Adenovirus-Mediated Human Immunodeficiency Virus-1 Nef Expression in Human Monocytes/Macrophages and Effect of Nef on Downmodulation of Fcγ Receptors and Expression of Monokines

HIV-1 infection of T cells and macrophages are differentially modulated by virion-associated Hck: a Nef-dependent phenomenon

The proline repeat motif (PxxP) of Nef is required for interaction with the SH3 domains of macrophage-specific Src kinase Hck. However, the implication of this interaction for viral replication and infectivity in macrophages and T lymphocytes remains unclear. Experiments in HIV-1 infected macrophages confirmed the presence of a Nef:Hck complex which was dependent on the Nef proline repeat motif. The proline repeat motif of Nef also enhanced both HIV-1 infection and replication in macrophages, and was required for incorporation of Hck into viral particles. Unexpectedly, wild-type Hck inhibited infection of macrophages, but Hck was shown to enhance infection of primary T lymphocytes. These results indicate that the interaction between Nef and Hck is important for Nef-dependent modulation of viral infectivity. Hck-dependent enhancement of HIV-1 infection of T cells suggests that Nef-Hck interaction may contribute to the spread of HIV-1 infection from macrophages to T cells by modulating events in the producer cell, virion and target cell.

Induction of CC-chemokines with antiviral function in macrophages by the human T lymphotropic virus type 2 transactivating protein, Tax2

Recent data provide evidence that co-infection with human immunodeficiency virus type 1 (HIV-1) and human T lymphotropic virus type 2 (HTLV-2) delays progression to AIDS compared to isolated HIV-1 infection. These results were linked to expression of the HTLV-2 transcriptional activating gene known as Tax2. Preliminary studies in lymphocytic systems suggest that Tax2 is responsible for induction of CC-chemokines, which play a major role in innate immune responses against HIV-1. In this study, the effect of Tax2 on CC-chemokines (MIP-1α/CCL3, MIP-1β/CCL4, and RANTES/CCL5) in monocyte-derived macrophages (MDMs) was evaluated. An immortalized human monocytic cell line (U937) and donor-derived MDMs were used to evaluate these interactions. These cells were cultured in vitro, allowed to mature into macrophages for 14 d, and treated with Tax2 or Tax1 (the transcriptional activator of HTLV-1) at three concentrations (1, 10, and 100 pM) daily thereafter. Extracellular bacterial extract (EBE) lacking the vector and untreated samples served as controls. An additional group of donor-derived MDMs were transduced with an adenovirus vector that expressed either Tax2 or green fluorescent protein (GFP). Liposomal transfection agents alone were used as controls. Supernatants were collected from each sample on multiple days post-maturation and evaluated for MIP-1α, MIP-1β, and RANTES, by enzyme-linked immunosorbent assay. Analysis of variance and Tukey's Honestly Significant Difference tests were used to analyze the results. In all systems, cells exposed to either Tax2 or Tax1 expressed significantly (p<0.01) higher concentrations of CC-chemokines than controls. There was no significant difference in chemokine expression between Tax1-treated and Tax2-treated samples, between EBE-treated and EBE-untreated samples, or between GFP-transduced MDMs and controls. This suggests that HTLV-2 could alter innate immune responses in macrophagic reservoirs of HIV-1 in HIV-1/HTLV-2 co-infected individuals, and could guide the development of HIV-1 treatments.

