VARIANTS OF HERPES SIMPLEX VIRUS: ISOLATION, CHARACTERIZATION, AND FACTORS INFLUENCING PLAQUE FORMATION

Immuno-Colorimetric Neutralization Test: A Surrogate for Widely Used Plaque Reduction Neutralization Tests in Public Health Virology

Since their first documentation in 1952, plaque reduction neutralization tests (PRNTs) have become the choice of test for the measurement of neutralizing antibodies against a particular virus. However, PRNTs can be performed only against viruses that cause cytopathic effects (CPE). PRNTs also require skilled personnel and can be time-consuming depending on the time required for the virus to cause CPE. Hence, their application limits large-scale studies or epidemiological and laboratory investigations. Since 1978, many surrogate PRNTs or immunocolorimetric assay (ICA)-based focus reduction neutralization tests (FRNT) have been developed. In this article, ICAs and their utility in FRNTs for the characterization of neutralizing antibodies, homologous or heterologous cross-neutralization, and laboratory diagnosis of viruses of public health importance have been discussed. Additionally, possible advancements and automations have been described that may help in the development and validation of novel surrogate tests for emerging viruses.

Assessment of plaque assay methods for alphaviruses

Viruses from the Alphavirus genus are responsible for numerous arboviral diseases impacting human health throughout the world. Confirmation of acute alphavirus infection is based on viral isolation, identification of viral RNA, or a fourfold or greater increase in antibody titers between acute and convalescent samples. In convalescence, the specificity of antibodies to an alphavirus may be confirmed by plaque reduction neutralization test. To identify the best method for alphavirus and neutralizing antibody recognition, the standard solid method using a cell monolayer overlay with 0.4% agarose and the semisolid method using a cell suspension overlay with 0.6% carboxymethyl cellulose (CMC) overlay were evaluated. Mayaro virus, Una virus, Venezuelan equine encephalitis virus (VEEV), and Western equine encephalitis virus (WEEV) were selected to be tested by both methods. The results indicate that the solid method showed consistently greater sensitivity than the semisolid method. Also, a "semisolid-variant method" using a 0.6% CMC overlay on a cell monolayer was assayed for virus titration. This method provided the same sensitivity as the solid method for VEEV and also had greater sensitivity for WEEV titration. Modifications in plaque assay conditions affect significantly results and therefore evaluation of the performance of each new assay is needed.

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.

Effect of snuff extract on the replication and synthesis of viral DNA and proteins in cells infected with herpes simplex virus

The water-extractable component of snuff (snuff extract) inhibits the replication of herpes simplex virus (HSV) by suppressing the synthesis of viral DNA. This process probably causes HSV to be oncogenic. To further understand the mechanism of inhibitory action of snuff extract on HSV replication, the effect of snuff extract on the synthesis of viral DNA and proteins in type 1 HSV (HSV-1) infected cells was investigated. Snuff extract inhibited the synthesis of viral DNA and altered the production of certain classes of viral proteins. The syntheses of ICP4, a viral alpha-protein, and ICP8, a beta-protein, were not generally reduced by noncytotoxic concentrations of snuff extract (where ICP = infected cell polypeptide). However, snuff extracts significantly inhibited the production of ICP gC (glycoprotein C), a gamma 2-protein, and the inhibition was in a concentration-dependent fashion: the higher the concentration of snuff extracts, the greater the inhibition. Based on the fact that the production of alpha- and beta-proteins is absolutely necessary for and precedes the viral DNA synthesis and that viral gamma 2-proteins are mostly produced by the newly synthesized viral DNA, it is concluded that snuff extract inhibits HSV-1 DNA replication directly rather than indirectly via the alteration of viral protein synthesis.

Active replication of human immunodeficiency virus type 1 by peripheral blood mononuclear cells following coincubation with herpes viruses

Patients with acquired immunodeficiency syndrome (AIDS) commonly suffer from opportunistic infections associated with members of the herpes virus family. To investigate whether certain of these other viruses might have an effect on the ability of the human immunodeficiency virus type 1 (HIV-1) to replicate, we coincubated peripheral blood mononuclear cells (PBMC) from nine HIV-1-seropositive donors with live preparations of various herpes viruses. In seven of nine cases, exposure of PBMC to preparations of either HSV-1, HSV-2, or CMV stimulated the cells to become active producers of HIV-1, as determined by reverse transcriptase activity and by the presence of infectious progeny virus. This increased production of HIV-1 particles appeared to be a consequence of mitogenic proliferation and of herpes virus-encoded transacting factors. These results supplement earlier findings on the molecular activation of the HIV-1 genome by both HSV and CMV genetic elements and point to a possible role for these viruses in the pathogenesis and ultimate clinical outcome of HIV-1 infections.

