Interferon induction by HIV glycoprotein 120: role of the V3 loop

Platelet and HIV Interactions and Their Contribution to Non-AIDS Comorbidities

Platelets are anucleate cytoplasmic cell fragments that circulate in the blood, where they are involved in regulating hemostasis. Beyond their normal physiologic role, platelets have emerged as versatile effectors of immune response. During an infection, cell surface receptors enable platelets to recognize viruses, resulting in their activation. Activated platelets release biologically active molecules that further trigger host immune responses to protect the body against infection. Their impact on the immune response is also associated with the recruitment of circulating leukocytes to the site of infection. They can also aggregate with leukocytes, including lymphocytes, monocytes, and neutrophils, to immobilize pathogens and prevent viral dissemination. Despite their host protective role, platelets have also been shown to be associated with various pathophysiological processes. In this review, we will summarize platelet and HIV interactions during infection. We will also highlight and discuss platelet and platelet-derived mediators, how they interact with immune cells, and the multifaceted responsibilities of platelets in HIV infection. Furthermore, we will give an overview of non-AIDS comorbidities linked to platelet dysfunction and the impact of antiretroviral therapy on platelet function.

Intranasal delivery of SARS-CoV-2 spike protein is sufficient to cause olfactory damage, inflammation and olfactory dysfunction in zebrafish

Anosmia, loss of smell, is a prevalent symptom of SARS-CoV-2 infection. Anosmia may be explained by several mechanisms driven by infection of non-neuronal cells and damage in the nasal epithelium rather than direct infection of olfactory sensory neurons (OSNs). Previously, we showed that viral proteins are sufficient to cause neuroimmune responses in the teleost olfactory organ (OO). We hypothesize that SARS-CoV-2 spike (S) protein is sufficient to cause olfactory damage and olfactory dysfunction. Using an adult zebrafish model, we report that intranasally delivered SARS-CoV-2 S RBD mostly binds to the non-sensory epithelium of the olfactory organ and causes severe olfactory histopathology characterized by loss of cilia, hemorrhages and edema. Electrophysiological recordings reveal impaired olfactory function to both food and bile odorants in animals treated intranasally with SARS-CoV-2 S RBD. However, no loss of behavioral preference for food was detected in SARS-CoV-2 S RBD treated fish. Single cell RNA-Seq of the adult zebrafish olfactory organ indicated widespread loss of olfactory receptor expression and inflammatory responses in sustentacular, endothelial, and myeloid cell clusters along with reduced numbers of T_regs. Combined, our results demonstrate that intranasal SARS-CoV-2 S RBD is sufficient to cause structural and functional damage to the zebrafish olfactory system. These findings may have implications for intranasally delivered vaccines against SARS-CoV-2.

Nef, the shuttling molecular adaptor of HIV, influences the cytokine network

Several viruses manipulate host innate immune responses to avoid immune recognition and improve viral replication and spreading. The viral protein Nef of Human Immunodeficiency Virus is mainly involved in this "hijacking" activity and is a well established virulence factor. In the last few years there have been remarkable advances in outlining a defined framework of its functions. In particular Nef appears to be a shuttling molecular adaptor able to exert its effects both on infected and non infected bystander cell. In addition it is emerging fact that it has an important impact on the chemo-cytokine network. Nef protein represents an interesting new target to develop therapeutic drugs for treatment of seropositive patients. In this review we have tried to provide a unifying view of the multiple functions of this viral protein on the basis of recently available experimental data.

Observation of inflammatory responses in mice orally fed with bacteriophage T7

AIMS

Analysis of inflammatory immune response upon bacteriophage intake in mice.

METHODS AND RESULTS

Bacteriophage therapy is emerging as an effective alternative to conventional antibiotics. However, its safety when applied to humans and animals remains a prime concern. This study investigated the inflammatory responses in mice fed orally with bacteriophages. The mice were fed with either murine norovirus (MNV) or bacteriophage T7 for 10 days and then sacrificed. No behavioural changes related to diet, movement or defecation were observed in either group. The inflammatory cytokine profiling showed an increased level of interleukins 1α (IL-1α), 1β (IL-1β), 2 (IL-2), 10 (IL-10), 12 (IL-12), 17A (IL-17A), interferon-γ (IFN-γ), tumour necrosis factor-α (TNF-α), granulocyte colony-stimulating factor (G-CSF) and granulocyte macrophage colony-stimulating factor (GM-CSF) in the serum from the mice fed with MNV, whereas only a slight increase in IL-17A was observed in the serum from the mice fed with bacteriophage T7. A histopathological analysis of tissue samples from the stomach, small intestine and colon revealed no significant pathological change.

CONCLUSIONS

The bacteriophage diet only caused a minimal inflammatory response in the mice.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides insights into safety concerns of orally fed bacteriophage therapy.

The simian immunodeficiency virus targets central cell cycle functions through transcriptional repression in vivo

A massive and selective loss of CD4+ memory T cells occurs during the acute phase of immunodeficiency virus infections. The mechanism of this depletion is poorly understood but constitutes a key event with implications for progression. We assessed gene expression of purified T cells in Rhesus Macaques during acute SIVmac239 infection in order to define mechanisms of pathogenesis. We observe a general transcriptional program of over 1,600 interferon-stimulated genes induced in all T cells by the infection. Furthermore, we identify 113 transcriptional changes that are specific to virally infected cells. A striking downregulation of several key cell cycle regulator genes was observed and shared promotor-region E2F binding sites in downregulated genes suggested a targeted transcriptional control of an E2F regulated cell cycle program. In addition, the upregulation of the gene for the fundamental regulator of RNA polymerase II, TAF7, demonstrates that viral interference with the cell cycle and transcriptional regulation programs may be critical components during the establishment of a pathogenic infection in vivo.

HIV-1 trans-activator protein dysregulates IFN-γ signaling and contributes to the suppression of autophagy induction

OBJECTIVE AND DESIGN

HIV-1 transactivator protein, Tat, has been identified as an activator of HIV-1 replication. It also dysregulates cytokine production and apoptosis in T-cells. Of the various cell death processes, autophagy is a self-digestion and degradation mechanism that recycles the contents of the cytosol, including macromolecules and cellular organelles, resulting in self-repair and conservation for survival. Recent reports demonstrated that autophagosomes can be activated by interferon-γ (IFN-γ) to participate in immune defence by processing foreign antigens for the recognition and killing of intracellular pathogens. As we previously showed that HIV-1 Tat perturbs IFN-γ signaling through the suppression of STAT1 phosphorylation and consequently inhibits major histocompatibility complex class-II antigen expression, we postulate that Tat plays a role in regulating autophagy.

