Search PubMed⌕ Search

Biomedical subjects

H F Clark

Publications and source records attributed to H F Clark.

At least 73 records · Page 4Linked to original sources
PubMed1979

Fer de Lance virus (FDLV): a probable paramyxovirus isolated from a reptile.

A new virus has been isolated by inoculation of lung tissues of diseased snakes into snake embryos. Homogenates of infected embryo tissues caused c.p.e. in cell cultures incubated at 30 degrees C. The virus replicates in a wide variety of reptilian or mammalian cell types incubated at 30 degrees C, inducing either syncytium formation or minimal or no cytopathic changes. Efficient replication occurs in embryonated hens' eggs at 27 to 30 degrees C. The virus haemagglutinates guinea pig and chick erythrocytes; it possesses a neuraminidase similar to the receptor-destroying enzyme of Vibrio cholera. Electron microscopic observations of infected cells examined in thin section revealed pleomorphic viruses 146 to 321 nm in diam. resembling known myxoviruses. Internal nucleocapsid strands are 15 to 16 nm in diam.; nucleocapsid observed in negatively stained preparations measures 14 nm in diam. The virus was determined to possess a nucleoprotein core containing a 50S single-stranded unsegmented RNA genome. All characters of the virus are similar to those of the paramyxovirus group except that the nucleocapsid diam. is intermediate between that of paramyxoviruses and pneumoviruses. The virus is antigenically distinct from known myxoviruses and is unique among myxoviruses in its restriction to growth at temperature below 37 degrees C.

Animals↗
PubMed1978

Rabies viruses increase in virulence when propagated in neuroblastoma cell culture.

Several strains of attenuated rabies virus lacking the capacity to kill adult mice acquired a high lethal potential for mice after one to five serial passages in murine or human neuroblastoma cells. The virulence acquired after passage in neuroblastoma cells is a stable genetic trait retained during subsequent passage of viruses in nonneuroblastoma cell systems.

Animals↗
PubMed1977

Pathogenic mycoplasmas: cultivation and vertebrate pathogenicity of a new spiroplasma.

A spiroplasma recovered from allantoic fluids of chick embryos infected with the tick-derived suckling mouse cataract agent was grown in continuous passage on a new artificial culture medium. The cultured organisms induced typical ocular and other disease symptoms in susceptible animals, and were reisolated from involved host tissues. Although spiroplasmas have been previously recognized as plant and insect pathogens, this is the first spiroplasma shown to multiply at 37 degrees C and to be pathogenic for vertebrates.

Animals↗
PubMed1977

Studies of mitochondria and mitochondrial DNA extracted from organelles harboring an intramitochondrial virus.

(1) Two viper cells lines were investigated, one which harbors IMV in the mitochondria (VSW cells) and one without detectable IMV (VH3 cells). (2) The size of closed circular mtDNA molecules from both VSW and VH3 cells was found to be significantly greater (5.4 to 5.6 micron) than the contour lengths of typical mammalian cells (4.8 to 5.2 micron). (3) A small percentage of mini-circles ranging in size from 0.1 to 0.6 micron was observed to band with closed circular mtDNA from both cell lines. Minicircles were especially abundant in VH3 cells. (4) MtDNA from VSW cells contained 34.1% dimers plus oligomers (10.2% oligomers), whereas VH3 cells had only 14.8% dimeric and oligomeric forms (5.4% oligomers). (5) Treatment of VSW cells with 1 microng/ml ethidium bromide for 48 hours resulted in an increased incidence of IMV (IMV in 15% of mitochondrial sections) as compared with untreated VSW cells (IMV in 3% of mitochondrial sections).

Cell Line↗
PubMed1977

Intracytoplasmic type A particles in viper spleen cells.

Structures resembling typical type A particles were observed in paranuclear inclusions in cultured C-type particle-producing viper cells (VSW cell line). The incidence of type A particle inclusions was low (approximately 0.5% of cell profiles examined) in untreated cells, but both the incidence and size of the inclusions were slightly increased in cells treated with ethidium bromide. This is apparently the first observation of type A particles in cells of a poikilothermic vertebrate.

Animals↗
PubMed1977

Differences in efficiency of protective effect caused by high ambient temperature in mice infected with diverse substrains of rabies virus.

