Downregulation of class I major histocompatibility complex surface expression by varicella-zoster virus involves open reading frame 66 protein kinase-dependent and -independent mechanisms

VZV IE4 downregulates cellular surface MHC-I via sequestering it to the Golgi complex

Varicella-zoster virus (VZV) infection downregulates surface major histocompatibility complex class I (MHC-I) expression and retains MHC-I in the Golgi complex of infected cells. However, the underlying mechanism is not fully understood. The VZV IE4 protein is a multifunctional protein that is essential for VZV infection. In this study, the human leucocyte antigen C (HLA-C) protein was identified as a novel cellular factor associated with IE4. Ectopically expressed IE4 co-localizes with HLA-C, sequesters HLA-C to the Golgi complex and downregulates cellular surface MHC-I. VZV, with a mutated Golgi localization signal in IE4, denoted as mutated IE4 (mIE4) VZV, was constructed. In mIE4 VZV-infected cells, the cellular surface MHC-I was restored, and HLA-C was not retained in the Golgi complex. In summary, for the first time, we demonstrate a novel role of VZV IE4 in interfering with the MHC-I presentation pathway, suggesting that it may contribute to the evasion of host antiviral adaptive immunity.

Varicella-zoster virus recapitulates its immune evasive behaviour in matured hiPSC-derived neurospheroids

Varicella-zoster virus (VZV) encephalitis and meningitis are potential central nervous system (CNS) complications following primary VZV infection or reactivation. With Type-I interferon (IFN) signalling being an important first line cellular defence mechanism against VZV infection by the peripheral tissues, we here investigated the triggering of innate immune responses in a human neural-like environment. For this, we established and characterised 5-month matured hiPSC-derived neurospheroids (NSPHs) containing neurons and astrocytes. Subsequently, NSPHs were infected with reporter strains of VZV (VZVeGFP-ORF23) or Sendai virus (SeVeGFP), with the latter serving as an immune-activating positive control. Live cell and immunocytochemical analyses demonstrated VZVeGFP-ORF23 infection throughout the NSPHs, while SeVeGFP infection was limited to the outer NSPH border. Next, NanoString digital transcriptomics revealed that SeVeGFP-infected NSPHs activated a clear Type-I IFN response, while this was not the case in VZVeGFP-ORF23-infected NSPHs. Moreover, the latter displayed a strong suppression of genes related to IFN signalling and antigen presentation, as further demonstrated by suppression of IL-6 and CXCL10 production, failure to upregulate Type-I IFN activated anti-viral proteins (Mx1, IFIT2 and ISG15), as well as reduced expression of CD74, a key-protein in the MHC class II antigen presentation pathway. Finally, even though VZVeGFP-ORF23-infection seems to be immunologically ignored in NSPHs, its presence does result in the formation of stress granules upon long-term infection, as well as disruption of cellular integrity within the infected NSPHs. Concluding, in this study we demonstrate that 5-month matured hiPSC-derived NSPHs display functional innate immune reactivity towards SeV infection, and have the capacity to recapitulate the strong immune evasive behaviour towards VZV.

Varicella Zoster Virus Downregulates Expression of the Nonclassical Antigen Presentation Molecule CD1d

BACKGROUND

The nonclassical antigen presentation molecule CD1d presents lipid antigens to invariant natural killer T (iNKT) cells. Activation of these cells triggers a rapid cytokine response providing an interface between innate and adaptive immune responses. The importance of CD1d and iNKT cells in varicella zoster virus (VZV) infection has been emphasized by clinical reports of individuals with CD1d or iNKT cell deficiencies experiencing severe, disseminated varicella postvaccination.

METHODS

Three strains of VZV (VZV-S, rOka, and VZV rOka-66S) were used to infect Jurkat cells. Flow cytometry of VZV- and mock-infected cells assessed the modulatory impact of VZV on CD1d protein. Infected cell supernatant and transwell co-culture experiments explored the role of soluble factors in VZV-mediated immunomodulation. CD1d transcripts were assessed by reverse-transcription polymerase chain reaction.

RESULTS

Surface and intracellular flow cytometry demonstrated that CD1d was strikingly downregulated by VZV-S and rOka in both infected and VZV antigen-negative cells compared to mock. CD1d downregulation is cell-contact dependent and CD1d transcripts are targeted by VZV. Mechanistic investigations using rOka-66S (unable to express the viral kinase ORF66) implicate this protein in CD1d modulation in infected cells.

CONCLUSIONS

VZV implements multiple mechanisms targeting both CD1d transcript and protein. This provides evidence of VZV interaction with and manipulation of the CD1d-iNKT cell axis.

Neurexin 3 Regulates Synaptic Connections Between Central Amygdala Neurons and Excitable Cells of the Lateral Parabrachial Nucleus in Rats with Varicella Zoster Induced Orofacial Pain

Introduction

Herpes Zoster in humans is the result of varicella zoster virus (VZV) infection. Injecting rats with varicella zoster virus produces pain similar to herpes zoster "shingles" pain in humans. . In a previous study, orofacial pain was induced by injecting the whisker pad of male rats with VZV and the pain response increased after attenuating neurexin 3 (Nrxn3) expression in the central amygdala. Neurons descend from the central amygdala to the lateral parabrachial nucleus and orofacial pain signals ascend to the lateral parabrachial nucleus. GABAergic neurons within the central amygdala regulate pain by inhibiting activity within the lateral parabrachial nucleus. Attenuating Nrxn3 expression in the central amygdala increased GABA release in the lateral parabrachial nucleus suggesting Nrxn3 controls pain by regulating GABA release. Nrxn3 can also control synaptic connections between neurons, and we hypothesized that Nrxn3 knockdown in the central amygdala would reduce the number of GABAergic synaptic connections in the lateral parabrachial nucleus and increase VZV associated pain.

Methods

To test this idea, the number of synaptic connections between GABAergic cells of the central amygdala and excitatory or dynorphin positive neurons within the lateral parabrachial nucleus were quantitated after infusion of a virus expressing synaptophysin. Synaptophysin is a synaptic vesicle protein that labels neuronal synaptic connections. These connections were measured in rats with and without whisker pad injection of VZV and knockdown of Nrxn3 within the central amygdala. Orofacial pain was measured using a place escape avoidance paradigm.

Results

GABAergic synaptic connections were reduced in the lateral parabrachial nucleus after Nrxn3 knockdown. Rats with a reduction in the number of connections had an increase in VZV associated orofacial pain. Immunostaining with the pain marker prodynorphin indicated that the reduction in GABAergic connections was primarily associated with prodynorphin positive neurons.

Discussion

The results suggest Nrxn3 reduces VZV associated orofacial pain, in part, by enhancing synaptic connections between GABA cells of the central amygdala and pain neurons within the lateral parabrachial nucleus.

Defining the role of natural killer cells in COVID-19

Natural killer (NK) cells are critical effectors of antiviral immunity. Researchers have therefore sought to characterize the NK cell response to coronavirus disease 2019 (COVID-19) and the virus that causes it, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The NK cells of patients with severe COVID-19 undergo extensive phenotypic and functional changes. For example, the NK cells from critically ill patients with COVID-19 are highly activated and exhausted, with poor cytotoxic function and cytokine production upon stimulation. The NK cell response to SARS-CoV-2 is also modulated by changes induced in virally infected cells, including the ability of a viral peptide to bind HLA-E, preventing NK cells from receiving inhibitory signals, and the downregulation of major histocompatibility complex class I and ligands for the activating receptor NKG2D. These changes have important implications for the ability of infected cells to escape NK cell killing. The implications of these findings for antibody-dependent NK cell activity in COVID-19 are also reviewed. Despite these advances in the understanding of the NK cell response to SARS-CoV-2, there remain critical gaps in our current understanding and a wealth of avenues for future research on this topic.

