Hepatitis C Virus–Infected Cells Downregulate NKp30 and Inhibit Ex Vivo NK Cell Functions

Abstract

Hepatitis C virus (HCV) successfully evades the immune system and establishes chronic infection in ∼80% of cases. Immune evasion may involve modulating NK cell functions. Therefore, we developed a short-term assay to assess immediate effects of HCV-infected cells on ex vivo NK cytotoxicity and cytokine production. Natural cytotoxicity, Ab-dependent cell–mediated cytotoxicity, IFN-γ production, and TNF-α production were all significantly inhibited by short-term direct exposure to HCV-infected hepatoma–derived Huh-7.5 cells. Inhibition required cell-to-cell contact and increased together with multiplicity of infection and HCV protein levels. Blocking potential interaction between HCV E2 and NK CD81 did not abrogate NK cell inhibition mediated by HCV-infected cells. We observed no change in expression levels of NKG2D, NKG2A, NKp46, or CD16 on NK cells exposed to HCV-infected Huh-7.5 cells for 5 h or of human histocompatibility-linked leukocyte Ag E on HCV-infected compared with uninfected Huh-7.5 cells. Inhibition of ex vivo NK functions did correspond with reduced surface expression of the natural cytotoxicity receptor NKp30, and downregulation of NKp30 was functionally reflected in reduced anti-NKp30 redirected lysis of P815 cells. Infection of Huh-7.5 cells with HCV JFH1T increased surface binding of an NKp30-IgG1 Fcγ fusion protein, suggesting upregulation of an antagonistic NKp30 ligand on HCV-infected cells. Our assay demonstrates rapid inhibition of critical NK cell functions by HCV-infected cells. Similar localized effects in vivo may contribute to establishment of chronic HCV infection and associated phenotypic and functional changes in the NK population.

NK Cells and Their Ability to Modulate T Cells during Virus Infections

“…88 Likewise, liver NK cells are impaired in function in HCV-infected individuals, 89 in part through HCV-mediated downregulation of NKp30. 90 HCV-infected cells can also inhibit NK cell cytotoxicity and cytokine production by expressing HCV-envelope that binds CD81 on NK cells, 91,92 or by HCV-core peptide mediated stabilization of HLA-E to inhibit NK cells through NKG2A. 93 In addition to interfering with NK cell receptor functions, certain viral proteins impact cytokine signaling as well, i.e., IL-10 homologs and IL-18 binding proteins.…”

Natural Killer Cell Function and Dysfunction in Hepatitis C Virus Infection

“…Nattermann et al reported an increased expression of NKG2A/CD94 inhibitory receptors on circulating NK cells in patients with chronic HCV infection; however, in an in vitro model representative of acute HCV infection, neither NKG2A nor HLA-E expression increased on NK or HCV-infected cells, respectively [67–69]. Nonetheless, to combat NK cell-mediated control of infection, HCV may employ multiple means of increasing expression of natural or decoy ligands for inhibitory NKRs as chronic infection develops and disease progresses.…”

“…Although no differences in NKG2C or NKG2D surface expression were noted, some in vitro experimental data suggested downregulated NKG2D and/or NKp30 surface expression after ex vivo exposure of NK cells to HCV-infected cells [68, 69]. Direct contact between NK cells and HCV-infected cells in vitro promotes downregulation of NKp30, suggesting that HCV can affect NK cell recognition and function through upregulation of an as yet unidentified ligand that physically interacts with NKp30 [69]. This possibility is supported by the demonstration of increased binding of recombinant NKp30 protein to HCV-infected Huh-7.5 cells [69].…”

IL-26 is overexpressed in chronically HCV-infected patients and enhances TRAIL-mediated cytotoxicity and interferon production by human NK cells

“…IL-26 enhanced the cytotoxic activity of NK cells against the TRAIL-sensitive Jurkat (figure 5A) and Huh7.5 cell lines (figure 5B). Previous studies have reported that a short time contact with HCV-infected cells is sufficient to reduce the killing activity of NK cells against infected cells; this process, suspected to participate to HCV immune escape, can be reverted by NK cell activation 9 34. We thus analysed the ability of IL-26-stimulated NK cells to kill HCV-replicating Huh7.5 cells.…”