The inhibitory effect of RANTES on the infection of primary macrophages by R5 human immunodeficiency virus type-1 depends on the macrophage activation state

The macrophage in HIV-1 infection: from activation to deactivation?

Macrophages play a crucial role in innate and adaptative immunity in response to microorganisms and are an important cellular target during HIV-1 infection. Recently, the heterogeneity of the macrophage population has been highlighted. Classically activated or type 1 macrophages (M1) induced in particular by IFN-γ display a pro-inflammatory profile. The alternatively activated or type 2 macrophages (M2) induced by Th-2 cytokines, such as IL-4 and IL-13 express anti-inflammatory and tissue repair properties. Finally IL-10 has been described as the prototypic cytokine involved in the deactivation of macrophages (dM). Since the capacity of macrophages to support productive HIV-1 infection is known to be modulated by cytokines, this review shows how modulation of macrophage activation by cytokines impacts the capacity to support productive HIV-1 infection. Based on the activation status of macrophages we propose a model starting with M1 classically activated macrophages with accelerated formation of viral reservoirs in a context of Th1 and proinflammatory cytokines. Then IL-4/IL-13 alternatively activated M2 macrophages will enter into the game that will stop the expansion of the HIV-1 reservoir. Finally IL-10 deactivation of macrophages will lead to immune failure observed at the very late stages of the HIV-1 disease.

Human peritoneal macrophages from ascitic fluid can be infected by a broad range of HIV-1 isolates

Macrophages are major HIV target cells. They support both productive and latent HIV-1 infection. Susceptibility of primary macrophages to HIV depends on the anatomical location and activation state of the cells. We demonstrate that peritoneal macrophages (PMs) are abundant in ascitic fluid of patients with liver cirrhosis and are susceptible to HIV-1 infection. PMs expressed CD68, a differentiation marker, exhibited phagocytic activity, and survived in culture for 2 months without additional growth factors. Freshly isolated PMs were susceptible to HIV-1 R5 strains but not to X4-T-cell line-adapted strains. Interestingly, after 7 days in culture, PMs acquired susceptibility to X4-T-cell line-adapted strains. HIV entry inhibitors, TAK779 and AMD3100, blocked HIV infection of PMs, indicating that infection by R5 and X4 strains was mediated by CCR5 and CXCR4, respectively. Although PMs did not express detectable cell surface levels of CXCR4 and CCR5, they did express mRNAs of these HIV coreceptors and responded to stimulation by their natural ligands, SDF-1alpha and RANTES. PMs were susceptible to HIV-1 X4, R5, and X4R5 primary isolates. PMs after 7 days in culture produced greater amounts of X4 and X4R5 HIV than freshly isolated PMs. The day-7 PMs were more susceptible to R5 infection in a single-cycle infection assay, but there was no increase in viral production in a multiple-round infection assay. The level of CXCR4 mRNA and production of CC-chemokines (MIP-1alpha, MIP-1beta, and RANTES) increased significantly during 7 days in culture. Our results indicate that PMs are susceptible to receptor-mediated infection by a broad range of HIV strains. These primary macrophages could provide a valuable system for investigating the role of primary macrophages in HIV pathogenesis.

Structural and functional studies of the potent anti-HIV chemokine variant P2-RANTES

The N-terminal region of the chemokine RANTES is critical for its function. A synthesized N-terminally modified analog of RANTES, P2-RANTES, was discovered using a phage display selection against living CCR5-expressing cells, and has been reported to inhibit HIV-1 env-mediated cell-cell fusion at subnanomolar levels (Hartley et al. J Virol 2003;77:6637-6644). In the present study we produced this protein using E. coli overexpression and extensively studied its structure and function. The x-ray crystal structure of P2-RANTES was solved and refined at 1.7 A resolution. This protein was found to be predominantly a monomer in solution by analytical ultracentrifugation, but a tetramer in the crystal. In studies of glycosaminoglycan binding, P2-RANTES was found to be significantly less able to bind heparin than wild type RANTES. We also tested this protein for receptor internalization where it was shown to be functional, in cell-cell fusion assays where recombinant P2-RANTES was a potent fusion inhibitor (IC(50) = 2.4 +/- 0.8 nM), and in single round infection assays where P2-RANTES inhibited at subnanomolar levels. Further, in a modified fusion assay designed to test specificity of inhibition, P2-RANTES was also highly effective, with a 65-fold improvement over the fusion inhibitor C37, which is closely related to the clinically approved inhibitor T-20. These studies provide detailed structural and functional information for this novel N-terminally modified chemokine mutant. This information will be very useful in the development of more potent anti-HIV agents. PDB Accession Number: 2vxw.

Interaction of RANTES with syndecan-1 and syndecan-4 expressed by human primary macrophages

Interaction of RANTES with its membrane ligands or receptors transduces multiple intracellular signals. Whether RANTES uses proteoglycans (PGs) belonging to the syndecan family to attach to primary cells expressing RANTES G-protein-coupled receptors (GPCRs) was investigated. We demonstrate that RANTES specifically binds to high and low affinity binding sites on human monocyte-derived macrophages (MDM). We show by co-immunoprecipitation experiments that RANTES is associated on these cells with syndecan-1 and syndecan-4, but neither with syndecan-2 nor with betaglycan, in addition to CD44 and its GPCRs, CCR5 and CCR1. Glycosaminidases pre-treatment of the monocyte derived-macrophages strongly decreases the binding of RANTES to syndecan-1 and syndecan-4 and also to CCR5, and abolishes RANTES binding to CD44. This suggests that glycosaminoglycans (GAGs) are involved in RANTES binding to the PGs and that such bindings facilitate the subsequent interaction of RANTES with CCR5, on the MDM, characterized by low membrane expression of CCR5. The role of these interactions in the pathophysiology of RANTES deserves further study.

