Interferon-gamma-induced downregulation of CD4 inhibits the entry of human immunodeficiency virus type-1 in primary monocytes

Elimination of Aicardi-Goutières syndrome protein SAMHD1 activates cellular innate immunity and suppresses SARS-CoV-2 replication

The lack of antiviral innate immune responses during severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections is characterized by limited production of interferons (IFNs). One protein associated with Aicardi-Goutières syndrome, SAMHD1, has been shown to negatively regulate the IFN-1 signaling pathway. However, it is unclear whether elevated IFN signaling associated with genetic loss of SAMHD1 would affect SARS-CoV-2 replication. In this study, we established in vitro tissue culture model systems for SARS-CoV-2 and human coronavirus OC43 infections in which SAMHD1 protein expression was absent as a result of CRISPR-Cas9 gene KO or lentiviral viral protein X-mediated proteosomal degradation. We show that both SARS-CoV-2 and human coronavirus OC43 replications were suppressed in SAMHD1 KO 293T and differentiated THP-1 macrophage cell lines. Similarly, when SAMHD1 was degraded by virus-like particles in primary monocyte-derived macrophages, we observed lower levels of SARS-CoV-2 RNA. The loss of SAMHD1 in 293T and differentiated THP-1 cells resulted in upregulated gene expression of IFNs and innate immunity signaling proteins from several pathways, with STAT1 mRNA being the most prominently elevated ones. Furthermore, SARS-CoV-2 replication was significantly increased in both SAMHD1 WT and KO cells when expression and phosphorylation of STAT1 were downregulated by JAK inhibitor baricitinib, which over-rode the activated antiviral innate immunity in the KO cells. This further validates baricitinib as a treatment of SARS-CoV-2-infected patients primarily at the postviral clearance stage. Overall, our tissue culture model systems demonstrated that the elevated innate immune response and IFN activation upon genetic loss of SAMHD1 effectively suppresses SARS-CoV-2 replication.

Interferon-gamma inhibits influenza A virus cellular attachment by reducing sialic acid cluster size

The mucosal antiviral role of type I and III interferon in influenza virus infection is well established. However, much less is known about the antiviral mechanism of type II interferon (interferon-gamma). Here, we revealed an antiviral mechanism of interferon-gamma by inhibiting influenza A virus (IAV) attachment. By direct stochastic optical reconstruction microscopy, confocal microscopy, and flow cytometry, we have shown that interferon-gamma reduced the size of α-2,3 and α-2,6-linked sialic acid clusters, without changing the sialic acid or epidermal growth factor receptor expression levels, or the sialic acid density within cluster on the cell surface of A549 cells. Reversing the effect of interferon-gamma on sialic acid clustering by jasplakinolide reverted the cluster size, improved IAV attachment and replication. Our findings showed the importance of sialic acid clustering in IAV attachment and infection. We also demonstrated the interference of sialic acid clustering as an anti-IAV mechanism of IFN-gamma for IAV infection.

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IFN-γ inhibits IAV replication

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IFN-γ reduces IAV attachment and infection by reducing sialic acid cluster size

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Reduction of sialic acid cluster size partially depends on F-actin depolymerization

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Higher sialic acid expression level does not correlate with increase IAV attachment

Direct Antiviral Mechanisms of Interferon-Gamma

Interferon-gamma (IFNG) is a pleiotropic cytokine that modulates both innate and adaptive immune networks; it is the most potent activator of macrophages and a signature cytokine of activated T lymphocytes. Though IFNG is now appreciated to have a multitude of roles in immune modulation and broad-spectrum pathogen defense, it was originally discovered, and named, as a secretory factor that interferes with viral replication. In contrast to the prototypical type I interferons produced by any cells upon viral infection, only specific subsets of immune cells can produce IFNG upon infection or stimulation with antigen or mitogen. Still, virtually all cells can respond to both types of interferons. This makes IFNG a versatile anti-microbial cytokine and also gives it a unique position in the antiviral defense system. The goal of this review is to highlight the direct antiviral mechanisms of IFNG, thereby clarifying its antiviral function in the effective control of viral infections.

Addition of maraviroc to antiretroviral therapy decreased interferon-γ mRNA in the CD4+ T cells of patients with suboptimal CD4+ T-cell recovery

The CCR5 antagonist, maraviroc (MVC), is associated with an enhanced CD4+ T-cell response independent of virological suppression; however, its mechanism of action has not been elucidated. In this study, we confirmed the effect of MVC on CD4+ T-cell count recovery in immunological non-responders, and compared the conventional combination antiretroviral therapy (cART) with MVC-intensified cART. We also investigated the effect of MVC on interferon-γ (IFN-γ) production in CD4+ T cells in vitro and in vivo, and evaluated the relationship between the mRNA level of IFN-γ and the degree of CD4+ T-cell count recovery. In vitro analysis indicated that MVC significantly decreased mRNA levels of IFN-γ in HIV-Tat stimulated CD4+ T cells from healthy donor peripheral blood mononuclear cells. Of the 18 HIV-infected patients treated with MVC-intensified cART, 12 had a significantly increased CD4+ T-cell count after 24 weeks of additional treatment with MVC. In patients exhibiting a response in CD4+ T-cell counts, mRNA levels of IFN-γ in CD4+ T cells were lower than those in patients showing a non-response at baseline and at week 24, while mRNA levels of IFN-γ decreased in both groups at 24 weeks. In conclusion, MVC decreased the mRNA level of IFN-γ in CD4+ T cells in vitro and in vivo, especially in patients whose CD4+ T-cell count increased significantly. We also found that the lower baseline IFN-γ mRNA level and the larger decreased rate of IFN-γ mRNA in CD4+ T cells were associated with a good response to MVC regarding CD4+ T-cell recovery.

