Enhanced HIV-1 replication by chemokines constitutively expressed in secondary lymphoid tissues

Cytokines Elevated in HIV Elite Controllers Reduce HIV Replication In Vitro and Modulate HIV Restriction Factor Expression

A subset of HIV-infected individuals termed elite controllers (ECs) maintain CD4⁺ T cell counts and control viral replication in the absence of antiretroviral therapy (ART). Systemic cytokine responses may differentiate ECs from subjects with uncontrolled viral replication or from those who require ART to suppress viral replication. We measured 87 cytokines in four groups of women: 73 ECs, 42 with pharmacologically suppressed viremia (ART), 42 with uncontrolled viral replication (noncontrollers [NCs]), and 48 HIV-uninfected (NEG) subjects. Four cytokines were elevated in ECs but not NCs or ART subjects: CCL14, CCL21, CCL27, and XCL1. In addition, median stromal cell-derived factor-1 (SDF-1) levels were 43% higher in ECs than in NCs. The combination of the five cytokines suppressed R5 and X4 virus replication in resting CD4⁺ T cells, and individually SDF-1β, CCL14, and CCL27 suppressed R5 virus replication, while SDF-1β, CCL21, and CCL14 suppressed X4 virus replication. Functional studies revealed that the combination of the five cytokines upregulated CD69 and CCR5 and downregulated CXCR4 and CCR7 on CD4⁺ T cells. The CD69 and CXCR4 effects were driven by SDF-1, while CCL21 downregulated CCR7. The combination of the EC-associated cytokines induced expression of the anti-HIV host restriction factors IFITM1 and IFITM2 and suppressed expression of RNase L and SAMHD1. These results identify a set of cytokines that are elevated in ECs and define their effects on cellular activation, HIV coreceptor expression, and innate restriction factor expression. This cytokine pattern may be a signature characteristic of HIV-1 elite control, potentially important for HIV therapeutic and curative strategies.IMPORTANCE Approximately 1% of people infected with HIV control virus replication without taking antiviral medications. These subjects, termed elite controllers (ECs), are known to have stronger immune responses targeting HIV than the typical HIV-infected subject, but the exact mechanisms of how their immune responses control infection are not known. In this study, we identified five soluble immune signaling molecules (cytokines) in the blood that were higher in ECs than in subjects with typical chronic HIV infection. We demonstrated that these cytokines can activate CD4⁺ T cells, the target cells for HIV infection. Furthermore, these five EC-associated cytokines could change expression levels of intrinsic resistance factors, or molecules inside the target cell that fight HIV infection. This study is significant in that it identified cytokines elevated in subjects with a good immune response against HIV and defined potential mechanisms as to how these cytokines could induce resistance to the virus in target cells.

Chemokine CXCL8 promotes HIV-1 replication in human monocyte-derived macrophages and primary microglia via nuclear factor-κB pathway

BACKGROUND

Chemokine CXCL8 is an important neutrophil chemoattractant implicated in various neurodegenerative disorders. Cytokine/chemokine imbalance, with an increase in proinflammatory cytokines like interleukin-1β and tumor necrosis factor-α within the central nervous system, is a hallmark of human immunodeficiency virus (HIV)-1 infection. We previously reported that HIV-1 infection is linked to upregulation of CXCL8 in brain tissues and human astrocytes. Chemokines play crucial roles in trafficking of leukocytes and trafficking of HIV-1-infected across the blood-brain barrier play an important role in HIV-1 central nervous system disease. In the post-antiretroviral therapy era, low level of productive replication of HIV-1 in brain is a critical component of neuropathogenesis regulation. The present study investigated the effect of CXCL8 on productive infection of HIV-1 in human monocytes-derived macrophages (MDM) and primary human microglia.

RESULTS

Human MDM and microglia were infected with the blood or brain derived HIV-1 isolates, HIV-1ADA or HIV-1JRFL. Treatment with CXCL8 significantly upregulated HIV-1p24 levels in supernatants of both HIV-1-infected MDM as well as microglia. In addition, the formation of 2-long terminal repeat (LTR) circles, a measure of viral genome integration, was significantly higher in CXCL8-treated, HIV-1-infected MDM and microglia. Transient transfection of U937 cells with HIV-1 LTR luciferase reporter construct resulted in increased promoter activity when treated with CXCL8. Moreover, increased nuclear translocation of nuclear factor-κB was seen in HIV-1-infected MDM following CXCL8 treatment. Blocking CXCL8 receptors CXCR1 and CXCR2 abrogated the CXCL8-mediated enhanced HIV-1 replication.

