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N Nathanson

Publications and source records attributed to N Nathanson.

At least 55 records · Page 3Linked to original sources
PubMed1989

The large viral RNA segment of California serogroup bunyaviruses encodes the large viral protein.

Reassortant bunyaviruses derived from two members of the California serogroup (La Crosse/original and Tahyna/181-57) viruses were used to demonstrate that the large Mr viral protein (L) is encoded by the L RNA segment. Radiolabelled viral proteins were analysed by discontinuous SDS-PAGE. The L protein of La Crosse virus was observed to migrate ahead of its Tahyna virus counterpart when electrophoresed through a 5% acrylamide resolving gel. Among the reassortant viruses, the L protein phenotype segregated with the viral L RNA segment. After confirming the genotype of the viruses used in this study, it was concluded that the L RNA species of California serogroup viruses codes for the L protein, the presumed viral polymerase.

Animals↗
PubMed1988

Organization of the middle RNA segment of snowshoe hare Bunyavirus.

The genetic organization of the M RNA segment of snowshoe hare (SSH) virus, a member of the Bunyavirus genus of the family Bunyaviridae, has been determined. The middle (M) RNA segment has a single open reading frame (ORF) of 1441 amino acids. We have used amino- and carboxy-terminus sequencing and synthetic peptides to map proteins within the ORF. The order of the proteins translated from the single large open reading frame is G2, NSm, G1. The G2 protein extends from amino acids 14 to 299. The molecule is 286 residues long, with a computed nonglycosylated molecular weight of 31,973 Da. It is preceded by a cleaved 13 amino acid signal sequence. G2 includes a long highly hydrophobic sequence and contains three potential N-linked glycosylation sites. The G1 protein occupies the C-terminal end of the open reading frame from amino acids 474 to 1441 (968 amino acid residues) and has a computed nonglycosylated, molecular weight of 108,981 kDa. It has two potential N-linked glycosylation sites, and a potential transmembrane region followed by a potential cytoplasmic domain at the C-terminal end. If membrane associated it has an orientation of N-terminus outer, C-terminus inner. Limited trypsin digestion removes a 33-kDa fragment from the N-terminal end, leaving a virion-associated truncated G1 molecule (amino acids 762 to 1441) with a single N-linked glycosylation site. Between the G2 and G1 molecules there are 174 amino acids, sufficient to code for 19 kDa of protein. Some antibodies raised against peptides within this region react with proteins of 11 kDa (NSm) and 10 kDa present in infected cell lysates, but the exact relationship of these proteins to the open reading frame remains to be determined.

Amino Acid Sequence↗
PubMed1987

A G1 glycoprotein epitope of La Crosse virus: a determinant of infection of Aedes triseriatus.

Arthropod-borne viruses (arboviruses) have specific vector-vertebrate host cycles in nature. The molecular basis of restriction of virus replication to a very limited number of vector species is unknown, but the present study suggests that viral attachment proteins are important determinants of vector-virus interactions. The principal vector of La Crosse (LAC) virus is the mosquito Aedes triseriatus, and LAC virus efficiently infects the mosquito when ingested. However, a variant (V22) of LAC virus, which was selected by growing the virus in the presence of a monoclonal antibody, was markedly restricted in its ability to infect Ae. triseriatus when it was ingested. Only 15% of the mosquitoes that ingested V22 became infected and 5% of these developed disseminated infections. In contrast, 89% of the mosquitoes that ingested LAC became infected and 74% developed disseminated infections. When V22 was passed three times in mosquitoes by feeding, a revertant virus, V22M3, was obtained that infected 85% of Ae. triseriatus ingesting this virus. In addition, V22M3 regained the antigenic phenotype and fusion capability of the parent LAC virus. These results suggest that the specificity of LAC virus-vector interactions is markedly influenced by the efficiency of the fusion function of the G1 envelope glycoprotein operating at the midgut level in the arthropod vector.

Aedes↗
PubMed1986

Virulence of La Crosse virus is under polygenic control.

