M Schutten, AC Andeweg, GF Rimmelzwaan and AD Osterhaus
Erasmus University Hospital Rotterdam, Institute of Virology, The Netherlands.
Recently, we and others have shown that the interaction between ...envelope
specific antibodies and primary human immunodeficiency virus type 1 (HIV-1)
isolates may result in either inhibition or enhancement of virus entry. The
outcome proved to be determined by the virus isolate rather than by the
specificity of the antiserum used. To study the mechanism underlying this
phenomenon, a series of HIV-1 envelope glycoproteins from closely related
primary virus isolates of different syncytium inducing phenotypes, together
with chimeras of these proteins, were tested in an envelope
trans-complementation assay for their sensitivity to either antibody
mediated inhibition or enhancement of HIV-1 entry. Based on the observation
that, in contrast to the inhibition of HIV-1 entry, antibody mediated
enhancement was not temperature dependent and could not be mediated by
F(ab) fragments, we concluded that the mechanisms underlying these
phenomena are different and that antibody mediated enhancement of HIV-1
entry is largely if not exclusively mediated by HIV-1 glycoprotein
cross-linking. The susceptibility of the envelope glycoprotein chimeric
viruses to neutralization or enhancement of infectivity proved to be
primarily determined by the configuration of the V3 loop, and the affinity
of the antibodies to monomeric HIV-1 gp 160 molecules, proved to be of
quantitative importance only. One human monoclonal antibody directed
against gp41 (IAM 2F5) inhibited entry of all the viruses studied,
irrespective of their phenotype, and directly proportional to its affinity
to monomeric HIV-1 gp 160.
1 Laboratory of Immunobiology, National Institute of Public Health and Environmental Protection, A. van Leeuwenhoeklaan 9, 3720 BA Bilthoven
and 2 Institute of Virology, Erasmus University, Dr ...Molewaterplein 50, PO Box 1738, 3000 DR Rotterdam, The Netherlands
Several studies have demonstrated a functional role for the V1-V2 region of the human immunodeficiency virus type 1 (HIV-1) envelope surface glycoprotein gp120 in the membrane fusion processes underlying viral entry and syncytium induction. In a study with chimeric primary envelope genes, we have previously demonstrated that the exchange of V2 regions was sufficient to transfer syncytium-inducing capacity to a non-syncytium-inducing envelope protein. The exchanged V2 regions, comprising a number of variable amino acids, conferred changes to both the predicted secondary structure and to the net positive charge of the V2 loops. In a syncytium-forming assay based on transient envelope protein expression in CD4 + SupT1 cells, we have extended this observation by mutating the variable positions of the V2 region to determine the relative contribution of individual amino acids to syncytium formation. It can be shown that simultaneous mutation of multiple amino acids is needed to interfere with the V2 region-determined syncytium-inducing phenotype. Single amino acid changes either influencing charge or predicted secondary structure of the V2 loop proved to be insufficient to abolish V2 region-controlled syncytium formation. This robust V2 organization may allow the virus to accumulate mutations, while retaining its biological phenotype.
* Author for correspondence. Fax +31 10 4365145. e-mail osterhaus@viro.fgg.eur.nl
Present address: Laboratory of Viral Pathogenesis, Biomedical Primate Research Centre, Rijswijk, The Netherlands.
Present address: Regional Primate Research Center and Department of Pathobiology, University of Washington, Seattle, Washington, USA.
Received 3 February 1995;
accepted 20 March 1995.
The genetic information, carried on mRNA 6 of feline infectious peritonitis virus (FIPV) strain 79–1146, was determined by sequence analysis of cDNA clones derived from the 3′ end of the FIPV genome. ...Two ORFs were found, encoding polypeptides of 11 K (ORF-1) and 22K (ORF-2). The FIPV sequence was compared to the 3′ end sequence of transmissible gastroenteritis virus (TGEV). ORF-1 has a homologous counterpart (ORF-X3) in the TGEV genome; both ORFs are located at the same position relative to the nucleocapsid gene. However, as a result of an in-frame insertion or deletion, ORF-1 is 69 nucleotides larger than ORF-X3. A similar event has occurred immediately downstream of ORF1: a 624-nucleotide segment, containing the complete ORF-2, is absent in the TGEV sequence. Most sequence similarity (98.5%) was found in the 3′ noncoding sequences. ORF-X3 and ORF-1 are preceded by the sequence AAC-TAAAC, which is assumed to be the transcription-initiation signal in FIPV and TGEV (
P. A. Kapke and D. A. Brian (1986)
Virology 151, 41–49). By S1 nuclease analysis, the 5′ end of FIPV RNA 6 was mapped immediately upstream of this sequence. A 700-nucleotide TGEV-specific RNA was found by cross-hybridization with an FIPV 3′ end probe, suggesting that TGEV ORF-X3 is also carried on a separate mRNA. The differences at the 3′ ends of the FIPV and TGEV genomes maybe the result of RNA recombination events.
The Dutch national open database on COVID-19 has been incrementally expanded since its start on 30 April 2020 and now includes datasets on symptoms, tests performed, individual-level positive cases ...and deaths, cases and deaths among vulnerable populations, settings of transmission, hospital and ICU admissions, SARS-CoV-2 variants, viral loads in sewage, vaccinations and the effective reproduction number. This data is collected by municipal health services, laboratories, hospitals, sewage treatment plants, vaccination providers and citizens and is cleaned, analysed and published, mostly daily, by the National Institute for Public Health and the Environment (RIVM) in the Netherlands, using automated scripts. Because these datasets cover the key aspects of the pandemic and are available at detailed geographical level, they are essential to gain a thorough understanding of the past and current COVID-19 epidemiology in the Netherlands. Future purposes of these datasets include country-level comparative analysis on the effect of non-pharmaceutical interventions against COVID-19 in different contexts, such as different cultural values or levels of socio-economic disparity, and studies on COVID-19 and weather factors.
To study HIV-1 envelope-mediated syncytium formation we have amplified, cloned, expressed, and sequenced individual envelope genes from a set of eight biological HIV-1 clones. These clones were ...obtained from two patients and display either a syncytium-inducing (SI) or nonsyncytium-inducing (NSI) phenotype. Upon expression through recombinant vaccinia virus, individual envelope gene products display heterogeneous syncytium-inducing capacities which reflect the phenotype of the parental biological HIV-1 clones in all cases. For the eight biological HIV-1 clones presented here, variation of the envelope gene alone is sufficient to explain the observed variable syncytium-inducing capacity of the respective parental viruses. In addition we determined the complete nucleotide sequence of these envelope genes. The predicted amino acid sequence revealed a considerable amount of variation located mainly in the previously denominated variable regions. In various regions of envelope genes obtained from the same patient, phenotype associated amino acid variation was found. This phenotype associated amino acid variation however, is not conserved between the two sets of envelope genes derived from different patients. Four envelope sequences derived from clones obtained from one patient showed phenotype-associated amino acid variation in the fusion domain. Sequencing of 12 additional fusion domains revealed that this same variation is found in four additional clones. However, a functional test performed on recombinant vaccinia expressing mutant envelope genes showed that this observed fusion domain variation does not contribute to the variation in syncytium-inducing capacity of the envelope gene product.
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