Viral nucleic acid synthesis in HSV infected neural cells

Interaction of herpes simplex virus type 2 with a rat glioma cell line

The interaction between herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) and two neural cell lines, mouse neuroblastoma (N1E-115) and rat glioma (C6-BU-1), was investigated. N1E-115 cells were permissive to both types of HSV. In C6-BU-1 cells, on the other hand, all the HSV-1 strains tested so far showed persistent infection, and the infectious virus of HSV-2 strains disappeared spontaneously. The HSV-2-infected C6-BU-1 cells were positive for HSV-2-specific DNA sequences, virus-specific RNA, HSV-2-specific antigens and thymidine kinase activity, when no infectious virus was detected. The HSV-2 was reactivated from those C6-BU-1 cells by superinfection with murine cytomegalovirus (MCMV), but not with UV-irradiated MCMV or human cytomegalovirus. The reactivated HSV-2 was identical to the parental virus, when examined by restriction endonuclease cleavage analysis.

Herpes simplex virus persistence in mouse neuroblastoma (C 1300) cell cultures: role of interferon

The Mp strain of herpes simplex virus type 1 (HSV1) induced a persistent infection in the mouse C 1300 neuronal cell line (clone N 115). C 1300 cultures infected at an MOI of 0.01 or 0.001 survived the initial infection and continued to produce infectious virus and viral antigens for 185 days and 31 days, respectively. Viral antigens were not detected in cultures no longer producing infectious virus; these "cured" cultures had comparable susceptibility to reinfection with HSV as previously uninfected C 1300 cells. While significant amounts of interferon were produced by C 1300 cells when challenged with Newcastle Disease Virus (NDV) or when treated with poly I:C, HSV-induced interferon could not be detected in either the acutely or persistently infected cell lines. The persistent state was not significantly altered by the addition of 1,000 units/ml of murine interferon alpha plus beta (MuIFN alpha + beta), nor was it affected by the addition of antibody to MuIFN. It appears that IFN does not play an important role in the establishment and/or maintenance of viral persistence in this neuronal system.

Use of aggregating brain cultures to study the replication of herpes simplex virus types 1 and 2 in central nervous system tissue

A novel tissue culture system consisting of reaggregated embryonic mouse brain cells was used to examine the replication of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) within central nervous system tissue. Brain aggregates cultured 30-40 days in vitro demonstrated progressive maturation and differentiation into cells recognizable as neurons, astrocytes and oligodendrocytes, with the latter cell type exhibiting myelin production. Mature aggregates were infected with HSV and sampled at timed intervals postinfection for morphological, virological, and biochemical assays. By electron microscopy mature nucleocapsids were observed in the nucleus of peripheral cells at 9 h and in all cell types by 33 h. Virus-specific antigens were observed, using the immunoperoxidase test, within peripheral cells at 12 h postinfection (p.i.). By 24 h p.i., antigen production had progressed throughout the infected aggregates. Growth curves of HSV-1 and HSV-2 for intracellular and extracellular infectious virus production correlated well with virus-induced morphological changes and antigen production. SDS-polyacrylamide slab gel electrophoresis of isotopically-labelled proteins and glycoproteins synthesized from 4 to 24 h p.i. in virus-infected aggregates revealed typical HSV-1 polypeptide profiles and HSV-1 and HSV-2 glycoprotein profiles. Our results suggest that aggregating brain cultures may provide a useful and more accurate in vitro model for the study of HSV-induced neurological disease.

Abortive infection of neural cells by herpes simplex virus type 2

The nature of the refractoriness of C6 rat glioma cells to herpes simplex virus type 2 (HSV-2) was examined. Infection of C6 cells with HSV-2 results in low virus yields, not exceeding the input virus. Although virus growth studies suggested a restricted cycle of virus replication, synthesis of HSV-2 DNA and HSV-2-specific antigens could not be detected. In addition, HSV-2 yields in C6 cells were unaffected by interferon, cycloheximide, tunicamycin, actinomycin D and cytosine arabinoside. However, trypsin, but not EDTA, treatment of infected C6 cells at 4 hours postinfection (p.i.) reduced maximal HSV-2 yields at 24 hours p.i. by 61 percent. These data: 1) indicate that HSV-2 fails to replicate in C6 cells and is prohibited from directing the synthesis of virus macromolecules; and 2) suggests that the increment of HSV-2 yields observed during the synthesis phase of the virus growth cycle represents re-envelopment and egress of a portion of the input virus.

Rabies serogroup viruses in neuroblastoma cells: propagation, "autointerference," and apparently random back-mutation of attenuated viruses to the virulent state

Each of several strains of fixed rabies virus was found to replicate to high titers in C1300 mouse neuroblastoma (clone NA) cells, without adaptation. Rabies serogroup Lagos bat, Mokola, and Duvenhage viruses also replicated efficiently in NA cells. Kotonkan and Obodhiang viruses replicated efficiently after adaptation, to titers not previously obtained in vitro. Infection in NA cells was frequently more cytopathic than in BHK-21 cells, allowing titration of Kotonkan and Obodhiang viruses by plaque assay. Duvenhage virus caused syncytium formation. Serial propagation of rabies viruses at a high multiplicity of infection in NA cells led to a rapid decline in virus yields; similar "autointerference" has not previously been demonstrated with rabies virus in other cell systems. Rabies virus infection in NA cells exhibited extreme sensitivity to interference by experimentally added defective interfering virions. Although several strains of attenuated rabies virus consistently reverted rapidly to virulence after propagation in NA cells, other strains of attenuated rabies and rabies serogroup viruses acquired increased virulence at a more gradual rate or not at all, suggesting that diverse characters may control virulence. When attenuated Flury HEP rabies virus was serially propagated at a low multiplicity of infection in either NA cells or suckling mouse brain, virulence appeared at a very variable rate, indicating that these systems may selectively enhance replication of randomly occurring virulent virus mutants.