Latency of herpes simplex virus in absence of neutralizing antibody: model for reactivation

Analysis of Herpes Simplex Virus Reactivation in Explant Reveals a Method-Dependent Difference in Measured Timing of Reactivation

Herpes simplex virus (HSV) infection is widespread in the human population. Following orofacial infection, HSV establishes latency in innervating sensory neurons, primarily located in the trigeminal ganglia. A central feature of HSV pathogenesis is the ability to periodically reactivate in those neurons and be transported back to the body surface. Both transmission and disease, such as keratitis, encephalitis, and neurodegeneration, have been linked to reactivation. Despite invaluable insights obtained from model systems, interactions between viral and host functions that regulate reactivation are still incompletely understood. Various assays are used for measuring reactivation in animal models, but there have been limited comparisons between methods and the accuracy of detecting the timing of reactivation and the corresponding amount of infectious virus produced in the ganglia per reactivation event. Here, we directly compare two approaches for measuring reactivation in latently infected explanted ganglia by sampling media from the explanted cultures or by homogenization of the ganglia and compare the results to viral protein expression in the whole ganglia. We show that infectious virus detection by direct homogenization of explanted ganglia correlates with viral protein expression, but detection of infectious virus in medium samples from explanted cultures does not occur until extensive spread of virus is observed in the ganglia. The medium-sampling method is therefore not reflective of the initial timing of reactivation, and the additional variables influencing spread of virus in the ganglia should be considered when interpreting results obtained using this method.

IMPORTANCE The development of treatments to prevent and/or treat HSV infection rely upon understanding viral and host factors that influence reactivation. Progress is dependent on experimental methods that accurately measure the frequency and timing of reactivation in latently infected neurons. In this study, two methods for detecting reactivation using the explant model are compared. We show through direct tissue homogenization that reactivation occurs much earlier than can be detected by the indirect method of sampling media from explanted cultures. Thus, the sampling method does not detect the initial timing of reactivation, and results obtained using this method are subject to additional variables with the potential to obscure reactivation outcomes.

Phocine herpesvirus 1 (PhHV-1) in harbor seals from Svalbard, Norway

Phocine herpesvirus 1 (PhHV-1) infections in seals are associated with disease and sometimes high mortality, primarily in young animals. PhHV-1 has been detected in seals from European waters as well as in waters on both coasts of North America. Serological surveys of various pinniped species have indicated a wide geographical distribution of PhHV-1. A quantitative and sensitive real-time PCR assay targeting the gene encoding glycoprotein B of PhHV-1 was developed for detection of PhHV-1 in ocular and nasal swab samples from wild harbor seals (Phoca vitulina) from Svalbard (Norway). PhHV-1 DNA was detected in samples from 6 (8%) seals collected in 2009 and 2 (3%) in 2010; all had herpesvirus DNA in the ocular swab sample, whereas only one of these animals also had herpesvirus DNA in the nasal swab sample. Four PCR positive animals were approximately 1 year of age and four were pups of the year. Serum samples obtained in 1998 (n=59), 1999 (n=74), 2000 (n=81), 2009 (n=69) and 2010 (n=83) were tested for anti-PhHV-1 antibodies in an indirect ELISA. The PhHV-1 seroprevalence in the population remained high throughout this period, varying from 77 to 100% between years. No eye disease was observed in this harbor seal population, but the ELISA and PCR findings reported here suggest that PhHV-1 is endemic in this globally northernmost harbor seal colony, and that the virus is shed on the mucosa of the eye and nose.

Efficacy of polyclonal antibodies for treatment of ocular herpes simplex infection

PURPOSE

Herpes simplex virus (HSV) can cause corneal infections in humans and lead to permanent scarring, loss of vision, and blindness. Current treatment of epithelial HSV keratitis consists of using antiviral DNA analogs. In this study, we used in vitro and in vivo models to evaluate the efficacy of six polyclonal antibodies to HSV recombinant surface glycoprotein D in treating ocular epithelial HSV.

METHODS

Confluent cultures of African Green monkey kidney fibroblasts (Vero cells) and normal 3-to 5-lb female New Zealand White rabbits were infected with HSV type 1, strain RE. In vitro virucidal and antiviral assays were performed, and the best of the compounds was chosen for the in vivo stage. Animals were carefully monitored until day 5 after HSV-1 inoculation, then arbitrarily divided into groups receiving, for 14 days, varying doses of: polyclonal antibodies four times a day, polyclonal antibodies three times a day, trifluorothymidine (current treatment of choice and the positive control) nine times a day, or 0.9% physiologic saline nine times a day. The animals were followed up in a masked fashion and carefully monitored for severity and resolution of the HSV infection by biomicroscopy (slit lamp) examination and viral cultures using standardized plaque assays.

RESULTS

All six of the compounds tested were effective in vitro, but one compound in particular, SP-510-50, was superior. It was used for the in vivo testing and showed antiviral efficacy in a dose-dependent manner, and at dosing four times a day, it was of comparable efficacy to trifluorothymidine (nine times a day).

CONCLUSIONS

We conclude that polyclonal antibodies to glycoprotein D appear to be effective antiviral agents in vitro and in vivo in a rabbit model of HSV-1 keratitis and show promise as a new antiviral treatment for ophthalmic use.

The immune response to ocular herpes simplex virus type 1 infection

Herpes simplex virus type 1 (HSV-1) is a prevalent microbial pathogen infecting 60% to 90% of the adult world population. The co-evolution of the virus with humans is due, in part, to adaptations that the virus has evolved to aid it in escaping immune surveillance, including the establishment of a latent infection in its human host. A latent infection allows the virus to remain in the host without inducing tissue pathology or eliciting an immune response. During the acute infection or reactivation of latent virus, the immune response is significant, which can ultimately result in corneal blindness or fatal sporadic encephalitis. In fact, HSV-1 is one of the leading causes of infectious corneal blindness in the world as a result of chronic episodes of viral reactivation leading to stromal keratitis and scarring. Significant inroads have been made in identifying key immune mediators that control ocular HSV-1 infection and potentially viral reactivation. Likewise, viral mechanisms associated with immune evasion have also been identified and will be discussed. Lastly, novel therapeutic strategies that are currently under development show promise and will be included in this review. Most investigators have taken full advantage of the murine host as a viable working in vivo model of HSV-1 due to the sensitivity and susceptibility to viral infection, ease of manipulation, and a multitude of developed probes to study changes at the cellular and molecular levels. Therefore, comments in this review will primarily be restricted to those observations pertaining to the mouse model and the assumption (however great) that similar events occur in the human condition.

