Synergistic induction of apoptosis in primary CD4(+) T cells by macrophage-tropic HIV-1 and TGF-beta1

Mycobacterium tuberculosis and host interactions in the manifestation of tuberculosis

The final step of epigenetic processes is changing the gene expression in a new microenvironment in the body, such as neuroendocrine changes, active infections, oncogenes, or chemical agents. The case of tuberculosis (TB) is an outcome of Mycobacterium tuberculosis (M.tb) and host interaction in the manifestation of active and latent TB or clearance. This comprehensive review explains and interprets the epigenetics findings regarding gene expressions on the host-pathogen interactions in the development and progression of tuberculosis. This review introduces novel insights into the complicated host-pathogen interactions, discusses the challengeable results, and shows the gaps in the clear understanding of M.tb behavior. Focusing on the biological phenomena of host-pathogen interactions, the epigenetic changes, and their outcomes provides a promising future for developing effective TB immunotherapies when converting gene expression toward appropriate host immune responses gradually becomes attainable. Overall, this review may shed light on the dark sides of TB pathogenesis as a life-threatening disease. Therefore, it may support effective planning and implementation of epigenetics approaches for introducing proper therapies or effective vaccines.

HIV-1 Transcription Inhibitor 1E7-03 Decreases Nucleophosmin Phosphorylation

Transcription activation of latent human immunodeficiency virus-1 (HIV-1) occurs due to HIV-1 rebound, the interruption of combination antiretroviral therapy, or development of drug resistance. Thus, novel HIV-1 inhibitors, targeting HIV-1 transcription are needed. We previously developed an HIV-1 transcription inhibitor, 1E7-03, that binds to the noncatalytic RVxF-accommodating site of protein phosphatase 1 and inhibits HIV-1 replication in cultured cells and HIV-1-infected humanized mice by impeding protein phosphatase 1 interaction with HIV-1 Tat protein. However, host proteins and regulatory pathways targeted by 1E7-03 that contribute to its overall HIV-1 inhibitory activity remain to be identified. To address this issue, we performed label-free quantitative proteome and phosphoproteome analyses of noninfected and HIV-1-infected CEM T cells that were untreated or treated with 1E7-03. 1E7-03 significantly reprogramed the phosphorylation profile of proteins including PPARα/RXRα, TGF-β, and PKR pathways. Phosphorylation of nucleophosmin (NPM1) at Ser-125 residue in PPARα/RXRα pathway was significantly reduced (>20-fold, p = 1.37 × 10-9), followed by the reduced phosphorylation of transforming growth factor-beta 2 at Ser-46 (TGF-β2, >12-fold, p = 1.37 × 10-3). Downregulation of NPM1's Ser-125 phosphorylation was further confirmed using Western blot. Phosphorylation mimicking NPM1 S125D mutant activated Tat-induced HIV-1 transcription and exhibited enhanced NPM1-Tat interaction compared to NPM1 S125A mutant. Inhibition of Aurora A or Aurora B kinases that phosphorylate NPM1 on Ser-125 residue inhibited HIV-1, further supporting the role of NPM1 in HIV-1 infection. Taken together, 1E7-03 reprogrammed PPARα/RXRα and TGF-β pathways that contribute to the inhibition of HIV-1 transcription. Our findings suggest that NPM1 phosphorylation is a plausible target for HIV-1 transcription inhibition.

