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M Orlich

Publications and source records attributed to M Orlich.

At least 37 records · Page 2Linked to original sources
PubMed1989

Increased viral pathogenicity after insertion of a 28S ribosomal RNA sequence into the haemagglutinin gene of an influenza virus.

The haemagglutinin glycoprotein HA of influenza viruses is responsible for the attachment of the virus to neuraminic acid-containing receptors at the cell surface and subsequent penetration by triggering fusion of the viral envelope with cellular membranes. To express full activity of the newly synthesized precursor, HA has to be modified by post-translational proteolytic cleavage into the polypeptides HA1 and HA2 by cellular enzymes. If proteases suitable for cleavage are not present in the host cell, the resulting virus particles are non-infectious. During adaptation of the apathogenic influenza virus A/turkey/Oregon/71 to chicken embryo cells, which are not permissive for HA cleavage, we obtained an infectious virus variant with increased pathogenicity. Sequence analysis revealed that during adaptation 54 nucleotides were inserted into the HA gene; their sequence corresponds to a region of the 28S ribosomal RNA. This insertion is probably responsible for increased cleavability of HA, as well as for infectivity and pathogenicity of the adapted virus.

Base Sequence↗
PubMed1989

Mutations at the cleavage site of the hemagglutinin after the pathogenicity of influenza virus A/chick/Penn/83 (H5N2).

Six variants that form plaques in chick embryo cells in the absence of trypsin have been isolated from the apathogenic avian influenza virus A/chick/Pennsylvania/1/83 (H5N2). Unlike the wild-type, the plaque variants contain a hemagglutinin that is cleaved in chick embryo cells and MDCK cells. The variants differ also from the wild-type in their pathogenicity for chickens. Nucleotide sequence and oligosaccharide analysis of the hemagglutinin have revealed that, unlike natural isolates with increased pathogenicity (Y. Kawaoka et al., 1984, Virology 139, 303-316; Y. Kawaoka and R. G. Webster, 1985, Virology 146, 130-137), the variants obtained in vitro have retained an oligosaccharide at asparagine 11 that is believed to interfere with the cleavage site of the wild-type. However, all variants showed mutations in the hemagglutinin resulting in an increased number of basic groups at the cleavage site. These observations demonstrate that masking of the cleavage site by an oligosaccharide is overcome by an enhancement of the basic charge at the cleavage site.

Amino Acid Sequence↗
PubMed1986

Studies on the temperature sensitivity of influenza A virus reassortants nonpathogenic for chicken.

Influenza A virus reassortants which are nonpathogenic for chickens are like mammalian influenza A viruses in that they are temperature sensitive for growth at 41 degrees C. We have investigated the mechanism of this temperature sensitivity using reassortants between the two highly pathogenic strains A/FPV/Rostock/34 (FPV, H7N1) and A/turkey/England/63 (TE, H7N3). These reassortants show a strict correlation between the pathogenicity for chickens and the constellation of the genes coding for the ribonucleoprotein complex, RNP. Evidence is presented which shows that all viral components are synthesized in sufficient amounts and that the block in the viral replication cycle at the nonpermissive temperature is a late one affecting virus maturation. It is suggested that the RNP, although still enzymatically functional, may lose its ability to interact normally with viral surface components, thus interfering with the process of virus maturation. Some of the nonpathogenic reassortants which possessed the neuraminidase of TE showed an interesting temperature-dependent phenomenon: the haemagglutinin synthesized at the elevated temperature could only agglutinate erythrocytes at 20 degrees C, when the neuraminidase was inhibited or the infected cells vigorously disrupted by ultrasonication. This phenomenon is possibly not directly related to the temperature-sensitive block.

Animals↗
PubMed1984

Studies on the adaptation of influenza viruses to MDCK cells.

The amino acid sequences and biological properties of the haemagglutinin of three variants of the influenza virus X-31 (H3N2) selected for their capacity to grow in MDCK cells are reported. In two variants, amino acid substitutions at HA1 residues 8 and 144 correlated with the loss of a site for glycosylation and specific changes in antigenicity, respectively. In all three variants substitution of an arginine residue for histidine at HA1 position 17 was correlated with increased pH optima of haemolysis. The importance of this substitution for cleavage of the haemagglutinin precursor required to produce infectious virus is discussed in relation to the three-dimensional structure of X-31 haemagglutinin.

Adaptation, Physiological↗
PubMed1984

Effect of inhibitors of glycosylation on proteolytic activation of avian influenza virus hemagglutinins: discrimination between tryptic cleavage and elimination of the connecting peptide.

The glycosylation inhibitors tunicamycin (TM), 2-deoxyglucose (2-dg), bromoconduritol (BC; 3,5/4,6-6-bromo 3,4,5-trihydroxycyclohex-1-ene), and N-methyl-deoxynojirimycin (MdN) have been used to study the role of glycosylation in the two proteolytic reactions involved in the biological activation of H7 influenza virus hemagglutinins (HAs): trypsinlike cleavage and subsequent elimination of the connecting peptide. The results obtained revealed that trypsin-like cleavage of the HAs of pathogenic strains does not require glycosylation, since these HAs were efficiently cleaved in the presence of TM and 2-dg. The elimination of the connecting peptide between HA1 and HA2, however, appears to require the transfer of oligosaccharides onto the HA polypeptide, since this activity was blocked by TM and by 2-dg. Elimination was not blocked by BC or MdN, which inhibit glucose trimming and subsequent conversion of the high-mannose type to the complex type of carbohydrate.

