Indoleamine 2,3-dioxygenase 1 regulates cell permissivity to astrovirus infection.

Astroviruses cause a spectrum of diseases spanning asymptomatic infections to severe diarrhea, but little is understood about their pathogenesis. We previously determined that small intestinal goblet cells were the main cell type infected by murine astrovirus-1. Here, we focused on the host immune response to infection and inadvertently discovered a role for indoleamine 2,3-dioxygenase 1 (Ido1), a host tryptophan catabolizing enzyme, in the cellular tropism of murine and human astroviruses. We identified that Ido1 expression was highly enriched among infected goblet cells, and spatially corresponded to the zonation of infection. Because Ido1 can act as a negative regulator of inflammation, we hypothesized it could dampen host antiviral responses. Despite robust interferon signaling in goblet cells, as well as tuft cell and enterocyte bystanders, we observed delayed cytokine induction and suppressed levels of fecal lipocalin-2. Although we found Ido-/- animals were more resistant to infection, this was not associated with fewer goblet cells nor could it be rescued by knocking out interferon responses, suggesting that IDO1 instead regulates cell permissivity. We characterized IDO1-/- Caco-2 cells and observed significantly reduced human astrovirus-1 infection. Together this study highlights a role for Ido1 in astrovirus infection and epithelial cell maturation.