To identify which RNA segments of the California serogroup bunyaviruses determine virulence, we prepared reassortant viruses by coinfecting BHK-21 cells with two wild-type parents, La Crosse/original and Tahyna/181-57 viruses, which differed about 30,000-fold in virulence. The progeny clones were screened by polyacrylamide gel electrophoresis to ascertain the phenotype of the M and S RNA segments, and RNA-RNA hybridization was used to determine the genotype of selected clones. Two or three clones of each of the six possible reassortant genotypes were characterized quantitatively for neuroinvasiveness by determining the PFU/50% lethal dose (LD50) ratio after subcutaneous injection into suckling mice. The reassortants fell into two groups. (i) Six of seven reassortants with a La Crosse M RNA segment were as virulent as the parent La Crosse virus (about 1 PFU/LD50); the one exception was strikingly different (about 1,000 PFU/LD50) and probably represents a spontaneous mutant. (ii) The seven reassortants with a Tahyna M RNA segment were about 10-fold more virulent than the parent Tahyna virus (median 1,600 PFU/LD50 for reassortants and 16,000 PFU/LD50 for Tahyna virus). A comparative pathogenesis study in suckling mice of one reassortant virus and the parent Tahyna virus confirmed the greater neuroinvasiveness of the reassortant virus. From these data it was concluded that the M RNA segment was the major determinant of virulence, but that the other two gene segments could modulate the virulence of a nonneuroinvasive California serogroup virus.

Animals↗
PubMed1985

Epitopes of the G1 glycoprotein of La Crosse virus form overlapping clusters within a single antigenic site.

Antigenic sites on the G1 glycoprotein of La Crosse bunyavirus were defined by constructing a panel of neutralizing and nonneutralizing monoclonal antibodies (F. Gonzalez-Scarano, R. E. Shope, C. H. Calisher, and N. Nathanson (1982), Virology 120, 42-53). To analyze the relationship between the individual epitopes delineated by monoclonal antibodies, 11 neutralizing antibodies were used to select variant viruses. These variant viruses were tested against the panel of anti-G1 protein monoclonal antibodies by neutralization and by ELISA. The neutralization tests assigned the 11 epitopes to five groups, consisting of 6, 2, 1, 1, and 1 epitopes. ELISA tests gave a similar pattern, but also demonstrated interrelationships between four of the five epitope groups, suggesting that there may be a single immunodominant antigenic site on the G1 protein. When eight nonneutralizing anti-G1 monoclonal antibodies were tested in ELISA, they fell into three of the five epitope groups defined by neutralization; there was no evidence of a separate noneutralizing antigenic site on the G1 protein.

Antibodies, Monoclonal↗
PubMed1985

An avirulent G1 glycoprotein variant of La Crosse bunyavirus with defective fusion function.

La Crosse virus, a member of the California serogroup of the family Bunyaviridae, causes encephalitis in humans and laboratory rodents. A variant virus (V22) selected with a monoclonal antibody against the large (G1) glycoprotein showed diminished neuroinvasiveness after peripheral inoculation. This variant has an alteration in its fusion function, requiring a lower pH for the activation of fusion and demonstrating reduced efficiency of cell-to-cell fusion of BHK-21 cultures. V22 was studied in detail following the infection by intraperitoneal or intracerebral routes in suckling, weanling, or adult CD-1 mice. It exhibited a marked reduction in its ability to replicate in striated muscle and to produce viremia; however, after intracerebral injection V22 virus replicated almost as rapidly in brain as its parent, La Crosse virus. V22 virus thus represents an example of reduced neuroinvasiveness associated with an alteration at a specific epitope of the G1 glycoprotein. This same epitope also influences the fusion activity of the glycoprotein.

Animals↗
PubMed1985

Precipitating antibodies in experimental visna and natural progressive pneumonia of sheep.