We have shown previously that a non-fatal outcome of infection with street rabies virus occurs more often when mice are exposed to a high ambient temperature (HAT = 35 degrees C) early in the course of the infection. To determine what influence the virus strain had on this protective effect of HAT, we have extended these observations to studies of a fixed rabies strain, CVS and several substrains of CVS virus derived from temperature-sensitive (ts) mutants. In all cases, mortality was reduced to some extent by exposure of the animals to HAT; however, dramatic strain-specific differences in the extent of the effect were noted. Although each of the virus substrains tested was revertant in the ts character (as tested in vitro using a non-permissive temperature of 40-5 degrees C), several substrains (ts 1, ts 4, RT51) caused disease that was sensitive (greater than 90% reduction in mortality) to HAT. Mortality induced by the parental CVS virus was reduced approx. 50% at HAT. A single CVS virus substrain, VSW89, caused disease that wal less affected by HAT than was disease induced by the parental strain. As in previous studies with street virus, the incubation periods for infection with CVS virus substrains were consistently prolonged at HAT.

Animals↗
PubMed1977

Role of host immune response in the development of either encephalitic or paralytic disease after experimental rabies infection in mice.

The clinical and histopathological manifestations of the infection of immunosuppressed (cyclophosphamide-treated) and immunocompetent (control) adult mice with the CVS ts 2 strain of fixed rabies virus were correlated with the kinetics of virus multiplication in the central nervous system and with the development of serum antibody. In immunocompetent mice severe paralytic disease causing 80% mortality was accompanied by marked inflammation and degeneration of the central nervous system parenchymatous tissue. Antirabies antibody was detected in all immunocompetent mice severely paralyzed from postinoculation day 6 on; virus was rarely isolated. In contrast, immunosuppressed mice developed encephalitic symptoms with only minor paralysis; the infection was 100% fatal. Histopathological changes in immunosuppressed mice were confined to degeneration and necrosis of individual neurons and mild microglial reaction; virus was isolated from all of these mice. No significant level of antibody was detected. Similar manifestations were seen after infection of immunodeficient (athymic) mice except that the athymic mice developed levels of antibody similar to those of control mice on day 6; antibodies in athymic mice were predominantly of immunoglobulin class M.

Animals↗
PubMed1977

Ultrastructural studies of cell-virus interaction in reptilian cell lines. IV. Effects of chloramphenicol and ethidium bromide on VSW cell mitochondria and associated virions.

Structural effects of chloramphenicol (CAP) and ethidium bromide (EB) on VSW cell mitochondria and intramitochondrial virions (IMV) have been studied on a comparative basis by thin-section electron microscopy. CAP-treated cells show a wide variety of mitochondrial alterations, frequently involving swelling of the organelle and loss of cristae orientation. IMV are generally severely disrupted, particularly in peripheral regions. In such configurations, strand-like material radiates in a spokelike fashion from the shell zone to adjacent cristae-matrix area. EB-treated cells also display considerable mitochondrial distortion evidenced primarily by the formation of small, localized multimembrane regions. IMV exposed to EB, however, are less structurally damaged than CAP-treated ones. The relative incidence of IMV production is enhanced approximately fourfold in EB-treated cells compared to CAP-treated ones, suggesting that virion synthesis may be under nuclear, rather than mitochondrial, control.

Animals↗
PubMed1977

Rabies virus infection in mouse neuroblastoma cells.

As part of an inquiry into factors that determine the virulence of fixed rabies virus, mouse neuroblastoma cells were infected in culture with high virulence and low virulence strains of Flury HEP virus. Low virulence virus infection differed from high virulence virus infection in (1) its more rapid production of progeny virus in the early cycles of virus infection as shown by the number of extracellular virus particles and the infectivity of the supernatant fluid; (2) its earlier development of viral antigens on the cell surface; and (3) its earlier and more severe morphologic alteration of the cell surface. Where applicable, the differences were corroborated by scanning and transmission electron microscopy of the infected cells using the critical point drying technique on whole cells. The number of cells susceptible to complement-dependent immunolysis was almost proportional to the number of cells that were surface antigen-positive regardless of the strain of the virus used. Implications of the difference in the kinetics of virus production and of the development of surface antigens between low and high virulence strains are discussed.

Animals↗
PubMed1976

Structural and enzymatic characterization of viper C-type virus.

