Rescue of a positive stranded RNA virus from antigen negative neuroblastoma cells

Single cell clones of latently infected mouse neuroblastoma cells were isolated from a culture chronically infected with mouse hepatitis virus in the presence of an antiviral antibody. These cell clones did not produce infections virus or exhibit viral cytopathic effects during cultivation at 32, 37, or 39°C. Infectious virus was isolated from single cell clones via fusion with permissive cells using polyethylene glycol, but not after fusion with inactivated Sendai virus or following treatment with metabolic inhibitors. One cell clone (S-3) from which virus was rescued was negative for viral antigen by immunofluorescence. The S-3 cell clone and no demonstrable virus antigen by complement-fixation tests using cytoplasmic extracts or virus-specified proteins detectable by polyacrylamide gel electrophoresis. The rescued viruses exhibited a temperature dependent growth defect at 32°C and have been classified as cold sensitive mutants. This study suggests that a complete genome of a positive stranded RNA virus can remain latent in infected cells without the expression of detectable virus antigen.