Activation and Coreceptor Expression of T Lymphocytes in HIV/AIDS Patients of China

The objective of this paper was to investigate the activation and coreceptor CCR5, CXCR4 expression of T lymphocytes in HIV/AIDS patients of China, and to study their association with disease progression. Seventy-seven HIV/AIDS patients and thirteen normal controls were enrolled and three-color flow-cytometry was used to detect the activation marker HLA-DR, CD38 and the coreceptor CCR5, CXCR4 expression on T lymphocytes in whole blood samples taken from the patients and the controls. The HLA-DR, CD38 and CCR5 expression on CD4, CD8⁺ T cells in AIDS patients was higher than in asymptomatic HIV-1 infected patients and normal controls (p < 0.05); The activation and CCR5 expression on T lymphocytes significantly correlated with CD4⁺ T lymphocyte number and viral load. The activation on T lymphocytes and the expression of CCR5 on T lymphocytes in HIV/AIDS patients of China are significantly correlated with disease progression.     

R5 HIV gp120-mediated cellular contacts induce the death of single CCR5-expressing CD4 T cells by a gp41-dependent mechanism

The use of CXC chemokine receptor 4 (CXCR4) and CC chemokine receptor 5 (CCR5) by X4 and R5 human immunodeficiency virus (HIV) envelopes (Env) influences HIV cytopathicity. Here, we have evaluated the role of CCR5 and gp41 in Env-induced cell death occurring during the contacts of uninfected, primary cells with MOLT cells infected with different R5 and X4 HIV isolates. As reported for X4-Env, R5 HIV-infected cells destroyed CD4 T cells expressing the appropriate coreceptor by inducing the formation of syncytia and the death of single target cells. Therefore, only the small (<10%) CCR5+ subset of primary CD4 T cells was sensitive to cellular presentation of R5-Env, and CCR5-CD4 T cells showed complete resistance to R5-Env-mediated cell death. X4- and R5-infected cells killed single primary cells by a common mechanism that was dependent on gp41 function and induced a rapid loss of mitochondrial membrane potential and plasma membrane integrity in target cells. Single-cell death was not affected by the blockade of HIV replication in target cells or G-protein signaling through CXCR4/CCR5. In contrast, caspase inhibition (Z-Val-Ala-Asp-fluoromethylketone) profoundly changed the outcome of cell-to-cell contacts by reducing the number of single dead CD4 T cells and increasing the rate of syncytium formation. In conclusion, X4 and R5 HIV Env share a common gp41-dependent mechanism to kill CD4 T cells during cellular contacts. Env tropism and coreceptor expression but not differential killing mechanisms seem to govern the extent of cytopathic effects induced by HIV infection.     

Activation of blood T lymphocytes down-regulates CXCR4 expression and interferes with propagation of X4 HIV strains

The chemokine receptor CXCR4 serves as a coreceptor for HIV-1 entry into CD4⁺ cells, in particular for strains emerging late in the infection. Cell surface expression of CXCR4 has, therefore, important implications for HIV-1 pathogenesis. Using blood lymphocytes cultured under various conditions, we studied the expression and regulation of CXCR4. Flow cytometry showed that only about 20 % of freshly isolated lymphocytes expressed CXCR4 on the cell surface whereas in 80 % of resting blood lymphocytes CXCR4 was located intracellularly. Within a few hours in culture, the intracellular CXCR4 was translocated to the surface and was expressed in the large majority of both naive and memory lymphocytes. A decrease in surface expression of CXCR4 was found when lymphocytes cultured overnight for maximal receptor expression were stimulated with phytohemagglutinin, anti-CD3 antibodies, phorbol 12-myristate 13-acetate and stromal cell-derived factor-1. The superantigen staphylococcal enterotoxin A, a more selective stimulus, induced a marked decrease in CXCR4 expression preferentially in cells positive for the CD25 activation marker. Confocal laser scanning microscopy demonstrated the presence of CXCR4 in the cytosol and on the surface of resting lymphocytes and also showed CXCR4 redistribution after activation. The number of cells infected by the X4 HIV strain NL4.3 paralleled the expression of CXCR4 in CD4⁺ T lymphocytes. Sustained reduction of CXCR4 cell surface expression upon activation with phytohemagglutinin correlated with a low number of CD4⁺ T lymphocytes expressing HIV p24 gag antigen. Our results indicate that activation of CD4⁺ T lymphocytes reduces surface expression of CXCR4 in part by receptor internalization and that cell activation-dependent CXCR4 down-regulation limits spread of infection by X4 viruses.     

