Stability of neurotropic mouse hepatitis virus (JHM strain) during chronic infection of neuroblastoma cells

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Abstract
A line of mouse neuroblastoma cells which was chronically infected with the neurotropic strain (JHM) of MHV, a member of the coronavirus group, was established. These cells, designated NJ, exhibited typical MHV cytopathic effects (CPE) at all passage levels along with the continual production of infectious virus. Most cells were positive for viral antigen by immunofluorescence. Viral particles consistent with the morphology of MHV were found by electron microscopy. The uninfected neuroblastoma cell line did not contain a detectable population of cells resistant to JHM, and persistence did not elicit the production of interferon. No plaque morphology or temperature sensitive mutants were selected for in the NJ culture, and we were unable to detect the presence of either a defective or defective interfering virus population. The addition of low concentration antiviral antibody modulated the infection to a carrier culture with viral antigen in the cytoplasm of the cells, but no infectious virus was produced, and the cells lacked both surface viral antigen and CPE. Possible mechanisms of viral persistencein vitro are discussed.