HEPATITIS

The hepatitis C virus and immune evasion: non-structural 3/4A transgenic mice are resistant to lethal tumour necrosis factor mediated liver disease

L Frelin¹, E D Brenndörfer², G Ahlén¹, M Weiland¹, C Hultgren¹, M Alheim¹, H Glaumann³, B Rozell⁴, D R Milich⁵, J G Bode², M Sällberg¹

¹ Division of Clinical Virology, Karolinska Institutet at Karolinska University Hospital, Huddinge, Stockholm, Sweden
² Department of Gastroenterology, Hepatology, and Infectious Diseases, Heinrich-Heine University, Düsseldorf, Germany
³ Division of Infectious Diseases, Karolinska Institutet at Karolinska University Hospital
⁴ Division of Pathology and Clinical Research Centre, Karolinska Institutet at Karolinska University Hospital
⁵ Vaccine Research Institute, San Diego, California, USA

Correspondence to:
Professor Matti Sällberg
Karolinska Institutet, Division of Clinical Virology, F 68, Karolinska University Hospital, Huddinge, S-141 86 Stockholm, Sweden; matti.sallberg{at}ki.se

Background: The hepatitis C virus (HCV) establishes chronic infection by incompletely understood mechanisms. The non-structural (NS) 3/4A protease/helicase has been proposed as a key complex in modulating the infected hepatocyte, although nothing is known about the effects this complex exerts in vivo.

Aim: To generate mice with stable and transient hepatocyte expression of the HCV NS3/4A proteins to study its effects in vivo.

Methods: NS3/4A expression was determined by western blot and immunohistochemistry. Two independent pathologists determined the liver histology. Hepatic immunity was characterised by quantifying intrahepatic immune cell subsets. Liver damage was induced using carbon tetrachloride (CCl₄), lipopolysaccaride (LPS), tumour necrosis factor (TNF), and anti-Fas antibody.

Results: Expression of NS3/4A was restricted to the cytoplasm of hepatocytes, and did not cause liver cancer or any spontaneous liver pathology. However, the presence of NS3/4A modulated the intrahepatic immunity, as follows: first, the CD4+ T cell and type I/II dendritic cell subsets were reduced in transgenic livers; second, NS3/4A protected hepatocytes from liver damage mediated in vivo by CCl₄, LPS, TNF, but not FAS; and third, both stable and transiently NS3/4A transgenic mice were resistant to lethal doses of liver targeted TNF, and the resistance could be reverted by treatment with a p38 mitogen activated protein kinase inhibitor (MAPK).

Conclusions: Hepatic expression of NS3/4A does not induce spontaneous liver disease. NS3/4A does, however, alter the intrahepatic immune cell subsets and protects hepatocytes against TNF induced liver damage in vivo. The TNF resistance can be reverted by treatment with a p38 MAPK inhibitor. This represents a new immune evasion strategy conferred by NS3/4A.

Abbreviations: D-Gal, D-glucosamine; HCV, hepatitis C virus; IP-WB, immunoprecipitation and western blot; LPS, lipopolysaccaride; MAPK, mitogen activated protein kinase inhibitor; NS, non-structural; RPA, Rnase protection assay; TBK1, TANK binding kinase-1; Tg, transgenic; TNF, tumour necrosis factor ; TRIF, TIR domain containing, adapter inducing interferon ß

Keywords: hepatitis C virus; HCV; NS3/4A; TNF; p38; transgenic mouse

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