An electron microscopic study of moderate and virulent virus-cell interactions of the parainfluenza virus SV5

Comparison of subacute sclerosing panencephalitis and measles viruses: an electron microscope study

The ultrastructure of CV-1 cells infected with subacute sclerosing panencephalitis (SSPE) viruses was compared with that of CV-1 cells infected with the wild or Edmonston strain of measles virus. Both SSPE viruses and the measles viruses produced two types of nucleocapsid structures: smooth filaments, 15 to 17 nm in diameter, and granular filaments, 22 to 25 nm. The smooth and granular filaments produced by SSPE and measles virus did not differ in appearance. In CV-1 cells infected with SSPE viruses, smooth filaments formed large intranuclear inclusions and granular filaments occupied a large area of the cytoplasm, but always spared the area under the cell membrane. Particles budding from the surface of these cells contained no nucleocapsids. In CV-1 cells infected with measles virus, only small aggregates of smooth filaments were seen in the nuclei. Granular filaments in the cytoplasm predominantly occupied the area under the cell membrane, and were aligned beneath the cell membrane in a parallel fashion and assembled into budding particles. These differences between SSPE and measles virus may be regarded as quantitative, but they do distinguish SSPE viruses from measles virus. Moreover, the formation of large nuclear inclusions filled with smooth filaments appears to be a characteristic process of SSPE, but not of measles, since this type of inclusion is invariably seen in SSPE brain tissues, brain cultures derived from them, and CV-1 cells infected with SSPE viruses.

Nucleocapsid protein subunits of simian virus 5, Newcastle disease virus, and Sendai virus

Helical nucleocapsids of each of the paramyxoviruses simian virus 5 (SV5), Newcastle disease virus (NDV), and Sendai virus have been isolated in two different forms. One form contains larger protein subunits and is obtained from mature virions or infected cells dispersed by ethylenediaminetetraacetic acid. The other form possesses smaller subunits and is obtained from infected cells dispersed by trypsin. The estimated molecular weights of the larger subunits in the three viruses are similar: SV5, 61,000; Sendai virus, 60,000; NDV, 56,000. The smaller nucleocapsid subunits are also very similar: SV5, 43,000; Sendai virus, 46,000; NDV, 47,000. The helical nucleocapsid composed of the smaller subunit appears to be less flexible and more stable than that formed by the larger subunit. There is suggestive evidence that conversion of the larger subunit to the smaller by proteolytic cleavage may occur intracellularly. The possibility that such a mechanism could be involved in the accumulation of nucleocapsid in cells persistently infected with paramyxoviruses is discussed.

Morphogenesis of the nucleoprotein of vesicular stomatitis virus

Accumulation of the nucleoprotein of vesicular stomatitis virus (VSV) in the cytoplasm of BHK-21 cells and in two of four human cell lines was demonstrated. Appearance and progression of the nucleoprotein inclusions paralleled development of virus-specific immunofluorescence and production of virus progeny. The inclusions appeared early as discrete foci of filamentous material which eventually increased in size to form large masses which replaced normal cytoplasmic constituents. The filamentous strands were found in close proximity to budding virions. The inclusion material was extracted from infected cells and purified in cesium chloride gradients. The isolated filaments resembled the ribonucleoprotein isolated from purified virions. They incorporated (3)H-uridine, exhibited virus-specific complement-fixing activity, had a buoyant density of 1.32 g/cm(3), and appeared as single wavy strands the width of which varied from 2.5 to 8.5 nm, depending on the angle of viewing.

Morphogenesis of respiratory syncytial virus in a green monkey kidney cell line (Vero)

The structure and morphogenesis of respiratory syncytial (RS) virus particles in a green monkey kidney cell line (Vero) were examined. Infected cells contained dense intracytoplasmic inclusions composed of filamentous structures. In places where inclusion material was associated with membranes, structural modifications were induced. There was a thickening of the membrane and an addition of projections 12 to 15 nm in length. The same changes were most frequently observed after association of isolated filamentous structures with the cytoplasmic membrane. The budding-off process was clearly visualized. The diameter of mature virus particles varied between 90 and 130 nm and that of the internal component varied between 11 and 15 nm. The similarities between ultrastructural features of cells infected with RS virus and pneumonia virus of mice are pointed out. It is proposed that these two viruses should be classified together in a third subgroup of myxoviruses.

