Herpes simplex virus genome replication and transcription during induced reactivation in the rabbit eye

A fur plucking model to study herpes simplex virus reactivation and recurrent disease

Herpes simplex viruses (HSV-1 and HSV-2) most commonly cause ulcerative epithelial lesions (cold sores and genital herpes). Importantly, HSV establishes life-long persistent (latent) infection in peripheral neurons. Reactivation from latency produces recurrent epithelial lesions, which constitute the greatest burden of HSV disease in people. The mechanisms that regulate latency and reactivation remain incompletely understood, in part due to limitations in the animal models available for studying HSV reactivation. We have developed a simple and tractable model to induce HSV-1 and HSV-2 reactivation from latency to cause recurrent skin disease. We infected C57BL/6 mice with HSV-1 (strains NS, F, SC16, 17syn+) or HSV-2 (strain 333) on flank skin depilated by manual plucking. After at least 35 days post-infection (dpi), we replucked the fur from the infected flank and observed recurrent lesions in the same dermatome as the primary infection. We detected HSV DNA in dermatome skin through 4 days post-replucking and observed viral antigen and reporter signal in skin lesions by histology, consistent with viral replication following reactivation. In addition to C57BL/6 mice, we were able to produce reactivation in Balb/c and SKH-1 mice. We found that shaving the ipsilateral flank or plucking the contralateral flank did not induce recurrent skin lesions, suggesting that fur plucking is a specific stimulus that induces HSV reactivation. Furthermore, we were able to induce multiple rounds of plucking-induced recurrent disease, providing a model to investigate the lifelong nature of HSV infection. This new model provides a tractable system for studying pathogenic mechanisms of and therapeutic interventions against HSV reactivation and recurrent disease.

IMPORTANCE

Herpes simplex viruses (HSV-1 and HSV-2) have infected over half of the US adult population to cause a lifelong, persistent infection; however, our understanding of the mechanisms that govern HSV reactivation and recurrent disease is incomplete. This is in part due to limitations in the animal models used to study recurrent disease, which are laborious and inefficient in mice. To address this technical gap, we developed a mouse model in which fur plucking after flank skin infection is sufficient to induce episodes of HSV reactivation and recurrent disease. Our work provides a model for the field to investigate the pathogenic mechanisms of HSV and immune responses during recurrent disease and provides an opportunity to investigate the neurobiology of HSV infection.

HSV1 latent transcription and non-coding RNA: A critical retrospective

Virologists have invested great effort into understanding how the herpes simplex viruses and their relatives are maintained dormant over the lifespan of their host while maintaining the poise to remobilize on sporadic occasions. Piece by piece, our field has defined the tissues in play (the sensory ganglia), the transcriptional units (the latency-associated transcripts), and the responsive genomic region (the long repeats of the viral genomes). With time, the observed complexity of these features has compounded, and the totality of viral factors regulating latency are less obvious. In this review, we compose a comprehensive picture of the viral genetic elements suspected to be relevant to herpes simplex virus 1 (HSV1) latent transcription by conducting a critical analysis of about three decades of research. We describe these studies, which largely involved mutational analysis of the notable latency-associated transcripts (LATs), and more recently a series of viral miRNAs. We also intend to draw attention to the many other less characterized non-coding RNAs, and perhaps coding RNAs, that may be important for consideration when trying to disentangle the multitude of phenotypes of the many genetic modifications introduced into recombinant HSV1 strains.