Macrophages and lymphocytes differentially modulate the ability of RANTES to inhibit HIV-1 infection

The beta-chemokines MIP-1alpha, MIP-1beta, and RANTES inhibit HIV-1 infection of CD4+ T cells by inhibiting interactions between the virus and CCR5 receptors. However, while beta-chemokine-mediated inhibition of HIV-1 infection of primary lymphocytes is well documented, conflicting results have been obtained using primary macrophages as the virus target. Here, we show that the beta-chemokine RANTES inhibits virus entry into both cellular targets of the virus, lymphocytes and macrophages. However, while virus entry is inhibited at the moment of infection in both cell types, the amount of virus progeny is lowered only in lymphocytes. In macrophages, early-entry restriction is lost during long-term cultivation, and the amount of virus produced by RANTES-treated macrophages is similar to the untreated cultures, suggesting an enhanced virus replication. We further show that at least two distinct cellular responses to RANTES treatment in primary lymphocytes and macrophages contribute to this phenomenon. In lymphocytes, exposure to RANTES significantly increases the pool of inhibitory beta-chemokines through intracellular signals that result in increased production of MIP-1alpha and MIP-1beta, thereby amplifying the antiviral effects of RANTES. In macrophages this amplification step does not occur. In fact, RANTES added to the macrophages is efficiently cleared from the culture, without inducing synthesis of beta-chemokines. Our results demonstrate dichotomous effects of RANTES on HIV-1 entry at the moment of infection, and on production and spread of virus progeny in primary macrophages. Since macrophages serve as a reservoir of HIV-1, this may contribute to the failure of endogenous chemokines to successfully eradicate the virus.

HIV coreceptors: role of structure, posttranslational modifications, and internalization in viral-cell fusion and as targets for entry inhibitors

The human immunodeficiency virus (HIV) envelope glycoprotein forms trimers on the virion surface, with each monomer consisting of two subunits, gp120 and gp41. The gp120 envelope component binds to CD4 on target cells and undergoes conformational changes that allow gp120 to interact with certain G-protein-coupled receptors (GPCRs) on the same target membranes. The GPCRs that function as HIV coreceptors were found to be chemokine receptors. The primary coreceptors are CCR5 and CXCR4, but several other chemokine receptors were identified as "minor coreceptors", indicating their ability support entry of some HIV strains in tissue cultures. Formation of the tri-molecular complexes stabilizes virus binding and triggers a series of conformational changes in gp41 that facilitate membrane fusion and viral cell entry. Concerted efforts are underway to decipher the specific interactions between gp120/CD4, gp120/coreceptors, and their contributions to the subsequent membrane fusion process. It is hoped that some of the transient conformational intermediates in gp120 and gp41 would serve as targets for entry inhibitors. In addition, the CD4 and coreceptors are primary targets for several classes of inhibitors currently under testing. Our review summarizes the current knowledge on the interactions of HIV gp120 with its receptor and coreceptors, and the important properties of the chemokine receptors and their regulation in primary target cells. We also summarize the classes of coreceptor inhibitors under development.

Human immunodeficiency virus type 1 attachment, coreceptor, and fusion inhibitors are active against both direct and trans infection of primary cells

Inhibitors of human immunodeficiency virus type 1 attachment (CD4-immunoglobulin G subclass 2), CCR5 usage (PRO 140), and fusion (T-20) were tested on diverse primary cell types that represent the major targets both for infection in vivo and for the inhibition of trans infection of target cells by virus bound to dendritic cells. Although minor cell-type-dependent differences in potency were observed, each inhibitor was active on each cell type and trans infection was similarly vulnerable to inhibition at each stage of the fusion cascade.

Vpr- and Nef-dependent induction of RANTES/CCL5 in microglial cells

Microglia are pivotal in the pathogenesis of AIDS dementia, as they serve as the major target of HIV infection in the CNS. In addition, activation of microglia correlates best with clinical dementia. Although the beta-chemokine RANTES/CCL5 is important in modulating HIV infection as well as cellular activation, no information is available regarding how its expression is regulated in microglia by HIV-1. Here we report that RANTES/CCL5 expression is induced in microglia by HIV-1, but that this requires infection by HIV-1. This conclusion was supported by (1) the delayed kinetics coinciding with viral replication; (2) the lack of effect of X4 viruses; (3) inhibition by the reverse transcriptase inhibitor AZT, and (4) the lack of effect of cytokine antagonists or antibodies. Interestingly, RANTES/CCL5 production was dependent on the viral accessory protein Vpr, in addition to Nef, demonstrating a novel role for Vpr in chemokine induction in primary macrophage-type cells. Furthermore, the specific p38 MAP kinase inhibitor SB203580 augmented chemokine expression in microglia, indicating a negative role played by p38. These data suggest unique features of RANTES/CCL5 regulation by HIV-1 in human microglial cells.