1-Deoxynojirimycin↗
PubMed1983

Pathogenicity reactivation of nonpathogenic influenza virus recombinants under von Magnus conditions.

The pathogenicity for the chicken of a number of nonpathogenic recombinants between fowl plague virus and various avian and mammalian influenza A viruses can be reactivated by passaging serially at high multiplicities (von Magnus conditions) at 41 degrees, which is the nonpermissive temperature of nonpathogenic recombinants. While the mechanism underlying this reactivation is unclear, it could be excluded that it was due to segregation of heterozygotes to the wild type homozygotes.

Animals↗
PubMed1983

Evidence for the contribution of the host species to the extent of antigenic variation of N1 influenza virus neuraminidase.

N1 influenza virus neuraminidases (NA) derived from avian, swine and human virus isolates, including the genetically related classic strains A/FPV/Rostock/34, A/Swine/1976/31, A/PR8/34 and A/FM1/47, were analysed serologically by neuraminidase inhibition (NI), inhibition of virus release (IVR) and competitive radio-immunoassays (competitive RIA). Comparing the three tests, competitive RIA appeared to be more reliable than NI and IVR for a quantitative assessment of antigenic relatedness. Together with evidence presented by others, these studies indicate that the host species contributes to the extent of antigenic variation of NAses. In contrast to NAses of human viruses where antigenic drift occurs readily, NAses of animal influenza viruses, from birds or mammalians, undergo far fewer antigen changes.

Animals↗
PubMed1981

Intrinsic interference between swine influenza and fowl plague virus.

Multiplication of swine influenza (SW) virus is inhibited by fowl plaque virus (FPV) at the level of RNA synthesis when host cells are infected with both viruses at a high multiplicity of infection. Under these conditions reassortment between the two viruses cannot be detected. The inhibitory effect of FPV is highly reduced and recombinants between the two viruses could be obtained when the cells were superinfected with FPV 1--2 hours after infection with SW virus, or after simultaneous infection with a low multiplicity of infection. The phenomenon is compatible with the intrinsic interference.

Animals↗
PubMed1980

Cleavability of hemagglutinin determines spread of avian influenza viruses in the chorioallantoic membrane of chicken embryo.

The spread of infection in the chorioallantoic membrane (CAM) has been analysed with pathogenic and non-pathogenic avian influenza A viruses. After allantoic inoculation of pathogenic strains, high titers of infectious virus were found in the allantoic fluid, and virus growth could be demonstrated by immunohistology and electron microscopy in the allantoic epithelium, the mesenchyma, and in the chorionic epithelium. By the same route of inoculation, non-pathogenic strains yielded also higher titers of infectious virus in the allantoic fluid, but virus replication was restricted to the allantoic epithelium and did not occur in the other cell layers. After chorionic inoculation of pathogenic strains, replication occurred in all layers of the CAM, and infectious virus was released into the allantoic fluid. However, when the chorionic epithelium was infected with a non-pathogenic strain, infection did not spread beyond the site of inoculation. These differences in virus spread are based on differential activation of the hemagglutinin by proteolytic cleavage. The hemagglutinin of pathogenic strains is cleaved in cells of each layer, whereas the hemagglutinin of non-pathogenic strains is cleaved only in the allantoic epithelium. In epithelial cells, virus budding occurred nearly exclusively at the apical side of the cell surface, but this polarization of virus maturation was found with both pathogenic and nonpathogenic strains, indicating that it does not account for the differences in virus spread and, thus, in pathogenicity.

Allantois↗
PubMed1979

Correlation of pathogenicity and gene constellation of influenza A viruses. III. Non-pathogenic recombinants derived from highly pathogenic parent strains.

We have demonstrated by recombination of two highly pathogenic avian influenza viruses [A/FPV/Rostock (Hav1N1) x A/turkey/England/63 (Hav1Nav3)] that recombinants can be isolated which are pathogenic as well as non-pathogenic for chickens. They carried the glycoproteins of either parent strains, and all are produced in infectious form in chick embryo cells. Genetic analysis revealed that the non-pathogenic recombinants possess a mixed RNA polymerase complex, consisting of pol 1, pol 2, ptra and NP gene products, while, with one exception, the pathogenic recombinants have the genes coding for the polymerase activity from one or other parent virus. The biological properties of the recombinant viruses did not correlate with their pathogenicity for chickens.

Animals↗
PubMed1976

Attenuation of pathogenicity of fowl plague virus by recombination with other influenza A viruses nonpathogenic for fowl: nonexculsive dependence of pathogenicity on hemagglutinin and neuraminidase of the virus.

A number of antigenic hybrids of influenza A viruses were produced possessing either the hemagglutinin or the neuraminidase of fowl plague virus and the corresponding antigen derived from another influenza A virus. Other recombinants were obtained carrying both surface antigens of fowl plague virus but differing from the parent in certain biological properties. None of the recombinants isolated were pathogenic for adult chickens. Most recombinants obtained after crosses between reciprocal recombinants carrying both fowl plague virus surface antigens were also apathogenic for chickens. Using the same parent recombinants for double infection some of the progeny "back-recombinants" were pathogenic, whereas others were not. From these results it is concluded that the surface components do not by themselves determine the pathogenicity of influenza A viruses.

Animals↗