Search

Background & Aims Hepatic innate immune control of viral infections has largely been attributed to Kupffer cells, the liver-resident macrophages. However, hepatocytes, the parenchymal cells of the liver, also possess potent immunological functions in addition to their known metabolic functions. Owing to their abundance in the liver and known immunological functions, we aimed to investigate the direct antiviral mechanisms employed by hepatocytes. Methods Using lymphocytic choriomeningitis virus (LCMV) as a model of liver infection, we first assessed the role of myeloid cells by depletion prior to infection. We investigated the role of hepatocyte-intrinsic innate immune signaling by infecting mice lacking canonical NF-κB signaling (IkkβΔHep) specifically in hepatocytes. In addition, mice lacking hepatocyte-specific interferon-α/β signaling-(IfnarΔHep), or interferon-α/β signaling in myeloid cells-(IfnarΔMyel) were infected. Results Here, we demonstrate that LCMV activates NF-κB signaling in hepatocytes. LCMV-triggered NF-κB activation in hepatocytes did not depend on Kupffer cells or TNFR1 signaling but rather on Toll-like receptor signaling. LCMV-infected IkkβΔHep livers displayed strongly elevated viral titers due to LCMV accumulation within hepatocytes, reduced interferon-stimulated gene (ISG) expression, delayed intrahepatic immune cell influx and delayed intrahepatic LCMV-specific CD8+ T cell responses. Notably, viral clearance and ISG expression were also reduced in LCMV-infected primary hepatocytes lacking IKKβ, demonstrating a hepatocyte-intrinsic effect. Similar to livers of IkkβΔHep mice, enhanced hepatocytic LCMV accumulation was observed in livers of IfnarΔHep mice, whereas IfnarΔMyel mice were able to control LCMV infection. Hepatocytic NF-κB signaling was also required for efficient ISG induction in HDV-infected dHepaRG cells and interferon-α/β-mediated inhibition of HBV replication in vitro. Conclusions Together, these data show that hepatocyte-intrinsic NF-κB is a vital amplifier of interferon-α/β signaling, which is pivotal for strong early ISG responses, immune cell infiltration and hepatic viral clearance. Lay summary Innate immune cells have been ascribed a primary role in controlling viral clearance upon hepatic infections. We identified a novel dual role for NF-κB signaling in infected hepatocytes which was crucial for maximizing interferon responses and initiating adaptive immunity, thereby efficiently controlling hepatic virus replication.

Salmonella Typhimurium (S.Tm) causes acute enteropathy resolving after 4-7 days. Strikingly, antibiotic therapy does not accelerate disease resolution. We screened for factors blocking remission using a S.Tm enterocolitis model. The antibiotic ciprofloxacin clears pathogen stool loads within 3-24 hr, while gut pathology resolves more slowly (ψ50: ∼48 hr, remission: 6-9 days). This delayed resolution is mediated by an interferon-γ (IFN-γ)-dependent response that is triggered during acute infection and continues throughout therapy. Specifically, IFN-γ production by mucosal T and NK cells retards disease resolution by maintaining signaling through the transcriptional regulator STAT1 and boosting expression of inflammatory mediators like IL-1β, TNF, and iNOS. Additionally, sustained IFN-γ fosters phagocyte accumulation and hampers antimicrobial defense mediated by IL-22 and the lectin REGIIIβ. These findings reveal a role for IFN-γ in delaying resolution of intestinal inflammation and may inform therapies for acute Salmonella enteropathy, chronic inflammatory bowel diseases, or disease resolution during antibiotic treatment.