Effect of smoked tobacco tar on the growth, cytolytic action, DNA synthesis, and gene expression of herpes simplex virus

Previous experiments have shown that topical application of smoked tobacco tar condensate to HSV-infected oral mucosae of mice promotes neoplastic changes. Although HSV is an oncogenic virus, the virus must be inactivated and lose its cytolytic activity to be oncogenic in vitro and in vivo. Therefore, we investigated the effect of the water-extractable components of smoked tobacco tar condensate (smoked tobacco tar extract) on the growth, cytolytic activity, DNA synthesis, and gene expression of type 1 herpes simplex virus (HSV-1). Diluted tar extracts in tissue culture medium markedly inhibited the replication and cytolytic activity of HSV-1 in vitro. The smoked tobacco tar extract also notably inhibited the synthesis of viral DNA and late gene expression in a dose-dependent manner. The synthesis of alpha- and beta-classes of viral proteins was not affected by the extract. Therefore, it is probable that the smoked tobacco tar extract inhibits the synthesis of viral DNA directly rather than indirectly by depressing early gene expression.

Effect of chlorhexidine on the in vitro and in vivo herpes simplex virus infection

Several investigations have recently shown that chlorhexidine (CHX) has antiviral activity, and they have indicated possible clinical use of CHX for the control of intraoral herpes simplex virus (HSV) infection. In the present study, we have evaluated the in vitro and in vivo therapeutic efficacy of CHX against type 1 HSV (HSV-1) infection. CHX moderately, but significantly, inhibited the replication and cytolytic activity of HSV-1 in Vero cell monolayers. When 0.2% CHX was applied topically onto the HSV-1 infected forehead skin of mice, the development of viral lesions and the viral titers in the skin and trigeminal ganglia were also moderately reduced. These data indicate that CHX oral rinse may be beneficial for the control of intraoral HSV-1 infection in certain patients, and warrants further controlled clinical study.

A human cytomegalovirus function inhibits replication of herpes simplex virus

Human embryonic lung (HEL) cells infected with human cytomegalovirus (HCMV) restricted the replication of herpes simplex virus type 1 (HSV-1). A delay in HSV replication of 15 h as well as a consistent, almost 3 log inhibition of HSV replication in HCMV-infected cell cultures harvested 24 to 72 h after superinfection were observed compared with controls infected with HSV alone. Treatment of HCMV-infected HEL cells with cycloheximide (100 micrograms/ml) for 3 or 24 h, conditions known to result in accumulation of HCMV immediate-early and early mRNA, was demonstrated effective in blocking HCMV protein synthesis, as shown by immunoprecipitation with HCMV antibody-positive polyvalent serum. Cycloheximide treatment of HCMV-infected HEL cells and removal of the cycloheximide block before superinfection inhibited HSV-1 replication more efficiently than non-drug-treated superinfected controls. HCMV DNA-negative temperature-sensitive mutants restricted HSV as efficiently as wild-type HCMV suggesting that immediate-early and/or early events which occur before viral DNA synthesis are sufficient for inhibition of HSV. Inhibition of HSV-1 in HCMV-infected HEL cells was unaffected by elevated temperature (40.5 degrees C). However, prior UV irradiation of HCMV removed the block to HSV replication, demonstrating the requirement for an active HCMV genome. HSV-2 replication was similarly inhibited in HCMV-infected HEL cells. However, replication of adenovirus, another DNA virus, was not restricted in these cells under the same conditions. Superinfection of HCMV-infected HEL cells with HSV-1 labeled with [3H]thymidine provided evidence that the labeled virus could penetrate to the nucleus of cells after superinfection. Evidence for penetration of superinfecting HSV into HCMV-infected cells was also provided by blot hybridization of HSV DNA synthesized in cells infected with HSV alone versus superinfected cell cultures at 0 and 48 h after superinfection. In addition, superinfection with vesicular stomatitis virus ruled out a role for interferon in restriction of HSV replication in this system.

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.

