CD8(+) T cells can block herpes simplex virus type 1 (HSV-1) reactivation from latency in sensory neurons

Immune control of HSV-1 latency

A hallmark of the herpes family of viruses is their ability to cause recurrent disease. Upon primary infection, Herpes Simplex virus (HSV) establishes a latent infection in sensory neurons that persists for the life of the individual. Reactivation of these latent viral genomes with virion formation is the source of virus for most HSV recurrent disease. This review details recent exciting findings supporting a role for the host immune system, particularly CD8+ T cells in maintaining HSV-1 in a latent state.

A herpes simplex virus type 1 mutant expressing a baculovirus inhibitor of apoptosis gene in place of latency-associated transcript has a wild-type reactivation phenotype in the mouse

The latency-associated transcript (LAT) is essential for the wild-type herpes simplex virus type 1 (HSV-1) high-reactivation phenotype since LAT- mutants have a low-reactivation phenotype. We previously reported that LAT can decrease apoptosis and proposed that this activity is involved in LAT's ability to enhance the HSV-1 reactivation phenotype. The first 20% of the primary 8.3-kb LAT transcript is sufficient for enhancing the reactivation phenotype and for decreasing apoptosis, supporting this proposal. For this study, we constructed an HSV-1 LAT- mutant that expresses the baculovirus antiapoptosis gene product cpIAP under control of the LAT promoter and in place of the LAT region mentioned above. Mice were ocularly infected with this mutant, designated dLAT-cpIAP, and the reactivation phenotype was determined using the trigeminal ganglion explant model. dLAT-cpIAP had a reactivation phenotype similar to that of wild-type virus and significantly higher than that of (i) the LAT- mutant dLAT2903; (ii) dLAT1.5, a control virus containing the same LAT deletion as dLAT-cpIAP, but with no insertion of foreign DNA, thereby controlling for potential readthrough transcription past the cpIAP insert; and (iii) dLAT-EGFP, a control virus identical to dLAT-cpIAP except that it contained the enhanced green fluorescent protein open reading frame (ORF) in place of the cpIAP ORF, thereby controlling for expression of a random foreign gene instead of the cpIAP gene. These results show that an antiapoptosis gene with no sequence similarity to LAT can efficiently substitute for the LAT function involved in enhancing the in vitro-induced HSV-1 reactivation phenotype in the mouse.

Long-term presence of virus-specific plasma cells in sensory ganglia and spinal cord following intravaginal inoculation of herpes simplex virus type 2

The tissue sites of long-term herpes simplex virus type 2 (HSV-2)-specific antibody production in mice and guinea pigs were identified. In addition to secondary lymphoid tissue and bone marrow, HSV-specific plasma cells were detected in spinal cords of mice up to 10 months after intravaginal inoculation with a thymidine kinase-deficient HSV-2 strain and in lumbosacral ganglia and spinal cords of guinea pigs inoculated with HSV-2 strain MS. The long-term retention of virus-specific plasma cells in the peripheral and central nervous systems following HSV infection may be important for resistance to reinfection of neuronal tissues or may play a role in modulation of reactivation from latency.

Gamma interferon can block herpes simplex virus type 1 reactivation from latency, even in the presence of late gene expression

Herpes simplex virus type 1 (HSV-1)-specific CD8+ T cells and the cytokine gamma interferon (IFN-gamma) are persistently present in trigeminal ganglia (TG) harboring latent HSV-1. We define "latency" as the retention of functional viral genomes in sensory neurons without the production of infectious virions and "reactivation" as a multistep process leading from latency to virion assembly. CD8+ T cells can block HSV-1 reactivation in ex vivo mouse TG cultures and appear to be the sole source of IFN-gamma in these cultures. Here we demonstrate that IFN-gamma alone can block HSV-1 reactivation in some latently infected neurons, and we identify points of intervention in the life cycle of the reactivating virus. Cell suspensions of TG that were latently infected with recombinant RE HSV-1 expressing enhanced green fluorescent protein from the promoter for infected cell protein 0 (ICP0) or glycoprotein C (gC) were depleted of endogenous CD8+ or CD45+ cells and cultured in the presence or absence of IFN-gamma. Our results demonstrate that IFN-gamma acts on latently infected neurons to inhibit (i) HSV-1 reactivation, (ii) ICP0 promoter activity, (iii) gC promoter activity, and (iv) reactivation in neurons in which the ICP0 or gC promoter is active. Interestingly, we detected transcripts for ICP0, ICP4, and gH in neurons that expressed the ICP0 promoter but were prevented by IFN-gamma from reactivation and virion formation. Thus, the IFN-gamma blockade of HSV-1 reactivation from latency in neurons is associated with an inhibition of the expression of the ICP0 gene (required for reactivation) and a blockade of a step that occurs after the expression of at least some viral structural genes.

Role of inflammatory cytokine-induced cyclooxygenase 2 in the ocular immunopathologic disease herpetic stromal keratitis

Ocular infection with herpes simplex virus (HSV) results in a blinding immunoinflammatory stromal keratitis (SK) lesion. Early preclinical events include polymorphonuclear neutrophil (PMN) infiltration and neovascularization in the corneal stroma. We demonstrate here that HSV infection of the cornea results in the upregulation of the cyclooxygenase 2 (COX-2) enzyme. Early after infection, COX-2 was produced from uninfected stromal fibroblasts as an indirect effect of virus infection. Subsequently, COX-2 may also be produced from other inflammatory cells that infiltrate the cornea. The induction of COX-2 is a critical event, since inhibition of COX-2 with a selective inhibitor was shown to reduce corneal angiogenesis and SK severity. The administration of a COX-2 inhibitor resulted in compromised PMN infiltration into the cornea, as well as diminished corneal vascular endothelial growth factor levels, likely accounting for the reduced angiogenic response. COX-2 stimulation by HSV infection represents a critical early event accessible for therapy and the control of SK severity.

Towards an understanding of the molecular basis of herpes simplex virus latency

The survival strategy of herpes simplex virus centres on the establishment of latency in sensory neurons innervating the site of primary infection followed by periodic reactivation to facilitate transmission. This is a highly evolved and efficient survival mechanism, which despite being the subject of intense research, has proven remarkably difficult to dissect at a molecular level. This review will focus on data, emerging from both in vitro and in vivo model systems, which provide a framework for a mechanistic understanding of latency and the existence and possible significance of non-uniform latent states.

Evidence that spontaneous reactivation of herpes virus does not occur in mice

Background

Some species, including humans and rabbits, exhibit periodic viral reactivation and shed infectious virus at the infected end organ. Mice may be an exception, because spontaneous shedding of infectious virus rarely, if ever, occurs. However, spontaneous molecular reactivation, i.e., the expression of a few viral genes and the synthesis of the viral glycoproteins coded for by these genes, has been reported. This finding has prompted the assumption that molecular reactivation is an indicator of reactivation and the production of infectious virus. The goal of this study was to differentiate between viral gene expression during latency and the episodic production of infectious virus in mice.

Results

Viral reactivation and infection were not seen in herpes simplex virus type 1 (HSV-1) latent ganglion graft recipient BALB/c scid or immunocompetent BALB/c mice, which survived the 65-day observation period with no evidence of viral infection although the immunocompetent mice developed cellular and humoral immunity to HSV-1. In contrast, BALB/c scid recipients of ganglia containing reactivating virus invariably developed a local and, subsequently, systemic viral infection and died within 14 days. Immunocompetent BALB/c mice that received ganglion grafts containing reactivating virus survived the infection and became immune to the virus. Trigeminal ganglia removed from scid and immunocompetent recipient graft sites 5, 14, and 28 days after transplantation contained latent virus and viable neurons.

