In vivo CRISPR gene editing in patients with herpetic stromal keratitis

In vivo CRISPR gene therapy holds large clinical potential, but the safety and efficacy remain largely unknown. Here, we injected a single dose of herpes simplex virus 1 (HSV-1)-targeting CRISPR formulation in the cornea of three patients with severe refractory herpetic stromal keratitis (HSK) during corneal transplantation. Our study is an investigator-initiated, open-label, single-arm, non-randomized interventional trial at a single center (NCT04560790). We found neither detectable CRISPR-induced off-target cleavages by GUIDE-seq nor systemic adverse events for 18 months on average in all three patients. The HSV-1 remained undetectable during the study. Our preliminary clinical results suggest that in vivo gene editing targeting the HSV-1 genome holds acceptable safety as a potential therapy for HSK.

Abstract 3512: Immunotherapy by STING activation in a CRISPR induce mouse model of GBM decrease tumor progression by CD8 T-cells and altered vascularity

Intrinsic malignant brain tumors, such as glioblastoma (GBM) are frequently resistant to immunotherapy with few hyper-mutated glioblastomas showing response. Here we have applied a long-term treatment with STING agonist and PD-1 inhibitors alone and in combination towards eliciting enhanced host immune response to combat GBM progression. To address these questions we generated mouse models of GBM by intracranial implantation of a murine GBM stem cell line or orthotopic CRISPR induced mutation to astrocytes. Systemic administration of STING agonist crosses the blood-brain barrier and induces a type-1 IFN signature in the brain and this was further enhanced in the tumor milieu. Treatment outcomes were addressed by MRi and treated animals showed a significant reduction in tumor volume and hence improved survival in comparison to the animals in the control group. Histochemical evaluation of tumor samples from the animals that received treatment showed elevated necrosis and aberrant/leaky vasculature in comparison to the control tumor samples. The presence of cytotoxic T-cells were similar between the groups but activated PD-1 positive T-cells were increased in treated tumors. Ex-vivo analysis of isolated T-cells from tumor baring mice confirms cytotoxic T-cells targeting the GBM cells. In conclusion, application of STING agonist promotes alteration of vasculitis and priming of T-cells in GBM results in increased survival and decreased tumor progression. These results reveal that GBM can be targeted by immune therapy through systemic activation of STING/IFN pathway.

Citation Format: Justin V. Joseph, Huiqiang Cai, Brian Hansen, Soren R. Paludan, Mikkel Vendelbo, Martin K. Thomsen. Immunotherapy by STING activation in a CRISPR induce mouse model of GBM decrease tumor progression by CD8 T-cells and altered vascularity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3512.

STING orchestrates the crosstalk between polyunsaturated fatty acid metabolism and inflammatory responses

Concerted alteration of immune and metabolic homeostasis underlies several inflammation-related pathologies, ranging from metabolic syndrome to infectious diseases. Here, we explored the coordination of nucleic acid-dependent inflammatory responses and metabolic homeostasis. We reveal that the STING (stimulator of interferon genes) protein regulates metabolic homeostasis through inhibition of the fatty acid desaturase 2 (FADS2) rate-limiting enzyme in polyunsaturated fatty acid (PUFA) desaturation. STING ablation and agonist-mediated degradation increased FADS2-associated desaturase activity and led to accumulation of PUFA derivatives that drive thermogenesis. STING agonists directly activated FADS2-dependent desaturation, promoting metabolic alterations. PUFAs in turn inhibited STING, thereby regulating antiviral responses and contributing to resolving STING-associated inflammation. Thus, we have unveiled a negative regulatory feedback loop between STING and FADS2 that fine-tunes inflammatory responses. Our results highlight the role of metabolic alterations in human pathologies associated with aberrant STING activation and STING-targeting therapies.