Characteristics and expression profiles of MHC class Ⅰ molecules in Carassius auratus

Major histocompatibility complex class Ⅰ (MHC Ⅰ) molecules play a vital role in adaptive immune systems in vertebrates by presenting antigens to effector T cells. Understanding the expression profiling of MHC Ⅰ molecules in fish is essential for improving our knowledge of the relationship between microbial infection and adaptive immunity. In this study, we conducted a comprehensive analysis of MHC Ⅰ gene characteristics in Carassius auratus, an important freshwater aquaculture fish in China that is susceptible to Cyprinid herpesvirus 2 (CyHV-2) infection. We identified approximately 20 MHC Ⅰ genes discussed, including U, Z, and L lineage genes. However, only U and Z lineage proteins were identified in the kidney of Carassius auratus using high pH reversed-phase chromatography and mass spectrometry. The L lineage proteins were either not expressed or present at an extremely low level in the kidneys of Carassius auratus. We also used targeted proteomics to analyze changes in protein MHC Ⅰ molecules abundance in healthy and CyHV-2-infected Carassius auratus. We observed that five MHC Ⅰ molecules were upregulated, and Caau-UFA was downregulated in the diseased group. This study is the first to reveal the expression of MHC Ⅰ molecules at a large scale in Cyprinids, which enhances our understanding of fish adaptive immune systems.

T cell immunity in HSV-1- and VZV-infected neural ganglia

Herpesviruses hijack the MHC class I (MHC I) and class II (MHC II) antigen-presentation pathways to manipulate immune recognition by T cells. First, we illustrate herpes simplex virus-1 (HSV-1) and varicella-zoster virus (VZV) MHC immune evasion strategies. Next, we describe MHC-T cell interactions in HSV-1- and VZV- infected neural ganglia. Although studies on the topic are scarce, and use different models, most reports indicate that neuronal HSV-1 infection is mainly controlled by CD8+ T cells through noncytolytic mechanisms, whereas VZV seems to be largely controlled through CD4+ T cell-specific immune responses. Autologous human stem-cell-derived in vitro models could substantially aid in elucidating these neuroimmune interactions and are fit for studies on both herpesviruses.

Regulation of alphaherpesvirus protein via post-translational phosphorylation

An alphaherpesvirus carries dozens of viral proteins in the envelope, tegument and capsid structure, and each protein plays an indispensable role in virus adsorption, invasion, uncoating and release. After infecting the host, a virus eliminates unfavourable factors via multiple mechanisms to escape or suppress the attack of the host immune system. Post-translational modification of proteins, especially phosphorylation, regulates changes in protein conformation and biological activity through a series of complex mechanisms. Many viruses have evolved mechanisms to leverage host phosphorylation systems to regulate viral protein activity and establish a suitable cellular environment for efficient viral replication and virulence. In this paper, viral protein kinases and the regulation of viral protein function mediated via the phosphorylation of alphaherpesvirus proteins are described. In addition, this paper provides new ideas for further research into the role played by the post-translational modification of viral proteins in the virus life cycle, which will be helpful for understanding the mechanisms of viral infection of a host and may lead to new directions of antiviral treatment.

Downregulation of Cell Surface Major Histocompatibility Complex Class I Expression Is Mediated by the Left-End Transcription Unit of Fowl Adenovirus 9

Major histocompatibility complex class I (MHC-I) molecules play a critical role in the host’s antiviral response by presenting virus-derived antigenic peptides to cytotoxic T lymphocytes (CTLs), enabling the clearance of virus-infected cells. Human adenoviruses evade CTL-mediated cell lysis, in part, by interfering directly with the MHC-I antigen presentation pathway through the expression of E3-19K, which binds both MHC-I and the transporter associated with antigen processing protein and sequestering MHC-I within the endoplasmic reticulum. Fowl adenoviruses have no homologues of E3-19K. Here, we show that representative virus isolates of the species Fowl aviadenovirus C, Fowl aviadenovirus D, and Fowl aviadenovirus E downregulate the cell surface expression of MHC-I in chicken hepatoma cells, resulting in 71%, 11%, and 14% of the baseline expression level, respectively, at 12 h post-infection. Furthermore, this work reports that FAdV-9 downregulates cell surface MHC-I through a minimum of two separate mechanisms—a lysosomal-independent mechanism that requires the presence of the fowl adenovirus early 1 (FE1) transcription unit located within the left terminal genomic region between nts 1 and 6131 and a lysosomal-dependent mechanism that does not require the presence of FE1. These results establish a new functional role for the FE1 transcription unit in immune evasion. These studies provide important new information about the immune evasion of FAdVs and will enhance our understanding of the pathogenesis of inclusion body hepatitis and advance the progress made in next-generation FAdV-based vectors.

Varicella Zoster Virus Impairs Expression of the Nonclassical Major Histocompatibility Complex Class I-Related Gene Protein (MR1)

The antigen presentation molecule MR1 (major histocompatibility complex, class I-related) presents ligands derived from the riboflavin (vitamin B) synthesis pathway, which is not present in mammalian species or viruses, to mucosal-associated invariant T (MAIT) cells. In this study, we demonstrate that varicella zoster virus (VZV) profoundly suppresses MR1 expression. We show that VZV targets the intracellular reservoir of immature MR1 for degradation, while preexisting, ligand-bound cell surface MR1 is protected from such targeting, thereby highlighting an intricate temporal relationship between infection and ligand availability. We also identify VZV open reading frame (ORF) 66 as functioning to suppress MR1 expression when this viral protein is expressed during transient transfection, but this is not apparent during infection with a VZV mutant virus lacking ORF66 expression. This indicates that VZV is likely to encode multiple viral genes that target MR1. Overall, we identify an immunomodulatory function of VZV whereby infection suppresses the MR1 biosynthesis pathway.

Evasion of the Cell-Mediated Immune Response by Alphaherpesviruses

Alphaherpesviruses cause various diseases and establish life-long latent infections in humans and animals. These viruses encode multiple viral proteins and miRNAs to evade the host immune response, including both innate and adaptive immunity. Alphaherpesviruses evolved highly advanced immune evasion strategies to be able to replicate efficiently in vivo and produce latent infections with recurrent outbreaks. This review describes the immune evasion strategies of alphaherpesviruses, especially against cytotoxic host immune responses. Considering these strategies, it is important to evaluate whether the immune evasion mechanisms in cell cultures are applicable to viral propagation and pathogenicity in vivo. This review focuses on cytotoxic T lymphocytes (CTLs), natural killer cells (NK cells), and natural killer T cells (NKT cells), which are representative immune cells that directly damage virus-infected cells. Since these immune cells recognize the ligands expressed on their target cells via specific activating and/or inhibitory receptors, alphaherpesviruses make several ligands that may be targets for immune evasion. In addition, alphaherpesviruses suppress the infiltration of CTLs by downregulating the expression of chemokines at infection sites in vivo. Elucidation of the alphaherpesvirus immune evasion mechanisms is essential for the development of new antiviral therapies and vaccines.

Insights into the pathogenesis of varicella viruses

Purpose of review

Varicella zoster virus (VZV) is a highly contagious, neurotropic alpha herpes virus that causes varicella (chickenpox). VZV establishes lifelong latency in the sensory ganglia from which it can reactivate to induce herpes zoster (HZ), a painful disease that primarily affects older individuals and those who are immune-suppressed. Given that VZV infection is highly specific to humans, developing a reliable in vivo model that recapitulates the hallmarks of VZV infection has been challenging. Simian Varicella Virus (SVV) infection in nonhuman primates reproduces the cardinal features of VZV infections in humans and allows the study of varicella virus pathogenesis in the natural host. In this review, we summarize our current knowledge about genomic and virion structure of varicelloviruses as well as viral pathogenesis and antiviral immune responses during acute infection, latency and reactivation. We also examine the immune evasion mechanisms developed by varicelloviruses to escape the host immune responses and the current vaccines available for protecting individuals against chickenpox and herpes zoster.

