Murine Herpesvirus Research Articles

Protective immune correlates can segregate by vaccine type in a murine herpes model system

A central tenet of vaccine development is to identify immune correlates of protection. Both plasmid-encoded gD as well as recombinant protein gD can protect mice from lethal herpes simplex virus (HSV) challenge. It is known that different vaccine modalities should induce different immune phenotypes. Yet, paradoxically, it is also thought that the basis for protection should rely on exploitation of vulnerabilities of the pathogen and therefore that the overlapping properties of these different vaccines would reveal insight into common immune mechanisms responsible for protection. We sought to investigate this question by comparing two different vaccine modalities in the HSV-2 mouse model. We observed that gD protein was a strong inducer of T(h)2-type immune responses, and overall antibody titers of IgG, IgE and IgA were significantly higher than those induced by plasmid gD vaccines. In contrast, the plasmid gD vaccine induced a strong T(h)1 bias. Following high-dose challenge the gD protein was most effective at providing protection. However, at lower lethal dose challenge, while both vaccines were protective with regards to survival, only the plasmid-vaccinated animals were protected from HSV-2 infection-induced morbidity. These studies suggest that these different vaccine modalities induce protection through unique non-overlapping mechanisms, supporting that vaccine correlates are associated with the types of immunogen rather than solely the pathogen.

In vivo models for Epstein-Barr virus (EBV)-associated B cell lymphoproliferative disease (BLPD).

EBV infects B lymphocytes in vivo and establishes a life-long persistent infection in the host. The latent infection is controlled by EBV-specific MHC class 1-restricted CTL. Immunosuppression reduces CTL activity, and this facilitates outgrowth of EBV+ve B cell lymphoproliferative disease (BLPD). BLPD are aggressive lesions with high mortality. This review presents some key facets in the development of EBV-associated BLPD and in vivo studies on its pathogenesis. The animal models used to date include the common marmoset (Callithrix jacchus), the cottontop tamarin (Saguinus oedipus oedipus), rhesus monkey, murine herpesvirus 68 (MHV68), and the severe combined immunodeficient (scid) mouse, each of which has been used to address particular aspects of EBV biology and BLPD development. Scid mice inoculated i.p. with PBMC from EBV-seropositive individuals develop EBV+ve BLPD-like tumours. Thus this small animal model (hu-PBMC-scid) is currently used by many laboratories to investigate EBV-associated diseases. We and others have studied BLPD pathogenesis in the hu-PBMC-scid model and shown that EBV+ve B cells on their own do not give rise to tumours in this model without inclusion of autologous T cell subsets in the inoculum. Based on the findings that (1) established tumours do not contain T cells and (2) tumour cells express a variety of B cell growth factors, a stepwise model of lymphomagenesis in the scid mouse model can be defined. Additionally, the hu-PBMC-scid model can be used to assess novel therapeutic regimes against BLPD before introduction into a clinical setting.

The rat cytomegalovirus R32 gene encodes a virion-associated protein that elicits a strong humoral immune response in infected rats.

A gene of rat cytomegalovirus (RCMV), designated R32, has been identified that encodes a homologue of the human cytomegalovirus (HCMV) pp150 (ppUL32) major tegument phosphoprotein. The R32 ORF has the capacity to encode a 667 amino acid polypeptide (pR32) with a calculated molecular mass of 73 kDa. The predicted amino acid sequence of pR32 shows similarity to that of polypeptides predicted to be encoded by the HCMV UL32, murine cytomegalovirus M32 and human herpesvirus types 6 and 7 U11 genes. The R32 gene is transcribed as a 2.5 kb mRNA during the late phase of RCMV infection in rat embryo fibroblasts in vitro. To study expression of the pR32 protein in vitro and in vivo, a rabbit polyclonal antiserum was raised against a recombinant protein that comprised amino acids 252-522 of pR32. By using this antiserum, pR32 could be detected predominantly in the cytoplasm of RCMV-infected fibroblasts at 24 and 48 h post-infection in vitro. The pR32 protein was also detected within virions isolated from the culture medium of RCMV-infected cells. Expression of pR32 in vivo was observed within the cytoplasm of salivary gland epithelial cells of RCMV-infected rats. In addition, recombinant pR32 was found to react with sera from rats that were previously infected with RCMV, whereas reactivity was not seen with sera from mock-infected rats. Together, these findings indicate that RCMV pR32 represents the homologue of HCMV ppUL32, both in primary structure and in function.