Enhanced Intestinal TGF-β/SMAD-Dependent Signaling in Simian Immunodeficiency Virus Infected Rhesus Macaques

Transforming growth factor-β signaling (TGF-β) maintains a balanced physiological function including cell growth, differentiation, and proliferation and regulation of immune system by modulating either SMAD2/3 and SMAD7 (SMAD-dependent) or SMAD-independent signaling pathways under normal conditions. Increased production of TGF-β promotes immunosuppression in Human Immunodeficiency Virus (HIV)/Simian Immunodeficiency Virus (SIV) infection. However, the cellular source and downstream events of increased TGF-β production that attributes to its pathological manifestations remain unknown. Here, we have shown increased production of TGF-β in a majority of intestinal CD3⁻CD20⁻CD68⁺ cells from acute and chronically SIV infected rhesus macaques, which negatively correlated with the frequency of jejunum CD4⁺ T cells. No significant changes in intestinal TGF-β receptor II expression were observed but increased production of the pSMAD2/3 protein and SMAD3 gene expression in jejunum tissues that were accompanied by a downregulation of SMAD7 protein and gene expression. Enhanced TGF-β production by intestinal CD3⁻CD20⁻CD68⁺ cells and increased TGF-β/SMAD-dependent signaling might be due to a disruption of a negative feedback loop mediated by SMAD7. This suggests that SIV infection impacts the SMAD-dependent signaling pathway of TGF-β and provides a potential framework for further study to understand the role of viral factor(s) in modulating TGF-β production and downregulating SMAD7 expression in SIV. Regulation of mucosal TGF-β expression by therapeutic TGF-β blockers may help to create effective antiviral mucosal immune responses.

TGFβRI antagonist inhibits HIV-1 Nef-induced CC chemokine family ligand 2 (CCL2) in the brain and prevents spatial learning impairment

BACKGROUND

HIV-1-associated neurocognitive disorders (HAND) progression is related to continued inflammation despite undetectable viral loads and may be caused by early viral proteins expressed by latently infected cells. Astrocytes represent an HIV reservoir in the brain where the early viral neurotoxin negative factor (Nef) is produced. We previously demonstrated that astrocytic expression of Nef in the hippocampus of rats causes inflammation, macrophage infiltration, and memory impairment. Since these processes are affected by TGFβ signaling pathways, and TGFβ-1 is found at higher levels in the central nervous system of HIV-1+ individuals and is released by astrocytes, we hypothesized a role for TGFβ-1 in our model of Nef neurotoxicity.

METHODS

To test this hypothesis, we compared cytokine gene expression by cultured astrocytes expressing Nef or green fluorescent protein. To determine the role of Nef and a TGFβRI inhibitor on memory and learning, we infused astrocytes expressing Nef into the hippocampus of rats and then treated them daily with an oral dose of SD208 (10 mg/kg) or placebo for 7 days. During this time, locomotor activity was recorded in an open field and spatial learning tested in the novel location recognition paradigm. Postmortem tissue analyses of inflammatory and signaling molecules were conducted using immunohistochemistry and immunofluorescence.

RESULTS

TGFβ-1 was induced in cultures expressing Nef at 24 h followed by CCL2 induction which was prevented by blocking TGFβRI with SD208 (competitive inhibitor). Interestingly, Nef seems to change the TGFβRI localization as suggested by the distribution of the immunoreactivity. Nef caused a deficit in spatial learning that was recovered upon co-administration of SD208. Brain tissue from Nef-treated rats given SD208 showed reduced CCL2, phospho-SMAD2, cluster of differentiation 163 (CD163), and GFAP immunoreactivity compared to the placebo group.

CONCLUSIONS

Consistent with our previous findings, rats treated with Nef showed deficits in spatial learning and memory in the novel location recognition task. In contrast, rats treated with Nef + SD208 showed better spatial learning suggesting that Nef disrupts memory formation in a TGFβ-1-dependent manner. The TGFβRI inhibitor further reduced the induction of inflammation by Nef which was concomitant with decreased TGFβ signaling. Our findings suggest that TGFβ-1 signaling is an intriguing target to reduce neuroHIV.