Innate immune activation is essential to mount an effective antiviral response and to prime adaptive immunity. Although a crucial role of CD169+ cells during vesicular stomatitis virus (VSV) infections is increasingly recognized, factors regulating CD169+ cells during viral infections remain unclear. Here, we show that tumor necrosis factor is produced by CD11b+ Ly6C+ Ly6G+ cells following infection with VSV. The absence of TNF or TNF receptor 1 (TNFR1) resulted in reduced numbers of CD169+ cells and in reduced type I interferon (IFN-I) production during VSV infection, with a severe disease outcome. Specifically, TNF triggered RelA translocation into the nuclei of CD169+ cells; this translocation was inhibited when the paracaspase MALT-1 was absent. Consequently, MALT1 deficiency resulted in reduced VSV replication, defective innate immune activation, and development of severe disease. These findings indicate that TNF mediates the maintenance of CD169+ cells and innate and adaptive immune activation during VSV infection. Fil: Shinde, Prashant V.. Heinrich Heine University; Alemania Fil: Xu, Haifeng C.. Heinrich Heine University; Alemania Fil: Maney, Sathish Kumar. Heinrich Heine University; Alemania Fil: Kloetgen, Andreas. Heinrich Heine University; Alemania Fil: Namineni, Sukumar. Helmholtz Zentrum Munich; Alemania Fil: Zhuang, Yuan. Heinrich Heine University; Alemania Fil: Honke, Nadine. Heinrich Heine University; Alemania Fil: Shaabani, Namir. The Scripps Research Institute; Estados Unidos Fil: Bellora, Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales. Universidad Nacional del Comahue. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales.; Argentina Fil: Doerrenberg, Mareike. Heinrich Heine University; Alemania Fil: Trilling, Mirko. Universitat Essen; Alemania Fil: Pozdeev, Vitaly I.. Heinrich Heine University; Alemania Fil: van Rooijen, Nico. Department Of Cell Biology, Vrije University; Países Bajos Fil: Scheu, Stefanie. Heinrich Heine University; Alemania Fil: Pfeffer, Klaus. Heinrich Heine University; Alemania Fil: Crocker, Paul R.. University of Dundee; Reino Unido Fil: Tanaka, Masato. Tokyo University. Laboratory Of Immune Regulation; Japón Fil: Duggimpudi, Sujitha. Heinrich Heine University; Alemania Fil: Knolle, Percy. Helmholtz Zentrum Munich; Alemania Fil: Heikenwalder, Mathias. Helmholtz Zentrum Munich; Alemania Fil: Ruland, Jürgen. Universitat Technical Zu Munich; Alemania Fil: Mak, Tak W.. University Health Network; Canadá Fil: Brenner, Dirk. University of Southern Denmark; Dinamarca Fil: Pandyra, Aleksandra A.. Universitat Essen; Alemania Fil: Hoell, Jessica I.. Heinrich Heine University; Alemania Fil: Borkhardt, Arndt. Heinrich Heine University; Alemania Fil: Häussinger, Dieter. Heinrich Heine University; Alemania Fil: Lang, Karl S.. Universitat Essen; Alemania Fil: Lang, Philipp A.. Heinrich Heine University; Alemania

Background & Aim Virus-induced fulminant hepatitis is a major cause of acute liver failure. During acute viral hepatitis the impact of type I interferon (IFN-I) on myeloid cells, including liver-resident Kupffer cells (KC), is only partially understood. Herein, we dissected the impact of locally induced IFN-I responses on myeloid cell function and hepatocytes during acute liver inflammation. Methods Two different DNA-encoded viruses, vaccinia virus (VACV) and murine cytomegalovirus (MCMV), were studied. In vivo imaging was applied to visualize local IFN-β induction and IFN-I receptor (IFNAR) triggering in VACV-infected reporter mice. Furthermore, mice with a cell type-selective IFNAR ablation were analyzed to dissect the role of IFNAR signaling in myeloid cells and hepatocytes. Experiments with Cx3cr1 +/gfp mice revealed the origin of reconstituted KC. Finally, mixed bone marrow chimeric mice were studied to specifically analyze the effect of IFNAR triggering on liver infiltrating monocytes. Results VACV infection induced local IFN-β responses, which lead to IFNAR signaling primarily within the liver. IFNAR triggering was needed to control the infection and prevent fulminant hepatitis. The severity of liver inflammation was independent of IFNAR triggering of hepatocytes, whereas IFNAR triggering of myeloid cells protected from excessive inflammation. Upon VACV or MCMV infection KC disappeared, whereas infiltrating monocytes differentiated to KC afterwards. During IFNAR triggering such replenished monocyte-derived KC comprised more IFNAR-deficient than -competent cells in mixed bone marrow chimeric mice, whereas after the decline of IFNAR triggering both subsets showed an even distribution. Conclusion Upon VACV infection IFNAR triggering of myeloid cells, but not of hepatocytes, critically modulates acute viral hepatitis. During infection with DNA-encoded viruses IFNAR triggering of liver-infiltrating blood monocytes delays the development of monocyte-derived KC, pointing towards new therapeutic strategies for acute viral hepatitis. Lay summary Viral infection can cause fulminant hepatitis, which in turn is a major cause of acute liver failure. Herein, we aimed to study the role of type 1 interferon responses in acute viral hepatitis. We identified that during infection with DNA-encoded viruses, type 1 interferon receptor triggering of blood monocytes delays the development of monocyte-derived Kupffer cells. This points to new therapeutic strategies for acute viral hepatitis.

