Productive HIV-2 infection in the brain is restricted to macrophages/microglia

OBJECTIVES

HIV-2 can use a broader range of co-receptors than HIV-1 in vitro, and is less dependent on CD4 for infection. The aim of this study was to detect productive HIV-2 infection in the brain and investigate whether HIV-2 has an expanded tropism for brain cells in vivo, in comparison with HIV-1, which productively infects macrophages/microglia.

DESIGN

Brain samples taken at autopsy from eight patients who died from AIDS, six HIV-2 and two HIV-1/HIV-2 dually seropositive, with HIV encephalitis (HIVE), collected in Abidjan, Côte d'Ivoire in 1991, were examined for the presence and localization of productive HIV-2 infection.

METHODS

Using immunohistochemistry, the presence of HIV-2 p26 in formalin-fixed, wax-embedded brain tissue sections was investigated. Double-staining with glial fibrillary acidic protein (GFAP), CD45- and CD68-specific antibodies was performed to identify infected cell types.

RESULTS

HIV-2 p26 was detected in brain tissue from four of the HIV-2 cases and one of the dually infected individuals. The productively infected cells were either microglia or infiltrating macrophages.

CONCLUSIONS

The productively infected cells in the brains of HIV-2 infected individuals are macrophages/microglia. No evidence was found for productive infection of astrocytes, neurons or oligodendrocytes. Thus, the broader in vitro cell tropism, promiscuous coreceptor usage and relative independence of CD4 by HIV-2 compared to HIV-1 does not broaden its range of target cells in the brain.

Identification of a subset of human immunodeficiency virus type 1 (HIV-1), HIV-2, and simian immunodeficiency virus strains able to exploit an alternative coreceptor on untransformed human brain and lymphoid cells

The chemokine receptors CCR5 and CXCR4 are the major coreceptors for human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV). At least 12 other chemokine receptors or close relatives support infection by particular HIV and SIV strains on CD4(+) transformed indicator cell lines in vitro. However, the role of these alternative coreceptors in vivo is presently thought to be insignificant. Infection of cell lines expressing high levels of recombinant CD4 and coreceptors thus does not provide a true indication of coreceptor use in vivo. We therefore tested primary untransformed cell cultures that lack CCR5 and CXCR4, including astrocytes and brain microvascular endothelial cells (BMVECs), for naturally expressed alternative coreceptors functional for HIV and SIV infection. An adenovirus vector (Ad-CD4) was used to express CD4 in CD4(-) astrocytes and thus confer efficient infection if a functional coreceptor is present. Using a large panel of viruses with well-defined coreceptor usage, we identified a subset of HIV and SIV strains able to infect two astrocyte cultures derived from adult brain tissue. Astrocyte infection was partially inhibited by several chemokines, indicating a role for the chemokine receptor family in the observed infection. BMVECs were weakly positive for CD4 but negative for CCR5 and CXCR4 and were susceptible to infection by the same subset of isolates that infected astrocytes. BMVEC infection was efficiently inhibited by the chemokine vMIP-I, implicating one of its receptors as an alternative coreceptor for HIV and SIV infection. Furthermore, we tested whether the HIV type 1 and type 2 strains identified were able to infect peripheral blood mononuclear cells (PBMCs) via an alternative coreceptor. Several strains replicated in Delta32/Delta32 CCR5 PBMCs with CXCR4 blocked by AMD3100. This AMD3100-resistant replication was also sensitive to vMIP-I inhibition. The nature and potential role of this alternative coreceptor(s) in HIV infection in vivo is discussed.

CD4-dependent and CD4-independent HIV-2: consequences for neutralization

BACKGROUND

HIV-2 is less pathogenic than HIV-1. In contrast to HIV-1, many isolates of HIV-2, including primary isolates, can infect cells independently of CD4.

OBJECTIVE

To compare the sensitivity of CD4-dependent and CD4-independent isolates of HIV-2 to antibody-mediated neutralization.

METHODS

The neutralization sensitivity of CD4-dependent and CD4-independent molecular clones of HIV-2 to a panel of HIV-2-positive serum samples was tested. Monoclonal antibodies to various epitopes across the viral envelope were used to determine whether a specific epitope conferred neutralization sensitivity. Neutralization sensitivity of primary isolates of HIV-2 able to infect in the absence of cellular CD4 was also investigated. Antibody binding to sensitive and resistant envelopes was analysed using enzyme-linked immunosorbent assay and flow cytometry.