Conclusion

The results suggest that, within the limits of detection of the experiments, spontaneous episodic production of immunogenic viral antigens but not of infectious virus occurs in mouse neural ganglia during latency.

Re-evaluating the role of natural killer cells in innate resistance to herpes simplex virus type 1

Background

Interferon-γ acts to multiply the potency with which innate interferons (α/β) suppress herpes simplex virus type 1 (HSV-1) replication. Recent evidence suggests that this interaction is functionally relevant in host defense against HSV-1. However, it is not clear which WBCs of the innate immune system, if any, limit HSV-1 spread in an IFN-γ dependent manner. The current study was initiated to determine if natural killer (NK) cells provide innate resistance to HSV-1 infection, and if so to determine if this resistance is IFN-γ-dependent.

Results

Lymphocyte-deficient scid or rag2^-/- mice were used to test four predictions of the central hypothesis, and thus determine if innate resistance to HSV-1 is dependent on 1. NK cell cytotoxicity, 2. NK cells, 3. WBCs, or 4. the IFN-activated transcription factor, Stat 1. Loss of NK cell cytotoxic function or depletion of NK cells had no effect on the progression of HSV-1 infection in scid mice. In contrast, viral spread and pathogenesis developed much more rapidly in scid mice depleted of WBCs. Likewise, loss of Stat 1 function profoundly impaired the innate resistance of rag2^-/- mice to HSV-1.

Conclusion

Lymphocyte-deficient mice possess a very tangible innate resistance to HSV-1 infection, but this resistance is not dependent upon NK cells.

Homing in on the cellular immune response to HSV-2 in humans

PROBLEM

Genital herpes simplex infections are generally limited to epithelia and neurons. Vaccines have had activity in herpes simplex virus (HSV)-seronegative women only. Understanding how HSV-specific T cells traffic to infected sites may assist in vaccine design.

METHOD OF STUDY

Herpes simplex virus epitopes recognized by HSV-specific CD8 T cells were identified and used to make fluorescent human leukocyte antigen (HLA)-peptide tetramers. Molecules related to lymphocyte rolling adhesion were studied by flow cytometry and cell binding. HSV-specific CD4 T cells identified ex vivo by cytokine accumulation or activation marker expression, or detected in vitro by 5-(and-6)-carboxyfluorescein diacetate, succinimidyl ester (CFSE) dilution, were similarly investigated.

RESULTS

Herpes simplex virus-specific T cells are 10- to 100-fold more prevalent in lesional skin compared with blood and greatly enriched in lesions compared with normal skin. Diverse viral antigens are recognized by HSV-specific T cells. Functionally active E-selectin ligand, and cutaneous lymphocyte antigen (CLA), are expressed by circulating HSV-2-specific CD8 cells. CD4 cells display lower levels of CLA that are dramatically up-regulated upon re-stimulation with antigen.

CONCLUSIONS

Herpes simplex virus-2-specific CD8 and CD4 T cells differ in constitutive expression of skin homing molecules. Vaccines designed to induce proper homing are postulated to have increased efficacy.

Involvement of IL-6 in the paracrine production of VEGF in ocular HSV-1 infection

Following ocular HSV-1 infection, neovascularisation of the avascular cornea is a critical event in the pathogenesis of herpetic stromal keratitis. This present study evaluates the role of proinflammatory cytokines such as IL-6 in corneal angiogenesis following virus infection. Both in vivo and in vitro data indicate that IL-6 produced from virus-infected cells can stimulate noninfected resident corneal cells and other inflammatory cells in a paracrine manner to secrete VEGF, a potent angiogenic factor. Antibody neutralisation of IL-6 resulted in a significant decrease in the number of VEGF producing cells in the cornea. Thus, our results further demonstrate the close relationship between proinflammatory cytokines and VEGF-induced corneal neovascularisation.

The locus encompassing the latency-associated transcript of herpes simplex virus type 1 interferes with and delays interferon expression in productively infected neuroblastoma cells and trigeminal Ganglia of acutely infected mice

The herpes simplex virus type 1 (HSV-1) latency-associated transcript (LAT) is the only abundant viral transcript expressed in latently infected neurons. LAT inhibits apoptosis, suggesting that it regulates latency by promoting the survival of infected neurons. The LAT locus also contains a newly described gene (AL), which is antisense to LAT and partially overlaps LAT encoding sequences. When human (SK-N-SH) or mouse (neuro-2A) neuroblastoma cells were infected with a virus that does not express LAT or AL gene products (dLAT2903), beta interferon (IFN-beta) and IFN-alpha RNA expression was detected earlier relative to the same cells infected with HSV-1 strains that express LAT and AL. Infection of neuro-2A cells with dLAT2903 also led to higher levels of IFN-beta promoter activity than in cells infected with wild-type (wt) HSV-1. In contrast, IFN RNA expression was the same when human lung fibroblasts were infected with dLAT2903 or wt HSV-1. When BALB/c mice were infected with dLAT2903, IFN-alpha and IFN-beta RNA expression was readily detected in trigeminal ganglia (TG) 4 days after infection. These transcripts were not detected in TG of mice infected with wt HSV-1 or dLAT2903R (marker-rescued dLAT2903) until 6 days postinfection. When TG single-cell suspensions from infected BALB/c mice were prepared and incubated in vitro with wt HSV-1 as a source of antigen, TG cultures prepared from mice infected with dLAT2903 produced and secreted higher levels of IFN protein than wt HSV-1 or dLAT2903R. Collectively, these studies suggest that the LAT locus interferes with and delays IFN expression.

Development and migration of protective CD8+ T cells into the nervous system following ocular herpes simplex virus-1 infection

After infection of epithelial surfaces, HSV-1 elicits a multifaceted antiviral response that controls the virus and limits it to latency in sensory ganglia. That response encompasses the CD8(+) T cells, whose precise role(s) is still being defined; immune surveillance in the ganglia and control of viral spread to the brain were proposed as the key roles. We tracked the kinetics of the CD8(+) T cell response across lymphoid and extralymphoid tissues after ocular infection. HSV-1-specific CD8(+) T cells first appeared in the draining (submandibular) lymph node on day 5 and were detectable in both nondraining lymphoid and extralymphoid tissues starting on day 6. However, although lymphoid organs contained both resting (CD43(low)CFSE(high)) and virus-specific cells at different stages of proliferation and activation, extralymphoid sites (eye, trigeminal ganglion, and brain) contained only activated cells that underwent more than eight proliferations (CD43(high)CFSE(neg)) and promptly secreted IFN-gamma upon contact with viral Ags. Regardless of the state of activation, these cells appeared too late to prevent HSV-1 spread, which was seen in the eye (from day 1), trigeminal ganglia (from day 2), and brain (from day 3) well before the onset of a detectable CD8(+) T cell response. However, CD8(+) T cells were critical in reducing viral replication starting on day 6 and for its abrogation between days 8 and 10; CD8-deficient animals failed to control the virus, exhibited persisting high viral titers in the brain after day 6, and died of viral encephalitis between days 7 and 12. Thus, CD8(+) T cells do not control HSV-1 spread from primary to tertiary tissues, but, rather, attack the virus in infected organs and control its replication in situ.

