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.

Somatic mutations in tet methylcytosine dioxygenase 2 (TET2), which encodes an epigenetic modifier enzyme, drive the development of haematopoietic malignancies1–7. In both humans and mice, TET2 deficiency leads to increased self-renewal of haematopoietic stem cells with a net developmental bias towards the myeloid lineage1,4,8,9. However, pre-leukaemic myeloproliferation (PMP) occurs in only a fraction of Tet2−/− mice8,9 and humans with TET2 mutations1,3,5–7, suggesting that extrinsic non-cell-autonomous factors are required for disease onset. Here we show that bacterial translocation and increased interleukin-6 production, resulting from dysfunction of the small-intestinal barrier, are critical for the development of PMP in mice that lack Tet2 expression in haematopoietic cells. Furthermore, in symptom-free Tet2−/− mice, PMP can be induced by disrupting intestinal barrier integrity, or in response to systemic bacterial stimuli such as the toll-like receptor 2 agonist. PMP was reversed by antibiotic treatment and failed to develop in germ-free Tet2−/− mice, which illustrates the importance of microbial signals in the development of this condition. Our findings demonstrate the requirement for microbial-dependent inflammation in the development of PMP and provide a mechanistic basis for the variation in PMP penetrance observed in Tet2−/− mice. This study will prompt new lines of investigation that may profoundly affect the prevention and management of haematopoietic malignancies.

Coeliac disease (CeD) is a complex, polygenic inflammatory enteropathy caused by exposure to dietary gluten that selectively occurs in a subset of genetically susceptible HLA-DQ8 and HLA-DQ2 individuals 1 , 2 . The need to develop non-dietary treatments is now widely recognized 3 , but it is hampered by the lack of a pathophysiologically relevant gluten- and HLA-dependent preclinical model. Furthermore, while human studies have led to major advances in our understanding of CeD pathogenesis 4 , direct demonstration of the respective roles of disease-predisposing HLA molecules, and adaptive and innate immunity in the development of tissue damage is missing. To address these unmet needs, we engineered a mouse model that reproduces the dual overexpression of IL-15 in the gut epithelium and the lamina propria (LP) characteristic of active CeD, expresses the predisposing HLA-DQ8 molecule, and develops villous atrophy (VA) upon gluten ingestion. We show that overexpression of IL-15 in both the epithelium and LP is required for the development of VA, demonstrating the location-dependent central role of IL-15 in CeD pathogenesis. Furthermore, our study reveals that CD4 + T cells and HLA-DQ8 are required for VA development, because of their critical role in the licensing of cytotoxic T cells to mediate intestinal epithelial cell (IEC) lysis. Finally, it establishes that IFN-γ and transglutaminase 2 (TG2) are central for tissue destruction. This mouse model, by reflecting the complex interplay between gluten, genetics and the IL-15-driven tissue inflammation, represents a powerful preclinical model for the characterization of cellular circuits critically involved in intestinal tissue damage in CeD, and the identification and testing of new therapeutic strategies.

The cytidine deaminase APOBEC3G (A3G) enzyme exerts an intrinsic anti–human immunodeficiency virus (HIV) defense by introducing lethal G-to-A hypermutations in the viral genome. The HIV-1 viral infectivity factor (Vif) protein triggers degradation of A3G and counteracts this antiviral effect. The impact of A3G on the adaptive cellular immune response has not been characterized. We examined whether A3G-edited defective viruses, which are known to express truncated or misfolded viral proteins, activate HIV-1–specific (HS) CD8+ cytotoxic T lymphocytes (CTLs). To this end, we compared the immunogenicity of cells infected with wild-type or Vif-deleted viruses in the presence or absence of the cytidine deaminase. The inhibitory effect of A3G on HIV replication was associated with a strong activation of cocultivated HS-CTLs. CTL activation was particularly marked with Vif-deleted HIV and with viruses harboring A3G. Enzymatically inactive A3G mutants failed to enhance CTL activation. We also engineered proviruses bearing premature stop codons in their genome as scars of A3G editing. These viruses were not infectious but potently activated HS-CTLs. Therefore, the pool of defective viruses generated by A3G represents an underestimated source of viral antigens. Our results reveal a novel function for A3G, acting not only as an intrinsic antiviral factor but also as an inducer of the adaptive immune system.