Delaying the expression of herpes simplex virus type 1 glycoprotein B (gB) to a true late gene alters neurovirulence and inhibits the gB-CD8+ T-cell response in the trigeminal ganglion

The atypical chemokine receptor-2 fine-tunes the immune response in herpes stromal keratitis

Herpes stromal keratitis (HSK) is a blinding corneal disease caused by herpes simplex virus-1 (HSV-1), a common pathogen infecting most of the world's population. Inflammation in HSK is chemokine-dependent, particularly CXCL10 and less so the CC chemokines. The atypical chemokine receptor-2 (ACKR2) is a decoy receptor predominantly for pro-inflammatory CC chemokines, which regulates the inflammatory response by scavenging inflammatory chemokines thereby modulating leukocyte infiltration. Deletion of ACKR2 exacerbates and delays the resolution of the inflammatory response in most models. ACKR2 also regulates lymphangiogenesis and mammary duct development through the recruitment of tissue-remodeling macrophages. Here, we demonstrate a dose-dependent upregulation of ACKR2 during corneal HSV-1 infection. At an HSV inoculum dose of 5.4 x 105 pfu, but not at higher dose, ACKR2 deficient mice showed prolonged clinical signs of HSK, increased infiltration of leukocytes and persistent corneal neovascularization. Viral clearance and T cell activation were similar in ACKR2-/- and wild type mice, despite a transient diminished expression of CD40 and CD86 in dendritic cells. The data suggest that ACKR2 fine-tunes the inflammatory response and the level of neovascularization in the HSK.

Channel catfish virus ORF25 and ORF63 genes are essential for viral replication in vitro

The channel catfish virus (CCV) is a lethal pathogen to aquatic animals that can provoke severe haemorrhagic disease in juvenile channel catfish. Although the CCV genome has been fully sequenced, the molecular mechanisms of CCV infection and pathogenesis are less well known. Genomic DNA replication is a necessary and key event for the CCV life cycle. In this study, the impacts of the putative helicase and primase encoded by viral ORF25 and ORF63 on CCV genome replication and infection were evaluated in channel catfish ovary (CCO) cells. The results showed that the number of CCV genome copies was decreased significantly in virus-infected CCO cells after knockdown of ORF25 and ORF63 using RNA interference. In contrast, the overexpression of ORF25 and ORF63 led to slight increase in the number of virus genome copies. Consistent with the above results, the present results also showed that the expressions of CCV true-late genes which strictly depend on viral DNA replication, were significantly increased or repressed by overexpression or RNA interference targeting viral ORF25 and ORF63 genes in virus-infected CCO cells. In addition, knockdown of ORF25 and ORF63 remarkably inhibited CCV-induced cytopathic effects and decreased progeny virus titres in CCO cells. Moreover, transmission electron microscopy observation of CCO cells infected with CCV accompanied by siRNA targeting the viral ORF25 and ORF63 genes showed that the number of virus particles was remarkably reduced. Taken together, these results indicated that ORF25 and ORF63 are essential for regulating CCV genome replication and CCV-induced infection. Our findings will provide an understanding of the replication mechanisms of CCV and contribute to the development of antiviral strategies for controlling CCV infection in channel catfish culture.

UL11 Protein Is a Key Participant of the Duck Plague Virus in Its Life Cycle

Tegument protein UL11 plays a critical role in the life cycle of herpesviruses. The UL11 protein of herpesviruses is important for viral particle entry, release, assembly, and secondary envelopment. Lipid raft is cholesterol-rich functional microdomains in cell membranes, which plays an important role in signal transduction and substance transport. Flotillin and prohibition, which are considered to be specific markers of lipid raft. However, little is known about the function of duck plague virus (DPV) UL11 in the life cycle of the viruses and the relationship between the lipid raft and UL11. In this study, an interference plasmid shRNA126 for UL11 was used. Results showed that UL11 is involved in the replication, cell to cell spread, viral particle assembly, and release processes. Furthermore, UL11 was verified that it could interact with the lipid raft through sucrose density gradient centrifugation and that function correlates with the second glycine of the UL11. When the lipid raft was depleted using the methyl-β-cyclodextrin, the release of the DPV was decreased. Moreover, UL11 can decrease several relative viral genes mRNA levels by qRT-PCR and Western blot test. Altogether, these results highlight an important role for UL11 protein in the viral replication cycle.