Effect of micromolar concentrations of delta-9-tetrahydrocannabinol on herpes simplex virus type 2 replication in vitro

The effect of micromolar concentrations of delta-9-tetrahydrocannabinol (delta-9-THC) on the in vitro replication and biosynthesis of herpes simplex virus type 2 (HSV2) was determined. A 100-fold increase in extracellular virus was recorded for infected Vero cells pretreated with 10(-6) M or 10(-5) M drug when compared to infected vehicle-treated controls. However, no significant differences were observed in the production of total infectious virus for any of the vehicle or drug-treated cultures. Immunofluorescence of virus-infected cells revealed that delta-9-THC did not alter the intracellular compartmentalization of virus-specified proteins. Analytical sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography of isotopically labeled, cell-associated virus-specified proteins revealed that delta-9-THC had no major effect on the production of early nonstructural proteins but decreased the synthesis of late structural proteins. Scanning electron microscopy and light microscopy revealed blebs on the surface and macrovacuoles in the cytoplasm of both infected and uninfected cells treated with drug. These results suggest that delta-9-THC at micromolar concentrations selectively targets the host cell with the consequence of perturbation of cellular membranes. The alteration of cellular membranes may account for the enhanced virus release and for the decreased expression of virus-specified, cell-associated late structural proteins.

Effect of smokeless tobacco on the replication of herpes simplex virus in vitro and on production of viral lesions in hamster cheek pouch

Previous experiments have shown that combination of herpes simplex virus (HSV) infection and simulated snuff-dipping in hamster buccal pouches enhances the development of micro-invasive squamous cell carcinoma in cheek pouch epithelium. The effect has now been determined of water-extractable components of snuff (snuff-extract) on the growth and the cell-lysing activity of HSV. Various dilutions of snuff-extract in tissue culture medium significantly inhibited the growth of HSV in Vero cell monolayers by inhibiting the viral DNA replication. Moreover, HSV was inactivated and its cell-lysing activity lost when it was incubated with snuff-extract in cell-free condition. Snuff also had a similar anti-herpetic effect in vivo; HSV infection of pouch tissues followed by simulated snuff-dipping resulted in significant inhibition of viral growth. Thus snuff interferes with the DNA synthesis and cytolytic activity of HSV in vitro and in vivo, and this in turn, may increase its oncogenic capacity.

Oral cancer induced in hamsters with herpes simplex infection and simulated snuff dipping

A number of epidemiologic studies indicate that snuff dipping is associated with an increased incidence of oral cancer in human beings. Since inactivated herpes simplex virus (HSV) has been shown to induce malignant changes in vitro and in vivo and is partially inactivated by snuff water extract, we examined the histopathologic changes of hamster buccal pouches after exposure to repeated HSV inoculation combined with long-term simulated snuff dipping. One hundred twenty-five Syrian hamsters were divided into seven groups, and the buccal pouches were inoculated with HSV-1, HSV-2, or culture medium. The mock and HSV inoculations were done once a month for 6 consecutive months. In an effort to determine the effect of snuff on the mock- or HSV-inoculated buccal pouches, a consistent amount of a commercially available snuff was placed into both the right and left pouches twice a day in half of the animals. At the end of the 6 months of simulated snuff dipping (4 weeks after the final mock or viral inoculation), the hamsters were killed and the buccal pouches were removed for the histopathologic evaluation. Neither simulated snuff dipping nor HSV infection alone induced neoplastic changes in hamster buccal pouches. However, HSV infection in combination with simulated snuff dipping resulted in epithelial dysplasia and invasive squamous cell carcinoma in more than 50% of the animals.

Effect of antibody to interferon on genital herpesvirus infection in mice

The effect of anti-mouse interferon (IFN) antibody on the course of genital herpes infection was studied in C57B1/6J mice. As we have previously described, intravaginal inoculation of C57 mice with herpes simplex virus type 2 (HSV-2) results in the development of genital lesions, subsequent encephalitis and death, with the mortality rate dependent on virus dose. In the present study, we found that intravaginal application of 1 x 10(5) units of anti-mouse (alpha/beta) IFN antibody did not significantly affect the course of infection. However, intraperitoneal or intravenous injection (the latter to a lesser extent) of anti-IFN antibody resulted in increased morbidity and mortality. In addition, intraperitoneal injection of anti-IFN antibody decreased the level of detectable endogenous IFN in peripheral blood and at the site of infection. The clear effect of anti-IFN antibody during early stages of infection points to the possible significance of early endogenous IFN production in ameliorating HSV-2 genital infection.

Synergistic effect of human leukocyte interferon and nonoxynol 9 against herpes simplex virus type 2

The nonionic surfactant nonoxynol 9 (NP9), in combination with human alpha interferon, synergistically reduced the titer of herpes simplex virus type 2 (HSV-2) in vitro. The degree of synergy was highest at an interferon concentration of 10(3) IU/ml and an NP9 dilution of 1:1,500. We postulate that NP9 inactivates extracellular HSV-2, whereas interferon inhibits HSV-2 replication at the intracellular level.