Viral infection of the ovaries compromises pregnancy and reveals innate immune mechanisms protecting fertility

Viral infections during pregnancy are a considerable cause of adverse outcomes and birth defects, and the underlying mechanisms are poorly understood. Among those, cytomegalovirus (CMV) infection stands out as the most common intrauterine infection in humans, putatively causing early pregnancy loss. We employed murine CMV as a model to study the consequences of viral infection on pregnancy outcome and fertility maintenance. Even though pregnant mice successfully controlled CMV infection, we observed highly selective, strong infection of corpus luteum (CL) cells in their ovaries. High infection densities indicated complete failure of immune control in CL cells, resulting in progesterone insufficiency and pregnancy loss. An abundance of gap junctions, absence of vasculature, strong type I interferon (IFN) responses, and interaction of innate immune cells fully protected the ovarian follicles from viral infection. Our work provides fundamental insights into the effect of CMV infection on pregnancy loss and mechanisms protecting fertility.

Targeting herpes simplex virus with CRISPR-Cas9 cures herpetic stromal keratitis in mice

Herpes simplex virus type 1 (HSV-1) is a leading cause of infectious blindness. Current treatments for HSV-1 do not eliminate the virus from the site of infection or latent reservoirs in the trigeminal ganglia. Here, we target HSV-1 genomes directly using mRNA-carrying lentiviral particles that simultaneously deliver SpCas9 mRNA and viral-gene-targeting guide RNAs (designated HSV-1-erasing lentiviral particles, termed HELP). We show that HELP efficiently blocks HSV-1 replication and the occurrence of herpetic stromal keratitis (HSK) in three different infection models. HELP was capable of eliminating the viral reservoir via retrograde transport from corneas to trigeminal ganglia. Additionally, HELP inhibited viral replication in human-derived corneas without causing off-target effects, as determined by whole-genome sequencing. These results support the potential clinical utility of HELP for treating refractory HSK.

Mutations in the TLR3 signaling pathway and beyond in adult patients with herpes simplex encephalitis

Herpes simplex encephalitis (HSE) in children has previously been linked to defects in type I interferon production downstream of Toll-like receptor (TLR)3. In the present study, we used whole-exome sequencing to investigate the genetic profile of 16 adult patients with a history of HSE. We identified novel mutations in IRF3, TYK2 and MAVS, molecules involved in generating innate antiviral immune responses, which have not previously been associated with HSE. Moreover, data revealed mutations in TLR3, TRIF, TBK1 and STAT1 known to be associated with HSE in children but not previously described in adults. All discovered mutations were heterozygous missense mutations, the majority of which were associated with significantly decreased antiviral responses to HSV-1 infection and/or the TLR3 agonist poly(I:C) in patient peripheral blood mononuclear cells compared with controls. Altogether, this study demonstrates novel mutations in the TLR3 signaling pathway in molecules previously identified in children, suggesting that impaired innate immunity to HSV-1 may also increase susceptibility to HSE in adults. Importantly, the identification of mutations in innate signaling molecules not directly involved in TLR3 signaling suggests the existence of innate immunodeficiencies predisposing to HSE beyond the TLR3 pathway.

Innate DNA sensing is impaired in HIV patients and IFI16 expression correlates with chronic immune activation

The innate immune system has been recognized to play a role in the pathogenesis of HIV infection, both by stimulating protective activities and through a contribution to chronic immune activation, the development of immunodeficiency and progression to AIDS. A role for DNA sensors in HIV recognition has been suggested recently, and the aim of the present study was to describe the influence of HIV infection on expression and function of intracellular DNA sensing. Here we demonstrate impaired expression of interferon-stimulated genes in responses to DNA in peripheral blood monuclear cells from HIV-positive individuals, irrespective of whether patients receive anti-retroviral treatment. Furthermore, we show that expression levels of the DNA sensors interferon-inducible protein 16 (IFI16) and cyclic guanosine monophosphate-adenosine monophosphate synthase were increased in treatment-naive patients, and for IFI16 expression was correlated with high viral load and low CD4 cell count. Finally, our data demonstrate a correlation between IFI16 and CD38 expression, a marker of immune activation, in CD4(+) central and effector memory T cells, which may indicate that IFI16-mediated DNA sensing and signalling contributes to chronic immune activation. Altogether, the present study demonstrates abnormal expression and function of cytosolic DNA sensors in HIV patients, which may have implications for control of opportunistic infections, chronic immune activation and T cell death.