Suppressive effect mediated by human adipose-derived stem cells on T cells involves the activation of JNK

Adipose-derived stem cells (ADSCs) have an immunomodulatory role in vascularized composite tissue allo-transplantation (VCA). However, the specific effects of ADSCs on lymphocytes remain to be fully elucidated. The present study examined the changes in T cells co-cultured with ADSCs in terms of the proliferation by Cell Counting Kit-8 assay, cell cycle profile and apoptosis by flow cytom-etry, inflammatory cytokine production by polymerase chain reaction and ELISA, in addition to the expression of survival proteins by western blotting. The ADSCs reduced the viability of Jurkat T cells and downregulated the transcription of tumor necrosis factor-α and transforming growth factor-β1. Co-culture with ADSCs also induced apoptosis and increased the levels of phosphorylated c-Jun N-terminal kinase in the T cells. Taken together, these findings confirmed that ADSCs modulate the host immune response by suppressing T cells.

The Role of Transforming Growth Factor Beta-1 in the Progression of HIV/AIDS and Development of Non-AIDS-Defining Fibrotic Disorders

Even after attainment of sustained viral suppression following implementation of highly active antiretroviral therapy, HIV-infected persons continue to experience persistent, low-grade, systemic inflammation. Among other mechanisms, this appears to result from ongoing microbial translocation from a damaged gastrointestinal tract. This HIV-related chronic inflammatory response is paralleled by counteracting, but only partially effective, biological anti-inflammatory processes. Paradoxically, however, this anti-inflammatory response not only exacerbates immunosuppression but also predisposes for development of non-AIDS-related, non-communicable disorders. With respect to the pathogenesis of both sustained immunosuppression and the increased frequency of non-AIDS-related disorders, the anti-inflammatory/profibrotic cytokine, transforming growth factor-β1 (TGF-β1), which remains persistently elevated in both untreated and virally suppressed HIV-infected persons, may provide a common link. In this context, the current review is focused on two different, albeit related, harmful activities of TGF-β1 in HIV infection. First, on the spectrum of anti-inflammatory/immunosuppressive activities of TGF-β1 and the involvement of this cytokine, derived predominantly from T regulatory cells, in driving disease progression in HIV-infected persons via both non-fibrotic and profibrotic mechanisms. Second, the possible involvement of sustained elevations in circulating and tissue TGF-β1 in the pathogenesis of non-AIDS-defining cardiovascular, hepatic, pulmonary and renal disorders, together with a brief comment on potential TGF-β1-targeted therapeutic strategies.

Regulation of the Immune Response by TGF-β: From Conception to Autoimmunity and Infection

Transforming growth factor β (TGF-β) is a pleiotropic cytokine involved in both suppressive and inflammatory immune responses. After 30 years of intense study, we have only begun to elucidate how TGF-β alters immunity under various conditions. Under steady-state conditions, TGF-β regulates thymic T-cell selection and maintains homeostasis of the naïve T-cell pool. TGF-β inhibits cytotoxic T lymphocyte (CTL), Th1-, and Th2-cell differentiation while promoting peripheral (p)Treg-, Th17-, Th9-, and Tfh-cell generation, and T-cell tissue residence in response to immune challenges. Similarly, TGF-β controls the proliferation, survival, activation, and differentiation of B cells, as well as the development and functions of innate cells, including natural killer (NK) cells, macrophages, dendritic cells, and granulocytes. Collectively, TGF-β plays a pivotal role in maintaining peripheral tolerance against self- and innocuous antigens, such as food, commensal bacteria, and fetal alloantigens, and in controlling immune responses to pathogens.

Plasma concentrations of transforming growth factor beta 1 in non-progressive HIV-1 infection correlates with markers of disease progression