Inhibiting Glucose Metabolism Results in Herpes Simplex Encephalitis

This report evaluates how HSV enters the brain to cause herpes simplex encephalitis following infection at a peripheral site. We demonstrate that encephalitis regularly occurred when BALB/c mice were infected with HSV and treated daily with 2-deoxy-d-glucose (2DG), which inhibits glucose use via the glycolysis pathway. The outcome of infection in the trigeminal ganglion (TG), the site to which the virus spreads, replicates, and establishes latency, showed marked differences in viral and cellular events between treated and untreated animals. In control-untreated mice, the replicating virus was present only during early time points, whereas in 2DG recipients, replicating virus remained for the 9-d observation period. This outcome correlated with significantly reduced numbers of innate inflammatory cells as well as T cells in 2DG-treated animals. Moreover, T cells in the TG of treated animals were less activated and contained a smaller fraction of expressed IFN-γ production compared with untreated controls. The breakdown of latency was accelerated when cultures of TG cells taken from mice with established HSV latency were cultured in the presence of 2DG. Taken together, the results of both in vivo and in vitro investigations demonstrate that the overall effects of 2DG therapy impaired the protective effects of one or more inflammatory cell types in the TG that normally function to control productive infection and prevent spread of virus to the brain.

Patterns of Herpes Simplex Virus 1 Infection in Neural Progenitor Cells

This study employed human induced pluripotent stem cells (hiPSCs) to model the interaction of HSV-1 with NPCs, which reside in the neurogenic niches of the CNS and play a fundamental role in adult neurogenesis. Herein, we provide evidence that in NPCs infected at an MOI as low as 0.001, HSV-1 can establish a latent state, suggesting that (i) a variant of classical HSV-1 latency can be established during earlier stages of neuronal differentiation and (ii) neurogenic niches in the brain may constitute additional sites of viral reactivation. Lytic HSV-1 infections impaired NPC migration, which represents a critical step in neurogenesis. A difference in susceptibility to HSV-1 infection between two-dimensional (2D) and three-dimensional (3D) NPC cultures was observed, highlighting the potential value of 3D cultures for modeling host-pathogen interactions. Together, our results are relevant in light of observations relating HSV-1 infection to postencephalitic cognitive dysfunction.

Herpes simplex virus 1 (HSV-1) can induce damage in brain regions that include the hippocampus and associated limbic structures. These neurogenic niches are important because they are associated with memory formation and are highly enriched with neural progenitor cells (NPCs). The susceptibility and fate of HSV-1-infected NPCs are largely unexplored. We differentiated human induced pluripotent stem cells (hiPSCs) into NPCs to generate two-dimensional (2D) and three-dimensional (3D) culture models to examine the interaction of HSV-1 with NPCs. Here, we show that (i) NPCs can be efficiently infected by HSV-1, but infection does not result in cell death of most NPCs, even at high multiplicities of infection (MOIs); (ii) limited HSV-1 replication and gene expression can be detected in the infected NPCs; (iii) a viral silencing mechanism is established in NPCs exposed to the antivirals (E)-5-(2-bromovinyl)-2′-deoxyuridine (5BVdU) and alpha interferon (IFN-α) and when the antivirals are removed, spontaneous reactivation can occur at low frequency; (iv) HSV-1 impairs the ability of NPCs to migrate in a dose-dependent fashion in the presence of 5BVdU plus IFN-α; and (v) 3D cultures of NPCs are less susceptible to HSV-1 infection than 2D cultures. These results suggest that NPC pools could be sites of HSV-1 reactivation in the central nervous system (CNS). Finally, our results highlight the potential value of hiPSC-derived 3D cultures to model HSV-1–NPC interaction.

IMPORTANCE This study employed human induced pluripotent stem cells (hiPSCs) to model the interaction of HSV-1 with NPCs, which reside in the neurogenic niches of the CNS and play a fundamental role in adult neurogenesis. Herein, we provide evidence that in NPCs infected at an MOI as low as 0.001, HSV-1 can establish a latent state, suggesting that (i) a variant of classical HSV-1 latency can be established during earlier stages of neuronal differentiation and (ii) neurogenic niches in the brain may constitute additional sites of viral reactivation. Lytic HSV-1 infections impaired NPC migration, which represents a critical step in neurogenesis. A difference in susceptibility to HSV-1 infection between two-dimensional (2D) and three-dimensional (3D) NPC cultures was observed, highlighting the potential value of 3D cultures for modeling host-pathogen interactions. Together, our results are relevant in light of observations relating HSV-1 infection to postencephalitic cognitive dysfunction.