Exogenous nef induces proinflammatory signaling events in murine macrophages

Despite the fact that murine cells are not permissive for human immunodeficiency virus type 1 (HIV-1) infection, several investigators have constructed transgenic (Tg) mice to model HIV-1-induced diseases to overcome this restriction. The generation of Tg mice expressing selected HIV-1 genes revealed that Nef harbors a major disease determinant. HIV-1 Nef protein is a molecular adapter able to interact with several cellular partners, interfering with cellular functions. The phenotype of Nef Tg mice was extensively characterized regarding in vivo development of AIDS-like disease and the effects of Nef expression in T lymphocytes, but the functions eventually corrupted by Nef in monocytes and macrophages were less studied. Nef treatment of human monocyte-derived macrophages induces the internalization of the protein and modulates the production and secretion of different chemokines and cytokines by activating specific intracellular signaling pathways (i.e., NF-κB, MAPK, and IRF3). Therefore we set up an in vitro murine macrophage-based model using stabilized cell lines and primary peritoneal macrophages, and treated them with recombinant myristoylated Nef(SF2) (recNef). Like human cells, murine macrophages responded to Nef treatment, activating IKK-α and IKK-β, JNK, and p38 MAP kinases. Activation of the NF-κB pathway is mandatory for the synthesis and release of a pool of cytokines and chemokines, including IFN-β, that induce tyrosine phosphorylation of the signal transducer and activator of transcription (STAT)-1, STAT-2, and STAT-3, in an autocrine and paracrine manner, confirming that murine macrophages respond to Nef similarly to human ones. These data extend the results previously obtained in human primary macrophages, allowing the use of murine cells in culture to study signaling events modulated by Nef in myeloid-derived cells. In particular, it may be feasible to use macrophages derived from mice knocked out in specific signaling intermediates to obtain greater insight into the mechanism of Nef-induced effects.

Evaluation of transduction efficiency in macrophage colony-stimulating factor differentiated human macrophages using HIV-1 based lentiviral vectors

BACKGROUND

Monocyte-derived macrophages contribute to atherosclerotic plaque formation. Therefore, manipulating macrophage function could have significant therapeutic value. The objective of this study was to determine transduction efficiency of two HIV-based lentiviral vector configurations as delivery systems for the transduction of primary human blood monocyte-derived macrophages.

RESULTS

Human blood monocytes were transduced using two VSV-G pseudotyped HIV-1 based lentiviral vectors containing EGFP expression driven by either native HIV-LTR (VRX494) or EF1α promoters (VRX1090). Lentiviral vectors were added to cultured macrophages at different times and multiplicities of infection (MOI). Transduction efficiency was assessed using fluorescence microscopy and flow cytometry. Macrophages transduced between 2 and 120 hours after culturing showed the highest transduction efficiency at 2-hours transduction time. Subsequently, cells were transduced 2 hours after culturing at various vector concentrations (MOIs of 5, 10, 25 and 50) to determine the amount of lentiviral vector particles required to maximally transduce human monocyte-derived macrophages. On day 7, all transduced cultures showed EGFP-positive cells by microscopy. Flow cytometric analysis showed with all MOIs a peak shift corresponding to the presence of EGFP-positive cells. For VRX494, transduction efficiency was maximal at an MOI of 25 to 50 and ranged between 58 and 67%. For VRX1090, transduction efficiency was maximal at an MOI of 10 and ranged between 80 and 90%. Thus, transductions performed with VRX1090 showed a higher number of EGFP-positive cells than VRX494.

CONCLUSIONS

This report shows that VSV-G pseudotyped HIV-based lentiviral vectors can efficiently transduce human blood monocyte-derived macrophages early during differentiation using low particle numbers that do not interfere with differentiation of monocytes into macrophages.

The expression of exogenous genes in macrophages: obstacles and opportunities

Over the past three decades many techniques for expressing exogenous genes in a variety of cells and cell lines have been developed. Exogenous gene expression in macrophages has lagged behind that of other nonhematopioetic cells. There are many reasons for this, but most are due to technical difficulties associated with transfecting macrophages. As professional phagocytes, macrophages are endowed with many potent degradative enzymes that can disrupt nucleic acid integrity and make gene transfer into these cells an inefficient process. This is especially true of activated macrophages which undergo a dramatic change in their physiology following exposure to immune or inflammatory stimuli. Viral transduction of these cells has been hampered because macrophages are end-stage cells that generally do not divide; therefore, some of the vectors that depend on integration into a replicative genome have met with limited success. Furthermore, macrophages are quite responsive to "danger signals," and therefore several of the original viral vectors that were used for gene transfer induced potent anti-viral responses in these cells making these vectors inappropriate for gene delivery. Many of these difficulties have been largely overcome, and relatively high efficiency gene expression in primary human or murine macrophages is becoming more routine. In the present chapter we discuss some of the gene expression techniques that have met with success and review the advantages and disadvantages of each.