Cytokine production and dysregulation in HIV pathogenesis: lessons for development of therapeutics and vaccines

Numerous studies have characterized the cytokine modulation observed in human immunodeficiency virus (HIV) infected individuals, from initial infection through chronic disease. Progressive and non-progressive HIV infection models show the cytokine milieu differs in terms of production and responsiveness in these two groups, suggesting an understanding of the role cytokines play during infection is necessary for directing the immune response toward viral control. This review will cover cytokine induction and dysfunction during HIV pathogenesis, with a focus on the interplay between cytokines and transcription factors, T cell activation, and exhaustion. We highlight cytokines that have either vaccine adjuvant or therapeutic potential and discuss the need to identify key factors required for prevention of progression, clearance of infection, or protection from acquisition.

Chikungunya disease: infection-associated markers from the acute to the chronic phase of arbovirus-induced arthralgia

At the end of 2005, an outbreak of fever associated with joint pain occurred in La Réunion. The causal agent, chikungunya virus (CHIKV), has been known for 50 years and could thus be readily identified. This arbovirus is present worldwide, particularly in India, but also in Europe, with new variants returning to Africa. In humans, it causes a disease characterized by a typical acute infection, sometimes followed by persistent arthralgia and myalgia lasting months or years. Investigations in the La Réunion cohort and studies in a macaque model of chikungunya implicated monocytes-macrophages in viral persistence. In this Review, we consider the relationship between CHIKV and the immune response and discuss predictive factors for chronic arthralgia and myalgia by providing an overview of current knowledge on chikungunya pathogenesis. Comparisons of data from animal models of the acute and chronic phases of infection, and data from clinical series, provide information about the mechanisms of CHIKV infection-associated inflammation, viral persistence in monocytes-macrophages, and their link to chronic signs.

HIV-1 and the macrophage

Macrophages and CD4+ T cells are natural target cells for HIV-1, and both cell types contribute to the establishment of the viral reservoir that is responsible for continuous residual virus replication during antiretroviral therapy and viral load rebound upon treatment interruption. Scientific findings that support a critical role for the infected monocyte/macrophage in HIV-1-associated diseases, such as neurological disorders and cardiovascular disease, are accumulating. To prevent or treat these HIV-1-related diseases, we need to halt HIV-1 replication in the macrophage reservoir. This article describes our current knowledge of how monocytes and certain macrophage subsets are able to restrict HIV-1 infection, in addition to what makes macrophages respond less well to current antiretroviral drugs as compared with CD4+ T cells. These insights will help to find novel approaches that can be used to meet this challenge.

HIV infection in the female genital tract: discrete influence of the local mucosal microenvironment

Women acquire HIV infections predominantly at the genital mucosa through heterosexual transmission. Therefore, the immune milieu at female genital surfaces is a critical determinant of HIV susceptibility. In this review, we recapitulate the evidence suggesting that several distinctive innate immune mechanisms in the female genital tract (FGT) serve to significantly deter or facilitate HIV-1 infection. Epithelial cells lining the FGT play a key role in forming a primary barrier to HIV entry. These cells express Toll-like receptors and other receptors that recognize and respond directly to pathogens, including HIV-1. In addition, innate biological factors produced by epithelial and other cells in the FGT have anti-HIV activity. Female sex hormones, co-infection with other pathogens and components in semen may also exacerbate or down-modulate HIV transmission. A combination of innate and adaptive immune factors and their interactions with the local microenvironment determine the outcome of HIV transmission. Improving our understanding of the female genital microenvironment will be useful in developing treatments that augment and sustain protective immune responses in the genital mucosa, such as microbicides and vaccines, and will provide greater insight into viral pathogenesis in the FGT.

Activation of interferon response genes and of plasmacytoid dendritic cells in HIV-1 positive subjects with GB virus C co-infection

GB virus C (GBV-C) coinfection has a protective role in Human Immunodeficiency Virus (HIV) infection, and increases the duration of suppression of HIV-1 viremia in patients under Highly Active Anti-Retroviral Therapy (HAART). Since innate antiviral response may be involved in the protection, we analyzed the possible role of GBV-C as activator of innate immunity. To this aim, we measured the extent of activation of the interferon (IFN) system and of circulating Dendritic Cells (DC) in vivo, and the ability of GBV-C to activate these functions in vitro. Activation of IFN system and of circulating DC was compared in GBV-positive and -negative HIV-1 co-infected patients with HAART-driven suppression of HIV-1 viremia. Endogenous levels of IFN-gamma and RNA-dependent protein kinase (PKR) mRNA were significantly higher in peripheral blood mononuclear cells (PBMC) from GBV-C-positive when compared to GBV-C-negative patients. IFN-gamma expression was correlated with all the Interferon response genes (IRGs) and with GBV-C viremia. The frequency of circulating plasmacytoid DC (pDC) expressing the CD80 activation marker was increased in GBV-C-positive patients, and was correlated with GBV-C viral load. In vitro experiments indicated that GBV-C is able to induce IFN-gamma expression in PBMC. In addition, in PBMC cultures GBV-C induced an increase of CD80 expression by pDC, that was reduced by antibody to IFN-gamma. Our data indicate that in HIV-positive patients GBV-C coinfection promotes the activation of IFN-gamma and downstream IRG expression, as well as with the activation/maturation of circulating pDC. GBV-C-driven IFN-gamma activation is, at least in part, responsible for the increased maturation of pDC. This crosstalk may suggest a role for GBV-C coinfection in boosting the innate antiviral response to HIV infection.