Serological responses of Icelandic sheep experimentally infected with visna virus (vv) were contrasted with responses in American Targhee sheep naturally infected with progressive pneumonia virus (PPV). Precipitating antibodies assayed by immunodiffusion were compared with the neutralising and complementing fixing antibody response. In experimental infections with vv, complement fixing and neutralising antibodies appeared early after infection and rose to high levels in all sheep, while precipitating antibodies were detected only at minimal titre. In natural infections with PPV, immune responses were less consistent and precipitating antibodies were detected more frequently than complement fixing or neutralising antibodies against PPV. These results may suggest important biological differences between the lytic fibroblast-tropic virus strains used for experimental infection of Icelandic sheep and the nonlytic macrophage-tropic strains of PPV circulating in nature. Lytic strains evoke a brisk response against the viral glycoprotein with high titre neutralising antibody while nonlytic strains induce a less consistent response to the glycoprotein.

Animals↗
PubMed1984

La Crosse bunyavirus can mediate pH-dependent fusion from without.

Lipid binding properties which are dependent on exposure to acid pH are an important mechanism for the cellular entry pathway for some enveloped viruses and for other macromolecules. Cell-to-cell fusion can be used to demonstrate this function. La Crosse virus, a member of the family Bunyaviridae, fused BHK-21 cells from without (FFWO) upon exposure of the absorbed virus to pH 6.3 or below. A high multiplicity of infection and temperature of 37 degrees were necessary for optimum fusion. The pH requirement was similar to that reported for Semliki forest virus, an alphavirus, but higher than that required for the demonstration of cell fusion by members of the Orthomyxoviridae. Virus inactivated by ultraviolet light also mediated FFWO. This is the first report of pH-mediated fusion for this family of viruses and it suggests, by analogy with other viruses, that their entry pathway includes exposure to acid.

Animals↗
PubMed1984

An epidemiologic and clinical evaluation of Guillain-Barré syndrome reported in association with the administration of swine influenza vaccines.

As a result of a court order, computerized summaries of approximately 1,300 cases reported as Guillain-Barré syndrome by state health departments to the Centers for Disease Control during the intensive national surveillance instituted following the swine influenza vaccination program in 1976-1977 became available for further study. Although the data were not uniformly adequate to confirm the diagnosis of Guillain-Barré syndrome, they were sufficient to enable classification according to extent of motor involvement. Vaccinated cases with "extensive" paresis or paralysis occurred in a characteristic epidemiologic pattern closely approximated by a lognormal curve, suggesting a causal relationship between the disease and the vaccine. Cases with "limited" motor involvement showed no such pattern, suggesting that this group included a substantial proportion of cases which were unrelated to the vaccine. The effect attributed to the vaccine lasted for at least six weeks and possibly for eight weeks but not longer. The relative risk of acquiring "extensive" disease over a six-week period following vaccination ranged from 3.96 to 7.75 depending on the particular baseline estimate of expected normal or endemic incidence that was chosen. Correspondingly, the number of cases that could be attributed to the vaccine over the six-week period ranged from 211 to 246, or very slightly higher over an eight-week period if the lowest baseline estimate was used. The total rate of Guillain-Barré syndrome cases attributed to prior use of the vaccine was 4.9 to 5.9 per million vaccinees.

Centers for Disease Control and Prevention, U.S.↗
PubMed1984

Mechanisms of bunyavirus virulence. Comparative pathogenesis of a virulent strain of La Crosse and an avirulent strain of Tahyna virus.

To analyze mechanisms of virulence in the California serogroup bunyaviruses, the virulent La Crosse/original (LAC/original) strain was compared with the avirulent Tahyna/181-57 strain. In suckling mice, both viruses were lethal upon intracerebral injection but differed markedly in their neuroinvasiveness following subcutaneous injection; 20 and 20,000 plaque-forming units, respectively, were equivalent to 1 subcutaneous LD50. The sequential course of infection was followed after subcutaneous injection of 700 plaque-forming units; LAC/original replicated in striated muscle, caused a high titer plasma viremia, invaded the central nervous system, and killed all mice; the same dose of avirulent Tahyna/181-57 failed to replicate in extraneural tissues, did not invade the central nervous system, and caused no apparent illness. Immunofluorescent examination of peripheral and central nervous system tissues showed the same distinctions between virulent and avirulent viruses and pinpointed striated muscle as the major extraneural target of virulent LAC/original virus. Paradoxically, after intracerebral injection of suckling or adult mice, Tahyna/181-57 virus killed more quickly than LAC/original. This difference was correlated with replication differences; Tahyna/181-57 multiplied marginally faster in the brain than did LAC/original virus.