Typical gene expression profile of pseudorabies virus reactivation from latency in swine trigeminal ganglion

Pseudorabies virus (PRV) establishes a lifelong latent infection in swine trigeminal ganglion (TG) following acute infection. Increased corticosteroid levels, due to stress, increases the incidence of reactivation from latency. Muscle injection combined with intravenous deliver of the synthetic corticosteroid dexamethasone (DEX) consistently induces reactivation from latency in pigs. In this study, PRV-free piglets were infected with PRV. Viral shedding in nasal and ocular swabs demonstrated that PRV infection entered the latent period. The anti-PRV antibody was detected by enzyme-linked immunosorbent assay and the serum neutralization test, which suggested that the PRV could establish latent infection in the presence of humoral immunity. Immunohistochemistry and viral genome detection of TG neurons suggested that PRV was reactivated from latency. Viral gene expressions of IE180, EP0, VP16, and LLT-intron were readily detected at 3-h post-DEX treatment, but gB, a γ1 gene, was not detectable. The differentially expressed phosphorylated proteins of TG neurons were analyzed by ITRAQ coupled with LC-MS/MS, and p-EIF2S2 differentially expression was confirmed by western blot assay. Taken together, our study provides the evidence that typical gene expression in PRV reactivation from latency in TG is disordered compared with known lytic infection in epithelial cells.

Herpes Simplex Virus 1-Specific CD8+ T Cell Priming and Latent Ganglionic Retention Are Shaped by Viral Epitope Promoter Kinetics

Reactivation of herpes simplex virus 1 (HSV-1) from neurons in sensory ganglia such as the trigeminal ganglia (TG) is influenced by virus-specific CD8⁺ T cells that infiltrate the ganglia at the onset of latency and contract to a stable activated tissue-resident memory population. In C57BL/6 mice, half of HSV-specific CD8⁺ T cells (gB-CD8s) recognize one dominant epitope (residues 498 to 505) on glycoprotein B (gB_498-505), while the remainder (non-gB-CD8s) recognize 19 subdominant epitopes from 12 viral proteins. To address how expression by HSV-1 influences the formation and ganglionic retention of CD8⁺ T cell populations, we developed recombinant HSV-1 with the native immunodominant gB epitope disrupted but then expressed ectopically from different viral promoters. In mice, the epitope expressed from the gB promoter restored full gB-CD8 immunodominance to 50%. Intriguingly, earlier expression from constitutive, immediate-early, and early promoters did not significantly increase immunodominance, indicating that these promoters cannot elicit more than half of the CD8 compartment. Epitope expressed from candidate viral promoters of "true late" HSV-1 genes either delayed or reduced the priming efficiency of gB-CD8s and their levels in the TG at early times. HSV expressing the epitope from the full latency-associated transcript promoter did not efficiently prime gB-CD8s; however, gB-CD8s primed by a concurrent wild-type flank infection infiltrated the TG and were retained long term, suggesting that latent epitope expression is sufficient to retain gB-CD8s. Taken together, the data indicate that viral promoters shape latent HSV-1-specific CD8⁺ T cell populations and should be an important consideration in future vaccine design.IMPORTANCE Latency of HSV-1 in host neurons enables long-term persistence from which reactivation may occur to cause recurrent diseases, such as blinding herpetic stromal keratitis. Latency is not antigenically silent, and viral proteins are sporadically expressed at low levels without full virion production. This protein expression is recognized by ganglion-resident HSV-1-specific CD8⁺ T cells that maintain a protective resident population. Since these T cells can influence lytic/latent decisions in reactivating neurons, we argue that improving their ganglionic retention and function may offer a strategy in vaccine design to reduce reactivation and recurrent disease. To understand factors driving the infiltration and retention of ganglionic CD8s, we examined several HSV recombinants that have different viral promoters driving expression of the immunodominant gB epitope. We show that the selection of epitope promoter influences CD8⁺ T cell population hierarchies and their function.