Establishment of latent herpes simplex virus type 1 infection in resistant, sensitive, and immunodeficient mouse strains

Productive infection with herpes simplex virus (HSV) type 1 is limited by both innate and adaptive immune mechanisms. The purpose of the current study was to determine whether these mechanisms also play a role in the establishment of latent HSV infection. First we examined the trigeminal ganglia (TG) of severe combined immunodeficiency (SCID), interferon-gamma knockout (GKO), and beige (a strain deficient in natural killer cell activity) mice following ocular inoculation with HSV. Although infection of SCID mice was invariably lethal, we consistently found latently infected neurons in the TG of these animals at 2-4 days postinoculation. HSV infection of GKO and beige mice, while not lethal, was characterized by a greater number of productively infected TG neurons and/or a delay in the time to peak productive infection compared to C57BL/6 controls. However, as assayed by both in situ hybridization for LAT expression and quantitative PCR (Q-PCR) for viral DNA, we found that HSV established a latent infection in GKO and beige mice as efficiently as in C57BL/6 controls. We subsequently examined the TG of "HSV-sensitive" strains of mice (Swiss-Webster, CBA, and BALB/c) following ocular infection with HSV. At the peak of acute ganglionic infection the number of productively infected TG neurons in each of these mouse strains was about sevenfold greater than in the "HSV-resistant" strain C57BL/6, consistent with previously reported differences in susceptibility to lethal challenge with HSV. However, as assayed by both in situ hybridization for LAT and Q-PCR for viral DNA, we found that HSV established a latent infection in Swiss-Webster, CBA, and BALB/c mice as efficiently as in C57BL/6 controls. We conclude that HSV efficiently establishes latent infection in the TG of mice in the absence of innate and adaptive immune mechanisms that are essential for limiting productive viral infection.

Role for gamma interferon in control of herpes simplex virus type 1 reactivation

Observation of chronic inflammatory cells and associated high-level gamma interferon (IFN-gamma) production in ganglia during herpes simplex type 1 (HSV-1) latent infection in mice (E. M. Cantin, D. R. Hinton, J. Chen, and H. Openshaw, J. Virol. 69:4898-4905, 1995) prompted studies to determine a role of IFN-gamma in maintaining latency. Mice lacking IFN-gamma (GKO mice) or the IFN-gamma receptor (RGKO mice) were inoculated with HSV-1, and the course of the infection was compared with that in IFN-gamma-competent mice with the same genetic background (129/Sv//Ev mice). A time course study showed no significant difference in trigeminal ganglionic viral titers or the timing of establishment of latency. Spontaneous reactivation resulting in infectious virus in the ganglion did not occur during latency in any of the mice. However, 24 h after the application of hyperthermic stress to mice, HSV-1 antigens were detected in multiple neurons in the null mutant mice but in only a single neuron in the 129/Sv//Ev control mice. Mononuclear inflammatory cells clustered tightly around these reactivating neurons, and by 48 h, immunostaining was present in satellite cells as well. The incidence of hyperthermia-induced reactivation as determined by recovery of infectious virus from ganglia was significantly higher in the null mutant than in control mice: 11% in 129/Sv//Ev controls, 50% in GKO mice (P = 0.0002), and 33% in RGKO mice (P = 0.03). We concluded that IFN-gamma is not involved in the induction of reactivation but rather contributes to rapid suppression of HSV once it is reactivated.

Cytokine and chemokine production in HSV-1 latently infected trigeminal ganglion cell cultures: effects of hyperthermic stress

The establishment of a primary trigeminal ganglion (TG) cell culture latently infected with herpes simplex virus type 1 (HSV-1) has been useful in studying stress-induced reactivation of the latent virus. However, the immune profile of this culture system prior to and after stress has never been established. In the present manuscript, cytokine and chemokine production were measured in primary cultures of TG cells obtained from uninfected and HSV-1 latently infected mice. Supernates from TG cell cultures contained detectable interleukin (IL)-6 but not IL-1beta, IL-2, IL-10, interferon (IFN)-gamma or tumor necrosis factor (TNF)-alpha as determined by ELISA. The basal level of IL-6 in uninfected TG cell cultures was 20.5 +/- 2.3 ng/ml, whereas latently infected TG cells produced significantly less IL-6 (12.1 +/- 1.9 ng/ml). Supernates from TG cell cultures also contained detectable levels of C-10, MCP-1 and eotaxin but little to no MIP-1alpha, MIP-1beta, or MIP-2. While there were no differences in the basal level of MCP-1 and eotaxin in TG cell cultures from HSV-1-infected and uninfected mice, C10 levels were significantly higher in TG cultures originating from infected mice compared to uninfected ones (5.86 +/- 0.61 ng/ml compared to 1.18 +/- 0.16 ng/ml). Hyperthermic stress (43 degrees C, 180 min), which induces reactivation of latent HSV-1 from TG cell cultures, significantly reduced IL-6 and C-10 levels from both uninfected and latently infected TG cell cultures. However, there was no correlation between cytokine/chemokine levels and HSV-1 reactivation. Immunofluorescent studies showed TG cell cultures contained 10% MAC-3+ staining cells (macrophage specific) but no dendritic cells. By comparison, cells from freshly isolated TG contained 6% positive dendritic cells but < 1% MAC-3 + cells. Both in vivo and in vitro TG consisted of a low percentage of CD3+ and CD8+ cells. Hyperthermic stress (43 degrees C for 3 h) eliminated the lymphocyte population as determined by RT-PCR. Whereas no spontaneous reactivation has been reported in mice, spontaneous reactivation occurred in 4.5% (10/220) of TG cell cultures surveyed over a 20 day period. Collectively, the dichotomy between HSV-1 replication and reactivation comparing the in vitro and in vivo HSV-1 latency models may reside, in part, to the differences in the levels of cytokines, chemokines and immune cell populations within the microenvironment of the in vitro and in vivo TG.

