Endogenously produced interferon alpha protects mice from herpes simplex virus type 1 corneal disease

The immunobiology of corneal HSV-1 infection and herpetic stromal keratitis

SUMMARYHuman alphaherpesvirus 1 (HSV-1) is a highly successful neurotropic pathogen that primarily infects the epithelial cells lining the orofacial mucosa. After primary lytic replication in the oral, ocular, and nasal mucosal epithelial cells, HSV-1 establishes life-long latency in neurons within the trigeminal ganglion. Patients with compromised immune systems experience frequent reactivation of HSV-1 from latency, leading to virus entry in the sensory neurons, followed by anterograde transport and lytic replication at the innervated mucosal epithelial surface. Although recurrent infection of the corneal mucosal surface is rare, it can result in a chronic immuno-inflammatory condition called herpetic stromal keratitis (HSK). HSK leads to gradual vision loss and can cause permanent blindness in severe untreated cases. Currently, there is no cure or successful vaccine to prevent latent or recurrent HSV-1 infections, posing a significant clinical challenge to managing HSK and preventing vision loss. The conventional clinical management of HSK primarily relies on anti-virals to suppress HSV-1 replication, anti-inflammatory drugs (such as corticosteroids) to provide symptomatic relief from pain and inflammation, and surgical interventions in more severe cases to replace damaged cornea. However, each clinical treatment strategy has limitations, such as local and systemic drug toxicities and the emergence of anti-viral-resistant HSV-1 strains. In this review, we summarize the factors and immune cells involved in HSK pathogenesis and highlight alternate therapeutic strategies for successful clinical management of HSK. We also discuss the therapeutic potential of immunoregulatory cytokines and immunometabolism modulators as promising HSK therapies against emerging anti-viral-resistant HSV-1 strains.

Complement Suppresses the Initial Type 1 Interferon Response to Ocular Herpes Simplex Virus Type 1 Infection in Mice

The complement system (CS) contributes to the initial containment of viral and bacterial pathogens and clearance of dying cells in circulation. We previously reported mice deficient in complement component 3 (C3KO mice) were more sensitive than wild-type (WT) mice to ocular HSV-1 infection, as measured by a reduction in cumulative survival and elevated viral titers in the nervous system but not the cornea between days three and seven post infection (pi). The present study was undertaken to determine if complement deficiency impacted virus replication and associated changes in inflammation at earlier time points in the cornea. C3KO mice were found to possess significantly (p < 0.05) less infectious virus in the cornea at 24 h pi that corresponded with a decrease in HSV-1 lytic gene expression at 12 and 24 h pi compared to WT animals. Flow cytometry acquisition found no differences in the myeloid cell populations residing in the cornea including total macrophage and neutrophil populations at 24 h pi with minimal infiltrating cell populations detected at the 12 h pi time point. Analysis of cytokine and chemokine content in the cornea measured at 12 and 24 h pi revealed that only CCL3 (MIP-1α) was found to be different between WT and C3KO mice with >2-fold increased levels (p < 0.05, ANOVA and Tukey's post hoc t-test) in the cornea of WT mice at 12 h pi. C3KO mouse resistance to HSV-1 infection at the early time points correlated with a significant increase in type I interferon (IFN) gene expression including IFN-α1 and IFN-β and downstream effector genes including tetherin and RNase L (p < 0.05, Mann-Whitney rank order test). These results suggest early activation of the CS interferes with the induction of the type I IFN response and leads to a transient increase in virus replication following corneal HSV-1 infection.

Interferon inhibits the release of herpes simplex virus-1 from the axons of sensory neurons

IMPORTANCE

Herpes simplex virus-1 (HSV-1) is a human pathogen known to cause cold sores and genital herpes. HSV-1 establishes lifelong infections in our sensory neurons, with no cure or vaccine available. HSV-1 can reactivate sporadically and travel back along sensory nerves, where it can form lesions in the oral and genital mucosa, eye, and skin, or be shed asymptomatically. New treatment options are needed as resistance is emerging to current antiviral therapies. Here, we show that interferons (IFNs) are capable of blocking virus release from nerve endings, potentially stopping HSV-1 transmission into the skin. Furthermore, we show that IFNγ has the potential to have widespread antiviral effects in the neuron and may have additional effects on HSV-1 reactivation. Together, this study identifies new targets for the development of immunotherapies to stop the spread of HSV-1 from the nerves into the skin.

Interferon production by Viral, Bacterial & Yeast system: A comparative overview in 2023

Interferons play a critical role in the innate immune response against several infections and play a key role in the control of a variety of viral and bacterial infectious diseases such as hepatitis, covid-19, cancer, and multiple sclerosis. Therefore, natural or synthetic IFN production is important and had three common methods, including bacterial fermentation, animal cell culture, and recombinant nucleic acid technology. However, the safety, purity, and accuracy of the most preferred INF production systems have not been extensively studied. This study provides a comprehensive comparative overview of interferon production in various systems that include viral, bacterial, yeast, and mammalian. We aim to determine the most efficient, safe, and accurate interferon production system available in the year 2023. The mechanisms of artificial interferon production were reviewed in various organisms, and the types and subtypes of interferons produced by each system were compared. Our analysis provides a comprehensive overview of the similarities and differences in interferon production and highlights the potential for developing new therapeutic strategies to combat infectious diseases. This review article offers the diverse strategies used by different organisms in producing and utilizing interferons, providing a framework for future research into the evolution and function of this critical immune response pathway.

Osteopontin contributes to virus resistance associated with type I IFN expression, activation of downstream ifn-inducible effector genes, and CCR2+CD115+CD206+ macrophage infiltration following ocular HSV-1 infection of mice

Ocular pathology is often associated with acute herpes simplex virus (HSV)-1 infection of the cornea in mice. The present study was undertaken to determine the role of early T lymphocyte activation 1 protein or osteopontin (OPN) in corneal inflammation and host resistance to ocular HSV-1 infection. C57BL/6 wild type (WT) and osteopontin deficient (OPN KO) mice infected in the cornea with HSV-1 were evaluated for susceptibility to infection and cornea pathology. OPN KO mice were found to possess significantly more infectious virus in the cornea at day 3 and day 7 post infection compared to infected WT mice. Coupled with these findings, HSV-1-infected OPN KO mouse corneas were found to express less interferon (IFN)-α1, double-stranded RNA-dependent protein kinase, and RNase L compared to infected WT animals early post infection that likely contributed to decreased resistance. Notably, OPN KO mice displayed significantly less corneal opacity and neovascularization compared to WT mice that paralleled a decrease in expression of vascular endothelial growth factor (VEGF) A within 12 hr post infection. The change in corneal pathology of the OPN KO mice aligned with a decrease in total leukocyte infiltration into the cornea and specifically, in neutrophils at day 3 post infection and in macrophage subpopulations including CCR2+CD115+CD206+ and CD115+CD183+CD206+ -expressing cells. The infiltration of CD4+ and CD8+ T cells into the cornea was unaltered comparing infected WT to OPN KO mice. Likewise, there was no difference in the total number of HSV-1-specific CD4+ or CD8+ T cells found in the draining lymph node with both sets functionally competent in response to virus antigen comparing WT to OPN KO mice. Collectively, these results demonstrate OPN deficiency directly influences the host innate immune response to ocular HSV-1 infection reducing some aspects of inflammation but at a cost with an increase in local HSV-1 replication.