Influence of an immunodominant herpes simplex virus type 1 CD8+ T cell epitope on the target hierarchy and function of subdominant CD8+ T cells

Herpes simplex virus type 1 (HSV-1) latency in sensory ganglia such as trigeminal ganglia (TG) is associated with a persistent immune infiltrate that includes effector memory CD8+ T cells that can influence HSV-1 reactivation. In C57BL/6 mice, HSV-1 induces a highly skewed CD8+ T cell repertoire, in which half of CD8+ T cells (gB-CD8s) recognize a single epitope on glycoprotein B (gB498-505), while the remainder (non-gB-CD8s) recognize, in varying proportions, 19 subdominant epitopes on 12 viral proteins. The gB-CD8s remain functional in TG throughout latency, while non-gB-CD8s exhibit varying degrees of functional compromise. To understand how dominance hierarchies relate to CD8+ T cell function during latency, we characterized the TG-associated CD8+ T cells following corneal infection with a recombinant HSV-1 lacking the immunodominant gB498-505 epitope (S1L). S1L induced a numerically equivalent CD8+ T cell infiltrate in the TG that was HSV-specific, but lacked specificity for gB498-505. Instead, there was a general increase of non-gB-CD8s with specific subdominant epitopes arising to codominance. In a latent S1L infection, non-gB-CD8s in the TG showed a hierarchy targeting different epitopes at latency compared to at acute times, and these cells retained an increased functionality at latency. In a latent S1L infection, these non-gB-CD8s also display an equivalent ability to block HSV reactivation in ex vivo ganglionic cultures compared to TG infected with wild type HSV-1. These data indicate that loss of the immunodominant gB498-505 epitope alters the dominance hierarchy and reduces functional compromise of CD8+ T cells specific for subdominant HSV-1 epitopes during viral latency.

Further evidence of Chelonid herpesvirus 5 (ChHV5) latency: high levels of ChHV5 DNA detected in clinically healthy marine turtles

The Chelonid herpesvirus 5 (ChHV5) has been consistently associated with fibropapillomatosis (FP), a transmissible neoplastic disease of marine turtles. Whether ChHV5 plays a causal role remains debated, partly because while FP tumours have been clearly documented to contain high concentrations of ChHV5 DNA, recent PCR-based studies have demonstrated that large proportions of asymptomatic marine turtles are also carriers of ChHV5. We used a real-time PCR assay to quantify the levels of ChHV5 Glycoprotein B (gB) DNA in both tumour and non-tumour skin tissues, from clinically affected and healthy turtles drawn from distant ocean basins across four species. In agreement with previous studies, higher ratios of viral to host DNA were consistently observed in tumour versus non-tumour tissues in turtles with FP. Unexpectedly however, the levels of ChHV5 gB DNA in clinically healthy turtles were significantly higher than in non-tumour tissues from FP positive turtles. Thus, a large proportion of clinically healthy sea turtle populations worldwide across species carry ChHV5 gB DNA presumably through persistent latent infections. ChHV5 appears to be ubiquitous regardless of the animals’ clinical conditions. Hence, these results support the theory that ChHV5 is a near ubiquitous virus with latency characteristics requiring co-factors, possibly environmental or immune related, to induce FP.

Expression of immunogenic structural proteins of cyprinid herpesvirus 3 in vitro assessed using immunofluorescence

Cyprinid herpesvirus 3 (CyHV-3), also called koi herpesvirus (KHV), is the aetiological agent of a fatal disease in carp and koi (Cyprinus carpio L.), referred to as koi herpesvirus disease. The virus contains at least 40 structural proteins, of which few have been characterised with respect to their immunogenicity. Indirect immunofluorescence assays (IFAs) using two epitope-specific monoclonal antibodies (MAbs) were used to examine the expression kinetics of two potentially immunogenic and diagnostically relevant viral antigens, an envelope glycoprotein and a capsid-associated protein. The rate of expression of these antigens was determined following a time-course of infection in two CyHV-3 susceptible cell lines. The results were quantified using an IFA, performed in microtitre plates, and image analysis was used to analyse confocal micrographs, enabling measurement of differential virus-associated fluorescence and nucleus-associated fluorescence from stacks of captured scans. An 8-tenfold increase in capsid-associated protein expression was observed during the first 5 days post-infection compared to a ≤ 2-fold increase in glycoprotein expression. A dominant protein of ~100 kDa reacted with the capsid-associated MAb (20F10) in western blot analysis. This band was also recognised by sera obtained from carp infected with CyHV-3, indicating that this capsid-associated protein is produced in abundance during infection in vitro and is immunogenic to carp. Mass spectrometry carried out on this protein identified it as a previously uncharacterised product of open reading frame 84. This abundantly expressed and immunogenic capsid-associated antigen may be a useful candidate for KHV serological diagnostics.