Human alpha-fetoprotein binds to primary macrophages

We have previously reported that alpha-fetoprotein (AFP) inhibits infection of human monocyte-derived macrophages (MDM) by R5-HIV-1 strains and that a peptide mimicking the clade B HIV-1 gp120 consensus V3 domain (V3Cs) binds to CCR5. We demonstrate here that AFP binds high- and low-affinity binding sites of MDM, characterized, respectively, by 5.15 and 100nM K(d) values. Heat denaturation or neuraminidase treatment of AFP inhibits this binding, suggesting the involvement of protein-protein and lectin-carbohydrate interactions. Moreover, AFP displaces V3Cs binding to MDM. In addition, MIP-1beta, the most specific CCR5 ligand, displaces AFP binding to MDM (IC(50)=4.3nM). Finally, we demonstrate that AFP binds to a ligand of HIV-gp120 V3Cs domain, CCR5, expressed by MDM and by HeLa cells expressing CCR5. Such binding is not observed in the presence of HeLa cells lacking CCR5. The present results provide strong evidence that AFP directly binds to CCR5 expressed by human primary macrophages and by transfected CCR5+ HeLa cells.

GM-CSF and M-CSF modulate beta-chemokine and HIV-1 expression in microglia

Significant numbers of patients with acquired immunodeficiency syndrome (AIDS) develop CNS infection primarily in macrophages and microglial cells. Therefore, the regulation of human immunodeficiency virus type 1 (HIV-1) infection and activation of the brain mononuclear phagocytes subsequent to infection are important areas of investigation. In the current report, we studied the role of granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage-CSF (M-CSF) in the expression of antiviral beta-chemokines and HIV-1 p24 in cultures of primary human fetal microglia. We found that stimulation with GM-CSF or M-CSF induced macrophage inflammatory proteins (MIP-1alpha and MIP-1beta) and augmented RANTES expression, after HIV-1 infection of microglia. This was not due to the effect of GM-CSF on viral expression because GM-CSF was neither necessary nor stimulatory for viral infection, nor did GM-CSF enhance the expression of env-pseudotyped reporter viruses. Blocking GM-CSF-induced microglial proliferation by nocodazole had no effect on beta-chemokine or p24 expression. The functional significance of the GM-CSF-induced beta-chemokines was suggested by the finding that, in the presence of GM-CSF, exogenous beta-chemokines lost their anti-HIV-1 effects. We further show that although HIV-1-infected microglia produced M-CSF, they failed to produce GM-CSF. In vivo, GM-CSF expression was localized to activated astrocytes and some inflammatory cells in HIV-1 encephalitis, suggesting paracrine activation of microglia through GM-CSF. Our results demonstrate a complex interplay between CSFs, chemokines, and virus in microglial cells and may have bearing on the interpretation of data derived in vivo and in vitro.

Synthesis and characterization of biologically functional biotinylated RANTES

Development of specifically labeled chemokines that retain their biological properties should be useful for analyzing their mechanisms of action both under physiological and pathological conditions. Here, we report the chemical synthesis and characterization of RANTES (regulated upon activation normal T cell expressed and secreted) derivatives that were biotinylated at residues 1, 25, 33, 45, or 67. Gel filtration and ultracentrifugation experiments showed that biotinylation at position 45 or 67 decreased the aggregation tendency of the chemokine to a dimeric state. Competition experiments, using a stably transfected CHO-K1 cell line overexpressing human CCR5, a RANTES receptor, indicated that derivatives biotinylated at positions 1, 25, and 67 bound to CCR5 with the same affinity as native RANTES. Flow cytometry analysis showed that RANTES biotinylated at residue 67 (B67-RANTES) bound more efficiently to primary macrophages than the other derivatives. Such binding was dependent on cell surface glycosaminoglycans (GAGs) since it was reduced when macrophages or HeLa cells expressing or not CCR5 were first treated with GAG-specific enzymes. In addition, B67-RANTES modulated CCR5 expression on lymphocytes and elicited chemotaxis of monocytes in the same manner as unmodified RANTES. Thus, B67-RANTES acts as a CCR5 agonist and may be useful to study the role of RANTES in pathologies such as, for example, human immunodeficiency virus (HIV) infection and inflammatory disorders.

Involvement of integrin alphavbeta3 in the pathogenesis of human immunodeficiency virus type 1 infection in monocytes

Attachment of HIV to macrophages is a critical early event in the establishment of infection. In the present study, we demonstrate the involvement of integrin alphavbeta3 (vitronectin receptor) in HIV infection of peripheral blood monocyte-derived macrophages. Culturing monocytes in the presence of M-CSF for 3 days upregulated expression of the alphav-containing integrins, alphavbeta3 and alphavbeta5. The increase in alphavbeta3 expression was accompanied by increased HIV-1 replication by monocytes. Immunoblot analysis showed that purified HIV-gp120 protein interacted with CD4 and alphavbeta3 in immunoprecipitation experiments. Neutralizing antibodies against the alphavbeta3 integrin interfered with the coprecipitation of alphavbeta3 with an anti-gp120 antibody and substantially inhibited HIV infection of monocytes. Neutralizing antibodies against alphavbeta5 or beta1 integrins did not significantly affect HIV infection. These results indicate that HIV infection of primary monocytes requires differentiation of these cells and may involve alphavbeta3 interaction with the HIV-1 envelope protein gp120 for productive infection.