Secretion of antiretroviral chemokines by human cells cultured with acyclic nucleoside phosphonates

Acyclic nucleoside phosphonates are novel class of clinically broadly used antivirotics effective against replication of both DNA viruses and retroviruses including human immunodeficiency virus (HIV). We have investigated their in vitro effects on immune defence mechanisms in human peripheral blood mononuclear cells, with the main emphasis on expression of cytokines which are able to suppress the entry of HIV in cells. Included in the study were prototype acyclic nucleoside phosphonates, i.e. 9-[2-(phosphonomethoxy)ethyl]adenine (PMEA; adefovir), 9-[2-(phosphonomethoxy)ethyl]-2,6-diaminopurine (PMEDAP), (R)-and (S)-enantiomers of 9-[2-(phosphonomethoxy)propyl]adenine [(R)-PMPA; tenofovir] and [(S)-PMPA], and of 9-[2-(phosphonomethoxy)propyl]-2,6-diaminopurine [(R)-PMPDAP] and [(S)-PMPDAP], and their N(6)-substituted derivatives. Some of the compounds were found to substantially enhance secretion of chemokines such as macrophage inflammatory protein-1alpha (MIP-alpha/CCL3), and "regulated on activation of normal T cell expressed and secreted" (RANTES/CCL5). Secretion of MIP-1beta/CCL4 was only marginally increased, whereas production of interleukin-16 (IL-16) and interferon-gamma (IFN-gamma) remained uninfluenced. The most effective proved to be the N(6)-cyclooctyl-PMEDAP, N(6)-isobutyl-PMEDAP, N(6)-pyrrolidino-PMEDAP, N(6)-cyclopropyl-(R)-PMPDAP, and N(6)-cyclopentyl-(R)-PMPDAP derivatives. Remarkably enhanced secretion of chemokines was reached within 2-4 h of the cell culture, and was observed at concentration of 2-5 microM. It may be suggested that acyclic nucleoside phosphonates represent a new generation of antivirotics with combined antimetabolic and therapeutically prospective immunostimulatory properties.

Antibodies against a multiple-peptide conjugate comprising chemically modified human immunodeficiency virus type-1 functional Tat peptides inhibit infection

We demonstrated recently that selective side-chain modification of functional cysteine-rich (Tat(21-40)) and arginine-rich (Tat(53-68)) domains of the HIV-1 Tat protein blocks pathogenic activities of these peptides while retaining their immunological characteristics. In the present study, we have synthesized a multiple-peptide conjugate system comprising modified Tat(21-40) and Tat(53-68) peptides (HIV-1-Tat-MPC). Immunization of mice with this highly homogeneous 10.7 kDa HIV-1-Tat-MPC synthetic construct induced an effective immune response in mice. The antibodies generated against HIV-1-Tat-MPC efficiently suppressed Tat-induced viral replication and significantly reduced HIV-associated cytopathic effects in human monocytes. These results indicate that epitope-specific antibodies directed against functional sites of Tat protein using non-pathogenic peptides inhibit HIV pathogenesis. The HIV-1-Tat-MPC, therefore, has potential for the development of a safe, effective, and economical therapeutic vaccine to reduce the progression of HIV infection.

Selective side-chain modification of cysteine and arginine residues blocks pathogenic activity of HIV-1-Tat functional peptides

Extracellular Tat protein of HIV-1 activates virus replication in HIV-infected cells and induces a variety of host factors in the uninfected cells, some of which play a critical role in the progression of HIV infection. The cysteine-rich and arginine-rich basic domains represent key components of the HIV-Tat protein for pathogenic effects of the full-length Tat protein and, therefore, could be ideal candidates for the development of a therapeutic AIDS vaccine. The present study describes selective modifications of the side-chain functional groups of cysteine and arginine amino acids of these HIV-Tat peptides to minimize the pathogenic effects of these peptides while maintaining natural peptide linkages. Modification of cysteine by introducing either a methyl or t-butyl group in the free sulfhydryl group and replacing the guanidine group with a urea linkage in the side chain of arginine in the cysteine-rich and arginine-rich Tat peptide sequences completely blocked the ability of these peptides to induce HIV replication, chemokine receptor CCR-5 expression, and NF-kappaB activity in monocytes. Such modifications also inhibited angiogenesis and migration of Kaposi's sarcoma cells normally induced by Tat peptides. Such chemical modifications of the cysteine-rich and arginine-rich peptides did not affect their reactivity with antibodies against the full-length Tat protein. With an estimated 40 million HIV-positive individuals worldwide and approximately 4 million new infections emerging every year, a synthetic subunit HIV-Tat vaccine comprised of functionally inactive Tat domains could provide a safe, effective, and economical therapeutic vaccine to reduce the progression of HIV disease.