Recent findings

Data from recent studies suggest that infected T cells are important for viral dissemination to the cutaneous sites of infection as well as site of latency and that a viral latency-associated transcript might play a role in the transition from lytic infection to latency and then reactivation.

Summary

Recent studies have provided exciting insights into mechanisms of varicelloviruses pathogenesis such as the critical role of T cells in VZV/SVV dissemination from the respiratory mucosa to the skin and the sensory ganglia; the ability of VZV/SVV to interfere with host defense; and the identification of VLT transcripts in latently infected ganglia. However, our understanding of these phenomena remains poorly understood. Therefore, it is critical that we continue to investigate host-pathogen interactions during varicelloviruses infection. These studies will lead to a deeper understanding of VZV biology as well as novel aspects of cell biology.

Manipulation of the Innate Immune Response by Varicella Zoster Virus

Varicella zoster virus (VZV) is the causative agent of chickenpox (varicella) and shingles (herpes zoster). VZV and other members of the herpesvirus family are distinguished by their ability to establish a latent infection, with the potential to reactivate and spread virus to other susceptible individuals. This lifelong relationship continually subjects VZV to the host immune system and as such VZV has evolved a plethora of strategies to evade and manipulate the immune response. This review will focus on our current understanding of the innate anti-viral control mechanisms faced by VZV. We will also discuss the diverse array of strategies employed by VZV to regulate these innate immune responses and highlight new knowledge on the interactions between VZV and human innate immune cells.

Varicella-Zoster Virus and the Enteric Nervous System

Varicella zoster virus (VZV) infects and becomes latent in sensory, enteric, and other autonomic neurons during the viremia of varicella. Reactivation of VZV in neurons that project to the skin causes the rash of zoster; however, reactivation of VZV in enteric neurons can cause a painful gastrointestinal disorder ("enteric zoster") without cutaneous manifestations. Detection of VZV DNA in saliva of patients with gastrointestinal symptoms may suggest enteric zoster. This diagnosis is reinforced by observing a response to antiviral therapy and can be confirmed by detecting VZV gene products in intestinal mucosal biopsies. We developed an in vivo guinea pig model that may be useful in studies of VZV latency and reactivation. VZV-infected lymphocytes are used to induce latent infection in sensory and enteric neurons; evidence suggests that exosomes and stimulator of interferon genes (STING) may, by preventing proliferation play roles in the establishment of neuronal latency.

Attenuation of Simian Varicella Virus Infection by Enhanced Green Fluorescent Protein in Rhesus Macaques

Simian varicella virus (SVV), the primate counterpart of varicella-zoster virus, causes varicella (chickenpox), establishes latency in ganglia, and reactivates to produce zoster. We previously demonstrated that a recombinant SVV expressing enhanced green fluorescent protein (rSVV.eGFP) is slightly attenuated both in culture and in infected monkeys. Here, we generated two additional recombinant SVVs to visualize infected cells in vitro and in vivo One harbors eGFP fused to the N terminus of open reading frame 9 (ORF9) (rSVV.eGFP-2a-ORF9), and another harbors eGFP fused to the C terminus of ORF66 (rSVV.eGFP-ORF66). Both recombinant viruses efficiently expressed eGFP in cultured cells. Both recombinant SVV infections in culture were comparable to that of wild-type SVV (SVV.wt). Unlike SVV.wt, eGFP-tagged SVV did not replicate in rhesus cells in culture. Intratracheal (i.t.) or i.t. plus intravenous (i.v.) inoculation of rhesus macaques with these new eGFP-tagged viruses resulted in low viremia without varicella rash, although SVV DNA was abundant in bronchoalveolar lavage (BAL) fluid at 10 days postinoculation (dpi). SVV DNA was also found in trigeminal ganglia of one monkey inoculated with rSVV.eGFP-ORF66. Intriguingly, a humoral response to both SVV and eGFP was observed. In addition, monkeys inoculated with the eGFP-expressing viruses were protected from superinfection with SVV.wt, suggesting that the monkeys had mounted an efficient immune response. Together, our results show that eGFP expression could be responsible for their reduced pathogenesis.IMPORTANCE SVV infection in nonhuman primates has served as an extremely useful animal model to study varicella-zoster virus (VZV) pathogenesis. eGFP-tagged viruses are a great tool to investigate their pathogenesis. We constructed and tested two new recombinant SVVs with eGFP inserted into two different locations in the SVV genome. Both recombinant SVVs showed robust replication in culture but reduced viremia compared to that with SVV.wt during primary infection in rhesus macaques. Our results indicate that conclusions on eGFP-tagged viruses based on in vitro results should be handled with care, since eGFP expression could result in attenuation of the virus.

Simian varicella virus inhibits the interferon gamma signalling pathway

The alphaherpesvirus simian varicella virus (SVV) causes varicella and zoster in nonhuman primates. Herpesviruses evolved elaborate mechanisms to escape host immunity, but the immune evasion strategies employed by SVV remain ill-defined. We analysed whether SVV impairs the cellular response to key antiviral cytokine interferon-γ (IFNγ). SVV infection inhibited the expression of IFNγ-induced genes like C-X-C motif chemokine 10 and interferon regulatory factor 1. Phosphorylation and nuclear translocation of the signal transducer and activator of transcription 1 (STAT1) was blocked in SVV-infected cells, which did not involve cellular and viral phosphatases. SVV infection did not downregulate IFNγ receptor α and β chain expression on the cell surface. Instead, STAT1, Janus tyrosine kinases 1 (JAK1) and JAK2 protein levels were significantly decreased in SVV-infected cells. Collectively, these results demonstrate that SVV targets three proteins in the IFNγ signal transduction pathway to escape the antiviral effects of IFNγ.

Sex differences underlying orofacial varicella zoster associated pain in rats

BACKGROUND

Most people are initially infected with varicella zoster virus (VZV) at a young age and this infection results in chickenpox. VZV then becomes latent and reactivates later in life resulting in herpes zoster (HZ) or "shingles". Often VZV infects neurons of the trigeminal ganglia to cause ocular problems, orofacial disease and occasionally a chronic pain condition termed post-herpetic neuralgia (PHN). To date, no model has been developed to study orofacial pain related to varicella zoster. Importantly, the incidence of zoster associated pain and PHN is known to be higher in women, although reasons for this sex difference remain unclear. Prior to this work, no animal model was available to study these sex-differences. Our goal was to develop an orofacial animal model for zoster associated pain which could be utilized to study the mechanisms contributing to this sex difference.

METHODS

To develop this model VZV was injected into the whisker pad of rats resulting in IE62 protein expression in the trigeminal ganglia; IE62 is an immediate early gene in the VZV replication program.

RESULTS

Similar to PHN patients, rats showed retraction of neurites after VZV infection. Treatment of rats with gabapentin, an agent often used to combat PHN, ameliorated the pain response after whisker pad injection. Aversive behavior was significantly greater for up to 7 weeks in VZV injected rats over control inoculated rats. Sex differences were also seen such that ovariectomized and intact female rats given the lower dose of VZV showed a longer affective response than male rats. The phase of the estrous cycle also affected the aversive response suggesting a role for sex steroids in modulating VZV pain.

CONCLUSIONS

These results suggest that this rat model can be utilized to study the mechanisms of 1) orofacial zoster associated pain and 2) the sex differences underlying zoster associated pain.

