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

Unpacking the 'black box' of total pathogen burden: is number or type of pathogens most predictive of all-cause mortality in the United States?

A 'black box' paradigm has prevailed in which researchers have focused on the association between the total number of pathogens for which individuals are seropositive (i.e. total pathogen burden) and various chronic diseases, while largely ignoring the role that seropositivity for specific combinations of pathogens may play in the aetiology of such outcomes and consequently mortality. We examined the association between total pathogen burden as well as specific pathogen combinations and all-cause mortality in the United States. Data were from individuals aged ⩾25 years tested for cytomegalovirus (CMV), herpes simplex virus (HSV)-1, HSV-2 and Helicobacter pylori, with mortality follow-up to 31 December 2006 in the National Health and Nutrition Examination Survey (NHANES) III (N = 6522). We did not observe a statistically significant graded relationship between total pathogen burden level and all-cause mortality. Furthermore, compared to those seronegative for all four pathogens, the greatest statistically significant rate of all-cause mortality was for those CMV+/HSV-2+ (hazard ratio 1·95, 95% confidence interval 1·13-3·35) adjusting for age, gender, race/ethnicity, education level, body mass index (kg/m2) and smoking status. Interventions targeting prevention or treatment of particular pathogens may be more effective for reducing mortality than those focused solely on reducing overall pathogen burden.

Human cytomegalovirus IE1 protein enhances herpes simplex virus type 1-induced syncytial formation in U373MG cells

Co-infection of herpes simplex virus type 1 (HSV-1) and human cytomegalovirus (HCMV) is not uncommon in immunocompromised hosts. Importantly, organ transplant recipients concurrently infected with HSV-1 and HCMV have a worse clinical outcome than recipients infected with a single virus. However, factors regulating the pathologic response in HSV-1, HCMV co-infected tissues are unclear. We investigated the potential biologic role of HCMV gene product immediate early 1 (IE1) protein in HSV-1-induced syncytial formation in U373MG cells. We utilized a co-infection model by infecting HSV-1 to U373MG cells constitutively expressing HCMV IE1 protein, UMG1-2. Syncytial formation was assessed by enumerating nuclei number per syncytium and number of syncytia. HSV-1-induced syncytial formation was enhanced after 24 hr in UMG1-2 cells compared with U373MG controls. The amplified phenotype in UMG1-2 cells was effectively suppressed by roscovitine in addition to inhibitors of viral replication. This is the first study to provide histological evidence of the contribution of HCMV IE1 protein to enhanced cytopathogenic responses in active HSV-1 infection.

Efficient quiescent infection of normal human diploid fibroblasts with wild-type herpes simplex virus type 1

Quiescent infection of cultured cells with herpes simplex virus type 1 (HSV-1) provides an important, amenable means of studying the molecular mechanics of a nonproductive state that mimics key aspects of in vivo latency. To date, establishing high-multiplicity nonproductive infection of human cells with wild-type HSV-1 has proven challenging. Here, we describe simple culture conditions that established a cell state in normal human diploid fibroblasts that supported efficient quiescent infection using wild-type virus and exhibited many important properties of the in vivo latent state. Despite the efficient production of immediate early (IE) proteins ICP4 and ICP22, the latter remained unprocessed, and viral late gene products were only transiently and inefficiently produced. This low level of virus activity in cultures was rapidly suppressed as the nonproductive state was established. Entry into quiescence was associated with inefficient production of the viral trans-activating protein ICP0, and the accumulation of enlarged nuclear PML structures normally dispersed during productive infection. Lytic replication was rapidly and efficiently restored by exogenous expression of HSV-1 ICP0. These findings are in agreement with previous models in which quiescence was established with HSV mutants disrupted in their expression of IE gene products that included ICP0 and, importantly, provide a means to study cellular mechanisms that repress wild-type viral functions to prevent productive replication. We discuss this model in relation to existing systems and its potential as a simple tool to study the molecular mechanisms of quiescent infection in human cells using wild-type HSV-1.