RESULTS

CD4-independent ROD B was highly sensitive to neutralization by HIV-2-positive sera compared with the CD4-dependent isolate ROD A. Induction of ROD A to infect CD4-negative cells by soluble CD4 rendered it equally sensitive to antibody neutralization. Similarly, primary X4, R5 or dual-tropic isolates of HIV-2 were significantly more susceptible to neutralization when utilizing a CD4-independent route of infection. Neutralization sensitivity was not epitope specific but several conformation-dependent antibodies accentuated this phenotype. Antibody binding to monomeric or oligomeric envelope did not correlate with neutralization sensitivity.

CONCLUSIONS

HIV-2 isolates utilizing a CD4-independent route of infection are more sensitive to antibody-mediated neutralization. Cellular CD4 may protect HIV-2 from neutralization. This sensitivity to neutralization may, in part, explain the lower virus load and slower progression to disease in HIV-2-infected individuals.

Human Leydig cells are productively infected by some HIV-2 and SIV strains but not by HIV-1

OBJECTIVES

With the use of highly active antiretroviral therapy, the identification of HIV reservoirs within the body has become an important issue. However, the testis has been largely ignored despite representing a pharmacologic sanctuary which could act as a viral reservoir.

DESIGN

Because alterations in testosterone production have frequently been reported in HIV-infected individuals, we investigated whether the testosterone-producing Leydig cells could become directly infected by HIV-1, HIV-2 or SIV.

METHODS

Purified Leydig cells were infected with a panel of HIV-1, HIV-2 and SIV strains and examined for expression of HIV/SIV receptors. Additionally, the impact of CD4 transduction on Leydig cell infection was determined.

RESULTS

Leydig cells were unable to support productive infection of the seven HIV-1 isolates tested. No CD4, CXCR4 or CCR5 expression was evident on the surface of Leydig cells and transduction with a CD4 expressing adenovirus did not induce HIV-1 infection. In contrast, some primary and laboratory adapted CD4-independent HIV-2 and SIV strains were able to enter and replicate productively in Leydig cells.

CONCLUSIONS

Our results suggest that Leydig cells do not represent a target for HIV-1 infection within the testis. In contrast, Leydig cells support HIV-2 and SIV infection and thus represent a potential target for infection. Receptor use and significance of HIV-2/SIV infection of Leydig cells remain to be determined.

HIV-1 receptors and cell tropism

HIV virus particles interact with several receptors on cell surfaces. Two receptors, CD4 and a co-receptor act sequentially to trigger fusion of viral and cellular membranes and confer virus entry into cells. For HIV-1, the chemokine receptor CCR5 is the predominant co-receptor exploited for transmission and replication in vivo. Variants that switch to use CXCR4 and perhaps other co-receptors evolve in some infected individuals and have altered tropism and pathogenic properties. Other cell surface receptors including mannose binding protein on macrophages and DC-SIGN on dendritic cells also interact with gp120 on virus particles but do not actively promote fusion and virus entry. These receptors may tether virus particles to cells enabling interactions with suboptimal concentrations of CD4 and/or co-receptors. Alternatively such receptors may transport cell surface trapped virions into lymph nodes before transmitting them to susceptible cells. Therapeutic strategies that prevent HIV from interacting with receptors are currently being developed. This review describes how the interaction and use of different cellular receptors influences HIV tropism and pathogenesis in vivo.

Primary human immunodeficiency virus type 2 (HIV-2) isolates infect CD4-negative cells via CCR5 and CXCR4: comparison with HIV-1 and simian immunodeficiency virus and relevance to cell tropism in vivo