Neuropeptide S and its receptor NPSR enhance the susceptibility of hosts to pseudorabies virus infection

The neuropeptide S (NPS) and its receptor (NPSR) represent a signaling system in the brain. Increased levels of NPS and NPSR have been observed in PK15 cells and murine brains in response to pseudorabies virus (PRV) infection, but it remains unclear whether elevated levels of NPS and NPSR are involved in the pathogenic process of PRV infection. In this study, the activities of both NPS and NPSR during PRV pathogenesis were explored in vitro and in vivo by reverse transcription polymerase chain reaction (RT-PCR), PCR, real-time quantitative RT-PCR (qRT-PCR), qPCR, TCID50, and Western blotting methods. NPSR-deficient cells were less susceptible to PRV infection, as evidenced by decreased viral production and PRV-glycoprotein E (gE) expression. In vitro studies showed that exogenous NPS promoted the expression of interleukin 6 (IL-6) mRNA but inhibited interferon β (IFN-β) mRNA expression in PK15 cells after PRV infection. In vivo studies showed that NPS-treated mice were highly susceptible to PRV infection, with decreased survival rates and body weights. In addition, NPS-treated mice showed elevated levels of IL-6 mRNA and STAT3 phosphorylation. However, the expression of IFN-β mRNA was greatly decreased after virus challenge. Contrasting results were obtained from the NPSR-ir-treated groups, which further highlighted the effects of NPS. This study revealed that NPS-treated hosts are more susceptible to PRV infection than controls. Moreover, excessive IL-6/STAT3 and defective IFN-β responses in NPS-treated mice may contribute to the pathogenesis of PRV.

E3 ligase RNF5 inhibits type I interferon response in herpes simplex virus keratitis through the STING/IRF3 signaling pathway

Herpes simplex keratitis (HSK), caused by the herpes simplex virus 1 (HSV-1), is a major blinding disease in developed countries. HSV-1 can remain latent in the host for life and cannot be eradicated. The infection causes the secretion of various cytokines and aggregation of inflammatory cells. In the early stage of inflammation, mainly neutrophils infiltrate the cornea, and CD4⁺ T cells mediate the immunopathological changes in herpetic stromal keratitis in the subsequent progression. The STING/IRF3-mediated type I interferon (IFN) response can effectively inhibit viral replication and control infection, but the activity of STING is affected by various ubiquitination modifications. In this study, we found that the expression of RNF5 was elevated in corneal tissues and corneal epithelial cells after infection with HSV-1. Immunofluorescence staining confirmed that RNF5 was mainly expressed in the corneal epithelial layer. We silenced and overexpressed RNF5 expression in corneal epithelial cells and then inoculated them with HSV-1. We found that the expressions of STING, p-IRF3, p-TBK1, and IFN-β mRNA increased after RNF5 silencing. The opposite results were obtained after RNF5 overexpression. We also used siRNA to silence RNF5 in the mouse cornea and then established the HSK model. Compared with the siRNA-control group, the siRNA-RNF5 group showed significantly improved corneal inflammation, reduced clinical scores and tear virus titers, and significantly increased corneal IFN-β expression. In addition, the expressions of the proinflammatory cytokines IL-6 and TNF-α in the corneal tissue were significantly decreased, indicating that RNF5 silencing could effectively promote IFN-I expression, inhibit virus replication, alleviate inflammation, and reduce corneal inflammatory damage. In summary, our results suggest that RNF5 limits the type I IFN antiviral response in HSV corneal epithelitis by inhibiting STING/IRF3 signaling.

A Comparison of Pseudorabies Virus Latency to Other A-Herpesvirinae Subfamily Members

Pseudorabies virus (PRV), the causative agent of Aujeszky’s disease, is one of the most important infectious pathogens threatening the global pig industry. Like other members of alphaherpesviruses, PRV establishes a lifelong latent infection and occasionally reactivates from latency after stress stimulus in infected pigs. Latent infected pigs can then serve as the source of recurrent infection, which is one of the difficulties for PRV eradication. Virus latency refers to the retention of viral complete genomes without production of infectious progeny virus; however, following stress stimulus, the virus can be reactivated into lytic infection, which is known as the latency-reactivation cycle. Recently, several research have indicated that alphaherpesvirus latency and reactivation is regulated by a complex interplay between virus, neurons, and the immune system. However, with those limited reports, the relevant advances in PRV latency are lagging behind. Therefore, in this review we focus on the regulatory mechanisms in PRV latency via summarizing the progress of PRV itself and that of other alphaherpesviruses, which will improve our understanding in the underlying mechanism of PRV latency and help design novel therapeutic strategies to control PRV latency.

Analysis of MicroRNA Expression in Tears of Patients with Herpes Epithelial Keratitis: A Preliminary Study

Purpose

Herpes epithelial keratitis (HEK) is the most common form of herpes simplex virus (HSV) eye involvement, and understanding the molecular mechanisms underlying HEK is important. We investigated the expression of microRNAs (miRNAs) in the tears of patients with HEK.

Methods

Tear samples from eight patients with HEK and seven age-matched controls were evaluated. Clinical ophthalmologic evaluation was performed, and an anterior segment photograph was obtained after fluorescence staining. Dendritic or geographic ulcer areas were measured using ImageJ software. The expression of 43 different miRNAs in tears was measured using real-time polymerase chain reaction and compared between patients with HEK and controls. Differences in miRNA expression between the dendritic and geographic ulcer groups and correlations involving miRNA expression and ulcer area were evaluated.

Results

Of the 43 miRNAs, 23 were upregulated in patients with HEK compared to normal controls. MiR-15b-5p, miR-16-5p, miR-20b-5p, miR-21-5p, miR-23b-3p, miR-25-3p, miR-29a-3p, miR-30a-3p, miR-30d-5p, miR-92a-3p, miR-124-3p, miR-127-3p, miR-132-3p, miR-142-3p, miR-145-5p, miR-146a-5p, miR-146b-5p, miR-155-5p, miR-182-5p, miR-183-5p, miR-221-3p, miR-223-3p, and miR-338-5p were significantly upregulated in patients with HEK. MiR-29a-3p exhibited significant differences between the dendritic and geographic ulcer groups. All 23 miRNAs with significant differences between patients with HEK and the control group were not significantly correlated with ulcer area.

Conclusions

Twenty-three miRNAs were significantly upregulated in the tears of patients with HEK, and the expression of miRNAs may play important roles in herpes infection in relation to host immunity.

Tripartite-Motif 21 (TRIM21) Deficiency Results in a Modest Loss of Herpes Simplex Virus (HSV)-1 Surveillance in the Trigeminal Ganglia Following Cornea Infection

Tripartite-motif 21 (TRIM21) is thought to regulate the type I interferon (IFN) response to virus pathogens and serve as a cytosolic Fc receptor for immunoglobulin. Since herpes simplex virus (HSV)-1 is sensitive to type I IFN and neutralizing antibody, we investigated the role of TRIM21 in response to ocular HSV-1 infection in mice. In comparison to wild type (WT) mice, TRIM21 deficient (TRIM21 KO) mice were found to be no more susceptible to ocular HSV-1 infection than WT animals, in terms of infectious virus recovered in the cornea. Similar pathology, in terms of neovascularization, opacity, and loss of peripheral vision function, was observed in both WT and TRIM21 KO mice. However, TRIM21 KO mice did possess a significant increase in infectious virus recovered in the trigeminal ganglia, in comparison to the WT animals. The increased susceptibility was not due to changes in HSV-1-specific CD4+ or CD8+ T cell numbers or functional capabilities, or in changes in type I IFN or IFN-inducible gene expression. In summary, the absence of TRIM21 results in a modest, but significant, increase in HSV-1 titers recovered from the TG of TRIM21 KO mice during acute infection, by a mechanism yet to be determined.