The Herpes Simplex Virus Latency-Associated Transcript Gene Is Associated with a Broader Repertoire of Virus-Specific Exhausted CD8+ T Cells Retained within the Trigeminal Ganglia of Latently Infected HLA Transgenic Rabbits

Persistent pathogens, such as herpes simplex virus 1 (HSV-1), have evolved a variety of immune evasion strategies to avoid being detected and destroyed by the host's immune system. A dynamic cross talk appears to occur between the HSV-1 latency-associated transcript (LAT), the only viral gene that is abundantly transcribed during latency, and the CD8(+)T cells that reside in HSV-1 latently infected human and rabbit trigeminal ganglia (TG). The reactivation phenotype of TG that are latently infected with wild-type HSV-1 or with LAT-rescued mutant (i.e., LAT(+)TG) is significantly higher than TG latently infected with LAT-null mutant (i.e., LAT(-)TG). Whether LAT promotes virus reactivation by selectively shaping a unique repertoire of HSV-specific CD8(+)T cells in LAT(+)TG is unknown. In the present study, we assessed the frequency, function, and exhaustion status of TG-resident CD8(+)T cells specific to 40 epitopes derived from HSV-1 gB, gD, VP11/12, and VP13/14 proteins, in human leukocyte antigen (HLA-A*0201) transgenic rabbits infected ocularly with LAT(+)versus LAT(-)virus. Compared to CD8(+)T cells from LAT(-)TG, CD8(+)T cells from LAT(+)TG (i) recognized a broader selection of nonoverlapping HSV-1 epitopes, (ii) expressed higher levels of PD-1, TIM-3, and CTLA-4 markers of exhaustion, and (iii) produced less tumor necrosis factor alpha, gamma interferon, and granzyme B. These results suggest a novel immune evasion mechanism by which the HSV-1 LAT may contribute to the shaping of a broader repertoire of exhausted HSV-specific CD8(+)T cells in latently infected TG, thus allowing for increased viral reactivation.

IMPORTANCE

A significantly larger repertoire of dysfunctional (exhausted) HSV-specific CD8(+)T cells were found in the TG of HLA transgenic rabbits latently infected with wild-type HSV-1 or with LAT-rescued mutant (i.e., LAT(+)TG) than in a more restricted repertoire of functional HSV-specific CD8(+)T cells in the TG of HLA transgenic rabbits latently infected with LAT-null mutant (i.e., LAT(-)TG). These findings suggest that the HSV-1 LAT locus interferes with the host cellular immune response by shaping a broader repertoire of exhausted HSV-specific CD8(+)T cells within the latency/reactivation TG site.

HSV-1 latent rabbits shed viral DNA into their saliva

Background

Rabbits latent with HSV-1 strain McKrae spontaneously shed infectious virus and viral DNA into their tears and develop recurrent herpetic-specific corneal lesions. The rabbit eye model has been used for many years to assess acute ocular infections and pathogenesis, antiviral efficacy, as well as latency, reactivation, and recurrent eye diseases. This study used real-time PCR to quantify HSV-1 DNA in the saliva and tears of rabbits latent with HSV-1 McKrae.

Methods

New Zealand white rabbits used were latent with HSV-1 strain McKrae and had no ocular or oral pathology. Scarified corneas were topically inoculated with HSV-1. Eye swabs and saliva were taken from post inoculation (PI) days 28 through 49 (22 consecutive days). Saliva samples were taken four times each day from each rabbit and the DNA extracted was pooled for each rabbit for each day; one swab was taken daily from each eye and DNA extracted. Real-time PCR was done on the purified DNA samples for quantification of HSV-1 DNA copy numbers. Data are presented as copy numbers for each individual sample, plus all the copy numbers designated as positive, for comparison between left eye (OS), right eye (OD), and saliva.

Results

The saliva and tears were taken from 9 rabbits and from 18 eyes and all tested positive at least once. Saliva was positive for HSV-1 DNA at 43.4% (86/198) and tears were positive at 28.0% (111/396). The saliva positives had 48 episodes and the tears had 75 episodes. The mean copy numbers ± the SEM for HSV-1 DNA in saliva were 3773 ± 2019 and 2294 ± 869 for tears (no statistical difference).

Conclusion

Rabbits latent with strain McKrae shed HSV-1 DNA into their saliva and tears. HSV-1 DNA shedding into the saliva was similar to humans. This is the first evidence that documents HSV-1 DNA in the saliva of latent rabbits.