The p59 oligoadenylate synthetase-like protein possesses antiviral activity that requires the C-terminal ubiquitin-like domain

Viral infection of mammalian cells prompts the innate immune system to initiate an antiviral response. The recognition of the virus triggers several antiviral signalling pathways, which among others include the family of 2'-5' oligoadenylate synthetase (OAS) proteins. The p59 protein encoded by the OAS-like (OASL) gene is an atypical member of the OAS family in the sense that it lacks the characteristic 2'-5' oligoadenylate synthetase activity. We decided to investigate the putative antiviral activity of p59 by ectopically expressing this protein in Vero cells and then infecting these cells with virus. We demonstrate that OASL has an antiviral effect against the single-stranded RNA virus picornavirus, encephalomyocarditis virus, but not against a large DNA virus, herpes simplex virus 1. Importantly, this antiviral activity was lost in a truncated version of p59 lacking the ubiquitin-like C-terminal domain of p59. Taken together our results indicate that p59 is indeed an antiviral protein that works through a novel mechanism distinct from other OAS proteins.

Two neisseria meningitidis strains with different ability to stimulate toll-like receptor 4 through the MyD88-independent pathway

Neisseria meningitidis causes acute severe diseases, including sepsis and meningitis, and more benign manifestations such as chronic meningococcemia or colonization of the upper respiratory tract. The inflammatory response, which contributes to the pathogenesis of meningococcal disease, is initiated by pattern recognition receptors, among which Toll-like receptors (TLR)s have been ascribed a particularly important role. We have previously demonstrated that N. meningitidis induce proinflammatory cytokine expression through TLR2 and TLR4. Here we characterize the molecular basis for differential activation of the inflammatory response by two N. meningitidis strains. This difference was due to differential ability to activate signal transduction through TLR4, as HEK293 cells expressing TLR4 produced significantly different levels of interleukin-8 in response to these strains. At the level of signal transduction, the two strains differed substantially in their ability to activate the pathway to nuclear factor kappaB in HEK293-TLR4/MD2 cells at late, but not early, time points. TLR4 activates two signal transduction pathways: one dependent on the adaptor molecule MyD88 and one independent of MyD88, and these pathways induce distinct patterns of gene expression in response to TLR4 ligands. By using macrophages from TLR2-/- mice, we observed that the two strains differed in their ability to activate the TLR4-induced MyD88-independent pathway, but not the MyD88-dependent pathway. This idea was further supported by experiments where either of the two pathways was inhibited and IL-8 secretion was measured. These data therefore provide molecular insight into activation of the inflammatory response by N. meningitidis, which is one of the key events in the pathogenesis of meningococcal disease.

Mannan-binding lectin modulates the response to HSV-2 infection

Viruses have developed numerous strategies to escape recognition by the immune system. However, some viruses such as herpes simplex virus-2 (HSV-2) are recognized by initiators of the complement system, e.g. mannan-binding lectin (MBL). To study the effects of MBL deficiency during viral infection we have chosen a model of generalized HSV-2 infection. We infected MBL-A and MBL-C double knock-out mice (DKO) with HSV-2 via the intraperitoneal (i.p.) route. DKO mice cleared HSV-2 from the liver less efficiently than the comparable wild-type animals. The impairment to effectively neutralize HSV-2 correlated with compromised liver function as measured by increased plasma levels of alanine-amino transferase. No differences in the viral burden were found in other organs such as spleen or brain. Thus, MBL-mediated protection was limited to the effects of preservation of liver homeostasis. Reconstitution with recombinant human MBL before and during the HSV-2 infection dramatically lowered the viral titres in the liver. Taken together, the data show that MBL modulates the response to HSV-2 in mice by affecting neutralization of the virus. To analyse if MBL plays a role in establishment and progression of human HSV-2 infection we analysed MBL levels in the serum samples from asymptomatic (virus-exposed people who have never displayed symptoms of HSV-2 infection) and symptomatic HSV-2 patients (people with recurrent HSV-2 infections). We found that the frequency of the MBL deficiency (<100 ng/ml) was higher in the symptomatic group and significantly different from that in the asymptomatic group (P = 0.0369). This suggests that lack of MBL-mediated complement activation increases susceptibility to viral infection.