Experimental development of herpes simplex virus infection in hamster buccal pouch

In the present study, we have developed an intraoral herpes simplex virus type 1 (HSV-1) infection model in the hamster buccal pouch. This animal model could be used for further oral cancer research related to herpes simplex virus infection.

Study of herpes simplex virus type 1 populations obtained from recurrences and primary infections

The analysis of 23 clinical isolates of herpes simplex virus type 1 (HSV-1) showed that 15 of 15 isolates that had undergone a few passages in tissue culture (fresh isolates) and two of eight isolates that had never been passaged (new isolates) were composed of a mixed population with respect to plaque morphology in Vero cells. Cloning and characterization of 10 large plaque viruses (L variants) and nine small plaque viruses (S variants), obtained from seven different isolates, showed the following. BamHI DNA restriction patterns of the L and the S variants from a single isolate differed only with respect to the electrophoretic mobility of the fragments that contain reiteration of specific sequences; they did not differ regarding the presence or the absence of restriction endonuclease cleavage sites. The L and S variants differed with respect to the electrophoretic profiles of infected cell glycoproteins, thermosensitivity of growth and plaquing efficiency at 39 degrees C, and, at least in the case of the two couples of variants that we tested, pathogenicity for the mouse. The hypothesis that the L variants might arise from the S variant during in vivo replication is discussed.

In vitro effect of (E)-5-(2-bromovinyl)-2'-deoxyuridine, 5'-amino-5-iodo-2',5'-dideoxyuridine and 2-deoxy-D-glucose on latent ganglionic herpes simplex virus infection

(E)-5-(2-Bromovinyl)-2'-deoxyuridine (BVDU) and 5'-amino-5-iodo-2',5'-dideoxy-uridine AIdUrd, blocked the reactivation of latent ganglionic herpes simplex virus in vitro. Furthermore, BVDU, but not AIdUrd, blocked the multiplication of reactivated latent virus and transiently suppressed emergence of reactivated virus from the sensory ganglia after removal of drug from the medium. 2-Deoxy-D-glucose (2-DG) neither prevented the in vitro reactivation of latent virus nor blocked the further multiplication of reactivated latent virus.

Evaluation of the effectiveness of 2H-1,3-oxazine-2,6(3H)-dione (oxauracil) in the treatment of herpes simplex virus (HSV)-induced acute encephalitis in mice

Treatment of suckling mice with the pyrimidine analogue 2H-1,3-oxazine-2,6(3H)-dione (oxauracil) proved successful in reducing mortality associated with HSV-2-induced encephalitis. Oxauracil did not decrease mortality associated with HSV-1 infection; however, there was an increased survival time and a decrease in the amount of infectious virus recovered from the brains of HSV-1-infected animals.

Efficacy of (E)-5-(2-bromovinyl)-2'-deoxyuridine in the treatment of experimental herpes simplex virus encephalitis in mice

Systemic treatment of mice with (E)-5-(2-bromovinyl)-2'-deoxyuridine (BVDU) showed a significant therapeutic efficacy against herpes simplex type 1 virus (HSV-1) encephalitis. With treatment initiated 12 h after viral inoculation and continued for 10 consecutive days, BVDU administered intraperitoneally in daily doses of 100-500 mg/kg increased the 21-day survival rates from 30 to 100% and reduced brain virus titers by 3-4 log10 on day 6 post-infection. Furthermore, at doses of 300-500 mg/kg per day BVDU prevented the establishment of latent virus infection in the trigeminal ganglia following intracerebral HSV-1 inoculation.

A micro solid-phase radioimmunoassay for detection of herpesvirus type-specific antibody: parameters involved in standardization

A micro solid-phase radioimmunoassay (micro-SPRIA) was developed to demonstrate type-specific antibodies to herpes simplex virus types 1 and 2 (HSV1 and HSV2). Glycoproteins from the 123,000 dalton region of HSV1 (VP123) and the 119,000 dalton region of HSV2 (VP119) were isolated on preparative polyacrylamide gels for use as antigens in the micro-SPRIA. Human sera selected from clinical samples by virological history and appropriate microneutralization data were used to standardize the micro-SPRIA. Optimization of the assay required the use of siliconized microtiter wells for adsorption of antigen. Maximized results were highly dependent on the concentrations of antigen, primary antibody, and secondary antibody as well as the diluents used for these principal test reagents. Incorporation of HSV glycoproteins of each respective type with the optimal condition established in this study facilitates the direct detection of type-specific antibody in human sera.