The herpes simplex virus 1 latency-associated transcript promotes functional exhaustion of virus-specific CD8+ T cells in latently infected trigeminal ganglia: a novel immune evasion mechanism

Following ocular herpes simplex virus 1 (HSV-1) infection of C57BL/6 mice, HSV-specific (HSV-gB(498-505) tetramer(+)) CD8(+) T cells are induced, selectively retained in latently infected trigeminal ganglia (TG), and appear to decrease HSV-1 reactivation. The HSV-1 latency-associated transcript (LAT) gene, the only viral gene that is abundantly transcribed during latency, increases reactivation. Previously we found that during latency with HSV-1 strain McKrae-derived viruses, more of the total TG resident CD8 T cells expressed markers of exhaustion with LAT(+) virus compared to LAT(-) virus. Here we extend these findings to HSV-1 strain 17syn+-derived LAT(+) and LAT(-) viruses and to a virus expressing just the first 20% of LAT. Thus, the previous findings were not an artifact of HSV-1 strain McKrae, and the LAT function involved mapped to the first 1.5 kb of LAT. Importantly, to our knowledge, we show here for the first time that during LAT(+) virus latency, most of the HSV-1-specific TG resident CD8 T cells were functionally exhausted, as judged by low cytotoxic function and decreased gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α) production. This resulted in LAT(-) TG having more functional HSV-gB(498-505) tetramer(+) CD8(+) T cells compared to LAT(+) TG. In addition, LAT expression, in the absence of other HSV-1 gene products, appeared to be able to directly or indirectly upregulate both PD-L1 and major histocompatibility complex class I (MHC-I) on mouse neuroblastoma cells (Neuro2A). These findings may constitute a novel immune evasion mechanism whereby the HSV-1 LAT directly or indirectly promotes functional exhaustion (i.e., dysfunction) of HSV-specific CD8(+) T cells in latently infected TG, resulting in increased virus reactivation.

Impairment in reactivation of a latency associated transcript (LAT)-deficient HSV-2 is not solely dependent on the latent viral load or the number of CD8(+) T cells infiltrating the ganglia

The HSV latency-associated transcript (LAT) is abundantly expressed during virus latency. Previous studies have shown that the latent viral load and CD8(+) T cells in ganglia influence the rate of reactivation of HSV. While LAT is important for efficient reactivation and establishment of latency, it is uncertain how LAT affects either the HSV latent viral load or CD8(+) T cell infiltration of ganglia. We infected mice with LAT-deficient or LAT-restored HSV-2 at a wide range of inocula. We found that the reduced rate of spontaneous ex-vivo reactivation of the LAT-deficient virus was not associated with a higher number of CD8(+) T cells in the ganglia. Reactivation rates were lower for LAT-deficient than LAT restored HSV-2 even when the latent viral loads were similar, indicating that differences in reactivation were not solely dependent on the latent viral load. Therefore, LAT likely has additional functions important for reactivation.

Level of herpes simplex virus type 1 latency correlates with severity of corneal scarring and exhaustion of CD8+ T cells in trigeminal ganglia of latently infected mice

A hallmark of infection with herpes simplex virus type 1 (HSV-1) is the establishment of latency in ganglia of the infected individual. During the life of the latently infected individual, the virus can occasionally reactivate, travel back to the eye, and cause recurrent disease. Indeed, a major cause of corneal scarring (CS) is the scarring induced by HSV-1 following reactivation from latency. In this study, we evaluated the relationship between the amount of CS and the level of the HSV-1 latency-associated transcript (LAT) in trigeminal ganglia (TG) of latently infected mice. Our results suggested that the amount of CS was not related to the amount of virus replication following primary ocular HSV-1 infection, since replication in the eyes was similar in mice that did not develop CS, mice that developed CS in just one eye, and mice that developed CS in both eyes. In contrast, mice with no CS had significantly less LAT, and thus presumably less latency, in their TG than mice that had CS in both eyes. Higher CS also correlated with higher levels of mRNAs for PD-1, CD4, CD8, F4/80, interleukin-4, gamma interferon, granzyme A, and granzyme B in both cornea and TG. These results suggest that (i) the immunopathology induced by HSV-1 infection does not correlate with primary virus replication in the eye; (ii) increased CS appears to correlate with increased latency in the TG, although the possible cause-and-effect relationship is not known; and (iii) increased latency in mouse TG correlates with higher levels of PD-1 mRNA, suggesting exhaustion of CD8+ T cells.

