U. Klocker et al., Endotoxin stimulates liver macrophages to release mediators that inhibit an early step in hepadnavirus replication, J VIROLOGY, 74(12), 2000, pp. 5525-5533
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.