Characterization of a murine model of recurrent herpes simplex viral keratitis induced by ultraviolet B radiation

The authors characterized a murine model of herpes simplex virus (HSV) reactivation in which recurrent herpetic keratitis was obtained in up to 80% of animals. Five weeks after ganglionic latency was established in National Institutes of Health inbred mice after corneal inoculation, HSV type 1 (HSV-1) was reactivated by irradiating the previously inoculated eye with ultraviolet (UV) light. Comparison of different UV wavelengths showed UVB to be optimal for reactivation, with peak viral recurrence being induced by a total exposure of approximately 250 mJ/cm2. Reactivated infectious virus generally began to appear in trigeminal ganglia 2 days postirradiation and was subsequently detectable in the cornea by both corneal swabbing and immunostaining for viral antigens. Two consecutive outbreaks of viral recurrence at the ocular surface were induced in selected animals by serial exposure to UVB. Advantages of this model over other models of recurrent keratitis are discussed.

Pathogenicity and latency competence for rabbits of the herpes simplex virus type 1 ANGpath gC and gE defective mutants

A total of 139 rabbits was infected to the right scarified cornea with HSV type 1 strains Kupka, ANG, ANGpath and their gE defective (ANGpathI2-4), gC defective (ANGpathgC18), gC/gE negative (ANGpathCI-8) and gC/ICP4 deletion (ANGpathY1) mutants. Strains ANG, ANGpath, ANGpathgC18 and ANGpathY1 were, in contrast to the two gE negative mutants, highly lethal, but 79% of rabbits infected with the non-encephalitogenic Kupka strain survived. Strain Kupka and strain ANGpath gE-negative mutants I2-4 and gCI-8 were tested for their latency competence. While Kupka established latency in the homolateral trigeminal ganglia from 80% of infected rabbits, I2-4 did so in one of 10 animals only, and the gC/gE mutant gCI-8 was not harboured in any of infected animals in an inducible form. Significant correlation was found between shedding into the culture fluid of reactivated virus from the explanted ganglion and brain stem fragments at one hand and the presence of the viral DNA in these organs on the other hand as judged by spot blot hybridization with the HSV-1 strain 17 Kpn I fragments h and i to DNA extracts prepared from these organs. Hybridizations were predominantly negative with the DNA from the corresponding non-cultured organs, except in a few cases of non-cultured ganglion and brain stem from rabbits previously infected with the gE deletion mutants which displayed positive hybridization, although no virus reactivation could be observed in corresponding explants.

Induction of cellular transcription factors in trigeminal ganglia of mice by corneal scarification, herpes simplex virus type 1 infection, and explantation of trigeminal ganglia

In a mouse model for herpes simplex virus type 1 (HSV-1) latency in which the virus was inoculated via the eye after corneal scarification, HSV-1 replicated in corneal epithelial cells and infected the nerve cell endings. HSV-1 reached the trigeminal ganglia by fast axonal transport between 2 and 10 days postinfection (p.i.) and established a latent infection in neuronal cells or replicated and spread to nonneuronal cells. By using in situ hybridization, we showed that cellular transcription factors are stimulated by HSV-1 infection in trigeminal ganglia. This stimulation is biphasic, peaking at 1 and 3 to 4 days p.i. The first peak involves c-jun and oct-1 expression in neurons, and the second involves c-jun, c-fos, and oct-1 expression in neurons and nonneuronal cells. Corneal scarification, alone or followed by infection with UV-inactivated HSV-1, induced monophasic c-jun and oct-1 expression in some neurons of the trigeminal ganglia, with a peak at 1 day p.i. Corneal infection without prior scarification induced c-jun, c-fos, and oct-1 expression in some neuronal and nonneuronal cells of the trigeminal ganglia 2 to 9 days p.i. Explanation of ganglia from latently infected animals resulted in reactivation of the latent virus. Independently of the presence of latent HSV-1 in explanted ganglia, expression of c-fos, c-jun, and oct-1 was induced first in nonneuronal cells, peaking 6 to 10 h postexplantation, and then in neuronal cells, with a peak at 24 h after explantation when expression of viral replicative genes was first detectable. Since ocular HSV-1 infection, corneal scarification, and explantation of trigeminal ganglia all resulted in induction of expression of cellular transcription factors in ganglia, these factors may play a critical role in the permissiveness of cells for HSV-1 replication during acute infection, latency, and reactivation.

