1,720,971 research outputs found
Co‐receptor Usage of BOB/GPR15 in Addition to CCR5 Has No Significant Effect on Replication of Simian Immunodeficiency Virus In Vivo
No full textMHC Class I Alleles Influence Set-Point Viral Load and Survival Time in Simian Immunodeficiency Virus-Infected Rhesus Monkeys
No full textComparison of early plasma RNA loads in different macaque species and the impact of different routes of exposure on SIV/SHIV infection
No full textThe Human Immunodeficiency Virus Type 1 nef Gene Can to a Large Extent Replace Simian Immunodeficiency Virus nef In Vivo
No full textABSTRACT
The
nef
gene of the pathogenic simian immunodeficiency virus (SIV) 239 clone was replaced with primary human immunodeficiency virus type 1 (HIV-1)
nef
alleles to investigate whether HIV-1 Nef can substitute for SIV Nef in vivo. Initially, two rhesus macaques were infected with the chimeric viruses (Nef-SHIVs). Most of the
nef
alleles obtained from both animals predicted intact open reading frames. Furthermore, forms containing upstream nucleotide substitutions that enhanced expression of the inserted gene became predominant. One animal maintained high viral loads and slowly progressed to immunodeficiency.
nef
long terminal repeat sequences amplified from this animal were used to generate a second generation of Nef-SHIVs. Two macaques, which were subsequently infected with a mixture of cloned chimeric viruses, showed high viral loads and progressed to fatal immunodeficiency. Five macaques received a single molecular clone, named SHIV-40K6. The SHIV-40K6
nef
allele was active in CD4 and class I major histocompatibility complex downregulation and enhanced viral infectivity and replication. Notably, all of the macaques inoculated with SHIV-40K6 showed high levels of viral replication early in infection. During later stages, however, the course of infection was variable. Three animals maintained high viral loads and developed immunodeficiency. Of the remaining two macaques, which showed decreasing viral loads after the acute phase of infection, only one efficiently controlled viral replication and remained asymptomatic during 1.5 years of follow-up. The other animal showed an increasing viral load and developed signs of progressive infection during later stages. Our data demonstrate that HIV-1
nef
can, to a large extent, functionally replace SIVmac
nef
in vivo
T-Cell Response
No full textABSTRACT
Deletion of the
nef
gene from simian immunodeficiency virus (SIV) strain SIVmac239 yields a virus that undergoes attenuated growth in rhesus macaques and offers substantial protection against a subsequent challenge with some SIV wild-type viruses. We used a recently described model to identify sites in which the SIVΔ
nef
vaccine strain replicates and elicits immunity in vivo. A high dose of SIVΔ
nef
was applied to the palatine and lingual tonsils, where it replicated vigorously in this portal of entry at 7 days. Within 2 weeks, the virus had spread and was replicating actively in axillary lymph nodes, primarily in extrafollicular T-cell-rich regions but also in germinal centers. At this time, large numbers of perforin-positive cells, both CD8
+
T cells and CD3-negative presumptive natural killer cells, were found in the tonsil and axillary lymph nodes. The number of infected cells and perforin-positive cells then fell. When autopsy studies were carried out at 26 weeks, only 1 to 3 cells hybridized for viral RNA per section of lymphoid tissue. Nevertheless, infected cells were detected chronically in most lymphoid organs, where the titers of infectious virus could exceed by a log or more the titers in blood. Immunocytochemical labeling at the early active stages of infection showed that cells expressing SIVΔ
nef
RNA were CD4
+
T lymphocytes. A majority of infected cells were not in the active cell cycle, since 60 to 70% of the RNA-positive cells in tissue sections lacked the Ki-67 cell cycle antigen, and both Ki-67-positive and -negative cells had similar grain counts for viral RNA. Macrophages and dendritic cells, identified with a panel of monoclonal antibodies to these cells, were rarely infected. We conclude that the attenuated growth and protection observed with the SIVΔ
nef
vaccine strain does not require that the virus shift its characteristic site of replication, the CD4
+
T lymphocyte. In fact, this immunodeficiency virus can replicate actively in CD4
+
T cells prior to being contained by the host, at least in part by a strong killer cell response that is generated acutely in the infected lymph nodes
The Acidic Region and Conserved Putative Protein Kinase C Phosphorylation Site in Nef Are Important for SIV Replication in Rhesus Macaques