Observations on recovery from and recurrence of HSV-2 infections in adult mice that were rescued from lethal vaginal infection by antiviral therapy

An adult mouse model for studies of latency and recurrence after vaginal HSV-2 infection is not available at present, largely because the infection kills most mice within 14 days. We describe here an antiviral therapy that rescues most vaginally infected mice from death. Vaginally infected mice were nearly all rescued by combined treatment with one dose of monoclonal anti-HSV glycoprotein D 3 days after infection plus valacyclovir in the drinking water on days 3, 4, 5, 7, 9, 11, 13, and 15 after infection. At 60 days after infection, PCR measurements revealed that most rescued mice had viral DNA in their lumbosacral dorsal root ganglia, lumbosacral spinal cords, and paracervical autonomic ganglia, consistent with the possibility that latent infections were established. At this time, immunolabeling revealed CD45+ lymphoid cells in these neural tissues in rescued mice but not in normal control mice. In vivo depletion of T lymphocytes with monoclonal antibodies caused a recurrence of herpes illness symptoms earlier and in a larger proportion of rescued mice than was observed in non-depleted rescued mice. Interestingly, many rescued mice (46/114) spontaneously developed a syndrome of typical herpes illness symptoms that began with ruffled fur on a mouse that previously had sleek fur and progressed to arched backs, feeble gait, hindlimb paralysis, and death or euthanasia, or in some cases to recovery to health. This high incidence of apparent spontaneous recurrence of HSV-2 infection in rescued mice suggests that it may be possible, with some refinement of the procedure, to obtain an effective adult mouse model for studies of therapeutic vaccination to inhibit or prevent HSV-2 recurrence after genital tract infection.

Immune control of herpes simplex virus during latency

Herpes simplex virus type 1 (HSV-1) persists within the host in the presence of concomitant immunity by establishing a latent infection within sensory neurons. HSV-1 latency is widely viewed as a neuron-enforced quiescent state of the virus, in which a lack of viral protein synthesis prevents recognition of the infected neuron by the host immune system. On the basis of recent findings, however, we propose a more dynamic view of HSV-1 latency characterized by persistent or intermittent low-level viral gene expression in some latently infected neurons. We further propose that HSV-1-specific memory/effector CD8(+) T lymphocytes that are retained in the ganglion in close apposition to the neurons prevent full reactivation and virion formation through IFN-gamma production and an additional undefined mechanism(s).

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

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

Protective and pathological roles of virus-specific and bystander CD8+ T cells in herpetic stromal keratitis

Herpetic stromal keratitis (HSK), resulting from corneal HSV-1 infection, represents a T cell-mediated immunopathologic lesion. In T cell transgenic mice on a SCID or RAG knockout background, the T cells mediating lesions are unreactive to viral Ags. In these bystander models, animals develop ocular lesions but are unable to control infection. Transfer of HSV-immune cells into a CD8(+) T cell bystander model resulted in clearance of virus from eyes, animals survived, and lesions developed to greater severity. However, the adoptively transferred CD8(+) T cells were not evident in lesions, although they were readily detectable in the lymphoid tissues as well as in the peripheral and CNS. Our results indicate that viral-induced tissue damage can be caused by bystander cells, but these fail to control infection. Immune CD8(+) T cells trigger clearance of virus from the eye, but this appears to result by the T cells acting at sites distal to the cornea. A case is made that CD8(+) T cell control is expressed in the trigeminal ganglion, serving to curtail a source of virus to the cornea.

Role of IL-6 and IL-1beta in reactivation by acetylcholine of latently infecting pseudorabies virus

We previously reported that the latently infecting Pseudorabies virus (PrV) could be reactivated by injection of swine or mice with acetylcholine. However, the mechanism of the reactivation was not clear yet. In this study, we analyzed the kinetics of cytokines related to stress to clarify the relationship between virus reactivation by acetylcholine and the immune system. IL-6 and IL-1beta were detected in mice after stimulation with acetylcholine. This shows that acetylcholine induced physiological stress conditions. However, there seemed to be no relationship between the kinetics of the cytokine levels and PrV excretion. Moreover, neither IL-6 nor IL-1beta alone could reactivate latently infecting PrV. Thus, acetylcholine causes the reactivation of latent PrV via a mechanism not involving these immunological factors.

Mathematical analysis demonstrates that interferons-beta and -gamma interact in a multiplicative manner to disrupt herpes simplex virus replication

Several studies suggest that the innate interferons (IFNs), IFN-alpha and IFN-beta, can act in concert with IFN-gamma to synergistically inhibit the replication of cytomegalovirus and herpes simplex virus type 1 (HSV-1). The significance of this observation is not yet agreed upon in large part because the nature and magnitude of the interaction between IFN-alpha/beta and IFN-gamma is not well defined. In the current study, we resolve this issue by demonstrating three points. First, the hyperbolic tangent function, tanh (x), can be used to describe the individual effects of IFN-beta or IFN-gamma on HSV-1 replication over a 320,000-fold range of IFN concentration. Second, pharmacological methods prove that IFN-beta and IFN-gamma interact in a greater-than-additive manner to inhibit HSV-1 replication. Finally, the potency with which combinations of IFN-beta and IFN-gamma inhibit HSV-1 replication is accurately predicted by multiplying the individual inhibitory effects of each cytokine. Thus, IFN-beta and IFN-gamma interact in a multiplicative manner. We infer that a primary antiviral function of IFN-gamma lies in its capacity to multiply the potency with which IFN-alpha/beta restricts HSV-1 replication in vivo. This hypothesis has important ramifications for understanding how T lymphocyte-secreted cytokines such as IFN-gamma can force herpesviruses into a latent state without destroying the neurons or leukocytes that continue to harbor these viral infections for the lifetime of the host.

Elucidating the protective and pathologic T cell species in the virus-induced corneal immunoinflammatory condition herpetic stromal keratitis

Herpetic stromal keratitis (HSK) results in postinfection with Herpes simplex virus type 1 (HSV-1). The pathogenesis involves tissue damage by the host immune system, classifying HSK as an immunopathological disease. The crucial disease orchestrating cells is thought to be the T lymphocytes. The present study elucidates pathogenic and protective T cell subsets involved in the development of HSK using the gBT mice, which possess a monoclonal population of CD8+ T cells reactive to a HSV immunodominant epitope. Results show that HSV-reactive CD8+ T cells enter infected corneas during the acute but not the chronic phase of the disease during which the predominant population is CD4+ T cells. Adoptive transfer experiments in T and B cell-deficient recombination-activating gene knockout mice revealed that HSV-reactive CD8+ T cells are capable of ocular virus clearance, possibly through a combination of corneal and peripheral nervous system antiviral effects, but are not involved in lesion development. CD4+ T cells of the virus-specific or nonspecific species emerged as the pathogenic T cells capable of precipitating disease. These observations have the potential to yield important treatment strategies by targeting specific cell types in HSK.

