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

Lactic acid bacteria efficiently protect human and animal intestinal epithelial and immune cells from enteric virus infection

This study aimed to examine the potential antiviral activity of lactic acid bacteria (LAB) using animal and human intestinal and macrophage cell line models of non tumor origin. To this end, LAB strains selected on the basis of previous in vitro trials were co-incubated with cell line monolayers, which were subsequently challenged with rotavirus (RV) and transmissible gastroenteritis virus (TGEV). In order to elucidate the possible mechanism responsible for the antiviral activity, the induction of reactive oxygen species (ROS) release as well as the attachment ability of LAB on the cell lines was investigated. Various strains were found to exhibit moderate to complete monolayer protection against viral RV or TGEV disruption. Highest protection effects were recorded with the known probiotics Lactobacillus rhamnosus GG and Lactobacillus casei Shirota against both RV and TGEV, while notable antiviral activity was also attributed to Enterococcus faecium PCK38, Lactobacillus fermentum ACA-DC179, Lactobacillus pentosus PCA227 and Lactobacillus plantarum PCA236 and PCS22, depending on the cell line and virus combination used. A variable increase (of up to 50%) on the release of NO(-) and H(2)O(2) (ROS) was obtained when LAB strains were co-incubated with the cell lines, but the results were found to be LAB strain and cell line specific, apart from a small number of strains which were able to induce strong ROS release in more than one cell line. In contrast, the ability of the examined LAB strains to attach to the cell line monolayers was LAB strain but not cell line specific. Highest attachment ability was observed with L. plantarum ACA-DC 146, L. paracasei subsp. tolerans ACA-DC 4037 and E. faecium PCD71. Clear indications on the nature of the antiviral effect were evident only in the case of the L. casei Shirota against TGEV and with L. plantarum PCA236 against both RV and TGEV. In the rest of the cases, each interaction was LAB-cell line-virus specific, barring general conclusions. However, it is probable that more than one mechanism is involved in the antiviral effect described here. Further investigations are required to elucidate the underlying mode of action and to develop a cell line model as a system for selection of probiotic strains suited for farm animal applications.

Inhibition of TNFα-induced iNOS expression in HSV-tk transduced 9L glioblastoma cell lines by Marasmius oreades substances through NF-κB- and MAPK-dependent mechanisms

Nitric oxide (NO) is a gaseous, radical molecule that plays a role in various physiological processes. Previously, we reported that transduction of murine colon cancer cells (MC38) with herpes simplex virus thymidine kinase (HSV-tk) gene resulted in a significant over-expression of cyclooxygenase-2 (COX-2) and activation of NF-kB pathway. In this study we show that TNFα, but not LPS, was significantly able to stimulate the production of NO in HSV-tk transduced 9L glioblastoma cell lines, mediated by the up-regulation of iNOS transcript and iNOS protein. The TNFα-induced up-regulation of iNOS expression was mediated by MAPK and NF-κB signaling pathways as revealed by using selective pharmaceutical inhibitors. A culture liquid extract of the edible and medicinal mushroom Marasmius oreades that was previously shown to inhibit iNOS expression in MCF-7 was utilized to prepare fractions and evaluate their ability to affect TNFα-induced iNOS expression in HSV tk transduced 9L cell lines. While most of the tested fractions were shown to inhibit TNFα-induced iNOS expression, they targeted different signaling pathways in a selective fashion. Here, we report that fraction SiSiF1 interfered with IKBα phosphorylation and consequently interfered with NF-κB activation pathway. SiSiF1 showed minimal interference with the phosphorylation of p38 and JNK proteins. In contrast, fraction SiSiF3 selectively inhibited the phosphorylation of p38 and fractions SiSiF4 and SiSiF5 selectively inhibited the phosphorylation of JNK with no observed effect against IKBα and p38 phosphorylation. Our data illustrate the complexity of iNOS regulation in HSV tk transduced 9L cell lines and also the richness of natural products with bioactive substances that may act synergistically through different signaling pathways to affect iNOS gene expression.