Virus-cell interactions regulating induction of tumor necrosis factor alpha production in macrophages infected with herpes simplex virus

Macrophages respond to virus infections by rapidly secreting proinflammatory cytokines, which play an important role in the first line of defense. Tumor necrosis factor alpha (TNF-alpha) is one of the major macrophage-produced cytokines. In this study we have investigated the virus-cell interactions responsible for induction of TNF-alpha expression in herpes simplex virus (HSV)-infected macrophages. Both HSV type 1 (HSV-1) and HSV-2 induced TNF-alpha expression in macrophages activated with gamma interferon (IFN-gamma). This induction was to some extent sensitive to UV treatment of the virus. Virus particles unable to enter the cells displayed reduced capacity to stimulate TNF-alpha expression but retained a significant portion which was abolished by HSV-specific antibodies. Recombinant HSV-1 glycoprotein D was able to trigger TNF-alpha secretion in concert with IFN-gamma. Sugar moieties of HSV glycoproteins have been reported to be involved in induction of IFN-alpha but did not contribute to TNF-alpha expression in macrophages. Moreover, the entry-dependent portion of the TNF-alpha induction was investigated with HSV-1 mutants and found to be independent of the tegument proteins VP16 and UL13 and partly dependent on nuclear translocation of the viral DNA. Finally, we found that macrophages expressing an inactive mutant of the double-stranded RNA (dsRNA)-activated protein kinase (PKR) produced less TNF-alpha in response to infectious HSV infection than the empty-vector control cell line but displayed the same responsiveness to UV-inactivated virus. These results indicate that HSV induces TNF-alpha expression in macrophages through mechanisms involving (i) viral glycoproteins, (ii) early postentry events occurring prior to nuclear translocation of viral DNA, and (iii) viral dsRNA-PKR.

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

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

Expression of TNF-alpha by herpes simplex virus-infected macrophages is regulated by a dual mechanism: transcriptional regulation by NF-kappa B and activating transcription factor 2/Jun and translational regulation through the AU-rich region of the 3' untranslated region

Here we have investigated the regulation of TNF-alpha expression in macrophages during HSV-2 infection. Despite a low basal level of TNF-alpha mRNA present in resting macrophages, no TNF-alpha protein is detectable. HSV-2 infection marginally increases the level of TNF-alpha mRNA and protein in resting macrophages, whereas a strong increase is observed in IFN-gamma-activated cells infected with the virus. By reporter gene assay it was found that HSV infection augments TNF-alpha promoter activity. Moreover, treatment of the cells with actinomycin D, which totally blocked mRNA synthesis, only partially prevented accumulation of TNF-alpha protein, indicating that the infection lifts a block on translation of TNF-alpha mRNA. EMSA analysis showed that specific binding to the kappaB#3 site of the murine TNF-alpha promoter was induced within 1 h after infection and persisted beyond 5 h where TNF-alpha expression is down-modulated. Binding to the cAMP responsive element site was also induced but more transiently with kinetics closely following activation of the TNF-alpha promoter. Inhibitors against either NF-kappaB activation or the activating transcription factor 2 kinase p38 abrogated TNF-alpha expression, showing a requirement for both signals for activation of the promoter. This observation was corroborated by reporter gene assays. As to the translational regulation of TNF-alpha, the AU-rich sequence in the 3' untranslated region of the mRNA was found to be responsible for this control because deletion of this region renders mRNA constitutively translationable. These results show that TNF-alpha production is induced by HSV-2 in macrophages through both transcriptional and translational regulation.

