Abstract
Hepatitis C virus (HCV) infection is characterized by a high frequency of chronic cases owing to the impairment of innate and adaptive immune responses. The modulation of natural killer (NK) cell functions by HCV leads to an impaired innate immune response. However, the underling mechanisms and roles of HCV proteins in this immune evasion are controversial, especially in the early phase of HCV infection. To investigate the role of HCV nonstructural proteins especially NS3 in the impairment of NK functions, NK cells were isolated from the PBMCs by negative selection. To assess the direct cytotoxicity and IFN-γ production capability of NK cells, co-cultured with uninfected, HCV-infected, HCV-NS3 DNA-transfected Huh-7.5, or HCV-NS replicon cells. To determine the effect of an NS3 serine protease inhibitor, HCV-infected Huh-7.5 cells were treated with BILN-2061. Then, NK cells were harvested and further co-cultured with K-562 target cells. NK cell functions were analyzed by flow cytometry and enzyme-linked immunosorbent assay. When co-cultured with HCV-infected Huh-7.5 cells, the natural cytotoxicity and IFN-γ production capability of NK cells were significantly reduced. NK cell functions were inhibited to similar levels upon co-culture with HCV-NS replicon cells, NS3-transfected cells, and HCV-infected Huh-7.5 cells. These reductions were restored by BILN-2061-treatment. Furthermore, BILN-2061-treatment significantly increased degranulation against K-562 target cells and IFN-γ productivity in NK cells. Consistent with these findings, the expression levels of activating NK cell receptors, such as NKp46 and NKp30, were also increased. In HCV-infected cells, the serine protease NS3 may play a role in the abrogation of NK cell functions in the early phase of infection through downregulation of NKp46 and NKp30 receptors on NK cells. Together, these results suggest that NS3 represents a novel drug target for the treatment of HCV infections.
Highlights
Hepatitis C virus (HCV) is an enveloped, positive-sense RNA virus belonging to the Flaviviridae family [1]
These data demonstrate that HCV-infected cells regulate natural killer (NK) cell functions via cell-to-cell interaction and that HCV-NS proteins might be involved in this modulation
NK cells were pre-incubated with uninfected, HCV-NS replicon, or HCV-NS3-transfected Huh-7.5 cells for 18 h, and harvested the NK cells co-cultured with K-562 cells at a 1:1 ratio with treatment of 10 ng/mL IL-12 and 100 ng/mL IL-15 for 6 h
Summary
Hepatitis C virus (HCV) is an enveloped, positive-sense RNA virus belonging to the Flaviviridae family [1]. We found that cell-to-cell contact with HCV NS3-transfected cells reduced NK cell functions to a similar extent as in HCV-infected cells These reductions were restored by treatment of HCV-infected Huh-7.5 cells with the NS3 serine protease inhibitor, BILN-2061, and this restoration correlated with the increased expression of the activating NK cell receptors, NKp46 and NKp30. These findings suggest that the HCV serine protease NS3 plays a role in the impairment of NK cell functions in the early phase of infection
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