Molecular mechanisms of IFN-gamma to up-regulate MHC class I antigen processing and presentation

IFN-gamma up-regulates MHC class I expression and antigen processing and presentation on cells, since IFN-gamma can induce multiple gene expressions that are related to MHC class I antigen processing and presentation. MHC class I antigen presentation-associated gene expression is initiated by IRF-1. IRF-1 expression is initiated by phosphorylated STAT1. IFN-gamma binds to IFN receptors, and then activates JAK1/JAK2/STAT1 signal transduction via phosphorylation of JAK and STAT1 in cells. IFN-gamma up-regulates MHC class I antigen presentation via activation of JAK/STAT1 signal transduction pathway. Mechanisms of IFN-gamma to enhance MHC class I antigen processing and presentation were summarized in this literature review.

Herpes simplex virus type 2-induced mortality following genital infection is blocked by anti-tumor necrosis factor alpha antibody in CXCL10-deficient mice

The role of tumor necrosis factor alpha (TNF-alpha) was evaluated for CXCL10-deficient (CXCL10(-/-)) mice which succumbed to genital herpes simplex virus type 2 (HSV-2) infection and possessed elevated levels of virus and TNF-alpha but not other cytokines in the central nervous system (CNS) and vaginal tissue within the first 7 days following virus exposure. Anti-TNF-alpha but not control antibody treatment offsets the elevated mortality rate of CXCL10(-/-) mice, despite increased CNS viral titers. In addition, TNF-alpha neutralization suppressed recruitment of leukocyte subpopulations into the CNS, which is associated with reduced CCL2 and CXCL9 expression. Collectively, the results implicate TNF-alpha as the principal mediator of mortality in response to genital HSV-2 infection.

Intracellular immune dysfunction in myalgic encephalomyelitis/chronic fatigue syndrome: state of the art and therapeutic implications

BACKGROUND

Evidence in support of intracellular immune dysfunctions in people with myalgic encephalomyelitis (ME)/chronic fatigue syndrome (CFS) is accumulating, but few studies have addressed intracellular immunity as a potential therapeutic target.

OBJECTIVE

To provide an overview of our present understanding of intracellular immunity in ME/CFS, to relate the intracellular immune dysfunctions to other aspects of the illness like decreased natural killer cell function, the presence of infections and poor exercise performance, and to point to potential therapeutic targets.

METHODS

An in-depth review of the scientific literature of intracellular immunity in people with ME/CFS was performed.

RESULTS/CONCLUSION

From the scientific literature it is concluded that proteolytic cleavage of the native RNase L enzyme is characteristic of the dysregulation of intracellular immunity in people with ME/CFS, but the origin of the dysregulation is speculative. There is increasing evidence for immune cell apoptosis and upregulation of various aspects of the 2'-5' oligoadenylate (2-5A) synthetase/RNase L pathway in ME/CFS. This review provides the theoretical rationale for conducting studies examining the effectiveness of direct or indirect drug targeting of the 2-5A synthetase/RNase L pathway in ME/CFS patients.

Inhibition of the NF-kappaB pathway by varicella-zoster virus in vitro and in human epidermal cells in vivo

Varicella-zoster virus (VZV) is an alphaherpesvirus that causes varicella and herpes zoster. Using human cellular DNA microarrays, we found that many nuclear factor kappa B (NF-kappaB)-responsive genes were down-regulated in VZV-infected fibroblasts, suggesting that VZV infection inhibited the NF-kappaB pathway. The activation of this pathway causes a cellular antiviral response, including the production of alpha/beta interferon, cytokines, and other proteins that restrict viral infection. In these experiments, we demonstrated that VZV interferes with NF-kappaB activation in cultured fibroblasts and in differentiated epidermal cells in skin xenografts of SCIDhu mice infected in vivo. VZV infection of fibroblasts caused a transient nuclear translocation of p50 and p65, the canonical NF-kappaB family members. In a process that was dependent upon the presence of infectious VZV, these proteins rapidly became sequestered in the cytoplasm of VZV-infected cells. Exclusion of NF-kappaB proteins from nuclei was associated with the continued presence of IkappaBalpha, which binds p50 and p65 and prevents their nuclear accumulation. IkappaBalpha levels did not diminish even though the protein became phosphorylated and ubiquitinated, as determined based on detection of the characteristic high-molecular-weight form of the protein, and the 26S proteasome remained functional in VZV-infected cells. VZV infection also inhibited the characteristic degradation of IkappaBalpha that is induced by exposure of fibroblasts to tumor necrosis factor alpha. As expected, herpes simplex virus 1 caused the persistent nuclear translocation of NF-kappaB proteins, which has been shown to facilitate its replication, whereas VZV infection progressed without persistent NF-kappaB nuclear localization. We suggest that VZV has evolved a mechanism to limit host cell antiviral defenses by sequestering NF-kappaB proteins in the cytoplasm, a strategy that appears to be unique among the herpesviruses.

