Macrophages genetically resistant to mouse hepatitis virus converted in vitro to susceptible macrophages.

Genetic resistance to mouse hepatitis, which resides largely in the macrophages of resistant C3H mice, may be altered by exposing the cells in vitro to fluid from allogeneic mixed lymphocytes. A 1,000-fold increase in susceptibility was produced in these genetically resistant cells by exposure to this fluid. This presumed lymphokine was effective without producing any change in host adaption of the virus.