Enhanced replication of R5 HIV-1 over X4 HIV-1 in CD4(+)CCR5(+)CXCR4(+) T cells

To enter human cells, HIV-1 usually uses CD4 and 1 of 2 coreceptors: CCR5 and CXCR4. Interestingly, even though CCR5 is expressed on far fewer T cells than is CXCR4, many patients in early- and late-stage HIV disease maintain high levels of CCR5-tropic (R5) viruses. We hypothesized that such high R5 viral loads may be sustained because, relative to CXCR4-tropic (X4) HIV-1 infection, R5 HIV-1 infection of permissive CD4(+)CCR5(+)CXCR4(+) T cells results in the production of significantly more infectious virus particles per target cell. To investigate this possibility, we compared the levels of virus production per target cell after isogenic R5 and X4 HIV-1 infection of 2 in vitro primary human lymphocyte culture systems: T-cell receptor-stimulated blood-derived CD4(+) T cells and tonsil histoculture (which requires no exogenous stimulation for ex vivo infection). We provide evidence that R5 HIV-1 does indeed compensate for a small target cell population by producing, on average, 5 to 10 times more infectious virus per CCR5(+) target cell than X4 HIV-1. This replicative advantage may contribute to the predominance of R5 HIV-1 in vivo.     

HIV-1 sexual transmission: early events of HIV-1 infection of human cervico-vaginal tissue in an optimized ex vivo model

Infection and dissemination of human immunodeficiency virus (HIV)-1 through the female body after vaginal intercourse depends on the activation/differentiation status of mucosal CD4 T cells. In this study, we investigated this status and the susceptibility to HIV-1 infection of human cervico-vaginal tissue ex vivo. We found that virtually all T cells are of the effector memory phenotype with broad CC chemokine receptor 5 (CCR5) expression. As it does in vivo, human cervico-vaginal tissue ex vivo preferentially supports the productive infection of R5 HIV-1 rather than that of X4 HIV-1 in spite of the broad expression of CXC chemokine receptor 4 (CXCR4). X4 HIV-1 replicated only in the few tissues that were enriched in CD27⁺CD28⁺ effector memory CD4 T cells. Productive infection of R5 HIV-1 occurred preferentially in activated CD38⁺CD4 T cells and was followed by a similar activation of HIV-1-uninfected (bystander) CD4 T cells that may amplify viral infection. These results provide new insights into the dependence of HIV-1 infection and dissemination on the activation/differentiation of cervico-vaginal lymphocytes.     

Distribution of the Human Immunodeficiency Virus Coreceptors CXCR4 and CCR5 on Leukocytes of Persons with Human Immunodeficiency Virus Type 1 Infection and Pulmonary Tuberculosis: Implications for Pathogenesis

Expression of CXCR4 was significantly reduced from normal on all cell subsets of persons with pulmonary tuberculosis (TB group), with HIV-1 infection (HIV group), and those with both infections (HIV/TB group), except for on monocytes in the HIV group. The reductions were most notable in the two TB groups. Interestingly, the duration of antituberculosis treatment was significantly negatively correlated with the expression of CXCR4 on CD4⁺ and CD8⁺CD45RO⁺ cells, monocytes and NK cells, viral load, and proportions of CD38-expressing CD8⁺ lymphocytes, in HIV/TB patients. By contrast, CCR5 expression on most cell subsets analyzed was increased in all the disease groups, except for on monocytes in the two TB groups. There was no change in CCR5 expression on CD4⁺ cells when based on the disease groupings. However, higher proportions of CD4⁺CD45RA⁺ and CD8⁺ lymphocytes as well as B cells expressing CCR5 correlated with advancing HIV-1 disease, as did decreased proportions of CXCR4-expressing CD4⁺CD45RA⁺ cells.     