Association of chemokine-mediated block to HIV entry with coreceptor internalization

Chemokines inhibit entry of HIV into CD4(+) T cells more effectively than into macrophages or transfected adherent cells. Here, we tested whether chemokine receptor internalization could account for cell type differences in the effectiveness of chemokines. Infection of CEM T cells expressing stably transduced wild-type CCR5 was much more readily inhibited by chemokine than were transduced HOS cells. This response correlated with the efficiency of CCR5 internalization. A mutated CCR5, termed M7-CCR5, in which the Ser/Thr phosphorylation sites in the cytoplasmic tail were changed to Ala, did not internalize in response to MIP-1alpha. M7-CCR5 was expressed at slightly higher levels than wild-type on stably transduced cell lines and was somewhat more potent as an HIV-1 coreceptor. The mutated receptor mobilized intracellular Ca(2+) in response to chemokine to a level 4-fold higher than did the wild type CCR5. Unexpectedly, the receptor was desensitized as efficiently as wild type, suggesting that desensitization does not require cytoplasmic tail phosphorylation. Entry of R5 HIV-1 reporter virus into cells stably expressing M7-CCR5 was largely resistant to blocking by MIP-1alpha. As much as 80% of entry inhibition was attributed to receptor internalization. Aminooxypentane (AOP)-MIP-1alpha was able to induce a low level of M7-CCR5 internalization in HOS and to weakly inhibit HIV-1 entry. Introduction of dominant negative dynamin into HOS cells reduced the ability of chemokine to inhibit infection. The inefficiency of internalization of chemokine receptors in some cell types could allow virus to replicate in vivo in the presence of endogenous chemokine. Last, M7-CCR5 is a useful tool for discriminating coreceptor internalization from binding site masking in the evaluation of small molecule inhibitors of HIV-1 entry.

Hemofiltrate CC chemokine 1[9-74] causes effective internalization of CCR5 and is a potent inhibitor of R5-tropic human immunodeficiency virus type 1 strains in primary T cells and macrophages

Proteolytic processing of the abundant plasmatic human CC chemokine 1 (HCC-1) generates a truncated form, HCC-1[9-74], which is a potent agonist of CCR1, CCR3, and CCR5; promotes calcium influx and chemotaxis of T lymphoblasts, monocytes, and eosinophils; and inhibits infection by CCR5-tropic human immunodeficiency virus type 1 (HIV-1) isolates. In the present study we demonstrate that HCC-1[9-74] interacts with the second external loop of CCR5 and inhibits replication of CCR5-tropic HIV-1 strains in both primary T cells and monocyte-derived macrophages. Low concentrations of the chemokine, however, frequently enhanced the replication of CCR5-tropic HIV-1 isolates but not the replication of X4-tropic HIV-1 isolates. Only HCC-1[9-74] and HCC-1[10-74], but not other HCC-1 length variants, displayed potent anti-HIV-1 activities. Fluorescence-activated cell sorter analysis revealed that HCC-1[9-74] caused up to 75% down-regulation of CCR5 cell surface expression, whereas RANTES (regulated on activation, normal T-cell expressed and secreted) achieved a reduction of only about 40%. Studies performed with green fluorescent protein-tagged CCR5 confirmed that both HCC-1[9-74] and RANTES, but not full-length HCC-1, mediated specific internalization of the CCR5 HIV-1 entry cofactor. Our results demonstrate that the interaction with HCC-1[9-74] causes effective intracellular sequestration of CCR5, but they also indicate that the effect of HCC-1[9-74] on viral replication is subject to marked cell donor- and HIV-1 isolate-dependent variations.

Role of N-glycans and SDF-1alpha on the coassociation of CD4 with CXCR4 at the plasma membrane of monocytic cells and blood lymphocytes

CXCR4 is a coreceptor, along with CD4, for human immunodeficiency virus type 1 (HIV-1). Trimolecular complexes between HIV-1 glycoprotein (gp)120, CD4 and CXCR4 constitute a prerequisite for HIV entry. We studied whether CD4 is associated with CXCR4 on CD4+ CXCR4+ cells. Using the conformation-dependent anti-CXCR4 mAb 12G5, CD4 was coimmunoprecipitated with CXCR4 from the membrane of U937 cells which support HIV-1(LAI) efficient infection, and from that of peripheral blood lymphocytes (PBL). CD4 association with CXCR4 increased upon PBL coculture for 5 days with autologous monocytes, decreased upon treatment of the cells or the CD4-CXCR4 complex with either N-glycanase or stromal cell derived factor-1alpha (SDF-1alpha) and was abolished by incubation of the cells with both, N-glycanase and SDF-1alpha. This indicates that glycans are partly involved in CD4 association with CXCR4 and may partly explain the inhibitory effect of SDF-1alpha on HIV infection.

CD40-activated macrophages become highly susceptible to X4 strains of human immunodeficiency virus type 1

Activating cells of the immune system may stimulate human immunodeficiency virus type 1 (HIV-1) replication and contribute to select pathogenic variants in vivo. Here, we examined the possible effect of a major pathway of immune activation, CD40 interaction with its ligand (CD40L), on the susceptibility of monocyte-derived macrophages (MDMs) to various HIV-1 strains. Stimulation of MDMs with CD40L led to reduced replication of R5 HIV-1(Ba-L), whereas this strongly enhanced the replication of X4 HIV-1(Lai) as well as of X4 primary isolates, and this was associated with strong cytopathic effects. The replication of X4 strains was inhibited by stromal cell-derived factor 1, an indication of the restricted usage of CXCR4 as virus coreceptor in this case. CD40L induced the activation of mitogen-activated protein kinases ERK1/ERK2 and stimulated MDMs to secrete RANTES (regulated on activation, normal T cell expressed and secreted), macrophage inflammatory protein 1alpha (MIP-1alpha), MIP-1beta, interleukin 6 (IL-6), IL-1beta, and tumor necrosis factor alpha. From this data, it may be hypothesized that activated macrophages represent a favorable environment for the replication of classically T lymphocyte-tropic X4 variants and, thus, may contribute significantly to the selection of such variants at late stages of clinical HIV-1 infection.