Androstenediol Antagonizes Herpes Simplex Virus Type 1-Induced Encephalitis Through the Augmentation of Type I IFN Production

Dehydroepiandrosterone and androstenediol (AED) have previously been found to protect mice from viral-induced encephalitis resulting in an increased survival rate of the animals. These hormones have been shown to antagonize corticosteroids, which have immunosuppressive effects in vivo and in vitro, suggesting the antiviral effect of DHEA and AED may be linked to the anticorticosteroid action. The present study was undertaken to address the immune response to herpes simplex virus type 1 (HSV-1) during the acute ocular infection with and without AED treatment focusing on the early immune events in the eye and trigeminal ganglion. AED treatment was found to significantly improve the survival of HSV-1-infected mice in a dose-dependent fashion. While AED did not antagonize the elevated serum corticosterone levels following acute infection, AED enhanced the expression of IFN-α mRNA and decreased the expression of HSV-1-infected cell polypeptide 27 mRNA in the trigeminal ganglion during the acute (day 6 postinfection) infection of mice, as determined by reverse transcription-PCR. However, there was no change in the viral load from the eye or trigeminal ganglion when comparing the AED-treated with the vehicle-treated mice. Neutralization Abs to IFN-α, -β, or -α/β, but not control Ab, blocked the protective effect following AED exposure, confirming the involvement of type I IFN in the enhancement of survival in AED-treated mice. Collectively, these results identify innate immunity as a key component in augmenting the survival of HSV-1-infected mice following AED treatment.

Herpes simplex virus DNA in normal corneas: persistence without viral shedding from ganglia

Herpes simplex virus type 1 (HSV-1) DNA has been shown to persist in the cornea not only after inoculation of experimental animals but also in surgical samples from patients with herpes keratitis. The further observation of corneal HSV-1 DNA in subjects without known HSV eye disease prompted the present study of the presence and distribution of HSV-1 in eye bank corneas. Prior to DNA extraction, the corneas were trephined, separating the central and peripheral cornea. With polymerase chain reaction (PCR) for HSV-1 thymidine kinase (TK) and glycoprotein D (gD) gene sequences, we found HSV-1 in 10 of 24 eye bank corneas, from the 4 mm wide corneal rim in 8 eyes and from the 8 mm diameter central cornea in 2 eyes. In 9 subjects, both eyes were assayed, and HSV-1 was detected in 6 subjects. In only one subject was HSV-1 detected in both eyes and in only one subject was HSV-1 detected in the central and peripheral cornea of the same eye. The biological role of HSV-1 DNA corneal sequences is unknown. To investigate this, a rabbit animal model was established by transplantation of corneas containing viral DNA sequences in HSV-1 naive recipients. Followed for 5 months, there was no evidence of sheeding of HSV-1 in the tear film or seroconversion of the recipient rabbits. At the end of this time, HSV-1 DNA was detected in the corneal graft at a similar intensity to the PCR signal from the donor rims.(ABSTRACT TRUNCATED AT 250 WORDS)

Herpes simplex virus type 1 gene expression and reactivation of latent infection in the central nervous system

Restricted gene expression takes place during latent infection of herpes simplex virus type 1 (HSV-1) in the human peripheral nervous system and has been linked with viral reactivation. The state of HSV-1 gene expression in the central nervous system (CNS) during latency is unclear and we, therefore, examined gene expression in the brainstem of experimental mice and normal humans. Only part of the transcription pattern present during latent infection in peripheral sensory ganglia (PSG) was identified in the human brainstem by in situ hybridization and Northern blot analysis for HSV-1-specific transcripts. Instead of three HSV-1 latency-associated transcripts (LATs) present in PSG and demonstrated by Northern blot analysis, only one was identified in mouse brainstem and none was detected in human brainstem. These findings might be attributed to the relatively low amounts of HSV-1-specific latency-associated RNAs in brainstem tissue. Combined with our inability to reactivate HSV-1 from explanted mouse brainstem, these findings suggest that tissue levels of latency-associated gene expression play a role in HSV-1 reactivation and have relevance to the very low incidence of HSV-1-induced CNS disease compared with peripheral mucocutaneous disease.

The role of the immune system in establishment of herpes simplex virus latency--studies using CD4+ T-cell depleted mice

The immunological mechanisms involved in establishment of herpes simplex virus (HSV) latency were studied in normal and CD4+ T-cell depleted C57BL/6J mice following intravaginal infection. During transition from acute to latent ganglionic infection two consecutive processes were observed: first, clearance of infectious virus from the ganglia, and second, reduction of the number of infected ganglia.

Latent infection of SCID mice with herpes simplex virus 1 and lethal cutaneous lesions in pregnancy

Some SCID mice survived primary infection with herpes simplex virus 1 without the development of peripheral lesions but established coculture-positive ganglionic latency when a low dose of a wild-type strain was inoculated intracutaneously. The latency was also evidenced by the development of the fatal zosteriform skin lesions and the isolation of the virus during pregnancy. We consider that the viral entry into neurons without successive replication, rather than the arrest of the lytic infection within the cells, is an important mechanism in the establishment of latency.