Characterization of a chemokine receptor CCR5-negative T cell line and its use in determining human immunodeficiency virus type 1 phenotype

A human CD4-positive T cell line from a donor homozygous negative for the chemokine receptor CCR5 was established, characterized, and used for determining the coreceptor usage of human immunodeficiency virus type 1 (HIV-1) isolates. Clones of this IL-2 dependent human T-cell lymphotropic virus type 1 (HTLV-I) immortalized cell line, named IsnoR5 clones 1 and 2, are susceptible to infection by HIV-1 isolates that use CXCR4 as a coreceptor but resistant to infection by CCR5 tropic HIV-1 viruses. HIV-1 isolates whose replication is inhibited in IsnoR5 cells in the presence of the bicyclam AMD 3100, a CXCR4 specific inhibitor, utilize a coreceptor distinct from CCR5 and CXCR4. Using a panel of primary HIV-1 isolates we have shown that a single T cell line is sufficient to discriminate between use of CCR5, CXCR4 or an alternative coreceptor. As IsnoR5 clone 1 cells revealed the existence of even minor populations of CXCR4-using virus variants, they could be useful for the early identification of changes in coreceptor usage in HIV infected individuals facilitating the timely introduction of appropriate clinical treatments.     

Effect of HIV-1 subtype and tropism on treatment with chemokine coreceptor entry inhibitors; overview of viral entry inhibition

Abstract

HIV-1 entry begins with viral envelope glycoprotein gp120 interacting with host-cell CD4 and an entry coreceptor (mainly chemokine receptors CCR5 or CXCR4). Inhibitors of particular coreceptors are being developed in order to exploit this step of cellular infection. However, effectiveness of these drugs requires matching of the administered therapeutic to coreceptor use by the viral variants infecting each patient. Patient viruses may use only CCR5 (R5), only CXCR4 (X4) or both (D/M). Most patients in early disease have R5 variants, with the presence of X4 variants increasing as disease progresses; the infecting subtype also affects the prevalence of X4 variants. Phenotypic, genotypic and clinical trial tests are in use to determine coreceptor utilization by HIV-1 variants, termed tropism, and to predict the response to entry inhibitors. Maraviroc is the only approved entry-coreceptor inhibitor and inhibits CCR5-gp120 interaction. Clinical trials of maraviroc in specific patient subgroups are elucidating the drug’s role in contemporary clinical practice. Treatment failure to this and other CCR5 inhibitors has been shown to result from either outgrowth of X4 variants or through resistance mutations leading to R5 variants that are able to enter cells using drug-bound CCR5; thus, new entry inhibitors seek to circumvent this mechanism of resistance.     

HIV/AIDS患者CCR5、CXCR4的表达与疾病进展的关系

目的　了解HIV AIDS患者淋巴细胞表面第二受体CCR5、CXCR4的表达 ,分析其与疾病进展的关系 ,探讨HIV感染的免疫基础。方法　收集 33例HIV AIDS患者及 13例健康对照的抗凝全血 ,用流式细胞仪检测第二受体CCR5、CXCR4的表达 ,并分析第二受体表达与病毒载量、CD4 + T淋巴细胞绝对值及T淋巴细胞活化 (HLA DR+ CD38+ )的相关性。结果　艾滋病组CD4 + 、CD8+ T淋巴细胞表面CCR5表达高于无症状HIV 1感染组及健康对照 (P <0 .0 0 1) ;艾滋病组CD8+ T淋巴细胞表面CXCR4表达低于健康对照 (P <0 .0 1)。HIV AIDS患者CD4 + 、CD8+ T淋巴细胞表面CCR5的表达与病毒载量明显正相关 (P <0 .0 1) ;与CD4 + T淋巴细胞绝对值明显负相关 (P <0 .0 1) ,与T淋巴细胞活化(HLA DR+ CD38+ )水平明显正相关 (P <0 .0 0 1)。结论　HIV 1感染者第二受体CCR5的表达与机体对HIV的免疫反应及疾病进展密切相关。     