Interactions of macrophages with probiotic bacteria lead to increased antiviral response against vesicular stomatitis virus

Macrophages are an important cellular component of the innate immune system and are normally rapidly recruited and/or activated at the site of virus infection. They can participate in the antiviral response by killing infected cells, by producing antiviral cytokines such as nitric oxide and by producing chemokines and immunoregulatory cytokines that enable the adaptive immune response to recognize infected cells and perform antiviral effector functions. Probiotics, as a part of the normal gut intestinal flora, are important in supporting a functional yet balanced immune system. Improving our understanding of their role in the activation of macrophages and their stimulation of proinflammatory cytokine production in early viral infection was the main goal of this study. Our in vitro model study showed that probiotic bacteria, either from the species Lactobacillus or Bifidobacteria have the ability to decrease viral infection by establishing the antiviral state in macrophages, by production of NO and inflammatory cytokines such as interleukin 6 and interferon-gamma. These effects correlated with the mitochondrial activity of infected macrophages, therefore, the measurements of mitochondrial dehydrogenases activity could be implied as the first indicator of potential inhibitory effects of the probiotics on virus replication. The interactions between probiotic bacteria, macrophages and vesicular stomatitis virus (VSV), markedly depended on the bacterial strain studied.

Requirement of tumor necrosis factor alpha and nuclear factor-kappaB in the induction by IFN-gamma of inducible nitric oxide synthase in macrophages

IFN-gamma induces NO production, inducible NO synthase (iNOS) protein, and promoter expression in mouse macrophage cells. Mutation of IFN regulatory factor 1 responsive element, gamma-activated site, as well as NF-kappaB elements in the murine iNOS promoter strongly reduced IFN-gamma-induced iNOS transcriptional activity. The role of NF-kappaB activation in iNOS induction by IFN-gamma was corroborated by overexpression of the NF-kappaB inhibitory protein IkappaBalpha, which inhibited iNOS promoter activity induced by IFN-gamma. In addition, IFN-gamma treatment induced p65 binding to the iNOS promoter by chromatin immunoprecipitation assay and NF-kappaB binding to DNA by EMSA, although with a delayed kinetics, suggesting an indirect autocrine role for another cytokine produced in response to IFN-gamma. It is interesting that we found that IFN-gamma induced TNF-alpha secretion, and the induction of iNOS expression by IFN-gamma was abolished in primary peritoneal macrophages from TNF-alpha-deficient (TNF-alpha-/-) mice or in RAW 264.7 cells treated with anti-TNF-alpha neutralizing antibodies. Moreover, exogenous addition of recombinant mouse TNF-alpha restored iNOS expression induced by IFN-gamma in TNF-alpha-/- mice. It is intriguing that NF-kappaB binding to DNA in response to IFN-gamma treatment was absent in TNF-alpha-/- mice. Taken together, our data suggest that the TNF-alpha produced in response to IFN-gamma is required for iNOS induction by activating NF-kappaB transcription factor.