Glycosphingolipids of plasma membranes of cultured cells and an enveloped virus (SV5) grown in these cells

Glycosphingolipids of rhesus monkey kidney (MK), bovine kidney (MDBK), and two lines of hamster kidney (BHK21-F and Hak) cells have been compared with those of parainfluenza (SV5) virions grow in these cells. There are qualitative and quantitative differences in the neutral glycolipids and gangliosides found in the various cells. Cells with a high neutral glycolipid content (MK and MDBK) contain little or no gangliosides, and those with a relatively high ganglioside content (BHK21-F and HaK) contain little neutral glycolipid. Glycosphingolipids are found predominantly in the plasma membranes. Neutral glycolipids of the host cell membrane are incorporated into the envelope of SV5 virions, but neither gangliosides nor protein-bound neuraminic acid are found in virions. The absence of neuraminic acid from the virion may be due to the action of viral neuraminidase.

Replication of Sendai virus. II. Steps in virus assembly

Chick embryo fibroblast cultures infected with Sendai virus were incubated with (3)H-uridine in the presence of actinomycin D beginning at 18 hr after infection. The 35 and 18S virus-specific ribonucleic acid (RNA) components were found in a ribonuclease-sensitive form in the cell and appeared to be associated with polyribosomes. Newly synthesized 57S viral RNA was rapidly coated with protein to form intracellular viral nucleocapsid, and no 57S RNA was found "free" (ribonucleasesensitive) in the 2,000 x g supernatant fraction of disrupted cells. The nucleocapsid from detergent-disrupted Sendai virus and that from disrupted cells were indistinguishable in ultrastructure and buoyant density, and neither was found to be infectious or have hemagglutinating activity. Kinetic studies of nucleocapsid and virus formation indicated a relative block in conversion of viral nucleocapsid to complete enveloped virus in these cells, resulting in accumulation of large amounts of nucleocapsid in the cell cytoplasm.

Phenotypic mixing of envelope proteins of the parainfluenza virus SV5 and vesicular stomatitis virus

Cells mixedly infected with parainfluenza virus SV5 and vesicular stomatitis virus (VSV) yield phenotypically mixed virions, in addition to both parental types. Two types of phenotypically mixed virions have been identified: 0.6 to 1.2% of the VSV plaque formers were neutralized by SV5 antiserum, but not by VSV antiserum, suggesting the presence of a VSV genome in an SV5 envelope; 9 to 45% of the VSV plaque formers were neutralized by both antisera, indicating the presence of both SV5 and VSV antigens in their envelopes. The presence of SV5 antigen in virions with the typical bullet-shaped appearance of VSV was confirmed with ferritin-labeled anti-SV5 antibody. In contrast to standard VSV, phenotypically mixed virions adsorbed to and eluted from chicken erythrocytes, indicating that these virions contained in their envelopes SV5 hemagglutinin, and possibly neuraminidase. Thus, the VSV nucleocapsid can interact with membranes which contain SV5 proteins in the manner which leads to virus maturation, and the production of a high yield of phenotypically mixed virions with the morphology of VSV indicates that this process can function efficiently. No evidence of genetic recombination between the two viruses was found. These results raise the possibility of an evolutionary relatedness between the paramyxoviruses and the rhabdoviruses.