The murine homolog (Mph) of human herpesvirus entry protein B (HveB) mediates entry of pseudorabies virus but not herpes simplex virus types 1 and 2.

A mouse member of the immunoglobulin superfamily, originally designated the murine poliovirus receptor homolog (Mph), was found to be a receptor for the porcine alphaherpesvirus pseudorabies virus (PRV). This mouse protein, designated here murine herpesvirus entry protein B (mHveB), is most similar to one of three related human alphaherpesvirus receptors, the one designated HveB and also known as poliovirus receptor-related protein 2. Hamster cells resistant to PRV entry became susceptible upon expression of a cDNA encoding mHveB. Anti-mHveB antibody and a soluble protein composed of the mHveB ectodomain inhibited mHveB-dependent PRV entry. Expression of mHveB mRNA was detected in a variety of mouse cell lines, but anti-mHveB antibody inhibited PRV infection in only a subset of these cell lines, indicating that mHveB is the principal mediator of PRV entry into some mouse cell types but not others. Coexpression of mHveB with PRV gD, but not herpes simplex virus type 1 (HSV-1) gD, inhibited entry activity, suggesting that PRV gD may interact directly with mHveB as a ligand that can cause interference. By analogy with HSV-1, envelope-associated PRV gD probably also interacts directly with mHveB during viral entry.

Four tRNA-like sequences and a serpin homologue encoded by murine gammaherpesvirus 68 are dispensable for lytic replication in vitro and latency in vivo.

Experimental infection of inbred strains of laboratory mice with murine herpesvirus 68 (MHV-68), a natural pathogen of wild rodents, results in acute productive infection of the lung followed by a latent infection of B lymphocytes. We have previously shown that MHV-68 encodes an open reading frame with similarity to poxvirus serpins, designated ORF1, and eight novel tRNA-like sequences. The latter are processed into mature, uncharged tRNAs and are abundantly expressed during both lytic and latent infection. In this study it is demonstrated that deletion of four of the tRNA-like sequences and ORF1 from the virus genome does not affect the ability of MHV-68 to replicate in vitro or to establish, and reactivate from, latency in vivo.

The Influence of Cyclosporin Immunosuppression on the Efficacy of Famciclovir or Valaciclovir Chemotherapy Studied in a Murine Herpes Simplex Virus Type 1 Infection Model

Mice with or without immunosuppression by cyclosporin (Cy) were inoculated with herpes simplex virus type 1 in the ear pinna. Without immunosuppression, 20% of the mice died; clinical signs resolved in survivors and infectious virus was cleared by 7 to 10 days post-inoculation (p.i.). With Cy, mortality was 50%, clinical signs increased and infectious virus persisted. Mice were treated with either valaciclovir (VACV) or famciclovir (FCV) from days 1–5 or 5–10 p.i. and both compounds moderated the disease, but only FCV led to rapid restoration of body weight and complete protection from mortality. Resolution of clinical signs was more marked with immunosuppression. On cessation of VACV therapy, infectious virus recurred on individual days. Without immunosuppression, recurrence was detected in neural tissues only, but with Cy, infectious virus also recurred in skin. No recurrences of infectious virus were observed in any FCV-treated mice.

The T-cell-independent role of gamma interferon and tumor necrosis factor alpha in macrophage activation during murine cytomegalovirus and herpes simplex virus infections.