CONCLUSION

Our results show that CXCL8 mediates productive infection of HIV-1 in MDM and microglia via receptors CXCR1 and CXCR2. These results demonstrate that CXCL8 exerts its downstream effects by increasing translocation of nuclear factor-κB into the nucleus, thereby promoting HIV-1 LTR activity.

HIV persistence: chemokines and their signalling pathways

Latently infected resting CD4+ T cells are the major barrier to curing HIV. We have recently demonstrated that chemokines, which bind to the chemokine receptors CCR7, CXCR3 and CCR6, facilitate efficient HIV nuclear localisation and integration in resting CD4+ T cells, leading to latency. As latently infected cells are enriched in lymphoid tissues, where chemokines are highly concentrated, this may provide a mechanism for the generation of latently infected cells in vivo. Here we review the role of chemokines in HIV persistence; the main signalling pathways that are involved; and how these pathways may be exploited to develop novel strategies to reduce or eliminate latently infected cells.

Enhanced levels of CCL19 in patients with advanced acquired immune deficiency syndrome (AIDS)

Based on the ability to recruit lymphocytes and dendritic cells to lymphoid tissue and to promote inflammation, we hypothesized a role for dysregulated CCL19 and CCL21 levels in human immunodeficiency virus (HIV)-infected patients with advanced immunodeficiency, and in particular in those with accompanying Mycobacterium avium complex (MAC) infection. The hypothesis was explored by studies in HIV-infected patients with and without MAC infection, as well as in vitro, examining the ability of proteins from MAC to promote CCL19 and CCL21 responses in peripheral blood mononuclear cells (PBMC) during highly active anti-retroviral therapy (HAART). Our main findings were: (i) raised serum levels of CCL19 in HIV-infected patients with CD4(+) T cell count <50 cells/µl compared with HIV-infected patients with CD4(+) T cell count >500 cells/µl and healthy controls, with particularly high levels in those with MAC infection; (ii) elevated plasma levels of CCL19 predicted a higher mortality in acquired immune deficiency syndrome (AIDS)-patients, independent of ongoing MAC infection; and (iii) marked production of CCL19 in MAC-stimulated peripheral blood mononuclear cells (PBMC) and pronounced disturbances in MAC-induced CCL19 production in PBMC from HIV patients that was partly reversed during HAART. Our findings suggest the involvement of CCL19 in AIDS patients with advanced immunodeficiency, potentially mediating both adaptive and maladaptive responses.

Short communication: persistence of high blood levels of the chemokines CCL2, CCL19, and CCL20 during the course of HIV infection

Dendritic cells (DCs) are important mediators of the immune response against HIV and yet blood DC numbers fall substantially during HIV infection. Here we report that blood levels of the DC-tissue tropic chemokines monocyte chemotactic protein (MCP-1/CCL2), macrophage inflammatory proteins (MIP-3α/CCL20), and MIP-3β/CCL19 remained elevated throughout the course of HIV infection suggesting that the relatively low levels of blood circulating DCs may be due to active recruitment of these cells to peripheral sites to fight disease progression.

Homeostatic chemokines CCL19 and CCL21 promote inflammation in human immunodeficiency virus-infected patients with ongoing viral replication