HIV-1 Tat mediates degradation of RON receptor tyrosine kinase, a regulator of inflammation

HIV encodes several proteins, including Tat, that have been demonstrated to modulate the expression of receptors critical for innate immunity, including MHC class I, mannose receptor, and beta(2)-microglobulin. We demonstrate that Tat targets the receptor tyrosine kinase recepteur d'origine nantais (RON), which negatively regulates inflammation and HIV transcription, for proteosome degradation. Tat decreases cell surface RON expression in HIV-infected monocytic cells, and Tat-mediated degradation of RON protein is blocked by inhibitors of proteosome activity. Tat specifically induced down-regulation of RON and not other cell surface receptors, such as the transferrin receptor, the receptor tyrosine kinase TrkA, or monocytic markers CD14 and ICAM-1. The Tat trans activation domain is required for RON degradation, and this down-regulation is dependent on the integrity of the kinase domain of RON receptor. We propose that Tat mediates degradation of RON through a ubiquitin-proteosome pathway, and suggest that by targeting signals that modulate inflammation, Tat creates a microenvironment that is optimal for HIV replication and progression of AIDS-associated diseases.

Dual-promoter lentiviral system allows inducible expression of noxious proteins in macrophages

In-depth studies of innate immunity require efficient genetic manipulation of macrophages, which is especially difficult in primary macrophages. We have developed a lentiviral system for inducible gene expression both in macrophage cell lines and in primary macrophages. A transgenic mouse strain C3H.TgN(SRA-rtTA) that expresses reverse tetracycline transactivator (rtTA) under the control of macrophage-specific promoter, a modified human Scavenger Receptor A (SRA) promoter was generated. For gene delivery, we constructed a dual-promoter lentiviral vector, in which expression of a "gene-of-interest" is driven by a doxycycline-inducible promoter and the expression of a selectable surface marker is driven by an independent constitutive promoter UBC. This vector is used for transduction of bone marrow-derived macrophage precursors. The transduced cells can be enriched to 95-99% purity using marker-specific monoclonal antibodies, expanded and differentiated into mature macrophages or myeloid dendritic cells. We also successfully used this approach for inducible protein expression in hard to transfect macrophage cell lines. Because many proteins, which are expressed by activated or infected macrophages, possess cytotoxic, anti-proliferative or pro-apoptotic activities, generation of stable macrophage cell lines that constitutively express those proteins is impossible. Our method will be especially useful to study immunity-related macrophage proteins in their physiological context during macrophage activation or infection.

Tumor hypoxia and targeted gene therapy

Hypoxia is an integral characteristic of the tumor microenvironment, primarily due to the microvascular defects that accompany the accelerated neoplastic growth. The presence of tumor hypoxic areas correlates with negative outcome after radiotherapy, chemotherapy, and surgery, as hypoxia not only provides an environment directly facilitating chemo- and radio-resistance, but also encourages the evolution of phenotypic changes inducing permanent resistance to treatment and metastatic spread. Therefore, successful treatment of hypoxic cells has the potential to not only improve local control but also impact overall patient survival. Specific and selective targeting of hypoxic tumor areas can be achieved at all three steps of a gene therapy treatment: delivery of the therapeutic gene to the tumor, regulation of gene expression, and therapeutic efficacy. In this review the latest developments and innovations in hypoxia-targeted gene therapy are discussed. In particular, approaches such as hypoxia-conditionally replicating viruses, cellular vehicles, and gene therapy means to disrupt the hypoxia-inducible factor (HIF) signaling are outlined.

HIV-1 infection of mononuclear phagocytic cells: the case for bacterial innate immune deficiency in AIDS

HIV-1 infection of mononuclear phagocytic cells, comprising monocytes, macrophages, and dendritic cells, has been the subject of extensive research over the past 20 years. The roles of mononuclear phagocytic cells in transmission of HIV-1 infection and as reservoirs of actively replicating virus have received particular attention. Experimental data have also accumulated about the effects of HIV-1 on the physiological function of mononuclear phagocytic cells, particularly their role in innate immunity to bacteria. The effects of HIV-1 on bacterial innate immune responses by mononuclear phagocytic cells are discussed here together with reports of direct interactions between HIV-encoded products and bacterial innate immune signalling pathways. These reports demonstrate mechanisms for HIV-mediated disruption of innate immune responses by mononuclear phagocytic cells that could provide novel therapeutic targets in HIV-infected patients. The clinical urgency is highlighted by greatly increased risk of invasive bacterial disease in this population, even in the era of highly active antiretroviral therapy. HIV-mediated injury to bacterial innate immunity provides an experimental paradigm that could broaden our overall understanding of innate immunity and be used to study responses to pathogens other than bacteria.

