Human cytomegalovirus persistent infection in a human central nervous system cell line: production of a variant virus with different growth characteristics.

The susceptibility of human central nervous system cell lines to human cytomegalovirus (HCMV) and the fate of infected cultures were studied. Significant amounts of infectious progeny virus were produced in 118MGC glioma and IMR-32 neuroblastoma, but not in KGC oligodendroglioma cells when the cultures were infected with wild-type virus (HCMVwt) at an m.o.i. of 10 p.f.u. per cell. Further passage of infected 118MGC cells resulted in the establishment of a long-term persistent infection. This infection, designated 118MGC/Towne, continuously produced infectious virus (HCMVpi) with titres ranging from 10(2) to 10(5) p.f.u./10(6) cells up to 360 days post-infection (corresponding to 50 subcultures). Since no temperature-sensitive mutants, defective interfering particles or interferon-like activity were found in the 118MGC/Towne cultures, maintenance of the persistent infection seemed to be due to a balance between the release of infectious virus and the growth of uninfected cells. The HCMVpi produced in long-term persistently infected cultures was shown to be different from the HCMVwt originally used to infect by the following characteristics: HCMVpi replicated slowly and yielded lower amounts of progeny virus than HCMVwt; HCMVpi induced a 73,000 mol. wt. immediate early protein that was not synthesized in HCMVwt-infected cells; HCMVpi had a different DNA structure from that of HCMVwt. These results suggest that HCMVpi is a slower growing variant of HCMVwt and probably plays an important role in the maintenance of the persistent infection.

Encephalitis induced in non-human primates by canine distemper virus adapted to human neural cells.

The Onderstepoort strain of canine distemper virus (CDV) adapted to human oligodendroglioma, neuroblastoma and glioblastoma cells, was intracerebrally inoculated into cynomolgus monkeys. All the three viruses caused periventricular encephalitis involving the brain stem. When the neurovirulence of these viruses were compared in terms of clinical signs and histopathological changes, the oligodendroglioma-adapted virus showed the neurovirulence of the highest degree inducing degeneration of axons and glial cells. Chronic encephalitis was also observed. The neuroblastoma-adapted virus induced predominantly nerve-cell degeneration although clinically this virus showed slightly lower degree of neurovirulence than the oligodendroglioma-adapted viruses. The glioblastoma-adapted virus showed clinically much lower neurovirulence than the other two viruses; all monkeys infected with this virus survived and produced high level of antibody in most cases. Histopathologically degeneration of axons and glial cells was characteristics although the incidence was less frequent than the oligodendroglioma-adapted virus. Predominant involvement of nerve cells by neuroblastoma-adapted virus and predominant involvement of axon and glial cells by oligodendroglioma-adapted virus and by glioblastoma-adapted virus suggest that in vitro tropism of the virus to neural cells is partially reflected on tropism of the virus in the CNS.

Characterization of canine distemper viruses adapted to neural cells and their neurovirulence in mice.

Interaction of the Onderstepoort strain of canine distemper virus (CDV) with three established human neural cells, i.e. IMR-32 neuroblastoma, 118-MGC glioma and KG-1 oligodendroglioma, was examined, and adaptation of CDV to these cells was also attempted. The unadapted virus was found to grow at relatively low titers in the three neural cells inducing moderate to minimal cytopathic effects (CPE). The virus was successfully grown at high titers in these cells after 8 to 10 passages. Biological characteristics such as growth rate, morphology of CPE and plaque size changed after adaptation. Analysis by SDS-polyacrylamide gel electrophoresis, however, failed to show any difference in the molecular weight of component proteins among the unadapted and three adapted viruses. Inbred DDD strain of mice developed clinical signs after intracerebral inoculation with the unadapted virus but most of them survived with histological lesions of encephalitis. Neuroblastoma-adapted virus induced only transient clinical signs in some animals with mild encephalitic lesions in the gray matter. Increases in neurovirulence were found for viruses adapted to glioma and oligodendroglioma cells. Almost all mice inoculated with these two viruses at 3 weeks of age died within 8 days with histological lesions consisting of hyperemia, edema, severe degeneration of nerve cells and a few giant cells. Demyelinating lesions in the absence of inflammatory changes were observed in the cerebellum, pons and medulla oblongata of animals inoculated with oligodendroglioma-adapted virus.

Evidence for polyomaviruses in human neurological diseases.

Polyomaviruses have been implicated in several chronic human neurological diseases. In progressive multifocal leukoencephalopathy there is an opportunistic and lytic infection of oligodendrocytes of the central nervous system leading to subacute demyelinating disease. Although aspects of the pathogenesis remain undefined, the causal role of the viruses seems firm. Nonpermissive infection of neural cells with resultant cerebral tumors has been suggested by epidemiological studies, virus isolations, and detection of viral antigens and nucleic acids. Nevertheless, it is uncertain whether papovaviruses are causally related to human tumors. Possible association of papovavirus infection with other neurological diseases needs further study.