A new study in mice has shown that levels of dietary fibre can influence the balance of microbes in the gut in ways that make the airways more or less prone to the inflammation seen in allergic airway diseases.
Metabolites from intestinal microbiota are key determinants of host-microbe mutualism and, consequently, the health or disease of the intestinal tract, researchers said.
However, whether such host-microbe crosstalk influences inflammation in peripheral tissues, such as the lung, is poorly understood.
"We found that dietary fermentable fibre content changed the composition of the gut and lung microbiota, in particular by altering the ratio of Firmicutes to Bacteroidetes," researchers from the University Hospital of Lausanne in Switzerland and colleagues wrote in the journal Nature Medicine.
The gut microbiota metabolised the fibre, consequently increasing the concentration of circulating short-chain fatty acids (SCFAs), researchers said.
Mice fed a high-fibre diet had increased circulating levels of SCFAs and were protected against allergic inflammation in the lung, whereas a low-fibre diet decreased levels of SCFAs and increased allergic airway disease.
Treatment of mice with the SCFA propionate led to alterations in bone marrow hematopoiesis that were characterised by enhanced generation of macrophage and dendritic cell (DC) precursors and subsequent seeding of the lungs by DCs with high phagocytic capacity but an impaired ability to promote T helper type 2 (TH2) cell effector function.
The effects of propionate on allergic inflammation were dependent on G protein coupled receptor 41 (GPR41, also called free fatty acid receptor 3 or FFAR3), but not GPR43 (also called free fatty acid receptor 2 or FFAR2).
"Our results show that dietary fermentable fibre and SCFAs can shape the immunological environment in the lung and influence the severity of allergic inflammation," researchers said.