The role of herpesvirus type 1 thymidine kinase in experimental ocular infections

Herpesvirus type 1 thymidine-kinase-negative mutants are readily selected for in tissue culture and in humans by acyclovir, a promising antiviral agent. We investigated the ocular pathogenicity of thymidine-kinase-negative mutants in the rabbit. The natural course of untreated keratitis induced by the herpesvirus type 1 thymidine-kinase-negative strain was characterized by superficial dendrites and geographic ulcers that healed spontaneously without loss of corneal clarity. We also studied the relationship between herpesvirus type 1 thymidine-kinase activity and virulence in the rabbit with three strains of herpesvirus type 1: NIH thymidine-kinase-positive (100% thymidine-kinase activity), NIH thymidine-kinase-intermediate (25% thymidine-kinase activity), and NIH thymidine-kinase-negative (0% thymidine-kinase activity). Despite comparable ocular titers, the NIH thymidine-kinase-positive strain proved to be the most virulent, causing significantly (P less than .002) more keratitis, encephalitis, and death than the other strains.

Activation of herpes simplex virus (HSV) type 1 genome by temperature-sensitive mutants of HSV type 2

Previous studies have demonstrated that herpes simplex viruses (HSV) type 1 (HSV-1) and type 2 (HSV-2) can be maintained in a repressed form in human embryo lung cells. Reducing the incubation temperature or superinfecting with a heterologous herpesvirus, human cytomegalovirus (HCMV), results in activation of virus replication. We now report that superinfection with a partially homologous herpesvirus, HSV-2, also resulted in activation of HSV-1. To minimize excessive synthesis of infectious HSV-2 while allowing virus gene expression, repressed HSV-l-infected cultures were superinfected with HSV-2 temperature-sensitive (ts) mutants (tsF3, tsB5, or tsH9). The predominant virus replicated after HSV-2 ts mutant superinfection at a nonpermissive temperature was identified as activated parental-like HSV-1 by (i) plaquing efficiency at permissive (34 degrees) and nonpermissive (40.5 degrees) temperatures, (ii) sensitivity to inhibition by the HSV-l-specific antiviral agent (E)-5-(2-bromovinyl)-2'-deoxyuridine, and (iii) restriction endonuclease cleavage analysis. In addition, the fact that superinfection with HSV-2 tsB5 or tsH9, which are unable to synthesize virus DNA and express only early virus genes at nonpermissive temperature, resulted in synthesis of virus demonstrated that HSV-2 DNA synthesis is not required for activation. This system has provided the basis for further studies concerning the regulation of HSV gene expression in human cells.

Repression and activation of the genome of herpes simplex viruses in human cells

We have described previously a cell culture system in which the herpes simplex virus (HSV) type 2 (HSV-2) genome is maintained in a repressed form after treatment of infected cells with 1-beta-D-arabinofuranosylcytosine and increase of incubation temperature from 37 degrees C to 39.5 degrees C. Infectious HSV-2 production was activated by altering incubation temperature or by superinfecting with human cytomegalovirus. We now report the establishment of an analogous system utilizing HSV type 1 (HSV-1). Human embryo lung cells were infected with HSV-1 and treated with 1-beta-D-arabinofuranosylcytosine (25 micrograms/ml) for 7 days to minimize both synthesis of virus DNA and infectious virus while allowing expression of early virus genes. HSV-1 was maintained in an undetectable form for at least 72 days when the incubation temperature was raised from 37 degrees C to 40.5 degrees C after removal of the inhibitor. HSV-1 gene expression was then predictably turned on by superinfection with human cytomegalovirus or by reducing the incubation temperature. Virus replicated after activation was compared with the respective parental virus with regard to inhibition by the HSV-1-specific antiviral (E)-5-(2-bromovinyl)-2'-deoxyuridine and EcoRI, HindIII, and Xba I restriction endonuclease cleavage patterns. The results show activation of HSV gene expression in human cells by a human cytomegalovirus early gene function(s), followed by synthesis of parental-like HSV.

Strain characteristics and features of ocular infection of herpes simplex virus type 1 isolates

Herpes simplex virus type 1 isolates from 63 patients with herpetic keratoconjunctivitis were investigated. For the purpose of detecting strain differences neurovirulence was determined in mice, and viral DNA's were analyzed by digestion with EcoRI and Hind III restriction endonucleases. Neurovirulence differed by a factor up to 10(5) between individual strains and proved to be independent of the ratio between infectious and noninfectious particles in the stocks used. The endonuclease cleavage patterns revealed differences of the viral DNA structure which permitted us to distinguish seven clusters of strains. Correlations between neurovirulence and DNA markers could not be established nor could correlations be found between these markers and features of disease. The main reason for not finding a relationship in the latter case may be attributed to the significant role of host factors in the course of herpetic diseases.