Virus-cell interactions: impact on cytokine production, immune evasion and tumor growth

The outcome of a viral infection ranges from benign to fatal with the clinical pictures being very diverse. This is largely due to the virus-cell interactions that occur in the infected organism. Rapidly after infection, cells initiate a first line of defense against the virus. The cells sense viruses through several mechanisms. Among these the ability to respond to accumulation of double-stranded RNA has been particularly well studied and seems to be of importance. On the other hand, the close co-existence of virus and host has allowed viruses to develop mechanisms to down-modulate the initial reaction or to exploit this proinflammatory response in its own advance. This review describes how virus infections affect cellular signal transduction and the mechanisms through which certain viruses modulate this response to dampen the immune response or prevent cell death.

Interferon (IFN)-gamma and Herpes simplex virus/tumor necrosis factor-alpha synergistically induce nitric oxide synthase 2 in macrophages through cooperative action of nuclear factor-kappa B and IFN regulatory factor-1

The radical nitric oxide (NO) constitutes an important part of the innate immune response to many viruses, and among these notably Herpes simplex virus (HSV). We have previously shown that HSV/tumor necrosis factor-alpha (TNF-alpha) and IFN-gamma synergistically induce NO production in macrophages, and here we have investigated the molecular mechanism underlying this phenomenon. The enhancement of NO production was regulated at the level of NO synthase 2 (NOS2, iNOS) transcription. The ISRE element of the NOS2 promoter, which binds IFN regulatory factor (IRF)-1, was essential both for full responsiveness to IFN-gamma and the synergistic response. The GAS motif, binding signal transducer and activator of transcription 1 (STAT1), did not contribute to the cross-talk with virus/TNF-induced signals, but was necessary for full responsiveness to IFN-gamma. The distal binding site for nuclear factor (NF)-kappa B was important for the cooperative response, while the proximal kappa B site was not involved in the cooperative promoter activation but played a role in full promoter inducibility. By ectopic expression of IRF-1 and NF-kappa B (p65), we found that these factors synergistically induce NO accumulation. Together, our results show that binding of IRF-1 and NF-kappa B to their respective sites in the distal domain of the NOS2 promoter, creates a potent trans-activating complex with the ability to induce NOS2 transcription synergistically in response to simultaneous HSV-2/TNF-alpha and IFN-gamma treatment.

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.

Inhibition of NO production in macrophages by IL-13 is counteracted by Herpes simplex virus infection through tumor necrosis factor-alpha-induced activation of NK-kappa B

Interleukin (IL)-13 is known to antagonize many interferon (IFN)-gamma-activated functions in macrophages and among these, nitric oxide (NO) production. We have previously shown that this function of IL-13 is reduced in Herpes simplex virus type 2 (HSV-2)-infected macrophages. In the present study we show that IL-13 and IFN-gamma are indeed produced during infection of BALB/c mice with HSV-2. The lack of inhibitory function of IL-13 in infected macrophages, which was not overcome even at very high concentrations of IL-13, was not due to impaired IL-13 signalling, since virus infection did not affect IL-13-mediated activation of STAT6 (signal transducer and activator of transcription 6). Neutralizing tumour necrosis factor (TNF)-alpha antibodies, however, largely restored the effect of IL-13 on NO production in virus-infected macrophages. The same was observed after treatment of the cells with inhibitors of nuclear factor (NF)-kappa B activation, known to be involved in enhancement of IFN-gamma-induced NO production. Even though IL-13 reduced TNF-alpha secretion by 50%, this did not impair NF-kappa B activation in IFN-gamma-treated cells infected with HSV-2. The results indicate that TNF-alpha, secreted by virus-infected macrophages, activates NF-kappa B which impairs the IL-13-mediated inhibition of inducible NO synthase (iNOS) expression. This could imply that a sustained NO production would be focused to sites of active virus replication.