METHODS

The role of STAT1 in IFN-γ-induced autophagy in primary human blood macrophages was examined using a small molecule inhibitor or siRNA specific for STAT1. The effect of HIV-1 Tat on autophagy was investigated by pretreating the macrophages with HIV-1 Tat and followed by IFN-γ stimulation. The expressions of autophagy-associated genes and their effects on engulfing mycobacteria were examined.

RESULTS

The activation of STAT1 resulted in IFN-γ-induced LC3B protein expression and autophagosome formation. As postulated, HIV-1 Tat protein suppressed IFN-γ-induced autophagy processes, including LC3B expression. Additionally, HIV-1 Tat restricted the capturing of mycobacteria by autophagosomes.

CONCLUSION

HIV-1 Tat suppressed the induction of autophagy-associated genes and inhibited the formation of autophagosomes. Perturbation of such cellular processes by HIV-1 would impair the effective containment of invading pathogens, thereby providing a favorable environment for opportunistic microbes in HIV-infected individuals.

Pepscan mapping of viral hemorrhagic septicemia virus glycoprotein G major lineal determinants implicated in triggering host cell antiviral responses mediated by type I interferon

Surface glycoproteins of enveloped virus are potent elicitors of type I interferon (IFN)-mediated antiviral responses in a way that may be independent of the well-studied genome-mediated route. However, the viral glycoprotein determinants responsible for initiating the IFN response remain unidentified. In this study, we have used a collection of 60 synthetic 20-mer overlapping peptides (pepscan) spanning the full length of glycoprotein G (gpG) of viral hemorrhagic septicemia virus (VHSV) to investigate what regions of this protein are implicated in triggering the type I IFN-associated immune responses. Briefly, two regions with ability to increase severalfold the basal expression level of the IFN-stimulated mx gene and to restrict the spread of virus among responder cells were mapped to amino acid residues 280 to 310 and 340 to 370 of the gpG protein of VHSV. In addition, the results obtained suggest that an interaction between VHSV gpG and integrins might trigger the host IFN-mediated antiviral response after VHSV infection. Since it is known that type I IFN plays an important role in determining/modulating the protective-antigen-specific immune responses, the identification of viral glycoprotein determinants directly implicated in the type I IFN induction might be of special interest for designing new adjuvants and/or more-efficient and cost-effective viral vaccines as well as for improving our knowledge on how to stimulate the innate immune system.

Type I interferon in HIV treatment: from antiviral drug to therapeutic target

Type I interferons (IFNs) are soluble molecules that exert potent antiviral activity and are currently used for the treatment of a panel of viral infections. In the case of HIV, the use of type I IFN has had limited success, and has almost been abandoned. During the last decade, a series of studies has highlighted how HIV infection may cause overactivation of type I IFN production, which contributes to the exhaustion of the immune system and to disease progression. This review describes the transition from the proposed use of type I IFN as antiviral drugs in HIV infection, to the idea that blocking their activity or production may provide an immunologic benefit of much greater importance than their antiviral activity.

CD4 binding affinity determines human immunodeficiency virus type 1-induced alpha interferon production in plasmacytoid dendritic cells

Plasmacytoid dendritic cells (PDC) are major producers of type I interferons (IFN) in response to human immunodeficiency virus type 1 (HIV-1) infection. To better define the underlying mechanisms, we studied the magnitude of alpha IFN (IFN-alpha) induction by recombinant viruses containing changes in the Env protein that impair or disrupt CD4 binding or expressing primary env alleles with differential coreceptor tropism. We found that the CD4 binding affinity but not the viral coreceptor usage is critical for the attachment of autofluorescing HIV-1 to PDC and for subsequent IFN-alpha induction. Our results illustrate the importance of the gp120-CD4 interaction in determining HIV-1-induced immune stimulation via IFN-alpha production.

Infectious salmon anaemia virus replication and induction of alpha interferon in Atlantic salmon erythrocytes

Background

Infectious salmon anaemia (ISA) virus (ISAV), which causes ISA in marine-farmed Atlantic salmon, is an orthomyxovirus belonging to the genus Isavirus, family Orthomyxoviridae. ISAV agglutinates erythrocytes of several fish species and it is generally accepted that the ISAV receptor destroying enzyme dissolves this haemagglutination except for Atlantic salmon erythrocytes. Recent work indicates that ISAV isolates that are able to elute from Atlantic salmon erythrocytes cause low mortality in challenge experiments using Atlantic salmon. Previous work on ISAV-induced haemagglutination using the highly pathogenic ISAV strain NBISA01 and the low pathogenic ISAV strain RPC/NB-04-0851, showed endocytosis of NBISA01 but not RPC/NB-04-0851. Real-time RT-PCR was used to assess the viral RNA levels in the ISAV-induced haemagglutination reaction samples, and we observed a slight increase in viral RNA transcripts by 36 hours in the haemagglutination reaction with NBISA01 virus when the experiment was terminated. However, a longer sampling interval was considered necessary to confirm ISAV replication in fish erythrocytes and to determine if the infected cells mounted any innate immune response. This study examined the possible ISAV replication and Type I interferon (IFN) system gene induction in Atlantic salmon erythrocytes following ISAV haemagglutination.

Results

Haemagglutination assays were performed using Atlantic salmon erythrocytes and one haemagglutination unit of the two ISAV strains, NBISA01 and RPC/NB-04-0851, of differing genotypes and pathogenicities. Haemagglutination induced by the highly pathogenic NBISA01 but not the low pathogenic RPC/NB-04-0851 resulted in productive infection as evidenced by increased ISAV segment 8 transcripts and increase in the median tissue culture infectious dose (TCID₅₀) by 5 days of incubation. Moreover, reverse transcription (RT) quantitative PCR used to compare mRNA levels of key Type I IFN system genes in erythrocyte lysates of haemagglutination reactions with the two ISAV strains showed a higher relative fold increase of IFN-α in NBISA01 haemagglutinations compared to RPC/NB-04-085-1 haemagglutinations (33.0 – 44.26 relative fold increase compared to 11.29). Erythrocytes exposed to heat-inactivated virus or to polyinosinic:polycytidylic acid (polyI:C) or to L-15 medium alone (negative control assays) had minimal late induction (<3.5 relative fold increase) of STAT1 and/or ISG15 and Mx genes, whereas erythrocytes exposed to UV-inactivated virus lacked any cytokine induction.