Reactivation of herpes simplex virus type 2 from a quiescent state by human cytomegalovirus

The ability of human cytomegalovirus to stimulate replication of herpes simplex virus type 2 (HSV-2) was examined. The system used involved HSV-2-infected human embryonic lung cells under conditions (39.5-40 degrees C) in which HSV-2 remains undetectable. Reactivation of HSV-2 was maximal and persisted for the longest duration when cultures were superinfected with 0.02 plaque-forming unit of human cytomegalovirus per cell. Infectious HSV-2 appeared 2 days after superinfection with human cytomegalovirus and ranged from 10(2) to 10(6) plaque-forming units per culture. Virus reactivated from these cultures was neutralized by rabbit immune serum produced against HSV-2. The specificity of this interaction was demonstrated by various criteria: production of HSV-2 was not observed in cultures treated with mock infecting fluid, and inactivation of human cytomegalovirus by heat, ultraviolet irradiation, or immune serum prior to superinfection eliminated its ability to induce HSV-2 replication. These results sugges that interaction between these two human herpesviruses may be of importance in herpesvirus latency in vivo.

Therapy of experimental herpes simplex encephalitis with aciclovir in mice

This report is concerned with the capacities of aciclovir to protect mice challenged intracerebrally with multiple lethal doses of type 1 herpes simplex virus and to control multiplication of this virus in the brain. With treatment initiated 12 h after inoculation and continued for 4 consecutive days, aciclovir administered subcutaneously in daily doses ranging from 40 to 100 mg/kg led to 21-day survival rates of from 33 to 73% and reduced virus titers by 1 to (1/2) x 4 logs on postchallenge day 8. The therapeutic accomplishments of the 100-mg/kg doses of aciclovir were comparable to those of 1,000-mg/kg doses of vidarabine (9-beta-d-arabinofuranosyladenine); however, as measured by impact on body weight, aciclovir was better tolerated than vidarabine at these similarly effective doses.

Suppression of in vitro growth of virulent and avirulent herpes simplex viruses by cell-mediated immune mechanisms, antibody, and interferon

A rounding cell-forming--GC strain, which is a variant of a syncytial giant cell-forming herpes simplex virus (+GC Miyama strain), was highly attenuated for Swiss, BALB/c nu/nu, and nu/+ mice, whereas +GC was highly virulent to all the mice tested. +GC and -GC were antigenically indistinguishable from each other by cross-neutralization and cross-immunization. Immunosuppression induced by cyclophosphamide converted the nonlethal -GC infection of mice into a fatal infection. -GC replication in tissue culture was more effectively suppressed by spleen cells immunized with either +GC or -GC than was the +GC replication. -GC replication was also inhibited more effectively by antibody or the antibody-dependent cell-mediated system than was the +GC replication. -GC is highly sensitive to mouse interferon, but +GC was relatively resistant. These findings indicate that attenuation of this avirulent -GC strain may be due to a high susceptibility of its replication to humoral and cell-mediated defense factors. The probable roles of each defense factor in recovery from the infection with virulent and attenuated herpes simplex virus are also discussed.

Ultracentrifugal inoculation of herpes simplex virus

By ultracentrifugation of 30 ml of highly dilute suspensions of herpes simplex virus (HSV) directly onto monolayer cultures grown in centrifuge tubes, infectivity was significantly greater than without centrifugation. Ultracentrifugation at 20,000 to 25,000 rpm (28,000 to 45,000 X g) for 1.5 to 2.3 h was utilized with good preservation of cultures. With low-speed centrifugation at 3,000 rpm (1,100 X g), infectivity was almost 10-fold greater than without centrifugation. With ultracentrifugal inoculation, infectivity was about 100-fold greater than without centrifugation. Ultracentrifugal inoculation permitted the detection of HSV at concentrations as low as 0.05 plaque-forming units per ml. Similarly, ultracentrifugal inoculation of cultures was almost 100-fold more sensitive a method of detecting infectious HSV than was pelleting HSV from dilute suspensions followed by resuspension and inoculation of cultures. Ultracentrifugal inoculation of cultures may permit the isolation of HSV in situations where virus cannot be detected by ordinary means and may prove applicable to the study of other viruses.

Biochemical Transformation of mouse cells by herpes simplex virus types 1 and 2: comparison of different methods for inactivation of viruses

Comparison of methods to inactivate lytic properties of herpes simplex viruses revealed that ultraviolet irradiation, photodynamic procedures, and heat all destroyed infectivity effectively. Ability to biochemically transform thymidine kinase deficient cells to an enzyme positive phenotype was retained after limited exposure to heat or ultraviolet light but appeared to be destroyed by photodynamic methods employing neutral red. Exposure to 56 degrees C quickly and effectively destroyed transforming activity with lower temperatures being less effective. The most reproducible transforming assays were obtained following inactivation by ultraviolet light. Cell cultures developed by this procedure were virus-free but retained ability to synthesize virus-specific antigens.