Herpes simplex virus type 2 infection of macrophages impairs IL-4-mediated inhibition of NO production through TNF-alpha-induced activation of NF-kappaB

Nitric oxide (NO) production in macrophages by the interferon (IFN)-gamma-inducible NO synthase has been shown to play a role in clearance of viral infections. We have previously shown that IFN-gamma-induced NO production is augmented by herpes simplex virus type 2 (HSV-2) infection through autocrine tumour necrosis factor (TNF)-alpha secretion and is inhibited by interleukin (IL)-4. Here we investigated the effect of HSV-2 infection on the inhibitory function of IL-4. Virus infection of mouse J774A.1 macrophages strongly reduced the ability of IL-4 to inhibit IFN-gamma-induced NO production, even at very high IL-4 concentrations. The effect of HSV-2 infection did not involve the IL-4 signal transduction pathway through STAT6. IL-4 reduced virus-induced TNF-alpha secretion and nuclear factor (NF)-kappaB activation significantly, but less in cells concomitantly treated with IFN-gamma. Furthermore, neutralisation of residual TNF-alpha activity or inhibition of NF-kappaB activation largely restored the inhibitory effect of IL-4. The data show that inhibition of IFN-gamma-induced NO production by IL-4 is impaired by HSV-2 infection due to autocrine TNF-alpha-mediated NF-kappaB activation. We suggest that the described phenomenon might be beneficial for the host by limiting high and sustained NO production to infectious foci.

Synergistic action of pro-inflammatory agents: cellular and molecular aspects

Generation of an inflammatory response is a complex process involving multiple factors acting in parallel and in concert. Viruses, parasites, and bacteria, particularly lipopolysaccharide (LPS), a component of the cell wall of gram-negative bacteria, act cooperatively with the cytokine interferon (IFN)-gamma to induce many of the genes involved in inflammation. In addition, these components synergistically induce secretion of tumor necrosis factor alpha (TNF-alpha), which also synergizes strongly with IFN-gamma. The molecular mechanisms underlying the synergistic gene induction discussed in this review involve cooperative activation of transcription factors. IFN-gamma-activated signal transducer and activator of transcription 1 and interferon regulatory factor-1 function synergistically with nuclear factor kappaB activated by LPS and TNF-alpha. In addition, cross-talk between the signal transduction pathways upstream of the activation of the transcription factors contributes to generation of the synergistic action. Cooperative activity of proinflammatory agents profoundly influences the immune response to infections and the efficiency of cellular clearance mechanisms.

Interleukin-4-mediated inhibition of nitric oxide production in interferon-gamma-treated and virus-infected macrophages

Upon interferon-gamma (IFN-gamma) stimulation, murine macrophages (Mphi) produce nitric oxide (NO) through expression of inducible nitric oxide synthase (iNOS). Interleukin (IL)-4 treatment, even delayed 12 h relative to IFN-gamma, antagonized this induction, whereas infection with herpes simplex virus type 2 (HSV-2) or treatment with tumour necrosis factor-alpha exerted a synergistic effect, which partly compensated for the antagonistic effect of IL-4. Neither IL-4 nor HSV-2 affected the IFN-gamma-activated Jak-STAT (Janus kinase-signal transducer and activator of transcription) pathway or altered the levels of IFN-gamma-induced interferon regulatory factor (IRF)-1 expression, which is STAT1-dependent and known to play a central role in IFN-gamma-mediated gene induction. The effect of IL-4 was completely dependent on de novo protein synthesis, indicating that a direct activation of latent inhibitors is not sufficient to explain the inhibitory effect of IL-4. Furthermore, IL-4 substantially augmented the IFN-gamma-induced expression of IRF-2, which is known to compete with IRF-1 for the DNA recognition site, ISRE (interferon-stimulated response element). Our findings could indicate that IL-4 suppresses IFN-gamma-stimulated iNOS transcription by elevating the level of IRF-2 which, through competition, prevents IRF-1 from binding to ISRE in the iNOS promoter. The virus-induced effects on iNOS and NO levels in IFN-gamma-stimulated Mphi do not seem to involve the Jak/STAT pathway or a differential expression of IRF-1 and IRF-2.

