Complete envelope genes were amplified from autopsy brain tissue of five individuals who had died of AIDS and had neurological complications. Lymph node samples were included for two of the patients. Nineteen different envelope clones from the five patients had distinct V1V2 sequences. Thirteen of the envelopes were functional and conferred fusigenicity and infectivity for CD4 ؉ CCR5 ؉ cells. Infectivity and cell-cell fusion assays showed that most envelopes used both CCR5 and CCR3. One brain-derived envelope used a broad range of coreceptors, while three other brain envelopes from one individual were restricted to CCR5. However, there was no correlation between tissue of origin and coreceptor use. Envelopes showed two very distinct phenotypes depending on their capacity to infect macrophages and to exploit low levels of CD4 and/or CCR5 for infection. Envelopes that were highly fusigenic and tropic for macrophages were identified in brain tissue from four of the five patients. The enhanced macrophage tropism correlated with reduced sensitivity to inhibition by Q4120, a CD4-specific antibody, but not with sensitivity to the CCR5 inhibitor, TAK779. The highly macrophage-tropic envelopes were able to infect cells expressing low levels of CD4 and/or CCR5. Comparison with several wellcharacterized macrophage-tropic envelopes showed that the four identified patient envelopes were at the top limit of macrophage tropism. In contrast, all four lymph node-derived envelopes exhibited a non-macrophagetropic phenotype and required high levels of CD4 for infection. Our data support the presence of envelopes that are highly fusigenic and tropic for macrophages in the brains of patients with neurological complications. These envelopes are able to infect cells that express low levels of CD4 and/or CCR5 and may have adapted for replication in brain macrophages and microglia, which are known to express limited amounts of CD4.Human immunodeficiency virus type 1 (HIV-1) replication in the brain results in the development of severe neurological disorders known as AIDS dementia complex in about 30% of AIDS patients (29). The mechanisms that cause the loss of up to 40% of neurons (10) as well as result in dementia are unclear. In the rhesus macaque simian immunodeficiency virus (SIV) model, both neurotropic and neurovirulent SIV MAC variants have been described (11,22,38). It is therefore suspected that specific neurotropic and neurovirulent HIV-1 variants exist and are associated with dementia.CCR5-using HIV-1 strains are predominant in the brain (13), and CCR5 ϩ perivascular macrophages and microglia are the cell types most frequently infected (19,35,37,43,49,50). The role of other cell types resident in the brain is less clear. There is evidence that CD4Ϫ astrocytes become infected, particularly in pediatric AIDS cases (32,36,37,43). Astrocyte infection is relatively unproductive with early HIV mRNAs (e.g., for rev and nef) detectable, but no late mRNAs encoding the structural gag and env proteins needed to produce progeny virus par...

The introduction of a label which can be detected in living cells opens new possibilities for the direct analysis of dynamic processes in virus replication, such as the transport and assembly of structural proteins. Our aim was to generate a tool for the analysis of the trafficking of the main structural protein of human immunodeficiency virus type 1 (HIV-1), Gag, as well as for the analysis of virus-host cell interactions in an authentic setting. We describe here the construction and characterization of infectious HIV derivatives carrying a label within the Gag polyprotein. Based on our initial finding that a short epitope tag could be inserted near the C terminus of the matrix domain of Gag without affecting viral replication, we constructed HIV derivatives carrying the egfp gene at the analogous position, resulting in the expression of a Gag-EGFP fusion protein in the authentic viral context. Particles displaying normal viral protein compositions were released from transfected cells, and Gag-EGFP was efficiently processed by the viral protease, yielding the expected products. Furthermore, particles with mature morphology were observed by thin-section electron microscopy. The modified virus was even found to be infectious, albeit with reduced relative infectivity. By preparing mixed particles containing equimolar amounts of Gag-EGFP and Gag, we were able to obtain highly fluorescently labeled virion preparations which displayed normal morphology and full wild-type infectivity, demonstrating that the process of HIV particle assembly displays a remarkable flexibility. The fluorescent virus derivative is a useful tool for investigating the interaction of HIV with live cells.

Productive entry of human immunodeficiency virus (HIV) is believed to occur by direct fusion at the plasma membrane. Endocytic uptake of HIV particles has been observed in several studies but is considered to be nonproductive, leading to virus degradation in the lysosome. We show here that endocytosis contributes significantly to productive HIV entry in HeLa cells by using trans dominant-negative mutants of dynamin and Eps15. Inducible expression of a dominant-negative mutant of dynamin in a CD4-positive HeLa cell line reduced HIV infection by 40 to 80%. This effect was independent of the infectious dose and was observed for three different isolates. Analysis of reverse transcription products by real-time PCR and of virus entry by delivery of a virion-associated Vpr-␤-lactamase fusion protein revealed a similar reduction, indicating that the block occurred at the entry stage. A strong reduction of HIV entry was also observed upon transient transfection of a different trans dominant-negative variant of dynamin, and this reduction correlated with the relative inhibition of transferrin endocytosis. Expression of a dominant-negative variant of Eps15, which is specific for clathrin-dependent endocytosis, reduced HIV entry in HeLa cells by ca 95%, confirming the role of endocytosis for productive infection. In contrast, no effect was observed for a dominant-negative variant of caveolin. We conclude that dynamin-dependent, clathrin-mediated endocytosis can lead to productive entry of HIV in HeLa cells, suggesting this pathway as an alternative route of virus entry.