Conclusion

ISAV-induced haemagglutination by a highly pathogenic virus strain results in virus uptake and productive infection of Atlantic salmon erythrocytes accompanied by significant induction of IFN-α. This study also highlights the critical role of ISAV strain variation in the initial stages of the virus-cell interaction during haemagglutination, and possibly in the pathogenesis of ISA. Moreover, the study shows for the first time that fish erythrocytes immunologically respond to ISAV infection.

Plasmacytoid dendritic cells and type I IFN: 50 years of convergent history

It has been 50 years since the initial descriptions of what are now known as plasmacytoid dendritic cells (pDC) and type I IFN. pDC, which are infrequent cells found in the peripheral blood and lymphoid organs, are the most potent producers of type I and type III IFNs in the body. pDC produce IFN-alpha in response to both DNA and RNA enveloped viruses by virtue of their ribonucleic acids signaling in the endosome through TLR9 and TLR7, respectively. This stimulation, which also occurs with DNA or RNA-containing immune complexes and synthetic TLR7 and -9 agonists, is dependent upon the transcription factor IRF-7, which is expressed at high constitutive levels in pDC. In addition to releasing as much as 3-10pg of IFN-alpha/cell, pDC are also potent modulators of the immune response. In this review, we discuss the signaling pathways in pDC, their roles in linking innate and adaptive immunity, and their roles in infectious disease and autoimmunity.

The role of type I interferon production by dendritic cells in host defense

Type I interferons (IFN) and dendritic cells (DC) share an overlapping history, with rapidly accumulating evidence for vital roles for both production of type 1 IFN by DC and the interaction of this IFN both with DC and components of the innate and adaptive immune responses. Within the innate immune response, the plasmacytoid DC (pDC) are the "professional" IFN producing cells, expressing specialized toll-like receptors (TLR7 and -9) and high constitutive expression of IRF-7 that allow them to respond to viruses with rapid and extremely robust IFN production; following activation and production of IFN, the pDC subsequently mature into antigen presenting cells that help to shape the adaptive immune response. However, like most cells in the body, the myeloid or conventional DC (mDC or cDC) also produce type I IFNs, albeit typically at a lower level than that observed with pDC, and this IFN is also important in innate and adaptive immunity induced by these classic antigen presenting cells. These two major DC subsets and their IFN products interact both with each other as well as with NK cells, monocytes, T helper cells, T cytotoxic cells, T regulatory cells and B cells to orchestrate the early immune response. This review discusses some of the converging history of DC and IFN as well as mechanisms for IFN induction in DC and the effects of this IFN on the developing immune response.

In vitro treatment of human monocytes/macrophages with myristoylated recombinant Nef of human immunodeficiency virus type 1 leads to the activation of mitogen-activated protein kinases, IkappaB kinases, and interferon regulatory factor 3 and to the release of beta interferon

The viral protein Nef is a virulence factor that plays multiple roles during the early and late phases of human immunodeficiency virus (HIV) replication. Nef regulates the cell surface expression of critical proteins (including down-regulation of CD4 and major histocompatibility complex class I), T-cell receptor signaling, and apoptosis, inducing proapoptotic effects in uninfected bystander cells and antiapoptotic effects in infected cells. It has been proposed that Nef intersects the CD40 ligand signaling pathway in macrophages, leading to modification in the pattern of secreted factors that appear able to recruit and activate T lymphocytes, rendering them susceptible to HIV infection. There is also increasing evidence that in vitro cell treatment with Nef induces signaling effects. Exogenous Nef treatment is able to induce apoptosis in uninfected T cells, maturation in dendritic cells, and suppression of CD40-dependent immunoglobulin class switching in B cells. Previously, we reported that Nef treatment of primary human monocyte-derived macrophages (MDMs) induces a cycloheximide-independent activation of NF-kappaB and the synthesis and secretion of a set of chemokines/cytokines that activate STAT1 and STAT3. Here, we show that Nef treatment is capable of hijacking cellular signaling pathways, inducing a very rapid regulatory response in MDMs that is characterized by the rapid and transient phosphorylation of the alpha and beta subunits of the IkappaB kinase complex and of JNK, ERK1/2, and p38 mitogen-activated protein kinase family members. In addition, we have observed the activation of interferon regulatory factor 3, leading to the synthesis of beta interferon mRNA and protein, which in turn induces STAT2 phosphorylation. All of these effects require Nef myristoylation.

Kaposi's sarcoma-associated herpesvirus virions inhibit interferon responses induced by envelope glycoprotein gpK8.1

The Kaposi's sarcoma-associated herpesvirus (KSHV) envelope glycoprotein gpK8.1 contributes to cellular attachment through binding cell surface heparan sulfate proteoglycans. By using a soluble recombinant form of gpK8.1, we discovered that a consequence of gpK8.1 interaction with human fibroblasts is the induction of an antiviral response, as characterized by the activation of interferon regulatory factor 3 (IRF-3), production of interferon beta (IFN-beta), and expression of interferon-stimulated antiviral genes. In contrast, neither IFN-beta expression nor a functional antiviral response is observed in cells treated with KSHV virions. The interferon response induced by soluble gpK8.1 can be inhibited by simultaneous treatment with UV-inactivated virions, while the induction of an indicator inflammatory cytokine, interleukin-6, was readily evident in the response to both gpK8.1 and KSHV. In addition, KSHV virions abrogate gpK8.1-mediated activation of IRF-3, an early transcriptional regulator for cellular antiviral responses. Although innate immune responses are initiated during contact between gpK8.1 and cellular receptor(s), these results suggest that the virion contains one or more structural elements that selectively repress an effective antiviral response while allowing cellular responses favorable to the KSHV life cycle.