The human immunodeficiency virus (HIV) infection shows variable rate of disease progression. The underlying biological and molecular mechanisms involved in determining progression of HIV infection are not fully understood. The aims of this study were to determine plasma concentrations of active TGF β 1, Th1 and Th2 cytokines in patients with non-progressive and those with progressive HIV-1 infection, as well as to determine if there is an association of these cytokines to disease progression. In a cross-sectional study of 61 HIV-1 infected individuals categorized according to disease progression as having non-progressive HIV-1 infection (n=14) and progressive infection (n=47), plasma levels of active TGF β 1, INF-γ, TNF-α, IL-10, IL-1β, IL-12p70 and IL-13 were compared with HIV uninfected healthy controls (n=12). Plasma concentration of these cytokines was measured using a highly sensitive luminex200 XMAP assay. Pearson correlation test was used to assess the correlation of cytokines with CD4+ and CD8+ T cells, CD4:CD8 ratio and plasma HIV-1 RNA in the different study groups. Plasma concentrations of TGF β 1 and IL-10 were significantly decreased while IL-1β, IL-12p70 and TNF-α were increased in patients with non-progressive HIV-1 infection compared to patients with progressive infection. Plasma levels of TGF β 1 and IL-10 showed an inverse correlation with CD8+ T cell counts and CD4:CD8 ratios in patients with non-progressive HIV-1 infection, while plasma HIV-1 RNA positively correlated with CD4+ T cell counts. Plasma levels of TNF-α, IL-1β, IL-12p70 and IL-13 positively correlated with CD4+ T cell counts and inversely correlated with plasma HIV-1 RNA, CD8+ T cell count and CD4:CD8 ratio in patients with non-progressive infection. The correlation of cytokines to the state of T-lymphocyte and plasma HIV-1 RNA found in this study may provide insight into the role of cytokines in both progressive and non-progressive HIV-1 infection. Additionally, these findings may have implications for systemic cytokine-based therapies in HIV-1 infection.

Mechanisms of apoptosis of T-cells in human tuberculosis

The role of TGF-beta TNF-alpha FasL and Bcl-2 in apoptosis of CD4 T-cells during active TB was studied. Coculture of PBMC from TB patients with neutralizing antibodies to TGF-beta or TNF-alpha decreased spontaneous (P < or = 0.05) and MTB-induced (P < or = 0.02) T-cell apoptosis by 50-90%, but effects were not additive. Interestingly, only levels of TGF-beta in supernatants correlated with rates of spontaneous and MTB-induced apoptosis. FasL surface and mRNA expression were higher in unstimulated and MTB-stimulated PBMC from patients than controls, and neutralization of FasL abrogated apoptosis of T-cells from patients only. Intracellular Bcl-2 protein was lower among unstimulated CD4 T-cells from patients than those from controls (P < or = 0.02), and MTB stimulation reduced intracellular Bcl-2 content in CD4 T-cells from patients only (P < or = 0.001). These findings may indicate that, during TB, predisposition of CD4 T-cells to apoptosis may involve both low expression of Bcl-2, and excessive expression of TGF-beta TNF-alpha and FasL.

Human immunodeficiency virus types 1 and 2 have different replication kinetics in human primary macrophage culture

This study compares the replication of primary isolates of human immunodeficiency virus type 2 (HIV-2) and type 1 (HIV-1) in monocyte-derived macrophages (MDMs). Eleven HIV-2 and five HIV-1 primary isolates that use CCR5, CXCR4 or both coreceptors to enter cells were included. Regardless of coreceptor preference, 10 of 11 HIV-2 viruses could enter, reverse transcribe and produce fully infectious virus in MDMs with efficiency equal to that in peripheral blood mononuclear cells. However, the kinetics of replication of HIV-2 compared with HIV-1 over time were distinct. HIV-2 had a burst of virus replication 2 days after infection that resolved into an apparent 'latent state' at day 3. HIV-1, however, continued to produce infectious virions at a lower, but steady, rate throughout the course of infection. These results may have implications for the lower pathogenesis and viral-load characteristics of HIV-2 infection.

Apoptosis as a mechanism of natural resistance to HIV-1 infection in an exposed but uninfected population

BACKGROUND

Apoptosis, also known as programmed cell death, has been reported not only as a pathogenic mechanism, but also as a mechanism of resistance and control of a variety of infections. Particularly during HIV-1 infection, apoptosis is the main mechanism by which infected and uninfected CD4+ lymphocytes are eliminated. However, apoptosis as a mechanism of natural resistance to HIV infection has this far not been explored.