Pathways of viral gene expression during acute neuronal infection with HSV-1

Pathways of viral gene expression were investigated during the acute phase of sensory ganglionic infection with HSV-1. To facilitate these studies we constructed KOS/62-3, an HSV-1 vector in which the Escherichia coli lac-Z gene was inserted behind both copies of the promoter for the viral latency-associated transcripts. Following footpad inoculation of mice with the virus, acutely infected dorsal root ganglion (DRG) neurons were assayed by dual immunofluorescence for the presence of beta-galactosidase and HSV viral antigens. Most infected neurons stained for either beta-galactosidase or viral antigens. Less than 0.2% of neurons staining for viral antigens also expressed beta-galactosidase, and less than 10% of neurons expressing beta-galactosidase also stained for viral antigen. As a consequence of these findings, we propose that there are essentially two populations of HSV-infected neurons during the acute phase of ganglionic infection. In one population of neurons there is abundant viral protein synthesis but minimal transcription of latency-associated transcripts, whereas in a second population of neurons viral gene expression is severely restricted except for the synthesis of latency-associated transcripts. Since DRG neurons are a heterogeneous population of cells, we further sought to determine whether either pathway of gene expression was more likely to occur in a particular neuronal phenotype. To accomplish this, antibodies were used to characterize the DRG neuronal phenotypes acutely infected with the virus. The results indicated that the pathway of neuronal infection characterized by transcription of abundant latency-associated transcripts and minimal viral protein synthesis was much more likely to occur in DRG neurons expressing the cellular antigen SSEA-3. These data indicate that the neuron plays a major role in regulating the outcome of infection with HSV. Finally, we sought to determine whether DNA replication occurs in the course of establishment of a latent infection. We found that the DNA content of neurons latently infected with KOS(M) strain HSV was not affected by treatment with nucleotide analogues during the acute phase of ganglionic infection, suggesting that viral DNA replication does not occur during the establishment of latent infection.

Herpes simplex virus latency in the nervous system--a new model

Permissive herpes simplex virus (HSV) infection in tissue culture results in host cell destruction. Latent HSV infection in vivo occurs in neurons of peripheral sensory ganglia (PSG) and it therefore can not take place in neurons in which the virus has completed a lytic replication cycle similar to that present in vitro. Our hypothesis, based on experimental data and observations in humans, suggests that establishment of latent infection and reactivation of HSV-1 does not involve neuronal cell loss. Latency is established in neurons in which the virus does not replicate and is determined, in part, by the tissue levels of a herpes transactivating protein (Vmw65) that is a component of the viral tegument. We also suggest that reactivation of latent infection does not involve destruction of neurons and is due to replication of virus at the peripheral mucocutaneous tissues to where virus or viral DNA have been transported from the nervous tissue. Alternatively, reactivation is initiated in the PSG using a replication cycle which does not involve irreversible damage to neurons. This model explains the lack of damage to neurons which continue to serve as permanent reservoirs of latent virus for the entire life of the host.

Effect of Herpes simplex virus infection on the trigeminal jaw-opening reflex in guinea pigs

Herpes simplex virus (HSV) infection induces numerous electrophysiological and microscopic changes in neurons in vitro. To investigate the effect of HSV infection on in vivo neuronal activity, we induced an acute, latent and reactivated HSV infection of the trigeminal ganglia of guinea pigs through orofacial HSV inoculation and studied its effect on the trigeminal jaw-opening reflex of anesthetized guinea pigs. During the acute viral infection period both the threshold for elicitation of the reflex, and the latency to the onset of the reflex response were increased. During the latent viral infection in the trigeminal ganglia, the jaw-opening reflexes in the viral infected animals were not different from those of non-infected control animals. However, reactivation of the latent viral infection in these animals resulted in increases in both the threshold and latency of the jaw-opening reflex. These changes were similar to those found in animals with the acute viral infection. These results indicate that acute or reactivated latent HSV infection of the nervous system results in functional changes in the reflex pathways involving the trigeminal gasserian ganglia and brainstem neurons harboring infectious HSV-1.

Detection of herpes simplex virus DNA sequences in corneal transplant recipients by polymerase chain reaction assays

Polymerase chain reaction (PCR) assays were used to amplify herpes simplex virus type 1 (HSV-1) thymidine kinase (TK) sequences in DNA extracted from formalin-fixed, paraffin embedded corneas of patients undergoing corneal transplantation. PCR reamplification with an internal (nested) set of primers was required for detection in 10 of the 12 positive corneas indicating very low abundance of viral sequences. Three of the positive corneal samples were from failed corneal grafts. Overall, TK sequences were detected in 8 of 11 corneas from subjects with a past history of herpes keratitis and in 4 of 11 corneas from subjects with no past history of herpetic eye disease.

A herpes simplex virus type 1 mutant containing a nontransinducing Vmw65 protein establishes latent infection in vivo in the absence of viral replication and reactivates efficiently from explanted trigeminal ganglia

Vmw65, a herpes simplex virus type 1 (HSV-1) tegument protein, in association with cellular proteins, transactivates viral immediate early genes. In order to examine the role of Vmw65 during acute and latent infection in vivo, a mutant virus (in1814), containing a 12-base-pair insertion in the Vmw65 gene, which lacks the transactivating function of Vmw65 (C. I. Ace, T. A. McKee, J. M. Ryan, J. M. Cameron, and C. M. Preston, J. Virol. 63:2260-2269, 1989) was examined in mice. Following corneal inoculation, the parental virus (17+) and the revertant (1814R) replicated effectively in eyes and trigeminal ganglia with 30 to 60% mortality. At either equal PFU or equal particle numbers, in1814 did not replicate in trigeminal ganglia and none of the infected mice died. Although in1814 did not replicate following corneal inoculation, it established latent infection in trigeminal ganglia. HSV-1 in1814 reactivated at explant as efficiently and rapidly as did 17+ and 1814R. Even low amounts of inoculated in1814 (10(2) PFU) were sufficient to establish latent infection in some animals. Since infectious in1814 was not detected at any time in mouse trigeminal ganglia, in1814 provided a unique opportunity to determine how soon after primary infection latency begins. Latent in1814 infection was detected shortly after virus reached the sensory ganglia, between 24 to 48 h postinfection. Thus, though Vmw65 may be required for lytic infection in vivo, it is dispensable for the establishment of and reactivation from latent infection. These data support the hypotheses that the latent and lytic pathways of HSV-1 are distinct and that latency is established soon after infection without a requirement for viral replication. However, the levels of Vmw65 reaching neuronal nuclei may be a critical determinant of whether HSV-1 forms a lytic or latent infection.

