Dietary fibre is an important regulator of the gut microbiome and is associated with many health benefits. However, high levels of fibre intake have also been reported to exacerbate some diseases. Her Show more
Dietary fibre is an important regulator of the gut microbiome and is associated with many health benefits. However, high levels of fibre intake have also been reported to exacerbate some diseases. Here, we show that mice fed semi-synthetic diets supplemented with purified inulin fibre develop chronic infections with the parasitic whipworm Trichuris muris, concomitant with dysregulated innate antimicrobial defences, exacerbated mucosal inflammation, and altered tryptophan metabolism. Inhibition of tryptophan catabolism or neutralizing either IL-27 or IL-18 restored infection resistance. Inulin-fed mice developed gut microbiota dysbiosis during parasite infection, with Proteobacteria becoming dominant. However, despite drastic differences in gut microbiota compositions in control- and inulin-fed mice, microbiota transfer and depletion experiments demonstrated that dietary inulin triggered chronic T. muris infection in a microbiota-independent manner. Importantly, removing inulin from the diet within a critical immune development window rapidly restored anti-parasite immunity, indicating direct, time-dependent modulation of mucosal immune responses. These data reveal T. muris-induced dysbiosis as a consequence rather than a causative factor of diet-driven changes in host susceptibility, and establish a direct link between dietary fibre and host defence at mucosal surfaces. Video Abstract. Show less