OBJECTIVE

To determine whether apoptosis could explain, at least in part, the natural resistance to HIV infection observed in some exposed but uninfected individuals (ESN).

RESULTS

Our data shows that peripheral blood monocytes in the ESN group has a predisposition to undergo spontaneous apoptosis, as well as apoptosis induced by HIV infection in vitro, compared with monocyte population from the control group at low risk of HIV infection.

CONCLUSIONS

These findings suggest that, in some ESN individuals, monocytes could play an important role in the control of HIV infection by undergoing apoptosis. However, since the variability among individuals is large, studies with larger cohorts focusing in monocyte apoptosis as pathogenic mechanisms are required.

Transforming growth factor-beta1 increases CXCR4 expression, stromal-derived factor-1alpha-stimulated signalling and human immunodeficiency virus-1 entry in human monocyte-derived macrophages

Stromal-derived factor-1 (SDF-1/CXCL12) and its receptor CXCR4 play crucial roles in leukocyte migration and activation, as well as embryogenesis, angiogenesis, cancer and viral pathogenesis. CXCR4 is one of the major human immunodeficiency virus-1 (HIV-1) coreceptors on macrophages. In many tissues macrophages are one of the predominant cell types infected by HIV-1 and act as a reservoir for persistent infection and viral dissemination. In patients infected by HIV-1, blood and tissue levels of transforming growth factor-beta1 (TGF-beta1) are increased. The purpose of this study was to evaluate the effects of TGF-beta1 on CXCR4 expression and function in primary human monocyte-derived macrophages (MDMs) and rat microglia. TGF-beta1 up-regulated CXCR4 and enhanced SDF-1alpha-stimulated ERK1,2 phosphorylation in these cells. The increased CXCR4 expression in human MDMs resulted in increased susceptibility of the cells to entry by dual-tropic CXCR4-using HIV-1 (D-X4). In contrast, TGF-beta1 failed to increase CCR5 expression or infection by a CCR5-using virus in MDMs. Our data demonstrate that TGF-beta1 enhances macrophage responsiveness to SDF-1alpha stimulation and susceptibility to HIV-1 by selectively increasing expression of CXCR4. The results suggest that increased expression of CXCR4 on macrophages may contribute to the emergence of dual-tropic X4 viral variants at later stages of HIV-1 infection.

Role of cytokines and chemokines in the regulation of innate immunity and HIV infection

The earliest defense against microbial infection is represented by the responses of the innate (or natural) immune system, that also profoundly regulates the adaptive (or acquired) T- and B-cell immune responses. Activation of the innate immune system is primed by microbial invasion in response to conserved structures present in large groups of microorganisms (LPS, peptidoglycan, double-stranded RNA), and is finely tuned by different cell types (including dendritic cells, macrophages, natural killer cells, natural killer T cells, and gammadelta T cells). In addition, several soluble factors (complement components, defensins, mannose-binding lectins, interferons, cytokines and chemokines) can play a major role in the regulation of both the innate and adaptive immunity. In this review, we will briefly overview the regulation of some cellular subsets of the innate immune system particularly involved in human immunodeficiency virus (HIV) infection and then focus our attention on those cytokines and chemokines whose levels of expression are more profoundly affected by HIV infection and that, conversely, can modulate virus infection and replication.

