Cleavage of the IPS-1/Cardif/MAVS/VISA does not inhibit T cell-mediated elimination of hepatitis C virus non-structural 3/4A-expressing hepatocytes
- G Ahlén1,
- E Derk1,
- M Weiland1,
- J Jiao1,
- N Rahbin1,
- S Aleman2,
- D L Peterson3,
- K Pokrovskaja4,
- D Grandér4,
- L Frelin1,
- M Sällberg1
- 1Division of Clinical Microbiology, Karolinska Institutet at Karolinska University Hospital Huddinge, Stockholm, Sweden
- 2Centre for Gastroenterology, Karolinska University Hospital Solna, Sweden
- 3Commonwealth University, Richmond, Virginia, USA
- 4Department of Oncology and Pathology, Cancer Center Karolinska, Karolinska University Hospital Solna and Karolinska Institutet, Stockholm, Sweden
- Professor M Sällberg, Karolinska Institutet, Division of Clinical Microbiology, F 68, Karolinska University Hospital Huddinge, S-141 86 Stockholm, Sweden;
- Revised 9 July 2008
- Accepted 25 July 2008
- Published Online First 8 August 2008
Background: Hepatitis C virus (HCV) effectively establishes persistent infection in human livers. The non-structural (NS) 3/4A complex participates in this process by cleavage of interferon β (IFNβ) promoter stimulator-1 (IPS-1; also termed Cardif/MAVS/VISA), which inhibits responses to double stranded (ds) RNA. However, it is not known whether this effect extends beyond innate responses.
Aims: To test if HCV NS3/4A affects innate and adaptive immune responses in vivo.
Methods: NS3 levels were semi-quantified in human liver biopsies, transfected cells, and in transgenic (Tg) mouse livers by western blot. The effect of NS3/4A on dsRNA-mediated signalling and on the integrity of IPS-1 was analysed using in vitro translation, transfected cells and Tg mice. Cytotoxic T cell (CTL)-mediated clearance of transient firefly luciferase (FLuc)- and/or NS3/4A-Tg hepatocytes was determined using in vivo imaging and western blot.
Results: NS3 protein levels were in a comparable range (0.1–49 μg/g tissue) in infected human livers and Tg mouse livers. Importantly, these levels of NS3/4A reduced murine innate responses to synthetic dsRNA in vivo, supporting the possibility that this occurs also in infected humans. The likely explanation for this was the NS3/4A-mediated cleavage of mouse IPS-1, albeit less efficiently than human IPS-1. Despite this, FLuc- and/or NS3/4A-expressing murine hepatocytes were effectively eliminated by hepatic CTLs, utilising the classical molecules for virus-infected cell lysis, including CD8, IFNγ, perforin and FasL.
Conclusions: Although HCV NS3/4A inhibits the innate immunity, this does not prevent CTL-mediated clearance of NS3/4A-expressing hepatocytes in vivo. Thus, other HCV proteins are most likely responsible for interfering with the adaptive immunity.
Competing interests: None.
Funding: The present study was supported by the Swedish Science Council, the Cancer Foundation, the Stockholm County Council, and the European Commission through the VIRGIL Network of Excellence. LF was supported by grants from the Swedish Society of Medicine, the Swedish Society for Medical Research, the Royal Swedish Academy of Sciences, the Goljes Memorial Fund, the Ruth and Richard Juhlin Foundation, the Jonas Söderqvists Fund, and from the Karolinska Institutet.
Ethics approval: The local ethics committee approved all sampling and analysis of liver biopsies on 20 January 2006. The ethics committee for animal research at Karolinska Institutet approved all animal experiments.