- Volume 40, Issue 2, 1978

The simultaneous occurrence of virus replication and of interferon production in Namalva lymphoblastoid cell cultures infected with measles virus has allowed the development of a semi-continuous production system yielding about 104 units of interferon for each 106 cells.

Cells of brain tissue of rabbits, rats and mice were dissociated and glial cells, neuronal perikarya and synaptosomes were separated by centrifugation on discontinuous Ficoll gradients. HSV was shown to attach well to rat and rabbit glial cells and synaptosomes but not to neuronal perikarya. Of intracerebrally infected mice the fractions with glial cells contained the infective virus. The interactions between HSV and neuronal cells and the implication of the observations on the HSV infection of the nervous system are discussed.

On the basis of gel precipitation, reactions with rabbit anti-pike fry rhabdovirus sera, a recent virus isolate (V75/94) from pike fry, and the grass carp rhabdovirus were found to be indistinguishable from pike fry rhabdovirus. The proteins of these viruses were compared to those of spring viraemia of carp virus. In ‘rocket’ immunoelectrophoresis the pike fry rhabdoviruses and the grass carp rhabdovirus showed up to 4 lines with homologous antiserum in which the precipitates formed by the G and M proteins were fused. With this antiserum, spring viraemia of carp virus gave only one precipitation are which was formed by the N protein. All the viruses are very similar to vesicular stomatitis virus with respect to the mol. wt., localization and phosphorylation of structural proteins. In polyacrylamide-SDS slab gels the viruses showed minor differences in the migration of their respective NS proteins.

Special environmental conditions were used to induce systemic infection by tomato bushy stunt virus (TBSV) in Gomphrena globosa. Severe mottle symptoms were followed by the formation of necrotic lesions. The mottled tissue consisted of small patches of necrotic, chlorotic and green tissue closely intermingled. The ultrastructure of such systemically infected G. globosa leaves was investigated. In the mesophyll and bundle sheath cells of the chlorotic patches the chloroplasts were severely altered and often connected to multivesicular (MV) bodies, whose vesicles and vacuoles contained fibrillar material. The MV bodies are thought to originate from chloroplasts and may be involved in TBSV replication. Virus appeared in the cytoplasm and central vacuole as scattered particles or small paracrystalline aggregates. Dark spots, probably proteinaceous material, were present in the cytoplasm. The cells of the necrotic patches appeared completely collapsed and contained virus particles. The necrotic lesions were cytologically quite similar to those produced in hypersensitive conditions.

A non-specific reaction between human IgM and cytoplasmic structures of virus infected cells can often be observed if IgM antibodies to virus antigens are detected by indirect immunofluorescence or by immuno enzyme assays. Formaldehyde selectively inactivates the cytoplasmic receptors for human IgM without affecting the virus structural proteins. Alternatively, receptor-free antigens can be obtained by isolation of nuclei from virus infected cells. Due to reduced back-ground, a more specific and more sensitive detection of IgM antibodies to Epstein-Barr virus, cytomegalovirus or central European encephalitis virus is possible.

Plaque neutralization assays were carried out using the rhabdoviruses of pike fry (2 isolates), spring viraemia of carp and grass carp. When rabbit anti-pike fry rhabdovirus sera were used, no neutralizing activity was observed but plaque counts increased with heat-inactivated sera or sera that had been stored at -20 °C for prolonged periods. Antibody binding to the virus was demonstrated by gradient centrifugation experiments. The use of immune serum alone or in combination with anti-rabbit gamma globulin serum resulted in aggregation of radioactive virus. Aggregation was also observed when anti-rabbit gamma globulin serum was added under neutralization test conditions. Addition of non-inactivated guinea-pig serum to mixtures of pike fry rhabdovirus and rabbit antiserum to spring viraemia of carp virus resulted in strong neutralization, whereas this antiserum alone or in the presence of inactivated guinea-pig serum gave an increase in plaque numbers. The increase in plaque number and the complement-dependent neutralization phenomena were weak or absent in the homologous spring viraemia of carp virus system.

Immunization of pike with pike fry rhabdovirus resulted in an increase in virus neutralizing activity which could be attributed to the macroglobulin fraction of the serum. After immunizations over a period of 6 months with virus antigens, no further increase in neutralizing activity was observed. Pike sera showed 50% plaque reduction at concentrations between 0.017 and 0.3%. Using these sera it could be demonstrated that the grass carp virus and the V 75/94 isolate from pike fry were indistinguishable from the original pike fry rhabdovirus, whereas spring viraemia of carp virus was different.

Two virus clones, VSV-mp and VSV-sp, were isolated from L cells persistently infected with VSV (New Jersey serotype). Both clones were more temperature sensitive than the parent virus, VSV-o, and grew more slowly, gave smaller plaques, less c.p.e. and lower virus yields in L cells. Unlike the parent virus, both persistent viruses induced interferon production in L cells. Stable carrier cultures could be obtained from L cells infected with VSV-sp at low multiplicities without pretreatment with interferon. This may be related to the fact that VSV-sp is more sensitive to interferon than either VSV-mp or VSV-o.