Binding of LFA-1 (CD11a) to intercellular adhesion molecule 3 (ICAM-3; CD50) and ICAM-2 (CD102) triggers transmigration of human immunodeficiency virus type 1-infected monocytes through mucosal epithelial cells

Transmigration of human immunodeficiency virus (HIV)-infected mononuclear cells through the genital mucosa is one of the possible mechanisms of sexual transmission of HIV. Here, we investigated the transmigration of cell-associated R5-tropic HIV type 1 (HIV-1) through a tight monolayer of human epithelial cells in vitro. We show that this process is dependent on an initial interaction between alphaLbeta2 integrin CD11a/CD18 on infected monocytic cells and intercellular adhesion molecule 2 (ICAM-2; CD102) and ICAM-3 (CD50) on the apical membrane of epithelial cells. The CD50 and CD102 ligands were overexpressed on epithelial cells when the cells were activated by proinflammatory cytokines in the cellular microenvironment. An accumulation of proviral DNA was found in the transmigrated cells, clearly reflecting the preferential transepithelial migration of HIV-1-infected cells under proinflammatory conditions. Our observations provide new insights supporting the hypothesis that HIV-infected mononuclear cells contained in genital secretions from infected individuals may cross the epithelial genital mucosa of an exposed receptive sexual partner, particularly under inflammatory conditions of damaged genital tissue. Understanding the fundamental aspects of the initial HIV entry process during sexual transmission remains a critical step for preventing human infection and developing further vaccinal strategies and virucidal agents.

Human immunodeficiency virus type-1 and chemokines: beyond competition for common cellular receptors

The chemokines and their receptors have been receiving exceptional attention in recent years following the discoveries that some chemokines could specifically block human immunodeficiency virus type 1 (HIV-1) infection and that certain chemokine receptors were the long-sought coreceptors which, along with CD4, are required for the productive entry of HIV-1 and HIV-2 isolates. Several chemokine receptors or orphan chemokine receptor-like molecules can support the entry of various viral strains, but the clinical significance of the CXCR4 and CCR5 coreceptors appear to overshadow a critical role for any of the other coreceptors and all HIV-1 and HIV-2 strains best employ one or both of these coreceptors. Binding of the HIV-1 envelope glycoprotein gp120 subunit to CD4 and/or an appropriate chemokine receptor triggers conformational changes in the envelope glycoprotein oligomer that allow it to facilitate the fusion of the viral and host cell membranes. During these interactions, gp120 appears to be capable of inducing a variety of signaling events, all of which are still not defined in detail. In addition, the more recently observed dichotomous effects, of both inhibition and enhancement, that chemokines and their receptor signaling events elicit on the HIV-1 entry and replication processes has once again highlighted the intricate and complex balance of factors that govern the pathogenic process. Here, we will review and discuss these new observations summarizing the potential significance these processes may have in HIV-1 infection. Understanding the complexities and significance of the signaling processes that the chemokines and viral products induce may substantially enhance our understanding of HIV-1 pathogenesis, and perhaps facilitate the discovery of new ways for the prevention and treatment of HIV-1 disease.

Human alpha1-acid glycoprotein binds to CCR5 expressed on the plasma membrane of human primary macrophages

We have reported previously that human alpha(1)-acid glycoprotein (AGP) inhibits the infection of human monocyte-derived macrophages (MDM) by R5 HIV-1, and that a disulphide-bridged peptide mimicking the clade B HIV-1 gp120 consensus V3 domain (V3Cs) binds specifically to CCR5 (the major co-receptor of R5 HIV strains) on these cells [Seddiki, Rabehi, Benjouad, Saffar, Ferriere, Gluckman and Gattegno (1997) Glycobiology 7, 1229-1236]. The present study demonstrates that AGP binds specifically to MDM at high- and low-affinity binding sites with K(d) values of 16 nM and 4.9 microM respectively. The fact that heat denaturation of AGP only partly inhibited this binding (43%) suggests that protein-protein interactions are involved, as well as AGP glycans which are resistant to heat denaturation. Mannan, but not dextran, is a significant inhibitor (52%) of this binding, and sequential exoglycosidase treatment of AGP, which exposes penultimate mannose residues, has a strong stimulatory effect ( approximately 2.8-fold). Therefore AGP glycans (probably mannose residues) are involved, at least partly, in the binding of AGP to MDM. In addition, AGP inhibits the binding of V3Cs and macrophage inflammatory protein-1beta (MIP-1beta) to MDM. The anti-CCR5 monoclonal antibody 2D7, specific for the second extracellular loop of CCR5, also inhibited AGP binding (67%), whereas anti-CCR5 antibodies specific for the C-terminus of CCR5 region had no effect. Native AGP, like V3Cs (but not heat-denatured AGP), binds to 46 and 33-36 kDa electroblotted AGP-bound MDM membrane ligands, characterized as CCR5 by their interactions with anti-CCR5 antibodies and with MIP-1beta. Therefore both AGP glycans and MDM CCR5 are involved in the binding of AGP to MDM. This suggests that the inhibitory effect of AGP on the infection of human primary macrophages by R5 HIV-1 may be related to specific binding of AGP to a macrophage membrane lectin or lectin-like component and to CCR5.