An improved model of recurrent herpetic eye disease in mice

Mice were passively immunized with serum containing antibodies to herpes simplex virus type 1 (HSV-1) before inoculation on the cornea with HSV-1 strain McKrae. After such immunization most mice survived and most had normal eyes. When primary infection had subsided, mice with normal eyes were selected and treated with cyclophosphamide, dexamethasone and UV irradiation of the inoculated eye or UV irradiation alone, to reactivate latent virus. After either treatment mice developed signs of recurrent infection (virus in eyewashings and recurrent corneal and/or lid disease). The incidence of such signs was 17/33 (52%) in mice receiving immunosuppressive drugs and UV irradiation and 19/32 (59%) in mice given UV irradiation alone. In mice treated with either stimulus dendritic or geographic ulceration of the cornea was seen. These closely resembled the herpetic lesions seen in humans. There was good correlation between the pattern and distribution of recurrent corneal disease and the distribution of cells containing virus antigens in corneal epithelial sheets. Again, as in humans, the induction of recurrent infection was found to correlate poorly with a rise in the level of serum neutralizing antibody. In mice treated with UV irradiation alone corneal ulcers healed and the eyes returned to normal. By contrast, in mice given immunosuppressive drugs and UV irradiation, the ulceration became more severe and the eyes became opaque and vascularized. The use of passive immunization has greatly improved our previously reported model of recurrent herpetic eye disease since it has increased the incidence of mice suitable for the induction of recurrent infection and has increased the incidence of such infection.

Latency-associated transcript but not reactivatable virus is present in sensory ganglion neurons after inoculation of thymidine kinase-negative mutants of herpes simplex virus type 1

The presence of herpes simplex virus (HSV) latency-associated transcript (LAT) was investigated in sensory ganglion neurons of mice after inoculation with thymidine kinase (TK) mutants of HSV. Ganglion serial sections were examined in order to quantitate numbers of LAT-positive neurons. After inoculation with TK-positive HSV, virus was isolated during latency from explants of most ganglia, and LAT was detected by in situ hybridization in 96% of ganglia. After inoculation with HSV TK mutants, virus was isolated from 0% of ganglia, but LAT was detected in 95 to 100% of ganglia. After inoculation of TK mutants of HSV, therefore, although latent infection as indicated by the isolation of virus from ganglion explants was not detected, the presence of LAT was common. These results suggest that the lack of reactivatable virus after inoculation of HSV TK mutants may be related to a role for HSV TK expression in the reactivation process.

Establishment of latent ganglionic infection with herpes simplex virus via maxillary gingiva and viral re-activation in vivo after trauma

Herpes simplex virus can remain latent for months or years in sensory and automatic ganglia of animals and man, and can be re-activated in vivo by several procedures such as neurectomy, irritation of epithelial surfaces, and administration of immunosuppressive agents. The objective of this study was to determine whether dental stimuli can cause re-activation of the latent herpes simplex virus. Homogenization and explanation of ganglia from mice showed that herpes simplex virus (type 1) traveled from maxillary gingiva to trigeminal ganglia, and remained latent. It was also shown that mice passively immunized with rabbit antibody to herpes simplex virus, following the inoculation of herpes simplex virus by the maxillary gingiva route, developed a latent infection in the trigeminal ganglia. Neutralizing antibody was cleared from the circulation and could not be detected in most of these animals after five weeks. A neutralizing test showed that antibody-negative mice with latent infection were able to produce antibody to re-infection with herpes simplex virus, suggesting that re-activation can be identified by measurement of serum antibody. By use of this mouse model system, it was shown that when maxillary gingiva was traumatized with dry ice, viral re-activation occurred in 58% of these animals, as demonstrated by the appearance of neutralizing antibody. Irradiation by a Stomalaser beam had no effect on the re-activation of latent herpes simplex virus. Our mouse model system may serve as a useful model for obtaining new information on re-activating or inhibitory factors in dentistry.

Serological assessment of acyclovir treatment of herpes genitalis

Oral acyclovir was given to 60 patients with herpes genitalis--20 experiencing a first attack and 40 with recurrent attacks. All patients were followed up for 1 year. Serial serum samples from the patients as well as from 20 controls were studied to determine the effect of therapy on the immune response to herpes simplex virus (HSV). No toxicity was observed, and very few patients had rather insignificant side effects (e.g., diarrhea). The frequency of recurrence (number of recurrences per year) of genital herpes in acyclovir-treated patients was found significantly lower than in controls. More frequent recurrences were observed in those who had high antibody titer in their early convalescent phase sera than in those without or with a low titer of such antibodies. The antibody titers were reduced in those who received acyclovir as compared with controls. The mean time to seroconversion was longer in the acyclovir-treated group than in controls. Oral acyclovir is thus effective and well tolerated in patients with herpes genitalis. Treatment with acyclovir also diminishes the humoral antibody response to HSV, but it does not prevent recurrence. The effects of acyclovir on the immune response to HSV are discussed.

Herpes simplex virus latent infection: reactivation and elimination of latency after neurectomy

Section of the sciatic nerve during the period of herpes simplex virus (HSV) latent infection was performed to evaluate residual latency in mouse dorsal root ganglion. In control mice without sciatic neurectomy, latency was present in 90-100%, while in those which underwent a neurectomy procedure, latent infection was surprisingly decreased to 28-50%. To investigate the hypothesis that the decrease of latency resulted from HSV reactivation and replication (with subsequent neuron destruction), groups of mice were treated with acyclovir to inhibit HSV reactivation, after having undergone a neurectomy procedure. Acyclovir treatment largely prevented the neurectomy-related elimination of latency and supported the hypothesized mechanism.

