Different sizes of restriction endonuclease fragments from the terminal repetitions of the herpes simplex virus type 1 genome latent in trigeminal ganglia of mice

Demonstration of either endogenous recurrence or exogenous reinfection by restriction endonuclease cleavage analysis of herpes simplex virus from patients with recrudescent genital herpes

By using restriction endonuclease (RE) cleavage analysis, either endogenous recurrence or exogenous reinfection of herpes simplex virus (HSV) was clarified in 45 male and 20 female subjects with recrudescent genital herpes. All of the plural (two to ten) isolates from 63 (205 isolates) out of 65 subjects (97%) were HSV-2. Two isolates from only one of 65 subjects (1.5%) were HSV-1, and they showed the same RE profile. In addition, an HSV-1 and five HSV-2 isolates were obtained from the remaining one female patient (1.5%), indicating that an exogenous HSV-1 strain has been reinfected during HSV-2 recrudescences. HSV-2 isolates were furthermore classified into genotypes of HSV-2 using 16 different RE markers with five REs. Two hundred and ten HSV-2 isolates from 64 subjects were classified into 27 distinct genotypes, in which some predominant genotypes and seven new genotypes were found. Plural HSV-2 isolates obtained from 63 out of 64 subjects, including one subject from whom an HSV-1 and five HSV-2 strains were isolated, were classified into the same genotypes, indicating that they may be regarded as recrudescent genital herpes by the reactivation of the same endogenous strain. However, the RE profiles of two HSV-2 strains from the remaining one subject were different. Thus, it was finally found that only two out of 65 subjects (3%) were reinfected with exogenous strains. These results lead to the conclusion that almost all recrudescent genital herpes are due to the reactivation of an initially infected HSV-2 strain, and are occasionally due to reinfection with distinct HSV strains of either the same or a different type.

Detection of viral DNA within skin of healed recurrent herpes simplex infection and erythema multiforme lesions

The polymerase chain reaction (PCR) was used to detect HSV DNA in genomic DNA extracted from skin biopsies obtained from healed skin of five patients with hyperpigmented macules following recurrent cutaneous HSV infections and from eight patients with HSV-associated erythema multiforme (EM). A 92-bp HSV-1 DNA fragment was found in all the skin biopsies from the site of recurrent HSV infection and in five of eight (62%) biopsies from the EM patients. Virus DNA was not found in tissues distant from the site of HSV recurrence or from a patient without a history of HSV infection. These findings confirm the presence of HSV in healed skin from the site of recurrent HSV disease and are consistent with the concept that HSV is involved in EM pathogenesis.

Enhanced replication of herpes simplex virus type 1 in human cells

The effects of DNA-damaging agents on the replication of herpes simplex virus type 1 (HSV-1) were assessed in vitro. Monolayers of human lung fibroblast cell lines were exposed to DNA-damaging agents (methyl methanesulfonate [MMS], methyl methanethiosulfonate [MMTS], ultraviolet light [UV], or gamma radiation [GR]) at specific intervals, before or after inoculation with low levels of HSV-1. The ability of cell monolayers to support HSV-1 replication was measured by direct plaque assay and was compared with that of untreated control samples. In this system, monolayers of different cell lines infected with identical HSV-1 strains demonstrated dissimilar levels of recovery of the infectious virus. Exposure of DNA-repair-competent cell cultures to DNA-damaging agents produced time-dependent enhanced virus replication. Treatment with agent before virus inoculation significantly (p less than 0.025) increased the number of plaques by 10 to 68%, compared with untreated control cultures, while treatment with agent after virus adsorption significantly increased (p less than 0.025) the number of plaques by 7 to 15%. In a parallel series of experiments, cells deficient in DNA repair (xeroderma pigmentosum) failed to support enhanced virus replication. These results suggest that after exposure to DNA-damaging agents, fibroblasts competent in DNA repair amplify the replication of HSV-1, and that DNA-repair mechanisms that act on a variety of chromosomal lesions may be involved in the repair and biological activation of HSV-1 genomes.

A review of the molecular mechanism of HSV-1 latency

The neurotropic herpes viruses, as typified by herpes simplex virus type 1, are noted for their ability to form latent infections. The latent infection differs from the acute infection both in gene expression and the physical state of the viral genome. Latency can be divided into several stages--establishment, maintenance of reactivation--each of which are active areas of research. This review describes the molecular biology of HSV-1 latency and presents the current level of understanding of the molecular mechanism of HSV-1 latency.

