The pathogenesis of chronic hepatitis B virus infection

Single nucleotide polymorphisms and functional analysis of class II transactivator (CIITA) promoter IV in persistent HBV infection

BACKGROUND/AIMS

CIITA plays a pivotal role in immune response, and the outcome of HBV infection is influenced by immune response. The aims of this study were to analyze the effect of CIITA promoter IV polymorphisms on its activity, and their association with persistent HBV infection.

METHODS

The polymorphisms in promoter IV (C-1350T and G-944C) were analyzed by tetra-primer amplification refractory mutation system polymerase chain reaction (ARMS-PCR), and four haplotypes were assigned in 1420 HBV infected subjects. The functional analysis on haplotypes of promoter IV was studied using pGL3-basic and pGL3-promoter vectors.

RESULTS

There were significantly decreased-TG and increased-CC haplotype frequencies in persistent HBV infected subjects (34.8% and 41.3%), compared with spontaneously recovered subjects (46.5% and 36.2%). There were significantly higher CC/CC and lower TG/TG genotype frequencies in persistent infected subjects (20.3% and 11.1%) than in spontaneously recovered subjects (10.9% and 23.1%). The mean relative luciferase activity of promoter IV were the highest in TG haplotype (0.558+/-0.023), and the lowest in CC haplotype (0.302+/-0.016).

CONCLUSIONS

The polymorphisms of CIITA promoter IV are associated with persistent HBV infection. The CC haplotype with the lowest activity of promoter and CC/CC genotype are responsible for persistent HBV infection.

Impaired function of hepatic natural killer cells from murine chronic HBsAg carriers

In the present study, we demonstrated hepatic NK cells in murine chronic HBsAg carriers for the first time. It was found that the number of hepatic NK cells was decreased; natural activation of hepatic NK cells was declined; and cytotoxicity of hepatic NK cells was attenuated, which might relate to the down-regulated expression of TRAIL on hepatic NK cells. Additionally, the response of hepatic NK cells to the specific stimulation of Poly (I:C) in murine chronic HBsAg carriers was changed. The increase in anti-tumor cytotoxic activity of intrahepatic activated NK cells was markedly impaired in the transgenic mice. The transgenic mice used here had high incidence of hepatocellular carcinoma, which might result from the relative weak reactivity and impaired anti-tumor activity of NK cells in the liver. Furthermore, remarkable liver injury was observed after stimulation of Poly (I:C), demonstrating the hypersensitivity to Poly (I:C) of murine chronic HBsAg carriers which might be related to the accumulated NK cells in the liver. Why the murine chronic HBsAg carriers are characterized with impaired hepatic NK cells and the implication of the impaired hepatic NK cells in pathogenesis of HBV-related diseases, such as hepatocellular carcinoma and recrudescent hepatitis, is worth of further investigating. These results of the functions of hepatic NK cells in murine chronic HBsAg carriers would contribute to interpreting the immune responses of NK cells in the liver and the immunological mechanisms of liver diseases in human chronic HBsAg carriers.

Activation and function of hepatic NK cells in hepatitis B infection: an underinvestigated innate immune response

Natural killer (NK) cells are abundant in the normal liver, accounting for around one-third of intrahepatic lymphocytes and are important in the defence against hepatitis B virus (HBV) infection as innate immune responses. In this review, we discuss the mechanisms of hepatic NK cell activity against HBV. Whether directly activated by HBV infection or indirectly activated by other lymphocytes such as NKT cells or antigen-presenting cells (APCs), hepatic NK cells exert their anti-viral functions by natural cytotoxicity and production of high levels of cytokines. However, activated NK cells play an important role in regulating adaptive immune responses by interaction with other lymphocytes such as T, B and APCs. In addition, NK cells may contribute to the lymphocyte-mediated liver injury during HBV infection that was previously considered to be mediated only by CD8+ T cells or/and NKT cells.