CCL19 and CCL21 and their receptor CCR7 are expressed constitutively within lymphoid organs, regulating lymphocyte homing. Recent studies suggest that these chemokines may have inflammatory properties. We hypothesized a role of CCL19/CCL21 in human immunodeficiency virus (HIV) infection by promoting inflammation. We examined the expression of CCL19 and CCL21 in mononuclear cells from peripheral blood mononuclear cells (PBMC) and bone marrow mononuclear cells (BMMC) in HIV-infected patients before and during highly active anti-retroviral therapy (HAART). We also examined the ability of CCL19/CCL21 to promote inflammatory responses in these patients. PBMC from untreated HIV-infected patients (n = 29) released enhanced levels of CCL19 spontaneously compared with cells from controls (n = 20), particularly in those with symptomatic disease (n = 15, P < 0.01 versus controls). During HAART (n = 9), there was a decrease in the spontaneous CCL19 release and an increase in the phytohaemagglutinin-stimulated CCL19 release in both PBMC (P < 0.01) and BMMC (P < 0.05). In patients with enhanced HIV replication there was an increased proportion of inflammatory CD8(+)CCR7(-)CD45RA(-) T cells in peripheral blood [P < 0.01 and P < 0.05 versus controls, untreated (n = 9) and treatment failure (n = 8), respectively]. In vitro, CCL19/CCL21 promoted an inflammatory response in PBMC when accompanied by high viral load, irrespective of HAART. The HIV-tat protein significantly boosted the inflammatory effect of CCL19/CCL21 in PBMC. These findings link a dysregulated CCL19/CCL21/CCR7 system in HIV-infected patients to persistent inflammation and HIV replication, not only in untreated HIV infection, but also in treatment failure during HAART.

Enhanced levels of the CCR7 ligands CCL19 and CCL21 in HIV infection: correlation with viral load, disease progression and response to highly active antiretroviral therapy

The CCR7 ligands, CCL19 and CCL21, coordinate lymph node homing of naive and central memory T cells. In untreated HIV-infected patients, serum levels of CCL19 and CCL21 showed a biphasic pattern during progression; a marked increase was followed by a decline in patients with advanced immunodeficiency. During highly active antiretroviral therapy, a decrease in CCL19/CCL21 levels was restricted to virologic responders. We suggest that dysregulation of CCR7 ligands may play an important role in progression of HIV infection.

Role of CD151, A tetraspanin, in porcine reproductive and respiratory syndrome virus infection

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) is a RNA virus causing respiratory and reproductive diseases in swine. The susceptibility for PRRSV varies between the different breeds of swine. In cell culture, PRRSV virus can be propagated in primary porcine alveolar macrophages and some African green monkey kidney cell lines, such as MARC-145 cells. Previous studies have shown that 3' untranslated region (UTR) RNAs of the arteriviruses play an important role in the replication of the virus through interactions with cellular proteins. To better understand the differences in the replication capability of PRRSV in different cell lines, we sought to identify the host cellular proteins interacting with PRRSV 3' UTR RNA. We constructed a cDNA library of MARC-145 cell line in lambda ZAP Express vector and screened the library with the positive sense 3' UTR RNA of PRRSV.

Results

We found that CD151, a host cellular protein, interacting with PRRSV 3' UTR RNA. The specificity of the interaction between CD151 and PRRSV 3' UTR RNA was examined by gel shift assay as well as North-Western hybridization. The transfection of CD151 expression clone into BHK-21 rendered these cells susceptible to PRRSV infection, and the transfection of siRNA against CD151 into MARC-145 significantly reduced the level of PRRSV infection. Also, anti-CD151 antibody treatment to MARC-145 completely blocked PRRSV infection.

Conclusion

Based on our results, we suggest that CD151 should cooperate in PRRSV infection in vitro in MARC-145 and BHK-21 cells.

Mechanisms for Macrophage-Mediated HIV-1 Induction

Viral latency is a long-term pathogenic condition in patients infected with HIV-1. Low but sustained virus replication in chronically infected cells can be activated by stimulation with proinflammatory cytokines such as TNF-alpha, IL-1 beta, or other host factors. However, the precise mechanism by which cellular activation induces latently infected cells to produce virions has remained unclear. In the present report, we present evidence that activation of HIV-1 replication in latently infected U1 or ACH2 cells by human macrophages is mediated by a rapid nuclear localization of NF-kappaB p50/p65 dimer with concomitant increased expression of proinflammatory cytokines. Multiplexed RT-PCR amplification of mRNA isolated from cocultures of macrophages and U1 and ACH2 cells showed significant induction of IL-1beta, IL-6, IL-8, TNF-alpha, and TGF-beta expression within 3 h of coincubation. Fixation of macrophages, U-1, or ACH2 cells with paraformaldehyde before coculture completely abrogated the induction of NF-kappaB subunits and HIV-1 replication, suggesting that cooperative interaction between the two cell types is an essential process for cellular activation. Pretreatment of macrophage-U1 or macrophage-ACH2 cocultures with neutralizing anti-TNF-alpha Ab down-regulated the replication of HIV-1. In addition, pretreatment of macrophage-U1 or macrophage-ACH2 cocultures with the NF-kappaB inhibitor (E)3-[(4-methylphenyl)sulfonyl]-2-propenenitrile (BAY 11-7082) prevented the induction of cytokine expression, indicating a pivotal role of NF-kappaB-mediated signaling in the reactivation of HIV-1 in latently infected cells by macrophages. These results provide a mechanism by which macrophages induce HIV-1 replication in latently infected cells.