Endogenously produced interferon alpha protects mice from herpes simplex virus type 1 corneal disease

Intravenous (i.v.) injection of u.v. light-inactivated herpes simplex virus type 1 (UV HSV-1) at the time of HSV-1 corneal infection reduced the cytotoxic T lymphocyte (CTL) response to HSV-1, and significantly reduced the incidence of HSV-1-induced corneal stromal disease in A/J mice. The spread of HSV-1 through the eye after corneal infection, detected using engineered HSV-1 (US3::Tn5-lacZ) with the lacZ gene under the transcriptional control of the viral late gene promoter for glycoprotein C, was also markedly reduced by i.v. UV HSV-1 injection. The restriction of HSV-1 corneal invasiveness in i.v. UV HSV-1-injected mice preceded the onset of a detectable specific cell-mediated or humoral immune response to HSV-1, and was accompanied by an elevated serum titre of interferon (IFN-alpha), reversed by anti-IFN-alpha/beta antibody, and mimicked by systemic IFN-alpha treatment. IFN-alpha-treated mice developed a normal CTL response to HSV-1 after corneal infection, but the corneal invasiveness of the virus was markedly reduced and none of the treated mice developed corneal stromal disease. Together with our previous findings that HSV-1-specific CTLs participate in the pathogenesis of corneal stromal disease, these results indicate that i.v. injection of UV HSV-1 at the time of corneal infection may prevent stromal disease by the combined effects of IFN-mediated reduction of the spread of virus in the cornea and inhibition of the activity of the HSV-specific T lymphocytes that induce tissue destruction in the corneal stroma.

Expression of the herpes simplex virus 1 alpha transinducing factor (VP16) does not induce reactivation of latent virus or prevent the establishment of latency in mice

A feature of the cascade regulation of herpes simplex virus 1 gene expression in productive infection is that the first genes to be expressed, the alpha genes, are transactivated by a structural component of the virion designated as the alpha transinducing factor (alpha TIF). In this study, we have tested the hypothesis that latent infection of sensory neurons results from the failure of alpha TIF, a tegument protein, to be transported from the nerve endings to the nucleus of the sensory neuron. Two viruses were constructed. The first recombinant virus (R6003) contained a second copy of the alpha TIF gene placed under the control of a metallothionein promoter. The second recombinant virus (R6004) is identical to R6003 except for the presence of a stop codon inserted at amino acid 70 of the second alpha TIF gene. The metallothionein promoter inserted into the viral genome was shown to be expressed, and alpha TIF mRNA was detected by in situ hybridization of sections of trigeminal ganglia of mice infected with R6003, both untreated and those given cadmium injections. In all experiments, there were no significant differences in the recovery of latent virus from mice infected with R6003 or R6004, whether injected with cadmium or not. Cadmium administration at the time of infection and at intervals thereafter did not preclude establishment of latency. In another series of experiments, transgenic mice expressing the metallothionein-driven alpha TIF did not differ from nontransgenic siblings with respect to the incidence of latent virus in trigeminal ganglia. We conclude that the absence of alpha TIF cannot alone account for the establishment of latency.

Neurovirulent strains of herpes simplex virus type 1 are not necessarily competent for reactivatable latency

Ability of two neurovirulent strains (F and +GC (LPV) Miyama) of herpes simplex virus type 1 (HSV-1) to establish and maintain reactivatable latency in trigeminal ganglia (TG) was compared after intranasal inoculation of mice. The +GC (LPV) Miyama strain showed a very low rate of virus reactivation in explant cultures of TG, while the F strain showed a high rate of reactivation. These data indicate that neurovirulent strains of HSV-1 are not always competent for reactivatable latency, although most virulent strains of HSV-1 thus far reported were competent for reactivatable latency.

