Adult mouse hepatocytes in primary monolayer culture express genetic resistance to mouse hepatitis virus type 3.

Abstract Hepatocytes isolated from mice with inborn resistance to MHV 3 (a hepatotropic Coronavirus with high virulence for many mouse strains) were able to express partial resistance to in vitro infection with this virus. In cultures of hepatocytes from susceptible C57BL/6 mice, the virus grew to high titers and the cells fused rapidly to huge syncytia. However, in cultures of cells from resistant A/J or semi-resistant A/Sn, C3H/HeJ, or CBA mice, maximal virus titers were 200- to 2000-fold lower and were delayed 6 to 9 h. Cell fusion was likewise delayed and was, after low multiplicity of infection, restricted to small foci. Resistance was specific for MHV 3, because resistant cells were fully permissive for a hepatotropic influenza A virus, a rhabdovirus and a herpes virus. Immuno-fluorescent labeling with convalescent anti-MHV 3 sera or with antisera directed against the two isolated viral envelope proteins, E1 and E2, showed a lower intensity of viral-specific staining in resistant as compared with susceptible cells. However, after infection at high multiplicity, resistant cells were all specifically fluorescent and thus were all infected. By electron microscopy, adsorption and penetration of virions appeared to be similar in resistant and susceptible hepatocytes. Viruses budding from intracellular membranes could easily be found in cells from susceptible but not from resistant mice. Antibodies to interferon (IFN) did not eliminate hepatocellular resistance, and exogenous IFN did not protect resistant cells any better than susceptible ones. Resistance of hepatocytes as found in vitro is also likely to act during infection in vivo. Therefore, resistance of hepatocytes, a cell type not usually considered as playing an important role in the host's antiviral defence, may be an essential component of inborn resistance to MHV 3 in vivo.