Growth in chick chorioallantoic membranes of strains of Newcastle disease virus of differing virulence

The growth of eight strains of Newcastle disease virus in chick embryo chorioallantoic membranes was studied by comparing, at different times after infection, the amounts of haemagglutinin released into the allantoic fluid (extracellular haemagglutinin) with that associated with the membrane (cell-associated haemagglutinin). The virulence of the strains examined differed in that some killed chick embryos more rapidly than others. All strains released similar amounts of extracellular haemagglutinin and maximum titres were achieved about 12 hr. after infection. With virulent strains cell-associated haemagglutinin titres increased exponentially until the death of the host and maximum titres were much higher than those of extracellular haemagglutinin. With avirulent strains cell-associated haemagglutinin titres increased exponentially for only a limited time and titres were always lower than the titres of extracellular haemagglutinin.Similar results were obtained when the titres of neuraminidase and viral ribo-nucleoprotein were measured during the growth of two virulent and two avirulent strains. Virulence appears to be associated with the continued intracellular accumulation of viral antigens.

Morphogenesis of Newcastle disease virus in chorioallantoic membrane

Chick embryo chorioallantoic membrane, infected with the Blacksburg strain of Newcastle disease virus, was examined with an electron microscope to investigate the sequence of viral-induced host cell alterations. These were evident mostly in the endodermal epithelial cells lining the allantoic sac and were divided arbitrarily into three stages. Stage 1 was characterized by commencement of cell hypertrophy and hyperplasia and presence of fewer cytoplasmic inclusion bodies normally found in the cells; in stage 2, juxtanuclear nucleocapsid-glycogen aggregates appeared, and there were increased numbers of microvilli; stage 3 was characterized by increased cytoplasmic density and evidence of viral assembly and release. The morphological features of viral assembly and the virion are also described.

Electron microscopy of equine infectious anemia virus

Equine infectious anemia (EIA) virus was observed in thin sections of infected cultured horse leukocytes by electron microscopy. The virus particles had a spherical shape and were between 80 and 120 nm in diameter. Most of them contained an electron-dense nucleoid 40 to 60 nm in diameter. They were observed to form by a process of budding from the plasma membrane and appeared to have thin surface projections. The particles described were not detected in uninfected cultured cells, and their appearance could be prevented by adding EIA immune serum to the inoculum. The implications of these findings in the classification of EIA virus are discussed.

Effect of puromycin and actinomycin D on a persistent mumps virus infection in vitro

Puromycin and actinomycin D were used to treat a line of human conjunctiva cells persistently infected with mumps virus (C-M cells) in order to determine where virus synthesis is inhibited. Although 90% of the cells in C-M cultures are infected, little or no infectious virus is produced by most cells in a growing culture. Adding puromycin to inhibit protein synthesis resulted in the production of infectious virus. Thus, all the viral proteins needed for virus completion were made in the growing cells. When actinomycin D was added to growing cells, infectious virus was again produced. Since mumps virus synthesis is actinomycin D-insensitive, this suggested a host control of the virus. Interferon was not detected. The possible mechanisms of host control are discussed.

Electron microscopy of measles virus replication

Replication of measles virus in HeLa cells was examined by electron microscopy with ultrathin sectioning and phosphotungstic acid negative staining methods. The cytoplasmic inclusion bodies consisted of masses of helical nucleocapsid which was similar in structure to the nucleocapsid found in measles virions. The cytoplasmic helical nucleocapsid appeared to align near the HeLa cell membrane, and the membrane differentiated into the internal membrane of the viral envelope and the outer layer of the short projections. The viral particles were released by a budding process involving incorporation into the viral envelope of membrane which was contiguous to but morphologically altered from the membrane of the HeLa cells. The intranuclear inclusion bodies were composed of tubular structures similar to those found in the cytoplasmic inclusion bodies. These structures aggregated to crystalline arrangement. The relationship between nuclear inclusion body and replication of measles virus was not clear.