We defined the normal and innate (without functional B or T cells) inflammatory response to infection with mouse cytomegalovirus (MCMV) or herpes simplex virus (HSV). Intraperitoneal infection with MCMV or HSV induced an inflammatory infiltrate consisting largely of macrophages (M phi) in both normal CB17 and severe combined immunodeficient (SCID) mice (lacking functional B or T cells). M phi from infected mice were activated as shown by (i) spread morphology, (ii) increased expression of major histocompatibility complex (MHC) class II, MHC class I, and intercellular adhesion molecule-1 molecules, and (iii) downregulation of M phi-specific cell surface protein F4/80. In vivo administration of neutralizing antibodies specific for gamma interferon (IFN gamma) or tumor necrosis factor alpha (TNF alpha) inhibited MHC class II induction on infiltrating M phi in both normal and CB17 SCID mice. Anti-TNF alpha decreased the number of M phi in virus-induced inflammatory exudates. The MCMV titer increased in the spleen and liver of IFN gamma-depleted SCID mice, while TNF alpha depletion increased only splenic titers. MCMV-induced pathology was also increased in spleens of IFN gamma- and TNF alpha-depleted SCID mice. We conclude that (i) M phi activation is a prominent part of inflammatory responses to herpesvirus infection and (ii) IFN gamma and TNF alpha play a critical role in both virus-induced M phi activation and control of herpesvirus growth independent of T and B cells. This suggests that IFN gamma- and TNF alpha-mediated M phi activation is an important aspect of innate immunity to viral infection. As the M phi may be involved in MCMV latency, IFN gamma- and TNF alpha-dependent M phi activation during primary infection may be relevant to establishment of viral latency.

Interactions of the murine gammaherpesvirus with the immune system

Our understanding of the host response to gammaherpesviruses comes largely from studies on Epstein-Barr virus. A recent addition to this family is murine herpesvirus-68 which, like Epstein-Barr virus, establishes a latent infection in B lymphocytes and is associated with lymphoproliferative disease. This virus provides a unique opportunity to explore the relationship between gammaherpesviruses and the immune system.

The analysis of polypeptides in the nuclei and cytoplasm of cells infected with murine herpesvirus 72

Twenty-six polypeptides in murine herpesvirus isolate 72 (MHV-72) were identified and the synthesis and accumulation of 21 virus-specific polypeptides in Vero cells during the course of productive infection with MHV-72 were examined. Five of the infected cell polypeptides accumulated within the nuclei and nine accumulated within the cytoplasm of MHV-72-infected cells. Seven polypeptides were identified within the nuclei and cytoplasm in equivalent amounts. The major capsid protein was shown to have an M(r) of 161K. Thirteen virus-specific polypeptides were solubilized with Nonidet P-40 or radioimmunoprecipitation assay buffer and immunoprecipitated with rabbit and mouse immune sera. Analysis of the polypeptides of MHV-72 indicate a closer resemblance between MHV-72 and the gammaherpesviruses herpesvirus saimiri and Epstein-Barr virus than with the alphaherpesvirus herpes simplex virus type 1.

Exacerbation of murine herpes simplex virus-mediated stromal keratitis by Th2 type T cells.

Corneal infection of susceptible mice with HSV-1 causes herpetic stromal keratitis (HSK), which serves as a model of human HSK. To study the properties of the T lymphocytes involved in HSK, susceptible mice were immunized with the synthetic peptide corresponding to the amino terminal of HSV-1-associated glycoprotein D (gD 5-23). A CD4+ long-term T cell line and a clone bearing V beta 8.2 TCR were derived from peptide-primed lymph node cells. These T cells recognize gD 5-23 peptide in the context of I-Ed and require CD4 and LFA-1 for Ag-specific proliferation. Significantly, a truncated peptide gD 15-23 induced vigorous proliferation, indicating that these 9 amino acids constitute an epitope recognized by these T cells. The gD-specific T cells produced IL-4 and used it as the autocrine growth factor and hence belong to the Th2 subtype. Adoptive transfer of gD-specific Th2 cells into susceptible mice increased both the onset and severity of HSK after corneal HSV-1 infection. Injection of gD-specific Th2 cells without HSV-1 infection failed to cause eye damage. In addition, an irrelevant Ag-specific Th2 clone failed to induce similar tissue damage when the corresponding Ag was applied to the eye. These data indicate that the T cell-mediated exacerbation of HSK in these studies is dependent on the specific recognition of gD after corneal HSV-1 infection. Finally, gD-specific Th2 cell transfer also rendered HSK-resistant mice susceptible for HSK, suggesting that the freedom from HSK in resistant mice may primarily be due to their inability to produce the pathogenic Th2 cells. The data collectively implicate an important role for Th2 cells in the induction of HSV-mediated keratitis in mice.

