A gut commensal protist protects against virus-mediated loss of oral tolerance

Abstract Loss of oral tolerance (LOT) to gluten, characterized by a T helper 1 (Th1) gluten-specific immune response, is a hallmark of celiac disease (CeD) and can be triggered by enteric viral infections. We hypothesized that certain gut microbes have the capacity to protect against virus-mediated LOT. By using our previously defined reovirus-mediated LOT CeD model, we discovered that the gut colonizing protist Tritrichomonas (T.) arnold promotes oral tolerance and protects against reovirus-mediated LOT by suppressing the reovirus-induced proinflammatory program of dietary-antigen-presenting CD103 + dendritic cells. Importantly, T. arnold did not affect antiviral host immunity, suggesting that T. arnold -mediated protection against T1L-induced LOT is not attributable to differences in antiviral host responses. Additionally, using gnotobiotic mice, we found that Tritrichomonas arnold colonization is sufficient to protect against reovirus-mediated LOT in the absence of the microbiota. Mechanistically, we show that Tritrichomonas arnold colonization restrains reovirus-induced inflammatory responses in dendritic cells and thus limit their ability to promote Th1 immune responses ex vivo . Finally, our studies using human stool samples support a role for Tritrichomonas sp. colonization in protecting against development of CeD. This study will motivate the design of effective therapies to prevent LOT to gluten in at-risk individuals and to reinstate tolerance to gluten in CeD patients. One Sentence Summary Tritrichomonas arnold protects against virus-mediated loss of oral tolerance to gluten and is underrepresented in celiac disease patients.