Restricted replication of primary HIV-1 isolates using both CCR5 and CXCR4 in Th2 but not in Th1 CD4(+) T cells

We have previously reported that CCR5-dependent human immunodeficiency virus type-1 (HIV-1; R5), but not CXCR4-restricted (X4) virus, efficiently replicates in T helper cell type 1 (Th1), Th2, or Th0 polyclonal T cells obtained from human umbilical cord blood (CB lines). The X4 virus restriction was env-dependent but did not occur at the level of viral entry. Here, we describe that in contrast to these monotropic HIVs, primary HIV-1 isolates capable of using CCR5 or CXCR4 indifferently for entry (i.e., R5X4 viruses) efficiently replicated in Th2 but not in Th1 CB lines. Although Th1 cells secreted significantly higher amounts of the three CCR5-binding chemokines in comparison with Th2 cells, this restriction was not explained by a defective infection of Th1 cells. Interferon-gamma (IFN-gamma) down-regulated CCR5 in Th1 cells and inhibited, whereas interleukin-4 (IL-4) up-regulated CXCR4 and enhanced the spreading of R5 and R5X4 viruses in polarized CB lines. However, both cytokines did not rescue the replication of X4 and dualtropic viruses in both types of CB lines or in Th1 cells, respectively, whereas addition of anti-IL-4- or anti-IFN-gamma-neutralizing antibodies did not activate virus expression. These findings together suggest the existence of post-entry restriction pathways influenced by gp120 Env/chemokine coreceptor interaction that may significantly contribute to the superior capacity of R5 and R5X4 HIV-1 strains to spread in vivo in comparison to X4 monotropic viruses.     

Genetic and phenotypic features of blood and genital viral populations of clinically asymptomatic and antiretroviral-treatment-naive clade a human immunodeficiency virus type 1-infected women

In the present study, we assessed whether human immunodeficiency virus type 1 (HIV-1) genetic compartmentalization was associated with phenotypic CCR5 (R5) or CXCR4 (X4) coreceptor usage differences between the systemic and the genital viral populations. Four clinically asymptomatic and treatment-na?ve clade A HIV-1-infected patients were selected from a cohort of 274 African women, because they were free of all the biological cofactors known to modify the kinetics of viral production in the genital tract. HIV RNA envelope sequences (V1 to V3) derived from plasma and cervicovaginal secretions (CVS) were amplified, subcloned, and sequenced. CCR5 or CXCR4 coreceptor usage was determined by production of recombinant viral particles, followed by single-cycle infection assays of indicator cell lines, using the tropism recombinant test. In these four selected patients, CVS-derived sequences appeared to be genetically distinct from blood-derived sequences (P < or = 0.001). Two patients were found to harbor virus populations with only the R5 phenotype in both compartments, whereas viruses using CXCR4 in addition to CCR5 were detected in two other patients. In particular, one woman harbored genital virus populations with mixed R5 and X4 phenotypes associated with peripheral blood populations with only the R5 phenotype. These results demonstrate genetic compartmentalization of HIV between the plasma and genital secretions of clinically asymptomatic, treatment-na?ve, clade A-infected women. Also, for one patient, we report phenotypic coreceptor usage differences between the systemic (R5) and genital (R5/X4) viral populations. These features may be critical for the development of further mucosal vaccines, therapies, or new preventive strategies to block heterosexual transmission.     