Persistent expression of chemokine and chemokine receptor RNAs at primary and latent sites of herpes simplex virus 1 infection

Inflammatory cytokines and infiltrating T cells are readily detected in herpes simplex virus (HSV) infected mouse cornea and trigeminal ganglia (TG) during the acute phase of infection, and certain cytokines continue to be expressed at lower levels in infected TG during the subsequent latent phase. Recent results have shown that HSV infection activates Toll-like receptor signaling. Thus, we hypothesized that chemokines may be broadly expressed at both primary sites and latent sites of HSV infection for prolonged periods of time. Real-time reverse transcriptase-polymrease chain reaction (RT-PCR) to quantify expression levels of transcripts encoding chemokines and their receptors in cornea and TG following corneal infection. RNAs encoding the inflammatory-type chemokine receptors CCR1, CCR2, CCR5, and CXCR3, which are highly expressed on activated T cells, macrophages and most immature dendritic cells (DC), and the more broadly expressed CCR7, were highly expressed and strongly induced in infected cornea and TG at 3 and 10 days postinfection (dpi). Elevated levels of these RNAs persisted in both cornea and TG during the latent phase at 30 dpi. RNAs for the broadly expressed CXCR4 receptor was induced at 30 dpi but less so at 3 and 10 dpi in both cornea and TG. Transcripts for CCR3 and CCR6, receptors that are not highly expressed on activated T cells or macrophages, also appeared to be induced during acute and latent phases; however, their very low expression levels were near the limit of our detection. RNAs encoding the CCR1 and CCR5 chemokine ligands MIP-1α, MIP-1β and RANTES, and the CCR2 ligand MCP-1 were also strongly induced and persisted in cornea and TG during the latent phase. These and other recent results argue that HSV antigens or DNA can stimulate expression of chemokines, perhaps through activation of Toll-like receptors, for long periods of time at both primary and latent sites of HSV infection. These chemokines recruit activated T cells and other immune cells, including DC, that express chemokine receptors to primary and secondary sites of infection. Prolonged activation of chemokine expression could provide mechanistic explanations for certain aspects of HSV biology and pathogenesis.

CD8(+) T cells control corneal disease following ocular infection with herpes simplex virus type 1

The role that T cell subsets play in herpetic stromal keratitis (HSK) has been the subject of intense research efforts. While most studies implicate CD4(+) T cells as the principal cell type mediating primary corneal disease, recent reports using knockout mice have suggested that both CD4(+) and CD8(+) T cell subsets may play integral roles in modulating the disease. Furthermore, recent studies suggest that CD8(+) T cells are directly involved in maintaining virus latency in infected trigeminal ganglia. This work has addressed these discrepancies by infecting the corneas of mice lacking CD4(+) and CD8(+) T cells with herpes simplex virus type 1 (HSV-1) and monitoring both corneal disease and latent infection of trigeminal ganglia. Results indicated that mice lacking CD8(+) T cells had more severe corneal disease than either BALB/c or B6 parental strains. In contrast, mice lacking CD4(+) T cells had a milder disease than parental strains. When mice were evaluated for persistence of infectious virus, only transient differences were observed in periocular tissue and corneas. No significant differences were found in persistence of virus in trigeminal ganglia or virus reactivation from explanted ganglia. These data support the following conclusions. CD4(+) T cells are not required for resistance to infection with HSV-1 and probably mediate HSK. Mice lacking CD8(+) T cells do not display differences in viral loads or reactivation and thus CD8(+) T cells are not absolutely required to maintain latency. Finally, CD8(+) T cells probably play a protective role by regulating the immunopathological response that mediates HSK.

Herpes simplex virus-specific CD8+ T cells can clear established lytic infections from skin and nerves and can partially limit the early spread of virus after cutaneous inoculation

HSV infects skin or mucosal epithelium as well as entering the sensory nerves and ganglia. We have used TCR-transgenic T cells specific for the immunodominant class I-restricted determinant from HSV glycoprotein B (gB) combined with a flank zosteriform model of infection to examine the ability of CD8+ T cells to deal with infection. During the course of zosteriform disease, virus rapidly spreads from the primary inoculation site in the skin to sensory dorsal root ganglia and subsequently reappears in the distal flank. Virus begins to be cleared from all sites about 5 days after infection when gB-specific CD8+ T cells first appear within infected tissues. Although activated gB-specific effectors can partially limit virus egress from the skin, they do so only at the earliest times after infection and are ineffective at halting the progression of zosteriform disease once virus has left the inoculation site. In contrast, these same T cells can completely clear ongoing lytic replication if transferred into infected immunocompromised RAG-1-/- mice. Therefore, we propose that the role of CD8+ T cells during the normal course of disease is to clear replicating virus after infection is well established rather than limit the initial spread of HSV from the primary site of inoculation.

Absence of tumour necrosis factor facilitates primary and recurrent herpes simplex virus-1 infections

Tumour necrosis factor (TNF) is an important cytokine in the innate immune response against various infections, including herpes simplex virus (HSV) infection. It has recently become a molecular target of anti-cytokine treatment in certain inflammatory diseases. TNF depletion resulted in a more rapid emergence of infectious HSV-1 in the explant cultures of latently infected trigeminal ganglia (TG), compared with controls. To further evaluate the importance of TNF in the host's defence responses against HSV-1, TNF-knockout mice were challenged via scarified cornea. These mice were more susceptible to primary acute corneal HSV-1 infection than controls, as manifested by an increased mortality rate and higher infectious virus titres in the eyes and TG, indicating that TNF is critical for defence during acute HSV infection. These results imply that the administration of anti-inflammatory TNF antagonists might facilitate the propagation of infectious HSV, resulting in an exacerbation of primary and recurrent acute lesions.

Herpes simplex virus type 1 infection associated with atrial myxoma

Some findings suggest an infectious factor in cardiac myxoma and certain histopathological features indicate herpes simplex virus type 1 (HSV-1) infection. We hypothesized that HSV-1 may be involved in the pathogenesis of cardiac myxoma. Paraffin-embedded tissue samples from 17 patients with atrial myxoma were investigated for HSV-1 antigen by immunohistochemistry and viral genomic DNA by nested polymerase chain reaction. The histogenesis and oncogenesis of atrial myxoma were assessed by the expression of calretinin, Ki67, and p53 protein, respectively. Autopsy myocardial samples, including endocardium from 12 patients who died by accident or other conditions, were used for comparison. HSV-1 antigen was detected in atrial myxoma from 12 of 17 patients: 8 of these 12 samples were positive also for HSV-1 DNA. No HSV-1 antigen or DNA was found in tissue from the comparison group. Antigens of HSV-2, varicella-zoster virus, Epstein-Barr virus, and cytomegalovirus were not found in atrial myxoma. Calretinin was found in myxoma cells of all 17 cases but Ki67 was present only in smooth muscle cells or infiltrating cells in some cases. p53 was not detectable in any myxoma. Most infiltrating cells were cytotoxic T lymphocytes. These data suggest that HSV-1 infection is associated with some cases of sporadic atrial myxoma and that these may result from a chronic inflammatory lesion of endocardium.

Latent herpesvirus infection in human trigeminal ganglia causes chronic immune response

The majority of trigeminal ganglia (TGs) are latently infected with alpha-herpesviruses [herpes simplex virus type-1 (HSV-1) and varicella-zoster virus (VZV)]. Whereas HSV-1 periodically reactivates in the TGs, VZV reactivates very rarely. The goal of this study was to determine whether herpesvirus latency is linked to a local immune cell infiltration in human TGs. T cells positive for the CD3 and CD8 markers, and CD68-positive macrophages were found in 30 of 42 examined TGs from 21 healthy individuals. The presence of immune cells correlated constantly with the occurrence of the HSV-1 latency-associated transcript (LAT) and only irregularly with the presence of latent VZV protein. In contrast, uninfected TGs showed no immune cell infiltration. Quantitative RT-PCR revealed that CD8, interferon-gamma, tumor necrosis factor-alpha, IP-10, and RANTES transcripts were significantly induced in TGs latently infected with HSV-1 but not in uninfected TGs. The persisting lymphocytic cell infiltration and the elevated CD8 and cytokine/chemokine expression in the TGs demonstrate for the first time that latent herpesviral infection in humans is accompanied by a chronic inflammatory process at an immunoprivileged site but without any neuronal destruction. The chronic immune response seems to maintain viral latency and influence viral reactivation.

