Murine cytomegalovirus: Observations on growth in vitro, cytopathic effect, and inhibition with 5-iododeoxyuridine

Summary

Growth characteristics, CPE and inhibition with IUdR have been describedin vitro for the murine cytomegalovirus (Smith strain). The virus produced a CPE only in mouse embryonic fibroblasts. Its one-step growth cycle was 28 hours though the length of the eclipse period and time of onset of CPE depended on the multiplicity of infection. Once formed, new virus was rapidly released from infected cells. Interferon was produced in low titre as a result of the initial adsorption of inoculated virus, and later in much higher titre with development and spread of the infection. In stained cultures, cytopathic changes consisted of intranuclear inclusions, nucleolar hypertrophy, chromatin margination, cytomegalia, occasional amitotic nuclear division and cell lysis. Cytoplasmic inclusions comparable to HCMV infection were not observed. With inputs less than 1.0 PFU/eell, viral DNA first appeared 12 hours after infection, preceding assembly of mature virus by 5–6 hours.

A plaque reduction-neutralization test was developed for MCMV using tissue culture adapted virus as the test antigen. Neutralizing antibody was obtained from experimentally infected mice and from rabbits inoculated with ultracentrifuged virus suspensions.

IUdR inhibited synthesis of infectious virus, but did not prevent the CPE. However, with IUdR, inclusions were smaller, less well defined, and frequently multiple as compared to controls. They showed green fluorescence with acridine orange, and their nature is not clear.

In vitro, MCMV differs in several respects from the human cytomegalovirus and these differences are briefly discussed.