Vaccination Targeting Native Receptors to Enhance the Function and Proliferation of Chimeric Antigen Receptor (CAR)-Modified T Cells

Purpose: The multiple mechanisms used by solid tumors to suppress tumor-specific immune responses are a major barrier to the success of adoptively transferred tumor-specific T cells. As viruses induce potent innate and adaptive immune responses, we hypothesized that the immunogenicity of viruses could be harnessed for the treatment of solid tumors if virus-specific T cells (VST) were modified with tumor-specific chimeric antigen receptors (CAR). We tested this hypothesis using VZV-specific T cells (VZVST) expressing a CAR for GD2, a disialoganglioside expressed on neuroblastoma and certain other tumors, so that the live-attenuated VZV vaccine could be used for in vivo stimulation.Experimental Design: We generated GMP-compliant, GD2.CAR-modified VZVSTs from healthy donors and cancer patients by stimulation of peripheral blood mononuclear cells with overlapping peptide libraries spanning selected VZV antigens, then tested their ability to recognize and kill GD2- and VZV antigen-expressing target cells.Results: Our choice of VZV antigens was validated by the observation that T cells specific for these antigens expanded in vivo after VZV vaccination. VZVSTs secreted cytokines in response to VZV antigens, killed VZV-infected target cells and limited infectious virus spread in autologous fibroblasts. However, while GD2.CAR-modified VZVSTs killed neuroblastoma cell lines on their first encounter, they failed to control tumor cells in subsequent cocultures. Despite this CAR-specific dysfunction, CAR-VZVSTs retained functional specificity for VZV antigens via their TCRs and GD2.CAR function was partially rescued by stimulation through the TCR or exposure to dendritic cell supernatants.Conclusions: Vaccination via the TCR may provide a means to reactivate CAR-T cells rendered dysfunctional by the tumor microenvironment (NCT01953900). Clin Cancer Res; 23(14); 3499-509. ©2017 AACR.

Clinical and immunological assessment of therapeutic immunization with a subunit vaccine for recurrent ocular canine herpesvirus-1 infection in dogs

Latent canine herpesvirus-1 (CHV-1) infections are common in domestic dogs and reactivation of latent virus may be associated with recurrent ocular disease. The objectives of the present study were to evaluate the ability of a subunit CHV-1 vaccine to stimulate peripheral CHV-1 specific immunity and prevent recurrent CHV-1 ocular disease and viral shedding. Mature dogs with experimentally-induced latent CHV-1 infection received a 2-dose CHV-1 vaccine series. Recurrent ocular CHV-1 infection was induced by corticosteroid administration in the prevaccinal, short-term postvaccinal (2 weeks post-vaccination), and long-term postvacccinal (34 weeks post-vaccination) periods. Immunological, virological, and clinical parameters were evaluated during each study period. Quantitative assessment of peripheral immunity included lymphocyte immunophenotyping, proliferation response, and interferon-γ production; and CHV-1 virus neutralizing antibody production. In the present study, vaccination did not prevent development of ocular disease and viral shedding; however, there was a significant decrease in clinical ocular disease scores in the short-term postvaccinal period. Significant alterations in peripheral immunity detected in the dogs during the short-term and long-term postvaccinal periods included increased T and B lymphocyte subpopulation percentage distributions, increased lymphocyte expression of major histocompatibility complex class I and II, increased CHV-1 virus neutralizing antibody titers, decreased lymphocyte proliferation, and decreased interferon-γ production. Vaccination of latently infected mature dogs with the selected subunit CHV-1 vaccine was not effective in preventing recurrent ocular CHV-1 infection and viral shedding induced by corticosteroid administration. The vaccine did induce long-term CHV-1 specific immunity and may decrease the severity of clinical ocular disease in the immediate postvaccinal period.

Modulation of host CD59 expression by varicella-zoster virus in human xenografts in vivo

Varicella-zoster virus (VZV) is the causative agent of both chickenpox (varicella) and shingles (zoster). VZV survives host defenses, even with an intact immune system, and disseminates in the host before causing disease. To date, several diverse immunomodulatory strategies used by VZV to undermine host immunity have been identified; however, few studies have addressed the complement evasion strategies used by this virus. Here, we show that expression of CD59, which is a key member of host regulators of complement activation (RCA), is significantly upregulated in response to VZV infection in human T cells and dorsal root ganglia (DRG) but not in human skin xenografts in SCID-hu mice in vivo. This is the first report demonstrating that VZV infection upregulates host CD59 expression in a tissue-specific manner in vivo, which may aid VZV in complement evasion and pathogenesis.

Insights into the function of tegument proteins from the varicella zoster virus

Chickenpox (varicella) is caused by primary infection with varicella zoster virus (VZV), which can establish long-term latency in the host ganglion. Once reactivated, the virus can cause shingles (zoster) in the host. VZV has a typical herpesvirus virion structure consisting of an inner DNA core, a capsid, a tegument, and an outer envelope. The tegument is an amorphous layer enclosed between the nucleocapsid and the envelope, which contains a variety of proteins. However, the types and functions of VZV tegument proteins have not yet been completely determined. In this review, we describe the current knowledge on the multiple roles played by VZV tegument proteins during viral infection. Moreover, we discuss the VZV tegument protein-protein interactions and their impact on viral tissue tropism in SCID-hu mice. This will help us develop a better understanding of how the tegument proteins aid viral DNA replication, evasion of host immune response, and pathogenesis.

The ORF61 Protein Encoded by Simian Varicella Virus and Varicella-Zoster Virus Inhibits NF-κB Signaling by Interfering with IκBα Degradation

Varicella-zoster virus (VZV) causes chickenpox upon primary infection and establishes latency in ganglia. Reactivation from latency causes herpes zoster, which may be complicated by postherpetic neuralgia. Innate immunity mediated by interferon and proinflammatory cytokines represents the first line of immune defense upon infection and reactivation. VZV is known to interfere with multiple innate immune signaling pathways, including the central transcription factor NF-κB. However, the role of these inhibitory mechanisms in vivo is unknown. Simian varicella virus (SVV) infection of rhesus macaques recapitulates key aspects of VZV pathogenesis, and this model thus permits examination of the role of immune evasion mechanisms in vivo. Here, we compare SVV and VZV with respect to interference with NF-κB activation. We demonstrate that both viruses prevent ubiquitination of the NF-κB inhibitor IκBα, whereas SVV additionally prevents IκBα phosphorylation. We show that the ORF61 proteins of VZV and SVV are sufficient to prevent IκBα ubiquitination upon ectopic expression. We further demonstrate that SVV ORF61 interacts with β-TrCP, a subunit of the SCF ubiquitin ligase complex that mediates the degradation of IκBα. This interaction seems to inactivate SCF-mediated protein degradation in general, since the unrelated β-TrCP target Snail is also stabilized by ORF61. In addition to ORF61, SVV seems to encode additional inhibitors of the NF-κB pathway, since SVV with ORF61 deleted still prevented IκBα phosphorylation and degradation. Taken together, our data demonstrate that SVV interferes with tumor necrosis factor alpha (TNF-α)-induced NF-κB activation at multiple levels, which is consistent with the importance of these countermechanisms for varicella virus infection.

IMPORTANCE

The role of innate immunity during the establishment of primary infection, latency, and reactivation by varicella-zoster virus (VZV) is incompletely understood. Since infection of rhesus macaques by simian varicella virus (SVV) is used as an animal model of VZV infection, we characterized the molecular mechanism by which SVV interferes with innate immune activation. Specifically, we studied how SVV prevents activation of the transcription factor NF-κB, a central factor in eliciting proinflammatory responses. The identification of molecular mechanisms that counteract innate immunity might ultimately lead to better vaccines and treatments for VZV, since overcoming these mechanisms, either by small-molecule inhibition or by genetic modification of vaccine strains, is expected to reduce the pathogenic potential of VZV. Moreover, using SVV infection of rhesus macaques, it will be possible to study how increasing the vulnerability of varicella viruses to innate immunity will impact viral pathogenesis.