The synergistic effect of IFN-alpha and IFN-gamma against HSV-2 replication in Vero cells is not interfered by the plant antiviral 1-cinnamoyl-3, 11-dihydroxymeliacarpin

Background

Recent studies have shown that gamma interferon (IFN-γ) synergizes with IFN-α/β to inhibit herpes simplex virus type 1 (HSV-1) replication in vitro. Since IFN response represents an early host defense event against viral infection and the fact that treatment with meliacine, a plant antiviral, ameliorate the severity of the herpetic infection in female mice infected intravaginally with HSV-2, we wanted to investigate whether the administration of meliacine to HSV-2 infected mice could altered the homoestasis of IFNs host response. For this purpose we studied the effect of the compound 1-cinnamoyl-3,11-dihydroxymeliacarpin (CDM), which is the responsible for meliacine antiviral action, on the HSV-2 inhibition exerted by IFN α, IFN-γ or their combination.

Results

We have found that like HSV-1, IFN-γ synergizes with IFN-α to inhibit HSV-2 replication in Vero cells. While treatment with IFN-α or IFN-γ alone has weak antiviral action, HSV-2 plaque formation, viral replication and the onset of viral CPE in Vero cells are synergistically inhibited by interferon combination. In addition, CDM treatment contributes to protect cells from virus cytopathic effect and causes a strong inhibition of HSV-2 titer. Moreover, the presence of CDM for 2 h before IFN induction, during the 16 h induction period, only for 24 h after infection or during the complete IFN treatment period, reduces virus yields in an additive way without affecting IFN antiviral action.

Conclusion

The results reported here indicated that the presence of CDM did not alter the antiviral activity of IFN-α, IFN-γ or the synergism exerted by their combination. As a result we can envision that the administration of CDM in vivo could not affect the biological activity of IFNs, which are so important mediators of the innate resistance to HSV-2 infection.

Chronic fatigue syndrome: exercise performance related to immune dysfunction

PURPOSE

To date, the exact cause of abnormal exercise response in chronic fatigue syndrome (CFS) remains to be revealed, but evidence addressing intracellular immune deregulation in CFS is growing. Therefore, the aim of this cross-sectional study was to examine the interactions between several intracellular immune variables and exercise performance in CFS patients.

METHODS

After venous blood sampling, subjects (16 CFS patients) performed a maximal exercise stress test on a bicycle ergometer with continuous monitoring of cardiorespiratory variables. The following immune variables were assessed: the ratio of 37 kDa Ribonuclease (RNase) L to the 83 kDa native RNase L (using a radiolabeled ligand/receptor assay), RNase L enzymatic activity (enzymatic assay), protein kinase R activity assay (comparison Western blot), elastase activity (enzymatic-colorimetric assay), the percent of monocytes, and nitric oxide determination (for monocytes and lymphocytes; flow cytometry, live cell assay).

RESULTS

Forward stepwise multiple regression analysis revealed 1) that elastase activity was the only factor related to the reduction in oxygen uptake at a respiratory exchange ratio (RER) of 1.0 (regression model: R = 0.53, F (1,14) = 15.5, P < 0.002; elastase activity P < 0.002); 2) that the protein kinase R activity was the principle factor related to the reduction in workload at RER = 1.0; and 3) that elastase activity was the principle factor related to the reduction in percent of target heart rate achieved.

CONCLUSION

These data provide evidence for an association between intracellular immune deregulation and exercise performance in patients with CFS. To establish a causal relationship, further study of these interactions using a prospective longitudinal design is required.