Impaired virus-induced interferon-alpha2 release in adult asthmatic patients

BACKGROUND

Interferon-alpha (IFN-alpha) not only serves as a first defence line of the immune system against viral attacks but also interacts with T-helper type 1 (Th1)/ T-helper type 2 (Th2) regulation and various other cell types like basophils and monocytes, thereby linking innate and acquired immunity. Recently, we demonstrated that children with allergic asthma produced significantly lower amounts of virus-induced IFN-alpha2 compared with healthy children or those with intrinsic asthma.

OBJECTIVE

In this study, we extend our analysis to examine in a cohort study whether IFN-alpha2 is also reduced in allergic asthma of adults.

METHODS

Adults with allergic asthma and healthy controls were prospectively recruited. Blood cultures were stimulated with different viruses (respiratory syncytial virus (RSV), newcastle disease virus (NDV)) and analysed for IFN-alpha2 protein release and gene transcription.

RESULTS

Virus-induced IFN-alpha2 release from blood cells of allergic asthmatic patients was significantly reduced compared with healthy controls, independent of the virus used (NDV(asthma)=221+/-134 pg/mL, NDV(healthy)=555+/-341 pg/mL, P=0.003 and RSV(asthma)=46+/-27 pg/mL, RSV(healthy)=108+/-90 pg/mL, P=0.014). Values=mean+/-standard deviation). It was not influenced by medication, especially cortico-steroids. IFN-alpha2 mRNA expression 5 h after NDV stimulation confirmed the ELISA results and correlated well with release data (r=0.397, P=0.033).

CONCLUSION

Like children, adults with allergic asthma show impaired virus-induced IFN-alpha2 release in whole blood, indicating a systemic phenomenon in patients with bronchial asthma and atopic phenotype. Impaired virus-induced IFN-alpha release could be a marker of inflammation in chronic allergic asthma.

Toll-like receptor 3 agonist poly(I:C)-induced antiviral response in human corneal epithelial cells

The objective of this study was to examine the expression of Toll-like receptor 3 (TLR3) by human corneal epithelial cells (HCECs) and to determine whether exposure to the TLR3 agonist polyinosinic-polycytidylic acid [poly(I:C)] induces an antiviral response in these cells. Fluorescence-activated cell sorter (FACS) analysis revealed TLR3 to be constitutively expressed and distributed intracellularly in HCECs. Stimulation of HCECs with the TLR3 agonist poly(I:C) induced the activation of nuclear factor (NF)-kappaB and production of the proinflammatory cytokine interleukin (IL)-6 and the chemokine IL-8. Upon exposure to poly(I:C), HCECs initiated a potent antiviral response resulting in an increase of interferon (IFN)-beta mRNA expression (7-fold). Poly(I:C) stimulation also up-regulated mRNA expression of the antiviral chemokine IFN-gamma inducible protein 10 (IP10), myxovirus resistance gene A and 2',5'-oligoadenylate synthetase (5-, 10- and 9-fold, respectively), and secretion of IP10. These responses were also induced by exogenously added type 1 IFNs, but could not be blocked by pretreatment of the cells with anti-TLR3 monoclonal antibody, suggesting that the receptor was not expressed on the cell surface. Furthermore, incubation of HCECs with an endosomal acidification inhibitor, chloroquine, markedly inhibited poly(I:C)-mediated IFN-beta expression in HCECs. These results suggest that corneal epithelial cells are important sentinels of the corneal innate immune system against viral infection, and that stimulation of TLR3 can induce the expression of key proinflammatory cytokines and chemokines and antiviral genes that help in the defence of the cornea against viral infection.

HIV-infected cells are major inducers of plasmacytoid dendritic cell interferon production, maturation, and migration

Plasmacytoid dendritic cells (PDC), natural type-1 interferon (IFN) producing cells, could play a role in the innate anti-HIV immune response. Previous reports indicated that PDC IFN production is induced by HIV. Our results show a more robust IFN induction when purified PDC (>95%) were exposed to HIV-infected cells. This effect was not observed with non-viable cells, DNA, and RNA extracted from infected cells, and viral proteins. The response was blocked by anti-CD4 and neutralizing anti-gp120 antibodies as well as soluble CD4. IFN induction by HIV-infected cells was also prevented by low-dose chloroquine, which inhibits endosomal acidification. PDC IFN release resulted in reduced HIV production by infected CD4+ cells, supporting an anti-HIV activity of PDC. Stimulated CD4+ cells induced PDC activation and maturation; markers for PDC migration (CCR7) were enhanced by HIV-infected CD4+ cells only. This latter finding could explain the decline in circulating PDC in HIV-infected individuals.

HIV-1 induces IL-10 production in human monocytes via a CD4-independent pathway

In HIV-infected patients, increased levels of IL-10, mainly produced by virally infected monocytes, were reported to be associated with impaired cell-mediated immune responses. In this study, we investigated how HIV-1 induces IL-10 production in human monocytes. We found that CD14(+) monocytes infected by either HIV-1(213) (X4) or HIV-1(BaL) (R5) produced IL-10, IL-6, tumor necrosis factor-alpha (TNF-alpha), and to a lesser extent, IFN-gamma. However, the capacity of HIV-1 to induce these cytokines was not dependent on virus replication since UV-inactivated HIV-1 induced similar levels of these cytokines. In addition, soluble HIV-1 gp160 could induce CD14(+) monocytes to produce IL-10 but at lower levels. Cross-linking CD4 molecules (XLCD4) with anti-CD4 mAbs and goat anti-mouse IgG (GAM) resulted in high levels of IL-6, TNF-alpha and IFN-gamma but no IL-10 production by CD14(+) monocytes. Interestingly, neither anti-CD4 mAbs nor recombinant soluble CD4 (sCD4) receptor could block IL-10 secretion induced by HIV-1(213), HIV-1(BaL) or HIV-1 gp160 in CD14(+) monocytes, whereas anti-CD4 mAb or sCD4 almost completely blocked the secretion of the other cytokines. Furthermore, HIV-1(213) could induce IL-10 mRNA expression in CD14(+) monocytes while XLCD4 by anti-CD4 mAb and GAM failed to do so. As with IL-10 protein levels, HIV-1(213)-induced IL-10 mRNA expression in CD14(+) monocytes could not be inhibited by anti-CD4 mAb or sCD4. Taken together, HIV-1 binding to CD14(+) monocytes can induce CD4-independent IL-10 production at both mRNA and protein levels. This finding suggests that HIV induces the immunosuppressive IL-10 production in monocytes and is not dependent on CD4 molecules and that interference with HIV entry through CD4 molecules may have no impact on counteracting the effects of IL-10 during HIV infection.