Pathogenesis and virulence of herpes simplex virus

Two of the most prevalent human viruses worldwide, herpes simplex virus type 1 and type 2 (HSV-1 and HSV-2, respectively), cause a variety of diseases, including cold sores, genital herpes, herpes stromal keratitis, meningitis and encephalitis. The intrinsic, innate and adaptive immune responses are key to control HSV, and the virus has developed mechanisms to evade them. The immune response can also contribute to pathogenesis, as observed in stromal keratitis and encephalitis. The fact that certain individuals are more prone than others to suffer severe disease upon HSV infection can be partially explained by the existence of genetic polymorphisms in humans. Like all herpesviruses, HSV has two replication cycles: lytic and latent. During lytic replication HSV produces infectious viral particles to infect other cells and organisms, while during latency there is limited gene expression and lack of infectious virus particles. HSV establishes latency in neurons and can cause disease both during primary infection and upon reactivation. The mechanisms leading to latency and reactivation and which are the viral and host factors controlling these processes are not completely understood. Here we review the HSV life cycle, the interaction of HSV with the immune system and three of the best-studied pathologies: Herpes stromal keratitis, herpes simplex encephalitis and genital herpes. We also discuss the potential association between HSV-1 infection and Alzheimer's disease.

PML-NB-dependent type I interferon memory results in a restricted form of HSV latency

Herpes simplex virus (HSV) establishes latent infection in long-lived neurons. During initial infection, neurons are exposed to multiple inflammatory cytokines but the effects of immune signaling on the nature of HSV latency are unknown. We show that initial infection of primary murine neurons in the presence of type I interferon (IFN) results in a form of latency that is restricted for reactivation. We also find that the subnuclear condensates, promyelocytic leukemia nuclear bodies (PML-NBs), are absent from primary sympathetic and sensory neurons but form with type I IFN treatment and persist even when IFN signaling resolves. HSV-1 genomes colocalize with PML-NBs throughout a latent infection of neurons only when type I IFN is present during initial infection. Depletion of PML prior to or following infection does not impact the establishment latency; however, it does rescue the ability of HSV to reactivate from IFN-treated neurons. This study demonstrates that viral genomes possess a memory of the IFN response during de novo infection, which results in differential subnuclear positioning and ultimately restricts the ability of genomes to reactivate.

TRIM21 Aggravates Herpes Simplex Virus Epithelial Keratitis by Attenuating STING-IRF3-Mediated Type I Interferon Signaling

Herpes simplex virus-1 (HSV-1) is the leading cause of infectious blindness in the developed world. HSV-1 infection can occur anywhere in the eye, and the most common presentation is epithelial keratitis. In the HSV epithelial keratitis mice model, we detected the expression of TRIM21 and then investigated the clinical relationship between TRIM21 and HSV epithelial keratitis by silencing TRIM21. Through the clinical scores and histopathology examination, we found that TRIM21 can effectively reduce the severity of HSV epithelial keratitis. Furthermore, silencing TRIM21 significantly controlled the virus particle release at 1, 3, and 5 days post-HSV-1 infection. Notably, the production of IFN-β was enhanced, and the secretion of pro-inflammatory cytokines (IL-6 and TNF-a) was inhibited. Next, human corneal epithelial cells were pretreated with lentivirus or siRNA, respectively, so that TRIM21 expression was overexpressed or silenced. We focused on the regulation of STING-IRF3 and type I interferon signaling after infected with HSV-1. In conclusion, our results have identified that TRIM21 is abnormally high expressed in HSV epithelial keratitis. TRIM21 enhances the replication of HSV-1 in corneal epithelial cells via suppressing the production of type I IFN by inhibiting STING/IRF3 signaling. It also promotes the secretion of IL-6 and TNF-a, thereby aggravating the severity of HSV epithelial keratitis.

Nitric Oxide Influences HSV-1-Induced Neuroinflammation

Herpes simplex virus type 1 (HSV-1) has the ability to replicate in neurons and glial cells and to produce encephalitis leading to neurodegeneration. Accumulated evidence suggests that nitric oxide (NO) is a key molecule in the pathogenesis of neurotropic virus infections. NO can exert both cytoprotective as well as cytotoxic effects in the central nervous system (CNS) depending on its concentration, time course exposure, and site of action. In this study, we used an in vitro model of HSV-1-infected primary neuronal and mixed glial cultures as well as an intranasal model of HSV-1 in BALB/c mice to elucidate the role of NO and nonapoptotic Fas signalling in neuroinflammation and neurodegeneration. We found that low, nontoxic concentration of NO decreased HSV-1 replication in neuronal cultures together with production of IFN-alpha and proinflammatory chemokines. However, in HSV-1-infected glial cultures, low concentrations of NO supported virus replication and production of IFN-alpha and proinflammatory chemokines. HSV-1-infected microglia downregulated Fas expression and upregulated its ligand, FasL. Fas signalling led to production of proinflammatory cytokines and chemokines as well as induced iNOS in uninfected bystander glial cells. On the contrary, NO reduced production of IFN-alpha and CXCL10 through nonapoptotic Fas signalling in HSV-1-infected neuronal cultures. Here, we also observed colocalization of NO production with the accumulation of β-amyloid peptide in HSV-1-infected neurons both in vitro and in vivo. Low levels of the NO donor increased accumulation of β-amyloid in uninfected primary neuronal cultures, while the NO inhibitor decreased its accumulation in HSV-1-infected neuronal cultures. This study shows for the first time the existence of a link between NO and Fas signalling during HSV-1-induced neuroinflammation and neurodegeneration.

Pathogenesis of herpes simplex keratitis: The host cell response and ocular surface sequelae to infection and inflammation

Herpes simplex virus type 1 (HSV) keratitis is a leading cause of infectious blindness. Clinical disease occurs variably throughout the cornea from epithelium to endothelium and recurrent HSV stromal keratitis is associated with corneal scarring and neovascularization. HSV keratitis can be associated with ocular pain and subsequent neutrophic keratopathy. Host cell interactions with HSV trigger an inflammatory cascade responsible not only for clearance of virus but also for progressive corneal opacification due to inflammatory cell infiltrate, angiogenesis, and corneal nerve loss. Current antiviral therapies target viral replication to decrease disease duration, severity and recurrence, but there are limitations to these agents. Therapies directed towards viral entry into cells, protein synthesis, inflammatory cytokines and vascular endothelial growth factor pathways in animal models represent promising new approaches to the treatment of recurrent HSV keratitis.

PD-L1/B7-H1 Inhibits Viral Clearance by Macrophages in HSV-1-Infected Corneas

Immune privilege helps protect the cornea from damaging inflammation but can also impair pathogen clearance from this mucosal surface. Programmed death-ligand 1 (PD-L1 or B7-H1) contributes to corneal immune privilege by inhibiting the function of a variety of immune cells. We asked whether programmed death-1 (PD-1)/PD-L1 interaction regulates HSV-1 clearance from infected corneas. We show that PD-L1 is constitutively expressed in the corneal epithelium and is upregulated upon HSV-1 corneal infection, with peak expression on CD45⁺ cells NK cells, dendritic cells, neutrophils, and macrophages and CD45^- corneal epithelial cells at 4 d postinfection (dpi). As early as 1 dpi, HSV-1-infected corneas of B7-H1^-/- mice as compared with wild-type mice showed increased chemokine expression and this correlated with increased migration of inflammatory cells into the viral lesions and decreased HSV-1 corneal titers. Local PD-L1 blockade caused a similar increase in viral clearance, suggesting a local effect of PD-1/PD-L1 in the cornea. The enhanced HSV-1 clearance at 2 dpi resulting from PD-1/PD-L1 blockade is mediated primarily by a monocyte/macrophage population. Studies in bone marrow chimeras demonstrated enhanced viral clearance when PD-L1 was absent only from nonhematopoietic cells. We conclude that PD-L1 expression on corneal cells negatively impacts the ability of the innate immune system to clear HSV-1 from infected corneas.