On the role of microtubules in movement and alignment of nuclei in virus-induced syncytia

Infection of baby hamster kidney (BHK21-F) cells with the parainfluenza virus SV5 causes rapid and extensive cell fusion. Time-lapse cinematography shows that when cells fuse, their nuclei migrate straight to the center of the syncytium at rates of 1-2 micro/min. Nuclei are often arranged in long, tightly packed, parallel rows in syncytia derived from the fibroblastic BHK21-F cells. Polarization microscopy shows birefringent material between and parallel to these rows of nuclei, and electron microscopy shows bundles of cytoplasmic microtubules, approximately 250 A in diameter, and filaments, approximately 80 A in diameter, parallel to and between the rows of nuclei. Colchicine treatment causes disappearance of microtubules from BHK21-F cells and an apparent increase in the number of 80-A filaments. Although colchicine-treated, SV5-infected cells fuse, their nuclei do not migrate or form rows but remain randomly scattered through the syncytial cytoplasm. Incubation at 4 degrees C does not disrupt microtubules in BHK21-F cells. Rows of nuclei have been isolated from SV5-induced syncytia, and the nuclei in them have been found to be intimately associated with microtubules but not with other cytoplasmic structures. These results suggest that microtubules demarcate cytoplasmic channels through which nuclei migrate and that they may also be involved in the mechanism of nuclear movement.

Morphology of the nucleoprotein component of rabies virus

The intracytoplasmic ground substance, or matrix, associated with the development of rabies virus and the nucleocapsid of the virus were investigated. The filaments of the matrix were identified as virus-specific by means of ferritin-labeled antibodies. In thin sections, the diameter was 15 nm and the strands seemed to be incorporated into virions during morphogenesis of the virus. The nucleocapsid was isolated from purified virus preparations and was studied in negative contrast. The rabies nucleocapsid appeared as a single-stranded helix with a diameter of 16 nm and a periodicity of 7.5 nm; its length was in excess of 1 mum.

Electron microscopy of herpes simplex virus. IV. Studies with ferritin-conjugated antibodies

Small aggregates of viral antigen were encountered in the nuclear matrix. The capsids did not tag with antibodies specific for the virus or for the host cell. This observation remains unexplained. Nuclear and cytoplasmic membranes, as well as the envelope of the virus, reacted with both types of antibodies and appear, therefore, to contain host cell and viral protein. Large amounts of viral antigen are synthesized within the cytoplasm. This antigen was either diffusely spread or localized at the surface of membranes. The surface of infected cells contains viral antigen, which accumulates as infection progresses. At circumscribed sites, the cell wall becomes altered antigenically and structurally so as to resemble the envelope of the virus. Hypotheses are presented regarding the manner in which cell fusion occurs.

Unusual filamentous structures in the paragonia of male Drosophila

Drosophila paulistorum is a complex of five incipient species which when crossed produce sterile hybrid males and fertile females. Sterility of the male progeny can sometimes be induced by injecting females of one strain (Mesitas) with a homogenate of males of another strain (Santa Marta) or of hybrids between these strains, and then crossing the recipient females to Mesitas males. Filamentous structures have been found in cytoplasmic vacuoles in paragonial cells in males of these and other similar strains and their hybrids. These structures, which contain RNA, possess a helical substructure and resemble certain viruses. Large filamentous structures found in the lumen of the paragonia are also described.

Electron microscopy of herpes simplex virus. I. Entry

Although capsids of herpes simplex virus were encountered within phagocytic vesicles, they were more commonly observed free within the cytoplasm. Stages in the release of virus from vesicles were not seen. There appeared to be five distinct steps in the process whereby the virus initiates infection: attachment, digestion of the viral envelope, digestion of the cell wall, passage of the capsid directly into the cytoplasm, and digestion of the capsid with release of the core. Antibody probably interferes with the first two stages.

Myxovirus-like structures in a case of human chronic polymyositis

Intranuclear and intracytoplasmic aggregates of filaments with tubular structures and transverse striations occurred in muscle tissues biopsied from a patient with chronic polymyositis. The filamentous tubules bear a close resemblance to the incomplete form of myxovirus in which the envelope is missing. Three biopsies from the same patient, taken during a period of 1(1/2) years, all revealed these structures. This finding provides presumptive evidence that a chronic persistent viral infection may be involved in the pathogenesis of chronic polymyositis.