Induction and regulation of IFNs during viral infections

Interferons (IFN)s are involved in numerous immune interactions during viral infections and contribute to both induction and regulation of innate and adaptive antiviral mechanisms. IFNs play a pivotal rule in the outcome of a viral infection, as demonstrated by the impaired resistance against different viruses in mice deficient for the receptors IFNAR-2 and IFNGR. During viral infections, IFNs are involved in numerous immune interactions as inducers, regulators, and effectors of both innate and adaptive antiviral mechanisms. IFN-alpha/beta is produced rapidly when viral factors, such as envelope glycoproteins, CpG DNA, or dsRNA, interact with cellular pattern-recognition receptors (PRRs), such as mannose receptors, toll-like receptors (TLRs), and cytosolic receptors. These host-virus interactions signal downstream to activate transcription factors needed to achieve expression from IFN-alpha/beta genes. These include IFN regulatory factor-3 (IRF-3), IRF-5, IRF-7, c-Jun/ATF-2, and NF-kappaB. In contrast, IFN-gamma is induced by receptor-mediated stimulation or in response to early produced cytokines, including interleukin-2 (IL-12), IL-18, and IFN-alpha/beta, or by stimulation through T cell receptors (TCRs) or natural killer (NK) cell receptors. IFNs signal through transmembrane receptors, activating mainly Jak-Stat pathways but also other signal transduction pathways. Cytokine and TCR-induced IFN-gamma expression uses distinct signal transduction pathways involving such transcription factors as NFAT, Stats and NF-kappaB. This results in induction and activation of numerous intrinsic antiviral factors, such as RNA-activated protein kinase (PKR), the 2-5A system, Mx proteins, and several apoptotic pathways. In addition, IFNs modulate distinct aspects of both innate and adaptive immunity. Thus, IFN-alpha/beta and IFN-gamma affect activities of macrophages, NK cells, dendritic cells (DC), and T cells by enhancing antigen presentation, cell trafficking, and cell differentiation and expression profiles, ultimately resulting in enhanced antiviral effector functions. This review focuses on the latest findings regarding induction and regulation of IFNs, primarily during the early phase of an antiviral immune response. Both cellular and molecular aspects are discussed from the perspective of host-virus interactions.

Human cytomegalovirus elicits a coordinated cellular antiviral response via envelope glycoprotein B

Previous studies have shown that human cytomegalovirus (CMV) is a potent elicitor of interferon-stimulated gene (ISG) expression. Induction of the interferon pathway does not require replication-competent virus, and envelope glycoprotein B (gB) from CMV is a viral structural component that can directly induce transcription of ISGs. Here we extend these earlier findings by defining the consequences of inducing the interferon pathway. We found that cells respond to CMV or soluble gB by establishing a functional antiviral state within cell types critical in CMV biology, such as fibroblasts and endothelial cells. We have also discovered new insights into the mechanism by which the pathway is initiated. Interferon regulatory factor 3 (IRF3), a key transcriptional regulator of cellular interferon responses, is activated by CMV virions and soluble gB. Thus, IRF3 becomes activated via "outside-in" signal transduction events. This is a novel mechanism of activation of this key transcription factor by viruses. In comparison to soluble gB (gB(1-750)), which comprises the entire ectodomain of gB, a truncation mutant encompassing only the amino-terminal region of gB (gB(1-460)) was markedly less effective at inducing antiviral responses. This indicates that the region of gB from residues 461 to 750 is important for initiation of the antiviral response. In addition, CMV and gB establish an antiviral state in alpha/beta interferon null cells, illustrating that primary induction of ISGs by CMV and gB is sufficient to establish the antiviral response and that interferon secretion is not necessary for the antiviral effect. Taken together, our findings reveal that CMV initiates a coordinated antiviral response through contact between gB and an as-yet-unidentified cell surface receptor(s).

Induction of interferon-alpha and tumor necrosis factor-related apoptosis-inducing ligand in human blood mononuclear cells by hemagglutinin-neuraminidase but not F protein of Newcastle disease virus

To determine molecular viral components which can induce innate immune responses in human peripheral blood mononuclear cells (PBMC), we investigated the anti-neoplastic agent Newcastle disease virus (NDV) and its two spike proteins hemagglutinin-neuraminidase (HN) and fusion protein (F). NDV was an excellent inducer in PBMC of IFN-alpha production and capable of inducing upregulation of plasma membrane expression of tumor necrosis factor related apoptosis inducing ligand (TRAIL). Viral replication was not required for these responses because NDV inactivated for 5 min by UV was as good as live NDV. NDV-modified and paraformaldehyde-fixed BHK cells could also trigger IFN-alpha and TRAIL induction, indicating that contacts of responder cells with NDV-modified cell surfaces are sufficient to induce these activities in PBMC. Antibodies against HN but not F were able to block these responses. Finally we could show that HN but not F induced IFN-alpha and TRAIL in PBMC. This was possible through the use of respective gene transfectants generated with the help of Semliki Forest virus (SFV) replicase-based DNA recombinant expression systems. Upon contact with BHK cells expressing HN but not F at their cell surface, human PBMC produced IFN-alpha and some cells, including monocytes and T lymphocytes, upregulated cell surface TRAIL expression.