Macrophage activation and human immunodeficiency virus infection: HIV replication directs macrophages towards a pro-inflammatory phenotype while previous activation modulates macrophage susceptibility to infection and viral production

Macrophages are pivotal for the regulation of immune and inflammatory responses, but whether their role in HIV infection is protective or deleterious remains unclear. In this study, we investigated the effect of pro- and anti-inflammatory stimuli on macrophage sensitivity to two different aspects of HIV infection: their susceptibility to infection stricto sensu, which we measured by endpoint titration method, and their ability to support virus spread, which we measured by using an RT activity assay in infection kinetics. We show a partially protective role for pro-inflammatory agents as well as for IL-4. We also illustrate that various different stimuli display differential effects on macrophage susceptibility to HIV and on virus replication that occurs thereafter. On the other hand, HIV replication strongly repressed CD206 and CD163 expression, thus clearly orientating macrophages towards a pro-inflammatory phenotype, but independently of TNF. Taken together, our results emphasize that HIV infection of macrophages sets up inflammation at the cell level but through unexpected mechanisms. This may limit target susceptibility and participate in virus clearance but may also result in tissue damage.

Hemin Activation Ameliorates HIV-1 Infection via Heme Oxygenase-1 Induction

Hemin, a critical component of hemoglobin, is an active ingredient of a biologic therapeutic approved by the Food and Drug Administration for the treatment of acute porphyries. This report describes a biological function of this molecule in inducing host defense against HIV-1 infection via heme oxygenase-1 (HO-1) induction. Treatment of monocytes with hemin substantially inhibited HIV replication, as evident by nearly undetectable viral RNA and cell-free HIV-1 p24 protein in a dose-dependent manner. Hemin exposure of these cells before infection, at the time of infection, or after infection caused >90% reduction of HIV DNA with substantially low levels of HIV-1 p24 and HIV-associated cytopathic effects. In addition, hemin treatment significantly suppressed infection of both monocytes and T cells inoculated with R5, X4, R5X4 tropic strains, and reverse transcriptase-resistant, azidothymidine-resistant, ddC/ddI-resistant, nivirapine-resistant, and other clinical HIV isolates. Intraperitoneal administration of hemin 4 days after HIV infection reduced viral load in the serum of human PBMC-reconstituted nonobese diabetic SCID mice by >6-fold. Suppression of HIV replication in hemin-activated cells correlated with the induction of HO-1 and was attenuated by tin protoporphyrin (SnPP) IX, an inhibitor of HO-1 activity, suggesting a pivotal role of this endogenous enzyme in the regulation of HIV infection. Hemin-induced HO-1 induction in the CCR-5, CXCR-4, and CD4 coexpressing GHOST(3) cells was consistent with the inhibition of Tat-dependent activation of long terminal repeat promoter leading to reduced GFP expression. These findings suggest an important role of hemin-induced HO-1 activity as a host defense mechanism against HIV-1 infection.

Interferon-induced exonuclease ISG20 exhibits an antiviral activity against human immunodeficiency virus type 1

Interferons (IFNs) encode a family of secreted proteins that provide the front-line defence against viral infections. It was recently shown that ISG20, a new 3'-->5' exoribonuclease member of the DEDD superfamily of exonucleases, represents a novel antiviral pathway in the mechanism of IFN action. In this report, it was shown that ISG20 expression is rapidly and strongly induced during human immunodeficiency virus type 1 (HIV-1) infection. In addition, it was demonstrated that the replication kinetics of an HIV-1-derived virus expressing the ISG20 protein (HIV-1(NL4-3ISG20)) was delayed in both CEM cells and peripheral blood mononuclear cells. No antiviral effect was observed in cells overexpressing a mutated ISG20 protein defective in exonuclease activity, suggesting that the antiviral effect was due to the exonuclease activity of ISG20. Paradoxically, despite the antiviral activity of ISG20 protein, virus rescue observed in HIV-1(NL4-3ISG20)-infected cells was not due to mutation or partial deletion of the ISG20 transgene, suggesting that the virus was able to counteract the cellular defences. In addition, HIV-1-induced apoptosis was significantly reduced in HIV-1(NL4-3ISG20)-infected cells suggesting that emergence of HIV-1(NL4-3ISG20) was associated with the inhibition of HIV-1-induced apoptosis. Altogether, these data reflect the ineffectiveness of virus replication in cells overexpressing ISG20 and demonstrate that ISG20 represents a new factor in the IFN-mediated antiviral barrier against HIV-1.

Down-regulation of CXCR-4 and CCR-5 expression by interferon-gamma is associated with inhibition of chemotaxis and human immunodeficiency virus (HIV) replication but not HIV entry into human monocytes

Alterations in the expression of CXCR4 and CCR5, the co-receptors for HIV entry, may be associated with susceptibility of monocytic cells to HIV infection. Interferon (IFN)-gamma has been shown to inhibit HIV replication in monocytic cells, but the molecular mechanism involved is not well understood. To determine if IFN-gamma regulates HIV replication by altering CXCR-4/CCR-5 expression and hence virus entry into monocytic cells, we investigated the effects of IFN-gamma on CXCR-4 and CCR-5 expression and its biological implications with respect to HIV entry, replication and chemotaxis towards the CXCR-4 and CCR-5 ligands SDF-1 and MIP-1alpha, respectively. IFN-gamma decreased CXCR-4 and CCR-5 expression on monocytes derived from HIV-negative adults, HIV-positive adults and HIV-negative cord blood. This down-regulation of chemokine receptor expression did not result in a corresponding change in mRNA expression but was associated with elevated levels of the endogenously produced chemokines SDF-1 and RANTES. Furthermore, IFN-gamma inhibited chemotaxis in response to SDF-1 and MIP-1alpha, inhibited HIV replication, but failed to inhibit virus entry in monocytic cells. These results suggest that although IFN-gamma-induced down-regulation of CXCR-4 and CCR-5 expression is associated with an inhibition of SDF-1-/MIP-1alpha-mediated chemotaxis, IFN-gamma-induced inhibition of HIV replication may be mediated at levels subsequent to the virus entry.