The herpes simplex virus-1 Us3 protein kinase blocks CD8T cell lysis by preventing the cleavage of Bid by granzyme B

The Us3 kinase is part of the antiapoptotic arsenal that salvages herpes simplex virus (HSV)-1-infected cells from damage caused by different stimuli. We demonstrate that Us3 protects HSV-1-infected cells from lysis by MHC class I-restricted CD8T cells without affecting antigen presentation. Expression of Us3 was associated with inhibition of caspase activation and reduced cleavage of the proapoptotic protein Bid. Recombinant granzyme B (GrB) failed to cleave Bid in cytosolic extracts from Us3 positive cells, while recombinant Bid served as substrate for Us3 phosphorylation, suggesting that modification of Bid by Us3 blocks its processing by GrB. Our data illustrate a new strategy of viral escape, where modification of a cellular proapoptotic substrate may prevent lysis of the infected cells without affecting other T-cell functions.

Expression and function of chemokines during viral infections: from molecular mechanisms to in vivo function

Recruitment and activation of leukocytes are important for elimination of microbes, including viruses, from infected areas. Chemokines constitute a group of bioactive peptides that regulate leukocyte migration and also contribute to activation of these cells. Chemokines are essential mediators of inflammation and important for control of viral infections. The profile of chemokine expression contributes to shaping the immune response during viral infection, whereas viral subversion of the chemokine system allows the virus to evade antiviral activities of the host. In this review, we discuss the role of chemokines in host-defense against virus infections, and we also look deeper into the virus-cell interactions that trigger chemokine expression as well as the cellular signaling cascades involved.

Latent herpes simplex virus infection of sensory neurons alters neuronal gene expression

The persistence of herpes simplex virus (HSV) and the diseases that it causes in the human population can be attributed to the maintenance of a latent infection within neurons in sensory ganglia. Little is known about the effects of latent infection on the host neuron. We have addressed the question of whether latent HSV infection affects neuronal gene expression by using microarray transcript profiling of host gene expression in ganglia from latently infected versus mock-infected mouse trigeminal ganglia. (33)P-labeled cDNA probes from pooled ganglia harvested at 30 days postinfection or post-mock infection were hybridized to nylon arrays printed with 2,556 mouse genes. Signal intensities were acquired by phosphorimager. Mean intensities (n = 4 replicates in each of three independent experiments) of signals from mock-infected versus latently infected ganglia were compared by using a variant of Student's t test. We identified significant changes in the expression of mouse neuronal genes, including several with roles in gene expression, such as the Clk2 gene, and neurotransmission, such as genes encoding potassium voltage-gated channels and a muscarinic acetylcholine receptor. We confirmed the neuronal localization of some of these transcripts by using in situ hybridization. To validate the microarray results, we performed real-time reverse transcriptase PCR analyses for a selection of the genes. These studies demonstrate that latent HSV infection can alter neuronal gene expression and might provide a new mechanism for how persistent viral infection can cause chronic disease.

CD8 T cell responses to infectious pathogens

CD8 T cells respond to viral infections but also participate in defense against bacterial and protozoal infections. In the last few years, as new methods to accurately quantify and characterize pathogen-specific CD8 T cells have become available, our understanding of in vivo T cell responses has increased dramatically. Pathogen-specific T cells, once thought to be quite rare following infection, are now known to be present at very high frequencies, particularly in peripheral, nonlymphoid tissues. With the ability to visualize in vivo CD8 T cell responses has come the recognition that T cell expansion is programmed and, to a great extent, independent of antigen concentrations. Comparison of CD8 T cell responses to different pathogens also highlights the intricate relationship between microbially induced innate inflammatory responses and the kinetics, magnitude, and character of long-term T cell responses. This review describes recent progress in some of the major murine models of CD8 T cell-mediated immunity to viral, bacterial, and protozoal infection.

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

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

Herpes simplex virus-specific memory CD8+ T cells are selectively activated and retained in latently infected sensory ganglia

This study challenges the concept that herpes simplex virus type 1 (HSV-1) latency represents a silent infection that is ignored by the host immune system, and suggests antigen-directed retention of memory CD8(+) T cells. CD8(+) T cells specific for the immunodominant gB(498-505) HSV-1 epitope are selectively retained in the ophthalmic branch of the latently infected trigeminal ganglion, where they acquire and maintain an activation phenotype and the capacity to produce IFN-gamma. Some CD8(+) T cells showed TCR polarization to junctions with neurons. A gB(498-505) peptide-specific CD8(+) T cell clone can block HSV-1 reactivation from latency in ex vivo trigeminal ganglion cultures. We conclude that CD8(+) T cells provide active surveillance of HSV-1 gene expression in latently infected sensory neurons.

Cutting edge: conventional CD8 alpha+ dendritic cells are preferentially involved in CTL priming after footpad infection with herpes simplex virus-1

CTL play a major role in immunity to HSV type 1, but little is known about the priming process. In this study, we have examined the class I-restricted presentation of an immunodominant determinant from HSV-1 glycoprotein B after footpad infection. We have found that the only cell types capable of presenting this determinant in draining popliteal lymph nodes within the first 3 days after infection are the CD11c(+)CD8alpha(+)CD45RA(-) dendritic cells. Given that such class I-restricted presentation is essential for CTL priming, this implies that these conventional CD8alpha(+) dendritic cells are the key subset involved in CTL immunity to this virus.

Quantitative analysis of herpes simplex virus reactivation in vivo demonstrates that reactivation in the nervous system is not inhibited at early times postinoculation

Recent studies utilizing an ex vivo mouse model of herpes simplex virus (HSV) reactivation have led to the hypothesis that, under physiologic conditions inducing viral reactivation, the immune cells within the infected ganglion block the viral replication cycle and maintain the viral genome in a latent state. One prediction from the ex vivo study is that reactivation in ganglia in vivo would be inhibited at early times postinoculation, when the numbers of inflammatory cells in the ganglia are greatest. To distinguish between an effect of the immune infiltrates on (i) infectious virus produced and/or recovered in the ganglion and (ii) the number of neurons undergoing lytic transcriptional activity (reactivating), an assay to quantify the number of neurons expressing lytic viral protein in ganglia in vivo was developed. Infectious virus and HSV protein-positive neurons were quantified from days 9 through 240 postinoculation in latently infected trigeminal ganglia before and at 22 h after hyperthermic-stress-induced reactivation. Significant increases in the amount of virus and the number of positive neurons were detected poststress in ganglia at all times examined. Unexpectedly, the greatest levels of reactivation occurred at the times examined most proximal to inoculation. Acyclovir was utilized to stop residual acute-phase virus production, and this treatment did not reduce the level of reactivation on day 14. Thus, the virus measured after induction was a product of reactivation. These data indicate that, in contrast to observations in the ex vivo model, immune cells in the ganglia during the resolution of acute infection do not inhibit reactivation of the virus in ganglia in vivo.