Combinatorial Effects of the Glucocorticoid Receptor and Krüppel-Like Transcription Factor 15 on Bovine Herpesvirus 1 Transcription and Productive Infection

Bovine herpesvirus 1 (BoHV-1), an important bovine pathogen, establishes lifelong latency in sensory neurons. Latently infected calves consistently reactivate from latency following a single intravenous injection of the synthetic corticosteroid dexamethasone. The immediate early transcription unit 1 (IEtu1) promoter, which drives bovine ICP0 (bICP0) and bICP4 expression, is stimulated by dexamethasone because it contains two glucocorticoid receptor (GR) response elements (GREs). Several Krüppel-like transcription factors (KLF), including KLF15, are induced during reactivation from latency, and they stimulate certain viral promoters and productive infection. In this study, we demonstrate that the GR and KLF15 were frequently expressed in the same trigeminal ganglion (TG) neuron during reactivation and cooperatively stimulated productive infection and IEtu1 GREs in mouse neuroblastoma cells (Neuro-2A). We further hypothesized that additional regions in the BoHV-1 genome are transactivated by the GR or stress-induced transcription factors. To test this hypothesis, BoHV-1 DNA fragments (less than 400 bp) containing potential GR and KLF binding sites were identified and examined for transcriptional activation by stress-induced transcription factors. Intergenic regions within the unique long 52 gene (UL52; a component of the DNA primase/helicase complex), bICP4, IEtu2, and the unique short region were stimulated by KLF15 and the GR. Chromatin immunoprecipitation studies revealed that the GR and KLF15 interacted with sequences within IEtu1 GREs and the UL52 fragment. Coimmunoprecipitation studies demonstrated that KLF15 and the GR were associated with each other in transfected cells. Since the GR stimulates KLF15 expression, we suggest that these two transcription factors form a feed-forward loop that stimulates viral gene expression and productive infection following stressful stimuli.IMPORTANCE Bovine herpesvirus 1 (BoHV-1) is an important viral pathogen that causes respiratory disease and suppresses immune responses in cattle; consequently, life-threatening bacterial pneumonia can occur. Following acute infection, BoHV-1 establishes lifelong latency in sensory neurons. Reactivation from latency is initiated by the synthetic corticosteroid dexamethasone. Dexamethasone stimulates lytic cycle viral gene expression in sensory neurons of calves latently infected with BoHV-1, culminating in virus shedding and transmission. Two stress-induced cellular transcription factors, Krüppel-like transcription factor 15 (KLF15) and the glucocorticoid receptor (GR), cooperate to stimulate productive infection and viral transcription. Additional studies demonstrated that KLF15 and the GR form a stable complex and that these stress-induced transcription factors bind to viral DNA sequences, which correlates with transcriptional activation. The ability of the GR and KLF15 to synergistically stimulate viral gene expression and productive infection may be critical for the ability of BoHV-1 to reactivate from latency following stressful stimuli.

The serum and glucocorticoid-regulated protein kinases (SGK) stimulate bovine herpesvirus 1 and herpes simplex virus 1 productive infection

Serum and glucocorticoid-regulated protein kinases (SGK) are serine/threonine protein kinases that contain a catalytic domain resembling other protein kinases: AKT/protein kinase B, protein kinase A, and protein kinase C-Zeta for example. Unlike these constitutively expressed protein kinases, SGK1 RNA and protein levels are increased by growth factors and corticosteroids. Stress can directly stimulate SGK1 levels as well as stimulate bovine herpesvirus 1 (BoHV-1) and herpes simplex virus 1 (HSV-1) productive infection and reactivation from latency suggesting SGK1 can stimulate productive infection. For the first time, we provide evidence that a specific SGK inhibitor (GSK650394) significantly reduced BoHV-1 and HSV-1 replication in cultured cells. Proteins encoded by the three BoHV-1 immediate early genes (bICP0, bICP4, and bICP22) and two late proteins (VP16 and gE) were consistently reduced by GSK650394 during early stages of productive infection. In summary, these studies suggest SGK may stimulate viral replication following stressful stimuli.

Bacterial artificial chromosome derived simian varicella virus is pathogenic in vivo

Background

Varicella zoster virus (VZV) is a neurotropic alphaherpesvirus that infects humans and results in chickenpox and herpes zoster. A number of VZV genes remain functionally uncharacterized and since VZV is an obligate human pathogen, rigorous evaluation of VZV mutants in vivo remains challenging. Simian varicella virus (SVV) is homologous to VZV and SVV infection of rhesus macaques (RM) closely mimics VZV infection of humans. Recently the SVV genome was cloned as a bacterial artificial chromosome (BAC) and BAC-derived SVV displayed similar replication kinetics as wild-type (WT) SVV in vitro.

Methods

RMs were infected with BAC-derived SVV or WT SVV at 4x10⁵ PFU intrabronchially (N=8, 4 per group, sex and age matched). We collected whole blood (PBMC) and bronchoalveolar lavage (BAL) at various days post-infection (dpi) and sensory ganglia during latent infection (>84 dpi) at necropsy and compared disease progression, viral replication, immune response and the establishment of latency.

Results

Viral replication kinetics and magnitude in bronchoalveolar lavage cells and whole blood as well as rash severity and duration were similar in RMs infected with SVV BAC or WT SVV. Moreover, SVV-specific B and T cell responses were comparable between BAC and WT-infected animals. Lastly, we measured viral DNA in sensory ganglia from both cohorts of infected RMs during latent infection.

Conclusions

SVV BAC is as pathogenic and immunogenic as WT SVV in vivo. Thus, the SVV BAC genetic system combined with the rhesus macaque animal model can further our understanding of viral ORFs important for VZV pathogenesis and the development of second-generation vaccines.

Type I interferon and lymphangiogenesis in the HSV-1 infected cornea - are they beneficial to the host?

Herpes simplex virus type 1 (HSV-1) is a highly successful pathogen that can result in significant human morbidity. Within the cornea, it was thought the initial recognition of the pathogen was through Toll-like receptors expressed on/in resident cells that then elicit pro-inflammatory cytokine production, activation of anti-viral pathways, and recruitment of leukocytes. However, our lab has uncovered a novel, TLR-independent innate sensor that supersedes TLR induction of anti-viral pathways following HSV-1 infection. In addition, we have also found HSV-1 induces the genesis of lymphatic vessels into the cornea proper by a mechanism independent of TLRs and unique in the field of neovascularization. This review will focus on these two innate immune events during acute HSV-1 infection of the cornea.

Mucosal herpes immunity and immunopathology to ocular and genital herpes simplex virus infections

Herpes simplex viruses type 1 and type 2 (HSV-1 and HSV-2) are amongst the most common human infectious viral pathogens capable of causing serious clinical diseases at every stage of life, from fatal disseminated disease in newborns to cold sores genital ulcerations and blinding eye disease. Primary mucocutaneous infection with HSV-1 & HSV-2 is followed by a lifelong viral latency in the sensory ganglia. In the majority of cases, herpes infections are clinically asymptomatic. However, in symptomatic individuals, the latent HSV can spontaneously and frequently reactivate, reinfecting the muco-cutaneous surfaces and causing painful recurrent diseases. The innate and adaptive mucosal immunities to herpes infections and disease remain to be fully characterized. The understanding of innate and adaptive immune mechanisms operating at muco-cutaneous surfaces is fundamental to the design of next-generation herpes vaccines. In this paper, the phenotypic and functional properties of innate and adaptive mucosal immune cells, their role in antiherpes immunity, and immunopathology are reviewed. The progress and limitations in developing a safe and efficient mucosal herpes vaccine are discussed.