Detection of HSV nucleic acid sequences in the cornea during acute and latent ocular disease

This study evaluated the continued presence of herpes simplex virus (HSV) nucleic acid sequences after resolution of acute herpetic stromal keratitis in the rabbit ocular model. Forty-four rabbits were inoculated bilaterally with 10(5) plaque-forming units of RE strain HSV-1 by intrastromal injection. All eyes were cultured for the presence of HSV during acute disease and immediately before the animals were killed. Full-thickness corneal buttons were then removed and processed for in situ hybridization with a 3H-labelled HSV DNA probe representing the full-length HSV genome. HSV nucleic acid sequences were detected autoradiographically at all time intervals examined. HSV nucleic acid sequences were localized in the epithelium and the anterior stromal keratocytes during acute disease and in all corneal layers during latent infection. Retention of HSV nucleic acid sequences, either HSV DNA or HSV RNA, or both, in corneal tissues (epithelium, stroma, and endothelium) may be a contributing factor in the development of HSV-induced stromal keratitis.

Regulation of viral and cellular genes in a human neuroblastoma cell line latently infected with herpes simplex virus type 2

A latent state of the herpes simplex virus type 2 genome was established in a human neuroblastoma cell line (SMS-KCNR) to initiate studies on the mechanism by which host cells interact and regulate latent viral genes. To establish viral latency, it was necessary to prevent virus replication by briefly exposing the infected cells to antiherpetic acycloguanosine (20 microM) and human interferon (120 U/ml). Subsequently however, these cells could be propagated without any antiherpetic agents and almost 60% of the cell population contained viral genome. While these cells did not produce any infectious virus, immunoblot analysis revealed two intracellular polypeptides with molecular weights of 87.5 kDa and 67 kDa, respectively, that interacted with hyperimmune anti-HSV2 rabbit serum. Two cellular enzymes, acetylcholinesterase and choline acetyltransferase, involved in metabolism of neurotransmitters were expressed at a higher level in the latently infected cells than in the mock-infected control cells. Infectious HSV-2 could be reactivated from these cells only after the cells had undergone massive morphological differentiation and maturation to flat cell types by extensive treatment with 20 micron bromodeoxyuridine.

Homology of the HSV-2 "a-sequence" to cellular sequences

Bgl-II fragments of the genome of Herpes simplex virus type 2 (HSV-2) HG-52 were cloned into the vector p-Neo and were used to screen the complete HSV-2 genome for regions cross-hybridizing with the genome of HEL cells. Most extensive cross-hybridizing activity was observed with a 530 bp SstII subfragment of the viral BamHI G DNA-fragment (contained in Bgl II F), which spans the joint and the viral a-sequence. From a lambda-L47 library, a cellular 15 kb HindIII DNA fragment was subcloned in pBR 322 which contained a 1920 bp SstII subfragment having strong cross-hybridizing activity with the 530 bp Sst II fragment of HSV-2 BamHI G. Within this 1920 bp Sst II fragment the cross-hybridizing activity was confined to a 230 bp Bgl I/Hpa II subfragment. This 230 bp fragment (including the flanking sequences) was analyzed in comparison to the viral a-sequence. Sequence data revealed a (G + C) content of 66% in the cellular and 81% in the viral DNA fragment, which is mainly determined by an extremely (G + C) rich 16-fold direct repeat (DR2) at the 5'-end. The homology between both DNA-fragments varies between 56% and 79% within the L-S inversion region. Both sequences, furthermore, show homology to the human c-myc protooncogene.

Establishment of latency in vitro with herpes simplex virus temperature-sensitive mutants at nonpermissive temperature

This report describes a latency model using human embryo lung cells that were infected with herpes simplex virus type 1 (HSV-1) temperature-sensitive (ts) mutants and cultivated at nonpermissive temperature (40.5 degrees C). ts mutants tsG8 (parental strain HSV-1 KOS) and tsG5 (parental strain HSV-1 13) could be maintained in a latent state at 40.5 degrees C for at least 40 days without exhibiting virus infectivity. During this time, viable virus could be reactivated by reducing the incubation temperature to the permissive level (34 degrees C). Virus replication could be detected 2 to 6 days after temperature reduction and the virus reactivated from the latent state seemed to retain the same ts phenotype as the input virus for at least 14 days.

Reactivation of latent herpes simplex virus infection by ultraviolet light: a human model

Infection with herpes simplex virus often results in a latent infection of local sensory ganglia and a disease characterized by periodic viral reactivation and mucocutaneous lesions. The factors that trigger reactivation in humans are still poorly defined. In our study, five patients with documented histories of recurrent herpes simplex virus infection on the buttocks or sacrum were exposed to three times their minimal erythema dose of ultraviolet light. Site-specific cutaneous herpes simplex virus infection occurred at 4.4 +/- 0.4 days after exposure to ultraviolet light in 8 of 13 attempts at reactivation. We conclude that ultraviolet light can reactivate herpes simplex virus under experimentally defined conditions. This model in humans should prove useful in evaluating the pathophysiology and prevention of viral reactivation.

