Hepatocytes as cytotoxic effector cells can induce cell death by CD95 ligand-mediated pathway

Authors

  • Clifford S. Guy,

    1. Molecular Virology and Hepatology Research, Division of Basic Medical Sciences, Memorial University, St. John's, Newfoundland A1B 3V6, Canada
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  • Jinguo Wang,

    1. Molecular Virology and Hepatology Research, Division of Basic Medical Sciences, Memorial University, St. John's, Newfoundland A1B 3V6, Canada
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  • Tomasz I. Michalak

    Corresponding author
    1. Molecular Virology and Hepatology Research, Division of Basic Medical Sciences, Memorial University, St. John's, Newfoundland A1B 3V6, Canada
    2. Discipline of Laboratory Medicine, Faculty of Medicine, Health Sciences Centre, Memorial University, St. John's, Newfoundland A1B 3V6, Canada
    • Molecular Virology and Hepatology Research, Faculty of Medicine, Health Sciences Centre, Memorial University of Newfoundland, St. John's, NL, Canada A1B 3V6
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    • fax: 709-777-8279.


  • Potential conflict of interest: Nothing to report.

Abstract

The liver plays an increasingly recognized role in the host's immune responses. The direct contribution of hepatocytes as effector cells to local immunity, pathogen containment, and liver disease is not determined. This in vitro study examined whether hepatocytes can eliminate other cells via a CD95 ligand (CD95L or FasL)/CD95 (Fas)–mediated mechanism and whether this cytotoxic activity can be modulated by cytokines such as interferon gamma (IFN-γ) or tumor necrosis factor alpha (TNF-α). We have found that normal woodchuck and human hepatocytes, both cultured and primary freshly isolated, as well as human HepG2 cells, intrinsically transcribe not only CD95 but also CD95L when examined by reverse transcription-polymerase chain reaction (RT-PCR) assays. The functional competence of CD95L, which was detectable in hepatocytes and HepG2 cells by Western blotting, was confirmed in bioassays by induction of apoptosis of CD95-bearing P815 and LS102.9 cell targets and validated by inhibition of the cell killing with CD95 antagonistic antibody or with a general caspase inhibitor. Furthermore, exposure of cultured hepatocytes to IFN-γ or their stable transfection with IFN-γ cDNA or TNF-α cDNA increased hepatocyte CD95L/CD95–mediated cell killing. In conclusion, hepatocytes express both CD95L and CD95 and they can induce death of other cells by a CD95L-dependent mechanism. IFN-γ and, to a lesser extent, TNF-α can enhance hepatocyte CD95L-mediated cytotoxicity. This suggests that the local cytokine environment may modulate the hepatocyte contribution to liver immunity. (HEPATOLOGY 2006;43:1231–1240.)

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