Optimal inhibition of X4 HIV isolates by the CXC chemokine stromal cell-derived factor 1 alpha requires interaction with cell surface heparan sulfate proteoglycans

The chemokine stromal cell-derived factor 1 (SDF-1) is the natural ligand for CXC chemokine receptor 4 (CXCR4). SDF-1 inhibits infection of CD4+ cells by X4 (CXCR4-dependent) human immunodeficiency virus (HIV) strains. We previously showed that SDF-1 alpha interacts specifically with heparin or heparan sulfates (HSs). Herein, we delimited the boundaries of the HS-binding domain located in the first beta-strand of SDF-1 alpha as the critical residues. We also provide evidence that binding to cell surface heparan sulfate proteoglycans (HSPGs) determines the capacity of SDF-1 alpha to prevent the fusogenic activity of HIV-1 X4 isolates in leukocytes. Indeed, SDF-1 alpha mutants lacking the capacity to interact with HSPGs showed a substantially reduced capacity to prevent cell-to-cell fusion mediated by X4 HIV envelope glycoproteins. Moreover, the enzymatic removal of cell surface HS diminishes the HIV-inhibitory capacity of the chemokine to the levels shown by the HS-binding-disabled mutant counterparts. The mechanisms underlying the optimal HIV-inhibitory activity of SDF-1 alpha when attached to HSPGs were investigated. Combining fluorescence resonance energy transfer and laser confocal microscopy, we demonstrate the concomitant binding of SDF-1 alpha to CXCR4 and HSPGs at the cell membrane. Using FRET between a Texas Red-labeled SDF-1 alpha and an enhanced green fluorescent protein-tagged CXCR4, we show that binding of SDF-1 alpha to cell surface HSPGs modifies neither the kinetics of occupancy nor activation in real time of CXCR4 by the chemokine. Moreover, attachment to HSPGs does not modify the potency of the chemokine to promote internalization of CXCR4. Attachment to cellular HSPGs may co-operate in the optimal anti-HIV activity of SDF-1 alpha by increasing the local concentration of the chemokine in the surrounding environment of CXCR4, thus facilitating sustained occupancy and down-regulation of the HIV coreceptor.

The maturation of dendritic cells results in postintegration inhibition of HIV-1 replication

Maturation of dendritic cells (DC) is known to result in decreased capacity to produce HIV due to postentry block of its replicative cycle. In this study, we compared the early phases of this cycle in immature DC (iDC) and mature DC (mDC) generated from monocytes cultured with GM-CSF and IL-4, trimeric CD40 ligand (DC(CD40LT)), or monocyte-conditioned medium (DC(MCM)) being added or not from day 5. Culture day 8 cells exposed to X4 HIV-1(LAI) or R5 HIV-1(Ba-L) were analyzed by semiquantitative R-U5 PCR, which detects total HIV DNA. CXC chemokine receptor 4(low) (CXCR4(low)) CCR5(+) iDC harbored similar viral DNA amounts when exposed to either strain. HIV-1(LAI) entered more efficiently into DC(CD40LT) or DC(MCM) with up-regulated CXCR4. CCR5(low) DC(CD40LT) still allowed entry of HIV-1(Ba-L), whereas CCR5(-) DC(MCM) displayed reduced permissivity to this virus. Comparing amounts of late (long terminal repeat (LTR)-gag PCR) and total (R-U5 PCR) viral DNA products showed that HIV-1(Ba-L) reverse transcription was more efficient than that of HIV-1(LAI), but was not affected by DC maturation. Southern blot detection of linear, circular, and integrated HIV DNA showed that maturation affected neither HIV-1 nuclear import nor integration. When assessing virus transcription by exposing iDC to pNL4-3.GFP or pNL4-3.Luc viruses pseudotyped with the G protein of vesicular stomatitis virus (VSV-G), followed by culture with or without CD40LT or MCM, GFP and luciferase activities decreased by 60-75% in mDC vs iDC. Thus, reduced HIV replication in mDC is primarily due to a postintegration block occurring mainly at the transcriptional level. We could not relate this block to altered expression and nuclear localization of NF-kappa B proteins and SP1 and SP3 transcription factors.

Glycans are involved in RANTES binding to CCR5 positive as well as to CCR5 negative cells

We show that cell surface glycans, sialic acid and mannose-containing species, are involved beside glycosaminoglycans (GAGs), heparan sulfate and chondroitin sulfate in the binding of full length (1--68) RANTES not only to CCR5 positive human primary lymphocytes or macrophages but also to CCR5 negative monocytic U937 cells. Pretreating the cells with neuraminidase, heparitinase, chondroitinase or adding soluble glycans such as mannan or GAGs (heparin or chondroitin sulfate), significantly inhibited RANTES binding. Such effects were not observed with truncated (10--68) RANTES. Heat-denaturation of (1--68) RANTES strongly decreased its binding to the cells, demonstrating involvement of the three-dimensional structure. Accordingly, full length, but not truncated (10--68) RANTES, specifically bound to soluble mannan as well as to mannose-divinylsulfone-agarose affinity matrix and to soluble heparin or chondroitin sulfate as well as to heparin-agarose. Soluble heparin exerts, depending on its concentration, inhibitory or enhancing effects on RANTES binding to mannose-divinylsulfone-agarose, which indicates that RANTES interaction with glycans is modulated by GAGs. These data demonstrate that full length RANTES, but not its (10--68) truncated counterpart, interacts with glycans and GAGs, in soluble forms or presented either by affinity matrices or CCR5 positive as well as CCR5 negative cells.