Ocular herpes simplex virus reactivation in mice latently infected with latency-associated transcript mutants

A mouse model for ocular reactivation of herpes simplex virus type 1 (HSV-1) was modified and used to study the effect of strain difference on the frequency of ocular HSV reactivation. Outbred male NIH white mice were immunized with 1.0 ml of anti-HSV serum with a neutralizing titer of 1:400 24 hr before infection and bilaterally infected at 10(5) plaque-forming units/eye with one of three HSV-1 strains: 17 Syn+, LAT+ (XC-20), or LAT- (X10-13). Latency-associated transcripts (LAT) are produced by strain 17 Syn+ and LAT+ but not by LAT-. The primary infection was monitored by ocular swabbing for HSV. Reactivation was induced by intravenous (i.v.) injection of cyclophosphamide (5 mg) followed 24 hr later by i.v. dexamethasone (0.2 mg). These drugs significantly reduced the white cell count between 0 and 6 days post-administration. The eyes were swabbed for 7 consecutive days to monitor reactivation, and HSV-1 reactivation was induced at the following frequencies in individual eyes: 17 Syn+ (32.5%), LAT+ (18.5%), and LAT- (2.5%) (P less than or equal to 0.002). Co-culture of trigeminal ganglia was done, and random isolates were checked to ascertain their identity. The HSV was recovered from individual trigeminal ganglia at the following frequencies: 17 Syn+ (83%), LAT+ (100%), and LAT- (67%) (P less than or equal to 0.091). These results confirm that the mouse can be used as a reactivation model for ocular HSV infection and that the presence of LAT facilitates reactivation in vivo in the mouse.

Investigation of herpes simplex virus type 1 (HSV-1) gene expression and DNA synthesis during the establishment of latent infection by an HSV-1 mutant, in1814, that does not replicate in mouse trigeminal ganglia

In previous studies, the herpes simplex virus type 1 (HSV-1) mutant, in1814, which lacks the trans-inducing function of Vmw65, did not replicate in the trigeminal ganglia of mice following corneal inoculation but did establish a reactivatable latent infection in the ganglia 12 to 24 h after ocular infection. Since in1814 did not replicate in vivo, the molecular events during the establishment phase of latent HSV-1 infection could be characterized without the complications of concurrent productive viral infection. In comparison to parental HSV-1 strain 17+, the expression of viral immediate early (IE), early and late genes and the levels of viral DNA in the trigeminal ganglia of mice following in1814 infection were greatly reduced. However, accumulation of latency-associated transcripts, a prominent feature of latent HSV-1 infection, occurred in a wild-type fashion. Furthermore, low levels of viral gene expression and an increase in the level of viral DNA in the in1814-infected ganglia were not detected until 1 to 2 days after the establishment of HSV-1 latency. Thus, IE gene expression and replication of viral DNA in the trigeminal ganglia are not prerequisites for the establishment of HSV-1 latency. These results suggest that the pathways leading to productive and latent infections in neurons may diverge at an early stage of the host-HSV-1 interaction and that the level of viral IE gene expression has a key role in determining the outcome of infection.

Ultrastructural immunocytochemical localization of herpes simplex virus (type 1) in trigeminal ganglion neurons

Four days after corneal inoculation of mice with herpes simplex (type 1) virus (HSV), infected trigeminal ganglion cells with and without calcitonin gene-related peptide (CGRP) antigenicity were examined by electron microscopy in sections treated with colloidal gold labeled antibodies. Cells that contain CGRP were identified by the dense gold labeling of small vesicles about 100 nm in diameter. Adjacent thin sections were stained using an indirect colloidal gold immunocytochemical technique to reveal HSV-1 antigens. In CGRP-positive neurons, HSV antigens were located over both nuclear and cytoplasmic compartments. HSV label was found over cytoplasmic vesicles that were significantly larger than those labeled with anti-CGRP antisera; the HSV-containing vesicles ranged in profile diameter from less than 170 to greater than 400 nm. There was no overlap in the distribution of the two labels. Thus, for this time period, the organelles involved in transport of the endogenous neuropeptide and HSV appear to remain discrete. Furthermore, there was no significant difference in the distribution of HSV in CGRP-reactive and CGRP-negative trigeminal ganglion cells. Thus, there is no indication of a preferential distribution or limited replication of HSV in CGRP-positive neurons.