Study of HSV-1 DNA species from trigeminal ganglia of rabbits during acute and latent infections

Recurrent herpetic keratitis remains a major cause of corneal blindness in developed countries. A fundamental unanswered question regarding herpes simplex virus infection concerns the relationship between the virus and host cell DNA during latency. In the present study DNA was extracted from trigeminal ganglia during both acute and latent infection following ocular inoculation. Extracted, purified DNA was utilized for transfection and for hybridization studies using a 32P-labeled HSV-1 DNA probe. DNA extracted during acute infection was complete, linear and non-integrated. Autoradiographic patterns of DNA isolated during latent infection were suggestive of two separate DNA species.

Herpesvirus (pseudorabies virus) latency in swine: occurrence and physical state of viral DNA in neural tissues

The occurrence of the pseudorabies virus (PRV, herpes suis 1) genome in various neural tissues of latently infected pigs was investigated. During the latent phase of infection, between 7 and 52 weeks p.i., the average amount of PRV DNA ranged between 0.3 and 0.05 genome copies per cell. The results obtained by in situ cytohybridization and reassociation kinetic experiments indicated that each latently infected cell harbored at least 30 viral genome copies. PRV DNA could be demonstrated in similar frequencies (about 30% of cases) in the trigeminal ganglia, the olfactory bulb, and the medulla oblongata, and less frequently in the brain stem and the spinal cord. Southern blot analysis showed that in general the physical state of the latent genome was linear and nonintegrated. Only in 2 of 15 animals could the presence of circular or concatemeric viral DNA be observed. Thus, we could show that over a period of 13 months after infection the PRV genome persisted both qualitatively and quantitatively in a stable state in different areas of both the peripheral and the central nervous system.

Detection of HSV1 DNA by in situ hybridisation in human brain after immunosuppression

Human brain cells were examined for the presence of herpes simplex virus type 1 (HSV1) DNA sequences by in situ hybridisation. Viral genome was detected in immunosuppressed patients with virological evidence of past HSV infection but not in immunosuppressed patients with no such evidence. In patients who had not been immunosuppressed, no HSV DNA sequences were detectable.

Detection of herpes simplex virus-specific DNA sequences in latently infected mice and in humans

Herpes simplex virus-specific DNA sequences have been detected by Southern hybridization analysis in both central and peripheral nervous system tissues of latently infected mice. We have detected virus-specific sequences corresponding to the junction fragment but not the genomic termini, an observation first made by Rock and Fraser (Nature [London] 302:523-525, 1983). This "endless" herpes simplex virus DNA is both qualitatively and quantitatively stable in mouse neural tissue analyzed over a 4-month period. In addition, examination of DNA extracted from human trigeminal ganglia has shown herpes simplex virus DNA to be present in an "endless" form similar to that found in the mouse model system. Further restriction enzyme analysis of latently infected mouse brainstem and human trigeminal DNA has shown that this "endless" herpes simplex virus DNA is present in all four isomeric configurations.

Latent herpes simplex virus type 1 DNA contains two copies of the virion DNA joint region

Southern blot analysis of latent herpes simplex virus DNA detected in mouse brain and digested with a restriction enzyme revealed two copies of the virion DNA joint fragment. Thus, the absence of free ends noted previously in latent herpes simplex virus type 1 DNA is due to joining of the termini.

Fusion of the termini of the murine cytomegalovirus genome after infection

The genome of murine cytomegalovirus, extracted from extracellular virions, is a linear double-stranded DNA molecule ca. 240 kilobase pairs long. In our initial cloning of subgenomic fragments of the murine cytomegalovirus genome, we obtained a HindIII clone which contained fused HindIII-terminal fragments. By hybridizing this cloned DNA fragment to infected-cell DNA, we identified an intracellular restriction fragment which was the length of the sum of the two authentic termini. This fusion fragment was not present in virion DNA but could be detected as early as 2 h postinfection and reached its highest level shortly after the onset of DNA replication at 16 h postinfection. The prereplicative increase of fused ends was not inhibited by a level of phosphonoacetic acid which effectively shut off viral DNA synthesis, nor was the early conversion from free to fused ends prevented by inhibitors of protein or RNA synthesis. The results are consistent with the fused state of viral DNA being a replicative intermediate and precursor to DNA synthesis.