Viral infections have been proposed to elicit pathological processes leading to the initiation of T helper 1 (TH1) immunity against dietary gluten and celiac disease (CeD). To test this hypothesis and gain insights into mechanisms underlying virus-induced loss of tolerance to dietary antigens, we developed a viral infection model that makes use of two reovirus strains that infect the intestine but differ in their immunopathological outcomes. Reovirus is an avirulent pathogen that elicits protective immunity, but we discovered that it can nonetheless disrupt intestinal immune homeostasis at inductive and effector sites of oral tolerance by suppressing peripheral regulatory T cell (pTreg) conversion and promoting TH1 immunity to dietary antigen. Initiation of TH1 immunity to dietary antigen was dependent on interferon regulatory factor 1 and dissociated from suppression of pTreg conversion, which was mediated by type-1 interferon. Last, our study in humans supports a role for infection with reovirus, a seemingly innocuous virus, in triggering the development of CeD.

Lambda interferon (IFN-) has potent antiviral effects against multiple enteric viral pathogens, including norovirus and rotavirus, in both preventing and curing infection. Because the intestine includes a diverse array of cell types, however, the cell(s) upon which IFN-acts to exert its antiviral effects is unclear. Here, we sought to identify IFN--responsive cells by generation of mice with lineagespecific deletion of the receptor for IFN-, Ifnlr1. We found that expression of IFNLR1 on intestinal epithelial cells (IECs) in the small intestine and colon is required for enteric IFN-antiviral activity. IEC Ifnlr1 expression also determines the efficacy of IFN-in resolving persistent murine norovirus (MNoV) infection and regulates fecal shedding and viral titers in tissue. Thus, the expression of Ifnlr1 by IECs is necessary for the response to both endogenous and exogenous IFN-. We further demonstrate that IEC Ifnlr1 expression is required for the sterilizing innate immune effects of IFN-by extending these findings in Rag1-deficient mice. Finally, we assessed whether our findings pertained to multiple viral pathogens by infecting mice specifically lacking IEC Ifnlr1 expression with reovirus. These mice phenocopied Ifnlr1-null animals, exhibiting increased intestinal tissue titers and enhanced reovirus fecal shedding. Thus, IECs are the critical cell type responding to IFN-to control multiple enteric viruses. This is the first genetic evidence that supports an essential role for IECs in IFN--mediated control of enteric viral infection, and these findings provide insight into the mechanism of IFN--mediated antiviral activity.IMPORTANCE Human noroviruses (HNoVs) are the leading cause of epidemic gastroenteritis worldwide. Type III interferons (IFN-) control enteric viral infections in the gut and have been shown to cure mouse norovirus, a small-animal model for HNoVs. Using a genetic approach with conditional knockout mice, we identified IECs as the dominant IFN--responsive cells in control of enteric virus infection in vivo. Upon murine norovirus or reovirus infection, Ifnlr1 depletion in IECs largely recapitulated the phenotype seen in Ifnlr1 Ϫ/Ϫ mice of higher intestinal tissue viral titers and increased viral shedding in the stool. Moreover, IFN--mediated sterilizing immunity against murine norovirus requires the capacity of IECs to respond to IFN-. These findings clarify the mechanism of action of this cytokine and emphasize the therapeutic potential of IFN-for treating mucosal viral infections.KEYWORDS innate immunity, interferons, mucosal immunity, norovirus, reovirus

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Chikungunya virus (CHIKV) is an arthritogenic alphavirus that causes debilitating musculoskeletal disease. CHIKV displays broad cell, tissue, and species tropism, which may correlate with the attachment factors and entry receptors used by the virus. Cell-surface glycosaminoglycans (GAGs) have been identified as CHIKV attachment factors. However, the specific types of GAGs and potentially other glycans to which CHIKV binds and whether there are strain-specific differences in GAG binding is not fully understood. To identify the types of glycans bound by CHIKV, we conducted glycan microarray analyses and discovered that CHIKV preferentially binds GAGs. Microarray results also indicate that sulfate groups on GAGs are essential for CHIKV binding and that CHIKV binds most strongly to longer GAG chains of heparin and heparan sulfate. To determine whether GAG-binding capacity varies among CHIKV strains, a representative strain from each genetic clade was tested. While all strains directly bound to heparin and chondroitin sulfate in ELISAs and depended on heparan sulfate for efficient cell-binding and infection, we observed some variation by strain. Enzymatic removal of cell-surface GAGs and genetic ablation that diminishes GAG expression reduced CHIKV binding and infectivity of all strains. Collectively, these data demonstrate that GAGs are the preferred glycan bound by CHIKV, enhance our understanding of the specific GAG moieties required for CHIKV binding, define strain differences in GAG engagement, and provide further evidence for a critical function of GAGs in CHIKV cell attachment and infection. IMPORTANCE Alphavirus infections are a global health threat, contributing to outbreaks of disease in many parts of the world. Recent epidemics caused by CHIKV, an arthritogenic alphavirus, resulted in more than 8.5 million cases as the virus has spread into new geographic regions, including the Western Hemisphere. CHIKV causes disease in the majority of people infected, leading to severe and debilitating arthritis. Despite the severity of CHIKV disease, there are no licensed therapeutics. Since attachment factors and receptors are determinants of viral tropism and pathogenesis, understanding these virus-host interactions can enhance our knowledge of CHIKV infection. We analyzed over 670 glycans and identified GAGs as the main glycan bound by CHIKV. We defined specific GAG components required for CHIKV binding and assessed strain-specific differences in GAG-binding capacity. These studies provide insight about cell-surface molecules that CHIKV binds, which could facilitate the development of antiviral therapeutics targeting the CHIKV attachment step.