Not interferon, but interleukin-6 controls early gene expression in hepatitis B virus infection.

UNLABELLED: With about 350 million virus carriers, hepatitis B virus (HBV) infection remains a major health problem. HBV is a noncytopathic virus causing persistent infection, but it is still unknown whether host recognition of HBV may activate an innate immune response. We describe that upon infection of primary human liver cells, HBV is recognized by nonparenchymal cells of the liver, mainly by liver macrophages (Kupffer cells), although they are not infected. Within 3 hours, this recognition leads to the activation of nuclear factor kappa B (NF-kappaB) and subsequently to the release of interleukin-6 (IL-6) and other proinflammatory cytokines (IL-8, TNF-alpha, IL-1beta), but does not induce an interferon response. The activation of proinflammatory cytokines, however, is transient, and even inhibits responsiveness toward a subsequent challenge. IL-6 released by Kupffer cells after activation of NF-kappaB controls HBV gene expression and replication in hepatocytes at the level of transcription shortly after infection. Upon binding to its receptor complex, IL-6 activates the mitogen-activated protein kinases exogenous signal-regulated kinase 1/2, and c-jun N-terminal kinase, which inhibit expression of hepatocyte nuclear factor (HNF) 1alpha and HNF 4alpha, two transcription factors essential for HBV gene expression and replication. CONCLUSION: Our results demonstrate recognition of HBV patterns by nonparenchymal liver cells, which results in IL-6-mediated control of HBV infection at the transcriptional level. Thus, IL-6 ensures early control of the virus, limiting activation of the adaptive immune response and preventing death of the HBV-infected hepatocyte. This pattern recognition may be essential for a virus, which infects a new host with only a few virions. Our data also indicate that therapeutic neutralization of IL-6 for treatment of certain diseases may represent a risk if the patient is HBV-infected.

A concerted action of HNF4alpha and HNF1alpha links hepatitis B virus replication to hepatocyte differentiation.

Hepatitis B virus (HBV) is an important human pathogen, which targets the liver extremely efficient, gaining access to hepatocytes by a so far unknown receptor and replicating in a hepatocyte-specific fashion. Cell differentiation seems to determine HBV replication. We here show that the level of hepatocyte differentiation, as indicated by hepatocyte polarization and metabolic activity, is closely correlated to the transcription of the HBV RNA pregenome. Pregenome transcription determined the level of HBV replication in various cell lines of hepatocellular origin and in primary human hepatocytes. A variety of hepatocyte-enriched nuclear factors have been described to regulate transcription of the pregenome, but it remained unknown which factors link HBV replication to hepatocyte differentiation. We determined that high expression levels of HNF4alpha but not its potential cofactors or other hepatocyte-enriched transcription factors were essential for efficient HBV replication, and link it to hepatocyte differentiation. HNF1alpha contributed to the control of HBV replication because it regulated the expression of HNF4alpha. Thus, a concerted action of HNF4alpha and HNF1alpha, which also determines morphological and functional differentiation of hepatocytes, links HBV replication to hepatocyte differentiation.

Dendritic cells take up viral antigens but do not support the early steps of hepatitis B virus infection.

Dendritic cells (DC) of hepatitis B virus (HBV) carriers have been reported to exhibit functional impairment. Possible explanations for this phenomenon are infection of HBV by DC or alteration of DC function by HBV. We therefore analyzed whether DC support the different steps of HBV infection and replication: uptake, deposition of the HBV genome in the nucleus, antigen expression, and progeny virus release. When HBV genomes were artificially introduced into monocyte-derived DC by adenoviral vectors, low-level expression of hepatitis B surface antigen (HBsAg) and hepatitis B e antigen (HBeAg) but no HBV replication was detected. When monocyte-derived DC were subjected to wild-type HBV or a recombinant HBV expressing Renilla luciferase under a non-liver-specific promoter, intracellular HBV DNA was detected in a low percentage of cells. However, neither nuclear cccDNA was formed nor luciferase activity was detected, indicating that either uncoating or nucleocytoplasmic transport were blocked. To verify our observation in the in vivo situation, myeloid and plasmacytoid DC were isolated from blood of high viremic HBV carriers, and analyzed by quantitative polymerase chain reaction (PCR) and electron microscopy. Although circulating DC had in vivo been exposed to more than 10(4) HBV virions per cell, HBV genomic DNA was hardly detected, and no nuclear cccDNA was detected at all. By using electron microscopy, subviral particles were found in endocytic vesicles, but virions were undetectable as were viral capsids in the cytoplasm. In conclusion, circulating DC may take up HBV antigens, but neither support nucleocytoplasmic transport nor replication of HBV.