Accelerated liver fibrosis in hepatitis B virus transgenic mice: Involvement of natural killer T cells

Abstract

The immunopathogenic process from hepatitis B virus (HBV) infection to liver fibrosis is incompletely understood because it lacks an animal model. In this study we observed the development of liver fibrosis in HBV transgenic (HBV-tg) mice and found the roles of natural killer T (NKT) cells in HBV-related liver fibrosis. We found liver fibrosis spontaneously developed in HBV-tg mice with the elevated transcription of col1a1, matrix metalloproteinase (MMP)2, and tissue inhibitor of metalloproteinase (TIMP)1. Mice were then injected with repetitive hepatotoxin carbon tetrachloride (CCl(4) ) to induce prominent liver fibrosis. After chronic CCl(4) treatment, the serum alanine aminotransferase (ALT) was higher, the liver regenerative nodules became more and bigger, and the fibrosis area was remarkably increased in HBV-tg mice than in C57BL/6 mice. Moreover, the increase in col1a1 and MMP2 transcription was greater, with a sustaining high level of TIMP1 and a greater activation of hepatic stellate cells (HSCs) in the livers of CCl(4) -treated HBV-tg mice. Our data also showed that there were more liver mononuclear cells (MNCs) in HBV-tg mice after CCl(4) injection, and Rag1(-/-) mice adoptive transferred lymphocytes from HBV-tg mice displayed increased collagen deposition. Further study demonstrated the number of liver NKT cells increased after CCl(4) treatment and NKT cells were overactivated in HBV-tg mice in the long term. It was further confirmed that NKT cells were critical for HSCs activation by depletion of NKT cells of HBV-tg mice and adoptive transfer of purified NKT cells from HBV-tg mice into recipient Rag1(-/-) mice. The inflammatory cytokines IL-4 and IL-13 produced by NKT cells played a pivotal role in HSCs activation in an in vitro coculture experiment. These data suggest that NKT cells from HBV-tg mice induce the HSC activation in liver fibrogenesis.