Reduction of herpes simplex virus-type 2 plaque formation by urea

The effect of urea on plaque formation by herpes simplex virus type 2 (HSV-2) was examined in two systems at concentrations within or approximating the range found in human urine. Approximately 7--10 mg urea/ml, added 2, 4, or 8 hours after infection, reduced plaque formation by 50% in African green monkey kidney cells. The growth of this system was affected slightly by continuous treatment with urea at 7--10 mg/ml. Plaque formation was reduced in the monkey kidney system, albeit diminishingly, even after addition of urea 12 hours after infection. In the human lung fibroblast system, urea at 10 mg/ml reduced plaque numbers by 50% but depressed the growth of cells completely.

Prolongation of herpes simplex virus latency in cultured human cells by temperature elevation

Treatment of herpes simplex virus type 2 (HSV-2)-infected human fibroblast cells with cytosine arabinoside (ara-C) at 25 microgram/ml resulted in complete inhibition of virus replication. Removal of ara-C after 7 days of treatment ultimately resulted in renewed virus replication, but after a delay of at least 5 days. If however, the temperature was elevated from 37 degrees C to 39.5 to 40 degrees C at the time of ara-C reversal, infectious HSV-2 did not reappear. As long as the cultures were maintained at 39.5 to 40 degrees C (up to at least 128 days), HSV-2 was latent and infectious virus was undetectable. If the temperature was reduced to 37 degrees C at any time during the latent period, infectious virus was always reactivated, but only after a period of incubation at 37 degrees C of a least 11 days. Infectious-center assays performed with latent cultures indicated that only a very small fraction of cells could reactivate virus. The infectious-center titer did not show significant changes during much of the period of latency. This seemed to argue against the possibility that the latent cultures were synthesizing very small amounts of infectious virus. Additional studies were aimed at determining the minimum incubation period at 37 degrees C required to reactivate infectious HSV-2. Latent cultures reduced from 39.5 to 40 degrees C to 37 degrees C for less than 96 h did not yield infectious HSV-2, but those incubated at 37 degrees C for 96 h or more did.

Differential effect of arabinofuranosylthymine of the replication of human herpesviruses

The thymidine analog 1-beta-arabinofuranosylthymine (ara-T) has previously been found to selectively inhibit herpes simplex virus replication. At a relatively nontoxic conentration (50 microgram/ml), ara-T reduced herpes simplex virus yields by 4 to 5 log10. Ara-T was also effective in inhibiting the replication of varicellazoster virus (VZV) in vitro in human embryo fibroblasts, completely preventing VZV-specific cytopathic effects. The inhibition of VZV was reversible upon drug removal at 48 h after addition but was not reversible after 5 days of treatment. ara-T also reduced cell-free virus infectivity and the plaque-forming cell yield of VZV. Compared with the untreated controls, which demonstrated a 1-log10 increase over input plaque-forming cells at 24 h after infection, 50 microgram of ara-T per ml resulted in a 1-log10 decrease. In contrast to herpes simplex virus and VZV, cytomegalovirus replication was relatively resistant to ara-T. Neither cytopathic effects nor the incorporation of [3H]thymidine into acid-insoluble material in cytomegalovirus-infected cells was markedly affected. Analysis of the newly synthesized labeled DNA by CsCl buoyant density determinations indicated that the same relative proportions of cell and virus DNA were synthesized with or without added drug. Interpretation of these results with regard to virus-induced deoxypyrimidine kinase is discussed.

Host range temperature-sensitive mutants of herpes simplex virus type 2

Two small-plaque mutants of herpes simplex virus type 2 (HSV-2) (strain 333), whose growth at 39 C was blocked in certain cell types (cell-dependent temperature sensitivity), were compared compared with parental virus in a number of biological assays. One mutant (no. 69) was found to produce a large number of morphologically normal, but noninfectious, particles; under nonpermissive conditions, these mutant particles were able to interfere with the replication of wild-type HSV-2. The other mutant (no. 74), which is known to belong to a different complementation group, appeared to direct little virus DNA synthesis, even at the permissive temperature. Progeny production and virus DNA synthesis in cells infected by mutant 74 were delayed in comparison with wild-type virus-infected cells. Both mutants were found to be more sensitive to UV irradiation than the parental virus; this was especially marked in the case of mutant 74. Moreover, this mutant was found to have a high transforming efficiency at much lower doses of irradiation than those needed to abolish the cytopathic effect of wildtype HSV-2.