Macrophages and cytokines in the early defence against herpes simplex virus

Herpes simplex virus (HSV) type 1 and 2 are old viruses, with a history of evolution shared with humans. Thus, it is generally well-adapted viruses, infecting many of us without doing much harm, and with the capacity to hide in our neurons for life. In rare situations, however, the primary infection becomes generalized or involves the brain. Normally, the primary HSV infection is asymptomatic, and a crucial element in the early restriction of virus replication and thus avoidance of symptoms from the infection is the concerted action of different arms of the innate immune response. An early and light struggle inhibiting some HSV replication will spare the host from the real war against huge amounts of virus later in infection. As far as such a war will jeopardize the life of the host, it will be in both interests, including the virus, to settle the conflict amicably. Some important weapons of the unspecific defence and the early strikes and beginning battle during the first days of a HSV infection are discussed in this review. Generally, macrophages are orchestrating a multitude of anti-herpetic actions during the first hours of the attack. In a first wave of responses, cytokines, primarily type I interferons (IFN) and tumour necrosis factor are produced and exert a direct antiviral effect and activate the macrophages themselves. In the next wave, interleukin (IL)-12 together with the above and other cytokines induce production of IFN-gamma in mainly NK cells. Many positive feed-back mechanisms and synergistic interactions intensify these systems and give rise to heavy antiviral weapons such as reactive oxygen species and nitric oxide. This results in the generation of an alliance against the viral enemy. However, these heavy weapons have to be controlled to avoid too much harm to the host. By IL-4 and others, these reactions are hampered, but they are still allowed in foci of HSV replication, thus focusing the activity to only relevant sites. So, no hero does it alone. Rather, an alliance of cytokines, macrophages and other cells seems to play a central role. Implications of this for future treatment modalities are shortly considered.

Nitric Oxide-Induced Nitrative Stress Involved in Microbial Pathogenesis

The pathogenic mechanism of infections is a complicated but important scientific theme that is now attracting great attention because of its association with host-derived as well as microbial factors. Recent advances in free radical research revealed that reactive oxygen and nitrogen oxide species such as superoxide (O(2)(-)) and nitric oxide (NO) play a leading role in the pathogenesis of infections caused by viral pathogens including influenza virus and other RNA viruses. Although NO and O(2)(-) have antimicrobial activity against bacteria, fungi, and parasites, in some viral infections they have an opposite effect. This exacerbation caused by NO and O(2)(-) is mediated by reactive nitrogen oxides, for example, peroxynitrite (ONOO(-)), generated by reaction of NO with O(2)(-). These nitrogen oxides have strong oxidation and nitration potential and can modify biological molecules, thereby creating oxidative and nitrative stress that contributes to pathogenic processes during viral infection. Nitrative stress-mediated 8-nitroguanosine formation during influenza or Sendai virus infection has been the focus of enormous interest because it involves unique biochemical and pharmacological properties such as redox activity and mutagenic potential. In this review, we discuss the nature and impact of nitrative stress in viral infection, with emphasis on nitrative stress-mediated viral pathogenesis, which we have recently been investigating.

Chronic fatigue syndrome: intracellular immune deregulations as a possible etiology for abnormal exercise response

The exacerbation of symptoms after exercise differentiates Chronic fatigue syndrome (CFS) from several other fatigue-associated disorders. Research data point to an abnormal response to exercise in patients with CFS compared to healthy sedentary controls, and to an increasing amount of evidence pointing to severe intracellular immune deregulations in CFS patients. This manuscript explores the hypothetical interactions between these two separately reported observations. First, it is explained that the deregulation of the 2-5A synthetase/RNase L pathway may be related to a channelopathy, capable of initiating both intracellular hypomagnesaemia in skeletal muscles and transient hypoglycemia. This might explain muscle weakness and the reduction of maximal oxygen uptake, as typically seen in CFS patients. Second, the activation of the protein kinase R enzyme, a characteristic feature in atleast subsets of CFS patients, might account for the observed excessive nitric oxide (NO) production in patients with CFS. Elevated NO is known to induce vasidilation, which may limit CFS patients to increase blood flow during exercise, and may even cause and enhanced postexercise hypotension. Finally, it is explored how several types of infections, frequently identified in CFS patients, fit into these hypothetical pathophysiological interactions.

Monosodium urate crystals synergize with IFN-gamma to generate macrophage nitric oxide: involvement of extracellular signal-regulated kinase 1/2 and NF-kappa B