The structural polypeptides of purified viper range in molecular weight from 11,000 to 97,000 daltons and consist of 3 major and about 13 minor polypeptides. The virus contains both protein kinase and reverse transcriptase activities. Several of the structural polypeptides are phosphorylated in vitro by the virus-associated protein kinase. However, most (possibly all) of the viral structural polypeptides are not phosphorylated in vivo. DeoxyATP is as efficient as ATP in donating phosphate for in vitro phosphorylation of viral proteins. In vitro protein phosphorylation always precedes transcription and the virus-associated protein kinase and reverse transcriptase activities can be partially separated by sedimentation in a sucrose gradient.

Adenosine Triphosphate↗
PubMed1976

Temperature-sensitive mutants of rabies virus in mice: a mutant (ts2) revertant mixture selectively pathogenic by the peripheral route of inoculation.

Analysis of the pathogenic potential in mice of a variety of rabies and rabies serogroup viruses revealed that an apparently revertant population of virus derived from CVS mutant ts 2 had a unique capacity to selectively induce paralytic disease when given by a peripheral [intraplantar (i.pl.)] route of inoculation. Little paralytic disease was induced by high concentrations of virus administered by the intracerebral (i.c.) route, whereas paralytic disease and death were characteristically induced in mice given only a few infectious doses of virus i.c. Disease induced by i.pl. inoculation was dose dependent. Mice frequently survived paralytic disease induced by i. pl. inoculation, with clinical signs often persisting indefinitely; mice surviving i.c. inoculation of high concentrations of virus frequently exhibited chronic nonspecific signs of minor debility. Analysis of the ts 2 virus population indicated that it was composed of a mixture of ts and revertant virions, each with characteristic pathogenic (or nonpatholgnic) propensities, none of which was identical to the original composite ts 2 virus populations. Despite the heterogeneity of the ts 2 virus population, the typical pathogenic pattern of selective pathogenic capicity after i. pl. inoculation at high doses was retained during 11 ocnsecutive passages in suckling mouse brain. ts 2 virus was demonstrated to interfere with the disease-producing capacity of CVS fixed rabies virus when ts 2-CVS mixtures were inoculated i.c. However, attempts to demonstrate a particular propensity for induction in vitro of "autointerference" by ts 2 in serial passage in BHK-21 cell culture inoculated at high multiplicity were unsuccessful.

Animals↗
PubMed1976

Thermal inactivation of rabies and other rhabdoviruses: stabilization by the chelating agent ethylenediaminetetraacetic acid at physiological temperatures.

Thermal inactivation of rabies and several other rhabdoviruses was studied using virus suspended in several different diluents. Rabies serogroup viruses were more stable than Kern Canyon or vesicular stomatitis viruses. Limited studies of two fish rhabdoviruses requiring low temperatures (less than 33 C) for replication indicated that they were not markedly more thermolabile than rabies virus. Bovine serum protein components in complex cell culture media stabilized virus at 56 C, but at temperatures of less than or equal to 37 C, sodium tris (hydroxymethyl)-aminomethane (NT) buffer containing ethylenediaminetetraacetic acid (EDTA) (NTE) was a much more efficient stabilizer of virus infectivity. Chelating agents EDTA and ethyleneglycol-bis-(beta-aminoethyl ether)tetraacetic acid were equally efficient in protection of rabies virus infectivity; the effect of each was lost when excess Ca2+ was added. Bovine serum in NT or NTE buffers produced a thermostabilizing effect at 37 C not provided by the same serum concentration in complex cell culture media. Bovine serum was more efficient than EDTA in stabilizing virus infectivity during repeated cycles of freezing and thawing.

Animals↗
PubMed1976

An ultrastructural study and model of membrane-intramitochondrial virus relationships.

Intramitochondrial virions (IMV), in many respects structurally similar to 'C-type' viruses of higher organisms, are synthesized in close topographical association with inner mitochondrial membranes of the viper spleen cell line, VSW. Cristal membranes contribute to the formation of a trilaminar viral envelope, whereas the outer mitochondrial membrane does not appear to play any structural role in virion maturation. Two schematic models, correlated with electron microscopic images, are presented to depict: (a) the relative location of the particles within a three-dimensional view of the mitochondrion, and (b) the sequence of virion-mitochondrial membrane relationships during morphogenesis.

Animals↗