In Vitro Exposure to Highly Cytopathic HIV-1 X4 Strains Increases Expression of Mucosa-Associated Integrins on CD4 T Cells

To determine whether infection with HIV-1 strains of different tropisms would influence expression of the mucosa-associated integrins α4β7 and αEβ7 or the lymph node homing receptor L-selectin on peripheral T lymphocytes, cells were infected with the CXCR4-tropic (X4)/syncytium-inducing (SI) HIV-1_IIIB strain or with X4/SI or CCR5-tropic (R5)/non-SI (NSI) primary human isolates. Flow cytometric analyses of CD4⁺ T cells from cultures infected with HIV-1_IIIB and one X4/SI primary HIV-1 isolate revealed a significant increase in surface expression of α4β7 and αEβ7 12 days after infection. L-selectin expression was not significantly affected on CD4⁺ T cells. However, infection with another X4/SI and two R5/NSI primary HIV-1 isolates did not significantly alter homing receptor expression on CD4⁺ T cells. Since a higher degree of CD4 cytopathicity occurred in those cultures having increased integrin expression, these data suggest that significantly altered mucosal homing receptor expression on CD4⁺ T cells may result as a “bystander” effect after infection with some cytopathic isolates of HIV-1.     

Absence of coreceptor switch with disease progression in human immunodeficiency virus infections in India

The envelope glycoprotein of the human immunodeficiency virus (HIV) utilizes CD4 as a receptor and CCR5 and/or CXCR4 as coreceptor to gain entry into the cell. The CCR5-tropic viruses, observed early in infection, could be important in transmission and the CXCR4-tropic viruses, observed late, may play an important role in disease progression. Viruses from 40 HIV-positive, asymptomatic or symptomatic individuals in India were isolated. Of 40 isolates 39 used CCR5. Thirty-three isolates were subtype C, 3 isolates were subtype A, and 4 isolates were HIV-2. Only 1 HIV-2 isolate, from a symptomatic individual, was dualtropic. Therefore, a majority of isolates from India belonged to subtype C and all the isolates utilized CCR5 exclusively irrespective of HIV disease status.     

Entry coreceptor use and fusion inhibitor T20 sensitivity of dual-tropic R5X4 HIV-1 in primary macrophage infection

Macrophages are important targets for HIV-1, and R5X4 strains play a central role in pathogenesis, especially in late-stage patients who may receive the fusion inhibitor T20 (enfuvirtide). Sensitivity to T20 varies markedly among HIV-1 strains and is influenced by viral and cellular factors that affect Env/CD4/coreceptor interactions. We addressed the relation between T20 inhibition and the pathway by which R5X4 HIV-1 infects primary macrophages, which express both coreceptors. In U87/CD4/coreceptor cells, T20 sensitivity for entry through CCR5 and CXCR4 was correlated. In macrophages, the proportion of total entry mediated by each coreceptor differed among isolates. Neither pathway was uniformly more or less sensitive to T20, however, nor did the proportion of entry mediated by each coreceptor predict T20 sensitivity. T20 sensitivity for macrophage infection overall correlated modestly with that for entry through CCR5 but not through CXCR4; however, unlike U87 cells, sensitivity of entry through CCR5 and CXCR4 was not correlated. These results suggest that strain-specific factors influence R5X4 T20 sensitivity regardless of the coreceptor used, an absence of systematic differences in efficiency by which R5X4 strains use the 2 coreceptors, and that efficiency and kinetics of interactions with CCR5 are central determinants of macrophage entry even when both pathways are utilized.     

Inhibition of R5X4 dualtropic HIV-1 primary isolates by single chemokine co-receptor ligands