Expression of herpes simplex virus type 1 latency-associated transcripts in the trigeminal ganglia of mice during acute infection and reactivation of latent infection

Herpes simplex virus type 1 (HSV-1) establishes a latent infection in the trigeminal ganglia of mice infected via the eye. In these ganglia three viral transcripts, of 2.0, 1.5, and 1.45 kilobases (kb), which are at least partially colinear, have been identified by Northern (RNA) blot analysis. These RNAs partially overlap ICPO, but are transcribed in the opposite direction (J. G. Spivack and N. W. Fraser, J. Virol. 61:3841-3847, 1987). The accumulation of these latency-associated transcripts, as well as other viral RNAs, was studied during an acute infection and the reactivation of a latent HSV-1 infection in mice. The 2.0-kb latency-associated transcript was detected in trigeminal ganglia of mice as early as 4 days postinfection, and the 1.45- and 1.5-kb RNA doublet was detected at 14 days postinfection. The levels of these latency-associated transcripts increased steadily over a 60-day period. In contrast, other HSV-1 transcripts were detected at 2 to 3 days postinfection, reached a peak on day 4, and rapidly declined below detectable levels by day 7. The data indicate that the temporal expression of the latency-associated genes during acute infection in the trigeminal ganglia of mice is different from the temporal expression of genes involved in HSV-1 replication. During the reactivation of latent HSV-1 from explanted trigeminal ganglia, the latency-associated RNAs decreased about twofold, but were present at significant levels even after HSV-1 DNA increased and infectious virus was recovered. The decrease of the latency-associated transcripts occurred when reactivation was blocked by phosphonoacetic acid or novobiocin, which suggests that this decrease may be an early event in the entry of latent HSV-1 into the viral replication cycle.

Effect of recombinant mouse interferon-beta on acute and latent herpes simplex infection in mice

The antiviral effect of recombinant mouse interferon-beta (rMuIFN-beta) on herpes simplex virus type 1 (HSV-1) in experimentally infected mice was examined at several stages of infection as a model for the treatment of human HSV infection. Recombinant MuIFN-beta protected mice from lethal intraperitoneal challenge with virulent HSV-1 strains. The in vitro reactivation of HSV from latently infected trigeminal ganglia was also suppressed by treatment with rMuIFN-beta. Thus, rMuIFN-beta was effective against HSV-1 during acute infection and during in vitro reactivation of latent HSV. However, rMuIFN-beta was not effective in preventing the establishment of latent infection, or in eliminating a previously established latent infection.

Latent herpes simplex virus in human trigeminal ganglia. Detection of an immediate early gene "anti-sense" transcript by in situ hybridization

We used in situ hybridization to study the expression of herpes simplex virus type 1 genes during latent infections of human sensory ganglia. Trigeminal ganglia were recovered at autopsy from 24 subjects with no evidence of an active herpetic infection. These ganglia were hybridized to 35S-labeled single-stranded RNA probes spanning 72 percent of the herpes simplex genome. In the ganglia of 16 subjects, 0.2 to 4.3 percent of the neuronal cells contained abundant nuclear signals for viral RNA. Ganglia from three patients with low or undetectable levels of antibodies to herpes simplex type 1 lacked viral RNA signals, whereas the ganglia from all of six patients with elevated antibody titers showed viral RNA signals. Transcription was detected only from the region of the viral genome containing a gene that encodes an immediate early protein known as the infected-cell protein number zero (ICP0). However, normal ("sense") transcripts of this gene, which are prominent in an acute infection, were not detected. In contrast, a novel transcript was found overlapping with, but opposite in direction to, the ICP0 transcript (and was therefore "anti-sense"). Although this transcript has been only partially characterized, we believe that it may have a role in maintaining the latency of herpes simplex virus.

Immunological mechanisms giving rise to latency of herpes simplex virus in the spinal ganglia of the mouse

In the model of genital herpes simplex virus (HSV)-infection of mice, early latency could be induced by passive immunization with HSV-specific antibodies and, to a lesser degree, by adoptive transfer of immune lymphocytes prepared from spleen and draining lymph nodes of genitally infected syngeneic mice. Conversely, spontaneously occurring latency was inhibited by treatment of the animals with cyclophosphamide (Cph) and, to a lesser degree, with cyclosporin A (CyA). Whereas the effect of CyA could be compensated by passively administered HSV-specific antibodies, that of Cph could not. Apparently specific antibodies cooperate with a non-specific proliferating cell type, probably macrophages and/or NK-cells, as could be demonstrated by significantly reduced antibody effect in silica-treated mice. Moreover, F(ab)2 fragments, in contrast to complete antibody molecules, were inactive. HSV-specific antibodies and also immune lymphocytes had little effect on virus production in the mucous membranes, immune lymphocytes being at least as active as antibodies. It is therefore not probable that latency is induced by attenuation of the peripheral disease. It can rather be concluded that the neuron itself is the target for the action of specific antibodies, cooperating in turn with macrophages and/or NK cells.

Oncogenic potential of sexually transmitted viruses with special reference to oral cancer

Recent changes in social mores have been accompanied by a noted increase in the frequency of sexually transmitted diseases. Viruses that have been identified as causative agents for a large proportion of these diseases have also been associated with various malignant states. Concomitantly, the number of cases of oral cancer (considered to occur usually around or after the fifth decade of life) reportedly has been increasing among young adults. The oncogenic potential of several sexually transmitted viruses (HSV, HPV, CMV, and LAV/HTLV III) and their possible role in the development of malignant conditions, in particular oral cancer, are discussed in this review.

Effect of tar condensate from smoking tobacco and water-extract of snuff on the oral mucosa of mice with latent herpes simplex virus

Upper lips were inoculated with virus to establish a latent infection in the trigeminal ganglia. During the latent period, tobacco smoke tar condensate or water-extract of snuff were topically applied to the primary inoculation site for two or three consecutive months. Tar condensate induced re-activation of latent HSV in the ganglia of 10 to 20 per cent of animals but snuff extract did not. Infectious virus was also detected in lips after the chronic application of tar condensate in 10 per cent of animals. Three months' exposure to tobacco produced epithelial dysplasia and other changes in a significant number of latent HSV-infected mice, whereas tobacco alone did not induce dysplasia in the labial epithelium of uninfected mice.