Identification of cell surface targets for HIV-1 therapeutics using genetic screens

Human immunodeficiency virus (HIV) drugs designed to interfere with obligatory utilization of certain host cell factors by virus are less likely to encounter development of resistant strains than drugs directed against viral components. Several cellular genes required for productive infection by HIV were identified by the use of genetic suppressor element (GSE) technology as potential targets for anti-HIV drug development. Fragmented cDNA libraries from various pools of human peripheral blood mononuclear cells (PBMC) were expressed in vitro in human immunodeficiency virus type 1 (HIV-1)-susceptible cell lines and subjected to genetic screens to identify GSEs that interfered with viral replication. After three rounds of selection, more than 15000 GSEs were sequenced, and the cognate genes were identified. The GSEs that inhibited the virus were derived from a diverse set of genes including cell surface receptors, cytokines, signaling proteins, transcription factors, as well as genes with unknown function. Approximately 2.5% of the identified genes were previously shown to play a role in the HIV-1 life cycle; this finding supports the biological relevance of the assay. GSEs were derived from the following 12 cell surface proteins: CXCR4, CCR4, CCR7, CD11C, CD44, CD47, CD68, CD69, CD74, CSF3R, GABBR1, and TNFR2. Requirement of some of these genes for viral infection was also investigated by using RNA interference (RNAi) technology; accordingly, 10 genes were implicated in early events of the viral life cycle, before viral DNA synthesis. Thus, these cell surface proteins represent novel targets for the development of therapeutics against HIV-1 infection and AIDS.

Productive HIV infection of resting CD4+ T cells: role of lymphoid tissue microenvironment and effect of immunomodulating agents

The ability of resting CD4+ T cells to support HIV replication is relevant to understanding how the reservoir of HIV-1-infected resting CD4+ T cells is generated, maintained and, hopefully, how it might be reduced or eliminated. We have utilized a tonsillar histoculture system to demonstrate that HIV, particularly X4 strains, can productively infect phenotypically resting CD4+ T cells in vitro and that this event is largely dependent on the lymphoid tissue microenvironment. Highly purified CD4+ tonsillar T cells that lack expression of both cell surface and nuclear antigens characteristic of classic T cell activation produce X4 HIV-1 mRNA, p24, and infectious virus while maintaining a resting phenotype when cultured in a tonsillar tissue microenvironment; in contrast, comparable purified resting CD4+ tonsillar T cells that have been exposed to X4 HIV do not support HIV replication when cultured in the absence of a lymphoid tissue microenvironment. HIV production from phenotypically resting CD4+ T cells is dramatically inhibited by anti-proinflammatory cytokine agents or immunosuppressive cytokines, but is only modestly suppressed by an inhibitor of the cell cycle. The ability of resting CD4+ T cells to support HIV replication in the microenvironment of the lymphoid tissue has implications in the pathogenesis of HIV disease and may provide an additional avenue for therapeutic intervention.