The HIV-1 Nef protein as a target for antiretroviral therapy

HIV-1 Nef is a peripheral membrane protein that affects both signal transduction and membrane trafficking in infected cells. Alterations in these cellular processes enhance the efficiency of viral replication and the pathogenesis of AIDS in vivo. The precise mechanisms by which Nef functions are not fully elucidated. Nef is not an enzyme but appears to act as a linker molecule, mediating a variety of protein-protein interactions. Structural, biochemical and mutational data have allowed tentative identification of the key interactive surfaces on Nef, their cellular partners and their roles in Nef activity. Nef contains an SH3-binding surface through which it can interact with cellular Src-family tyrosine kinases and/or activator molecules for small GTPases involved in signal transduction. This SH3-binding surface is important for the ability of Nef to facilitate the activation of host T-lymphocytes, a process which renders the cells more permissive for viral replication. Nef also contains two relatively unstructured, solvent-exposed loops, through which it interacts with the cellular proteins that coat vesicles involved in membrane trafficking. These surfaces are important for Nef-mediated alterations in the subcellular distribution of transmembrane proteins, a process which causes diverse effects, including the assembly of maximally infectious viral particles and viral evasion of the host immune system. These data provide precise molecular targets within the Nef protein. Molecules that bind these interactive surfaces are predicted to inhibit Nef activity and provide the basis for novel chemotherapeutic agents for the treatment of HIV-infection.

HIV-1 Nef interferes with M-CSF receptor signaling through Hck activation and inhibits M-CSF bioactivities

HIV-1 Nef protein is a major determinant of the pathogenicity of the virus. It has been shown that Nef activates Hck, a member of Src family kinase, in monocytes/macrophages and that the interaction is critical for AIDS-like disease progression in a mouse model. However, it was unclear how the molecular interaction in monocytes/macrophages leads to disease progression. Here, we show for the first time that Nef interferes with the macrophage colony-stimulating factor (M-CSF)/M-CSF receptor signal pathway. In this study, we introduced a conditionally active Nef into myeloid leukemia TF-1-fms cells and analyzed their responsiveness to M-CSF. We found that Nef-activated Hck constitutively associated with the M-CSF receptor complex. The formation of the molecular complex should occur under physiologic conditions, that is, on M-CSF stimulation. Because of aberrant molecular association, the tyrosine-phosphorylation/activation of the receptor in response to M-CSF was markedly diminished in Nef-active cells. Consequently, Nef activation caused the inhibition of M-CSF-mediated proliferation of TF-1-fms cells and macrophage differentiation of the cells induced by M-CSF and 12-O-tetradecanoylphorbol 13-acetate. These results indicate that HIV-1 Nef interferes with M-CSF receptor signaling through Hck activation and thereby inhibits M-CSF functions in monocytes/macrophages.

Cdc42 and RhoB activation are required for mannose receptor-mediated phagocytosis by human alveolar macrophages

Human alveolar macrophages (AMs) phagocytose Pneumocystis (Pc) organisms predominantly through mannose receptors, although the molecular mechanism mediating this opsonin-independent process is not known. In this study, using AMs from healthy individuals, Pc phagocytosis was associated with focal F-actin polymerization and Cdc42, Rac1, and Rho activation in a time-dependent manner. Phagocytosis was primarily dependent on Cdc42 and RhoB activation (as determined by AM transfection with Cdc42 and RhoB dominant-negative alleles) and mediated predominantly through mannose receptors (as determined by siRNA gene silencing of AM mannose receptors). Pc also promoted PAK-1 phosphorylation, which was also dependent on RhoGTPase activation. HIV infection of AMs (as a model for reduced mannose receptor expression and function) was associated with impaired F-actin polymerization, reduced Cdc42 and Rho activation, and markedly reduced PAK-1 phosphorylation in response to Pc organisms. In healthy AMs, Pc phagocytosis was partially dependent on PAK activation, but dependent on the Rho effector molecule ROCK. These data provide a molecular mechanism for AM mannose receptor-mediated phagocytosis of unopsonized Pc organisms that appears distinct from opsonin-dependent phagocytic receptors. Reduced AM mannose receptor-mediated Cdc42 and Rho activation in the context of HIV infection may represent a mechanism that contributes to the pathogenesis of opportunistic pneumonia.