NF-kappaB activation is responsible for the synergistic effect of herpes simplex virus type 2 infection on interferon-gamma-induced nitric oxide production in macrophages

Nitric oxide (NO), produced in interferon (IFN)-gamma-activated murine macrophages by the enzyme inducible nitric oxide synthase (iNOS), has been found to have antiviral properties. We have previously shown that herpes simplex virus type 2 (HSV-2) infection of macrophages synergistically enhances IFN-gamma-induced NO production, and we now extend these findings by providing evidence that virus-induced tumour necrosis factor (TNF)-alpha mediates activation of the transcription factor nuclear factor (NF)-kappaB, which in turn is responsible for the synergistic effect. HSV-2 infection and IFN-gamma stimulation of macrophages synergistically induced TNF-alpha secretion and nuclear translocation of NF-kappaB, which bound to a sequence corresponding to a kappaB site in the iNOS promoter. The effect of HSV-2 on NF-kappaB and NO production was eliminated when cells were treated with antibodies to TNF-alpha, and direct inhibition of NF-kappaB activation with pyrrolidinedithiocarbamate (PDTC) also blocked the effect of HSV-2 infection on NO production. The effect of the NF-kappaB activation inhibitor was not mediated through inhibition of the production of interferon regulatory factor (IRF)-1 or of TNF-alpha itself, and a possible alternative mechanism of activation of NF-kappaB through virus-induced activation of the kinase PKR was also ruled out. Thus, our data indicate that NF-kappaB activation, through virus-induced autocrine TNF-alpha secretion, is responsible for the synergistic effect of HSV-2 infection on IFN-gamma-induced NO production, and that such activation might constitute a mechanism by which high-output NO production is targeted to infectious foci.

Interleukin-4 and interferon-gamma: the quintessence of a mutual antagonistic relationship

The two cytokines interleukin (IL)-4 and interferon (IFN)-gamma play major roles in the generation and regulation of immune responses. Central in this respect is their mutually antagonistic functions. First, IL-4 promotes T helper cell type 2 (Th2) differentiation and stability and inhibits Th1-cell differentiation. A direct role of IFN-gamma in Th1-cell differentiation is debatable, whereas inhibition of Th2-cell differentiation and roles in Th1-cell stabilization are well established functions of IFN-gamma. Secondly, IL-4 and IFN-gamma also affect antibody class switch and expression of Fc receptors differentially, which strongly affect the effector mechanisms following antibody production. Thirdly, macrophage activities induced or enhanced by IFN-gamma, such as expression of certain cytokines, surface molecules and enzymes, are antagonized by IL-4. Together, these functions of IL-4 and IFN-gamma place the two cytokines at cardinal positions in the regulation of immune reactions. In this review the known molecular mechanisms underlying the observed functions of IL-4 and IFN-gamma are presented and discussed.

Effect of IL-4 and IL-13 on IFN-gamma-induced production of nitric oxide in mouse macrophages infected with herpes simplex virus type 2

Interleukin (IL)-4 and IL-13 share a wide range of activities. Prominent among these is the ability to antagonize many interferon (IFN)-gamma-induced activities. Here we demonstrate that IL-4 and IL-13 totally abrogate IFN-gamma-induced nitric oxide (NO) production and inducible nitric oxide synthase (iNOS) mRNA and protein synthesis in a murine macrophage cell line. IFN-gamma-treated cells infected with herpes simplex virus type 2 (HSV-2) or costimulated with tumor necrosis factor (TNF)-alpha showed an enhanced reactivity, which was only partially reduced by IL-4/13. The results indicate that IL-4 and IL-13 function by intervening with a step prior to iNOS transcription by antagonizing IFN-gamma-induced signal(s) without counteracting synergistic virus- or TNF-alpha-induced signals. The beneficial effect of a sustained NO production in foci of virus infection is suggested.