An in vitro model of latency and reactivation of varicella zoster virus in human stem cell-derived neurons

Varicella zoster virus (VZV) latency in sensory and autonomic neurons has remained enigmatic and difficult to study, and experimental reactivation has not yet been achieved. We have previously shown that human embryonic stem cell (hESC)-derived neurons are permissive to a productive and spreading VZV infection. We now demonstrate that hESC-derived neurons can also host a persistent non-productive infection lasting for weeks which can subsequently be reactivated by multiple experimental stimuli. Quiescent infections were established by exposing neurons to low titer cell-free VZV either by using acyclovir or by infection of axons in compartmented microfluidic chambers without acyclovir. VZV DNA and low levels of viral transcription were detectable by qPCR for up to seven weeks. Quiescently-infected human neuronal cultures were induced to undergo renewed viral gene and protein expression by growth factor removal or by inhibition of PI3-Kinase activity. Strikingly, incubation of cultures induced to reactivate at a lower temperature (34°C) resulted in enhanced VZV reactivation, resulting in spreading, productive infections. Comparison of VZV genome transcription in quiescently-infected to productively-infected neurons using RNASeq revealed preferential transcription from specific genome regions, especially the duplicated regions. These experiments establish a powerful new system for modeling the VZV latent state, and reveal a potential role for temperature in VZV reactivation and disease.

Most adults worldwide harbor latent VZV in their ganglia, and reactivation from it causes herpes zoster. This painful disease is frequently complicated by long-term pain, neurological sequelae, or vision loss that require improved prevention and treatment strategies. Study of VZV latency and reactivation has been severely hampered by the inability to reproduce a persistent state in vitro or in vivo that can be experimentally reactivated. Our study establishes a system using human neurons derived from embryonic stem cells where multiple stimuli can induce reactivation from long term experimental latency. A potential role for temperature in VZV reactivation has been revealed with this system, which can now be used to study the latent/lytic switch of VZV for the first time.

Varicella-Zoster Virus and Herpes Simplex Virus 1 Differentially Modulate NKG2D Ligand Expression during Productive Infection

Natural killer (NK) cell-deficient patients are particularly susceptible to severe infection with herpesviruses, especially varicella-zoster virus (VZV) and herpes simplex virus 1 (HSV-1). The critical role that NK cells play in controlling these infections denotes an intricate struggle for dominance between virus and NK cell antiviral immunity; however, research in this area has remained surprisingly limited. Our study addressed this absence of knowledge and found that infection with VZV was not associated with enhanced NK cell activation, suggesting that the virus uses specific mechanisms to limit NK cell activity. Analysis of viral regulation of ligands for NKG2D, a potent activating receptor ubiquitously expressed on NK cells, revealed that VZV differentially modulates expression of the NKG2D ligands MICA, ULBP2, and ULBP3 by upregulating MICA expression while reducing ULBP2 and ULBP3 expression on the surface of infected cells. Despite being closely related to VZV, infection with HSV-1 produced a remarkably different effect on NKG2D ligand expression. A significant decrease in MICA, ULBP2, and ULBP3 was observed with HSV-1 infection at a total cellular protein level, as well as on the cell surface. We also demonstrate that HSV-1 differentially regulates expression of an additional NKG2D ligand, ULBP1, by reducing cell surface expression while total protein levels are unchanged. Our findings illustrate both a striking point of difference between two closely related alphaherpesviruses, as well as suggest a powerful capacity for VZV and HSV-1 to evade antiviral NK cell activity through novel modulation of NKG2D ligand expression.

IMPORTANCE

Patients with deficiencies in NK cell function experience an extreme susceptibility to infection with herpesviruses, in particular, VZV and HSV-1. Despite this striking correlation, research into understanding how these two alphaherpesviruses interact with NK cells is surprisingly limited. Through examination of viral regulation of ligands to the activating NK cell receptor NKG2D, we reveal patterns of modulation by VZV, which were unexpectedly varied in response to regulation by HSV-1 infection. Our study begins to unravel the undoubtedly complex interactions that occur between NK cells and alphaherpesvirus infection by providing novel insights into how VZV and HSV-1 manipulate NKG2D ligand expression to modulate NK cell activity, while also illuminating a distinct variation between two closely related alphaherpesviruses.

Varicella Viruses Inhibit Interferon-Stimulated JAK-STAT Signaling through Multiple Mechanisms

Varicella zoster virus (VZV) causes chickenpox in humans and, subsequently, establishes latency in the sensory ganglia from where it reactivates to cause herpes zoster. Infection of rhesus macaques with simian varicella virus (SVV) recapitulates VZV pathogenesis in humans thus representing a suitable animal model for VZV infection. While the type I interferon (IFN) response has been shown to affect VZV replication, the virus employs counter mechanisms to prevent the induction of anti-viral IFN stimulated genes (ISG). Here, we demonstrate that SVV inhibits type I IFN-activated signal transduction via the JAK-STAT pathway. SVV-infected rhesus fibroblasts were refractory to IFN stimulation displaying reduced protein levels of IRF9 and lacking STAT2 phosphorylation. Since previous work implicated involvement of the VZV immediate early gene product ORF63 in preventing ISG-induction we studied the role of SVV ORF63 in generating resistance to IFN treatment. Interestingly, SVV ORF63 did not affect STAT2 phosphorylation but caused IRF9 degradation in a proteasome-dependent manner, suggesting that SVV employs multiple mechanisms to counteract the effect of IFN. Control of SVV ORF63 protein levels via fusion to a dihydrofolate reductase (DHFR)-degradation domain additionally confirmed its requirement for viral replication. Our results also show a prominent reduction of IRF9 and inhibition of STAT2 phosphorylation in VZV-infected cells. In addition, cells expressing VZV ORF63 blocked IFN-stimulation and displayed reduced levels of the IRF9 protein. Taken together, our data suggest that varicella ORF63 prevents ISG-induction both directly via IRF9 degradation and indirectly via transcriptional control of viral proteins that interfere with STAT2 phosphorylation. SVV and VZV thus encode multiple viral gene products that tightly control IFN-induced anti-viral responses.

In this manuscript we demonstrate that the immediate early protein ORF63 encoded by varicella zoster virus (VZV) and simian varicella virus (SVV) interferes with interferon type I-mediated activation of JAK-STAT signaling and thereby inhibits the expression of interferon stimulated genes. ORF63 blocks this pathway by degrading IRF9, which plays a central role in JAK-STAT signaling. In addition, both viruses code for immune evasion mechanisms affecting the JAK-STAT pathway upstream of IRF9, which results in the inhibition of STAT2 phosphorylation. By fusing a degradation domain derived from dihydrofolate reductase (DHFR) to ORF63 we further demonstrate that this protein is essential for SVV growth and gene expression, indicating that ORF63 also affects IFN-signaling indirectly by regulating the expression of other immune evasion genes.

Dendritic cells as Achilles' heel and Trojan horse during varicella zoster virus infection

Varicella zoster virus (VZV), a human alphaherpesvirus, causes varicella and subsequently establishes latency within sensory nerve ganglia. Later in life VZV can reactivate to cause herpes zoster. A reduced frequency of VZV-specific T cells is strongly associated with herpes zoster illustrating that these immune cells are central to control latency. Dendritic cells (DCs) are required for the generation of VZV-specific T cells. However, DCs can also be infected in vitro and in vivo allowing VZV to evade the antiviral immune response. Thus, DCs represent the immune systems' Achilles heel. Uniquely among the human herpesviruses, VZV infects both DCs and T cells, and exploits both as Trojan horses. During primary infection VZV-infected DCs traffic to the draining lymph nodes and tonsils, where the virus is transferred to T cells. VZV-infected T cells subsequently spread infection throughout the body to give the typical varicella skin rash. The delicate interplay between VZV and DCs and its consequences for viral immune evasion and viral dissemination will be discussed in this article.