Targets of herpes simplex virus type 1 infection in a mouse corneal model

In animal models, spread of herpes simplex virus type 1 (HSV-1) from epithelial replication sites to the peripheral and central nervous system is known from analysis of individually dissected tissues. To examine virus spread in undissociated tissues, corneas of adult mice were inoculated with HSV-1. After 1 to 13 days groups of mice were perfused with formalin, and decalcified blocks of head and neck were embedded in paraffin. At intervals, serial sections were screened for HSV antigen. On days 1 and 2, viral antigen was restricted to cornea and conjunctiva but by days 3 and 4 was also seen in autonomic ganglia and the trigeminal system. On day 6, HSV antigen reached its maximum extent; infected sites included the trigeminal complex (ganglion, root, peripheral ophthalmic and maxillary branches and spinal nucleus and tract), ethmoid sinus and olfactory bulb, visual system, and autonomic ganglia (ciliary, pterygopalatine and superior cervical). Antigen progressively diminished on days 8 and 10, and was not detected on day 13. This method demonstrates a broader range of infected tissues and suggests a more complex pattern of HSV spread than has been previously recognized. Virus appears to reach the intracranial compartment by four different neural routes. When effects of higher and lower corneal inoculation doses were compared, a lower dose resulted in lower peak HSV titers in trigeminal ganglion and brain stem and later virus appearance in these tissues. Thus, dose may influence the kinetics of HSV spread from the peripheral inoculation site to the CNS.

Restricted expression of herpes simplex virus lytic genes during establishment of latent infection by thymidine kinase-negative mutant viruses

Infection of cells by herpes simplex virus (HSV) can lead to either lytic, productive infection or nonlytic, latent infection. The factors influencing this infection pathway decision are largely unknown. Thymidine kinase-negative mutant viruses can establish latent infection in neurons of mouse trigeminal ganglia but do not replicate productively in these cells. We show that during the early stages of establishment of latency by these mutants, expression of viral lytic genes is drastically reduced or undetectable as assayed by in situ hybridization. Thus, establishment of latent infection by HSV can occur despite severely restricted levels of lytic gene expression. This suggests that the block to productive replication during establishment of latent infection by HSV occurs before or early during the expression of alpha genes.

Characterization of herpes simplex virus type 2 transcription during latent infection of mouse trigeminal ganglia

Using a cornea trigeminal ganglion model, we have investigated transcription by herpes simplex virus type 2 (HSV-2) during latency in mice. Latency was verified 2 months postinoculation by reactivation of HSV-2 after explant cocultivation of trigeminal ganglia from the majority of mice (83%). Transcription during latent HSV-2 infection was limited to the repeat regions of the viral genome as determined by in situ hybridization using restriction fragment probes representing 100% of the HSV-2 genome. Further mapping of the positively hybridizing region by using subfragments showed that transcription occurred from approximately 11.5 kb of contiguous DNA fragments. A 1.0-kb PvuI-BamHI fragment within the BamHI F fragment and a 0.3-kb BamHI-SalI fragment and a 3.4-kb SalI-BamHI fragment within the BamHI P fragment hybridized more strongly than other subfragments in in situ hybridization experiments. All positive signals were confined to the nucleus. The RNA that hybridized to the 3.4-kb SalI-BamHI DNA fragment probe by in situ hybridization corresponded to a 2.3-kb transcript on Northern (RNA) blots. Under our conditions for Northern blot hybridization, the 3.4-kb SalI-BamHI probe of HSV-2 hybridized to a limited degree with the latency-associated transcripts of HSV-1. Shorter spliced species of latency-associated transcript RNA, which are seen during HSV-1 latency, have not been detected in latent HSV-2 RNA. However, viral gene expression during HSV-2 latency appears to be very similar to that during HSV-1 latency.

