Of hepcidin peptide and over-expression of hepcidin could attenuate HCV replication in cell order K162 models. Recently, there is a study suggesting that hepcidin is a cofactor for HCV replication [40] and studies also report that HAMP siRNA inhibits HCV replication [40,41]. The different conclusions may result from thedifferent cell culture models. They used Huh7 cells to test the effect of hepcidin silencing on JFH1 replication. Our results show that Huh7 cells express higher level of hepcidin than Huh7.5 cells (Fig. 1A). There is another possibility that the HAMP siRNA used in their study has off-target effects which affect HCV replication. Activation of the type I interferon pathway by siRNA is a major contributor to the off-target effects of RNA interference in mammalian cells. Various forms of siRNA have been reported to trigger IFN activation both in vitro and in vivo [42,43,44,45,46]. Besides its interaction with ferroportin, hepcidin also is known for its antimicrobial activity against bacteria and fungi [5,6,7]. It is a surprise to us that hepcidin exhibits direct anti-HCV effect in cell culture system. Our experiment did show that the antiviral effect is related to STAT3 activation (Fig. 5A). How hepcidin activates STAT3 remains to be determined. The possible mechanism is related to phosphorylation of JAKs. STAT3 knockdown experiment further confirmed its role in hepcidin-induced antiviral activity (Fig. 5C). The antiviral effect is similar to Interleukin-1 effect as we have previously reported [47]. We have to point out that how hepcidin activates STAT3 in the antiviral process in hepatocytes is unknown. Extensive experimentation is needed to determine the signaling events upon hepatocytes exposure to hepcidin. The other interesting aspect is the fact that STAT3 itself is needed for hepcidin expression [28]. It regulates hepcidin expression through direct interaction with the STAT3 binding site localized 
in the proximal part of the hepcidin promoter. Because hepcidin peptide treatment can induce cellular hepcidin expression (Fig. 6), it is possible that hepcidin has a positive feedback system to boost its antiviral effect. We investigated the possibility that the antiviral activity of hepcidin is associated with intracellular antiviral state. The presence of IFN in the hepcidin treated cells was not directed, but some of the IFN-inducible genes, such as OAS1 and IFIT1 (ISG56), were significantly induced in hepcidin-treated cells (Fig. 7). It is possible that IFIT1 is directly involved in the hepcidin mediated antiviral effect. IFIT1 is known to be an important A 196 cost protein in intracellular antiviral state. Translation of the HCV positive-sense RNA genome is initiated by IRES-dependent ribosome recruitment, which requires eIF3 [48]. The direct binding of IFIT1 to eIF3 can inhibit HCV translation initiation both in vitro and within cells [49]. Future experiments should be performed to determine how hepcidin activates IFIT1 
and what the mechanism of action is. Our work demonstrates hepcidin effectively inhibits HCV replication in cell culture and HCV reduces hepcidin expression. It is plausible that hepcidin is a mediator in innate immunity and HCV has developed a strategy to suppress its expression. It is possible to develop a therapy using hepcidin. Besides its antiviral effect, the potential advantage of hepcidin therapy for HCV patients is restoration of iron homeostasis. It will be interesting to investigate the therapeutic efficacy of bo.Of hepcidin peptide and over-expression of hepcidin could attenuate HCV replication in cell models. Recently, there is a study suggesting that hepcidin is a cofactor for HCV replication [40] and studies also report that HAMP siRNA inhibits HCV replication [40,41]. The different conclusions may result from thedifferent cell culture models. They used Huh7 cells to test the effect of hepcidin silencing on JFH1 replication. Our results show that Huh7 cells express higher level of hepcidin than Huh7.5 cells (Fig. 1A). There is another possibility that the HAMP siRNA used in their study has off-target effects which affect HCV replication. Activation of the type I interferon pathway by siRNA is a major contributor to the off-target effects of RNA interference in mammalian cells. Various forms of siRNA have been reported to trigger IFN activation both in vitro and in vivo [42,43,44,45,46]. Besides its interaction with ferroportin, hepcidin also is known for its antimicrobial activity against bacteria and fungi [5,6,7]. It is a surprise to us that hepcidin exhibits direct anti-HCV effect in cell culture system. Our experiment did show that the antiviral effect is related to STAT3 activation (Fig. 5A). How hepcidin activates STAT3 remains to be determined. The possible mechanism is related to phosphorylation of JAKs. STAT3 knockdown experiment further confirmed its role in hepcidin-induced antiviral activity (Fig. 5C). The antiviral effect is similar to Interleukin-1 effect as we have previously reported [47]. We have to point out that how hepcidin activates STAT3 in the antiviral process in hepatocytes is unknown. Extensive experimentation is needed to determine the signaling events upon hepatocytes exposure to hepcidin. The other interesting aspect is the fact that STAT3 itself is needed for hepcidin expression [28]. It regulates hepcidin expression through direct interaction with the STAT3 binding site localized in the proximal part of the hepcidin promoter. Because hepcidin peptide treatment can induce cellular hepcidin expression (Fig. 6), it is possible that hepcidin has a positive feedback system to boost its antiviral effect. We investigated the possibility that the antiviral activity of hepcidin is associated with intracellular antiviral state. The presence of IFN in the hepcidin treated cells was not directed, but some of the IFN-inducible genes, such as OAS1 and IFIT1 (ISG56), were significantly induced in hepcidin-treated cells (Fig. 7). It is possible that IFIT1 is directly involved in the hepcidin mediated antiviral effect. IFIT1 is known to be an important protein in intracellular antiviral state. Translation of the HCV positive-sense RNA genome is initiated by IRES-dependent ribosome recruitment, which requires eIF3 [48]. The direct binding of IFIT1 to eIF3 can inhibit HCV translation initiation both in vitro and within cells [49]. Future experiments should be performed to determine how hepcidin activates IFIT1 and what the mechanism of action is. Our work demonstrates hepcidin effectively inhibits HCV replication in cell culture and HCV reduces hepcidin expression. It is plausible that hepcidin is a mediator in innate immunity and HCV has developed a strategy to suppress its expression. It is possible to develop a therapy using hepcidin. Besides its antiviral effect, the potential advantage of hepcidin therapy for HCV patients is restoration of iron homeostasis. It will be interesting to investigate the therapeutic efficacy of bo.