The susceptibility of HIV-1 to chemokine-mediated inhibition may be lost as a consequence of the expanded usage of chemokine co-receptors frequently occurring in clade B isolates obtained from individuals with advanced disease. Since chemokine-based immune intervention is under intense investigation, it is crucial to determine its potential effect on primary dualtropic HIV isolates characterized by simultaneous utilization of CCR5 and CXCR4 chemokine co-receptors (R5X4 viruses). In the present study, the CCR5 binding chemokine regulated upon activation normal T cell expressed and secreted (RANTES) strongly inhibited the replication of two of eight primary R5X4 viruses in mitogen-activated primary peripheral blood mononuclear cells (PBMC). The CXCR4 antagonist AMD3100 efficiently suppressed the replication of other two HIV isolates, whereas the remaining four viruses were partially inhibited by treatment with either RANTES or AMD3100. The potency of chemokine-mediated inhibition was influenced by PBMC donor variability, but it was usually independent from the levels of expression of CCR5 or CXCR4. Dual co-receptor usage was maintained by the viruses after two serial passages on U87.CD4 astrocytic cell lines expressing exclusively either CCR5 or CXCR4. The gp120 env variable domains were sequenced before and after passages on U87.CD4 cells. Virus replication into U87.CD4-CXCR4 cells did not result in changes in the V3 region but perturbed the dominant env V4 sequence. Interestingly, double passage onto U87.CD4-CXCR4 cells determined the loss of susceptibility to RANTES inhibition. In conclusion, interference with CCR5 may efficiently inhibit the replication of at least some dualtropic HIV-1 strains, whereas forced CXCR4 usage may result in viral escape from CCR5-dependent inhibitory effects.     

R5X4 HIV-1 coreceptor use in primary target cells: implications for coreceptor entry blocking strategies

Entry coreceptor use by HIV-1 plays a pivotal role in viral transmission, pathogenesis and disease progression. In many HIV-1 infected individuals, there is an expansion in coreceptor use from CCR5 to include CXCR4, which is associated with accelerated disease progression. While targeting HIV-1 envelope interactions with coreceptor during viral entry is an appealing approach to combat the virus, the methods of determining coreceptor use and the changes in coreceptor use that can occur during disease progression are important factors that may complicate the use of therapies targeting this stage of HIV-1 replication. Indicator cells are typically used to determine coreceptor use by HIV-1 in vitro, but the coreceptors used on these cells can differ from those used on primary cell targets. V3 based genetic sequence algorithms are another method used to predict coreceptor use by HIV-1 strains. However, these algorithms were developed to predict coreceptor use in cell lines and not primary cells and, furthermore, are not highly accurate for some classes of viruses. This article focuses on R5X4 HIV-1, the earliest CXCR4-using variants, reviewing the pattern of coreceptor use on primary CD4+ lymphocytes and macrophages, the relationship between primary cell coreceptor use and the two principal approaches to coreceptor analysis (genetic prediction and indicator cell phenotyping), and the implications of primary cell coreceptor use by these strains for treatment with a new class of small molecule antagonists that inhibit CCR5-mediated entry. These are important questions to consider given the development of new CCR5 blocking therapies and the prognosis associated with CXCR4 use.     

CD4+ NK cells can be productively infected with HIV, leading to downregulation of CD4 expression and changes in function

NK cells mediate the innate immune response, and HIV-infected individuals demonstrate altered NK cell phenotype and function. We find that CD4+ NK cells are susceptible to HIV infection; this could account for the NK cell dysfunction seen in HIV-infected individuals. CD4+ NK cells express CXCR4 and can be infected with X4-tropic viruses and some primary R5-utilizing viral isolates. Treatment with the CXCR4 ligands AMD3100 and SDF-1α partially blocks infection with X4-tropic virus, treatment with anti-CCL Igs upregulates CCR5 surface expression and enables infection with HIV-Bal. HIV infection of NK cells results in CD4 downregulation and the production of infectious virus. HIV-infected CD4+ NK cells mediate NK cell cytotoxicity, however, HIV infection is associated with decreased chemotaxis towards IL-16. Thus, HIV infection of CD4+ NK cells could account for the NK cell dysfunction observed in HIV-infected individuals. Furthermore infected NK cells could serve as a viral reservoir of HIV in vivo.     

