Mouse Fibroblast Mutants Selected for Survival Against Mouse Hepatitis Virus Infection Show Increased Resistance to Infection and Virus-Induced Cell Fusion

Abstract

We describe here a genetic approach to the analysis of host cell functions involved in determining permissiveness to mouse hepatitis virus (MHV). Using the chemical mutagen, ethyl methane sulfonate (EMS), mouse fibroblast cell mutants were generated which were selected for resistance to cell-killing by MHV. These mutants were then screened for their susceptibility to MHV infection, ability to replicate MHV and relative sensitivity to MHV-induced cell fusion. In contrast to wild type L-2 cells which were acutely and terminally infected by MHV, all five mutants examined replicated MHV in a persistent manner. These mutants showed a reduced susceptibility to MHV infection and an increased resistance to MHV-induced cell fusion. Fusion resistance was specific to that mediated by the MHV E2 protein; mutant as well as wild type L-2 cells were equally sensitive to fusion by polyethylene glycol. The combined effect of reduced infectability and increased fusion resistance was to limit MHV infection to only a small percentage of the total cells in culture, thereby permitting survival of both virus and cells. The observed high rate of generation of the cell mutants suggests that the conversion of a fully MHV-susceptible cell to a semi-resistant one (capable of supporting a persistent infection) is a fairly common event, possibly involving a single mutation.