Pathogenesis of murine gammaherpesvirus infection in mice deficient in CD4 and CD8 T cells.

Murine gammaherpesvirus is a natural pathogen of wild mice. The virus infects alveolar cells and spleen cells during the primary infection and establishes a latent/persistent infection in B lymphocytes. Little is known about the immunological response to gammaherpesviruses during a primary infection. To address this issue, we investigated the pathogenesis of murine herpesvirus 68 (MHV-68) infection in mice deficient in CD4 or CD8 T-cell populations. Infection of the lung and spleen were greatly exacerbated in CD8-deficient mice, reflected by elevated virus titers in the lung and an increase in the number of infected splenocytes located around germinal centers. This finding contrasts with clearance of virus from the lung and spleen by day 12 postinfection in CD4-depleted animals. These data clearly indicate a major role for CD8 T cells in recovery from an acute MHV-68 infection. Whereas CD4 T cells fail to influence the course of infection in the lung, they do contribute to lymphoproliferation seen in the spleen (splenomegaly) during the primary infection. The significance of these results are discussed in relation to the immune response to other herpesviruses, in particular Epstein-Barr virus, with which MHV-68 shares similar molecular and biological properties.

Biological response modifier-mediated resistance to herpesvirus infections requires induction of α/β interferon

The role of interferon α/β (IFN) induction by the immunomodulators pICLC and CL246,738 was investigated in CD-1 mice infected with murine cytomegalovirus (MCMV) or herpes simplex virus type 2 (HSV-2). Mice were treated with either normal sheep serum or anti-α/β IFN antiserum, inoculated with the immunomodulators, and infected with virus. Because anti-IFN treatment also decreased natural resistance to HSV-2 and MCMV, two viral challenge doses were used to ensure that the mice with control serum or anti-IFN antiserum received biologically equivalent infections. Antiviral protection of pICLC and CL246,738 against HSV-2 infection was completely abrogated by treatment with anti-α/β interferon antiserum. Mice treated with pICLC also lost antiviral protection against MCMV when interferon α/β was depleted. These results indicate that induction of interferon α/β appears to be a major mechanism for both natural resistance and pICLC-induced antiviral protection against MCMV and HSV-2 herpesvirus infections.

Anti-viral activity of sulfated chitin derivatives against Friend murine leukaemia and herpes simplex type-1 viruses

Sulfated chitin derivatives, selected for their low toxicity and high inhibitory activity of melanoma metastasis, were examined for anti-viral activity against Friend murine leukaemia, herpes simplex type-1 (HSV) and Sendai viruses. Carboxymethyl chitin with a 7.66% degree of sulfation (SCM-chitin III) showed a significant inhibition of Friend murine leukaemia helper virus (F-MuLV) and HSV, but not of Sendai virus growth in vitro. Sulfated N-deacetylated chitin had a significant but weak activity against F-MuLV and HSV infections. Carboxymethyl chitin showed no effect on these infections in vitro. SCM-chitin III also exhibited anti-viral activity in vivo by suppressing the splenomegaly which was caused by prior infection of mice with FV, a complex of F-MuLV and spleen focus-forming virus.