Elevated NO production has been detected in patients suffering from various arthropathies; however, its role and regulation during gouty arthritis remain largely unexplored. Monosodium urate (MSU) crystals, the causative agent of gout, have been shown to induce NO generation in vivo and inducible NO synthase (iNOS) expression in human monocytes. The present study was designed to evaluate the ability of MSU crystals to modulate macrophage (M phi) iNOS expression and NO synthesis and to investigate the molecular mechanisms underlying these cellular responses. We found that MSU crystals did not induce NO production in murine J774 M phi. However, a synergistic effect on the level of iNOS expression and NO generation was observed in cells exposed to MSU crystals in combination with IFN-gamma. Characterization of the second messengers involved revealed the requirement of IFN-gamma-mediated Janus kinase 2/STAT1 alpha activation even though MSU crystals did not modulate this signaling cascade by themselves. MSU crystals exerted their up-regulating effect by increasing extracellular signal-regulated kinase (ERK) 1/2 phosphorylation and NF-kappa B nuclear translocation in response to IFN-gamma. The use of specific inhibitors against either NF-kappa B or the ERK1/2 pathway significantly reduced MSU + IFN-gamma-inducible NF-kappa B activity, iNOS expression, and NO production. Altogether, these data indicate that MSU crystals exert a potent synergistic effect on the IFN-gamma-inducible M phi NO generation via ERK1/2- and NF-kappa B-dependent pathways. Understanding the molecular mechanisms through which MSU crystals amplify M phi responses to proinflammatory cytokines such as IFN-gamma will contribute to better define their role in NO regulation during gout, in particular, and inflammation, in general.

Active and inactive influenza virus induction of tumor necrosis factor-alpha and nitric oxide in J774.1 murine macrophages: modulation by interferon-gamma and failure to induce apoptosis

Infection of J774.1 murine macrophages by influenza A virus (IAV) induces two major responses, production of host defense molecules and death by apoptosis. We investigated whether induction of two cytotoxic compounds, tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO), directly caused IAV-induced apoptosis, and whether induction could be modulated by interferon-gamma (IFN-gamma) or the replication competence of the virus. Live IAV potently induced production of both TNF-alpha and NO, but UV inactivated virus was a poor inducer of both molecules. When cells were pre-treated with IFN-gamma, inactive IAV became as effective an inducer of NO, but not TNF-alpha, as live IAV. Amantadine, which antagonizes viral entry and replication, partly inhibited TNF-alpha and NO production in unprimed cells, but did not inhibit NO in IFN-gamma primed cells. IAV-induced cytotoxicity was not due to the induction of TNF-alpha or NO. Cells were insensitive to either TNF-alpha-containing supernatants or to recombinant TNF-alpha. Anti-TNF-alpha antibody did not protect cells from IAV-induced cell death, and anti-oxidants that inhibited TNF-alpha production also failed to increase cell survival. Inhibitors of NO production did not protect from IAV-induced cell death, either alone or in combination with superoxide dismutase (SOD). We conclude that, even though IAV was a potent inducer of TNF-alpha and NO in macrophages, IAV-induced apoptosis was not mediated directly by them. Importantly, viral replication was not required for the induction of TNF-alpha or NO, and the action of inactive IAV could be potentiated by IFN-gamma.

Hemozoin increases IFN-gamma-inducible macrophage nitric oxide generation through extracellular signal-regulated kinase- and NF-kappa B-dependent pathways

NO overproduction has been suggested to contribute to the immunopathology related to malaria infection. Even though a role for some parasite molecules (e.g., GPI) in NO induction has been proposed, the direct contribution of hemozoin (HZ), another parasite metabolite, remains to be established. Therefore, we were interested to determine whether Plasmodium falciparum (Pf) HZ and synthetic HZ, beta-hematin, alone or in combination with IFN-gamma, were able to induce macrophage (Mphi) NO synthesis. We observed that neither Pf HZ nor synthetic HZ led to NO generation in B10R murine Mphi; however, they significantly increased IFN-gamma-mediated inducible NO synthase (iNOS) mRNA and protein expression, and NO production. Next, by investigating the transductional mechanisms involved in this cellular regulation, we established that HZ induces extracellular signal-regulated kinase (ERK)1/2 mitogen-activated protein kinase phosphorylation as well as NF-kappaB binding to the iNOS promoter, and enhances the IFN-gamma-dependent activation of both second messengers. Of interest, cell pretreatment with specific inhibitors against either NF-kappaB or the ERK1/2 pathway blocked the HZ + IFN-gamma-inducible NF-kappaB activity and significantly reduced the HZ-dependent increase on IFN-gamma-mediated iNOS and NO induction. Even though selective inhibition of the Janus kinase 2/STAT1alpha pathway suppressed NO synthesis in response to HZ + IFN-gamma, HZ alone did not activate this signaling pathway and did not have an up-regulating effect on the IFN-gamma-induced Janus kinase 2/STAT1alpha phosphorylation and STAT1alpha binding to the iNOS promoter. In conclusion, our results suggest that HZ exerts a potent synergistic effect on the IFN-gamma-inducible NO generation in Mphi via ERK- and NF-kappaB-dependent pathways.

