementation of soluble fiber was shown to upregulate sputum expression of the GPR41 and GPR43 genes; consequently, decreasing airway inflammation and improving lung function in mice6. Consumption of soluble fiber was also shown to change the gut microbiota composition, which resulted in increased levels of short chain fatty acids – molecules that have been shown to be protective against allergic inflammation in mice7. Discussion. While more research needs to be down a treatment is discovered, the information above regarding probiotic supplementation, fecal transplants, and dietary changes may be valuable in directing scientists towards developing much-needed therapies that prevent, and eventually cure, IAADs.

  1.  Fujimura KE, Demoor T, Rauch M. House dust exposure mediates gut microbiome Lactobacillus enrichment and airway immune defense against allergens and virus infection. Proceedings of the National Academy of Sciences. 2013;111(2):805-810.
  2. Strasser B, Gostner JM. Probiotic Supplements Beneficially Affect Tryptophan–Kynurenine Metabolism and Reduce the Incidence of Upper Respiratory Tract Infections in Trained Athletes: A Randomized, Double-Blinded, Placebo-Controlled Trial. Nutrients. 2016;8(11).
  3. Schuijt TJ, Lankelma JM, Scicluna BP. The gut microbiota plays a protective role in the host defence against pneumococcal pneumonia. Gut. 20185;65(4):575-584.
  4. Liao H-Y, Tao L, Zhao J. Clostridium butyricum in combination with specific immunotherapy converts antigen-specific B cells to regulatory B cells in asthmatic patients. Scientific Reports. 2016;6(1).
  5. Cahenzil J, Koller Y, Wyss M. Intestinal Microbial Diversity during Early-Life Colonization Shapes Long-Term IgE Levels. Cell Host Microbe. 2013;14(5):559-570.
  6. Halnes I, Baines K, Berthon B. Soluble Fibre Meal Challenge Reduces Airway Inflammation and Expression of GPR43 and GPR41 in Asthma. Nutrients. 2017;9(1).
  7. Trompette, A., et al. (2014). “Gut microbiota metabolism of dietary fiber influences allergic airway disease and hematopoiesis.” Nature medicine 20(2): 159-166.