Viral haemorrhagic septicaemia virus induces vig-2, a new interferon-responsive gene in rainbow trout

An mRNA differential display methodology was used to study the rainbow trout response to viral infection. A new transcript (vig-2) induced by viral haemorrhagic septicaemia virus (VHSV) in rainbow trout leucocytes was identified from the head-kidney. vig-2 was also induced in vivo during experimental infection and following DNA immunisation with a plasmid containing a gene encoding the viral glycoprotein. Viral induction of vig-2 was blocked by cycloheximide (CHX), indicating its dependency on a newly synthesised intermediate protein. This intermediate protein is most probably related to interferon because treatment of cells with a conditioned medium displaying an interferon-like activity resulted in a strong vig-2 expression, which was not blocked by CHX treatment. The cDNA sequence of the vig-2 transcript displays several mRNA destabilisation motifs and two signals characteristic of immediate-early gene expression. Curiously, vig-2 has no evident encoding potential except for a small 51 amino acid putative polypeptide with no clear similarity to any sequence available in the databanks. Therefore, the complete vig-2 genomic sequence was determined from a lambda phage clone retrieved from a genomic DNA library of rainbow trout. The genomic organisation of vig-2 shows five exons delimited with typical splice acceptor and donor sites. A promoter with a canonical ISRE, confirming that vig-2 is an interferon-responsive gene, is also present 115 nt upstream of the first exon.

Molecular pathways in virus-induced cytokine production

Virus infections induce a proinflammatory response including expression of cytokines and chemokines. The subsequent leukocyte recruitment and antiviral effector functions contribute to the first line of defense against viruses. The molecular virus-cell interactions initiating these events have been studied intensively, and it appears that viral surface glycoproteins, double-stranded RNA, and intracellular viral proteins all have the capacity to activate signal transduction pathways leading to the expression of cytokines and chemokines. The signaling pathways activated by viral infections include the major proinflammatory pathways, with the transcription factor NF-kappaB having received special attention. These transcription factors in turn promote the expression of specific inducible host proteins and participate in the expression of some viral genes. Here we review the current knowledge of virus-induced signal transduction by seven human pathogenic viruses and the most widely used experimental models for viral infections. The molecular mechanisms of virus-induced expression of cytokines and chemokines is also analyzed.

Antibody-dependent induction of type I interferons by poliovirus in human mononuclear blood cells requires the type II fcgamma receptor (CD32)

The induction of type I interferons (IFNs) in peripheral blood mononuclear cells (PBMCs) can be triggered by viral infection or exposure to viral glycoproteins. Here we show that the IFN-alpha-inducing capacity of attenuated poliovirus vaccine strains is dramatically enhanced in the presence of human polyvalent immunoglobulin G (IgG). The transcription of both IFN-alpha and IFN-beta genes was detected by RT-PCR in stimulated cells. This antibody-dependent activation of type I IFNs genes was also observed with Formalin-inactivated or UV-inactivated poliovirus, but not with empty poliovirus capsids. The ability of poliovirus-antibody complexes to induce IFN-alpha was specifically inhibited when PBMCs were preincubated with an excess of the Fc fragment of IgG. Monoclonal antibodies directed to FcgammaRII (CD32) were also inhibitory, whereas antibodies to the two other classes of Fcgamma receptors, CD16 and CD64, were not. Also, aggregation of FcgammaRII by anti-CD32 antibodies alone failed to induce IFN-alpha production. Our results suggest that induction of type I interferons by poliovirus-antibody complexes depends on CD32-mediated phagocytosis of RNA-containing viral particles. As suggested by the results of an ELISPOT analysis, only a fraction of the IFN-alpha-producing cells are able to synthesize IFN-alpha in response to poliovirus-IgG complexes.

Transient IFN-gamma synthesis in the lymph node draining a dermal site loaded with UV-irradiated herpes simplex virus type 1: an NK- and CD3-dependent process regulated by IL-12 but not by IFN-alpha/beta

Our previous studies have shown that UV-inactivated, non-replicating herpes simplex virus type 1 (UV-HSV-1) triggers early and transient synthesis of IFN-alpha/beta in the mouse regional lymph node when delivered upstream (i.e. in the ear dermis). In this study, it is demonstrated, by use of a quantitative RT-PCR readout assay, that IFN-gamma mRNA expression was rapidly and transiently upregulated in draining lymph nodes when UV-HSV-1 was delivered in the ear dermis of C57Bl/6 mice. An increased number of IFN-gamma-producing cells was also detected in the lymph node by flow cytometric analysis. Two different subsets of cells, namely DX5(+) NK cells and CD3epsilon(+) T cells, accounted for this early IFN-gamma synthesis. Prompt upregulation of IFN-alpha and IL-12p40 mRNA was also recorded. We took advantage of IFN-alpha/beta-receptor knockout and wild-type 129 mice to study a potential role of IFN-alpha/beta in the signalling pathway leading to IFN-gamma transcription/translation. IFN-gamma mRNA upregulation still occurred in IFN-alpha/beta-receptor(-/-) mice, showing that IFN-alpha/beta was dispensable. The use of IL-12-neutralizing antibodies, prior to UV-HSV-1 delivery, confirmed the major role played by IL-12 in the early/transient IFN-gamma burst.

Innate immune system damage in human immunodeficiency virus type 1 infection. Implications for acquired immunity and vaccine design

HIV infection affects the innate as well as the acquired immune systems. Critically, it changes the function of macrophages, which link the innate and acquired responses through their ability to present antigen to CD4(+) T lymphocytes. Patients with HIV infection have a reduced capacity to deal with subsequent pathogen exposure and many suffer from chronic pulmonary infections. We have produced complex synthetic peptides that mimic the function of viral gp120 and may represent prototypes of molecules that can prevent or ameliorate HIV-induced damage to the immune system.

Evasion of host defenses by measles virus: wild-type measles virus infection interferes with induction of Alpha/Beta interferon production

Measles is a highly contagious disease currently responsible for over one million childhood deaths, particularly in the developing world. Since alpha/beta interferons (IFNs) are pivotal players both in nonspecific antiviral immunity and in specific cellular responses, their induction or suppression by measles virus (MV) could influence the outcome of a viral infection. In this study we compare the IFN induction and sensitivity of laboratory-passaged attenuated MV strains Edmonston and Moraten with those of recent wild-type viruses isolated and passaged solely on human peripheral blood mononuclear cells (PBMC) or on the B958 marmoset B-cell line. We report that two PBMC-grown wild-type measles isolates and two B958-grown strains of MV induce 10- to 80-fold-lower production of IFN by phytohemagglutinin-stimulated peripheral blood lymphocytes (PBL) compared to Edmonston and Moraten strains of measles. Preinfection of PBL with these non-IFN-inducing MV isolates prevents Edmonston-induced but not double-stranded-RNA-induced IFN production. This suggests that the wild-type viruses can actively inhibit Edmonston-induced IFN synthesis and that this is not occurring by double-stranded RNA. Furthermore, the wild-type MV is more sensitive than Edmonston MV to the effect of IFN. MV is thus able to suppress the synthesis of the earliest mediator of antiviral immunity, IFN-alpha/beta. This could have important implications in the virulence and spread of MV.