The C-X-C chemokine IP-10 stimulates HIV-1 replication

Chemokines play critical roles in HIV-1 infection, serving both to modulate viral replication and to recruit target cells to sites of infection. Interferon-gamma-inducible protein 10 (IP-10/CXCL10) is a C-X-C chemokine that acts specifically upon activated T cells and macrophages and attracts T cells into the cerebrospinal fluid (CSF) in HIV-associated neurological disease. We now demonstrate that IP-10 stimulates HIV-1 replication in monocyte-derived macrophages and peripheral blood lymphocytes. We further demonstrate that neutralization of endogenous IP-10 or blocking the function of its receptor, CXCR3, reduces HIV-1 replication in these same cells. Therefore, blocking the interaction between IP-10 and CXCR3 represents a possible new target for anti-retroviral therapy.

The influence of cytokines, chemokines and their receptors on HIV-1 replication in monocytes and macrophages

Monocytes, macrophages and dendritic cells play an important role in the initial infection and contribute to its pathogenesis throughout the course of infection. Myeloid cells express CD4 and chemokine receptors known for HIV-1 fusion and entry. The beta-chemokine receptor, CCR5, is the major co-receptor in conjunction with CD4 for macrophage (M)-tropic or (R5) isolates of HIV-1, whereas the alpha-chemokine receptor, CXCR4, facilitates entry of T-tropic or (X4) HIV-1 strains. Cells of myeloid lineage may be infected predominantly with R5- strains, although infection with dual-tropic isolates of HIV-1 (exhibiting the capacity to use CCR-5 and/or CXCR-4 for entry) or some strains of X4- isolates has also been reported. The expression of chemokine receptors, HIV-1 infection and replication is under continuous regulation by a complex cytokine network produced by a variety of cells. The effects of cytokines/chemokines on HIV-1 replication in cells of myeloid lineage can be inhibitory (IFN-alpha, IFN-beta, IFN-gamma, GM-CSF, IL-10, IL-13 and IL-16 and beta-chemokines), stimulatory (M-CSF, TNF-alpha, TNF-beta, IL-1, IL-6) or bifunction al, that is both inhibitory and stimulatory (IL-4). This review focuses on the overall expression of chemokine receptors on cells of myeloid lineage and considers the mechanisms of entry of R5-, X4- and dual-tropic strains of HIV-1 into these cells. The effects of cytokines/chemokines on viral entry and productive HIV-1 infection are also reviewed.

Activation by 9-(R)-[2-(phosphonomethoxy)propyl]adenine of chemokine (RANTES, macrophage inflammatory protein 1alpha) and cytokine (tumor necrosis factor alpha, interleukin-10 [IL-10], IL-1beta) production

Development of a novel group of antiviral agents, acyclic nucleoside phosphonates, has provided a new perspective for treating human immunodeficiency virus (HIV) infection. One of the compounds, 9-(R)-[2-(phosphonomethoxy)propyl]adenine (PMPA) (tenofovir), has been shown to confer complete protection against AIDS in a simian model of the infection. The aim of our study was to investigate whether the antiviral efficacy of PMPA, which depends mainly on inhibition of virus-induced DNA polymerase or of reverse transcriptase, could be contributed by immunomodulatory potential of this drug. We screened for its ability to activate production of cytokines and chemokines that are known to interfere with the replication and/or the entry of HIV in cells. Using the in vitro test system of mouse macrophages and lymphocytes, it has been found that PMPA stimulates macrophage secretion of interleukin-1beta (IL-1beta), IL-10, and tumor necrosis factor alpha. Production of the chemokines RANTES and macrophage inflammatory protein 1alpha was activated in both macrophages and lymphocytes, and also in human cell line U937. Other cytokines--i.e., IL-2, IL-12, IL-13, and gamma interferon-remained uninfluenced by PMPA. The cytokines were stimulated in a dose-dependent fashion, with rapid onset, and peak concentrations were achieved within 5 to 24 h. The findings contribute to a more complex understanding of mechanisms of antiviral effectiveness of PMPA and support the view that this drug could become a promising candidate for therapeutic exploitation in anti-HIV preventive medicine.