Simian immunodeficiency virus dramatically alters expression of homeostatic chemokines and dendritic cell markers during infection in vivo

Dendritic cells (DCs) are potent antigen-presenting cells that likely play multiple roles in human immunodeficiency virus type 1 (HIV-1) pathogenesis. We used the simian immunodeficiency virus (SIV)/macaque model to study the effects of infection on homeostatic chemokine expression and DC localization directly in secondary lymphoid tissues. SIV infection altered the expression of chemokines (CCL19/MIP-3beta, CCL21/ 6Ckine, and CCL20/MIP-3alpha) and of chemokine receptors (CCR7 and CCR6) that drive DC trafficking. CCL19/MIP-3beta, CCL20/MIP-3alpha, CCR6, and CCR7 expression increased in lymph nodes during the early systemic burst of viral replication (acute infection), whereas CCL21/6Ckine expression progressively decreased throughout disease to AIDS. Parallel with the SIV-induced perturbations in chemokine expression were changes in the expression of the DC-associated markers, DC-SIGN, DC-LAMP, and DECTIN-1. During AIDS, DC-LAMP mRNA expression levels were significantly reduced in lymph nodes and spleen, and DC-SIGN levels were significantly reduced in spleen. These findings suggest that the disruption of homeostatic chemokine expression is responsible, in part, for alterations in the networks of antigen-presenting cells in lymphoid tissues, ultimately contributing to systemic immunodeficiency.

HIV-1 gp120 modulates the immunological function and expression of accessory and co-stimulatory molecules of monocyte-derived dendritic cells

Initiation of a primary immune response requires antigen specific CD4(+) T helper (T(h)) cells to assist in priming of CD8(+) cytotoxic T cell (CTL) activity. This is optimal when T(h) cells and CTL recognize antigen when presented to them by a dendritic cell (DC) in the context of major histocompatibility complex (MHC) class I and class II complexes. We have hypothesized that human DC exposed to HIV-1 gp120 IIIB envelope glycoprotein may activate or alter the immunological activation of DCs. Our findings have led us to conclude that HIV-1 gp120 LAV/IIIB activates monocyte-derived DC when they are in their immature state while HIV-1 gp120 exhibits highly selective effects on mature DC. We have observed that following maturation of DCs with lipopolysaccharide (LPS) that they are less susceptible to the modulatory effects of gp120. Although HIV-1 gp120 activates immature DC, it does so in a manner that abrogates their normal function in host immune responses and consequently disturbs the homeostatic balance of host immune response to infection. We suggest that HIV-1 gp120 may support sustained productive infection and transinfection of activated T cells that cluster with gp120-activated DC. We believe that these are promoted by mechanisms that are dependent, at least in part, on altered cytokine responses, enhanced expression of cellular adhesion molecules and augmented DC-mediated activation of T cells in nonspecific and antigen-specific immune reactivities. Consequently, HIV-1 gp120 may actively contribute to the immunopathogenesis of AIDS.

Molecular cloning and sequencing of 25 different rhesus macaque chemokine cDNAs reveals evolutionary conservation among C, CC, CXC, AND CX3C families of chemokines

Chemokines are small chemoattractant cytokines involved in normal and pathological immune processes. Although extensive nucleotide sequence data are available for human and murine chemokine cDNA sequences, very few data are currently available regarding rhesus macaque sequences. To increase our understanding of immune function in nonhuman primates, we have used reverse-transcription polymerase chain reaction (RT-PCR) to clone and sequence rhesus macaque cDNAs from each of the C, CC, CXC, and CX3C groups of chemokines. Relative to the respective human chemokines, these 25 chemokine cDNA sequences were from 77% to 98% identical. Of the amino acid differences between the rhesus macaque and human chemokines, 51% were species-specific when compared together with the respective murine chemokine sequences. These studies of rhesus macaque chemokine sequences demonstrate that chemokine genes are highly conserved across species, and provide a large foundation for the study of chemokine biology and genetics in nonhuman primates.

Increased expression of the inflammatory chemokine CXC chemokine ligand 9/monokine induced by interferon-gamma in lymphoid tissues of rhesus macaques during simian immunodeficiency virus infection and acquired immunodeficiency syndrome