Herpes simplex virus latency-associated transcript sequence downstream of the promoter influences type-specific reactivation and viral neurotropism

Herpes simplex virus (HSV) establishes latency in sensory nerve ganglia during acute infection and may later periodically reactivate to cause recurrent disease. HSV type 1 (HSV-1) reactivates more efficiently than HSV-2 from trigeminal ganglia while HSV-2 reactivates more efficiently than HSV-1 from lumbosacral dorsal root ganglia (DRG) to cause recurrent orofacial and genital herpes, respectively. In a previous study, a chimeric HSV-2 that expressed the latency-associated transcript (LAT) from HSV-1 reactivated similarly to wild-type HSV-1, suggesting that the LAT influences the type-specific reactivation phenotype of HSV-2. To further define the LAT region essential for type-specific reactivation, we constructed additional chimeric HSV-2 viruses by replacing the HSV-2 LAT promoter (HSV2-LAT-P1) or 2.5 kb of the HSV-2 LAT sequence (HSV2-LAT-S1) with the corresponding regions from HSV-1. HSV2-LAT-S1 was impaired for reactivation in the guinea pig genital model, while its rescuant and HSV2-LAT-P1 reactivated with a wild-type HSV-2 phenotype. Moreover, recurrences of HSV-2-LAT-S1 were frequently fatal, in contrast to the relatively mild recurrences of the other viruses. During recurrences, HSV2-LAT-S1 DNA increased more in the sacral cord compared to its rescuant or HSV-2. Thus, the LAT sequence region, not the LAT promoter region, provides essential elements for type-specific reactivation of HSV-2 and also plays a role in viral neurotropism. HSV-1 DNA, as quantified by real-time PCR, was more abundant in the lumbar spinal cord, while HSV-2 DNA was more abundant in the sacral spinal cord, which may provide insights into the mechanism for type-specific reactivation and different patterns of central nervous system infection of HSV-1 and HSV-2.

Human herpesvirus latency

Herpesviruses are among the most successful human pathogens. In healthy individuals, primary infection is most often inapparent. After primary infection, the virus becomes latent in ganglia or blood mononuclear cells. Three major subfamilies of herpesviruses have been identified based on similar growth characteristics, genomic structure, and tissue predilection. Each herpesvirus has evolved its own unique ecological niche within the host that allows the maintenance of latency over the life of the individual (e.g. the adaptation to specific cell types in establishing latent infection and the mechanisms, including expression of different sets of genes, by which the virus remains latent). Neurotropic alphaherpesviruses become latent in dorsal root ganglia and reactivate to produce epidermal ulceration, either localized (herpes simplex types 1 and 2) or spread over several dermatomes (varicalla-zoster virus). Human cytomegalovirus, the prototype betaherpesvirus, establishes latency in bone marrow-derived myeloid progenitor cells. Reactivation of latent virus is especially serious in transplant recipients and AIDS patients. Lymphotropic gammaherpesviruses (Epstein-Barr virus) reside latent in resting B cells and reactivate to produce various neurologic complications. This review highlights the alphaherpesvirus, specifically herpes simplex virus type 1 and varicella-zoster virus, and describes the characteristics of latent infection.