Mixed viral infections: detection and management

An analysis was done of the incidence and nature of mixed virus infections diagnosed in the same clinical specimen from immunocompetent patients; respiratory viruses were emphasized. Few studies have addressed mixed viral infections in any systematic fashion. The relevant studies reviewed focused on clinical relationships or diagnostic methods. Data relating to multiple infections were usually derived incidentally to the purpose of the investigations. Sixty-three percent of the reports with data on mixed infections identified them in < 5% of the total number of viral infections. Respiratory syncytial virus was the most common coinfecting virus, and respiratory syncytial virus and influenza virus were the most common virus pair identified. In considering rapid diagnostic techniques, in 87% of the reports with available data a virus was diagnosed in > 10% of specimens that were negative for the virus targeted by one method. There was no indication that mixed infections were associated with increased disease in immunocompetent patients or in certain immunocompromised patients. Immunocompromised patients, however, appeared to have a greater incidence of multiple infections. Mixed infections of single cells also occur and may have important clinical implications relative to reactivation of latent viruses and enhanced disease. The requirement for a comprehensive strategy for viral diagnosis involving multiple techniques was indicated by these findings.

Suppression of herpes simplex virus type 1 reactivation from latency by (+-)-9-([(Z)-2-(hydroxymethyl)cyclohexyl]methyl) guanine (L-653,180) in vitro

Latent herpes simplex virus type 1 (HSV-1) infection was induced in human embryonic lung cells in vitro by using a combination of viral replication inhibitors and elevated temperature. Under reactivating conditions (superinfection by human cytomegalovirus or temperature manipulation), a nonantiviral thymidine kinase inhibitor (L-653,180) was found to suppress or delay reactivation of HSV-1 from latently infected human embryonic lung cells. L-653,180 alone or in combination with interferon was ineffective as a primary or acute viral replication inhibitor and was unable to induce latent HSV-1 infection in cell culture. These data suggest that initial or acute virus replication and replication resulting from reactivation from latency are separate events.

Interaction of herpes simplex virus type 2 with a rat glioma cell line

The interaction between herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) and two neural cell lines, mouse neuroblastoma (N1E-115) and rat glioma (C6-BU-1), was investigated. N1E-115 cells were permissive to both types of HSV. In C6-BU-1 cells, on the other hand, all the HSV-1 strains tested so far showed persistent infection, and the infectious virus of HSV-2 strains disappeared spontaneously. The HSV-2-infected C6-BU-1 cells were positive for HSV-2-specific DNA sequences, virus-specific RNA, HSV-2-specific antigens and thymidine kinase activity, when no infectious virus was detected. The HSV-2 was reactivated from those C6-BU-1 cells by superinfection with murine cytomegalovirus (MCMV), but not with UV-irradiated MCMV or human cytomegalovirus. The reactivated HSV-2 was identical to the parental virus, when examined by restriction endonuclease cleavage analysis.

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.

Herpes simplex virus type 1 persistence and latency in cultured rabbit corneal epithelial cells, keratocytes, and endothelial cells

Cell cultures of rabbit corneal epithelium, keratocytes, and endothelium were used to determine the lytic cycle of herpes simplex virus type 1. Viral growth was fastest in epithelial cells. A novel HSV-1 in-vitro latency system was established in the three distinct cell types. Cell cultures were inoculated at low multiplicities of infection with HSV-1. Temperature manipulation alone was used to induce and reactivate latent HSV-1 infections. The presence of cellular stress proteins was demonstrated at supraoptimal temperatures. All cell types were capable of maintaining latent viral infections under these conditions. Viral persistence was present in 20% of epithelial cell cultures at supraoptimal temperatures, but not in keratocyte cultures or endothelial cell cultures.

The relationship of the herpesvirus family to sudden hearing loss: a prospective clinical study and literature review

The herpesvirus family is associated with sudden hearing loss syndrome and the evidence includes clinical findings (HV-Z), temporal bone studies (CMV and HV-Z), and serologic studies. The data presented demonstrate that herpes infections, in association with sudden viral hearing loss, occur as part of a multiple viral infection in 70% of instances. This feature is unique to the herpesvirus infections when compared to other neurotropic viral agents. The study also demonstrates that the variables of viral hearing loss, such as degree of hearing loss, percentage of recovery, or the incidence of vertigo are unaffected by the presence of herpesvirus infection. Mechanisms for inner ear injury may be influenced by temporary alterations in cellular immunity secondary to simultaneous viral infections as well as the native virulence of the infecting herpesvirus.

Herpes simplex virus latency in a hyperresistant clone of mouse neuroblastoma (Cl300) cells

Herpes simplex virus (HSV) hyperresistant neuroblastoma cells (clone Cl300 RII) were latently infected with HSV-1 if cultured in presence of HSV-neutralizing antibody for one or two passages after infection and then passaged further without antibody. By superinfecting HSV-1 latently infected Cl300 RII cells with HSV-2, progeny virus with HSV-1 characteristics was regularly rescued. Such retrieval of HSV-1 decreased with passage of the latently infected cells.