Two microRNAs encoded within the bovine herpesvirus 1 latency-related gene promote cell survival by interacting with RIG-I and stimulating NF-κB-dependent transcription and beta interferon signaling pathways

Sensory neurons latently infected with bovine herpesvirus 1 (BHV-1) abundantly express latency-related (LR) RNA (LR-RNA). Genetic evidence indicates that LR protein expression plays a role in the latency-reactivation cycle, because an LR mutant virus that contains three stop codons downstream of the first open reading frame (ORF2) does not reactivate from latency. The LR mutant virus induces higher levels of apoptotic neurons in trigeminal ganglia, and ORF2 interferes with apoptosis. Although ORF2 is important for the latency-reactivation cycle, other factors encoded by the LR gene are believed to play a supportive role. For example, two microRNAs (miRNAs) encoded within the LR gene are expressed in trigeminal ganglia of latently infected calves. These miRNAs interfere with bICP0 protein expression and productive infection in transient-transfection assays. In this report, we provide evidence that the two LR miRNAs cooperate with poly(I·C), interferon (IFN) regulatory factor 3 (IRF3), or IRF7 to stimulate beta interferon (IFN-β) promoter activity. Both miRNAs also stimulated IFN-β promoter activity and nuclear factor-kappa B (NF-κB)-dependent transcription when cotransfected with a plasmid expressing retinoic acid-inducible gene I (RIG-I). In the presence of RIG-I, the LR miRNAs enhanced survival of mouse neuroblastoma cells, which correlated with activation of the antiapoptosis cellular transcription factor, NF-κB. Immunoprecipitation assays demonstrated that both miRNAs stably interact with RIG-I, suggesting that this interaction directly stimulates the RIG-I signaling pathway. In summary, the results of these studies suggest that interactions between LR miRNAs and RIG-I promote the establishment and maintenance of latency by enhancing survival of infected neurons.

Effects of interferon on immediate-early mRNA and protein levels in sensory neuronal cells infected with herpes simplex virus type 1 or pseudorabies virus

Most alphaherpesviruses are able to establish latency in sensory neurons and reactivate upon specific stimuli to cause recurrent symptoms. We have previously shown that interferon (IFN) is capable of inducing a quiescent HSV-1 and PRV infection that strongly resembles in vivo latency in primary cultures of TG neurons. This IFN-induced latency-like quiescence was found to correlate with suppression of the immediate-early protein ICP4 in HSV-1 and its ortholog IE180 in PRV. Here, we mechanistically investigated the IFN-mediated suppression of ICP4 and IE180 in sensory neuronal cells. RT-qPCR showed that mRNA levels of either HSV ICP4 or PRV IE180 at 4 hpi were mildly but not significantly different in IFN-treated samples versus control samples, whereas a strong reduction was observed at 8 hpi and 12 hpi. However, at 4 hpi, HSV ICP4 but not PRV IE180 protein expression was already markedly reduced in IFN-treated samples. In line with this difference in IFN-mediated suppression of HSV ICP4 versus PRV IE180 protein levels, we found that IFN resulted in an increase in phosphorylation of the translation initiation factor eIF2α in HSV-infected but not in PRV-infected cells. The latter finding indicates that PRV efficiently circumvents IFN-mediated translation inhibition by interfering with phosphorylation of eIF2α.

A Functional Type I Interferon Pathway Drives Resistance to Cornea Herpes Simplex Virus Type 1 Infection by Recruitment of Leukocytes

Type I interferons are critical antiviral cytokines produced following herpes simplex virus type-1 (HSV-1) infection that act to inhibit viral spread. In the present study, we identify HSV-infected and adjacent uninfected corneal epithelial cells as the source of interferon-α. We also report mice deficient in the A1 chain of the type I IFN receptor (CD118(-/-)) are extremely sensitive to ocular infection with low doses (100 PFU) of HSV-1 as seen by significantly elevated viral titers in the cornea compared to wild type (WT) controls. The enhanced susceptibility correlated with a loss of CD4(+) and CD8(+) T cell recruitment and aberrant chemokine production in the cornea despite mounting an adaptive immune response in the draining mandibular lymph node of CD118(-/-) mice. Taken together, these results highlight the importance of IFN production in both the innate immune response as well as eliciting chemokine production required to facilitate adaptive immune cell trafficking.

Interferon alpha induces establishment of alphaherpesvirus latency in sensory neurons in vitro

Background

Several alphaherpesviruses, including herpes simplex virus 1 (HSV-1) and pseudorabies virus (PRV), establish lifelong latency in neurons of the trigeminal ganglion (TG). Although it is thought that efficient establishment of alphaherpesvirus latency is based on a subtle interplay between virus, neurons and the immune system, it is not clear which immune components are of major importance for the establishment of latency.

Methodology/Principal Findings

Here, using an in vitro model that enables a natural route of infection, we show that interferon alpha (IFNalpha) has the previously uncharacterized capacity to induce a quiescent HSV-1 and PRV infection in porcine TG neurons that shows strong similarity to in vivo latency. IFNalpha induced a stably suppressed HSV-1 and PRV infection in TG neurons in vitro. Subsequent treatment of neurons containing stably suppressed virus with forskolin resulted in reactivation of both viruses. HSV and PRV latency in vivo is often accompanied by the expression of latency associated transcripts (LATs). Infection of TG neurons with an HSV-1 mutant expressing LacZ under control of the LAT promoter showed activation of the LAT promoter and RT-PCR analysis confirmed that both HSV-1 and PRV express LATs during latency in vitro.

Conclusions/Significance

These data represent a unique in vitro model of alphaherpesvirus latency and indicate that IFNalpha may be a driving force in promoting efficient latency establishment.

Identification of multiple sites suitable for insertion of foreign genes in herpes simplex virus genomes

Information on sites in HSV genomes at which foreign gene(s) can be inserted without disrupting viral genes or affecting properties of the parental virus are important for basic research on HSV and development of HSV-based vectors for human therapy. The intergenic region between HSV-1 UL3 and UL4 genes has been reported to satisfy the requirements for such an insertion site. The UL3 and UL4 genes are oriented toward the intergenic region and, therefore, insertion of a foreign gene(s) into the region between the UL3 and UL4 polyadenylation signals should not disrupt any viral genes or transcriptional units. HSV-1 and HSV-2 each have more than 10 additional regions structurally similar to the intergenic region between UL3 and UL4. In the studies reported here, it has been demonstrated that insertion of a reporter gene expression cassette into several of the HSV-1 and HSV-2 intergenic regions has no effect on viral growth in cell culture or virulence in mice, suggesting that these multiple intergenic regions may be suitable HSV sites for insertion of foreign genes.

Development and pathogenic evaluation of recombinant herpes simplex virus type 1 expressing two fluorescent reporter genes from different lytic promoters

To develop means to explore viral gene expression in ganglia without laborious histological sectioning and staining, we created a two color fluorescent recombinant HSV-1, in which enhanced green fluorescent protein (EGFP) and red fluorescent protein (RFP) are expressed from the glycoprotein B (gB) and glycoprotein C (gC) promoters respectively. We show that this virus retained growth and pathogenic capacity both in vitro and in vivo compared to wild type HSV-1; established latent infections with similar genome copy number in trigeminal ganglia (TG); induced a similar HSV-specific CD8(+) T cell infiltrate; did not induce CD8(+) T cells reactive to EGFP or RFP; and reactivated from latency with normal kinetics in ex vivo TG cultures. Fluorescent EGFP expression in plaques surrounding neurons preceded RFP expression and provided highly sensitive detection of reactivation and different stages of infection in ex vivo TG cultures. Expression of both EGFP and RFP in neurons was readily detectable in whole mounts of TG excised during acute infection and following in vivo sodium butyrate-induced reactivation from latency. This virus constitutes a useful reagent for monitoring lytic viral promoter activity in sensory neurons in vivo and in vitro.

