Several Rat Cell Lines Share a Common Defect in Their Inability to Internalize Murine Coronaviruses Efficiently

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Abstract
Infection of rat cells, Schwannoma RN2, hepatoma HTC or myoblast L6, with the murine coronavirus JHM strain results in a persistent infection characterized by the release of virus over an extended period of time with a limited cytopathology. Several stages of the viral replication cycle have been examined in these cells in comparison to those in mouse L2 cells, which are totally permissive to JHM infection. Although the rat cells bound as much virus as the mouse cells their ability to internalize it was 40-fold less efficient than the mouse cells. This lower internalization efficiency was not enhanced by pH shock of infected cells, but was by treatment with polyethylene glycol. In all cell types there appeared to be no major differences in the ability of the internalized virus to replicate the viral RNA as determined by slot-blot analysis with a radiolabelled viral cDNA. A similar genetic mechanism appears to be operative in the lines because somatic cell hybrids formed between these lines in various combinations were also deficient in the ability to internalize bound virus. Taken together these results imply that rate cell lines in general share a common deficiency in their inability to internalize murine coronaviruses efficiently. This low efficiency in viral internalization may explain in part the ability of these lines to sustain persistent infections.