Cytokines and HIV-1: interactions and clinical implications

Cytokines play an important role in controlling the homoeostasis of the immune system. Infection with HIV results in dysregulation of the cytokine profile in vivo and in vitro. During the course of HIV-1 infection secretion of T-helper type 1 (Th1) cytokines, such as interleukin (IL)-2, and antiviral interferon (IFN)-gamma, is generally decreased, whereas production of T helper type 2 (Th2) cytokines, IL-4, IL-10, proinflammatory cytokines (IL-1, IL-6, IL-8) and tumour necrosis factor (TNF)-alpha, is increased. Such abnormal cytokine production contributes to the pathogenesis of the disease by impairing cell-mediated immunity. A number of cytokines have been shown to modulate in vitro HIV-1 infection and replication in both CD4 T lymphocytes and cells of macrophage lineage. HIV-inductive cytokines include: TNF-alpha, TNF-beta, IL-1 and IL-6, which stimulate HIV-1 replication in T cells and monocyte-derived macrophages (MDM), IL-2, IL-7 and IL-15, which upregulate HIV-1 in T cells, and macrophage-colony stimulating factor, which stimulates HIV-1 in MDM. HIV-suppressive cytokines include: IFN-alpha, IFN-beta and IL-16, which inhibit HIV-1 replication in T cells and MDM, and IL-10 and IL-13, which inhibit HIV-1 in MDM. Bifunctional cytokines such as IFN-gamma, IL-4 and granulocyte-macrophage colony-stimulating factor have been shown to have both inhibitory and stimulatory effects on HIV-1. The beta-chemokines, macrophage-inflammatory protein (MIP)-1alpha, MIP-1beta and RANTES are important inhibitors of macrophage-tropic strains of HIV-1, whereas the alpha-chemokine stromal-derived factor-1 suppresses infection of T-tropic strains of HIV-1. This review outlines the interactions between cytokines and HIV-1, and presents clinical applications of cytokine therapy combined with highly active antiretroviral therapy or vaccines.

Interferon γ and interleukin 6 modulate the susceptibility of macrophages to human immunodeficiency virus type 1 infection

The effect of interferon γ (IFN-γ) and interleukin 6 (IL-6) on infection of macrophages with human immunodeficiency virus type 1 (HIV-1) was investigated. By using a polymerase chain reaction–based viral entry assay and viral infectivity assay, it was demonstrated that IL-6 and IFN-γ augmented susceptibility of monocyte-derived macrophages (MDMs) to infection with T-cell tropic CXCR4-utilizing (X4) HIV-1 strains. Consistent with this finding, IFN-γ and IL-6 augmented fusion of MDMs with T-tropic envelope-expressing cells. The enhanced fusion of cytokine-treated MDMs with T-tropic envelopes was inhibited by the CXCR4 ligand, SDF-1, and by T22 peptide. IFN-γ and IL-6 did not affect expression of surface CXCR4 or SDF-1–induced Ca++ flux in MDMs. In contrast to the effect of IFN-γ on the infection of MDMs with X4 strains, IFN-γ inhibited viral entry and productive infection of MDMs with macrophage-tropic (M-tropic) HIV-1. Consistent with this finding, IFN-γ induced a decrease in fusion with M-tropic envelopes that correlated with a modest reduction in surface CCR5 and CD4 on MDMs. It was further demonstrated that macrophage inflammatory protein (MIP)-1α and MIP-β secreted by cytokine-treated MDMs augmented their fusion with T-tropic–expressing cells and inhibited their fusion with M-tropic envelope-expressing cells. These data indicate that proinflammatory cytokines, which are produced during opportunistic infections or sexually transmitted diseases, may predispose macrophages to infection with X4 strains that, in turn, could accelerate disease progression.

Interferon γ and interleukin 6 modulate the susceptibility of macrophages to human immunodeficiency virus type 1 infection

The effect of interferon γ (IFN-γ) and interleukin 6 (IL-6) on infection of macrophages with human immunodeficiency virus type 1 (HIV-1) was investigated. By using a polymerase chain reaction–based viral entry assay and viral infectivity assay, it was demonstrated that IL-6 and IFN-γ augmented susceptibility of monocyte-derived macrophages (MDMs) to infection with T-cell tropic CXCR4-utilizing (X4) HIV-1 strains. Consistent with this finding, IFN-γ and IL-6 augmented fusion of MDMs with T-tropic envelope-expressing cells. The enhanced fusion of cytokine-treated MDMs with T-tropic envelopes was inhibited by the CXCR4 ligand, SDF-1, and by T22 peptide. IFN-γ and IL-6 did not affect expression of surface CXCR4 or SDF-1–induced Ca++ flux in MDMs. In contrast to the effect of IFN-γ on the infection of MDMs with X4 strains, IFN-γ inhibited viral entry and productive infection of MDMs with macrophage-tropic (M-tropic) HIV-1. Consistent with this finding, IFN-γ induced a decrease in fusion with M-tropic envelopes that correlated with a modest reduction in surface CCR5 and CD4 on MDMs. It was further demonstrated that macrophage inflammatory protein (MIP)-1α and MIP-β secreted by cytokine-treated MDMs augmented their fusion with T-tropic–expressing cells and inhibited their fusion with M-tropic envelope-expressing cells. These data indicate that proinflammatory cytokines, which are produced during opportunistic infections or sexually transmitted diseases, may predispose macrophages to infection with X4 strains that, in turn, could accelerate disease progression.