Herpes simplex virus type 2-mediated disease is reduced in mice lacking RNase L

RNase L helps mediate the antiviral state induced by type I interferons (IFNalphabeta). Although herpes simplex virus (HSV) encodes inhibitors of the IFNalphabeta-induced antiviral response, the IFNalphabeta system serves the body as a first line of defense against HSV. We investigated whether RNase L limits HSV-2 replication and virulence. RNaseL(-/-) and wild-type C57BL/6 mice were infected intravaginally with HSV-2 strain 333. Although initial replication in the genital epithelium was similar, mice lacking RNase L developed less severe genital and neurologic disease than wild-type mice, survived longer, and contained lower viral titers in the nervous system. CD4(+) T cell infiltration into the genital tract and spinal cord of RNase L(-/-) mice was reduced, suggesting that a restricted inflammatory response may account for reduction in disease. Thus, RNase L does not play a significant role in control of HSV-2 infection in vivo; instead, RNase L may regulate aspects of the inflammatory response that contribute to disease.

The cycle of human herpes simplex virus infection: virus transport and immune control

After infection of skin or mucosa, herpes simplex virus enters the sensory nerve endings and is conveyed by retrograde axonal transport to the dorsal root ganglion, where the virus develops lifelong latency. Intermittent reactivation, which is spontaneous in humans, leads to anterograde transport of virus particles and proteins to the skin or mucosa, where the virus is shed and/or causes disease. Immune control of viral infection and replication occurs at the level of skin or mucosa during initial or recurrent infection and also within the dorsal root ganglion, where immune mechanisms control latency and reactivation. This article examines current views on the mechanisms of retrograde and anterograde transport of the virus in axons and the mechanisms of innate and adaptive immunity that control infection in the skin or mucosa and in the dorsal root ganglion--in particular, the role of interferons, myeloid and plasmacytoid dendritic cells, CD4(+) and CD8(+) T cells, and interferon- gamma and other cytokines, including their significance in the development of vaccines for genital herpes.

B7-H1 (CD274) inhibits the development of herpetic stromal keratitis (HSK)

The co-signaling molecule B7-H1 (CD274) functions as both a co-inhibitor through programmed death-1 (PD-1) receptor and a co-stimulator via an as-yet-unidentified receptor on T cells. We investigated the physiological role of endogenous B7-H1 in the pathogenesis of herpetic stromal keratitis (HSK) caused by herpes simplex virus type 1 (HSV-1). Following HSV-1 infection of the cornea of mice, B7-H1 expression was up-regulated in the CD11b+ macrophage population in the draining lymph nodes (dLN) and in the inflamed cornea. In addition, HSV-1 infection significantly increased PD-1 expression on CD4+ T cells in the dLN and inflamed cornea. The administration of antagonistic B7-H1 monoclonal antibody resulted in the proliferation of HSV-specific CD4+ T cells that secreted interferon (INF)-gamma, and inhibited the apoptosis of HSV-specific CD4+ T cells, which exaggerated HSK. These results strongly suggest that the B7-H1 may be involved in suppression of the development of HSK.

Biocatalysed synthesis of beta-O-glucosides from 9-fluorenon-2-carbohydroxyesters. Part 3: IFN-inducing and anti-HSV-2 properties

In pursuing research on the antiviral, interferon (IFN)-inducing tilorone congeners, a new series of fluoren-carboxyhydroxyesters has been prepared and biologically explored. These esters have subsequently been used as sugar acceptors in the enzymatic transglycosylation reaction using the 'retaining' beta-glycosidase from the archaeon Sulfolobus solfataricus (Ssbeta-Gly). Both aglycones (1-6) and corresponding beta-glucosides (beta-glu 1-beta-glu 6) have been screened for cytotoxicity, interferon-stimulating and antiviral properties against HSV-2. It was found that the addition of compounds beta-glu 5, beta-glu 6 and beta-glu 4 to HSV-2 infected U937 cells downregulates viral replication and triggers cells to release IFN-alpha/beta. Taken together, the results showed improved pharmacological profiles as a consequence of glycosylation. A molecular modelling study carried out on this series of compounds completed the structural characterisation of the novel compounds.

The role of viral and host genes in corneal infection with herpes simplex virus type 1

Herpes simplex virus infection of the eye is the leading cause of blindness due to infection in the US despite the availability of several antiviral drugs. Studies with animal models have shown that three factors, innate host resistance, the host adaptive immune response, and the strain of virus interact to determine whether an infection is asymptomatic or proceeds to the development of blinding keratitis (HSK). Of these, the role of adaptive immunity has received the most attention. This work has clearly shown that stromal keratitis is an immunopathological disease, most likely due to the induction of a delayed type hypersensitivity response. Substantially less is known about the role of specific host genes in resistance to HSK. The fact that different strains of virus display different disease phenotypes indicates that viral 'virulence' genes are critical. Of the 80 plus HSV genes, few have been formally tested for their role in HSV keratitis. Most studies of virulence genes to date have focused on a single gene or protein and large changes in disease phenotypes are usually measured. Large changes in the ability to cause disease are likely to reduce the fitness of the virus, thus such studies, although useful, do not mimic the natural situation. Viral gene products are known to interact with each other, and with host proteins and these interactions are critical in determining the outcome of infection. In reality, the 'constellation' of genes encoded by each particular strain is critical, and how this constellation of genes works together and with host proteins determines the outcome of an infection. The goal of this review is to discuss the current state of knowledge regarding the role of host and viral genes in HSV keratitis. The roles of specific genes that have been shown to influence keratitis are discussed. Recent data showing that different viral genes cooperate to influence disease severity and confirming that the constellation of genes within a particular strain determines the disease phenotype are also discussed, as are the methods used to test the role of viral genes in virulence. It will become apparent that there is a paucity of information regarding the function of many viral genes in keratitis. Improving our knowledge of the role of viral genes is critical for devising more effective treatments for this disease.

Early events in HSV keratitis--setting the stage for a blinding disease

The last decade has seen herpes simplex virus (HSV)-induced stromal keratitis (SK) research shift from being a topic only of interest to vision researchers to one that fascinates the general field of inflammatory disease. Studies on experimental mouse lesions have uncovered several fundamental processes that explain lesion development. In this model, the chronic immuno-inflammatory lesions are mainly orchestrated by CD4+ T cells, but multiple early events occur that set the stage for the subsequent pathology. These include virus replication, the production of key cytokines and chemokines, neovascularization of the avascular cornea and the influx of certain inflammatory cell types. Many of these early events are subject to modulation, providing an approach to controlling this important cause of human blindness. We also comment on events ongoing during chronic SK, debating whether or not these represent virus-induced or autoimmune lesions.

Expression of cutaneous lymphocyte-associated antigen and E-selectin ligand by circulating human memory CD4+ T lymphocytes specific for herpes simplex virus type 2

Virus-specific memory T lymphocytes traffic to sites of viral infection. Herpes simplex virus (HSV) type 2-specific CD4(+) and CD8(+) T lymphocytes differ with regard to their homing kinetics to infected tissues. We studied the expression of cutaneous lymphocyte-associated antigen (CLA) and E-selectin ligand (ESL) by HSV-2-specific CD4(+) T lymphocytes. Virus-reactive T lymphocytes were identified ex vivo by CD154 or interferon-gamma up-regulation. We detected selective expression of CLA by HSV-2-reactive CD4(+) T lymphocytes, but at levels lower than those we previously observed for CD8(+) T lymphocytes. Short-term HSV-2-reactive CD4(+) lines generated from peripheral-blood mononuclear cells preferentially express CLA, compared with cytomegalovirus- or influenza-specific cells. CLA is expressed by HSV-2-reactive cells that are initially CLA negative before restimulation. Short-term culture-expanded HSV-2-specific CD4(+) T lymphocytes also selectively express ESL. These findings have implications for the optimization of vaccines for HSV and other cutaneous pathogens.

