Difference in sensitivity to interferon among mouse hepatitis viruses with high and low virulence for mice

Mouse hepatitis viruses (MHV) of different virulence for mice were studied with respect to interferon (IFN) sensitivity. The growth of low-virulent MHV-S and intermediately virulent MHV-JHM was significantly suppressed in IFN-treated L cells compared with untreated cells. However, a comparable suppression of the growth of highly virulent MHV-2 was not observed in IFN-treated cells. This differential effect of IFN treatment could also be demonstrated at the level of viral mRNA and viral proteins. In cells infected with MHV-S or MHV-JHM the amount of viral mRNAs was remarkably reduced by IFN treatment. Also the levels of the major intracellular viral proteins, in particular the E1 protein, were affected by IFN treatment. Similar effects could not be demonstrated in MHV-2-infected cells. These results suggest that during MHV-S or MHV-JHM infection IFN treatment suppresses virus replication at several stages. The significance of these results is discussed in terms of the pathogenecity of these viruses.