The early expression of glycoprotein B from herpes simplex virus can be detected by antigen-specific CD8+ T cells

The immune response to cutaneous herpes simplex virus type 1 (HSV-1) infection begins with remarkable rapidity. Activation of specific cytotoxic T lymphocytes (CTL) begins within hours of infection, even though the response within the draining lymph nodes peaks nearly 5 days later. HSV gene products are classified into three main groups, alpha, beta, and gamma, based on their kinetics and requirements for expression. In C57BL/6 mice, the immunodominant epitope from HSV is derived from glycoprotein B (gB(498-505)). While gB is considered a gamma or "late" gene product, previous reports have indicated that some level of gene expression may occur soon after infection. Using brefeldin A as a specific inhibitor of viral antigen presentation to major histocompatibility complex class I-restricted CTL, we have formally addressed the timing of gB peptide expression in an immunologically relevant manner following infection. Presentation of gB peptide detected by T-cell activation was first observed within 2 h of infection. Comparison with another viral epitope expressed early during infection, HSV-1 ribonucleotide reductase, demonstrated that gB is presented with the same kinetics as this classical early-gene product. Moreover, this rapidity of gB expression was further illustrated via rapid priming of naïve transgenic CD8(+) T cells in vivo after HSV-1 infection of mice. These results establish that gB is expressed rapidly following HSV-1 infection, at levels capable of effectively stimulating CD8(+) T cells.

Herpes simplex virus type 1 and bovine herpesvirus 1 latency

Primary infection by herpes simplex virus type 1 (HSV-1) can cause clinical symptoms in the peripheral and central nervous system, upper respiratory tract, and gastrointestinal tract. Recurrent ocular shedding leads to corneal scarring that can progress to vision loss. Consequently, HSV-1 is the leading cause of corneal blindness due to an infectious agent. Bovine herpesvirus 1 (BHV-1) has similar biological properties to HSV-1 and is a significant health concern to the cattle industry. Latency of BHV-1 and HSV-1 is established in sensory neurons of trigeminal ganglia, but latency can be interrupted periodically, leading to reactivation from latency and spread of infectious virus. The ability of HSV-1 and BHV-1 to reactivate from latency leads to virus transmission and can lead to recurrent disease in individuals latently infected with HSV-1. During latency, the only abundant HSV-1 RNA expressed is the latency-associated transcript (LAT). In latently infected cattle, the latency-related (LR) RNA is the only abundant transcript that is expressed. LAT and LR RNA are antisense to ICP0 or bICP0, viral genes that are crucial for productive infection, suggesting that LAT and LR RNA interfere with productive infection by inhibiting ICP0 or bICP0 expression. Numerous studies have concluded that LAT expression is important for the latency-reactivation cycle in animal models. The LR gene has recently been demonstrated to be required for the latency-reactivation cycle in cattle. Several recent studies have demonstrated that LAT and the LR gene inhibit apoptosis (programmed cell death) in trigeminal ganglia of infected animals and transiently transfected cells. The antiapoptotic properties of LAT map to the same sequences that are necessary for promoting reactivation from latency. This review summarizes our current knowledge of factors regulating the latency-reactivation cycle of HSV-1 and BHV-1.

Recent progress in herpes simplex virus immunobiology and vaccine research

Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) cause prevalent, chronic infections that have serious outcomes in some individuals. Neonatal herpes may occur when the infant traverses the cervix during maternal genital herpes. Genital herpes is a major risk factor for human immunodeficiency virus type 1 transmission. Considerable efforts have been made to design and test vaccines for HSV, focusing on genital infection with HSV-2. Several protein subunit vaccines based on HSV-2 envelope glycoproteins have reached advanced-phase clinical trials. These antigens were chosen because they are the targets of neutralizing-antibody responses and because they elicit cellular immunity. Encouraging results have been reported in studies of treatment of HSV-seronegative women with a vaccine consisting of truncated glycoprotein D of HSV-2 and a novel adjuvant. Because most sexual HSV transmission occurs during asymptomatic shedding, it is important to evaluate the impact of vaccination on HSV-2 infection, clinically apparent genital herpes, and HSV shedding among vaccine recipients who acquire infection. There are several other attractive formats, including subunit vaccines that target cellular immune responses, live attenuated virus strains, and mutant strains that undergo incomplete lytic replication. HSV vaccines have also been evaluated for the immunotherapy of established HSV infection.

Direct link between mhc polymorphism, T cell avidity, and diversity in immune defense

Major histocompatibility complex (mhc)-encoded molecules govern immune responses by presenting antigenic peptides to T cells. The extensive polymorphism of genes encoding these molecules is believed to enhance immune defense by broadening the array of antigenic peptides available for T cell recognition, but direct evidence supporting the importance of this mechanism in combating pathogens is limited. Here we link mhc polymorphism-driven diversification of the cytotoxic T lymphocyte (CTL) repertoire to the generation of high-avidity, protective antiviral T cells and to superior antiviral defense. Thus, much of the beneficial effect of the mhc polymorphism in immune defense may be due to its critical influence on the properties of the selected CTL repertoire.

Alpha/Beta interferon and gamma interferon synergize to inhibit the replication of herpes simplex virus type 1

In vivo evidence suggests that T-cell-derived gamma interferon (IFN-gamma) can directly inhibit the replication of herpes simplex virus type 1 (HSV-1). However, IFN-gamma is a weak inhibitor of HSV-1 replication in vitro. We have found that IFN-gamma synergizes with the innate IFNs (IFN-alpha and -beta) to potently inhibit HSV-1 replication in vitro and in vivo. Treatment of Vero cells with either IFN-beta or IFN-gamma inhibits HSV-1 replication by <20-fold, whereas treatment with both IFN-beta and IFN-gamma inhibits HSV-1 replication by approximately 1,000-fold. Treatment with IFN-beta and IFN-gamma does not prevent HSV-1 entry into Vero cells, and the inhibitory effect can be overcome by increasing the multiplicity of HSV-1 infection. The capacity of IFN-beta and IFN-gamma to synergistically inhibit HSV-1 replication is not virus strain specific and has been observed in three different cell types. For two of the three virus strains tested, IFN-beta and IFN-gamma inhibit HSV-1 replication with a potency that approaches that achieved by a high dose of acyclovir. Pretreatment of mouse eyes with IFN-beta and IFN-gamma reduces HSV-1 replication to nearly undetectable levels, prevents the development of disease, and reduces the latent HSV-1 genome load per trigeminal ganglion by approximately 200-fold. Thus, simultaneous activation of IFN-alpha/beta receptors and IFN-gamma receptors appears to render cells highly resistant to the replication of HSV-1. Because IFN-alpha or IFN-beta is produced by most cells as an innate response to virus infection, the results imply that IFN-gamma secreted by T cells may provide a critical second signal that potently inhibits HSV-1 replication in vivo.