Activity of herpes simplex virus type 1 latency-associated transcript (LAT) promoter in neuron-derived cells: evidence for neuron specificity and for a large LAT transcript

By using chloramphenicol acetyltransferase (CAT) assays in neuron-derived cell lines, we show here that promoter activity associated with the herpes simplex virus type 1 latency-associated transcript (LAT) had neuronal specificity. Promoter activity in these transient CAT assays coincided with a DNA region containing excellent RNA polymerase II promoter consensus sequences. Primer extension analysis in a LAT promoter-CAT plasmid construct placed the start of transcription about 28 nucleotides from the first T in the consensus TATA box sequence. Neuronal specificity of this promoter was suggested by examining the effect of sequences upstream of the promoter on CAT activity in neuronal versus nonneuronal cells. In nonneuronal cells, promoter activity was decreased 3- to 12-fold with the addition of upstream sequences. In contrast, in neuron-derived cells, the addition of upstream sequences did not decrease promoter activity. The LAT promoter predicted by our transient CAT assays was located over 660 nucleotides upstream from the 5' end of the previously mapped 2-kilobase (kb) LAT. This unusual location was explained by in situ and Northern (RNA) blot hybridization analyses that suggested that LAT transcription began near the promoter detected in our CAT assays, rather than near the 5' end of the 2-kb LAT. In situ hybridization with neurons from latently infected rabbits detected small amounts of LAT RNA within 30 nucleotides of the consensus TATA box sequence. This suggested that LAT transcription began near this TATA box. Northern blot hybridization of RNA from ganglia of latently infected rabbits revealed a faint 8.3-kb band of the same sense as LAT. We conclude that (i) the LAT promoter has neuronal specificity, (ii) the LAT promoter is located over 660 nucleotides upstream of the 5' end of the previously characterized stable 2-kb LAT, (iii) LAT transcription begins about 28 nucleotides from the first T of the consensus TATA box sequence and extends to near the first available polyadenylation site approximately 8.3 kb away, and (iv) this 8.3-kb RNA may be an unstable precursor of the more stable 2- and 1.3-kb LATs.

Vanadate promotes reactivation and iontophoresis-induced ocular shedding of latent HSV-1 W in different host animals

Vanadate is a potent inhibitor of calcium stimulated ATPase, Na, K-ATPase, and may have adrenergic activity. Using the iontophoresis method, we compared vanadate to a BSS control and the standard iontophoresis model (6-hydroxydopamine/epinephrine) by measuring induced ocular shedding of latent HSV-1 in different host animals. Latent trigeminal ganglionic infections were established in Balb/c mice and New Zealand rabbits following corneal inoculation with HSV-1 [W] strain, and later confirmed by cocultivation. Latently-infected animals (greater than 1 month post-infection) were divided into three treatment groups. Each group was iontophoresed with BSS, vanadate 1% or 6-HD 1%, and then treated topically for 10 days with BSS, vanadate or epinephrine respectively. Reactivation and recovery of latent HSV-1 was detected by daily ocular swabbing, plating, and observing progressive viral growth in Vero cells. The vanadate group had more virus-positive eyes than the BSS control group in mice, (8/32 vs. 1/32 P less than .01), and also in rabbits (14/20 vs 6/22 P less than .01). Virus-positive animals and total positive swabs were also higher for vanadate than BSS in both mice and rabbits. Furthermore, while vanadate was associated with fewer virus-positive eyes than 6-HD & EPI (8/32 vs. 17/32 P less than .02) in mice, there were no significant differences in rabbits. We conclude that vanadate promotes ocular shedding of latent HSV-1, and may act through an adrenergic mechanism.