Viral inhibition of the transporter associated with antigen processing (TAP): a striking example of functional convergent evolution

Herpesviruses are large DNA viruses that are highly abundant within their host populations. Even in the presence of a healthy immune system, these viruses manage to cause lifelong infections. This persistence is partially mediated by the virus entering latency, a phase of infection characterized by limited viral protein expression. Moreover, herpesviruses have devoted a significant part of their coding capacity to immune evasion strategies. It is believed that the close coexistence of herpesviruses and their hosts has resulted in the evolution of viral proteins that specifically attack multiple arms of the host immune system. Cytotoxic T lymphocytes (CTLs) play an important role in antiviral immunity. CTLs recognize their target through viral peptides presented in the context of MHC molecules at the cell surface. Every herpesvirus studied to date encodes multiple immune evasion molecules that effectively interfere with specific steps of the MHC class I antigen presentation pathway. The transporter associated with antigen processing (TAP) plays a key role in the loading of viral peptides onto MHC class I molecules. This is reflected by the numerous ways herpesviruses have developed to block TAP function. In this review, we describe the characteristics and mechanisms of action of all known virus-encoded TAP inhibitors. Orthologs of these proteins encoded by related viruses are identified, and the conservation of TAP inhibition is discussed. A phylogenetic analysis of members of the family Herpesviridae is included to study the origin of these molecules. In addition, we discuss the characteristics of the first TAP inhibitor identified outside the herpesvirus family, namely, in cowpox virus. The strategies of TAP inhibition employed by viruses are very distinct and are likely to have been acquired independently during evolution. These findings and the recent discovery of a non-herpesvirus TAP inhibitor represent a striking example of functional convergent evolution.

Viral immune evasion: Lessons in MHC class I antigen presentation

The MHC class I antigen presentation pathway enables cells infected with intracellular pathogens to signal the presence of the invader to the immune system. Cytotoxic T lymphocytes are able to eliminate the infected cells through recognition of pathogen-derived peptides presented by MHC class I molecules at the cell surface. In the course of evolution, many viruses have acquired inhibitors that target essential stages of the MHC class I antigen presentation pathway. Studies on these immune evasion proteins reveal fascinating strategies used by viruses to elude the immune system. Viral immunoevasins also constitute great research tools that facilitate functional studies on the MHC class I antigen presentation pathway, allowing the investigation of less well understood routes, such as TAP-independent antigen presentation and cross-presentation of exogenous proteins. Viral immunoevasins have also helped to unravel more general cellular processes. For instance, basic principles of ER-associated protein degradation via the ubiquitin-proteasome pathway have been resolved using virus-induced degradation of MHC class I as a model. This review highlights how viral immunoevasins have increased our understanding of MHC class I-restricted antigen presentation.

Neuronal changes induced by Varicella Zoster Virus in a rat model of postherpetic neuralgia

A significant fraction of patients with herpes zoster, caused by Varicella Zoster Virus (VZV), experience chronic pain termed postherpetic neuralgia (PHN). VZV-inoculated rats develop prolonged nocifensive behaviors and serve as a model of PHN. We demonstrate that primary rat cultures show a post-entry block for VZV replication, suggesting the rat is not fully permissive. However, footpads of VZV infected animals show reduced peripheral innervation and innervating dorsal root ganglia (DRG) contained VZV DNA and transcripts of candidate immediate early and early genes. The VZV-infected DRG showed changes in host gene expression patterns, with 84 up-regulated and 116 down-regulated genes seen in gene array studies. qRT-PCR validated the modulation of nociception-associated genes Ntrk2, Trpv1, and Calca (CGRP). The data suggests that VZV inoculation of the rat results in a single round, incomplete infection that is sufficient to induce pain behaviors, and this involves infection of and changes induced in neuronal populations.

Equine Herpesvirus 1 Multiply Inserted Transmembrane Protein pUL43 Cooperates with pUL56 in Downregulation of Cell Surface Major Histocompatibility Complex Class I

Herpesviruses have evolved an array of strategies to counteract antigen presentation by major histocompatibility complex class I (MHC-I). Previously, we identified pUL56 of equine herpesvirus 1 (EHV-1) as one major determinant of the downregulation of cell surface MHC-I (G. Ma, S. Feineis, N. Osterrieder, and G. R. Van de Walle, J. Virol. 86:3554-3563, 2012, http://dx.doi.org/10.1128/JVI.06994-11; T. Huang, M. J. Lehmann, A. Said, G. Ma, and N. Osterrieder, J. Virol. 88:12802-12815, 2014, http://dx.doi.org/10.1128/JVI.02079-14). Since pUL56 was able to exert its function only in the context of virus infection, we hypothesized that pUL56 cooperates with another viral protein. Here, we generated and screened a series of EHV-1 single-gene deletion mutants and found that the pUL43 orthologue was required for downregulation of cell surface MHC-I expression at the same time of infection as when pUL56 exerts its function. We demonstrate that the absence of pUL43 was not deleterious to virus growth and that expression of pUL43 was detectable from 2 h postinfection (p.i.) but decreased after 8 h p.i. due to lysosomal degradation. pUL43 localized within Golgi vesicles and required a unique hydrophilic N-terminal domain to function properly. Finally, coexpression of pUL43 and pUL56 in transfected cells reduced the cell surface expression of MHC-I. This process was dependent on PPxY motifs present in pUL56, suggesting that late domains are required for pUL43- and pUL56-dependent sorting of MHC class I for lysosomal degradation.

IMPORTANCE

We describe here that the poorly characterized herpesviral protein pUL43 is involved in downregulation of cell surface MHC-I. pUL43 is an early protein and degraded in lysosomes. pUL43 resides in the Golgi vesicles and needs an intact N terminus to induce MHC-I downregulation in infected cells. Importantly, pUL43 and pUL56 cooperate to reduce MHC-I expression on the surface of transfected cells. Our results suggest a model for MHC-I downregulation in which late domains in pUL56 are required for the rerouting of vesicles containing MHC-I, pUL56, and pUL43 to the lysosomal compartment.

A comparison of herpes simplex virus type 1 and varicella-zoster virus latency and reactivation

Herpes simplex virus type 1 (HSV-1; human herpesvirus 1) and varicella-zoster virus (VZV; human herpesvirus 3) are human neurotropic alphaherpesviruses that cause lifelong infections in ganglia. Following primary infection and establishment of latency, HSV-1 reactivation typically results in herpes labialis (cold sores), but can occur frequently elsewhere on the body at the site of primary infection (e.g. whitlow), particularly at the genitals. Rarely, HSV-1 reactivation can cause encephalitis; however, a third of the cases of HSV-1 encephalitis are associated with HSV-1 primary infection. Primary VZV infection causes varicella (chickenpox) following which latent virus may reactivate decades later to produce herpes zoster (shingles), as well as an increasingly recognized number of subacute, acute and chronic neurological conditions. Following primary infection, both viruses establish a latent infection in neuronal cells in human peripheral ganglia. However, the detailed mechanisms of viral latency and reactivation have yet to be unravelled. In both cases latent viral DNA exists in an 'end-less' state where the ends of the virus genome are joined to form structures consistent with unit length episomes and concatemers, from which viral gene transcription is restricted. In latently infected ganglia, the most abundantly detected HSV-1 RNAs are the spliced products originating from the primary latency associated transcript (LAT). This primary LAT is an 8.3 kb unstable transcript from which two stable (1.5 and 2.0 kb) introns are spliced. Transcripts mapping to 12 VZV genes have been detected in human ganglia removed at autopsy; however, it is difficult to ascribe these as transcripts present during latent infection as early-stage virus reactivation may have transpired in the post-mortem time period in the ganglia. Nonetheless, low-level transcription of VZV ORF63 has been repeatedly detected in multiple ganglia removed as close to death as possible. There is increasing evidence that HSV-1 and VZV latency is epigenetically regulated. In vitro models that permit pathway analysis and identification of both epigenetic modulations and global transcriptional mechanisms of HSV-1 and VZV latency hold much promise for our future understanding in this complex area. This review summarizes the molecular biology of HSV-1 and VZV latency and reactivation, and also presents future directions for study.