The R1 subunit of herpes simplex virus ribonucleotide reductase protects cells against apoptosis at, or upstream of, caspase-8 activation

The R1 subunit of herpes simplex virus (HSV) ribonucleotide reductase, which in addition to its C-terminal reductase domain possesses a unique N-terminal domain of about 400 amino acids, is thought to have an additional, as yet unknown, function. Here, we report that the full-length HSV-2 R1 has an anti-apoptotic function able to protect cells against death triggered by expression of R1(Delta2-357), an HSV-2 R1 subunit with its first 357 amino acids deleted. We further substantiate the R1 anti-apoptotic activity by showing that its accumulation at low level could completely block apoptosis induced by TNF-receptor family triggering. Activation of caspase-8 induced either by TNF or by Fas ligand expression was prevented by the R1 protein. As HSV R1 did not inhibit cell death mediated by several agents acting via the mitochondrial pathway (Bax overexpression, etoposide, staurosporine and menadione), it is proposed that it functions to interrupt specifically death receptor-mediated signalling at, or upstream of, caspase-8 activation. The N-terminal domain on its own did not exhibit anti-apoptotic activity, suggesting that both domains of R1 or part(s) of them are necessary for this new function. Evidence for the importance of HSV R1 in protecting HSV-infected cells against cytokine-induced apoptosis was obtained with the HSV-1 R1 deletion mutants ICP6Delta and hrR3. These results show that, in addition to its ribonucleotide reductase function, which is essential for virus reactivation, HSV R1 could contribute to virus propagation by preventing apoptosis induced by the immune system.

Therapeutic vaccination with vhs(-) herpes simplex virus reduces the severity of recurrent herpetic stromal keratitis in mice

Virion host shutoff (vhs)-deficient herpes simplex virus (HSV) was tested as a therapeutic vaccine in a mouse model of UV light-induced recurrent herpetic stromal keratitis. Four weeks after primary corneal infection, mice were vaccinated intraperitoneally with vhs(-) vaccine or control. Four weeks after vaccination, the eyes of latently infected mice were UV-B irradiated to induce recurrent virus shedding and disease. Post-irradiation corneal opacity in latently infected, vhs(-)-vaccinated mice was significantly reduced compared to control-vaccinated mice (P=0.007 to 0.035). The incidence and duration of recurrent virus shedding were the same in both groups. Antibody titres were increased (P=0.05) and delayed type hypersensitive responses were unaffected by vhs(-) vaccination. Combined with studies using different vaccination timing and vhs(-) genotypes, these data suggest that deletion of vhs is a useful strategy in the development of a therapeutic HSV vaccine, and that temporal and genetic factors influence vaccination outcome.

Immunologic control of HIV-1

By destroying CD4+ T cells, human immunodeficiency virus-1 (HIV-1) infection results in immunodeficiency and the inability of the immune system to contain the virus in most individuals. Although treatment of HIV-1 infection with potent antiretroviral medications has resulted in enormous clinical benefit, there is a growing recognition of the limitations of this therapy. As a result, novel approaches to treating HIV-1 infection are being considered. One such strategy is immunotherapy, which seeks to boost immune responses against HIV-1 and control the virus. This approach is based on studies of other viruses in which a coordinated immune response contains the chronic infection. Recent studies show that CD4+ helper responses, CD8+ T cell activity, and antibodies may contribute to control of the virus without antiretroviral therapy in some HIV-positive individuals. Based on this understanding of the immunologic correlates of control of HIV-1, exciting new immunotherapeutic strategies for HIV-1 infection are being designed and tested.

Analysis of bovine trigeminal ganglia following infection with bovine herpesvirus 1

Following primary infection of the eye, oral cavity, and/or nasal cavity, bovine herpesvirus 1 (BHV-1) establishes latency in trigeminal ganglionic (TG) neurons. Virus reactivation and spread to other susceptible animals occur after natural or corticosteroid-induced stress. Infection of calves with BHV-1 leads to infiltration of lymphocytes in TG and expression of IFN-gamma (interferon-gamma), even in latently infected calves. During latency, virus antigen and nucleic acid positive non-neural cells were occasionally detected in TG suggesting there is a low level of spontaneous reactivation. Since we could not detect virus in ocular or nasal swabs, these rare cells do not support high levels of productive infection and virus release or they do not support virus production at all. Dexamethasone (DEX) was used to initiate reactivation in latently infected calves. Foci of mononuclear or satellite cells undergoing apoptosis were detected 6h after DEX treatment, as judged by the appearance of TUNEL+ cells (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling). BHV-1 antigen expression was initially detected in lymphocytes and other non-neural cells in latently infected calves following DEX treatment. At 24h after DEX treatment, viral antigen expression and nucleic acid were readily detected in neurons. Our data suggest that persistent lymphocyte infiltration and cytokine expression occur during latency because a low number of cells in TG express BHV-1 proteins. Induction of apoptosis and changes in cytokine expression following DEX treatment correlates with reactivation from latency. We hypothesize that inflammatory infiltration of lymphoid cells in TG plays a role in regulating latency.

Latency sites and reactivation of duck enteritis virus

Duck virus enteritis (DVE) is a contagious disease caused by herpesvirus in waterfowl populations. Recovered birds become carriers and shed the virus periodically. Reactivation of latent duck enteritis virus (DEV) has been implicated in outbreaks of DVE in domestic and migrating waterfowl populations. In this study, the sites for virus latency were determined in white Pekin ducks infected with the DEV-97 strain. At 3 wk postinfection, infectious virus was not detectable in tissues or cloacal swabs (CSs). At 7 and 9 weeks postinfection, the viral DNA was detected by polymerase chain reaction in the trigeminal ganglia (TG), suggesting that the virus is latent. Viral DNA was detected in the peripheral blood lymphocytes (PBL), spleen, thymus, bursa, and CSs only after in vitro cocultivation. In vivo virus reactivation was demonstrated when dexamethasone or a combination of dexamethasone and cyclophosphamide was inoculated in latently infected ducks. The reactivation of DEV occurred without any clinical evidence of the disease, but the virus was detected in PBL and CSs. We conclude from this study that DEV establishes latency in TG and lymphoid tissues including PBL.

Therapeutic immunization with a virion host shutoff-defective, replication-incompetent herpes simplex virus type 1 strain limits recurrent herpetic ocular infection

Immunization of mice with herpes simplex virus type 1 (HSV-1) mutant viruses containing deletions in the gene for virion host shutoff (vhs) protein diminishes primary and recurrent corneal infection with wild-type HSV-1. vhs mutant viruses are severely attenuated in vivo but establish latent infections in sensory neurons. A safer HSV-1 mutant vaccine strain, Delta41Delta29, has combined vhs and replication (ICP8-) deficits and protects BALB/c mice against primary corneal infection equivalent to a vhs- strain (BGS41). Here, we tested the hypothesis that Delta41Delta29 can protect as well as BGS41 in a therapeutic setting. Because immune response induction varies with the mouse and virus strains studied, we first determined the effect of prophylactic Delta41Delta29 vaccination on primary ocular infection of NIH inbred mice with HSV-1 McKrae, a model system used to evaluate therapeutic vaccines. In a dose-dependent fashion, prophylactic Delta41Delta29 vaccination decreased postchallenge tear film virus titers and ocular disease incidence and severity while eliciting high levels of HSV-specific antibodies. Adoptive transfer studies demonstrated a dominant role for immune serum and a lesser role for immune cells in mediating prophylactic protection. Therapeutically, vaccination with Delta41Delta29 effectively reduced the incidence of UV-B-induced recurrent virus shedding in latently infected mice. Therapeutic Delta41Delta29 and BGS41 vaccination decreased corneal opacity and delayed-type hypersensitivity responses while elevating antibody titers, compared to controls. These data indicate that replication is not a prerequisite for generation of therapeutic immunity by live HSV mutant virus vaccines and raise the possibility that genetically tailored replication-defective viruses may make effective and safe therapeutic vaccines.

