Effect of multiplicity of infection on Newcastle disease virus-HeLa cell interaction

Enumeration of cell-infecting particles of Newcastle disease virus by the fluorescent antibody technique

A procedure has been developed for the determination of the concentration of infective Newcastle disease virus (NDV) based on the enumeration of singly infected and distributed HeLa cells which are visualized by staining with fluorescent antibody. Infective virus assayed by the fluorescent cell-counting procedure is expressed in terms of cell-infecting units (CIU). Adsorption of NDV to HeLa cell monolayers reached a plateau 1 to 1.5 hours after inoculation of coverslip cultures, and 12 per cent of the infective particles inoculated failed to adsorb. The half-life of NDV in protein-free Eagle's medium at 37 degrees C. was 2.1 hours. There was a linear relationship between virus concentration and the number of infected cells. The coefficient of variation of the mean of replicate determinations of infective NDV was 8.2 per cent. The distribution of single infected HeLa cells in the monolayer corresponded to the Poisson distribution. With NDV the cell-infecting unit (CIU) determined in HeLa cells is equivalent to the plaque-forming unit in chick embryo cells and the egg infective dose. In experiments on the mechanism of dissemination of NDV in monolayer cultures of HeLa cells, NDV was found to spread from cell to cell through the extracellular milieu.

Biochemical basis for alterations in structure and function of HeLa cells infected with Newcastle disease virus

The ability of NDV-infected HeLa cells to synthesize DNA, protein, and RNA was investigated by measuring the incorporation of tritiated precursors into these substances at intervals after infection of cells with a virus/cell multiplicity of 500:1. A significant decrease in incorporation of precursors into DNA and protein was first observed at 3¼ hours after infection. By 4½ hours, an 80 to 90 per cent decrease had occurred, and by 5¼ hours, incorporation of precursors into DNA and protein was almost completely inhibited. Incorporation of precursor into RNA decreased gradually following infection; by the 10th hour, a 40 per cent decrease had occurred. These results, integrated with earlier observations on biological aspects of infection, suggest the following causal relationships among events in NDV-infected cells: (a) The cessation of virus production is probably caused by inhibition of protein or RNA synthesis, and is not due to inhibition of DNA synthesis or to interferon. (b) The production of infective virus does not per se interfere with the ability of an infected cell to divide, nor is inhibition of mitosis caused by either inhibition of DNA synthesis or development of marked degenerative changes in infected cells. Inhibition of mitosis may be the result of inhibition of protein or RNA synthesis, (c) Marked cell damage could have been caused by inhibition of protein, DNA, or RNA synthesis, (d) Interference by NDV with the multiplication of influenza virus was probably due to the inhibitory effects of NDV on cellular biosynthetic activities.

Newcastle disease virus infection of L cells

Newcastle disease virus (NDV) California strain reportedly grows poorly in L cells but replicates very well in chicken embryo cells. NDV-infected L cell cultures show a characteristic virus growth curve with respect to uridine incorporation, but plaque assays of the virus produced 24 h postinfection (PI) show no infectious particles when assayed on L cell monolayers and only a very low titer on chick cell monolayers. Plasma membranes isolated and purified from infected L cells 8 h PI contain all of the major virion proteins. In addition, NDV-infected L cells show a 50% loss of H-2 antigenic activity, a phenomenon previously observed in cells productively infected with vesicular stomatitis virus. These results suggest that at least part of the normal process of NDV maturation occurs in NDV-infected L cells. Sodium dodecyl sulfate-polyacrylamide gel patterns of supernatant virus purified from cells radiolabeled with amino acids from 3 to 24 h PI in the presence of actinomycin D show that all the major NDV structural proteins are present. Electron micrographs of NDV-infected L cells show extensive virus maturation at cell membranes. It can be concluded that infection of L cells with NDV results in a normal production of virus-specific RNA, synthesis of all the major structural proteins, association of the viral envelope proteins with the L cell plasma membrane, and the loss of cell surface H-2 antigenic activity. However, most of the virus particles produced are noninfectious.

Immunofluorescence in the study of viruses in tissue culture. I. Development of an immunofluorescent focus assay for herpes simplex virus

A rapid and sensitive assay method has been developed for herpes simplex virus in kidney cells of Cercopithecus aethiops. Using immunofluorescence, foci of infection produced by this virus can be scored within 20–22 hours after inoculation. It has been demonstrated that this procedure gives reproducible results and exhibits a direct relationship between virus concentration and the number of fluorescent foci. The technique is slightly more sensitive than the conventional plaque assay method using the same host system.

The Production of Cytopathic Changes in Canine Cell Lines by Infectious Agents: Cell Lines Derived from Melanoma and Thyroidal Carcinoma

The cytopathic effect of more than 30 viruses and Toxoplasma gondii and Histoplasma capsulatum was determined in established canine thyroid adenocarcinoma and canine melanoma cell lines. Marked effect was observed with the viruses of canine hepatitis, pseudorabies, and canine distemper, and reo type 1 and vaccinia viruses in both cell lines. Moderate effect was found with human adenovirus type 1, swine adenovirus and the viruses of swine influenza and Newcastle disease. Cytopathic changes were produced with the virus of herpes simplex in the thyroid adenocarcinoma cells. A transient giant cell formation was produced by the virus of measles in the thyroid cell line. Hemadsorption was demonstrated in both cell lines with vaccinia virus. Toxoplasma gondii multiplied in both cell lines and produced cellular degeneration and necrosis. Histoplasma capsulatum grew in the thyroid adenocarcinoma cell line with little cellular degeneration.

On the role of the response of the cell membrane in determining virus virulence. Contrasting effects of the parainfluenza virus SV5 in two cell types

The simian myxovirus SV5 multiplies in a continuous line of baby hamster kidney (BHK21-F) cells causing extensive cell fusion, followed by cell death. After inoculation of 15 PFU/cell, the latent period was 7 hr, the doubling time approximately 60 min, and the yield 7 PFU per cell. Giant cell formation began about 6 hr after infection and rapidly progressed to the formation by 14 to 18 hr of a single syncytium which disintegrated by 24 to 36 hr. In contrast, SV5 multiplies in primary rhesus monkey kidney cells for long periods of time producing high yields of virus with little cytopathic effect. High multiplicities of SV5 induced cell fusion in BHK21-F cells within 1 hr in the absence of virus multiplication but had no visible effect on monkey kidney cells. Time-lapse photomicrography has demonstrated that giant cells form by fusion of infected cells, and that some polykaryocytes divide. During aberrant division of polykaryocytes giant nuclei are formed from the nuclear material of several parent nuclei. The cytoplasmic development of viral antigens as demonstrated by immunofluorescence is similar in BHK21-F and monkey kidney cells. Synthesis of cellular DNA, RNA, and protein in monkey kidney cells is not shut off by SV5-infection, and in BHK21-F cells synthesis of these macromolecules is not inhibited until after extensive cell fusion has occurred 12 to 15 hr after infection. Persistently infected BHK21-F and monkey kidney cells have been serially carried through 11 and 28 cell passages, respectively. The results suggest that whether SV5 acts as a moderate virus, as in monkey kidney cells, or a virulent virus, as in BHK21-F cells, depends on the response of the cell membrane to the virus.