Concurrent herpes simplex and cytomegalovirus retinitis and encephalitis in the acquired immune deficiency syndrome (AIDS)

We present a case of bilateral herpes simplex and cytomegalovirus retinitis and concurrent encephalitis following acyclovir therapy in a homosexual male with the acquired immune deficiency syndrome (AIDS). At autopsy, herpes simplex virus antigens were readily detected in all retinal layers, retinal pigment epithelium, and choriocapillaris, using an immunoperoxidase technique, whereas herpes simplex antigens in the brain were localized in restricted foci of vascular and subependymal parenchymal cells. Cytomegalovirus antigens were identified in cells in all layers of retina, in retinal pigment epithelium, and in subependymal parenchymal cells in the brain. No cytomegalovirus antigens were detected in any vascular endothelium, in choroid, or anterior to the ora serrata. The widespread expression of herpes simplex virus antigens in this patient's retinas is in marked contrast to the restricted foci of herpes simplex antigens limited to the subependymal region of the brain, and is similar to that seen in murine models of herpes simplex retinitis produced by acyclovir-resistant viral mutants.

Analysis of the herpes simplex virus genome during in vitro latency in human diploid fibroblasts and rat sensory neurons

We have previously designed in vitro model systems to characterize the herpes simplex virus type 1 (HSV-1) genome during in vitro virus latency. Latency was established by treatment of infected human embryo lung fibroblast (HEL-F) cells or rat fetal neurons with (E)-5-(2-bromovinyl)-2'-deoxyuridine and human leukocyte interferon and was maintained by increasing the incubation temperature after inhibitor removal. Virus was reactivated by reducing the incubation temperature. We have now examined the HSV-1-specific DNA content of latently infected HEL-F cells and rat fetal neurons treated with (E)-5-(2-bromovinyl)-2'-deoxyuridine and human leukocyte interferon and increased temperature. The HEL-F cell population contained, on an average, between 0.25 and 0.5 copies of most, if not all, HSV-1 HindIII and XbaI DNA fragments per haploid cell genome equivalent. In contrast, the latently infected neurons contained, on an average, 8 to 10 copies per haploid cell genome equivalent of most HSV-1 BamHI DNA fragments. There was no detectable alteration in size or molarity of the HSV-1 terminal or junction DNA fragments obtained by HindIII, XbaI, or BamHI digestion of the latently infected neuron or HEL-F cell DNA, as compared with digestion of a reconstruction mixture of purified HSV-1 virion and HEL-F cell DNAs. These data suggest that the predominant form of the HSV-1 genome in either latently infected cell population is nonintegrated, linear, and nonconcatameric.

Synergistic antiviral activity of acyclovir and interferon on human cytomegalovirus

The efficacy of human alpha interferon (IFN-alpha) combined with 9-(2'-hydroxyethoxymethyl)guanine (acyclovir; ACV), (E)-5-(2-bromovinyl)-2'-deoxyuridine, 9-beta-D-arabinofuranosyladenine, or 1-beta-D-arabinofuranosylcytosine on the inhibition of human cytomegalovirus (HCMV) replication in human embryonic lung cells was analyzed by plaque reduction assays. IFN-alpha combined with 9-beta-D-arabinofuranosyladenine or 1-beta-D-arabinofuranosylcytosine produced an additive antiviral activity with respect to HCMV plaque formation. IFN-alpha combined with (E)-5-(2-bromovinyl)-2'-deoxyuridine also exhibited additive antiviral activity. However, IFN-alpha combined with ACV at concentrations higher than 10 microM consistently yielded synergistic activity in HCMV plaque reduction assays. Kinetic analyses of HCMV replication demonstrated that approximately a 1,000-fold reduction can be attained through the synergistic interaction between ACV (200 microM) and IFN-alpha (42 IU/ml). These data suggest that combined ACV and IFN-alpha treatment may be useful against HCMV infection.