Progression of armed CTL from draining lymph node to spleen shortly after localized infection with herpes simplex virus 1

We have examined the generation of CTL immunity immediately after localized footpad infection with herpes simplex virus 1 (HSV-1) using three coordinated in vivo T cell tracking methodologies. Tetrameric MHC class I containing the immunodominant peptide from HSV-1 glycoprotein B (gB) showed that after infection the proportion of Ag-specific T cells peaked at day 5 within draining popliteal lymph nodes and 2 days later in the spleen. Preferential expression of the activation marker CD25 by tetramer-positive cells in draining popliteal nodes but not spleen suggested that gB-specific T cells were initially activated within the lymph node. In vivo cytotoxicity assays showed that Ag-specific effector cells were present within the draining lymph nodes as early as day 2 after infection, with a further 2-day lag before detection in the spleen. Consistent with the very early arming of effector CTL in the draining lymph node, adoptive transfer of CFSE-labeled gB-specific transgenic T cells showed that they had undergone one to four rounds of cell division by day 2 after infection. In contrast, proliferating T cells were first detected in appreciable numbers in the spleen on day 4, at which time they had undergone extensive cell division. These data demonstrate that HSV-1-specific T cells are rapidly activated and armed within draining lymph nodes shortly after localized HSV-1 infection. This is followed by their dissemination to other compartments such as the spleen, where they further proliferate in an Ag-independent fashion.

Type I interferons and herpes simplex virus infection: a naked DNA approach as a therapeutic option?

Herpes simplex virus (HSV) types 1 and 2 are highly successful human pathogens that can elicit blinding herpetic keratoconjunctivitis, fatal sporadic encephalitis, aseptic meningitis, and increase the risk of acquiring additional sexually transmitted diseases. Type I interferons (IFN) play a significant role in controlling HSV pathogenesis by antagonizing viral replication and spread. Taking advantage of the susceptibility of HSV to IFNs, a novel approach of employing plasmid DNA cassettes expressing type 1 IFNs to antagonize viral pathogenesis has been undertaken. This review will describe recent work in our lab and those of others using naked DNA encoding cytokines to antagonize HSV replication and virus trafficking or immune-mediated pathogenesis as a result of viral assault to ocular tissue.

Gamma interferon can prevent herpes simplex virus type 1 reactivation from latency in sensory neurons

We recently demonstrated that CD8(+) T cells could block herpes simplex virus type 1 (HSV-1) reactivation from latency in ex vivo trigeminal ganglion (TG) cultures without destroying the infected neurons. Here we establish that CD8(+) T-cell prevention of HSV-1 reactivation from latency is mediated at least in part by gamma interferon (IFN-gamma). We demonstrate that IFN-gamma was produced in ex vivo cultures of dissociated latently infected TG by CD8(+) T cells that were present in the TG at the time of excision. Depletion of CD8(+) T cells or neutralization of IFN-gamma significantly enhanced the rate of HSV-1 reactivation from latency in TG cultures. When TG cultures were treated with acyclovir for 4 days to insure uniform latency, supplementation with recombinant IFN-gamma blocked HSV-1 reactivation in 80% of cultures when endogenous CD8(+) T cells were present and significantly reduced and delayed HSV-1 reactivation when CD8(+) T cells or CD45(+) cells were depleted from the TG cultures. The effectiveness of recombinant IFN-gamma in blocking HSV-1 reactivation was lost when its addition to TG cultures was delayed by more than 24 h after acyclovir removal. We propose that when the intrinsic ability of neurons to inhibit HSV-1 gene expression is compromised, HSV-specific CD8(+) T cells are rapidly mobilized to produce IFN-gamma and perhaps other antiviral cytokines that block the viral replication cycle and maintain the viral genome in a latent state.

HSV and glycoprotein J inhibit caspase activation and apoptosis induced by granzyme B or Fas

HSV-1 inhibits apoptosis of infected cells, presumably to ensure that the infected cell survives long enough to allow completion of viral replication. Because cytotoxic lymphocytes kill their targets via the induction of apoptosis, protection from apoptosis could constitute a mechanism of immune evasion for HSV. Several HSV genes are involved in the inhibition of apoptosis, including Us5, which encodes glycoprotein J (gJ). Viruses deleted for Us5 showed defects in inhibition of caspase activation after Fas ligation or UV irradiation. Transfected cells expressing the Us5 gene product gJ were protected from Fas- or UV-induced apoptosis, as measured by morphology, caspase activation, membrane permeability changes, or mitochondrial transmembrane potential. In contrast, caspase 3 activation in mitochondria-free cell lysates by granzyme (gr)B was inhibited equivalently by Us5 deletion and rescue viruses, suggesting that gJ is not required for HSV to inhibition this process. However, mitochondria-free lysates from transfected cells expressing Us5/gJ were protected from grB-induced caspase activation, suggesting that Us5/gJ is sufficient to inhibit this process. Transfected cells expressing Us5/gJ were also protected from death induced by incubation with purified grB and perforin. These findings suggest that HSV has a comprehensive set of immune evasion functions that antagonize both Fas ligand- and grB-mediated pathways of CTL-induced apoptosis. The understanding of HSV effects on killing by CTL effector mechanisms may shed light on the incomplete control of HSV infections by the immune system and may allow more rational approaches to the development of immune modulatory treatments for HSV infection.

Three different vaccines based on the 140-amino acid MUC1 peptide with seven tandemly repeated tumor-specific epitopes elicit distinct immune effector mechanisms in wild-type versus MUC1-transgenic mice with different potential for tumor rejection

Low-frequency CTL and low-titer IgM responses against tumor-associated Ag MUC1 are present in cancer patients but do not prevent cancer growth. Boosting MUC1-specific immunity with vaccines, especially effector mechanisms responsible for tumor rejection, is an important goal. We studied immunogenicity, tumor rejection potential, and safety of three vaccines: 1) MUC1 peptide admixed with murine GM-CSF as an adjuvant; 2) MUC1 peptide admixed with adjuvant SB-AS2; and 3) MUC1 peptide-pulsed dendritic cells (DC). We examined the qualitative and quantitative differences in humoral and T cell-mediated MUC1-specific immunity elicited in human MUC1-transgenic (Tg) mice compared with wild-type (WT) mice. Adjuvant-based vaccines induced MUC1-specific Abs but failed to stimulate MUC1-specific T cells. MUC1 peptide with GM-CSF induced IgG1 and IgG2b in WT mice but only IgM in MUC1-Tg mice. MUC1 peptide with SB-AS2 induced high-titer IgG1, IgG2b, and IgG3 Abs in both WT and MUC1-Tg mice. Induction of IgG responses was T cell independent and did not have any effect on tumor growth. MUC1 peptide-loaded DC induced only T cell immunity. If injected together with soluble peptide, the DC vaccine also triggered Ab production. Importantly, the DC vaccine elicited tumor rejection responses in both WT and MUC1-Tg mice. These responses correlated with the induction of MUC1-specific CD4+ and CD8+ T cells in WT mice, but only CD8(+) T cells in MUC1-Tg mice. Even though MUC1-specific CD4+ T cell tolerance was not broken, the capacity of MUC1-Tg mice to reject tumor was not compromised.