Down-regulation of CXCR4 expression by SDF-KDEL in CD34 hematopoietic stem cells: An anti-human immunodeficiency virus strategy

CXCR4 plays an essential role as the first discovered coreceptor for the entry of T cell tropic isolates of HIV-1. Blocking the surface expression of this receptor may be a potential strategy to prevent HIV-1 infection. A lentiviral vector, pLenti6/V5-S-K, expressing a SDF-KDEL fusion protein was constructed and a replication-incompetent lentiviral stock was produced. The lentiviral stock was transduced into CD34⁺ hHSC and the transient expression of the recombinant protein, SDF-1, was assayed using indirect immunofluorescence. The surface expression of CXCR4 in CD34⁺ hHSC pretreated with different amounts of recombinant lentiviral vectors was detected by flow cytometric analysis. A marked down-regulation of CXCR4 expression in the cells transduced with recombinant lentiviral vectors pLenti6/V5-S-K was observed by flow cytometry with PE-conjugated anti-human CXCR4 monoclonal antibodies which showed the percentages of the inhibition effects of CXCR4-SDF-1 mediated syncytium formation are presented by concentration. P24 antigen levels of cell culture supernatants were detected on the 4th, 7th, and 10th day, with 10³ TCID50 HIV-1 infected CD34⁺ hHSC to evaluate the inhibitory effect of pLenti6/V5-S-K transduction on HIV-1 infection. The cells transfected with pLenti6/V5-S-K had a significant reduction of HIV-1 DP27 infection compared to controls (P < 0.05).     

Antibody to CD14 like CXCR4-specific antibody 12G5 could inhibit CXCR4-dependent chemotaxis and HIV Env-mediated cell fusion

The expression of HIV-1 coreceptors (CXCR4 and CCR5) on monocyte surface can be regulated by the ligand of CD14 (LPS), which stimulate the susceptibility of the cells to HIV-1. To investigate whether it exists potential association between CD14 and HIV-1 coreceptor CXCR4, we tested the impact of CD14-specific monoclonal antibodies (mAbs) upon CXCR4-dependent responses, such as SDF-induced chemotaxis and HIV Env-mediated membrane fusion. The anti-CD14 mAb TUK4 like CXCR4-specific mAb 12G5 could block SDF-induced chemotaxis of U937 cells in a dose-dependent manner, while another CD14-specific mAb UCHM-1 did not show any activity. More interestingly, syncytium assay indicated that only the CD14-specific mAb TUK4 inhibited HIV Env-mediated CXCR4-dependent cell fusion between U937 cells and HIV-1(HXB2) Env transfected CHO cells distinctly, consistent with its activity against CXCR4-dependent chemotaxis. These results provided experimental evidence for existence of close association between CD14 and HIV coreceptor CXCR4 on human monocytic cells.     

Asymmetric HIV-1 co-receptor use and replication in CD4(+) T lymphocytes

Susceptibility to infection by the human immunodeficiency virus type-1 (HIV-1), both in vitro and in vivo, requires the interaction between its envelope (Env) glycoprotein gp120 Env and the primary receptor (R), CD4, and Co-R, either CCR5 or CXCR4, members of the chemokine receptor family. CCR5-dependent (R5) viruses are responsible for both inter-individual transmission and for sustaining the viral pandemics, while CXCR4-using viruses, usually dualtropic R5X4, emerge in ca. 50% of individuals only in the late, immunologically suppressed stage of disease. The hypothesis that such a major biological asymmetry is explained exclusively by the availability of cells expressing CCR5 or CXCR4 is challenged by several evidences. In this regard, binding of the HIV-1 gp120 Env to the entry R complex, i.e. CD4 and a chemokine R, leads to two major events: virion-cell membrane fusion and a cascade of cell signaling. While the fusion/entry process has been well defined, the role of R/Co-R signaling in the HIV-1 life cycle has been less characterized. Indeed, depending on the cellular model studied, the capacity of HIV-1 to trigger a flow of events favoring either its own latency or replication remains a debated issue. In this article, we will review the major findings related to the role of HIV R/Co-R signaling in the steps following viral entry and leading to viral spreading in CD4(+) T lymphocytes.