Abstract
During chronic hepatitis C virus (HCV) infection, the role of intra-hepatic (IH) natural killer (NK) cells is still controversial. To clarify their functions, we investigated anti-viral and cytotoxic activity of NK cells in human fresh liver biopsies. We compared the functions of IH-NK cells in HCV-infected and NASH patients in physiological conditions as well as after stimulation using flow cytometric and immunohistochemical analyses. Interestingly, few IH-NK cells produced anti-viral cytokine IFN-γ in HCV-infected patients similarly as in non-infected individuals. Spontaneous degranulation activity was extremely low in peripheral NK cells compared to IH-NK cells, and was significantly higher in IH-NK cells from HCV-infected patients compared to non-infected individuals. Immunohistochemical analysis revealed that perforin granules were polarized at the apical pole of IH-NK cells. The presence of CD107a and perforin in IH-NK cells demonstrated that NK cells exerted a cytolytic activity at the site of infection. Importantly, IH-NK cell functions from HCV-infected patients were inducible by specific exogenous stimulations. Upon ex vivo K562 target cell stimulations, the number of degranulating NK cells was significantly increased in the pool of IH-NK cells compared to circulating NK cells. Interestingly, after stimulation, the frequency of IFN-γ-producing IH-NK cells in HCV-infected patients was significantly higher at early stage of inflammation whereas the spontaneous IH-NK cell degranulation activity was significantly impaired in patients with highest inflammation and fibrosis Metavir scores. Our study highlights that some IH-NK cells in HCV-infected patients are able to produce INF-γ and degranulate and that those two activities depend on liver environment including the severity of liver injury. Thus, we conclude that critical roles of IH-NK cells have to be taken into account in the course of the liver pathogenesis associated to chronic HCV infection.
Highlights
A large majority of hepatitis C virus (HCV)-infected patients develops a chronic disease with increasing hepatic injury over time [1,2]
Recent observations have shown that natural killer (NK) cell functions in mice are strongly influenced by their environment and that these cells display a greater capacity to adapt to their local context than was previously expected [18]
During acute HCV infection, the cytotoxic functions of peripheral NK cells and their production of IFN-c, that can directly inhibit viral replication and prime the adaptive immune response, are higher compared to healthy individuals [19]
Summary
A large majority of hepatitis C virus (HCV)-infected patients develops a chronic disease with increasing hepatic injury over time [1,2]. NK cells, as one of the major components of the innate immune system, have been known to play an important role in the control of viral hepatitis for many years. Functional mechanisms of NK cells include: i) secretion of interferon-c (IFN-c), which has an antiviral effect and participates in the induction of the adaptive immune response; ii) a direct cytotoxicity to target cells via the degranulation of cytotoxic granules (perforin, granzyme); iii) and the induction of target cells apoptosis via the up-regulation of Fas ligand and tumor necrosis-related apoptosis-inducing ligand on the surface of NK cells [3,4]. NK cell regulation depends on a fine balance between inhibitory and activating receptors which belong either to Immunoglobulin-like superfamily (Killer cell Immunoglobulin-like receptor or KIR), or to natural cytotoxicity receptors [4,5] that are described as activating receptor able to recognize viral determinants [6,7]
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