CD154 signaling regulates the Th1 response to herpes simplex virus-1 and inflammation in infected corneas

Approximately 7 days after HSV-1 corneal infection, BALB/c mice develop tissue-destructive inflammation in the cornea termed herpes stromal keratitis (HSK), as well as periocular skin lesions that are characterized by vesicles, edema, and fur loss. CD4(+) T cells and Th1 cytokines contribute to both the immunopathology in the cornea and the eradication of viral replication in the skin. We demonstrate that disruption of CD40/CD154 signaling does not impact the initial expansion of CD4(+) T cells in the draining lymph nodes, but dramatically reduces the persistence and Th1 polarization of these cells. Despite the reduced Th1 response, CD154(-/-) mice developed HSK and periocular skin disease with similar kinetics and severity (as assessed by clinical examination) as wild-type (WT) mice. However, when the composition of the inflammatory infiltrate was examined by flow cytometric analysis, CD154(-/-) mice exhibited significantly fewer CD4(+) and CD8(+) T cells and neutrophils than WT mice at the peak of HSK. Moreover, CD4(+) T cells from infected corneas of CD154(-/-) mice produced significantly less IFN-gamma than those of WT mice when stimulated with viral Ags in vitro. The IFN-gamma production of cells from infected corneas of WT mice was not affected by addition of anti-CD154 mAb to the stimulation cultures. This suggests that CD154 signaling is required at the inductive phase, but not at the effector phase, of the Th1 response within the infected cornea. We conclude that local disruption of CD40/CD154 signaling is not likely to be a useful therapy for HSK.

Distinctive roles for 2',5'-oligoadenylate synthetases and double-stranded RNA-dependent protein kinase R in the in vivo antiviral effect of an adenoviral vector expressing murine IFN-beta

To evaluate the anti-HSV-1 mechanisms of murine IFN-beta in ocular infection, mice were transduced with an adenoviral vector expressing murine IFN-beta (Ad:IFN-beta). Ocular transduction with Ad:IFN-beta resulted in enhanced survival following infection with HSV-1. The protective effect was associated with a reduction in 1) viral titer, 2) viral gene expression, 3) IFN-gamma levels, and 4) the percentage of CD8(+) T lymphocyte and NK cell infiltration in infected tissue. Expression of IFN-beta resulted in an elevation of the IFN-induced antiviral gene 2',5'-oligoadenylate synthetase (OAS1a) but not dsRNA-dependent protein kinase R (PKR) in the cornea and trigeminal ganglion (TG). Mice deficient in the downstream effector molecule of the OAS pathway, RNase L, were no more sensitive to ocular HSV-1 compared with wild-type controls in the TG based on measurements of viral titer. However, the efficacy of Ad:IFN-beta was transiently lost in the eyes of RNase L mice. By comparison, PKR-deficient mice were more susceptible to ocular HSV-1 infection, and the antiviral efficacy following transduction with Ad:IFN-beta was significantly diminished in the eye and TG. These results suggest that PKR is central in controlling ocular HSV-1 infection in the absence of exogenous IFN, whereas the OAS pathway appears to respond to exogenous IFN, contributing to the establishment of an antiviral environment in a tissue-restricted manner.

Herpes simplex virus 2 virion host shutoff protein interferes with type I interferon production and responsiveness

The herpes simplex virus 2 (HSV-2) virion host shutoff (vhs) protein is a ribonuclease contained in the virion tegument. vhs-deficient mutants of HSV-2 are profoundly attenuated in vivo, and we have previously shown that replication and virulence of vhs-deficient HSV-2 are largely restored to levels of wild-type virus in mice lacking the interferon alpha/beta receptor (IFNalphabetaR(-/-)). This result demonstrated that HSV-2 vhs interferes with the type I IFN response, but whether vhs inhibits production of type I IFN or synthesis or function of key mediators of the IFN-induced antiviral state was not clear. Here we address these questions using primary murine embryonic fibroblasts (MEFs), which produce and respond to IFNalphabeta. The vhs-deficient HSV-2 strain 333d41 replicated similarly to wild-type virus (333 clone SB5) and vhs rescue virus (333d41(R)) after infection of MEFs at high moi, but at low moi, 333d41 replication was severely attenuated, recapitulating the attenuated phenotype of vhs-deficient HSV-2 in vivo. Replication of 333d41 at low moi was restored to levels of wild-type virus in MEFs lacking the IFNalphabeta receptor or when IFNalphabeta was neutralized, thus establishing the IFNalphabeta response as the sole mechanism attenuating vhs-deficient HSV-2 replication in MEFs. MEFs infected with 333d41 produced >50-fold more IFNalphabeta than cells infected with 333 and 333d41(R). Pretreatment of MEFs with type I IFN inhibited replication of 333d41 more than 333 and 333d41(R), indicating that vhs also interferes with activation of the IFNalphabeta-induced antiviral response. We therefore examined vhs interference with PKR and RNase L, two key mediators of the IFNalphabeta response. 333d41 replication was restored to wild-type levels after low moi infection of PKR(-/-) and RNase L(-/-) MEFs, and was not inhibited in PKR(-/-) MEFs pretreated with IFNalpha. Together, these observations indicate that HSV-2 vhs is a broad and potent countermeasure to the IFN-mediated antiviral response in IFN-naïve and -sensitized MEFs.

Innate immunity to herpes simplex virus type 2

Herpes simplex virus type 2 (HSV-2) is responsible for most cases of genital herpes and also can cause fatal disseminated disease in perinatally infected newborns. Sexually transmitted infections initiate in the skin or mucosa and quickly spread into peripheral nerves to establish latency. Innate immunity, the first line of defense during both primary and recurrent infection, is essential during this period of acute infection to limit initial viral replication and to facilitate an appropriate adaptive immune response. The innate immune response consists of a complex multilayered system of mechanical and secreted defenses, immediate chemokine and IFN responses, and rapidly recruited cellular defenses. HSV has devised equally elaborate strategies to evade or interfere with innate immunity. This review summarizes our current understanding of the innate immune responses to HSV-2 and the mechanisms by which HSV-2 can overcome these barriers. Newly emerging links between products of innate responses and the development of adaptive immune responses are also discussed.

Immune defense at the ocular surface

The ocular surface is constantly exposed to a wide array of microorganisms. The ability of the outer ocular system to recognize pathogens as foreign and eliminate them is critical to retain corneal transparency, hence preservation of sight. Therefore, a combination of mechanical, anatomical, and immunological defense mechanisms has evolved to protect the outer eye. These host defense mechanisms are classified as either a native, nonspecific defense or a specifically acquired immunological defense requiring previous exposure to an antigen and the development of specific immunity. Sight-threatening immunopathology with autologous cell damage also can take place after these reactions. This article discusses the innate and acquired corneal elements of the immune defense at the ocular surface. The relative roles of the various factors contributing to prevention of eye infection remain to be fully defined.

Herpes simplex virus type 1 activates murine natural interferon-producing cells through toll-like receptor 9

Natural interferon-producing cells (IPCs) specialize in the production of high levels of type 1 interferons (IFNs) in response to encapsulated DNA and RNA viruses. Here we demonstrate that the secretion of type 1 IFN in response to herpes simplex virus type 1 (HSV-1) in vitro is mediated by the toll-like receptor 9 (TLR9)/MyD88 pathway. Moreover, IPCs produce interleukin-12 (IL-12) in response to HSV-1 in vitro, which is also dependent on TLR9/ MyD88 signaling. Remarkably, though TLR9/MyD88-deficiency abrogates IPC responses to HSV-1 in vitro, mice lacking either MyD88 or TLR9 are capable of controlling HSV-1 replication in vivo after local infection, demonstrating that TLR9- and MyD88-independent pathways in cells other than IPCs can effectively compensate for defective IPC responses to HSV-1.