A major portion of the latent pseudorabies virus genome is transcribed in trigeminal ganglia of pigs

Pseudorabies virus (PRV) is a porcine herpesvirus that establishes latent infections in trigeminal ganglia. To determine whether PRV expresses any transcripts that could play a role in latency, the trigeminal ganglia of 14 pigs previously inoculated through the nose and latently infected with PRV(Ka) were assayed by in situ nucleic acid hybridization for the presence of PRV-specific RNA. Hybridizations employing probes encompassing the entire viral genome revealed that an area extending from 0.64 to 0.82 map units was transcriptionally active. The DNA probe that most consistently detected transcripts was BamHI-8, a fragment which contains the gene for the immediate-early protein. With this probe, ganglia from 10 (71%) of 14 pigs scored positive for PRV RNA, although only 1 (8%) of 12 of the ganglia from the opposite side reactivated virus after explanation and culture of latently infected trigeminal ganglia. The RNA was transcribed from the strand opposite to that coding for the immediate-early protein; the signal was neuronally localized, with dense nuclear accumulation accompanied by variable numbers of grains over the cytoplasm. Northern RNA blot analysis showed that a discrete set of poly(A)- PRV transcripts were present in latently infected trigeminal ganglia. Additional in situ nucleic acid hybridization analysis revealed that the 3' limit of the transcriptionally active area was located in a 1.2-kilobase fragment upstream and adjacent to the 5' end of the immediate-early protein RNA, whereas the 5' limit was as much as 4.9 kilobases downstream from the 3' end of this RNA. PRV therefore expresses latent-phase transcripts that, although similar in many respects to latent-phase transcripts reported for other herpesviruses, have some unique properties.

Detection of latent pseudorabies virus in swine using in situ hybridization

We have examined methods for detection of pseudorabies virus (PRV) latency in three groups of swine; naturally infected animals obtained from a field case; animals which have been experimentally infected with Becker or Iowa strains of PRV; and single reactors (single seropositive animals within PRV-free herds). In situ hybridization was shown to be more sensitive than explanation/co-cultivation for the detection of latent virus. Nervous tissues, in particular the trigeminal ganglia, were found to be the most reliable source for detecting latent PRV. The presence of latent PRV was not detected in lymphoid tissues examined.

Quantitative polymerase chain reaction analysis of herpes simplex virus DNA in ganglia of mice infected with replication-incompetent mutants

To study the roles of viral genes in the establishment and maintenance of herpes simplex virus (HSV) latency, we have developed a polymerase chain reaction assay that is both quantitative and sensitive. Using this assay, we analyzed the levels of viral DNA in trigeminal ganglia of mice inoculated corneally with HSV mutants that are defective for virus replication at one or more sites in mice and for reactivation upon ganglionic explant. Ganglia from mice infected with thymidine kinase-negative mutants, which replicate at the site of inoculation and establish latency but do not replicate acutely in ganglia or reactivate upon explant, contained a range of levels of HSV DNA that overlapped with the range found in ganglia latently infected with wild-type virus. On average, these mutant-infected ganglia contained one copy of HSV DNA per 100 cell equivalents (ca. 10(4) molecules), which was 50-fold less than the average for wild-type virus. Ganglia from mice infected with a ribonucleotide reductase deletion mutant, which is defective for acute replication and reactivation upon ganglionic explant, also contained on average one copy of HSV DNA per 100 cell equivalents. We also detected substantial numbers of HSV DNA molecules (up to ca. 10(3] in ganglia of mice infected with an ICP4 deletion mutant and other replication-negative mutants that are severely impaired for viral DNA replication and gene expression. These results raise the possibility that such mutants can establish latency, which could have important implications for mechanisms of latency and for vaccine and antiviral drug development.

Polymerase chain reaction amplification of pseudorabies virus DNA from acutely and latently infected cells

A characteristic of alphaherpesviruses, including pseudorabies virus (PRV), is that the acute phase of the disease is followed by lifelong latency. Latently infected animals are asymptomatic but can transmit reactivated virus. Corticosteroid administration, tissue explanation, blot- and in situ hybridizations have been used to demonstrate the presence of latent PRV infections. The use of blot hybridization as a convenient method for defining the incidence of PRV infections in swine herds has been hampered by the detection limit of this method. The objective of this study was to increase this sensitivity of blot hybridization by polymerase chain reaction (PCR) amplification of target sequences. Two sets of 20-mer primers were synthesized and used to amplify gX and gII glycoprotein gene sequences in two different strains of PRV. The specificity of the amplification was verified by Southern blot hybridization and restriction endonuclease analysis of the amplified fragments. Amplification of target sequences by PRC increased their detection limit by a factor of at least 10(5). Porcine ganglion samples, in which latency had been demonstrated by in vitro explanation, were analyzed by PCR together with positive and negative controls. Duplicate slot blot analyses of a portion of the amplified products were used to demonstrate latency in seven of eight samples. It was concluded that blot hybridization of PCR amplified DNA appears to be both a sensitive and convenient method for the detection of PRV induced latency.