RON Receptor Tyrosine Kinase, a Negative Regulator of Inflammation, Inhibits HIV-1 Transcription in Monocytes/Macrophages and Is Decreased in Brain Tissue from Patients with AIDS

Activation of macrophages and microglia cells after HIV-1 infection and their production of inflammatory mediators contribute to HIV-associated CNS diseases. The mechanisms that initiate and maintain inflammation after HIV-1 infection in the brain have not been well studied. Furthermore, it is not understood why in HIV-associated CNS disease, macrophages and microglia are biased toward inflammation rather than production of mediators that control inflammation. We have focused on the receptor tyrosine kinase RON, a critical negative regulator of macrophage function and inflammation, to determine whether this receptor regulates HIV-1 expression. Overexpressing RON in monocytes/macrophages demonstrates that RON inhibits HIV-1 proviral transcription in part by decreasing the binding activity of NF-kappaB to the HIV-1 long terminal repeat. Because macrophages and microglia cells are a critical reservoir for HIV-1 in the CNS, we examined brain tissues for RON expression and detected RON in astrocytes, cortical neurons, and monocytoid cells. RON was detected in all control patients who were HIV seronegative (n = 7), whereas six of nine brain samples obtained from AIDS patients exhibited reduced RON protein. These data suggest that RON initiates signaling pathways that negatively regulate HIV-1 transcription in monocytes/macrophages and that HIV-1 suppresses RON function by decreasing protein levels in the brain to assure efficient replication. Furthermore, HIV-1 infection would compromise the ability of RON to protect against inflammation and consequent CNS damage.

Prolonged survival of rat liver allograft with adenoviral gene transfection of human immunodeficiency virus type 1 nef

HIV-1 nef is believed to allow immune evasion by modifying cell surface molecules because of certain mechanisms such as downregulation of the major histocompatibility complex (MHC) class I molecule complex as well as upregulation of FasL. In the present study, we successfully generated a recombinant adenovirus vector containing HIV-1 nef. We detected the expression of nef in liver infected with AxCANef by immune staining and Western blotting, and confirmed its expression as persistent for more than 4 weeks. Furthermore, the surface expression of MHC class I was downregulated in AxCANef-infected hepatic cells. In addition, we also observed nef-induced FasL upregulation of gene-transfected hepatic cells. Using a DA-to-Lewis orthotopic liver transplantation model, we transfected AxCANef to a liver graft to determine whether nef expression could have an effect on recipient survival. AxCANef significantly prolonged recipient survival time (14.5 days) compared with the uninfected group (11 days) (P <.001) and the AxCALacZ-infected group (11 days) (P <.001). Histologic analysis showed reduction in the number of accumulated inflammatory cells and an increase in apoptotic cells in grafts expressing nef. In conclusion, we showed that the nef gene could prolong survival of rat liver allografts, and this result suggested the potential clinical use of its transfection.

HIV-1 Nef control of cell signalling molecules: multiple strategies to promote virus replication

HIV-1 has at its disposal numerous proteins encoded by its genome which provide the required arsenal to establish and maintain infection in its host for a considerable number of years. One of the most important and enigmatic of these proteins is Nef. The Nef protein of HIV-1 plays a fundamental role in the virus life cycle. This small protein of approximately 27 kDa is required for maximal virus replication and disease progression. The mechanisms by which it is able to act as a positive factor during virus replication is an area of intense research and although some controversy surrounds Nef much has been gauged as to how it functions. Its ability to modulate the expression of key cellular receptors important for cell activation and control signal transduction elements and events by interacting with numerous cellular kinases and signalling molecules, including members of the Src family kinases, leading to an effect on host cell function is likely to explain at least in part its role during infection and represents a finely tuned mechanism where this protein assists HIV-1 to control its host.