Inhibition of the in vitro-reactivation of latent herpes simplex virus infection in spinal ganglia: comparison of various immune factors. Brief report

In order to study whether the latency of herpes simplex virus (HSV) is immunologically controlled, the influence of different immune mechanisms on the in vitro-reactivation of the virus in latently infected lumbosacral ganglia of mice was investigated. Combined addition of macrophages and antibodies to cultures of ganglionic tissue proved most effective in delaying virus reactivation. This was achieved to a lesser degree when applying antibodies only, whereas macrophages alone were not effective, nor were immune lymphocytes, nor was interferon from L-cells or from the peritoneal cavity of mice.

Vestibular neuronitis--serum and CSF virus antibody titer

The cerebrospinal fluid (CSF) findings of patients with vestibular neuronitis were virologically evaluated and discussed in contrast to those of herpes zoster. CSF samples obtained from seven patients with vestibular neuronitis, aged 28 to 55 years, were examined. The results were as follows: The CSF protein level in the vestibular neuronitis showed the peculiar change; i.e. its level was normal at the onset period of vertigo, but it rose to abnormal levels mostly in the period of two weeks, while the cell count remained normal throughout all phases of our study. Herpes simplex virus (HSV) type 1 IgG antibody titers measured by indirect immunofluorescent antibody technique (IF) in paired sera rose in one of the seven cases of vestibular neuronitis, but the antibody titers of the same virus in the CSF were not detected. HSV type 1 IgG antibody titers measured by IF in the CSF were detected in two of seven cases of vestibular neuronitis, but not significant. The ratio of EB virus (EBV) capsid antigen IgG antibody titers in CSF to that in serum ranged from 1:160 to 1:80 in vestibular neuronitis. There was no direct available evidence that vestibular neuronitis caused a break in blood-CSF barrier, an increase in IgG synthesis in the central nervous system or active infection with HSV, varicella zoster virus (VZV), or EBV. In this paper, we summarized the recent information on studies of the CSF and a latent herpes virus infection in order to give perspective to the pathogenesis of vestibular neuronitis.

Sequential analysis of antibody responses in serum, aqueous humor and tear film during latent and induced recurrent HSV infections

To study HSV specific antibody responses during latent HSV infection and induced HSV ocular shedding, rabbits were infected binocularly with McKrae strain HSV-1. The titer and class of anti-HSV antibody response in serum, aqueous humor and eye washes were determined sequentially during latent HSV infection and following intentional reactivation. In all instances the only antibody class detected was IgG. The highest anti-HSV titers were in the serum and aqueous humor, whereas a significantly lower level of anti-HSV IgG was found in eye washes. Anti-HSV IgG antibody titers were consistently 100-fold higher in serum than in the aqueous humor, which suggests an absence of local ocular antibody synthesis. Neither anti-HSV IgM nor secretory IgA antibodies were detected in any samples.

Humoral immune response to herpes simplex virus type 2 glycoproteins in patients receiving a glycoprotein subunit vaccine

Serial serum specimens from 22 herpes simplex virus (HSV)-seronegative recipients of an HSV type 2 (HSV-2) glycoprotein subunit vaccine were analyzed by radioimmunoprecipitation and polyacrylamide gel electrophoresis for the development of antibodies to HSV-2 gB, gD, and g80, a complex of gC and gE. Volunteers received 50 (n = 12) or 100 micrograms (n = 10) of vaccine at days 0, 28, and 140; sera were drawn weekly for 8 weeks and again at days 140, 147, and 365. Among seronegative volunteers, antibody to gB was detected 2 weeks after the first dose, while antibodies to g80 and gD were detected after the second dose (day 35). Antibodies to nonglycosylated HSV-specific proteins were not detected. A dose-response effect between recipients of 50- and 100-micrograms doses was observed in the proportion of vaccine recipients seroconverting to g80 and in the proportion of recipients retaining antibodies to both gD and g80 over time. Diminishing complement-independent neutralizing antibody titers occurred after the second dose and were associated with loss or reduction of detectable antibody to gD. Volunteers who were seropositive for HSV-1-specific antibody (n = 11) were also enrolled in the trial and received 50-micrograms doses of vaccine. Vaccination resulted in conversion to HSV-2 complement-independent neutralizing antibody specificity or indeterminant specificity in 10 of 11 volunteers. These shifts were accompanied by changes in the radioimmunoprecipitation and polyacrylamide gel electrophoresis profile. These changes, which were apparent by 14 days after the first vaccine dose, included de novo appearance or increased levels of antibody to g80 and increased levels of antibody to gD and gB. These studies document the immunogenicity of solubilized glycoproteins gB, gD, gC, and, possibly, gE in humans.

Immunocytochemical localization of herpes simplex virus antigen in the trigeminal ganglia of experimentally infected mice

The peroxidase anti-peroxidase (PAP) technique was used to study the distribution of herpes simplex virus (HSV) antigens in mouse ganglia during the acute infection and the transition into the latent infection. At 2 days after HSV inoculation by the corneal route, immunoperoxidase staining was present in occasional isolated neurons of the trigeminal ganglion and also in scattered satellite cells. By 4 days, more cells were stained with the infection centered in the medial portion of the ganglion. Inflammatory cells were present around PAP-labeled fragments from lysed cells. Stained satellite cells often with a hypertrophic appearance surrounded labeled or unlabeled neurons in a ring-like array. At 6 days after HSV inoculation, there was a decrease both in the number of cells stained and in the intensity of staining. By 8 days, HSV antigens could be detected by weak PAP staining only in neurons. Otherwise, these neurons appeared morphologically normal. No immunoperoxidase staining was present after the 8th day. These results are compatible with retrograde axoplasmic transport of HSV and cell to cell spread of virus in ganglia. Also the appearance of infected ganglion cells during the transition to latency suggests that neurons can be switched from an HSV-permissive to a non-permissive (latent) state.