The susceptibility of macrophages to human immunodeficiency virus type 1 X4 isolates depends on their activation state

The demonstration that macrophages express CXCR4 has led to a reexamination of their susceptibility to human immunodeficiency (HIV)-1 X4 strains. Here, we examined the susceptibility to X4 HIV-1Lai of two previously characterized macrophage populations, obtained either as 1) adherent cells of five-day cultures of blood mononuclear cells (PBMC), followed by two days without nonadherent PBMC nor added cytokines (MDM-5d); or 2) as adherent cells recovered from one-hour incubation of PBMC, which were cultured for seven days with macrophage colony-stimulating factor (MDM-MCSF). Exposing MDM-5d or MDM-MCSF to HIV-1Lai did not lead to productive infection, as indicated by a lack of (MDM-MCSF) or low (MDM-5d) viral p24 levels in culture supernatants. However, MDM-5d vigorously transmitted HIV-1 Lai to autologous T lymphocytes, which was not the case of HIV-1Lai-exposed MDM-MCSF. PCR analysis of the LTR RU5 region showed that X4 HIV-1Lai entered into both types of macrophages in the same manner as R5 HIV-1 BaL. However, in contrast to MDM-5d, there was a block of HIV-1 Lai retrotransciption in MDM-MCSF. Cytokine profile analysis of the two types of macrophages showed that TNF-alpha, IL-6 and RANTES levels were higher in MDM-5d than in MDM-MSCF, while the IL10 level was higher in MDM-MCSF, both producing similar IL16 levels. Altogether, these data indicate that HIV-1 X4 strains enter into macrophages but that their replication is blocked thereafter in a different manner according to the activation status of the cells.

Potent, broad-spectrum inhibition of human immunodeficiency virus type 1 by the CCR5 monoclonal antibody PRO 140

CCR5 serves as a requisite fusion coreceptor for clinically relevant strains of human immunodeficiency virus type 1 (HIV-1) and provides a promising target for antiviral therapy. However, no study to date has examined whether monoclonal antibodies, small molecules, or other nonchemokine agents possess broad-spectrum activity against the major genetic subtypes of HIV-1. PRO 140 (PA14) is an anti-CCR5 monoclonal antibody that potently inhibits HIV-1 entry at concentrations that do not affect CCR5's chemokine receptor activity. In this study, PRO 140 was tested against a panel of primary HIV-1 isolates selected for their genotypic and geographic diversity. In quantitative assays of viral infectivity, PRO 140 was compared with RANTES, a natural CCR5 ligand that can inhibit HIV-1 entry by receptor downregulation as well as receptor blockade. Despite their divergent mechanisms of action and binding epitopes on CCR5, low nanomolar concentrations of both PRO 140 and RANTES inhibited infection of primary peripheral blood mononuclear cells (PBMC) by all CCR5-using (R5) viruses tested. This is consistent with there being a highly restricted pattern of CCR5 usage by R5 viruses. In addition, a panel of 25 subtype C South African R5 viruses were broadly inhibited by PRO 140, RANTES, and TAK-779, although approximately 30-fold-higher concentrations of the last compound were required. Interestingly, significant inhibition of a dualtropic subtype C virus was also observed. Whereas PRO 140 potently inhibited HIV-1 replication in both PBMC and primary macrophages, RANTES exhibited limited antiviral activity in macrophage cultures. Thus CCR5-targeting agents such as PRO 140 can demonstrate potent and genetic-subtype-independent anti-HIV-1 activity.

Soluble glycosaminoglycans Do not potentiate RANTES antiviral activity on the infection of primary macrophages by human immunodeficiency virus type 1

Macrophages play an important role in human immunodeficiency virus (HIV)-1 infection. They exist in various differentiation and activation states in vivo, a heterogeneity that may affect their interactions with HIV-1 and susceptibility to drugs. Here, we found that RANTES and MIP-1beta, heparin, or soluble chondroitin sulfate B, but not chondroitin sulfate A, inhibited HIV-1(BaL) infection of macrophages obtained as the adherent cells of 5-day cultures of blood mononuclear cells (PBMC), followed by 2 days without either nonadherent PBMC or added cytokines (MDM-5d), whereas they did not affect infection of macrophages obtained as the adherent cells recovered from 1-h incubation of PBMC and subsequent 7-day culture with macrophage colony-stimulating factor (MDM-MCSF). Such different behavior was not related to differences in HIV-1 binding but rather to postbinding steps, as HIV-1(BaL) attached similarly to MDM-5d and MDM-MCSF, a binding that was affected by soluble glycosaminoglycans but not by RANTES. Of note, CCR5 expression on both types of MDM was comparable, and it was not downregulated by RANTES on either. Mixing RANTES with each of the glycosaminoglycans did not restore inhibition of MDM-MCSF infection by HIV-1; however, heparin at concentrations that had low antiviral activity for MDM-5d counteracted RANTES anti-HIV-1 activity for these cells, whereas chondroitin sulfate B had no additive effect on that of RANTES. Both glycosaminoglycans affected RANTES binding to MDM. Thus, in contrast to cell surface proteoglycans that contribute to the attachment of RANTES to macrophages and enhance its anti-HIV-1 activity, soluble glycosaminoglycans do not facilitate, and may even offset, the anti-HIV-1 activity of RANTES.