Herpes simplex virus latency and reactivation in isolated rat sensory neurons

An in vitro herpes simplex virus type 1 (HSV-1) latency model has been established using neurons isolated from dissociated rat fetus sensory ganglia as the host cell. Rat fetal neuron cells were pretreated for 24 hr at 37 degrees with (E)-5-(2-bromovinyl)-2'-deoxyuridine and human leukocyte interferon, infected with HSV-1 (approximately 2.5 plaque-forming units/cell), and treated for 7 days with the same inhibitor combination. Infectious HSV-1 became undetectable 3 days postinfection and remained undetectable during the remainder of the inhibitor treatment. After removal of inhibitors on day 7, infectious virus remained undetectable for 2-7 days; subsequently, virus replication ensued and neuronal cells were destroyed. Incubation of inhibitor-treated, infected neuron cells at 40.5 degrees after removal of inhibitors resulted in extension of the latent period to at least 15 days. HSV-1 was reactivated from latently infected neurons by reducing the incubation temperature from 40.5 to 37 degrees and virus-specific cytopathology was observed in neurons within 96 hr after reducing temperature. This in vitro model system will provide the first system to analyze, in a primary cell type of neuronal origin, the state of the HSV genome during establishment and maintenance of the latent state and during virus reactivation.

High efficiency latency and activation of herpes simplex virus in human cells

Herpes simplex virus (HSV) exists in humans in a latent form that can be activated. To characterize the molecular basis of the cell-virus interactions and to analyze the state of the latent HSV genome, an in vitro model system was established. In this system a large fraction of the latently infected cells contain an HSV genome that can be activated. Cell survival was reduced minimally after repression of high multiplicity HSV type 1 (HSV-1) infection of human fibroblast cells with (E)-5-(2-bromovinyl)-2'-deoxyuridine in combination with human leukocyte interferon (IFN-alpha). A minimum of 1 to 3 percent of the surviving cells contained an HSV genome that could be activated either by human cytomegalovirus superinfection or reduction in incubation temperature.

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.

Involvement of an early human cytomegalovirus function in reactivation of quiescent herpes simplex virus type 2

We have previously described an in vitro system in which the function lacking for herpes simplex virus type 2 (HSV-2) replication can be induced by human cytomegalovirus (HCMV). The mechanism of this reactivation of quiescent HSV-2 by HCMV has been further defined. The HCMV function(s) responsible for HSV-2 stimulation was examined temporally, and the fraction of cells in quiescent cultures producing HSV-2 after superinfection was determined. Using independent biological, genetic and molecular techniques we have made the following observations. (i) As early as 12 h after HCMV superinfection, HSV-2 RNA was expressed in latently infected cells. (ii) At 24 h after HCMV superinfection, a time when newly synthesized HCMV was not yet apparent, infectious HSV-2 was produced by reactivated cultures. (iii) Four HCMV temperature-sensitive mutants, which are DNA-negative at nonpermissive temperature and represent four different complementation groups, induced reactivation of HSV-2 at 39.5 degrees C. (iv) Early after HCMV superinfection, 1.6% of quiescent cells could be induced to transcribe HSV-2 information. (v) Early after HCMV superinfection, 0.3% of cells in the quiescent cultures could be induced to yield infectious HSV-2. The finding that a significant interaction can occur between HCMV and quiescent HSV-2 in an in vitro model is noteworthy in light of the knowledge that both of these herpesviruses often reside simultaneously in the human host.

Persistence of herpes simplex virus genes in cells of neuronal origin

The growth characteristics of the KOS strain of herpes simplex virus type 1 (HSV-1) in cell lines of nervous tissues origin were examined in an attempt to develop a tissue culture system mimicking the in vivo state of HSV-1 latency. We have previously reported that the B103 rat brain neuroma cell line is nonpermissive for growth of the KOS strain. In this report, we show that this nonpermissiveness is a temperature- and multiplicity-dependent phenomenon, with minimum virus yields at an elevated temperature and a low multiplicity of infection. Under these conditions, B103 cells survived infection with active wild-type or mutant HSV-1, whereas similarly treated Vero cells were killed. Six independent cultures of B103 cells surviving HSV-1 infection have been established. The surviving cells ceased production of any HSV-1 virus by 14 days postinfection and resumed growth and division at rates comparable to those of uninfected B103 cells. Survivor cells continued to express HSV-1-specific antigens, however, as detected by indirect immunofluorescence and by surface iodination followed by immunoprecipitation and polyacrylamide gel electrophoresis. The survivor cells did not express all of the surface proteins seen on productively infected B103 cells, and they were not susceptible to complement-mediated immune cytolysis with anti-HSV-1 antiserum. These results demonstrate that at least a portion of the HSV-1 genome is being harbored in these survivor cells.