Human cytomegalovirus 5-kilobase immediate-early RNA is a stable intron

Immediate-early viral gene products of human cytomegalovirus (HCMV) are derived from several genomic loci and largely serve to establish a cellular environment conducive to viral replication. We have further examined an unusual immediate-early transcript known as the 5-kb RNA, concluding that it is a stable intron encoded by HCMV. The 5-kb RNA is highly AT rich in sequence and lacks open reading frames likely to be translated into protein. We confirmed the absence of polyadenylation of the transcript and showed that it is primarily nuclear localized during viral infection. We mapped the 5' end of the 5-kb RNA to a consensus splice donor site and localized the 3' end in the vicinity of a splice acceptor site. In transfection studies, we showed that the 5-kb RNA can be spliced from a heterologous primary transcript. Using bacterial artificial chromosome technology, we constructed a viral recombinant containing a mutation in the 5' splice donor site that defines the 5' end of the RNA and found that this mutation eliminates expression of the 5-kb RNA during viral infection. This mutant grows in human fibroblasts without complementation. Taken together, these data support the conclusion that the 5-kb RNA is a stable intron expressed by HCMV.

Wide variations in herpes simplex virus type 1 inoculum dose and latency-associated transcript expression phenotype do not alter the establishment of latency in the rabbit eye model

The latency-associated transcript (LAT) is required for efficient reactivation of herpes simplex virus type 1 from latent infection in the rabbit eye model, but LAT's mechanism of action is unknown. In addition to reactivation, the LAT region seems to correspond to multiple functions, with some LAT deletion mutants exhibiting increased virulence, increased neuronal death, and restricted establishment of latency. While a LAT promoter deletion mutant (17DeltaPst) seems to be primarily restricted in reactivation in the rabbit, subtle effects on virulence or the establishment of latency cannot be precluded at the normal high levels of virus inoculum used in the rabbit model. Since such additional LAT phenotypes may be more evident with lower doses of virus, we evaluated the influence of initial viral inoculum and LAT expression on the progression of acute infection and the establishment of latency. We have assayed both virus recovery rates and viral genome loads in rabbit corneas and trigeminal ganglia. Our results show that (i) in the corneas and trigeminal ganglia, the maximum amount of virus present during acute infection is independent of the LAT genotype and inoculum dose, although greater viral yields are obtained earlier with higher inoculum doses, and (ii) the range in numbers of latent genomes detected in the ganglia is independent of the inoculum dose and the LAT genotype and therefore no difference in establishment of latency is observed.

Dimethyl sulfoxide blocks herpes simplex virus-1 productive infection in vitro acting at different stages with positive cooperativity. Application of micro-array analysis

BACKGROUND

Dimethyl sulfoxide (DMSO) is frequently used at a concentration of up to 95% in the formulation of antiherpetic agents because of its properties as a skin penetration enhancer. Here, we have analyzed the effect of DMSO on several parameters of Herpes Simplex Virus replication.

METHODS

Productive infection levels of HSV-1 were determined by plaque assay or by reporter gene activity, and its DNA replication was estimated by PCR. Transcript levels were evaluated with HSV-specific DNA micro-arrays.

RESULTS

DMSO blocks productive infection in vitro in different cell types with a 50% inhibitory concentration (IC50) from 0.7 to 2% depending upon the multiplicity of infection. The concentration dependence exhibits a Hill coefficient greater than 1, indicating that DMSO blocks productive infection by acting at multiple different points (mechanisms of action) with positive cooperativity. Consistently, we identified at least three distinct temporal target mechanisms for inhibition of virus growth by DMSO. At late stages of infection, DMSO reduces virion infectivity, and markedly inhibits viral DNA replication. A third mode of action was revealed using an oligonucleotide-based DNA microarray system for HSV. These experiments showed that DMSO reduced the transcript levels of many HSV-1 genes; including several genes coding for proteins involved in forming and assembling the virion. Also, DMSO markedly inhibited some but not all early transcripts indicating a previously unknown mode for inhibiting the early phase of HSV transcription-replication cycle.

CONCLUSION

These observations suggest that DMSO itself may have a role in the anti-herpetic activity of formulations utilizing it as a dispersant.