The challenges and opportunities for the development of a T-cell epitope-based herpes simplex vaccine

Herpes simplex virus type 1 and type 2 (HSV-1 & HSV-2) infections have been prevalent since the ancient Greek times. To this day, they still affect a staggering number of over a billion individuals worldwide. HSV-1 infections are predominant than HSV-2 infections and cause potentially blinding ocular herpes, oro-facial herpes and encephalitis. HSV-2 infections cause painful genital herpes, encephalitis, and death in newborns. While prophylactic and therapeutic HSV vaccines remain urgently needed for centuries, their development has been difficult. During the most recent National Institute of Health (NIH) workshop titled "Next Generation Herpes Simplex Virus Vaccines: The Challenges and Opportunities", basic researchers, funding agencies, and pharmaceutical representatives gathered: (i) to assess the status of herpes vaccine research; and (ii) to identify the gaps and propose alternative approaches in developing a safe and efficient herpes vaccine. One "common denominator" among previously failed clinical herpes vaccine trials is that they either used a whole virus or a whole viral protein, which contain both "pathogenic symptomatic" and "protective asymptomatic" antigens and epitopes. In this report, we continue to advocate developing "asymptomatic" epitope-based sub-unit vaccine strategies that selectively incorporate "protective asymptomatic" epitopes which: (i) are exclusively recognized by effector memory CD4(+) and CD8(+) T cells (TEM cells) from "naturally" protected seropositive asymptomatic individuals; and (ii) protect human leukocyte antigen (HLA) transgenic animal models of ocular and genital herpes. We review the role of animal models in herpes vaccine development and discuss their current status, challenges, and prospects.

Phosphorylation of a herpes simplex virus 1 dUTPase by a viral protein kinase, Us3, dictates viral pathogenicity in the central nervous system but not at the periphery

Herpes simplex virus 1 (HSV-1) encodes Us3 protein kinase, which is critical for viral pathogenicity in both mouse peripheral sites (e.g., eyes and vaginas) and in the central nervous systems (CNS) of mice after intracranial and peripheral inoculations, respectively. Whereas some Us3 substrates involved in Us3 pathogenicity in peripheral sites have been reported, those involved in Us3 pathogenicity in the CNS remain to be identified. We recently reported that Us3 phosphorylated HSV-1 dUTPase (vdUTPase) at serine 187 (Ser-187) in infected cells, and this phosphorylation promoted viral replication by regulating optimal enzymatic activity of vdUTPase. In the present study, we show that the replacement of vdUTPase Ser-187 by alanine (S187A) significantly reduced viral replication and virulence in the CNS of mice following intracranial inoculation and that the phosphomimetic substitution at vdUTPase Ser-187 in part restored the wild-type viral replication and virulence. Interestingly, the S187A mutation in vdUTPase had no effect on viral replication and pathogenic effects in the eyes and vaginas of mice after ocular and vaginal inoculation, respectively. Similarly, the enzyme-dead mutation in vdUTPase significantly reduced viral replication and virulence in the CNS of mice after intracranial inoculation, whereas the mutation had no effect on viral replication and pathogenic effects in the eyes and vaginas of mice after ocular and vaginal inoculation, respectively. These observations suggested that vdUTPase was one of the Us3 substrates responsible for Us3 pathogenicity in the CNS and that the CNS-specific virulence of HSV-1 involved strict regulation of vdUTPase activity by Us3 phosphorylation.