Interferon (IFN)-alpha/beta, interleukin (IL)-12 and IL-18 coordinately induce production of IFN-gamma during infection with herpes simplex virus type 2

Interferons (IFNs) are important mediators of antiviral activity. In this study we have investigated how production of IFN-gamma is induced during herpes simplex virus type 2 (HSV-2) infection in murine peritoneal cells (PCs). We found that HSV-2 infection of thioglycolate-activated PCs from BALB/c mice rapidly led to expression of type 1 IFNs (IFN-alpha/beta) and interleukin (IL)-12, which was followed by production of IFN-gamma. IL-12 alone induced the most expression of IFN-gamma, which was augmented by cotreatment with IFN-alpha or IL-18, or combinations of IFN-alpha and IL-18. Moreover, neutralization of any of these cytokines in vitro strongly reduced the production of IFN-gamma, and neutralization of all three cytokines totally prevented HSV-2-induced IFN-gamma expression. Our data suggest that IFN-gamma production is induced during HSV-2 infection through the coordinated action of IFN-alpha/beta, IL-12 and IL-18.

Induction of RANTES/CCL5 by herpes simplex virus is regulated by nuclear factor kappa B and interferon regulatory factor 3

Chemokines regulate migration of leukocytes to sites of infection. In this work, we have shown that the chemokine RANTES/CCL5 is produced after herpes simplex virus (HSV) infection of macrophages and fibroblasts and provide data on the underlying molecular mechanism. Reporter gene assays showed HSV-induced RANTES production to be regulated at the transcriptional level. Expression of RANTES was blocked by N-tosyl-L-phenylalanine, an inhibitor of the nuclear factor kappa B (NF-kappa B) pathway and also in cell lines stably expressing a dominant-negative mutant of I kappa B kinase beta. Cell lines stably expressing a dominant-negative mutant of interferon regulatory factor 3 (IRF-3) also produced dramatically decreased levels of RANTES after infection compared with the control cell line. In contrast, overexpression of dominant-negative p38 and also treatment with SB203580, an inhibitor of p38, did not significantly affect expression of RANTES. Taken together, these data suggest that HSV induces transcriptional activation of the RANTES gene through the transcription factors NF-kappa B and IRF-3.

Role of IFN-gamma and tumor necrosis factor-alpha in herpes simplex virus type 1 infection

One of the characteristics of herpes simplex virus type 1 (HSV-1) is that recurrent diseases often develop from latent infection established after acute infection. Cytokines have been proposed to play an important role in each stage of HSV-1 infection, but the exact role of cytokines remains unclear. In the present study, we investigated the role of interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) in acute infection and reactivation using IFN-gamma gene knockout (IFN-gamma(-/-)) mice and TNF-alpha gene knockout (TNF-alpha(-/-)) mice. We first examined the survival rate after corneal infection with HSV-1. The survival rates of wild-type C57BL/6 (B6) mice, IFN-gamma(-/-) mice, and TNF-alpha(-/-) mice were 97% (73 of 75), 57% (24 of 42), and 83% (60 of 72), respectively. These results suggest that TNF-alpha and IFN-gamma play a protective role in acute infection with HSV-1. We also examined the rate of reactivation induced by ultraviolet (UV) light in latently infected mice over 60 days postinoculation. The reactivation was confirmed by detecting viral DNA extracted from eyeballs by the polymerase chain reaction (PCR) method at day 2 after the UV light stimulation. The rates of reactivation in IFN-gamma(-/-) mice and TNF-alpha(-/-) mice were significantly higher than that in B6 mice; 16% (4 of 25) showed reactivation in B6 mice, 47% (9 of 19) in IFN-gamma(-/-) mice, and 48% (10 of 21) in TNF-alpha(-/-) mice. These results suggest that IFN-gamma and TNF-alpha play an important role in acute infection and reactivation from latency.