Chemokines are important mediators of cell trafficking during immune inductive and effector activities, and dysregulation of their expression might contribute to the pathogenesis of human immunodeficiency virus type 1 and the related simian immunodeficiency virus (SIV). To understand better the effects of SIV infection on lymphoid tissues in rhesus macaques, we examined chemokine messenger RNA (mRNA) expression patterns by using DNA filter array hybridization. Of the 34 chemokines examined, the interferon gamma (IFN-gamma)-inducible chemokine CXC chemokine ligand 9/monokine induced by interferon-gamma (CXCL9/Mig) was one of the most highly up-regulated chemokines in rhesus macaque spleen tissue early after infection with pathogenic SIV. The relative levels of expression of CXCL9/Mig mRNA in spleen and lymph nodes were significantly increased after infection with SIV in both quantitative image capture and analysis and real-time reverse transcriptase-polymerase chain reaction assays. In addition, in situ hybridization for CXCL9/Mig mRNA revealed that the patterns of expression were altered after SIV infection. Associated with the increased expression of CXCL9/Mig were increased numbers of IFN-gamma mRNA-positive cells in tissues and reduced percentages of CXC chemokine receptor (CXCR) 3(+)/CD3(+) and CXCR3(+)/CD8(+) lymphocytes in peripheral blood. We propose that SIV replication in vivo initiates IFN-gamma-driven positive-feedback loops in lymphoid tissues that disrupt the trafficking of effector T lymphocytes and lead to chronic local inflammation, thereby contributing to immunopathogenesis.

Chemokine receptors

Although chemokines were originally defined as host defense proteins it is now clear that their repertoire of functions extend well beyond this role. For example chemokines such as MGSA have growth regulatory properties while members of the CXC chemokine family can be mediators or inhibitors of angiogenesis and may be important targets for oncology. Recent work shows that the chemokine receptor CXCR4 and its cognate ligand SDF play important roles in the development of the immune, circulatory and central nervous systems. In addition, chemokine receptors play an important role in the pathogenesis of the AIDS virus, HIV-1. Taken together these findings expand the biological importance of chemokines from that of simple immune modulators to a much broader biological role than was at first appreciated and these and other properties of the chemokine receptor family are discussed in detail in this review.

Interleukin-8 stimulates human immunodeficiency virus type 1 replication and is a potential new target for antiretroviral therapy

Production of the C-X-C chemokines interleukin-8 (IL-8) and growth-regulated oncogene alpha (GRO-alpha) in macrophages is stimulated by exposure to human immunodeficiency virus type 1 (HIV-1). We have demonstrated previously that GRO-alpha then stimulates HIV-1 replication in both T lymphocytes and macrophages. Here we demonstrate that IL-8 also stimulates HIV-1 replication in macrophages and T lymphocytes. We further show that increased levels of IL-8 are present in the lymphoid tissue of patients with AIDS. In addition, we demonstrate that compounds which inhibit the actions of IL-8 and GRO-alpha via their receptors, CXCR1 and CXCR2, also inhibit HIV-1 replication in both T lymphocytes and macrophages, indicating potential therapeutic uses for these compounds in HIV-1 infection and AIDS.

Human CC chemokine liver-expressed chemokine/CCL16 is a functional ligand for CCR1, CCR2 and CCR5, and constitutively expressed by hepatocytes

Liver-expressed chemokine (LEC)/CCL16 is a human CC chemokine selectively expressed in the liver. Here, we investigated its receptor usage by calcium mobilization and chemotactic assays using mouse L1.2 pre-B cell lines stably expressing a panel of 12 human chemokine receptors. At relatively high concentrations, LEC induced calcium mobilization and chemotaxis via CCR1 and CCR2. LEC also induced calcium mobilization, but marginal chemotaxis via CCR5. Consistently, LEC was found to bind to CCR1, CCR2 and CCR5 with relatively low affinities. The binding of LEC to CCR8 was much less significant. In spite of its binding to CCR5, LEC was unable to inhibit infection of an R5-type HIV-1 to activated human peripheral blood mononuclear cells even at high concentrations. In human liver sections, hepatocytes were strongly stained by anti-LEC antibody. HepG2, a human hepatocarcinoma cell line, was found to constitutively express LEC. LEC was also present in the plasma samples from healthy adult donors at relatively high concentrations (0.3--4 nM). Taken together, LEC is a new low-affinity functional ligand for CCR1, CCR2 and CCR5, and is constitutively expressed by liver parenchymal cells. The presence of LEC in normal plasma at relatively high concentrations may modulate inflammatory responses.

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.