Glycans and proteoglycans are involved in the interactions of human immunodeficiency virus type 1 envelope glycoprotein and of SDF-1alpha with membrane ligands of CD4(+) CXCR4(+) cells

We demonstrate that human immunodeficiency virus HIV-1(LAI) envelope glycoprotein 120 (gp120(LAi)) specifically interacts with several membrane ligands on lymphoid CEM or monocytic U937 cells in addition to its previously identified receptor, CD4, and CXCR4, its coreceptor. In its native state, gp120(LAI) is able to elicit specific multimolecular complexes with these membrane ligands at the surface of the cells; most of the interactions are abolished by mannan or heparin but not by dextran. Similarly, stromal cell-derived factor (SDF)-1alpha interacts not only with CXCR4 expressed by CXCR4(+) CD4(+) U937, CEM, and HOS-CD4(+) CXCR4(+) cells but also with CD4 expressed by intact U937, CEM, and HOS-CD4(+) CXCR4(+/-) cells or electroblotted onto Immobilon. SDF-1alpha binding to CD4(+) CXCR4(+/-) cells, or soluble CD4 electroblotted onto Immobilon, is significantly inhibited by sCD4, whereas truncated sCD4 lacking D3 and D4 domains had no significant effect, which indicates that SDF-1 binds to CD4 but at regions different from the HIV-gp120-binding site. Heparin and mannan also inhibit SDF-1alpha binding to intact CD4(+) CXCR4(+/-) cells, and electroblotted soluble CD4. Heparitinase treatment of such cells reduced SDF-1alpha binding. These data demonstrate that glycans and glycosaminoglycans are directly or indirectly involved in the interactions of HIV-1 gp120(LAI) and of SDF-1alpha with membrane ligands of CD4(+) CXCR4(+) cells and thus could play a role both in HIV-1 infection and in the physiology of SDF-1alpha.

Soluble complexes of regulated upon activation, normal T cells expressed and secreted (RANTES) and glycosaminoglycans suppress HIV-1 infection but do not induce Ca(2+) signaling

Chemokines comprise a family of low-molecular-weight proteins that elicit a variety of biological responses including chemotaxis, intracellular Ca(2+) mobilization, and activation of tyrosine kinase signaling cascades. A subset of chemokines, including regulated upon activation, normal T cell expressed and secreted (RANTES), macrophage inflammatory protein-1alpha (MIP-1alpha), and MIP-1beta, also suppress infection by HIV-1. All of these activities are contingent on interactions between chemokines and cognate seven-transmembrane spanning, G protein-coupled receptors. However, these activities are strongly inhibited by glycanase treatment of receptor-expressing cells, indicating an additional dependence on surface glycosaminoglycans (GAG). To further investigate this dependence, we examined whether soluble GAG could reconstitute the biological activities of RANTES on glycanase-treated cells. Complexes formed between RANTES and a number of soluble GAG failed to induce intracellular Ca(2+) mobilization on either glycanase-treated or untreated peripheral blood mononuclear cells and were unable to stimulate chemotaxis. In contrast, the same complexes demonstrated suppressive activity against macrophage tropic HIV-1. Complexes composed of (125)I-labeled RANTES demonstrated saturable binding to glycanase-treated peripheral blood mononuclear cells, and such binding could be reversed partially by an anti-CCR5 antibody. These results suggest that soluble chemokine-GAG complexes represent seven-transmembrane ligands that do not activate receptors yet suppress HIV infection. Such complexes may be considered as therapeutic formulations for the treatment of HIV-1 infection.

HIV infection and pathogenesis: what about chemokines?

Several chemotactic cytokines, or chemokines. inhibit HIV replication by blocking or down regulating chemokine receptors that serve as entry cofactors for the virus. Although the role of chemokine receptors in HIV pathogenesis has been the subject of intense interest, chemokines are comparatively less seriously considered as potential correlates of protection from HIV infection and disease progression. However, a critical analysis of newly available data reveals substantial evidence to support a beneficial role for chemokines in HIV infection and disease. In this review we summarize the results of such studies and their promising implications for HIV infection.

The CC-chemokine RANTES increases the attachment of human immunodeficiency virus type 1 to target cells via glycosaminoglycans and also activates a signal transduction pathway that enhances viral infectivity

We have studied the mechanisms by which the CC-chemokine RANTES can enhance the infectivities of human immunodeficiency virus type 1 (HIV-1) and other enveloped viruses, when present at concentrations in excess of 500 ng/ml in vitro. Understanding the underlying mechanisms might throw light on fundamental processes of viral infection, in particular for HIV-1. Our principal findings are twofold: firstly, that oligomers of RANTES can cross-link enveloped viruses, including HIV-1, to cells via glycosaminoglycans (GAGs) present on the membranes of both virions and cells; secondly, that oligomers of RANTES interact with cell-surface GAGs to transduce a herbimycin A-sensitive signal which, over a period of several hours, renders the cells more permissive to infection by several viruses, including HIV-1. The enhancement mechanisms require that RANTES oligomerize either in solution or following binding to GAGs, since no viral infectivity enhancement is observed with a mutant form of the RANTES molecule that contains a single-amino-acid change (glutamic acid to serine at position 66) which abrogates oligomerization.