Aging↗
PubMed1983

Antigenic drift in visna: virus variation during long-term infection of Icelandic sheep.

A group of 20 Icelandic sheep were infected intracerebrally with visna virus strain 1514, and 209 virus isolates were obtained from the blood, cerebrospinal fluid, and central nervous system (CNS) over a period of 7 years, during which eight animals developed clinical signs of visna necessitating sacrifice. (i) Using type-specific antisera, it was found that 12 (16%) of 76 isolates tested escaped neutralization. These 12 variant viruses were distributed randomly among animals and over time, and did not replace the infecting strain even though all sheep developed homotypic antibody within 3 months of infection. The one exception was sheep no. 1557 (an animal without clinical visna), where the last six isolates were variants. (ii) A total of 35 blood and CNS isolates from seven of these sheep (including five with clinical visna) were tested against serial samples of their own sera. Autologous antisera neutralized all isolates tested with the exception of isolates from sheep 1557. None of the isolates obtained at sacrifice from the five sheep with clinical visna escaped neutralization with autologous antisera. These data suggest that although variant viruses are encountered at considerable frequency during long-term infection of Icelandic sheep, the variants usually do not replace the infecting strain. Antigenic drift does not appear to be essential for virus persistence or for the development of clinically evident CNS lesions.

Animals↗
PubMed1983

Monoclonal antibodies against the G1 and nucleocapsid proteins of LaCrosse and Tahyna viruses.

Monoclonal antibodies against the Gl (glycoprotein) and Nc (nucleocapsid) proteins of LaCrosse (LAC) and Tahyna (TAH) viruses were generated using a standard protocol. Monoclonal antibodies against Gl were either neutralizing or non-neutralizing, and there was close concordance between inhibition of hemagglutination and neutralizing activities. The LAC virus neutralizing antibodies could be further subdivided into strain-specific and cross-reactive groups on the basis of both neutralization and inhibition of hemagglutination. These data support the concept of a glycoprotein molecule with three antigenic sites, two involved in neutralization and hemagglutination, and an additional site with no biological function as yet defined. Preliminary information from LAC virus variants selected with these monoclonal antibodies agrees with this interpretation. Anti Nc antibodies were all cross-reactive in an ELISA assay. Patterns of monoclonal cross-reactivity against California serogroup viruses are compared with the currently accepted antigenic relationships.

Antibodies, Monoclonal↗
PubMed1982

Primary demyelination in visna. An ultrastructural study of Icelandic sheep with clinical signs following experimental infection.

Two Icelandic sheep with clinical signs of visna appearing 6-7 years after intracerebral infection with visna virus were killed, fixed by perfusion and the central nervous system lesions examined by light and electron microscopy. Both sheep showed similar pathological changes. In the brain there was a severe periventricular inflammatory process with small foci of liquefaction necrosis and scattered small granulomas. In some areas of inflammation there was evidence of primary demyelination but it was not prominent. In the spinal cord there were focal plaques of primary demyelination. At the ultrastructural level the spinal cord lesions showed unambiguous primary demyelination with many naked axons; various stages of remyelination with peripheral type of myelin were also common. These observations indicate that the CNS lesions of visna, as seen in Icelandic sheep, fall into two categories: (a) an inflammatory process which often begins within weeks of infection and which occurs in the majority of infected animals in the absence of clinical paresis; and (b) focal demyelinating lesions of the spinal cord which are seen in sheep with clinical paresis but are uncommon in animals prior to onset of clinical signs. Both types of lesions may coexist.

Animals↗