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.

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.

Protective T-cell-based immunity induced in neonatal mice by a single replicative cycle of herpes simplex virus

Newborns are very susceptible to infections because their immune systems are not fully developed and react to antigen exposure preferentially with unresponsiveness. UV-inactivated herpes simplex virus type 1 (HSV-1) represents such an antigen and does not induce an immune response in neonates. In contrast, protective T cells were primed in newborn mice by a single replicative cycle of DISC HSV-1 given once within 24 h of birth. Each of the HSV-1-primed CD4(+) or CD8(+) T cells induced in wild-type or interferon-deficient mice conferred resistance to naive animals exposed to a lethal virus challenge. Inactivated HSV-1, injected at variable doses up to 10(4) times that of DISC HSV-1, was ineffective in inducing any detectable immune responses in neonates. Thus, the capacity of HSV-1 to replicate once, but not the number of virus particles per se, was decisive in inducing protective T-cell-associated immunity in newborn mice.

Hematopoietic cells from CD155-transgenic mice express CD155 and support poliovirus replication ex vivo

Despite identification of the poliovirus (PV) receptor (CD155), mechanisms by which this molecule mediates paralytic disease remain obscure. Unanswered questions include CD155 localization in human tissues, the nature of cells supporting the first round of replication, identity of nonneural replication sites, and route of entry into the CNS. In earlier work, we showed that CD155 is expressed on primary human monocytes and that these cells support low, but statistically significant, levels of PV replication ex vivo without prior culturing. We hypothesize that monocytes support PV replication in vivo and that they contribute to pathogenesis. In the current study, we tested whether CD155-transgenic mouse hematopoietic cells express cell surface CD155 and whether these cells support PV replication. We found that the majority of monocyte/macrophages from peritoneal washes express CD155. In addition, 26-32% of CD155-transgenic bone marrow and spleen cells express CD155 on monocyte/macrophages, T cells and hematopoietic precursor cells. Various tissues supported PV replication without pre-culturing, however, pre-culturing or pre-treatment of mice with thioglycollate increased virus yield. These results are consistent with those from human cells and suggest that the CD155 transgenic mouse model is useful to help understand the role of hematopoietic cells in PV pathogenesis.

Early expression of IFN-alpha/beta and iNOS in the brains of Venezuelan equine encephalitis virus-infected mice

To investigate the roles of type I interferon (IFN-alpha/beta) and other mediators of innate immune responses (e.g., inducible nitric oxide synthase [iNOS]) in early dissemination of Venezuelan equine encephalitis virus (VEE) infection, we used mice with targeted deletions in either their IFN-alpha/beta-receptor (IFNAR-1-/-) or interferon regulatory factor 2 (IRF-2-/-) genes. Following footpad infection, both IFNAR-1-/- and IRF-2-/- mice were more susceptible than control mice to VEE. The IFNAR-1-/- mice also exhibit accelerated VEE dissemination to serum, spleen, and brain, and compared with control mice, they evidenced faster kinetics in the upregulation of proinflammatory genes. In contrast, in IRF-2-/- mice, iNOS gene induction was completely absent following peripheral virulent VEE infection. In evaluating the role of cells involved in iNOS production, primary microglial cell cultures were found to be highly permissive to VEE infection. Moreover, VEE infection increased levels of nitric oxide (NO) in resting microglial cultures but decreased NO production in IFN-gamma-stimulated microglia. Thus, these findings suggest that reactive nitrogen species play an important contributory role in VEE dissemination and survival of the host. Our results further suggest the necessity for a carefully balanced host response that follows a middle course between immunopathology and insufficient inflammatory response to VEE infection.