Pathogenesis of varicelloviruses in primates

Varicelloviruses in primates comprise the prototypic human varicella-zoster virus (VZV) and its non-human primate homologue, simian varicella virus (SVV). Both viruses cause varicella as a primary infection, establish latency in ganglionic neurons and reactivate later in life to cause herpes zoster in their respective hosts. VZV is endemic worldwide and, although varicella is usually a benign disease in childhood, VZV reactivation is a significant cause of neurological disease in the elderly and in immunocompromised individuals. The pathogenesis of VZV infection remains ill-defined, mostly due to the species restriction of VZV that impedes studies in experimental animal models. SVV infection of non-human primates parallels virological, clinical, pathological and immunological features of human VZV infection, thereby providing an excellent model to study the pathogenesis of varicella and herpes zoster in its natural host. In this review, we discuss recent studies that provided novel insight in both the virus and host factors involved in the three elementary stages of Varicellovirus infection in primates: primary infection, latency and reactivation.

Equid herpesvirus 1 (EHV1) infection of equine mesenchymal stem cells induces a pUL56-dependent downregulation of select cell surface markers

Equid herpesvirus 1 (EHV1) is an ubiquitous alphaherpesvirus that can cause respiratory disease, abortion and central nervous disorders. EHV1 is known to infect a variety of different cell types in vitro, but its tropism for cultured primary equine mesenchymal stem cells (MSC) has never been explored. We report that equine MSC were highly permissive for EHV1 and supported lytic replication of the virus in vitro. Interestingly, we observed that an infection of MSC with EHV1 resulted in a consistent downregulation of cell surface molecules CD29 (β1-integrin), CD105 (endoglin), major histocompatibility complex type I (MHCI) and a variable downregulation of CD172a. In contrast, expression of CD44 and CD90 remained unchanged upon wild type infection. In addition, we found that this selective EHV1-mediated downregulation of cell surface proteins was dependent on the viral protein UL56 (pUL56). So far, pUL56-dependent downregulation during EHV1 infection of equine cells has only been described for MHCI, but our present data indicate that pUL56 may have a broader function in downregulating cell surface proteins. Taken together, our results are the first to show that equine MSC are susceptible for EHV1 and that pUL56 induces downregulation of several cell surface molecules on infected cells. These findings provide a basis for future studies to evaluate the mechanisms underlying for this selective pUL56-induced downregulation and to evaluate the potential role of MSC during EHV1 pathogenesis.

An MHC class I immune evasion gene of Marek׳s disease virus

Marek׳s disease virus (MDV) is a widespread α-herpesvirus of chickens that causes T cell tumors. Acute, but not latent, MDV infection has previously been shown to lead to downregulation of cell-surface MHC class I (Virology 282:198-205 (2001)), but the gene(s) involved have not been identified. Here we demonstrate that an MDV gene, MDV012, is capable of reducing surface expression of MHC class I on chicken cells. Co-expression of an MHC class I-binding peptide targeted to the endoplasmic reticulum (bypassing the requirement for the TAP peptide transporter) partially rescued MHC class I expression in the presence of MDV012, suggesting that MDV012 is a TAP-blocking MHC class I immune evasion protein. This is the first unique non-mammalian MHC class I immune evasion gene identified, and suggests that α-herpesviruses have conserved this function for at least 100 million years.

Functional characterization of ocular-derived human alphaherpesvirus cross-reactive CD4 T cells

Intraocular varicella-zoster virus (VZV) and HSV type 1 (HSV-1) infections cause sight-threatening uveitis. The disease is characterized by an intraocular inflammatory response involving herpesvirus-specific T cells. T cell reactivity to the noncausative human alphaherpesvirus (αHHV) is commonly detected in the affected eyes of herpetic uveitis patients, suggesting the role of cross-reactive T cells in the disease. This study aimed to identify and functionally characterize intraocular human alphaherpesvirus cross-reactive T cells. VZV protein immediate early 62 (IE62), which shares extensive homology with HSV ICP4, is a previously identified T cell target in VZV uveitis. Two VZV-specific CD4 T cell clones (TCC), recovered from the eye of a VZV uveitis patient, recognized the same IE62918-927 peptide using different TCR and HLA-DR alleles. The IE62918-927 peptide bound with high affinity to multiple HLA-DR alleles and was recognized by blood-derived T cells of 5 of 17 HSV-1/VZV-seropositive healthy adults but not in cord blood donors (n = 5). Despite complete conservation of the IE62 epitope in the orthologous protein ICP4 of HSV-1 and HSV-2, the TCC recognized VZV and HSV-1- but not HSV-2-infected B cells. This was not attributed to proximal epitope-flanking amino acid polymorphisms in HSV-2 ICP4. Notably, VZV/HSV-1 cross-reactive CD4 T cells controlled VZV but not HSV-1 infection of human primary retinal pigment epithelium (RPE) cells. In conclusion, we report on the first VZV/HSV-1 cross-reactive CD4 T cell epitope, which is HLA-DR promiscuous and immunoprevalent in coinfected individuals. Moreover, ocular-derived peptide-specific CD4 TCC controlled VZV but not HSV-1 infection of RPE cells, suggesting that HSV-1 actively inhibits CD4 T cell activation by infected human RPE cells.

Molecular mechanisms of varicella zoster virus pathogenesis

Varicella zoster virus (VZV) is the causative agent of varicella (chickenpox) and zoster (shingles). Investigating VZV pathogenesis is challenging as VZV is a human-specific virus and infection does not occur, or is highly restricted, in other species. However, the use of human tissue xenografts in mice with severe combined immunodeficiency (SCID) enables the analysis of VZV infection in differentiated human cells in their typical tissue microenvironment. Xenografts of human skin, dorsal root ganglia or foetal thymus that contains T cells can be infected with mutant viruses or in the presence of inhibitors of viral or cellular functions to assess the molecular mechanisms of VZV-host interactions. In this Review, we discuss how these models have improved our understanding of VZV pathogenesis.

Varicella-zoster virus and herpes simplex virus 1 can infect and replicate in the same neurons whether co- or superinfected

The two human neurotropic alphaherpesviruses varicella-zoster virus (VZV) and herpes simplex virus type 1 (HSV1) both establish latency in sensory ganglia. Human trigeminal ganglia are known to frequently harbor both viruses, and there is evidence to suggest the presence of both VZV and HSV1 DNA in the same neuron. We ask here whether VZV and HSV1 can exclude themselves and each other and whether they can productively infect the same cells in human neurons and human foreskin fibroblasts (HFF). Simultaneous infection (coinfection) or consecutive infection (superinfection) was assessed using cell-free HSV1 and VZV expressing fluorescent reporter proteins. Automated analysis was carried out to detect singly and dually infected cells. We demonstrate that VZV and HSV1 both display efficient superinfection exclusion (SE) in HFF, with each virus excluding either itself or the other virus. While SE also occurred in neurons, it was with much lower efficiency. Both alphaherpesviruses productively infected the same neurons, whether applied simultaneously or even consecutively, albeit at lower frequencies.

IMPORTANCE

Superinfection exclusion by VZV for itself or the related neurotropic alphaherpesvirus HSV1 has been studied here for the first time. We find that while these viruses display classic SE in fibroblasts, SE is less efficient for both HSV1 and VZV in human neurons. The ability of multiple VZV strains to productively infect the same neurons has important implications in terms of recombination of both wild-type and vaccine strains in patients.

