In Vivo and In Vitro Models of Demyelinating Disease: Endogenous Factors Influencing Demyelinating Disease Caused by Mouse Hepatitis Virus in Rats and Mice

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Abstract
Intracerebral inoculation of JHM virus (JHMV), the neuropathic strain of mouse hepatitis virus, into Wistar Furth, Wistar Lewis, and Fischer 344 rats at various ages indicated that Wistar Furth rats are more susceptible to the virus than are the other strains. Fischer 344 and Wistar Lewis rats were more resistant to inoculation at 2 and 5 days of age and completely resistant by 10 days of age. In contrast, Wistar Furth rats which were very susceptible at both 2 and 5 days of age remained susceptible until 21 days of age. Intracerebral challenge of an F1 cross between Wistar Furth and Wistar Lewis rats at 10 days of age indicated that resistance to JHMV infection is dominant. Cyclophosphamide treatment 28 days after intracerebral inoculation exacerbated an inapparent infection, leading to paralysis in eight of nine and death in six of nine Wistar Furth test rats. In such immunosuppressed animals, grey- and white-matter lesions were noted throughout the central nervous system, in contrast to the purely demyelinating lesions noted previously. Since rats, unlike mice, were not susceptible to disease after intracerebral injection with the serorelated viscerotropic strain MHV-3, we wished to extend our understanding of the neurological disease process elicited by the two viruses in rodents. For this reason, various mouse strains, including some with recognized immunodeficiencies, were challenged by different routes of inoculation. Intraperitoneal infection of nude and beige mice with JHMV indicated that lack of natural killer cell functions does not markedly enhance the susceptibility to virus, whereas T-cell activity appears to be essential for resisting infection. JHMV and MHV-3 replication in peritoneal macrophages from highly resistant A/J mice was reduced in comparison with that noted in macrophages from susceptible C57BL6/J mice. An initial intraperitoneal inoculation of JHMV was able to protect C57BL6/J mice against fatal intracerebral challenge within 3 days, whereas A/J mice remained susceptible beyond day 3. The protective effect did not appear to result from increased levels of circulating interferon, preceded elevation in serum JHMV-neutralizing antibody titers, and persisted for at least several weeks after intraperitoneal inoculation. Based on the combined studies described here and on previous work by us and others, it appears that the factors influencing the outcome of coronavirus disease in rodents are age at inoculation, route of challenge, genetic constitution of the virus and host, and competence of the immune system, particularly cellular immunity involving T-cells.