The expression of HIV-1 tat and nef genes induces cell-specific changes in growth properties and morphology of different types of rat cells

Among the viral regulatory genes the tat and nef genes of HIV-1 encode the proteins playing a central role in viral replication and exerting pleiotropic effects on the survival and growth of the cells. These effects differ in various cell types, possibly due to the use of genes from different HIV-1 isolates. In this work, we studied the effects of the tat and nef genes on three types of cultured rat cells: primary embryo fibroblasts, pseudonormal Rat-2, and pheochromocytoma PC12. Both genes affected growth properties and morphology of cells, the effects being cell-specific. The proliferative activity of both Rat-2 and PC12 cells was considerably increased after transfection with the tat gene. In primary rat embryo fibroblasts the tat gene induced multilayered foci. More importantly, it was shown that the efficiency of transformation was higher in cells coexpressing tat and nef. The nef gene caused considerable suppression of Rat-2 cell proliferation, but no changes in their morphology. The nef gene transfection of PC12 cells also led to suppression of their proliferative activity. In addition, cellular agglomerates which were morphologically similar to multinuclear syncytial cells were detected in these cells for the first time.

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.

Fc receptor-mediated inhibitory effect of immunoglobulin therapy on autoimmune giant cell myocarditis: concomitant suppression of the expression of dendritic cells

In the present study, the mechanisms and importance of the Fc portion of immunoglobulin in experimental giant cell myocarditis were examined. Giant cell myocarditis was induced in rats by immunization of porcine cardiac myosin. Human intact immunoglobulin (1 g. kg(-1). d(-1)) or F(ab')(2) fragments of human immunoglobulin (1 g. kg(-1). d(-1)) were administered intraperitoneally daily on days 1 to 21. Intact immunoglobulin administration significantly ameliorated myocarditis, but F(ab')(2) fragments did not. The ribonuclease protection assay revealed that therapy with intact immunoglobulin, but not F(ab')(2) fragments, suppressed the mRNA expressions of inflammatory and proinflammatory cytokines. Immunohistochemical analysis showed that therapy with intact immunoglobulin, but not F(ab')(2) fragments, suppressed dendritic cell (DC) expression during both the early and the subsequent fulminant phases. Moreover, the early treatment of intact immunoglobulin until the 11th day or 14th day, when the expression of DCs was completely suppressed, ameliorated myocarditis. However, the late treatment of intact immunoglobulin beginning on day 15, when the expression of DCs had already been completed, failed to ameliorate the condition. An in vitro study showed that intact immunoglobulin, but not F(ab')(2) fragments, suppressed the lipopolysaccharide-induced interleukin-1beta production associated with the downregulation of CD32 antigen (Fcgamma receptor II) expression. Thus, intact immunoglobulin therapy markedly suppressed myocarditis as a result of Fc receptor-mediated anti-inflammatory action, and the suppression of the disease was associated with the suppression of DCs, ie, the suppression of the initial antigen-priming process in experimental giant cell myocarditis.

Requirements for the induction of interleukin-6 by herpes simplex virus-infected leukocytes

Cytokines play important roles in the clearance of herpes simplex virus (HSV) infections and in virus-induced immunopathology. One cytokine known to contribute to resistance against HSV is interleukin-6 (IL-6). Here we have investigated virus-cell interactions responsible for IL-6 induction by HSV in leukocytes. Both HSV type 1 and type 2 are potent inducers of IL-6, and this phenomenon is augmented in the presence of gamma interferon. The ability to induce IL-6 is dependent on de novo protein synthesis and is sensitive to UV irradiation of the virus. Virus mutants lacking the virion-transactivating protein VP16 or any of the immediate-early proteins ICP0, ICP4, or ICP27 displayed unaltered capacities to induce IL-6. However, wild-type virus was unable to induce IL-6 in a macrophage cell line overexpressing a mutant of double-stranded RNA-activated protein kinase (PKR). This suggests a role for PKR in HSV-induced IL-6 expression. HSV infection led to enhanced binding to the kappaB, CRE, and AP-1 sites of the IL-6 promoter, and inhibitors against NF-kappaB and the p38 kinase strongly reduced accumulation of IL-6 mRNA in infected cells. Moreover, macrophage cell lines expressing dominant negative mutants of IkappaBalpha and p38 responded to HSV-1 infection with reduced IL-6 expression compared to the control-vector-transfected cell line. The results show that induction of IL-6 by HSV in leukocytes is dependent on PKR and cellular signaling through NF-kappaB and a p38-dependent pathway.