In vitro and in vivo observations on a murine C-type virus

From 40 discrete mouse tissue culture cell lines examined by electron microscopy or complement fixation, or both, for the presence of detectable virus, one (NCTC 4705), initiated and maintained on chemically defined medium, was chosen for a more extensive study. Virus-like particles (100 to 110 mmu), morphologically similar to previously reported immature and mature C-type leukemia virus particles, were found budding from the plasma membrane and free in the intracellular spaces of cells in tissue culture and in fibrosarcomas resulting from intramuscular implants of these tissue cultures. Complement-fixation tests for group reactive murine leukemia antigens were positive, with titers consistently higher to a broadly reactive anti-serum than to anti-Friend, anti-Moloney, or anti-Rauscher sera. The 4705 virus was neutralized by Gross antiserum, but not by the F-M-R antisera. When injected into DD, BALB/c, or C3H/He newborn mice, the virus thus far has manifested no leukemogenicity, though virus from tumor extracts and tissue culture medium has been shown to be capable of infecting C3H and Swiss mouse embryo tissue cultures and successfully replicating in them. The role of the virus in accelerating or inducing neoplastic transformation in NCTC 4705 is still not known. When it was introduced into NCTC [ill], a non-neoplastic cell line in other respects similar to NCTC 4705, 4823 manifested no signs of neoplastic transformation after harboring the virus more than 300 days in vitro.

Immunofluorescence and cytochemical studies of visna virus in cell culture

Sequential morphological changes occurring in sheep choroid plexus cells infected with visna virus were studied by direct immunofluorescence, acridine orange, and hematoxylin and eosin staining methods. Specific immunofluorescence was first detected in the perinuclear cytoplasm of solitary cells 24 hr after infection. As the infection progressed, viral antigen appeared in an increasing number of cells, and rounded globular cells with long slender processes harboring intense fluorescence were seen. Nuclear fluorescence was not observed in infected monolayers. Polykaryocytes formed within 6 hr after inoculation due to the direct cell-fusing effect of the virus inoculum did not show specific fluorescence. Viral antigen was found, however, in the cytoplasm of multinucleated giant cells in cover slips harvested after new infective virus had been released, and later in the course of infection circular fluorescent inclusions were seen in the cytoplasm of polykaryocytes. Comparable eosinophilic inclusions were observed in hematoxylin and eosin preparations, and acridine orange staining of infected monolayers demonstrated similar inclusions which fluoresced with the color characteristic of single-stranded nucleic acid and were susceptible to digestion with ribonuclease. Visna virus appears to be a ribonucleic acid virus which replicates in the cytoplasm.

Studies on pneumonia virus of mice (PVM) in cell culture. II. Structure and morphogenesis of the virus particle

Pneumonia virus of mice (PVM) particles are spheres 80-120 mmicro in diameter, or filaments of similar diameter with lengths up to 3 micro. The particles possess an outer spike-covered envelope and helical internal component 120-150 A in diameter. Virus particles acquire their envelope by a budding process at the cell membrane; mature particles are seen only extracellularly. Dense inclusions are prominent in the cytoplasm of PVM-infected BHK21 cells by 48 hr after inoculation. The inclusions appear to consist of aggregates of the internal component of PVM, and the helical component has been isolated in a cesium chloride gradient from extracts of osmotically shocked cells. Murine erythrocytes, which are agglutinated by PVM, adsorb to the surface of infected cells and to budding and extracellular PVM particles. On the basis of its structure and morphogenesis, PVM appears to be a myxovirus; however, it does not fit into either of the established subgroups of myxoviruses. The 120-150 A diameter of the PVM internal component differs from the diameters of the internal components of the two established subgroups of myxoviruses, and suggests that a third subgroup of these viruses may exist.

Isolation and properties of the helical nucleocapsid of the parainfluenza virus SV5

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