Temperature-sensitive host range mutants of herpes simplex virus type 2

Herpesviruses are capable of several types of infection of a host cell. To investigate the early events which ultimately determine the nature of the virus-host cell interaction, a system was established utilizing temperature-sensitive mutants of herpes simplex virus type 2. Four mutants have been isolated which fail to induce cytopathic effects and do not replicate at 39 C in hamster embryo fibroblast cells. At least one mutant is virus DNA negative. Since intracellular complementation is detectable between pairs of mutants, a virus function is known to be temperature sensitive. However, all four mutants induce cytopathic effects and replicate to parental virus levels in rabbit kidney cells at 39 C. This suggests that a host cell function, lacking or nonfunctional in HEF cells but present in rabbit kidney cells at 39 C, is required for the replication of these mutants in hamster embryo fibroblasts cells at 39 C. Therefore, we conclude that these mutants are both temperature sensitive and exhibit host range properties.

Quantitative assay for transformation of 3T3 cells by herpes simplex virus type 2

The interaction of herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) with Swiss/3T3 cells was investigated. Virus-induced cytopathic effects developed in the absence of production of infectious virus. HSV-2 inactivated with UV light (2, 4, 6, and 8 min) also induced cell death in the absence of virus replication. Cell death was not detectable after infection by HSV-2 that had been inactivated by UV irradiation for 10, 12, and 14 min. 3T3 cells infected with UV-inactivated virus (10 and 12 min) continued to replicate past the contact-inhibited monolayer normally associated with these cells. Infection of 3T3 cells with UV-irradiated USV-2 also induced the development of transformed foci. Transformed cells with an epithelioid of fibroblastoid morphology were identified and isolated. All HSV-2-transformed cell lines contained HSV-2-specific antigens detectable by immunofluorescence techniques. The maximum frequency of HSV-2-induced transformation was 3 times 105 PFU per transformed focus, and the observed transformation could be inhibited by pretreatment of the virus with specific antiserum. No type C particles were detected within five cell culture passages after transformation by HSV-2. Type C virus particles were detected after 10 cell culture passages of the HSV-2-transformed cell lines.

Inhibition of herpes virus-induced cell fusion by concanavalin A, antisera, and 2-deoxy-D-glucose

Pseudorabies virus-induced cell fusion in rabbit kidney cells can be prevented by Concanavalin A added early after infection. The infected cells are not agglutinated and the infectivity of cell-free virus is not reduced. Sera from productively infected animals also inhibit polykaryocytosis, whereas a hyperimmune serum directed against virus structural components has no effect. 2-Deoxy-d-glucose reversibly disturbs virus-induced fusion and reduces significantly the virus infectivity.

Oncogenic transformation of hamster embryo cells after exposure to inactivated herpes simplex virus type 1

The in vitro transformation of hamster embryo fibroblasts by herpes simplex virus type 1 (HSV-1) after exposure of the virus to UV irradiation is described. Cell transformation was induced by 2 out of 12 strains of HSV-1 that were tested for transforming potential. Cells transformed by the KOS strain of HSV-1 were not oncogenic when injected into newborn Syrian hamsters. However, cells transformed by HSV-1 strain 14-012 induced tumors in 47% of the newborn hamsters injected. HSV-specific antigens were found in the cytoplasm of cells transformed by both virus strains. Sera from tumor-bearing hamsters contained HSV-1- and HSV-2-neutralizing antibodies as well as antibodies which reacted specifically with HSV antigens by the indirect immunofluorescence technique. Hamster oncornavirus antigens were not detected by immunofluorescence methods. These observations represent the first evidence of the oncogenic potential of HSV-1.

Immunologic manipulation of metastases due to herpesvirus transformed cells

Herpes simplex virus type 1 (HSV-1), type 2 (HSV-2), and simian virus 40 (SV40) fail to induce immunity in weanling Syrian hamsters to transplant of hamster cells transformed by HSV-2. However, the development of metastatic tumors is markedly enhanced by prior immunization with HSV-1. Immunization with SV40, ultraviolet-irradiated tumor cells, or ultraviolet-irradiated normal hamster embryo cells inhibits the development of metastases. The HSV-hamster system appears a good one for the study of development, prevention, and control of metastases by mammalian cells transformed by a common human virus.

Ocular pathogenicity of types 1 and 2 Herpesvirus hominis in rabbits

Type 2 strains of Herpesvirus hominis produced more severe lesions in rabbit corneas than type 1 strains.