Cell surface receptors exploited by human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) for infection are major determinants of tropism. HIV-1 usually requires two receptors to infect cells. Gp120 on HIV-1 virions binds CD4 on the cell surface, triggering conformational rearrangements that create or expose a binding site for a seven-transmembrane (7TM) coreceptor. Although HIV-2 and SIV strains also use CD4, several laboratory-adapted HIV-2 strains infect cells without CD4, via an interaction with the coreceptor CXCR4. Moreover, the envelope glycoproteins of SIV of macaques (SIV(MAC)) can bind to and initiate infection of CD4(-) cells via CCR5. Here, we show that most primary HIV-2 isolates can infect either CCR5(+) or CXCR4(+) cells without CD4. The efficiency of CD4-independent infection by HIV-2 was comparable to that of SIV, but markedly higher than that of HIV-1. CD4-independent HIV-2 strains that could use both CCR5 and CXCR4 to infect CD4(+) cells were only able to use one of these receptors in the absence of CD4. Our observations therefore indicate (i) that HIV-2 and SIV envelope glycoproteins form a distinct conformation that enables contact with a 7TM receptor without CD4, and (ii) the use of CD4 enables a wider range of 7TM receptors to be exploited for infection and may assist adaptation or switching to new coreceptors in vivo. Primary CD4(-) fetal astrocyte cultures expressed CXCR4 and supported replication by the T-cell-line-adapted ROD/B strain. Productive infection by primary X4 strains was only triggered upon treatment of virus with soluble CD4. Thus, many primary HIV-2 strains infect CCR5(+) or CXCR4(+) cell lines without CD4 in vitro. CD4(-) cells that express these coreceptors in vivo, however, may still resist HIV-2 entry due to insufficient coreceptor concentration on the cell surface to trigger fusion or their expression in a conformation nonfunctional as a coreceptor. Our study, however, emphasizes that primary HIV-2 strains carry the potential to infect CD4(-) cells expressing CCR5 or CXCR4 in vivo.

HIV coreceptors, cell tropism and inhibition by chemokine receptor ligands

HIV is a persistent virus that survives and replicates despite an onslaught by the host's immune system. A strategy for cell entry, requiring the use of two receptors, has evolved that may help evade neutralizing antibodies. HIV and SIV usually require both CD4 and a seven transmembrane (7TM) coreceptor for infection. At least eleven different 7TM coreceptors have been identified that confer HIV and/or SIV entry. For HIV-1, the major coreceptors are CCR5 and CXCR4, while the role of other coreceptors for replication and cell tropism in vivo is currently unclear. Polymorphisms in the CCR5 gene that reduce CCR5 expression levels, protect against disease progression, suggesting that drugs targeted to CCR5 could be effective. Such therapies however will not work if HIV simply adapts to use alternative coreceptors. In the light of these themes, this review will discuss the following topics: (i) the coreceptors used by primary HIV-1 and HIV-2 viruses, (ii) the properties and coreceptors of HIV-2 strains that infect cells without CD4, (iii) the role of coreceptors in HIV cell tropism and particularly macrophage infection and (iv) the properties of chemokine receptor ligands that block HIV infection.

CXCR4 as a functional coreceptor for human immunodeficiency virus type 1 infection of primary macrophages

The coreceptors used by primary syncytium-inducing (SI) human immunodeficiency virus type 1 isolates for infection of primary macrophages were investigated. SI strains using only CXCR4 replicated equally well in macrophages with or without CCR5 and were inhibited by several different ligands for CXCR4 including SDF-1 and bicyclam derivative AMD3100. SI strains that used a broad range of coreceptors including CCR3, CCR5, CCR8, CXCR4, and BONZO infected CCR5-deficient macrophages about 10-fold less efficiently than CCR5(+) macrophages. Moreover, AMD3100 blocked infection of CCR5-negative macrophages by these strains. Our results therefore demonstrate that CXCR4, as well as CCR5, is used for infection of primary macrophages but provide no evidence for the use of alternative coreceptors.

A broad range of chemokine receptors are used by primary isolates of human immunodeficiency virus type 2 as coreceptors with CD4

Like human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV), HIV-2 requires a coreceptor in addition to CD4 for entry into cells. HIV and SIV coreceptor molecules belong to a family of seven-transmembrane-domain G-protein-coupled receptors. Here we show that primary HIV-2 isolates can use a broad range of coreceptor molecules, including CCR1, CCR2b, CCR3, CCR4, CCR5, and CXCR4. Despite broad coreceptor use, the chemokine ligand SDF-1 substantially blocked HIV-2 infectivity of peripheral blood mononuclear cells, indicating that its receptor, CXCR4, was the predominant coreceptor for infection of these cells. However, expression of CXCR4 together with CD4 on some cell types did not confer susceptibility to infection by all CXCR4-using virus isolates. These data therefore indicate that another factor(s) influences the ability of HIV-2 to replicate in human cell types that express the appropriate receptors for virus entry.