A panel of primary syncytium-inducing (SI) human immunodeficiency virus type 1 isolates that infected several CD4 ؉ T-cell lines, including MT-2 and C8166, were tested for infection of blood-derived macrophages. Infectivity titers for C8166 cells and macrophages demonstrated that primary SI strains infected macrophages much more efficiently than T-cell line-adapted HIV-1 strains such as LAI and RF. These primary SI strains were therefore dual-tropic. Nine biological clones of two SI strains, prepared by limiting dilution, had macrophage/C8166 infectivity ratios similar to those of their parental viruses, indicating that the dual-tropic phenotype was not due to a mixture of non-SI/macrophage-tropic and SI/T-cell tropic viruses. We tested whether the primary SI strains used either Lestr (fusin) or CCR5 as coreceptors. Infection of cat CCC/CD4 cells transiently expressing Lestr supported infection by T-cell line-adapted strains including LAI, whereas CCC/CD4 cells expressing CCR5 were sensitive to primary non-SI strains as well as to the molecularly cloned strains SF-162 and JR-CSF. Several primary SI strains, as well as the molecularly cloned dual-tropic viruses 89.6 and GUN-1, infected both Lestr ؉ and CCR5 ؉ CCC/CD4 cells. Thus, these viruses can choose between Lestr and CCR5 for entry into cells. Interestingly, some dual-tropic primary SI strains that infected Lestr ؉ cells failed to infect CCR5 ؉ cells, suggesting that these viruses may use an alternative coreceptor for infection of macrophages. Alternatively, CCR5 may be processed or presented differently on cat cells so that entry of some primary SI strains but not others is affected.

BackgroundUpon cellular entry retroviruses must avoid innate restriction factors produced by the host cell. For human immunodeficiency virus (HIV) human restriction factors, APOBEC3 (apolipoprotein-B-mRNA-editing-enzyme), p21 and tetherin are well characterised.ResultsTo identify intrinsic resistance factors to HIV-1 replication we screened 19,121 human genes and identified 114 factors with significant inhibition of infection. Those with a known function are involved in a broad spectrum of cellular processes including receptor signalling, vesicle trafficking, transcription, apoptosis, cross-nuclear membrane transport, meiosis, DNA damage repair, ubiquitination and RNA processing. We focused on the PAF1 complex which has been previously implicated in gene transcription, cell cycle control and mRNA surveillance. Knockdown of all members of the PAF1 family of proteins enhanced HIV-1 reverse transcription and integration of provirus. Over-expression of PAF1 in host cells renders them refractory to HIV-1. Simian Immunodeficiency Viruses and HIV-2 are also restricted in PAF1 expressing cells. PAF1 is expressed in primary monocytes, macrophages and T-lymphocytes and we demonstrate strong activity in MonoMac1, a monocyte cell line.ConclusionsWe propose that the PAF1c establishes an anti-viral state to prevent infection by incoming retroviruses. This previously unrecognised mechanism of restriction could have implications for invasion of cells by any pathogen.

We have studied infectivity and neutralization of X4, R5, and R5X4 tropic HIV-1 mutants, which are lacking N-linked glycosylation sites for glycans g13, g14, g15, and g17 in the V3 loop region of gp120. X4-tropic NL4-3 mutants lacking combinations of g14/15 or g15/17 showed markedly higher infectivity in CXCR4-specific infection. The role of g15 in CCR5-specific infection was investigated using viruses with high (NL-918, R5-monotropic), medium (NL-991, R5-monotropic), and low (NL-952, R5X4-dualtropic) CCR5-specific infectivity. For NL-991, a reduction of infectivity on GHOST-CCR5 cells was observed for a mutant lacking g15. For NL-952 mutants all lacking g15, a complete loss of CCR5-specificity was observed and NL-952 was shifted from R5X4 to X4 tropism. For all mutants of NL4-3, NL-991, and NL-952, where the lack of g15 markedly influenced infectivity or coreceptor usage, neutralization was enhanced. In contrast, NL-918 mutants with or without g15 showed no difference in neutralization and no difference in GHOST-CCR5 infection rates. Thus, for viruses with a low or medium CCR5-specificity the role of g15 for changing CCR5-usage and sensitivity to neutralization was more significant than for viruses with high infection rates on GHOST-CCR5 cells. Our data demonstrate that V3 glycans play an important role in the usage of CXCR4 and CCR5. The lack of g15 was relevant for a more efficient use of CXCR4, whereas interaction with CCR5 was facilitated in the presence of g15. This study also demonstrates that glycan g15 is involved in blocking of neutralizing antibodies and shifting HIV tropism from R5X4 to X4.

The characterization of restrictions to lentivirus replication in cells identifies critical steps in the viral life cycle and potential therapeutic targets. We previously reported that a human immunodeficiency virus type 2 (HIV-2) isolate was restricted to infection in some human cells, which led us to identify a step in the life cycle of HIV-2 detected after reverse transcription but prior to nuclear entry. The block is bypassed with a vesicular stomatitis virus glycoprotein G (VSV-G) envelope ( Abrogation experiments with MLV demonstrate that the restriction is distinct from Fv1/Ref1/Lv1. We propose that this represents a new lentiviral restriction, Lv2. Thus, the envelope and capsid of HIV act to ensure that the virus is delivered into an appropriate cellular compartment that allows postentry events in viral replication to proceed efficiently.

Peptides derived from the heptad repeats of human immunodeficiency virus (HIV) gp41 envelope glycoprotein, such as T20, can efficiently inhibit HIV type 1 (HIV-1) entry. In this study, replication of HIV-1 was inhibited more than 100-fold in a T-helper cell line transduced with a retrovirus vector expressing membrane-anchored T20 on the cell surface. Inhibition was independent of coreceptor usage.