Antagonism of RNase L Is Required for Murine Coronavirus Replication in Kupffer Cells and Liver Sinusoidal Endothelial Cells but Not in Hepatocytes.

UNLABELLED

Mouse hepatitis virus strain A59 infection of mice is a useful tool for studying virus-host interaction during hepatitis development. The NS2 mutant is attenuated in liver replication due to loss of phosphodiesterase activity, which the wild-type (WT) virus uses to block the 2',5'-oligoadenylate synthetase (OAS)-RNase L (RNase L) antiviral pathway. The activation of RNase L by NS2 is cell type dependent and correlates with high basal expression levels of OAS, as found in myeloid cells. We tested the hypothesis that the resident liver macrophages, Kupffer cells (KC), represent the cell type most likely to restrict NS2 and prevent hepatitis. As found previously, A59 and NS2 replicate similarly in hepatocytes and neither activates RNase L, as assessed by an rRNA degradation assay. In contrast, in KC, A59 exhibited a 100-fold-higher titer than NS2 and NS2 induced rRNA degradation. Interestingly, in liver sinusoidal endothelial cells (LSEC), the cells that form a barrier between blood and liver parenchymal cells, NS2 activates RNase L, which limits viral replication. Similar growth kinetics were observed for the two viruses in KC and LSEC from RNase L mice, demonstrating that both use RNase L to limit NS2 replication. Depletion of KC by gadolinium(III) chloride or of LSEC by cyclophosphamide partially restores liver replication of NS2, leading to hepatitis. Thus, during mouse hepatitis virus (MHV) infection, hepatitis, which damages the parenchyma, is prevented by RNase L activity in both KC and LSEC but not in hepatocytes. This may be explained by the undetectable levels of RNase L as well as by the OASs expressed in hepatocytes.

IMPORTANCE

Mouse hepatitis virus infection of mice provides a useful tool for studying virus-host interactions during hepatitis development. The NS2 mutant is attenuated in liver replication due to loss of phosphodiesterase activity, by which the wild-type virus blocks the potent OAS-RNase L antiviral pathway. RNase L activation by NS2 is cell type dependent and correlates with high basal expression levels of OAS, as found in myeloid cells. We showed that the hepatocytes that comprise the liver parenchyma do not activate RNase L when infected with NS2 or restrict replication. However, both Kupffer cells (KC) (i.e., the liver-resident macrophages) and the liver sinusoidal endothelial cells (LSEC) which line the sinusoids activate RNase L in response to NS2 These data suggest that KC and LSEC prevent viral spread into the parenchyma, preventing hepatitis. Furthermore, hepatocytes express undetectable levels of OASs and RNase L, which likely explains the lack of RNase L activation during NS2 infection.