Cellular neuroimmunologic responses to ocular herpes simplex virus infection

Infectious herpes simplex virus type 1 (HSV-1) was cultivated from the trigeminal ganglion between days 3 and 21 after ocular infection. T lymphocytes were first seen 9 days after infection and were present in ganglia collected 21 days after corneal infection. Neuron cell bodies expressing cytoplasmic HSV-1 antigens were present in the ganglion by 6 days after infection and could be found up to 21 days after infection although the frequency was low and decreased with time. Neuron cell bodies containing nuclear viral DNA were seen with the same frequency as cells expressing cytoplasmic viral antigens. T lymphocytes were seen surrounding neuron cell bodies some of which contained either cytoplasmic HSV-1 antigens or nuclear HSV-1 DNA.

Structural and kinetic analyses of herpes simplex virus type 1 latency-associated transcripts in human trigeminal ganglia and in cell culture

Only one herpes simplex virus type 1 (HSV-1) gene is expressed in sensory neurons of latently infected animals and humans, yielding two RNAs, called latency-associated transcripts (LATs). The LATs appear to modulate virus reactivation. In mice and rabbits the 5' origins, kinetics of synthesis, and splicing pattern of the LATs are well established. Because these details of LAT structure and expression have not been defined in humans, we sought to do so. Using primer extension and Northern hybridization analyses, we demonstrate that in human trigeminal ganglia, the smaller (1.35 kb) HSV-1 transcript differs from the larger (1.85 kb) LAT by excision of an intron near its 5' end; they are otherwise colinear, and 5' coterminal. In infected cells only the 1.85 kb LAT is detected. Its expression is inhibited by cycloheximide or acyclovir, indicating this LAT is synthesized late in the viral replicative cycle. All of these features of the LATs in humans are consistent with those reported in rabbits and mice and further validate the animal models of human HSV-1 infection.

Specific inhibitors of herpes simplex virus thymidine kinase diminish reactivation of latent virus from explanted murine ganglia

Two specific inhibitors of herpes simplex virus thymidine kinase, N2-phenyl-2'-deoxyguanosine and N2-(m-trifluoromethylphenyl)guanine, were tested for their ability to inhibit the reactivation of virus from explant cultures of latently infected murine trigeminal ganglia. Both compounds significantly diminished the frequency of reactivation compared with that of untreated controls.

Nucleotide sequences responsible for the inability of a herpes simplex virus type 2 strain to grow in human lymphocytes are identical to those responsible for its inability to grow in mouse tissues following ocular infection

A study was undertaken to determine whether genes associated with herpes simplex virus (HSV) neuroinvasiveness in mice influence the growth of HSV in man, the virus's natural host. HSV-2(186), a nonneuroinvasive HSV strain, was found to replicate poorly (less than 3-fold) in cultures of phytohemagglutinin (PHA) stimulated human peripheral blood mononuclear cells (PBMC). In contrast, seven other HSV strains all multiplied 40- to 100-fold. The paucity of HSV-2(186) growth in PBMC was not due to a failure of this strain to grow in primary human cells because high titers (greater than 10(8) PFU/ml) were obtained following infection of human foreskin fibroblasts. The genetic basis for the deficient growth was analyzed by marker rescue experiments. Recombinant HSV-2 strains were generated in marker rescue experiments utilizing HSV-2(186) DNA and plasmids containing a cloned DNA polymerase gene isolated from a neuroinvasive HSV strain possessing the capacity to replicate in human PBMC. Progeny which rescued DNA from the cloned HSV DNA polymerase gene replicated 40- to 100-fold in PHA-stimulated PBMC. Moreover, unlike the HSV-2(186) parent, HSV-2(186) isolates possessing rescued DNA grew well in the eye, trigeminal ganglion, and brain of mice and induced fatal encephalitis. The results indicate that nucleotide sequences responsible for increasing the capacity of HSV-2(186) to grow in PBMC of man are identical to those responsible for increasing the capacity of this strain to grow in mouse tissues and to spread from the eye to the brain.