CD4-independent infection by HIV-2 (ROD/B): use of the 7-transmembrane receptors CXCR-4, CCR-3, and V28 for entry

We have assayed a variety of 7tm chemokine receptors (CCR-2b, CCR-3, CCR-4, CCR-5, CXCR-1, CXCR-4) and two orphan 7tm receptors (V28 and EBI.1) for their ability to allow infection of CD4-negative feline kidney CCC cells by the HIV-2 strains ROD/A and ROD/B. We found that ROD/B was able to use CXCR-4 transiently expressed in CCC cells, and infection by ROD/A was enhanced 15-fold in the presence of sCD4. Feline CCC cells also became permissive to ROD/B and ROD/A entry when transiently transfected with the chemokine receptor CCR-3 or the orphan 7tm receptor V2B, when cultured in the presence of sCD4. Entry of ROD/A into CCC cells expressing CCR-3 could be blocked by 800 ng/ml eotaxin, the natural ligand for CCR-3.

Role of the amino-terminal extracellular domain of CXCR-4 in human immunodeficiency virus type 1 entry

We have studied the role of the N-terminal extracellular domain of the human immunodeficiency virus type 1 (HIV-1) coreceptor, CXCR-4, in the entry and fusion of syncytium-inducing strains of HIV-1. Progressive deletions were introduced in the N-terminal extracellular domain of CXCR-4 and the effect on infection by different isolates was tested. Infection of cells expressing the different CXCR-4 deletion mutants by HIV-1 LAI and 89.6 was reduced only about twofold. In contrast, the HIV-1 GUN-1 and RF isolates were substantially more impaired in their ability to mediate cell-free infection and cell-cell fusion. Since LAI and RF are T-cell line-tropic viruses while 89.6 and GUN-1 are dual tropic, no clear correlation between tropism and requirements for CXCR-4 N-terminal sequences emerged. We also introduced point mutations at the two N-linked glycosylation sites. The isolates tested (LAI, RF, GUN-1, and 89.6) were not affected by the removal of predicted N-linked glycosylation sites in CXCR-4. We conclude that distinct virus strains interact differently with the CXCR-4 coreceptor and that the N-terminal extracellular domain is not the sole functional domain important for HIV-1 entry.

Inhibition of human immunodeficiency virus fusion by a monoclonal antibody to a coreceptor (CXCR4) is both cell type and virus strain dependent

CXCR4 (also termed fusin, LESTR, or HUMSTR) is a member of the G-protein-coupled chemokine receptor family with seven membrane-spanning domains. CXCR4 acts as a coreceptor for syncytium-inducing human immunodeficiency virus type 1 (HIV-1) strains, conferring entry into CD4+ cells. We show here that a novel mouse monoclonal antibody (12G5) that recognizes CXCR4 blocked cell-to-cell fusion and cell free-virus infection of CXCR4+ CD4+ RD rhabdomyosarcoma cells by seven HIV-1 and HIV-2 strains that had various cell tropisms for different CD4+ human cell types. Yet the majority of the members of the same virus panel resisted 12G5 inhibition on T-cell lines. When inhibition was observed on these cell types, it was both cell type and virus strain dependent. In at least one situation, 12G5 failed to block LAI infection of cells expressing CXCR4 as the only available coreceptor. Our observations suggest that CXCR4 could be processed or presented differently depending on the cell type, allowing some strains to evade 12G5 inhibition. Alternatively, since several of the viruses could infect certain CXCR4- CD4+ cell lines, it is conceivable that alternative coreceptors are active, enabling individual HIV strains to choose between compatible coreceptors during entry into cells. Moreover, the strain dependency of 12G5 inhibition implies that the interaction of different HIVs with CXCR4 varies.