No full textAbstractVariants of the pathogenic SIVmac239 clone with changes in Nef were analyzed to assess the functional relevance of two highly conserved regions in Nefin vitroandin vivo.Changes in a region with an acidic charge (Aci-Nef), or a potential protein kinase C phosphorylation site (PKC-Nef), impaired the ability of Nef to down-regulate CD4 and MHC class I surface expression and to alter CD3-initiated signal transduction in Jurkat T cells. The Aci-Nef, but not the PKC-Nef, associated with the previously described p65 phosphoprotein. SIV containing Aci-Nef, but not SIV containing PKC-Nef, showed reduced infectivity and replication in cell culture systems. One of two rhesus macaques infected with the PKC-Nef mutant virus showed rapid reversion and progressed to disease. In the second animal no reversions and nonprogressive infection was observed. In one of two macaques infected with the Aci-Nef variant, the mutations were stable during the first 40 weeks after infection. Thereafter, variants evolved in which up to six of the eight mutated positions in Nef were reverted and functional activityin vitrowas partially restored. These changes occurred concomitantly with increasing viral load and disease progression. The second animal infected with the Aci-Nef variant showed no reversions and remained asymptomatic. Our study suggests that the acidic region and conserved PKC phosphorylation site in Nef are important for SIV replication in rhesus macaques and for severalin vitroNef functions. An almost wild-type activity inin vitroinfectivity and replication assays seems insufficient to confer a fullnef-positive phenotypein vivo
Comparison ofin Vitroandin VivoInfectivity of Different Clade B HIV-1 Envelope Chimeric Simian/Human Immunodeficiency Viruses inMacaca mulatta
No full textSimian Immunodeficiency Virus in Which <i>nef</i> and U3 Sequences Do Not Overlap Replicates Efficiently In Vitro and In Vivo in Rhesus Macaques
No full textABSTRACT
The
nef
genes of human immunodeficiency virus and simian immunodeficiency virus (SIV) overlap about 80% of the U3 region of the 3′ long terminal repeat (LTR) and contain several essential
cis
-acting elements (here referred to as the TPI region): a T-rich region, the polypurine tract, and attachment (
att
) sequences required for integration. We inactivated the TPI region in the
nef
reading frame of the pathogenic SIVmac239 clone (239wt) by 13 silent point mutations. To restore viral infectivity, intact
cis
-regulatory elements were inserted just downstream of the mutated
nef
gene. The resulting SIV genome contains U3 regions that are 384 bp shorter than the 517-bp 239wt U3 region. Overall, elimination of the duplicated Nef coding sequences truncates the proviral genome by 350 bp. Nonetheless, it contains all known coding sequences and
cis
-acting elements. The TPI mutant virus expressed functional Nef and replicated like 239wt in all cell culture assays and in vivo in rhesus macaques. Notably, these SIVmac constructs allow us to study Nef function in the context of replication-competent viruses without the restrictions of overlapping LTR sequences and important
cis
-acting elements. The genomes of all known primate lentiviruses contain a large overlap between
nef
and the U3 region. We demonstrate that this conserved genomic organization is not obligatory for efficient viral replication and pathogenicity.
</jats:p
T-Cell Receptor : CD3 down-regulation is a selected in vivo function of simian immunodeficiency virus Nef but is not sufficient for effective viral replication in rhesus macaques
No full textWe investigated the function of severely truncated simian immunodeficiency virus (SIV) Nef proteins (tNef) in vitro and in vivo. These variants emerged in rhesus monkeys infected with SIVmac239 containing a 152-bp deletion in the nef-unique region and have been suggested to enhance SIV virulence (E. T. Sawai, M. S. Hamza, M. Ye, K. E. Shaw, and P. A. Luciw, J. Virol. 74:2038-2045, 2000). We found that the tNef proteins were unable to down-regulate the cell surface expression of major histocompatibility complex class I proteins, CD4, and CD28 and neither stimulated SIV replication nor enhanced virion infectivity. The tNef proteins did efficiently down-regulate T-cell receptor (TCR):CD3 cell surface expression. Nevertheless, the SIVmac239 tnef variants were strongly attenuated in six infected juvenile rhesus macaques. Thus, while the ability of SIV Nef to down-modulate TCR:CD3 cell surface expression apparently confers a selective advantage in vivo, it is insufficient for efficient viral replication in infected macaques. Additional mutations elsewhere in SIVmac239 tnef genomes are required for a virulent phenotype
- …