Interferon-beta suppresses herpes simplex virus type 1 replication in trigeminal ganglion cells through an RNase L-dependent pathway

The induction of an antiviral state by type I interferons (IFN) was evaluated in primary trigeminal ganglion cell cultures using herpes simplex virus type 1 (HSV-1). Cells treated with mouse IFN-beta consistently showed the greatest resistance to HSV-1 infection in comparison to cells treated with IFN-alpha1, IFN-alpha4, IFN-alpha5, IFN-alpha6, or IFN-alpha9. The antiviral efficacy was dose-dependent and correlated with the induction of the IFN-inducible, antiviral genes, 2'-5' oligoadenylate synthetase (OAS) and double-stranded RNA-dependent protein kinase. In trigeminal ganglion cells deficient in the downstream effector molecule of the OAS pathway, RNase L, the antiviral state induced by IFN-beta was lost.

Effect of immunization on herpes simplex virus type 1 latent infection in the trigeminal ganglion

PURPOSE

To quantify and characterize immune protection from herpes simplex virus (HSV) latent infection in mice following corneal challenge.

METHODS

Mice immunized or mock-immunized and boosted in the flank with an HSV replication-deficient mutant were challenged by corneal inoculation with wild type (wt) or thymidine kinase-negative (TK(-)) HSV. At specified times post challenge, trigeminal ganglia were assayed for in vitro reactivation, latent and acute viral load (using quantitative PCR), acute infection, and cellular infiltration (hematoxylin and eosin stained sections).

RESULTS

With wt HSV challenge infection, immunization led to reduced reactivation, significantly less latent and acute viral DNA, and no acute viral replication in ganglia, and rapid infiltration of inflammatory cells. Immunization had little effect on viral load following challenge with replication-conditional TK(-) mutant virus.

CONCLUSION

These results indicate that immune protection from latent HSV infection in mouse trigeminal ganglia following ocular infection can act under these experimental conditions to block acute viral replication in ganglia and is directed to antigenic targets within the ganglia.

Activation and inhibition of virus and interferon: the herpesvirus story

Viral infection of a host leads to induction of an immune system attack against the virus along with a counterattack by the virus against the host. Interferons are highly upregulated upon viral infection and function as key regulators of the host innate defense system. Whereas many RNA viruses are sensitive to the effects of interferon, several of the large DNA viruses are relatively resistant, given their capacity to encode proteins that disarms the host response. The herpesvirus family is a large and diverse family of viruses that infects vertebrates and invertebrates and possesses the ability to remain latent in their host for life. This paper summarizes the relationship between herpesviruses and interferon, including the ability of herpesviruses to induce interferon production, mechanisms by which interferon decreases herpesvirus replication, and strategies of herpesviruses to counteract these mechanisms.

Transient transfection of mouse fibroblasts with type I interferon transgenes provides various degrees of protection against herpes simplex virus infection

Type I interferons (IFN) constitute one of the initial and most potent components of the innate immune response against viral infections. While there is only one IFN-beta gene, there are several IFN-alpha genes whose products act through the same receptor calling into question the role of these gene products against viral infection. The focus of the present study was to compare the anti-viral state of cells transiently transfected with different murine type I IFN transgenes including IFN-alpha1, -alpha4, -alpha5, -alpha6, -alpha9, and IFN-beta. Transfected cells produced biologically active IFN ranging from 6 to 46 units/ml. L929 and 3T12.3 cells transfected with the IFN-beta transgene consistently showed a 2-4 fold reduction in herpes simplex virus type 1 (HSV-1) and HSV-2 viral titers compared with cells transfected with the IFN-alpha transgenes which were much less consistent based on HSV species and cell type. Parallel with the reduction in viral titers, cells transfected with the IFN-beta transgene showed the complete absence or significant reduction in viral immediate early, early, and late gene expression. Collectively, the results suggest that the IFN-beta transgene is superior to IFN-alpha transgenes against HSV infection in vitro in part due to a reduction in viral gene expression. These results indicate events downstream of the type I IFN receptor distinguish between the subtypes of IFN-alpha species relative to the activation of genes ultimately responsible for the establishment of the anti-HSV state.

The antiviral efficacy of the murine alpha-1 interferon transgene against ocular herpes simplex virus type 1 requires the presence of CD4(+), alpha/beta T-cell receptor-positive T lymphocytes with the capacity to produce gamma interferon

Alpha/beta interferons (IFN-alpha/betas) are known to antagonize herpes simplex virus type 1 (HSV-1) infection by directly blocking viral replication and promoting additional innate and adaptive, antiviral immune responses. To further define the relationship between the adaptive immune response and IFN-alpha/beta, the protective effect induced following the topical application of plasmid DNA containing the murine IFN-alpha 1 transgene onto the corneas of wild-type and T-cell-deficient mice was evaluated. Mice homozygous for both the T-cell receptor (TCR) beta- and delta-targeted mutations expressing no alpha beta or gamma delta TCR (alpha beta/gamma delta TCR double knockout [dKO]) treated with the IFN-alpha 1 transgene succumbed to ocular HSV-1 infection at a rate similar to that of alpha beta/gamma delta TCR dKO mice treated with the plasmid vector DNA. Conversely, mice with targeted disruption of the TCR delta chain and expressing no gamma delta TCR(+) cells treated with the IFN-alpha 1 transgene survived the infection to a greater extent than the plasmid vector-treated counterpart and at a level similar to that of wild-type controls treated with the IFN-alpha 1 transgene. By comparison, mice with targeted disruption of the TCR beta chain and expressing no alpha beta TCR(+) cells (alpha beta TCR knockout [KO]) showed no difference upon treatment with the IFN-alpha1 transgene or the plasmid vector control, with 0% survival following HSV-1 infection. Adoptively transferring CD4(+) but not CD8(+) T cells from wild-type but not IFN-gamma-deficient mice reestablished the antiviral efficacy of the IFN-alpha 1 transgene in alpha beta TCR KO mice. Collectively, the results indicate that the protective effect mediated by topical application of a plasmid construct containing the murine IFN-alpha 1 transgene requires the presence of CD4(+) T cells capable of IFN-gamma synthesis.

Differential effect of murine alpha/beta interferon transgenes on antagonization of herpes simplex virus type 1 replication

Alpha/beta interferons (IFN-alpha/beta) are potent, endogenous antiviral cytokines that suppress the replication of RNA and DNA viruses, including herpes simplex virus type 1 (HSV-1). The present study compared the efficacies of IFN-alpha/beta transgenes, including IFN-alpha1, -alpha4, -alpha5, -alpha6, -alpha9, and -beta, against HSV-1 infection. L929 cells transfected with the IFN-alpha/beta transgenes produced similar levels of IFN, as measured by bioassay and enzyme-linked immunosorbent assay. In addition, transfected cells were less susceptible to HSV-1 infection than were cells transfected with a plasmid vector control. The murine IFN-beta plasmid construct exhibited the greatest reduction, while the murine IFN-alpha5 transgene showed a modest inhibitory effect in viral titers recovered from the supernatants of transfected, infected L929 cultures. Consistent with this observation, the IFN-beta transgene antagonized viral transcript levels, including infected cell protein 27, thymidine kinase, and glycoprotein B, to a greater extent than did the IFN-alpha transgenes at 6 to 10 h postinfection as determined by real-time PCR. Cells transfected with the IFN-alpha4, IFN-alpha9, or IFN-beta transgenes showed the greatest reduction in viral protein expression relative to the other transfected cells, which was associated with increased STAT1 expression. The absence of the IFN-responsive protein kinase R (PKR) gene completely abrogated the antiviral induction by all IFN-alpha/beta against HSV-1. In the absence of RNase L, viral yields were increased 10-fold, but the antiviral effect of IFN was either unaffected or enhanced. These results suggest that the predominant IFN-mediated, antiviral pathway during HSV-1 infection taken by IFN-alpha/beta in L929 cells utilizes PKR.