Us3 kinase encoded by herpes simplex virus 1 mediates downregulation of cell surface major histocompatibility complex class I and evasion of CD8+ T cells

Detection and elimination of virus-infected cells by CD8⁺ cytotoxic T lymphocytes (CTLs) depends on recognition of virus-derived peptides presented by major histocompatibility complex class I (MHC-I) molecules on the surface of infected cells. In the present study, we showed that inactivation of the activity of viral kinase Us3 encoded by herpes simplex virus 1 (HSV-1), the etiologic agent of several human diseases and a member of the alphaherpesvirinae, significantly increased cell surface expression of MHC-I, thereby augmenting CTL recognition of infected cells in vitro. Overexpression of Us3 by itself had no effect on cell surface expression of MHC-I and Us3 was not able to phosphorylate MHC-I in vitro, suggesting that Us3 indirectly downregulated cell surface expression of MHC-I in infected cells. We also showed that inactivation of Us3 kinase activity induced significantly more HSV-1-specific CD8⁺ T cells in mice. Interestingly, depletion of CD8⁺ T cells in mice significantly increased replication of a recombinant virus encoding a kinase-dead mutant of Us3, but had no effect on replication of a recombinant virus in which the kinase-dead mutation was repaired. These results indicated that Us3 kinase activity is required for efficient downregulation of cell surface expression of MHC-I and mediates evasion of HSV-1-specific CD8⁺ T cells. Our results also raised the possibility that evasion of HSV-1-specific CD8⁺ T cells by HSV-1 Us3-mediated inhibition of MHC-I antigen presentation might in part contribute to viral replication in vivo.

Productive vs non-productive infection by cell-free varicella zoster virus of human neurons derived from embryonic stem cells is dependent upon infectious viral dose

Varicella Zoster virus (VZV) productively infects humans causing varicella upon primary infection and herpes zoster upon reactivation from latency in neurons. In vitro studies using cell-associated VZV infection have demonstrated productive VZV-infection, while a few recent studies of human neurons derived from stem cells incubated with cell-free, vaccine-derived VZV did not result in generation of infectious virus. In the present study, 90%-pure human embryonic stem cell-derived neurons were incubated with recombinant cell-free pOka-derived virus made with an improved method or VZV vaccine. We found that cell-free pOka and vOka at higher multiplicities of infection elicited productive infection in neurons followed by spread of infection, cytopathic effect and release of infectious virus into the medium. These results further validate the use of this unlimited source of human neurons for studying unexplored aspects of VZV interaction with neurons such as entry, latency and reactivation.

Age and immune status of rhesus macaques impact simian varicella virus gene expression in sensory ganglia

Simian varicella virus (SVV) infection of rhesus macaques (RMs) recapitulates the hallmarks of varicella-zoster virus (VZV) infection of humans, including the establishment of latency within the sensory ganglia. Various factors, including age and immune fitness, influence the outcome of primary VZV infection, as well as reactivation resulting in herpes zoster (HZ). To increase our understanding of the role of lymphocyte subsets in the establishment of viral latency, we analyzed the latent SVV transcriptome in juvenile RMs depleted of CD4 T, CD8 T, or CD20 B lymphocytes during acute infection. We have previously shown that SVV latency in sensory ganglia of nondepleted juvenile RMs is associated with a limited transcriptional profile. In contrast, CD4 depletion during primary infection resulted in the failure to establish a characteristic latent viral transcription profile in sensory ganglia, where we detected 68 out of 69 SVV-encoded open reading frames (ORFs). CD-depleted RMs displayed a latent transcriptional profile that included additional viral transcripts within the core region of the genome not detected in control RMs. The latent transcriptome of CD20-depleted RMs was comparable to the latent transcription in the sensory ganglia of control RMs. Lastly, we investigated the impact of age on the establishment of SVV latency. SVV gene expression was more active in ganglia from two aged RMs than in ganglia from juvenile RMs, with 25 of 69 SVV transcripts detected. Therefore, immune fitness at the time of infection modulates the establishment and/or maintenance of SVV latency.

T-cell immunity to human alphaherpesviruses

Human alphaherpesviruses (αHHV) - herpes simplex virus type 1 (HSV-1), HSV-2, and varicella-zoster virus (VZV) - infect mucosal epithelial cells, establish a lifelong latent infection of sensory neurons, and reactivate intermittingly to cause recrudescent disease. Although chronic αHHV infections co-exist with brisk T-cell responses, T-cell immune suppression is associated with worsened recurrent infection. Induction of αHHV-specific T-cell immunity is complex and results in poly-specific CD4 and CD8 T-cell responses in peripheral blood. Specific T-cells are localized to ganglia during the chronic phase of HSV infection and to several infected areas during recurrences, and persist long after viral clearance. These recent advances hold promise in the design of new vaccine candidates.

Immune regulation and evasion of Mammalian host cell immunity during viral infection

The mammalian host immune system has wide array of defence mechanisms against viral infections. Depending on host immunity and the extent of viral persistence, either the host immune cells might clear/restrict the viral load and disease progression or the virus might evade host immunity by down regulating host immune effector response(s). Viral antigen processing and presentation in the host cells through major histocompatibility complex (MHC) elicit subsequent anti-viral effector T cell response(s). However, modulation of such response(s) might generate one of the important viral immune evasion strategies. Viral peptides are mostly generated by proteolytic cleavage in the cytosol of the infected host cells. CD8(+) T lymphocytes play critical role in the detection of viral infection by recognizing these peptides displayed at the plasma membrane by MHC-I molecules. The present review summarises the current knowledge on the regulation of mammalian host innate and adaptive immune components, which are operative in defence mechanisms against viral infections and the variety of strategies that viruses have evolved to escape host cell immunity. The understanding of viral immune evasion strategies is important for designing anti-viral immunotherapies.

Immune regulation of human herpesviruses and its implications for human transplantation

Human herpesviruses including cytomegalovirus, Epstein-Barr virus, HHV6, HHV7, HHV8, Herpes simplex virus (HSV)-1 and HSV-2 and varicella zoster virus (VZV) have developed an intricate relationship with the human immune system. This is characterized by the interplay between viral immune evasion mechanisms that promote the establishment of a lifelong persistent infection and the induction of a broad humoral and cellular immune response, which prevents the establishment of viral disease. Understanding the immune parameters that control herpesvirus infection, and the strategies the viruses use to evade immune recognition, has been critical in understanding why immunological dysfunction in transplant patients can lead to disease, and in the development of immunological strategies to prevent and control herpesvirus associated diseases.

The host immune response to varicella zoster virus

Varicella zoster virus (VZV) is a highly successful human pathogen, which is never completely eliminated from the host. VZV causes two clinically distinct diseases, varicella (chickenpox) during primary infection and herpes zoster (shingles) following virus reactivation from latency. Throughout its lifecycle the virus encounters the innate and adaptive immune response, and in order to prevent eradication it has developed many mechanisms to evade and overcome these responses. This review will provide a comprehensive overview of the host immune response to VZV infection, during the multiple stages of the virus lifecycle and at key sites of VZV infection. We will also briefly describe some of the strategies employed by the virus to overcome the host immune response and the ongoing challenges in further elucidating the interplay between VZV and the host immune response in an attempt to lead to better therapies and a ‘second generation’ vaccine for VZV disease.

Human herpesviridae methods of natural killer cell evasion

Human herpesviruses cause diseases of considerable morbidity and mortality, ranging from encephalitis to hematologic malignancies. As evidence emerges about the role of innate immunity and natural killer (NK) cells in the control of herpesvirus infection, evidence of viral methods of innate immune evasion grows as well. These methods include interference with the ligands on infected cell surfaces that bind NK cell activating or inhibitory receptors. This paper summarizes the most extensively studied NK cell receptor/ligand pairs and then describes the methods of NK cell evasion used by all eight herpesviruses through these receptors and ligands. Although great strides have been made in elucidating their mechanisms, there is still a disparity between viruses in the amount of knowledge regarding innate immune evasion. Further research of herpesvirus innate immune evasion can provide insight for circumventing viral mechanisms in future therapies.

Herpes simplex virus and varicella zoster virus, the house guests who never leave

Human alphaherpesviruses including herpes simplex viruses (HSV-1, HSV-2) and varicella zoster virus (VZV) establish persistent latent infection in sensory neurons for the life of the host. All three viruses have the potential to reactivate causing recurrent disease. Regardless of the homology between the different virus strains, the three viruses are characterized by varying pathologies. This review will highlight the differences in infection pattern, immune response, and pathogenesis associated with HSV-1 and VZV.