Constitutive association of cell surface CCR5 and CXCR4 in the presence of CD4

Chemokine receptors CCR5 and CXCR4 are the major coreceptors of HIV-1 infection and also play fundamental roles in leukocyte trafficking, metastasis, angiogenesis, and embyogenesis. Here, we show that transfection of CCR5 into CXCR4 and CD4 expressing 3T3 cells enhances the cell surface level of CXCR4. In CCR5 high expressing cells, cell surface level of CXCR4 was incompletely modulated in the presence of the CXCR4 ligand CXCL12/SDF-1alpha. CCR5 was resistant to ligand-dependent modulation with the CCR5 ligand CCL5/RANTES. Confocal laser microscopy revealed that CCR5 was colocalized with CXCR4 on the cell surface. In CD4 expressing CCR5 and CXCR4 double positive NIH 3T3 cells, immunoprecipitation followed by Western blot analysis revealed that CCR5 was associated with CXCR4 and CD4. CXCR4 and CCR5 were not co-immunoprecipitated in cells expressing CCR5 and CXCR4 but without CD4 expression. Compared to NIH 3T3CD4 cells expressing CXCR4, the entry of an HIV-1 X4 isolate (HCF) into NIH 3T3CD4 expressing both CXCR4 and CCR5 was reduced. Our data indicate that chemokine receptors interact with each other, which may modulate chemokine-chemokine receptor interactions and HIV-1 coreceptor functions.

HIV-specific CD8+ T cells exhibit markedly reduced levels of Bcl-2 and Bcl-xL

Human immunodeficiency virus-specific CD8(+) T cells are highly sensitive to spontaneous and CD95/Fas-induced apoptosis, and this sensitivity may impair their ability to control HIV infection. To elucidate the mechanism behind this sensitivity, in this study we examined the levels of antiapoptotic molecules Bcl-2 and Bcl-x(L) in HIV-specific CD8(+) T cells from HIV-infected individuals. Bcl-2 expression was markedly decreased in HIV-specific CD8(+) T cells compared with CMV-specific and total CD8(+) T cells from HIV-infected individuals as well as total CD8(+) T cells from healthy donors. CD8(+) T cell Bcl-2 levels inversely correlated with spontaneous and CD95/Fas-induced apoptosis of CD8(+) T cells from HIV-infected individuals. HIV-specific CD8(+) T cells also had significantly lower levels of Bcl-x(L) compared with CMV-specific CD8(+) T cells. Finally, IL-15 induces both Bcl-2 and Bcl-x(L) expression in HIV-specific and total CD8(+) T cells, and this correlated with apoptosis inhibition and increased survival in both short- and long-term cultures. Our data indicate that reduced Bcl-2 and Bcl-x(L) may play an important role in the increased sensitivity to apoptosis of HIV-specific CD8(+) T cells and suggest a possible mechanism by which IL-15 increases their survival.

Amino-terminal processing of MIP-1?/CCL4 by CD26/dipeptidyl-peptidase IV

CD26 is a membrane-bound ectopeptidase with dipeptidyl peptidase IV (DPPIV) activity that has diverse functional properties in T cell physiology and in regulation of bioactive peptides. We have previously reported that activated human peripheral lymphocytes (PBL) secrete an amino-terminal truncated form of macrophage inflammatory protein (MIP)-1beta/(3-69) with novel functional specificity for CCR1, 2, and 5. In this report, we show that the full length MIP-1beta is processed by CD26/DPPIV to the truncated form and that cleavage can be blocked by DPPIV inhibitory peptides derived from HIV Tat(1-9) or the thromboxane A2 receptor, TAX2-R(1-9). Addition of Tat(1-9) or TAX2-R(1-9) peptides to PBL cultures partially blocks endogenous MIP-1beta processing. The kinetics of conversion of MIP-1beta from intact to MIP-1beta(3-69) in activated PBLs correlates with cell surface expression of CD26. Our results suggest that NH2-terminal processing of MIP-1beta and possibly other chemokines may depend on the balance between CD26/DPPIV enzymatic activity and cellular and viral proteins that modulate enzyme function.

