We have previously shown that Toll-like receptor (TLR)-activated murine nonparenchymal liver cells [(NPC); Kupffer cells (KC), liver sinusoidal endothelial cells (LSEC)]T he hepatitis B virus (HBV) is a hepatotropic DNA virus that can lead to chronic hepatitis, which can be complicated by the development of liver cirrhosis and hepatocellular carcinoma. Current approved therapeutic strategies for treatment HBV include interferon-alpha (IFN-␣) and nucleoside and nucleotide analogs. 1,2 However, only a minority of patients that are treated with these agents show a long-term sustained response with "eradication" [for example, hepatitis B surface antigen (HBsAg) loss] of the virus.

Hepatitis B virus (HBV) infection isCurrently, only interferon (IFN)-␣ and nucleoside or nucleotide analogues have been shown to be effective in suppressing HBV replication and in inducing clinical remission of liver disease. 2 However, increasing evidence suggests that immune mediators such as Toll-like receptor (TLR) ligands could be used successfully as therapeutic agents in HBV 3 or other viral infections. [4][5][6] TLRs play a crucial role in early host defense by recognizing so-called pathogen-associated molecular patterns that are essential for the survival of the microorganism but are not present in eukaryotes. 7 To date, 13 mammalian TLRs have been identified (10 in humans and 13 in mice), each containing a unique extracellular domain and a conserved cytoplasmic Toll/interleukin (IL)-1 receptor domain. 8 After ligand binding, the cytoplasmic Toll/IL-1 receptor domain of TLRs associates with intracellular adapters and activates downstream signaling molecules, including the transcription factors nuclear factor B, interferon regulatory factor-1, interferon regulatory factor-7, and mitogen-activated protein kinases, which lead to the activation of type I IFNs, proinflammatory cytokines, or costimulatory molecules. 9 Five adapter proteins

Hepatitis C virus (HCV) infection develops into chronicity in 80% of all patients, characterized by persistent low-level replication. To understand how the virus establishes its tightly controlled intracellular RNA replication cycle, we developed the first detailed mathematical model of the initial dynamic phase of the intracellular HCV RNA replication. We therefore quantitatively measured viral RNA and protein translation upon synchronous delivery of viral genomes to host cells, and thoroughly validated the model using additional, independent experiments. Model analysis was used to predict the efficacy of different classes of inhibitors and identified sensitive substeps of replication that could be targeted by current and future therapeutics. A protective replication compartment proved to be essential for sustained RNA replication, balancing translation versus replication and thus effectively limiting RNA amplification. The model predicts that host factors involved in the formation of this compartment determine cellular permissiveness to HCV replication. In gene expression profiling, we identified several key processes potentially determining cellular HCV replication efficiency.

Summary Little is known of how the Toll‐like receptor (TLR) system can modulate the function of non‐parenchymal liver cells (NPC) as a major component of the innate and adaptive immune system of the liver. To investigate the diversification of TLR signalling pathways in NPC, we isolated Kupffer cells (KC) and liver sinusoidal endothelial cells (LSEC) from wild‐type C57BL/6 mice and examined their responses to TLR1 to TLR9 agonists. The data show that KC respond to all TLR ligands by producing tumour necrosis factor‐α (TNF‐α) or interleukin‐6 (IL‐6), to TLR3 and TLR4 ligands only by producing interferon‐β (IFN‐β), to TLR1 and TLR8 ligands by significantly up‐regulating major histocompatibility complex (MHC) class II and costimulatory molecules, and to TLR1, ‐2, ‐4 and ‐6 ligands by inducing high levels of T‐cell proliferation and IFN‐γ production in the mixed lymphocyte reaction (MLR). Similarly, LSEC respond to TLR1 to ‐4, ‐6, ‐8 and ‐9 ligands by producing TNF‐α, to TLR3 and ‐4 ligands by producing IL‐6, and to TLR3 ligands by producing IFN‐β. Interestingly, despite significant up‐regulation of MHC class II and co‐stimulatory molecules in response to TLR8 ligands, LSEC stimulated by TLR1, ‐2 or ‐6 could stimulate allogeneic T cells as assessed by MLR. By contrast, myeloid dendritic cells, used as positive control for classical antigen‐presenting cells, respond to TLR1, ‐2, ‐4 and ‐9 ligands by both up‐regulation of CD40 and activation of allogeneic T cells. In conclusion, NPC display a restricted TLR‐mediated activation profile when compared with ‘classical’ antigen‐presenting cells which may, at least in part, explain their tolerogenic function in the liver.

Persistent infection with hepatitis C virus (HCV) can lead to chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. All current therapies of hepatitis C include interferon-alpha (IFN-a). Moreover, IFN-gamma (IFN-c), the only type II IFN, strongly inhibits HCV replication in vitro and is the primary mediator of HCV-specific antiviral Tcell responses. However, for both cytokines the precise set of effector protein(s) responsible for replication inhibition is not known. The aim of this study was the identification of IFN-a and IFN-c stimulated genes (ISGs) responsible for controlling HCV replication. We devised an RNA interference (RNAi)-based ''gain of function'' screen and identified, in addition to known ISGs earlier reported to suppress HCV replication, several new ones with proven antiviral activity. These include IFIT3 (IFN-induced protein with tetratricopeptide repeats 3), TRIM14 (tripartite motif containing 14), PLSCR1 (phospholipid scramblase 1), and NOS2 (nitric oxide synthase 2, inducible). All ISGs identified in this study were up-regulated both by IFN-a and IFN-c, demonstrating a substantial overlap of HCV-specific effectors induced by either cytokine. Nevertheless, some ISGs were more specific for IFN-a or IFN-c, which was most pronounced in case of PLSCR1 and NOS2 that were identified as main effectors of IFN-c-mediated anti-HCV activity. Combinatorial knockdowns of ISGs suggest additive or synergistic effects demonstrating that with either IFN, inhibition of HCV replication is caused by the combined action of multiple ISGs. Conclusion: Our study identifies a number of novel ISGs contributing to the suppression of HCV replication by type I and type II IFN. We demonstrate a substantial overlap of antiviral programs triggered by either cytokine and show that suppression of HCV replication is mediated by the concerted action of multiple effectors.

ISG15 plays an important role in the HCV replication cycle. Therefore, therapies based on the suppression of ISG15 may provide a promising strategy to overcome non-response to standard combination treatment in the future. Furthermore, analysis of ISG15 prior to therapy may be useful to predict short-term and long-term outcome and thus tailor antiviral therapy with pegIFN and ribavirin.

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