IMPORTANCE

Herpes simplex virus 1 (HSV-1) encodes a viral protein kinase Us3 which is critical for pathogenicity both in peripheral sites and in the central nervous systems (CNS) of mice following peripheral and intracranial inoculations, respectively. Whereas some Us3 substrates involved in Us3 pathogenicity in peripheral sites have been reported, those involved in Us3 pathogenicity in the CNS remain to be identified. Here, we report that Us3 phosphorylation of viral dUTPase (vdUTPase) at serine 187 (Ser-187), which has been shown to promote the vdUTPase activity, appears to be critical for viral virulence in the CNS but not for pathogenic effects in peripheral sites. Since HSV proteins critical for viral virulence in the CNS are, in almost all cases, also involved in viral pathogenicity at peripheral sites, this phosphorylation event is a unique report of a specific mechanism involved in HSV-1 virulence in the CNS.

Immunological control of herpes simplex virus infections

Herpes simplex virus type 1 (HSV-1) is capable of causing a latent infection in sensory neurons that lasts for the lifetime of the host. The primary infection is resolved following the induction of the innate immune response that controls replication of the virus until the adaptive immune response can clear the active infection. HSV-1-specific CD8⁺ T cells survey the ganglionic regions containing latently infected neurons and participate in preventing reactivation of HSV from latency. The long-term residence and migration dynamics of the T cells in the trigeminal ganglia appear to distinguish them from the traditional memory T cell subsets. Recently described tissue resident memory (T_RM) T cells establish residence and survive for long periods in peripheral tissue compartments following antigen exposure. This review focuses on the immune system response to HSV-1 infection. Particular emphasis is placed on the evidence pointing to the HSV-1-specific CD8⁺ T cells in the trigeminal belonging to the T_RM class of memory T cells and the role of T_RM cells in virus infection, pathogenesis, latency, and disease.

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.

A lentiviral vector-based, herpes simplex virus 1 (HSV-1) glycoprotein B vaccine affords cross-protection against HSV-1 and HSV-2 genital infections

Genital herpes is caused by herpes simplex virus 1 (HSV-1) and HSV-2, and its incidence is constantly increasing in the human population. Regardless of the clinical manifestation, HSV-1 and HSV-2 infections are highly transmissible to sexual partners and enhance susceptibility to other sexually transmitted infections. An effective vaccine is not yet available. Here, HSV-1 glycoprotein B (gB1) was delivered by a feline immunodeficiency virus (FIV) vector and tested against HSV-1 and HSV-2 vaginal challenges in C57BL/6 mice. The gB1 vaccine elicited cross-neutralizing antibodies and cell-mediated responses that protected 100 and 75% animals from HSV-1- and HSV-2-associated severe disease, respectively. Two of the eight fully protected vaccinees underwent subclinical HSV-2 infection, as demonstrated by deep immunosuppression and other analyses. Finally, vaccination prevented death in 83% of the animals challenged with a HSV-2 dose that killed 78 and 100% naive and mock-vaccinated controls, respectively. Since this FIV vector can accommodate two or more HSV immunogens, this vaccine has ample potential for improvement and may become a candidate for the development of a truly effective vaccine against genital herpes.

γ-Herpesvirus reactivation differentially stimulates epitope-specific CD8 T cell responses

The γ-herpesviruses are characterized by their ability to establish lifelong latency. Subsequent immune suppression leads to viral reactivation from latency and the onset of a variety of pathologies, including lymphoproliferative disease and cancers. CD8 T cells play a key role in preventing reactivation of latent virus. Therefore, to develop effective therapeutic immune strategies, it is essential to understand the maintenance of CD8 T cell responses during latency. Because the γ-herpesviruses are highly species-specific and mice cannot be infected with the human pathogens, EBV or Kaposi's sarcoma-associated herpesvirus, we have used a natural rodent γ-herpesvirus experimental infection model, γ-herpesvirus-68. In this report, we show that during long-term latent infection, naive CD8 T cells are recruited into the ongoing immune response in an epitope-specific manner. When virus reactivation is induced in vivo, the recruitment of CD8 T cells for some, but not all, epitopes is enhanced. The variation in recruitment is not due to differences in epitope presentation. We also show that CD8 T cells that are newly stimulated during reactivation are functionally impaired compared with acutely stimulated cells in terms of cytokine production. Thus, our results demonstrate unexpected complexity in the response of CD8 T cells specific for different viral epitopes that were stimulated during acute infection, quiescent latency, and reactivation.