Some recent advances in biology and diseases manifested by abnormal immune regulation

Diseases manifested by abnormal immune regulation represent perturbations of a system of heterologous genetic recombination. This heterologous recombination is mediated by plasmids and viruses, facilitated by immune multigene families, and may be affected by physical factors. Heterologous recombination facilitates individual adaptation to new environmental challenges, thereby promoting survival and evolution. Present evidence which supports this hypothesis and a means to test it are outlined. The medical implications of the hypothesis are briefly discussed.

Encephalitis resulting from reactivation of latent herpes simplex virus in mice

Herpes simplex virus (HSV) encephalitis was produced in mice from reactivation of latent virus. Two experimental models were used: the trigeminal model after corneal inoculation of HSV, and the hypoglossal model after tongue inoculation of HSV. In the trigeminal model, cyclophosphamide treatment induced reactivation of latent virus in ganglia but not in central nervous system tissue. Spread of the reactivated virus from ganglia to brain occurred only in mice deficient in anti-HSV antibody. In the hypoglossal model, sectioning of the hypoglossal nerve provoked chromatolysis in the corresponding central nervous system motor neurons and occasionally reactivated latent HSV in the brains of mice. These results suggest that HSV encephalitis can result from the spread of reactivated virus from ganglia to brain and also from in situ reactivation in brain.

In vitro neutralization of HSV-2: inhibition by binding of normal IgG and purified Fc to virion Fc receptor (FcR)

We designed experiments to assess the effects of binding of the HSV-2 Fc receptor (FcR) to purified rabbit nonimmune IgG and purified Fc. Purified Fc (75 micrograms) or nonimmune IgG (100 micrograms) when bound to HSV-2 did not reduce infectivity but did protect the virions against thermal inactivation at 37 degrees C. However, preincubation of these two reagents with HSV-2 virions significantly protected against neutralization by specific anti-HSV-2, F(ab')2 purified rabbit antiserum. The blockage of neutralization and protection against thermal inactivation afforded by FcR-Fc interaction on HSV-2 virions provide a tenable mechanism to explain viral persistence in an immune host.

Colonization of murine ganglia by a superinfecting strain of herpes simplex virus

We report on the colonization of murine trigeminal ganglia after sequential infection of mice by herpes simplex viruses (HSVs). In preliminary studies, we have established that whereas the HSV-1(F) strain efficiently colonizes ganglia when inoculated by either the ear or eye routes, the HSV-1 X HSV-2 recombinant C7D colonizes ganglia when inoculated by the eye route only. The experimental design consisted of inoculating the right eye with C7D on day 1 and with HSV-1(F) in both left and right eyes on day 26. Both right and left trigeminal ganglia were removed and analyzed independently for latent virus on day 52. Our studies indicate that HSV-1(F) viruses were recovered from all left trigeminal ganglia but from only a small number of right trigeminal ganglia. Some right trigeminal ganglia yielded no viruses, whereas others yielded both C7D and HSV-1(F) viruses identified on the basis of plaque morphology and restriction enzyme cleavage patterns of viral DNA. The results indicate that more than one virus may colonize the same ganglion and that trigeminal ganglia may be protected from colonization by a superinfecting virus by determinants acting at a local level in the absence of demonstrable virus.

The effects of dietary T-2 toxin on the immunological function and herpes simplex reactivation in Swiss mice

T-2 toxin, a trichothecene mycotoxin, is a potently cytotoxic and immunosuppressive secondary metabolite produced by Fusarium fungi. Young male white Swiss mice were fed a diet supplemented with T-2 toxin at levels of 5, 10, or 20 ppm, control diet ad libitum, or control diet at a restricted rate for 1, 2, 3, 4, and 6 weeks. The effect of the toxin on the immune system of these mice was assessed by counting total spleen cell numbers and the in vitro proliferative response of spleen cells from these mice to the polyclonal mitogens, concanavalin A (Con A), and lipopolysaccharide (LPS). Body weight gains were also measured. Initially, the ingestion of T-2 toxin and restricted diet depressed total spleen cell counts, but after 3 weeks, only the spleen cell counts of mice fed 20 ppm of T-2 toxin were significantly lower. Consumption of 20 ppm of T-2 toxin by mice for 1 to 4 weeks depressed the spleen proliferative responses to the T-cell mitogen Con A; however, the response to LPS, a B-cell mitogen, was depressed in mice fed 10 and 20 ppm of T-2 toxin as well as in mice fed a control diet at a restricted rate. In order to determine whether T-2 toxin could induce reactivation of herpes simplex virus type 1 (HSV-1), latency was established in the trigeminal ganglia of mice. Feeding of T-2 toxin at 5, 10, and 20 ppm levels for 3 or 6 weeks did not reactivate virus; however, treatment with liquid nitrogen and cyclophosphamide did reactivate virus. These results demonstrate that although T-2 can cause immunosuppression, this response is not sufficient to reactivate HSV-1.

Peripheral blood T and B lymphocyte subpopulations in Bell's palsy

A prospective clinical, virological and immunological study was performed on 25 consecutive Bell's palsy (BP) patients. Multiple cranial nerve involvement was found in 15 patients. A significant decrease in the peripheral blood T lymphocyte percentage as well as an increase in B lymphocyte percentage (p less than 0.001) were found in 13 of the BP patients during the first 24 days from the clinical onset of the paralysis. No correlation was found between the peripheral blood lymphocyte subpopulations and the patient's age, sex, degree of paralysis or recovery rate. No changes were detected in the levels of immunoglobulins (IgG, IgM), complement (C3, C4) and antiviral antibodies to herpes simplex and zoster, EBV, cytomegalic virus, adenovirus, influenza and mumps. The clinical and immunological data of BP show a similar pattern to those of Guillain-Barre syndrome suggesting that BP may be an antoimmune demyelinating cranial polyneuritis which may be caused by a preceding viral infection.

Latency of herpes simplex virus in ocular tissue of mice

At 5 to 7 months after corneal inoculation of herpes simplex virus type 1 in mice, explants of ocular tissue yielded virus. Immunoperoxidase study of explants undergoing reactivation revealed herpes simplex virus antigens in retinal tissue. These results indicate that herpes simplex virus can establish and maintain latency in ocular tissue, most probably in the retina.