CD4-independent infection by HIV-2 is mediated by fusin/CXCR4

Several members of the chemokine receptor family have been shown to function in association with CD4 to permit HIV-1 entry and infection. However, the mechanism by which these molecules serve as CD4-associated cofactors is unclear. In the present report, we show that one member of this family, termed Fusin/ CXCR4, is able to function as an alternative receptor for some isolates of HIV-2 in the absence of CD4. This conclusion is supported by the finding that (1) CD4-independent infection by these viruses is inhibited by an anti-Fusin monoclonal antibody, (2) Fusin expression renders human and nonhuman CD4-negative cell lines sensitive to HIV-2-induced syncytium induction and/or infection, and (3) Fusin is selectively down-regulated from the cell surface following HIV-2 infection. The finding that one chemokine receptor can function as a primary viral receptor strongly suggests that the HIV envelope glycoprotein contains a binding site for these proteins and that differences in the affinity and/or the availability of this site can extend the host range of these viruses to include a number of CD4-negative cell types.

How do general practitioners qualify for their PGEA?

On average, general practitioners (GPs) achieved their five-day annual target for the postgraduate educational allowance (PGEA) mainly by attending short meetings in the disease management category. The pattern of uptake closely resembled that of provision, with relatively few meetings and attendances in the health promotion category. Sponsored meetings attracted more participants than non-sponsored ones, but mean attendances at all types of meetings were low. Implications and recommendations are discussed.

Cost effectiveness of personal health education in primary care for people with angina in the greater Belfast area of Northern Ireland

STUDY OBJECTIVE

To investigate the cost effectiveness of personal health education for angina patients being treated in general practice.

DESIGN

A randomised controlled trial in which people were randomised to intervention and control groups. All were assessed at the start and end of the study, with details recorded of disease status, coronary heart disease risk factors, and self assessed quality of life. A note was taken of their current use of drugs and over the course of the study their use of all health services. Those in the intervention group had three visits per year from a health visitor, whose brief was discuss ways of living more easily with their disease and in which risks of further events might be reduced.

PATIENTS

Altogether 688 patents in the Greater Belfast area aged less than 75 years and known to have angina for at least six months.

MAIN RESULTS

Significant improvements in survival and self assessed quality of life were found between the study and control groups. The intervention was associated with a reduction in drug usage and there was no significant difference between the intervention and control groups in terms of their use of other health services.

CONCLUSION

Given the improvement in survival and self assessed quality of life and no significant differences in costs to the health service between the two groups, the intervention was deemed to be cost effective.

Location, exposure, and conservation of neutralizing and nonneutralizing epitopes on human immunodeficiency virus type 2 SU glycoprotein

Eleven rat monoclonal antibodies (MAbs) that recognize the SU glycoprotein of human immunodeficiency virus type 2 (HIV-2) ROD were produced and characterized. Binding sites for eight of these MAbs were mapped to epitopes within the Cl, V1/V2, C2, and V3 envelope regions. The three other MAbs defined at least two conformation-dependent, strain-specific epitopes outside Vl/V2, V3, and the CD4-binding site. The MAbs were used to probe the tertiary structure of oligomeric envelope glycoprotein expressed on the surfaces of infected cells. Epitopes at the apices of V2 and V3 were exposed on the native molecule, whereas other epitopes on V1/V2, Cl, and C2 were hidden. The MAbs defined three neutralization targets on exposed domains: two linear epitopes in the V2 and the V3 loops and one conformational epitope outside V1, V2, and V3.

A comparison of three measures of perceived distress: results from a study of angina patients in general practice in Northern Ireland

OBJECTIVE

To establish the effect of health education on the level of distress felt by patients with angina and to compare the results obtained using different measures.

DESIGN

Randomised controlled trial of personal health education given every four months.

SETTING

Eighteen general practices in the greater Belfast area.

SUBJECTS

These comprised 688 patients aged less than 75 years and known to have had angina for at least six months: 342 were randomised to receive education and 346 no education.

MAIN OUTCOME MEASURES

These were the Nottingham health profile (NHP), functional limitation profile (FLP), and a simple categorical scale (SCS).

RESULTS

The intervention group showed a statistically significant improvement in health relative to the control group in terms of physical mobility and social isolation using the NHP. In terms of overall wellbeing, both the NHP and SCS results showed the intervention group had experienced statistically significant improvements in health relative to the control group. Results obtained using the NHP, FLP, and SCS were found to be correlated regardless of whether weighted or unweighted scores were used.

CONCLUSION

The intervention produced a significant improvement in health status. Results from different survey instruments were correlated using both weighted and unweighted scores. An SCS was capable of detecting the improvement in health status.