Human receptor for measles virus (CD46) enhances nitric oxide production and restricts virus replication in mouse macrophages by modulating production of alpha/beta interferon

Complement regulatory protein CD46 is a human cell receptor for measles virus (MV). In this study, we investigated why mouse macrophages expressing human CD46 restricted MV replication and produced higher levels of nitric oxide (NO) in response to MV and gamma interferon (IFN-gamma). Treatment of MV-infected CD46-expressing mouse macrophages with antibodies against IFN-alpha/beta blocked NO production. Antibodies against IFN-alpha/beta also inhibited the augmenting effect of MV on IFN-gamma-induced NO production in CD46-expressing mouse macrophages. These antibodies did not affect NO production induced by IFN-gamma alone. These data suggest that MV enhances NO production in CD46-expressing mouse macrophages through action of IFN-alpha/beta. Mouse macrophages expressing a human CD46 mutant lacking the cytoplasmic domains were highly susceptible to MV. These cells produced much lower levels of NO and IFN-alpha/beta upon infection by MV, suggesting the CD46 cytoplasmic domains enhanced IFN-alpha/beta production. When mouse macrophages expressing tailless human CD46 were exposed to culture medium from MV-infected mouse macrophages expressing intact human CD46, viral protein synthesis and development of cytopathic effects were suppressed. Pretreating the added culture medium with antibodies against IFN-alpha/beta abrogated these antiviral effects. Taken together, these findings suggest that expression of human CD46 in mouse macrophages enhances production of IFN-alpha/beta in response to MV infection, and IFN-alpha/beta synergizes with IFN-gamma to enhance NO production and restrict viral protein synthesis and virus replication. This novel function of human CD46 in mouse macrophages requires the CD46 cytoplasmic domains.

vig-1, a new fish gene induced by the rhabdovirus glycoprotein, has a virus-induced homologue in humans and shares conserved motifs with the MoaA family

We used mRNA differential display methodology to analyze the shift of transcription profile induced by the fish rhabdovirus, viral hemorrhagic septicemia virus (VHSV), in rainbow trout leukocytes. We identified and characterized a new gene which is directly induced by VHSV. This VHSV-induced gene (vig-1) encodes a 348-amino-acid protein. vig-1 is highly expressed during the experimental disease in lymphoid organs of the infected fish. Intramuscular injection of a plasmid vector expressing the viral glycoprotein results in vig-1 expression, showing that the external virus protein is sufficient for the induction. vig-1 expression is also obtained by a rainbow trout interferon-like factor, indicating that vig-1 can be induced through different pathways. Moreover, vig-1 is homologous to a recently described human cytomegalovirus-induced gene. Accordingly, vig-1 activation may represent a new virus-induced activation pathway highly conserved in vertebrates. The deduced amino acid sequence of vig-1 is significantly related to sequences required for the biosynthesis of metal cofactors. This suggests that the function of vig-1 may be involved in the nonspecific virus-induced synthesis of enzymatic cofactors of the nitric oxide pathway.

Induction of interferon-alpha by glycoprotein D of herpes simplex virus: a possible role of chemokine receptors

The induction of type I interferons by most RNA viruses is initiated by virus-derived double-stranded (ds)RNA. However, retro- and DNA-viruses, which do not synthesize dsRNA, must rely on different mechanisms of induction. For human immunodeficiency virus type 1 (HIV-1), recombinant glycoproteins 120 or 160 suffice to induce interferon (IFN)-alpha in blood-derived lymphocytes [H. Ankel, M. R. Capobianchi, C. Castilletti, and F. Dianzani (1994). Virology 205, 34-43]. Here we show that for herpes simplex virus type 1 (HSV-1) recombinant glycoprotein, gD is the major inducer, whereas gB, gC, gE, gG, gI, and the complex of gH and gL are poor inducers. The recombinant extramembrane fragment of gD was sufficient to induce IFN-alpha levels comparable to that of intact virus. Like with HIV-1, induction was inhibited by a monoclonal antibody that recognizes cerebrosides and sulfatides. Furthermore, monoclonal antibodies specific for the chemokine receptors CCR3 and CXCR4 also blocked induction. We conclude that HSV-1 induces IFN-alpha by interaction of its glycoprotein gD with appropriate receptors on IFN-producing cells. Based on the known receptor roles of galactosyl cerebrosides and chemokine receptors in HIV infection, such structures on IFN-producing cells could also participate in the induction of IFN-alpha by HSV-1.

Coronavirus pseudoparticles formed with recombinant M and E proteins induce alpha interferon synthesis by leukocytes

Transmissible gastroenteritis virus (TGEV), an enteric coronavirus of swine, is a potent inducer of alpha interferon (IFN-alpha) both in vivo and in vitro. Incubation of peripheral blood mononuclear cells with noninfectious viral material such as inactivated virions or fixed, infected cells leads to early and strong IFN-alpha synthesis. Previous studies have shown that antibodies against the virus membrane glycoprotein M blocked the IFN induction and that two viruses with a mutated protein exhibited a decreased interferogenic activity, thus arguing for a direct involvement of M protein in this phenomenon. In this study, the IFN-alpha-inducing activity of recombinant M protein expressed in the absence or presence of other TGEV structural proteins was examined. Fixed cells coexpressing M together with at least the minor structural protein E were found to induce IFN-alpha almost as efficiently as TGEV-infected cells. Pseudoparticles resembling authentic virions were released in the culture medium of cells coexpressing M and E proteins. The interferogenic activity of purified pseudoparticles was shown to be comparable to that of TGEV virions, thus establishing that neither ribonucleoprotein nor spikes are required for IFN induction. The replacement of the externally exposed, N-terminal domain of M with that of bovine coronavirus (BCV) led to the production of chimeric particles with no major change in interferogenicity, although the structures of the TGEV and BCV ectodomains markedly differ. Moreover, BCV pseudoparticles also exhibited interferogenic activity. Together these observations suggest that the ability of coronavirus particles to induce IFN-alpha is more likely to involve a specific, multimeric structure than a definite sequence motif.