Natural truncation of the chemokine MIP-1 beta /CCL4 affects receptor specificity but not anti-HIV-1 activity

Activated lymphocytes synthesize and secrete substantial amounts of the beta-chemokines macrophage inflammatory protein (MIP)-1 alpha/CCL3 and MIP-1 beta/CCL4, both of which inhibit infection of cells with human immunodeficiency virus type 1 (HIV-1). The native form of MIP-1 beta secreted by activated human peripheral blood lymphocytes (MIP-1 beta(3-69)) lacks the two NH(2)-terminal amino acids of the full-length protein. This truncated form of MIP-1 beta has now been affinity-purified from the culture supernatant of such cells, and its structure has been confirmed by mass spectrometry. Functional studies of the purified protein revealed that MIP-1 beta(3-69) retains the abilities to induce down-modulation of surface expression of the chemokine receptor CCR5 and to inhibit the CCR5-mediated entry of HIV-1 in T cells. Characterization of the chemokine receptor specificity of MIP-1 beta(3-69) showed that the truncated protein not only shares the ability of intact MIP-1 beta to induce Ca(2+) signaling through CCR5, but unlike the full-length protein, it also triggers a Ca(2+) response via CCR1 and CCR2b. These results demonstrate that NH(2)-terminally truncated MIP-1 beta functions as a chemokine agonist with expanded receptor reactivity, which may represent an important mechanism for regulation of immune cell recruitment during inflammatory and antiviral responses.

T-cell responses against chronic lymphocytic leukemia cells: implications for immunotherapy

Chronic lymphocytic leukemia (CLL) cells are ineffective antigen-presenting cells (APCs) although CD40-activated CLL cells can stimulate proliferation of autologous and allogeneic T cells. We examined the antigen-presenting capacity of CD40-activated CLL cells as well as dendritic cells pulsed with apoptotic bodies of CLL cells to generate autologous and allogeneic immune responses against CLL cells. Both APC types were capable of generating T-cell lines that proliferate specifically in response to unstimulated CLL cells. Whereas cytotoxic responses against stimulated and unstimulated CLL cells could be repeatedly generated by allogeneic healthy donors, autologous cytotoxic immune responses against CD40-activated and native CLL cells were rarely detected. However, T cells isolated from patients with CLL could recognize and lyse allogeneic stimulated and unstimulated CLL cells, demonstrating that cytotoxic T cells from these tumor-bearing patients are functionally intact.

Role of tyrosine phosphorylation in ligand-independent sequestration of CXCR4 in human primary monocytes-macrophages

The chemokine stromal cell-derived factor (SDF)-1 and its receptor, CXCR4, play important roles in human immunodeficiency virus type 1 (HIV-1) pathophysiology, leukocyte trafficking, inflammation, hematopoiesis, embryogenesis, angiogenesis, and cancer metastasis. The effects of cytokines on the regulation of CXCR4 function were investigated in human primary monocytes-macrophages. The expression of functional CXCR4 on the cell surface was demonstrated by the detection of ligand-induced Ca(2+) mobilization, chemotaxis, and ligand-induced receptor endocytosis. Surface CXCR4 expression was down-regulated by cytokines interleukin-4 (IL-4), IL-13, and granulocyte-macrophage colony-stimulating factor (GM-CSF) and up-regulated by IL-10 and transforming growth factor-beta 1. Down-regulation was mediated post-translationally, in the absence of protein degradation, through an endocytotic mechanism. In contrast to SDF-1 alpha-induced CXCR4 endocytosis, cytokine-induced endocytosis of this receptor was independent of actin filament polymerization. GM-CSF increased the expression of G protein-coupled receptor kinase 3 (GRK3), beta-arrestin-1, Pyk2, and focal adhesion kinase (FAK). Cytokine treatment also increased the total and tyrosine-specific phosphorylation of CXCR4 as well as the phosphorylation of FAK on tyrosine 397. It also induced the formation of GRK3.CXCR4 or FAK.CXCR4 complexes. Infection of macrophages by primary R5X4 and X4 isolates of HIV-1 was inhibited by IL-4, IL-13, and GM-CSF, an effect that was associated with down-regulation of surface CXCR4 expression. These data indicate that ligand-dependent and ligand-independent endocytoses of CXCR4 are mediated by different mechanisms. Cytokine-induced endocytosis of chemokine receptors may be of therapeutic value in HIV-1 infection, inflammation, tumor metastasis, and defective hematopoiesis.