Endotoxin stimulates liver macrophages to release mediators that inhibit an early step in hepadnavirus replication

Hepadnaviruses are known to be sensitive to various extracellular mediators . Therefore, bacterial endotoxin, which induces the secretion of proinflamm atory mediators in the liver, was studied for its effect on hepadnavirus in fection in vitro using the duck hepatitis B virus (DHBV) model. In initial experiments, endotoxin was shown to inhibit DHBV replication in primary duc k hepatocyte cultures prepared by standard collagenase perfusion. As a prim ary endotoxin target, hepatic nonparenchymal cells (NPC) contaminating prim ary hepa tocyte cultures, and among these probably macrophages (Kupffer cel ls), were identified to secrete polypeptide mediators into the cell culture medium. When added during DHBV infection, these mediators elicited the pri ncipal antiviral effect in a dose-dependent fashion. On the molecular level , they inhibited accumulation of viral proteins as well as amplification of the nuclear extrachromosomal DHBV DNA templates. In hepatocytes with an es tablished DHBV infection, DHBV protein and progeny virus production was inh ibited while the levels of established nuclear DHBV DNA templates and viral transcripts remained unaffected. Finally, in hepatocytes infected with a r eplication-deficient recombinant DHBV-green fluorescent protein (GFP) virus , the endotoxin-induced mediators markedly reduced GFP expression from chim eric DHBV-GFP transcripts, indicating that the major effect is at a level o f translation of viral RNAs, Taken together, the data obtained demonstrate that antiviral mediators, and among these the cytokines alpha interferon (I FN-alpha) and IFN-gamma, are released from hepatic NPC, most probably liver macrophages, upon endotoxin stimulation; furthermore, these mediators act at a posttranscriptional step of hepadnavirus replication.