The Mannose Receptor Mediates Induction of IFN-α in Peripheral Blood Dendritic Cells by Enveloped RNA and DNA Viruses

Peripheral blood dendritic cells (DC) produce IFN-α in response to challenge by many enveloped viruses including herpes simplex virus (HSV) and HIV, whereas Sendai virus predominantly stimulates IFN-α production by monocytes. Glycosylated viral envelope proteins are known to be important for the induction of IFN-α. In this study we demonstrate that stimulation of IFN-α synthesis by HSV is inhibited by a number of monosaccharides, including fucose, N-acetylglucosamine, and N-acetylgalactosamine as well as the yeast polysaccharide mannan, supporting a role for lectin(s) in the IFN-α stimulation pathway. Furthermore, antiserum to the mannose receptor (MR) also inhibited HSV, vesicular stomatitis virus, and HIV-induced IFN-α production, but failed to inhibit the IFN-α induced by Sendai virus. We further demonstrated that freshly isolated blood DC and IFN-α-producing cells responding to HSV stimulation express the MR. This study therefore implicates the MR as an important receptor for the nonspecific recognition of enveloped viruses by DC and the subsequent stimulation of IFN-α production by these viruses. Thus, the MR probably serves as a critical link between innate and adaptive immunity to viruses, especially given the role of the MR in Ag capture by DC and the importance of IFN-α in shaping immunity.

Tissue chambers--a useful model for in vivo studies of cytokine production in the pig

An in vivo tissue chamber model was developed to enable studies of local cytokine production and cellular events during inflammatory and immune reactions in the pig. Tissue chambers made of sialistic rubber tubing were surgically implanted in the subcutaneous tissue- and samples of tissue chamber fluid (TCF) and inflammatory cells were collected by aspiration with a syringe. To evaluate the model for local cytokine production, two cytokine inducers, polyribinosinic-polyribocytidylic acid (poly I:C) and fixed Aujeszky's disease virus infected PK15 cells (ADV-PK15), were injected into the tissue chambers and samples of TCF were collected 0, 4, 8, 12, 24 and 48 h post injection. Poly I:C injections induced local production of interferon-alpha (IFN-alpha) as well as tumor necrosis factor (TNF) in the TCF but kinetic differences in the production of the cytokines were noted. Poly I:C also induced an increase in cell numbers in the TCF, mainly due to increased neutrophil numbers. Injections of ADV-PK15 induced local IFN-alpha production in the TCF as long as the pigs were serologically negative to ADV. Immunofluorescence and in situ hybridization techniques could be applied for characterization of TCF cells. Moreover, cells recovered from the tissue chambers were viable and could be used in functional in vitro tests. Taken together, this tissue chamber model could prove very useful in in vivo studies of inflammatory/immune responses and cytokine production in the pig.

Human immunodeficiency virus type 1 gp120 stimulates cytomegalovirus replication in monocytes: possible role of endogenous interleukin-8

Recombinant gp120, but not other human immunodeficiency type 1 (HIV-1) structural proteins, dose-dependently stimulates human cytomegalovirus (HCMV) immediate-early antigen (IEA) expression and infectious virus yield in freshly isolated normal monocytes infected with HCMV. Monoclonal antibodies (MAbs) recognizing the gp120 V3 loop, as well as V3 loop octameric multibranched peptides and antibody to galactocerebroside, but not sCD4, abrogate the gp120 stimulation of IEA expression, suggesting that the effect involves V3 loop-galactocerebroside interaction and is not mediated by CD4. Interleukin 8 (IL-8) gene expression is enhanced in monocytes treated with gp120 at the level of both mRNA and released protein. Exogenous IL-8 could replace gp120 in the stimulation of HCMV infection, while a MAb capable of neutralizing IL-8 activity abrogates the gp120-induced HCMV stimulation. These data indicate that HIV-1 glycoprotein induces stimulation of productive infection of monocytes with HCMV and that such stimulation may be mediated by the upregulation of IL-8 gene expression. This is the first evidence that HIV-1 may affect HCMV replication indirectly, via the interaction of gp120 with the monocyte membrane, in the complete absence of retroviral replication, through the stimulation of IL-8 release. Because in HIV-1-infected individuals, HCMV infection is frequently activated and the levels of circulating IL-8 are enhanced, these findings may be pathogenetically relevant.

HIV-1 envelope glycoprotein gp120 down-regulates CD4 expression in primary human macrophages through induction of endogenous tumour necrosis factor-alpha

Among immunological abnormalities present in human immunodeficiency virus type 1 (HIV-1)-infected individuals are dysregulation of cytokine production and CD4 down-regulation in both T-helper cells and monocytes/macrophages. The HIV-1 envelope glycoprotein 120 (gp120) has the ability to induce different cytokines in peripheral blood mononuclear cells and in monocytes/macrophages in vitro which in some instances have been reported to down-regulate macrophage CD4 expression. This study provides evidence that HIV-1 recombinant gp120 (rgp120) down-regulates both surface and total CD4 expression in primary tissue culture-differentiated macrophages (TCDM) at the level of transcription. The CD4 down-regulation observed in TCDM occurred between 6 and 12 hr after rgp120 treatment preceded by a peak of endogenous tumour necrosis factor-alpha (TNF-alpha) observed at 3-6 hr post-treatment. We demonstrate that the TCDM CD4 down-regulation observed after rgp120 treatment was inhibited by the use of an anti-huTNF-alpha monoclonal antibody (mAb), but not by mAb directed against other cytokines induced by rgp120, such as interleukin-1 beta (IL-1 beta) and interferon-alpha (IFN-alpha). The present findings roughly parallel those observed both in the sera of patients and in the monocytes/macrophages isolated from HIV-positive individuals, suggesting that gp120 by stimulating endogenous TNF-alpha production could be a good candidate for the CD4 down-regulation observed in the monocytes/macrophages of HIV-1-infected individuals. In contrast to CD4 down-regulation in HIV-infected lymphocytes, which results from a direct effect of viral genes on CD4 expression, soluble factors such as cytokines induced during HIV infection might explain the monocyte/macrophage CD4 dysregulation observed in acquired immune deficiency syndrome.