Human herpes virus infections and Alzheimer's disease

Herpes viruses cause acute and chronic diseases of the peripheral and central nervous systems and have been implicated in the aetiology of Alzheimer's disease (AD). In this investigation the relevance of human herpes virus infection to AD was assessed by in situ hybridization. The abundant latency associated transcript(s) of herpes simplex virus type 1 (HSV-1) were detected at a significantly higher incidence in the trigeminal ganglia of individuals with AD than in controls. But we could find no evidence of viral RNA in the central nervous system (CNS), looking specifically in the hippocampal cortex of demented individuals with extensive neuropathological changes of AD. These studies solve one problem in testing the viral hypothesis of causation, i.e. the sensitivity of the methods used in the search for latent infection. But the central issue remains unresolved because of necessity, only the end stage of a prolonged pathophysiological process has been examined. Our conclusions are qualified accordingly.

In situ hybridisation in herpetic lesions using a biotinylated DNA probe

In situ hybridisation was performed with a biotinylated DNA probe for herpes simplex virus (HSV) using high temperature denaturation on formalin fixed, paraffin wax sections of lung, brain, ganglion and keratinising and non-keratinising squamous epithelia. Eosinophilic viral nuclear inclusions or characteristically moulded multiple nuclei with altered chromatin, which were present in two cases of HSV encephalitis and one case of viral pneumonitis, all showed complete hybridisation visualised by an alkaline phosphatase/nitroblue tetrazolium detector system. HSV encephalitis and trigeminal ganglionitis, which were confirmed serologically or clinicopathologically but lacked nuclear changes, also gave positive dense nuclear signal in neurons, glias and satellite cells. No staining was present in the ganglion cells in trigeminal zoster, the glia in progressive multifocal leucoencephalopathy, or in a variety of cells in a lung coinfected with cytomegalovirus. In 10 herpetic blisters of squamous epithelia, infected cells hybridised strongly, while morphologically similar herpes zoster lesions remained negative. In neural tissues non-hybridisation staining was most obtrusive in corpora amylacea and seemed to reflect nonspecific probe adherence. In squamous epithelium, major non-hybridisation staining was caused by probe and antibody possibly adhering to intracellular keratin. The HSV probe permits specific detection of virus in the absence of characteristic nuclear changes and allows varicella zoster virus to be differentiated from HSV, provided that the aforementioned problems with non-hybridisation staining are borne in mind.

HSV (type 1) infection of the trigeminal complex

Following corneal inoculation with herpes simplex virus (Type 1) (HSV), virus spreads to the CNS by axonal transport in the central branches of trigeminal ganglion cell neurons. Although this mode of viral entry to the CNS is rare for humans, it appears to be the principal route of entry into the CNS in animal models of herpetic corneal disease. In this study, the corneas of BALB/c mice were unilaterally inoculated with HSV, and the distribution of HSV-immunoreactive label was studied to identify the central branches of the axons of infected trigeminal ganglion cells. Virus was first noted in the brainstem trigeminal complex 4 days after corneal inoculation, when HSV-labeled afferents were found throughout the course of the descending tract of V as well as in interstitial neurons in the tract. By 5 days labeled neurons were also found not only in the n. caudalis and portions of the n. interpolaris of the trigeminal complex but also in laminae I-IV of the dorsal horn of the upper cervical levels of the spinal cord. No immunoreactivity was seen in other regions of the complex, including the n. oralis or the main sensory n. of V. By 6 days, however, the infection had spread to the main sensory division of V.