Effect of famciclovir on herpes simplex virus type 1 corneal disease and establishment of latency in rabbits

Famciclovir (FCV) is efficacious in the treatment of acute herpes zoster and recurrent genital infections but has not been used to treat ocular herpes simplex virus (HSV) infections. We evaluated the efficacy of orally administered FCV in treating HSV-1 epithelial keratitis and determined its effects on the establishment of latency and subsequent reactivation. Rabbits were inoculated with HSV-1 strain 17 syn+ and treated twice daily with increasing concentrations of FCV (60 to 500 mg/kg of body weight). This resulted in a significant, dose-dependent improvement in keratitis scores, as well as prolonged survival. Regardless of the dose of drug used, all groups exhibited the high rates of spontaneous and induced reactivation characteristic of 17syn+. The efficacy of 250 mg of FCV per kg was also compared to topical treatment with 1% trifluorothymidine (TFT). Although TFT treatment was more effective at reducing eye disease, FCV-treated rabbits had a better survival rate. Real-time quantitative PCR analysis of rabbit trigeminal ganglia (TG) demonstrated that FCV significantly reduced the HSV-1 copy number compared to that after treatment with TFT or the placebo but not in a dose-dependent manner. In summary, oral FCV treatment significantly reduces the severity of corneal lesions, reduces the number of HSV-1 genomes in the TG, improves survival, and therefore may be beneficial in reducing the morbidity of HSV keratitis in the clinic.

Global analysis of herpes simplex virus type 1 transcription using an oligonucleotide-based DNA microarray

More than 100 transcripts of various abundances and kinetic classes are expressed during phases of productive and latent infections by herpes simplex virus (HSV) type 1. To carry out rapid global analysis of variations in such patterns as a function of perturbation of viral regulatory genes and cell differentiation, we have made DNA microchips containing sets of 75-mer oligonucleotides specific for individual viral transcripts. About half of these are unique for single transcripts, while others function for overlapping ones. We have also included probes for 57 human genes known to be involved in some aspect of stress response. The chips efficiently detect all viral transcripts, and analysis of those abundant under various conditions of infection demonstrates excellent correlation with known kinetics of mRNA accumulation. Further, quantitative sensitivity is high. We have further applied global analysis of transcription to an investigation of mRNA populations in cells infected with a mutant virus in which the essential immediate-early alpha27 (U(L)54) gene has been functionally deleted. Transcripts expressed at 6 h following infection with this mutant can be classified into three groups: those whose abundance is augmented (mainly immediate-early transcripts) or unaltered, those whose abundance is somewhat reduced, and those where there is a significant reduction in transcript levels. These do not conform to any particular kinetic class. Interestingly, levels of many cellular transcripts surveyed are increased. The high proportion of such transcripts suggests that the alpha27 gene plays a major role in the early decline in cellular gene expression so characteristic of HSV infection.

Early expression of herpes simplex virus (HSV) proteins and reactivation of latent infection

During the last decade, new data accumulated describing the early events during herpes simplex virus 1 (HSV-1) replication occurring before capsid formation and virion envelopment. The HSV virion carries its own specific transcription initiation factor (alpha-TIF), which functions together with other components of the cellular transcriptase complex to mediate virus-specific immediate early (IE) transcription. The virus-coded IE proteins are the transactivator and regulatory elements modulating early transcription and subsequent translation of nonstructural virus-coded proteins needed mainly for viral DNA synthesis and for the supply of corresponding nucleoside components. They also cooperate at the late transcription and translation of the virion (capsid, tegument and envelope) proteins. In addition, the transactivator IE proteins down-regulate their own transcription, while others facilitate viral mRNA processing or interfere with the presentation of newly synthesized virus antigens. Establishment of latency is closely related to the transcription of a separate category of transcripts, termed latency-associated (LAT). Formation of LATs occurs mainly in nondividing neurons which are metabolically less active and express lower levels of cellular transcription factors (nonpermissive cells). Expression of the stable non-spliced (2 kb), and especially of stable spliced (1.5 and 1.45 kb) LATs is a prerequisite for HSV reactivation. Different HSV genomes (from various HSV strains) do not undergo IE transcription at the same rate. Restricted IE transcription and the absence of viral DNA synthesis favors LAT formation and persistence of the silenced genome. Uneven levels of LAT expression and differences in the metabolic state of carrier neurons influence the reactivation competence. Under artificial or natural activation conditions, sufficient amounts of IE transactivator proteins and proteins promoting nucleoside metabolism are synthesized even in the absence of the viral alpha-TIF facilitating reactivation.