Recombinant human gamma interferon in human immunodeficiency virus-infected children: safety, CD4(+)-lymphocyte count, viral load, and neutrophil function (AIDS Clinical Trials Group Protocol 211)

Nineteen children with human immunodeficiency virus (HIV) infection were treated with recombinant human gamma interferon (rIFN-gamma) (50 microg/m2 subcutaneously three times each week during weeks 1 through 12 and 100 microg/m2 subcutaneously three times each week during weeks 13 through 24) in a phase I/II clinical trial. All children continued to receive previously prescribed therapy with oral zidovudine or didanosine. Children were assessed clinically and with laboratory studies during 24 weeks of study treatment and for 12 weeks after completion of rIFN-gamma therapy. In general, rIFN-gamma therapy was well tolerated. There were two clinical or laboratory adverse events thought to be possibly or probably study drug associated. One child developed acute pancreatitis; another child developed granulocytopenia. Median CD4(+)-lymphocyte counts and plasma HIV RNA concentrations did not change significantly during therapy. In vitro neutrophil bactericidal activity against Staphylococcus aureus and superoxide production were not significantly affected by rIFN-gamma therapy. We conclude that rIFN-gamma therapy in HIV-infected children receiving single-agent antiretroviral therapy is safe and does not produce consistent changes in CD4(+)-lymphocyte count, plasma HIV RNA concentration, or in vitro neutrophil function.

Interferon-γ Upregulates CCR5 Expression in Cord and Adult Blood Mononuclear Phagocytes

The C-C chemokine receptors CCR5 and CCR3 are fusion coreceptors for human immunodeficiency virus (HIV) entry into macrophages. The regulation of their expression influences infectivity by HIV. We report here that interferon-γ (IFN-γ) a cytokine that has bidirectional effects on HIV infection of macrophages, significantly upregulated CCR5 and CCR3 cell surface expression in human mononuclear phagocytes isolated from placental cord blood and adult peripheral blood. Monocytes treated with IFN-γ showed increased chemotaxis to the CCR5 ligands macrophage inflammatory protein-1 (MIP-1) and MIP-1β, confirming the functional relevance of IFN-γ–induced CCR5 expression. However, IFN-γ suppressed HIV entry into macrophages. Interestingly, we demonstrated that IFN-γ inhibited cell surface expression of CD4, the major receptor for HIV. This finding may explain the suppressive effect of IFN-γ on HIV entry into macrophages, despite its enhancing effect on the expression of CCR5 and CCR3 by these cells. In addition, IFN-γ–induced secretion of C-C chemokines (RANTES, MIP-1, and MIP-1β) by mononuclear phagocytes may also suppress HIV entry into macrophages. These data provide further evidence for cytokine-mediated regulation of CCR5 expression and are consistent with a novel paradigm in which cytokines regulate HIV infection and leukocyte migration by reciprocal and opposing effects on the expression of CD4 and chemokine receptors.

Interferon-γ Upregulates CCR5 Expression in Cord and Adult Blood Mononuclear Phagocytes

The C-C chemokine receptors CCR5 and CCR3 are fusion coreceptors for human immunodeficiency virus (HIV) entry into macrophages. The regulation of their expression influences infectivity by HIV. We report here that interferon-γ (IFN-γ) a cytokine that has bidirectional effects on HIV infection of macrophages, significantly upregulated CCR5 and CCR3 cell surface expression in human mononuclear phagocytes isolated from placental cord blood and adult peripheral blood. Monocytes treated with IFN-γ showed increased chemotaxis to the CCR5 ligands macrophage inflammatory protein-1 (MIP-1) and MIP-1β, confirming the functional relevance of IFN-γ–induced CCR5 expression. However, IFN-γ suppressed HIV entry into macrophages. Interestingly, we demonstrated that IFN-γ inhibited cell surface expression of CD4, the major receptor for HIV. This finding may explain the suppressive effect of IFN-γ on HIV entry into macrophages, despite its enhancing effect on the expression of CCR5 and CCR3 by these cells. In addition, IFN-γ–induced secretion of C-C chemokines (RANTES, MIP-1, and MIP-1β) by mononuclear phagocytes may also suppress HIV entry into macrophages. These data provide further evidence for cytokine-mediated regulation of CCR5 expression and are consistent with a novel paradigm in which cytokines regulate HIV infection and leukocyte migration by reciprocal and opposing effects on the expression of CD4 and chemokine receptors.

The role of interleukin-converting enzyme in Fas-mediated apoptosis in HIV-1 infection

Apoptosis of CD4+ lymphocytes is partially responsible for the depletion of these cells in HIV-infected individuals. CD4+ lymphocytes from HIV-1-infected patients express higher membrane levels of the Fas receptor, and are particularly susceptible to apoptosis after Fas triggering. IL-1beta- converting enzyme (ICE) is a key enzyme of the apoptotic machinery involved in Fas-mediated apoptosis of normal lymphocytes. The role of ICE in mediating the increased susceptibility of CD4+ lymphocytes from HIV-1-infected patients to apoptosis has not been examined. In this study, we found that ICE mRNA was present in T cells from both HIV-1-infected patients and controls. Active ICE proteins, p10 and p20, were demonstrated by immunoblot in lymphocytes from HIV-1-infected patients and in normal lymphocytes after treatment with Fas agonist, CH11 mAb. Cocultivation of lymphocytes from HIV-1-infected persons with Fas antagonist, antibody ZB4, resulted in decreased expression of ICE protein in lymphocytes from HIV-infected patients, and decreased apoptosis. Similar effects were obtained when cells were treated with synthetic ICE inhibitors, which blocked apoptosis in response to Fas triggering. When CD4+ and CD8+ cells were sorted by flow cytometry and analyzed by reverse transcriptase PCR, ICE mRNA was present in both CD8+ and CD4+ cells. However, flow cytometric analysis of lymphocytes with intracellular staining for ICE demonstrated ICE protein in the CD4+ but not the CD8+ cell fraction derived from blood of HIV-1-infected patients. These data suggest that activation of ICE occurs in vivo in CD4+ lymphocytes from HIV-1-infected individuals, and may account for the increased susceptibility of CD4+ cells to apoptosis.