A CCR5-dependent novel mechanism for type 1 HIV gp120 induced loss of macrophage cell surface CD4

Type 1 HIV gp120 is especially effective in disrupting immune cell function because it is able to cause dysregulation of both infected and uninfected cells. We report a novel CCR5-dependent mechanism of gp120-induced CD4 loss from macrophages. An M-tropic gp120, using CCR5, is able to induce 70% loss of cell surface CD4 from macrophages within an hour. This cell surface CD4 loss is more substantial and rapid than the 20% loss observed with T-tropic gp120(IIIB) by 3 h. The rapid and substantial CD4 loss induced by M-tropic gp120 is not observed on macrophages homozygous for the ccr5Delta32 mutation, which fail to express cell surface CCR5. We have used confocal imaging to show that gp120 and CD4 are internalized together by a process resembling receptor-mediated endocytosis, and that both proteins enter HLA-DR containing compartments of the macrophage. We have also shown by semiquantitative RT-PCR that, in response to CD4 loss from the cell surface, mRNA for CD4 is up-regulated and the intracellular pool of CD4 increases. CCR5 mRNA levels are also increased. It is proposed that internalization of self and viral protein and increased pools of intracellular CD4 could modulate Ag presentation efficiencies and have implications for the induction and maintenance of both productive immune responses and self-tolerance.

Nef modulation of HIV type 1 gene expression and cytopathicity in tissues of HIV transgenic mice

Transgenic mice bearing HIV-1 proviral DNA deleted in the gag/pol region (HIVd1443 mice) model a chronic, nonproductive form of viral gene expression in various cell types including macrophages. They display a disease phenotype that includes HIV-associated nephropathy (HIVAN), congenital cataracts, papillomatosis, and growth failure. The role of HIV-1 Nef in viral gene regulation and the development of disease was explored in mice bearing an isogenic HIV transgene in which nef was mutated by frameshift mutation. Like its Nef+ counterpart, HIVd1443[Nef-] mice expressed HIV gene products in the skin, muscle, kidney, and peritoneal macrophages. While these mice did not develop cataracts, papillomatous skin lesions, or display any apparent growth defect, they did develop HIVAN. Nef expression was introduced to HIVd1443[Nef-] mice through breeding to mice bearing an HIV LTR-linked nef transgene. Nef-complemented HIVd1443[Nef-] mice had reduced levels of viral gene products in the muscle and kidney. In contrast, HIV gene expression in the skin of these mice remained high and papillomatous lesions emerged that were more severe than those on wild-type HIVd1443 mice. Still, Nef had a negative effect on LPS-induced viral gene expression in visibly normal skin. In comparisons of peritoneal macrophages, viral RNA expression was significantly reduced in resident macrophages of Nef+ mice. HIV inflammatory macrophages expressed viral genes and displayed an altered FACS profile. In particular, Nef+ populations were marked by an increased proportion of F4/80med/Mac-1-cells as well as fewer Mac-1 cells and reduced F4/80 staining. This HIV proviral transgenic model has demonstrated the capacity of HIV-1 Nef to contribute to HIV cytopathicity by altering cellular maturation and viral gene expression in vivo.

Interactions of HIV-1 with antigen-presenting cells

There is currently much interest in the numerical and functional loss of antigen-presenting cells (APC) in HIV-1 disease and the contribution that this may make to HIV-1 pathology. The HIV-1 virus can interfere with the normal function of APC in a number of ways involving inappropriate signalling. These include changes in cytokine balance, cell-surface molecule expression and intracellular signalling pathways. This review examines how HIV-1 is able to disregulate APC function and discusses possible outcomes for the function of the immune system.