The molecular basis of herpes simplex virus latency

Herpes simplex virus type 1 is a neurotropic herpesvirus that establishes latency within sensory neurones. Following primary infection, the virus replicates productively within mucosal epithelial cells and enters sensory neurones via nerve termini. The virus is then transported to neuronal cell bodies where latency can be established. Periodically, the virus can reactivate to resume its normal lytic cycle gene expression programme and result in the generation of new virus progeny that are transported axonally back to the periphery. The ability to establish lifelong latency within the host and to periodically reactivate to facilitate dissemination is central to the survival strategy of this virus. Although incompletely understood, this review will focus on the mechanisms involved in the regulation of latency that centre on the functions of the virus-encoded latency-associated transcripts (LATs), epigenetic regulation of the latent virus genome and the molecular events that precipitate reactivation.

This review considers current knowledge and hypotheses relating to the mechanisms involved in the establishment, maintenance and reactivation herpes simplex virus latency.

Immunology in the Clinic Review Series; focus on host responses: T cell responses to herpes simplex viruses

Herpes virus infections are chronic and co-exist with acquired immune responses that generally prevent severe damage to the host, while allowing periodic shedding of virus and maintenance of its transmission in the community. Herpes simplex viruses type 1 and 2 (HSV-1, HSV-2) are typical in this regard and are representative of the viral subfamily Alphaherpesvirinae, which has a tropism for neuronal and epithelial cells. This review will emphasize recent progress in decoding the physiologically important CD8(+) and CD4(+) T cell responses to HSV in humans. The expanding data set is discussed in the context of the search for an effective HSV vaccine as therapy for existing infections and to prevent new infections.

B7 costimulation molecules encoded by replication-defective, vhs-deficient HSV-1 improve vaccine-induced protection against corneal disease

Herpes simplex virus 1 (HSV-1) causes herpes stromal keratitis (HSK), a sight-threatening disease of the cornea for which no vaccine exists. A replication-defective, HSV-1 prototype vaccine bearing deletions in the genes encoding ICP8 and the virion host shutoff (vhs) protein reduces HSV-1 replication and disease in a mouse model of HSK. Here we demonstrate that combining deletion of ICP8 and vhs with virus-based expression of B7 costimulation molecules created a vaccine strain that enhanced T cell responses to HSV-1 compared with the ICP8⁻vhs⁻ parental strain, and reduced the incidence of keratitis and acute infection of the nervous system after corneal challenge. Post-challenge T cell infiltration of the trigeminal ganglia and antigen-specific recall responses in local lymph nodes correlated with protection. Thus, B7 costimulation molecules expressed from the genome of a replication-defective, ICP8⁻vhs⁻ virus enhance vaccine efficacy by further reducing HSK.

The alphaherpesvirus US3/ORF66 protein kinases direct phosphorylation of the nuclear matrix protein matrin 3

The protein kinase found in the short region of alphaherpesviruses, termed US3 in herpes simplex virus type 1 (HSV-1) and pseudorabies virus (PRV) and ORF66 in varicella-zoster virus (VZV), affects several viral and host cell processes, and its specific targets remain an area of active investigation. Reports suggesting that HSV-1 US3 substrates overlap with those of cellular protein kinase A (PKA) prompted the use of an antibody specific for phosphorylated PKA substrates to identify US3/ORF66 targets. HSV-1, VZV, and PRV induced very different substrate profiles that were US3/ORF66 kinase dependent. The predominant VZV-phosphorylated 125-kDa species was identified as matrin 3, one of the major nuclear matrix proteins. Matrin 3 was also phosphorylated by HSV-1 and PRV in a US3 kinase-dependent manner and by VZV ORF66 kinase at a novel residue (KRRRT150EE). Since VZV-directed T150 phosphorylation was not blocked by PKA inhibitors and was not induced by PKA activation, and since PKA predominantly targeted matrin 3 S188, it was concluded that phosphorylation by VZV was PKA independent. However, purified VZV ORF66 kinase did not phosphorylate matrin 3 in vitro, suggesting that additional cellular factors were required. In VZV-infected cells in the absence of the ORF66 kinase, matrin 3 displayed intranuclear changes, while matrin 3 showed a pronounced cytoplasmic distribution in late-stage cells infected with US3-negative HSV-1 or PRV. This work identifies phosphorylation of the nuclear matrix protein matrin 3 as a new conserved target of this kinase group.