Viruses express a wide range of immune evasion proteins to modulate host immunity. The DNA-encoded poxvirus vaccinia virus (VACV) carries IFN-I inhibitors of which the viral IFN-I receptor B18 binds to the surface of host cells to compete with the endogenous host IFN-I receptor. Upon VACV infection WT mice survive infection with mild signs of disease, while IFN-I is not detectable in the serum. Surprisingly, IFN-I receptor deficient (IFNAR−/−) mice succumb to VACV infection within 5 days. Thus, we hypothesized that upon VACV infection local IFN-I responses were induced which significantly affected the disease course. To monitor local IFN-I responses, we infected IFN- β -luciferase reporter mice with VACV. By in vivo imaging we found that upon VACV infection local IFN- β responses were induced within secondary lymphoid organs. Studies with Mx2-luciferase reporter mice, which express luciferase upon IFNAR triggering, revealed significant IFNAR triggering within the liver and intermediate triggering in secondary lymphoid organs. Of note, viral titers in the liver of infected IFNAR−/− mice were increased when compared to WT mice. Additionally, VACV infected IFNAR−/− mice showed dramatically enhanced cytokine responses as well as elevated liver enzyme levels in the serum. Histological analysis of liver of VACV infected WT mice revealed that such mice developed mild hepatitis around day 5 post infection. In contrast, livers of infected IFNAR−/− mice showed signs of severe hepatitis, massive influx of lymphocytes and inflammatory islets including acute necrotic areas. VACV infection of macrophage-specific IFNAR−/− (LysM-Cre[wt/+]IFNARfl/fl) mice revealed that IFNAR signaling of macrophages was needed to protect mice from severe liver damage, whereas IFNAR signaling of hepatocytes (Alb-Cre[wt/+]IFNAR[fl/fl ]mice) was dispensable. Collectively our results indicated that locally induced IFN-I played a crucial role in balancing cytokine responses and were necessary to trigger macrophage-mediated liver protection.

Cytokines have been implicated in a variety of physiological processes involving lymphoid tissue development, lymphocyte activation, and control of regenerative processes such as wound healing. The first characterization of a cytokine implicated in abolishing or killing tumor cells – the tumor necrosis factor (TNF) – fostered and boosted a completely new field of research that in addition to cancer research started to generate an overwhelming amount of knowledge in immunology, various pathological processes, and other fields of research. Due to the complex networks and versatile functions of cytokines, it soon became clear that cytokines can possess diametric functions in various biological processes. As for tumor research it was shown that some cytokines – depending on the type of organ, the time of action, gender, and the cellular environment – can have either pro- or anticarcinogenic action. For those cytokines reported to be procarcinogenic, this could be accomplished by directly acting as oncogenes or generating an inflammatory environment that is procarcinogenic. Here we review a novel role for TNF family members – in particular lymphotoxin (LT) α and β – in physiology and in driving tumorigenesis, with special focus on the liver. We believe that recent findings on this particular cytokine might have strong implications for the therapy of liver cancer or other inflammation-induced cancer types.

Most viruses developed mechanisms that inhibit the induction or the function of type I interferon (IFN-I). Vaccinia virus (VACV), a large DNA-encoded poxvirus, encodes several IFN-I evasins, including the viral IFN-I receptor B18. Nevertheless, here we found that VACV infection still induced local IFN-I responses in secondary lymphoid organs, which are mainly sensed within the liver. VACV infected IFN-I receptor deficient (IFNAR−/−) mice developed fulminant disease, associated with high virus loads in organs such as liver and spleen, imbalanced cytokine responses within the blood, and eventually succumbed to infection. Elevated ALT/AST levels in the serum of VACV infected IFNAR−/− mice supported the hypothesis that IFNAR triggering of the liver played a major role in the antiviral response. Histological analysis of livers of VACV infected IFNAR−/− mice revealed a severe acute hepatitis, massive infiltration of immune cells, and acute tissue apoptosis in the absence of IFNAR-signaling. Interestingly, VACV infected mice with a hepatocyte selective IFNAR ablation (Alb-CreIFNARflox/flox) showed moderate hepatitis as observed in wild-type mice, whereas mice with a cell type-specific IFNAR deletion only in myeloid cells (LysM-CreIFNARflox/flox) showed enhanced hepatitis. Thus, local IFN-I responses sensed by myeloid cells prevented immunopathology within the liver, presumably due to the induction of myeloid derived suppressor cells (MDSC). Collectively these results indicate that although the induction of serum IFN-I is sequestered, VACV infection induces local IFN-I responses that play a central role in modulating immune responses and thus in reducing immunopathology and hepatitis.