Donald H. Harter

Electron microscopic observations of visna virus-infected cell cultures.

Abstract Electron microscopic observations of three cell lines infected with visna virus revealed two types of extracellular particles. The smaller of these was 65–110 mμ in diameter and contained a 20–30 mμ electron-dense core. Ordered arrays of the latter type of particle occurred rarely in the cytoplasm. After cesium chloride density gradient centrifugation of the virus, the band that contained maximal infectivity was composed of numerous particles with osmiophilic cores similar to those found in infected cell cultures. This finding suggests that such particles represent the infective agent. The second type of extracellular particle was larger (100–140 mμ in diameter), lacked an electron-dense core, and contained material similar in appearance to cellular cytoplasm. This form appeared to develop by budding from the cell surface.

Murine Influenza Virus Encephalomyelitis

The development and maturation of neurotropic WS-N strain of influenza virus in encephalitic mice was shown to occur preferentially along the “free” surface of ependymal and choroid plexus cells where it developed from the cell membrane. Virus maturation and “budding” was generally absent along the other surfaces of the same cells where they were apposed to other cells. This may suggest an inhibitory effect of adjacent cell membranes. Electron microscopic observations of ependymal surfaces may be of importance in demonstrating some viruses in human and animal tissues. Most of the virions were rounded in shape with surface spikes but a considerable number of filamentous forms were seen developing at the tips of villi. Filamentous forms had previously been described in tissue culture but not in animal encephalitic tissues. Intracellular virus within vacuoles was seen en masse and a few virus-like structures appeared to form from endoplasmic reticulum. Intracytoplasmic inclusions were demonstrated. The virus appeared ultrastructurally at a time preceding and overlapping the time at which virus replication reaches its maximum. The electron microscopic results were also considered in relation to immunofluorescence evidence in a companion paper, that virus antigen is present in deeper cells even though few mature virions appear in those sites. The combined data suggests that virus initially has a predilection for ependymal cells where mature virions develop at the surface of the cells. Later there is extension of virus antigen to deeper cells with a presumed transfer from cell to cell without the same degree of maturation of virions at cell surfaces.

Antiviral activity of oxidized polyamines and aldehydes

Abstract Amine oxidase was isolated from lamb serum, purified 50-fold by Chromatographic techniques, and used in the preparation of the aminoaldehydes of spermine and spermidine. Crude spermine aldehyde inactivated a number of animal viruses, but failed to affect virus hemagglutination. Chromatographic fractionation of the aldehyde of spermidine or spermine indicated that fractions containing peak amine aldehyde concentrations produced maximal inactivation of vesicular stomatitis virus. Inactivation of vesicular stomatitis virus by column-purified oxidized spermidine (a monoaldehyde) or spermine (a dialdehyde) was a function of the concentration of aldehydic groups. Viral inactivation produced by the amine aldehydes proceeds in a linear-first-order reaction with respect to time. Studies to determine structure-antiviral activity relationships were conducted with a number of aliphatic and aromatic aldehydes. These results suggest that the aldehyde moiety is the primary determinant of antiviral activity.

Murine influenza virus encephalomyelitis. I. Neuropathological and immunofluorescence findings.

The direct inoculation of neurotropic NWS strain of the influenza virus into the brains of Swiss albino white mice results in an acute meningoencephalomyelitis. The myelitis is described for the first time. The cerebral lesions are marked by a severe ventriculitis, characterized by a necrotizing ependymitis and a lesser involvement of the choroid plexus. During the first three to four days of the infection, increasingly frequent and prominent paraventricular inflammatory and degenerative lesions are seen in the brain and paracanalicular ones in the spinal cord. There is a gradual decrease in the number and severity of the lesions from the fifth to the seventh days. Intranuclear inclusions and fewer cytoplasmic ones are described for the first time in this experimental condition and are seen in both cerebral and spinal cord lesions. They are present in nerve cells but not in glial or other cells. Segmental demyelination is encountered sparingly and is most notable in the corpus callosum. Astrocytosis is a prominent and early feature of experimental murine influenzal meningoencephalitis and is probably reactive in character.

Characterization of visna virus nucleic acid

Abstract 1. Nucleic acid was extracted from radioactively labeled visna virus particles and analyzed by equilibrium zonal centrifugation in glycerol density gradients. 2. The major component recovered from virions has a sedimentation coefficient of 60–70 S; it is single-stranded RNA as shown by its complete sensitivity to ribonuclease and density after isopycnic gradient centrifugation in Cs 2 SO 4 . The virion also contains a slowly sedimenting 5-7-S nucleic acid species. 3. Visna virions contain nucleic acids that resemble in size and composition those present in RNA oncogenic viruses.

Nucleic acid sequence relationships among "slow" viruses of sheep.

Abstract The RNA genomes of the sheep “slow” viruses, visna, maedi, and progressive pneumonia, were compared by nucleic acid hybridization. The homology among these viral RNAs was determined from the extent competition of homologous viral RNA-cDNA hybrids by heterologous RNA and from the thermal stability of homologous and heterologous RNA-cDNA hybrids. The 70 S RNAs of visna and maedi virus were indistinguishable but only partially homologous to that of progressive pneumonia virus.

The relationship of visna, maedi and RNA tumor viruses as studied by molecular hybridization

Abstract The DNA product of the endogenous visna virus RNA-directed polymerase reaction annealed to maedi virus 60–70S RNA. Similarly, the DNA product of the endogenous maedi virus polymerase reaction hybridized to visna virus 60–70S RNA. The DNA products of endogenous visna and maedi virus polymerase reactions failed to anneal significantly either to Rauscher murine leukemia or mouse mammary tumor virus 60–70S RNAs.

Immunological cross-reactions of the major internal protein component from “slow” viruses of sheep

Abstract The major p27 polypeptides of the sheep “slow” viruses, visna, maedi, and progressive pneumonia, were compared by radioimmunoassay. The immunologic relatedness among these viral proteins was determined from the competition of homologous- and heterologous-disrupted virions with iodinated visna virus p27 for visna antisera. The p27 antigens of visna virus and maedi virus were indistinguishable from each other and were partially related to p27 of progressive pneumonia virus.

Replication of Neurotropic Influenza Virus in Organotypic Cultures of Embryonic Mouse Hypothalamus

Neurotropic influenza virus (WS-N strain) causes cytolytic changes in organotypic neural cultures derived from embryonic mouse hypothalamus. Initially, nerve cells develop enlarged, refractile nucleoli. In later stages, both nerve and glial cells undergo necrotic changes. These alterations are accompanied by synthesis of progeny virus and formation of intracellular viral antigen. Electron microscopic observations of infected cultures reveal virus particles with the morphology and dimensions of influenza virions. Organotypic neural cultures may prove useful in studies of influenza virus neurotropism.

Visna virus-induced fusion of continuous simian kidney cells

Syncytium formation was observed in four continuous monkey kidney cell lines (BS-C-1, VERO, LLC, MK2 and CV-1) after inoculation with visna virus at high multiplicity. Visna virus-induced cell fusion occurred most rapidly and extensively in BS-C-1 and VERO cells; it was least prominent in CV-1 cells. No evidence of significant visna virus multiplication was detected in any of the four monkey kidney cell lines. BS-C-1 cells were successfully used as an indicator cell line in a visna virus plaque assay.