Identification of a novel 0.7-kb polyadenylated transcript in the LAT promoter region of HSV-1 that is strain specific and may contribute to virulence

Herpes Simplex virus expresses latency-associated transcripts (LATs) the function of which remains obscure despite increasing knowledge of their structure and expression. Upstream of the LAT coding region is a region of the genome that is poorly characterized although it lies in an area that is responsible for modulation of reactivation efficiency in two different animal models. Transcript mapping with strains 17, McKrae, KOS, and F has revealed strain differences in this region of the viral genome. Strain 17 and McKrae expressed a novel polyadenylated 0.7-kb transcript that is absent from KOS and F. This transcript is expressed in the LAT direction and has the kinetics of a true late gene during the lytic cycle of infection. A deletion mutant, 17DeltaBsa, which does not express the 0.7-kb RNA, is less virulent than the parental strain 17. A rescuant with F sequence (17DeltaBsa/RF) shows virulence similar to F, whereas a rescuant with strain 17 sequence (17DeltaBsa/R17) is similar to strain 17. Virulence is altered by deletion or substitution in the region encoding the 0.7-kb transcript (BsaI-BsaI); however, reactivation in the mouse explant cocultivation assay or the adrenergically induced rabbit reactivation model remained unchanged. The importance of this region for virulence is discussed.

LAT expression during an acute HSV infection in the mouse

Previous studies using cell culture systems to evaluate LAT expression demonstrated that the LAT promoter expresses at much higher levels in neuroblastoma cell lines than fibroblast lines. The high level of LAT expression in neuronal-derived cell lines correlates with the high level of LAT accumulation observed in sensory ganglia neurons during a latent infection. We have found that using LAT promoters to express reporter genes from recombinant viruses in vivo produces high levels of LAT promoter activity in the epithelium of the mouse foot. An analysis of LAT promoter activity during an acute infection in the mouse clearly demonstrates that in contrast to studies performed with selected cell lines, the LAT promoter expresses similar levels of reporter gene product in peripheral cells and in neurons. In addition, the amount of reporter gene product is higher when the LAT promoter is located within the R(L) as compared to the U(L) region, and when expression is adjusted for copy number of the reporter construct, expression is roughly the same. These results suggest the activity of the LAT promoter varies greatly according to cell type and that high levels of expression is not limited solely to neurons, especially in the in vivo setting.

The polysulfonated compound suramin blocks adsorption and lateral difusion of herpes simplex virus type-1 in vero cells

Several polysulfonate compounds have been shown to have the potential to inhibit the replication of herpesviruses by blocking binding and penetration of the host cell. We analyzed the actions of the polysulfonate compound suramin on the replication of herpes simplex virus type 1 (HSV-1) and compared them with the actions of heparin. We used the expression of a reporter gene (beta-galactosidase) recombined into the latency-associated transcript region of the 17syn+ strain of HSV-1 to quickly evaluate productive cycle activity and have shown that it can be directly correlated with virus replication under the conditions used. We find that suramin, like heparin, blocks the binding of HSV-1 to the cell membrane. Also, suramin efficiently blocks the cell-to-cell spread of the virus; this effect has not been previously reported. Our control experiments demonstrate that heparin also has some effect on intercellular spread of HSV-1 but to a significantly lesser degree than does suramin. We suggest that suramin and related polysulfonate compounds have potential for developing of antiherpes treatments.