Immunomodulatory properties of antiviral acyclic nucleotide analogues: cytokine stimulatory and nitric oxide costimulatory effects

Acyclic nucleotide analogues exhibit strong activity against a broad range of viruses, including HIV-1 and -2. We have investigated their effects on in vitro secretion of cytokines and production of nitric oxide (NO) by murine peritoneal macrophages, factors known to play a role in virus replication. Included in the study were the most prominent compounds of the series: 9-(2-phosphonomethoxyethyl)adenine, 9-(2-phosphonomethoxyethyl)-2,6-diaminopurine, the (R)- and (S)-enantiomers of 9-(2-phosphonomethoxypropyl) adenine [(R)- or (S)-PMPA], (R)- and (S)-enantiomers of 9-(2-phosphonomethoxypropyl)-2,6-diaminopurine [(R)- or (S)-PMPDAP], 9-(2-phosphonomethoxyethyl)guanine (PMEG), and (S)-enantiomer of 1-(3-hydroxy-2-phosphonomethoxypropyl)cytosine [(S)-HPMPC]. PMEG, (R)-PMPA, and (S)-PMPA greatly enhanced the secretion of both tumour necrosis factor-alpha (TNF-alpha) and interleukin-10 (IL-10), (R)-PMPDAP stimulated only TNF-alpha, other test compounds were ineffective. None of them influenced the secretion of IL-2 or interferon-gamma (IFN-gamma). Both TNF-alpha and IL-10 have been found to be major factors determining enhancing effects of PMEG, (R)-PMPA, and (S)-PMPA on production of NO generated by exogenous IFN-gamma. The study points to a possible implication of immunomodulatory properties in the antiviral effects of some acyclic nucleotide analogues. In addition, our data support the view that endogenous IL-10 can stimulate certain macrophage functions.

Antiretroviral agent (R)-9-(2-phosphonomethoxypropyl)adenine stimulates cytokine and nitric oxide production

The immunomodulatory properties of (R)-enantiomer of 9-(2-phoshonomethoxypropyl)adenine ((R)-PMPA), one of the most potent acyclic nucleotide analogs effective against human immunodeficiency virus (HIV), were investigated under in vitro conditions using murine peritoneal macrophages. Remaining without influence on interferon-gamma and interleukin-2 expression, (R)-PMPA dramatically stimulated in a concentration- and time-dependent manner the secretion of tumor necrosis factor alpha (TNF-alpha) and interleukin-10. It also substantially augmented the production of nitric oxide (NO) induced by exogenous interferon-gamma. Inhibitory experiments using neutralizing antibodies against TNF-alpha and/or interleukin-10 demonstrated that these two cytokines are major factors responsible for triggering the underlying mechanism(s) leading to enhanced NO production. The novel findings on the immunomodulatory potential of acyclic nucleotide analogs are discussed in the context of their possible implication in antiviral therapeutic efficacy.

Role of Fas Ligand and Receptor in the Mechanism of T-Cell Depletion in Acquired Immunodeficiency Syndrome: Effect on CD4+ Lymphocyte Depletion and Human Immunodeficiency Virus Replication

Direct killing of CD4+ lymphocytes by human immunodeficiency virus-1 (HIV-1) probably cannot account for the magnitude of the loss of these cells during the course of HIV-1 infection. Experimental evidence supports a pathophysiologic role of the apoptotic process in depletion of CD4 cells in acquired immunodeficiency syndrome (AIDS). The Fas-receptor/Fas-ligand (Fas-R/Fas-L) system mediates signals for apoptosis of susceptible lymphocytes and lympoblastoid cell lines. A number of investigators have recently reported increased expression of the Fas receptor in individuals with HIV infection, along with increased sensitivity of their lymphocytes to anti-Fas antibody mimicking Fas ligand. We attempted to determine the role of Fas-mediated apoptosis in disease progression and viral replication. Increased Fas-receptor (CD95) expression on CD4+ and CD8+ lymphocytes was found in a large group of HIV-1–infected patients compared with normal controls; individuals with a diagnosis of AIDS and a history of opportunistic infection had significantly more Fas receptor expression than did asymptomatic HIV-infected persons and normal blood donor controls (P < .01). Triggering of the Fas-R by agonistic anti-Fas monoclonal antibody, CH11, was preferentially associated with apoptosis in the CD4+ cells; this effect was more pronounced in lymphocytes derived from HIV+ individuals. Soluble and membrane-bound forms of Fas-L were produced in greater amounts in peripheral blood mononuclear cells (PBMC) cultures and in plasma obtained from HIV-1–infected persons than from normal controls. Furthermore, triggering of lymphocytes from HIV-infected persons by CH11 increased levels of interleukin-1β converting enzyme (ICE), a protein associated with apoptosis. When PBMC were cultured in the presence of CH11, p24 production per number of viable cells was decreased as compared with the same PBMC without CH11 (P < .01). These findings suggest that multiple mechanisms, including increased production of Fas-L by infected PBMC, increased Fas-R expression, and induction of a protease of ICE family, may play roles in the apoptotic depletion of CD4+ cells in HIV infection.