Studies on the cytopathic effects of Newcastle disease virus: RNA synthesis in infected cells

Aerosol vaccination against Newcastle disease using the Ulster strain

The Ulster strain of Newcastle disease when administered as an aerosol vaccine has been shown to give a level of protection which is slightly lower than that produced by a commercial Hitchner B1 strain but which is not associated with any respiratory reaction. Both strains proved to be poor vaccines when used in chickens with high levels of maternal antibody. When used for vaccination of susceptible chickens the Ulster strain produced protection to experimental challenge for up to 3 weeks. Revaccination of these chickens with B1 vaccine produced a secondary response which was significantly higher than in the groups vaccinated initially with B1 vaccine. It is suggested that primary vaccination of fully susceptible chickens with the Ulster strain will induce a high degree of immunity with less reaction in the respiratory tract than is found to occur with currently used vaccines. This initial vaccination may then pave the way for further immunisation with higher levels of protection and less damage to the respiratory system.

Polypeptide synthesis in alphavirus-infected Aedes albopictus cells during the establishment of persistent infection

Polypeptide synthesis was examined in mosquito cells during the establishment of a persistent infection with two alphaviruses, Ross River virus (RRV) and Semliki Forest virus (SFV), and in vertebrate cells cytopathically-infected with the same viruses. In Aedes albopictus cell, RRV reached peak titres at 34--48 hours p.i. At 12 hours 85 per cent of cells assayed as infected by infective centre assay; by 48 hours when persistence was established, virus production was reduced and less than 5 per cent of cells assayed as infected. There was no shut-down of host polypeptide synthesis during infection. Viral polypeptide synthesis was maximal between 10 and 24 hours p.i. The major viral polypeptides labelled were nucleocapsid protein and envelope protein(s). The precursor polypeptide p95 which was prominent in infected BHK cells was not detected in mosquito cells. Similar results were obtained on SFV infection. During the establishment of persistence there was a coordinate decline in the synthesis of RRV polypeptides, reaching undetectable levels by 72 hours p.i. Subculturing persitently-infected cells led to a small increase in viral polypeptide synthesis and virus titre. In contrast, during RRV growth in BHK celos host protein synthesis was severly inhibited and by 9--11 hours p.i. virus-specific polypeptide synthesis represented more than 90 per cent of total protein synthetic activity.

Isolation and characterization of heat-resistant (HR) mutants of Newcastle disease virus

Heat-resistant (HR) mutants (MR 70 and HR 74) of Newcastle disease virus (NDV) which exhibited significantly higher thermostability in their infectivity than wild-type virus were isolated and characterized. They differ from each other in their plaque morphology; HR 70 produces small turbid plaques, whereas those of HR 74 are large and clear. Cytopathogenicity of these mutants is much lower than that of the wild-type virus in cultured cells such as CEF, LLCMK2 and HeLa cells. Moreover, these HR mutants exhibited extended mean embryo survival times. Synthesis of cellular RNA's and proteins in cells infected with HR mutants was not significantly reduced under conditions in which synthesis of these macromolecules was strongly reduced in cells infected with wild-type virus. No significant differences were observed between HR mutants and wild-type virus in their other phenotypic characteristics such as the capacity for interferon production, growth characteristics at a low multiplicity of infection, and cleavage of viral glycoproteins in infected cells. From these findings, it was suggested that the inhibitory effect of virus infection on cellular macromolecular synthesis is a possible determinant of cytopathogenicity of NDV.

Effect of pH on the growth and cytopathogenicity of avian infectious bronchitis virus in chick kidney cells

The growth of avian infectious bronchitis virus (IBV) in chick kidney cells at different pH values in the range 6.0-9.0 demonstrated that although the virus was released at a much faster rate at the higher pH values the titre tended to drop more quickly. At the acid pH values the virus was released more slowly but reached a maximum titre similar to that at the higher pH values and showed only minimum reduction in infectivity up to 49 hours post inoculation. The stability of virus in tissue culture medium was shown to be directly related to pH 6.0-8.0, being more stable at the acid pH values. The degree of cytopathogenicity induced in chick kidney cells following infection with IBV was directly related to the pH at which the cells were incubated, occurring earlier and more extensively in cells at the higher pH values. Cell macromolecule synthesis in chick kidney cells was inhibited following infection with IBV and was apparently due to cell damage and death.

Interaction of concanavalin A with the surface of virus-infected cells

Infection of untransformed cells with a wide-range of non-oncogenic enveloped viruses causes a significant increase in their susceptibility to agglutination by concanavalin A (Con A). The increased Con A agglutinability of these cells is not caused by an increase in the number of Con A sites on the cell surface but involves alteration in the surface properties of infected cells to allow redistribution of Con A receptors to form "patches" following binding of Con A to the cell surface. Similarities between Con A-mediated agglutination of normal cells infected with non-oncogenic viruses and the agglutination response to cells transformed by oncogenic viruses will be reviewed. Finally, the use of Con A as an experimental tool to modify the replication and cytopathogenicity of non-oncogenic viruses grown in mammalian cells will be presented.