Virological and pathological features of mice infected with murine gamma-herpesvirus 68.

The primary infection of BALB/c mice with murine herpesvirus 68 (MHV-68) was investigated. When the virus was introduced intranasally, the lung was the main tissue infected, the virus being associated with alveolar epithelium and mononuclear cells. A productive infection lasted for 10 days, after which viral DNA could be detected by in situ hybridization up to 30 days after infection. At that time lymphoproliferative accumulations were also observed in the lung, with formation of germinal centres. Virus could also be recovered from the heart, kidney, adrenal gland and spleen during the primary infection. In addition, the spleen appeared to be the major site of virus persistence, with latently infected cells detected up to 90 days post-infection. During the primary infection, there was atrophy of the thymus and spleen of clinically sick animals. In contrast, lymphoproliferative responses, typified by splenomegaly, were frequently seen in asymptomatic animals. The pattern of infection observed in MHV-68-infected mice is similar to that seen in infectious mononucleosis of man following Epstein-Barr virus infection. The model described in this paper may prove to be useful in studying natural gamma-herpesvirus infections of man and domestic animals.

Non-traumatic acquisition of herpes simplex virus infection through the eye.

Primary ocular herpes is usually seen as a follicular conjunctivitis and blepharitis, with or without involvement of the cornea. It is unknown, however, to what extent asymptomatic and/or subclinical primary disease occurs, and whether primary ocular herpes follows direct droplet spread to the eye. Previous models of murine ocular herpes have used trauma (scarification) to introduce virus into the cornea, producing disease which results in significant corneal scarring. To mimic a likely route of infection in humans, a droplet containing virus was placed on the mouse eye and clinical disease recorded. At least 1 month after inoculation, serum was assayed for neutralising antibodies and the cornea, iris, and trigeminal ganglion were investigated for evidence of herpes simplex virus type 1, by cocultivation and the polymerase chain reaction. Some animals showed a severe ulcerative blepharitis with little to no involvement of the cornea, while disease was undetectable in others. The development of disease depended on the dose and strain of virus and age of the animal, with older mice appearing more resistant. Virus was isolated from the trigeminal ganglion of younger animals inoculated with higher doses of virus, after 21 days in culture, suggesting that latency had been established. Neutralising antibodies were present in most mice irrespective of the presence of recognisable clinical disease. Using primers for the thymidine kinase and glycoprotein C regions of the viral genome, herpes simplex virus type 1 DNA was found in the cornea, iris, and trigeminal ganglion of most animals and showed a good correlation with the presence of neutralising antibodies. It would thus appear that herpes simplex virus type 1 is able to accede into the cornea, iris, and trigeminal ganglion following nontraumatic application of virus onto the mouse eye. This model mimics primary ocular disease in humans and may be useful for studies on recurrent disease and the spread of ocular herpes.

Phosphonylmethoxyalkyl purine and pyrimidine derivatives for treatment of opportunistic cytomegalovirus and herpes simplex virus infections in murine AIDS

Murine acquired immunodeficiency syndrome (MAIDS) was induced in C57BL/6 mice following infection with the LP-BM5 retrovirus complex. Infected mice developed splenomegaly, lymphadenopathy and loss of B- and T- cell functions 100 days after virus inoculation. Mice with AIDS were highly susceptible to opportunistic murine cytomegalovirus (MCMV) and herpes simplex virus (HSV-1) infections. The therapeutic activities of two phosphonylmethoxyalkyl derivatives, 9-(2-phosphonylmethoxyethyl)adenine (PMEA) and ( S)-1-(3-hydroxy-2-phosphonylmethoxy-propyl)cytosine (HPMPC), were evaluated in MAIDS immunosuppressed mice infected with MCMV or HSV-1. MCMV infection resulted in extensive viral replication in lung, liver and spleen and death occurred five to twelve days post-infection. Treatment with either HPMPC or ganciclovir (DHPG) reduced mortality and viral replication in target organs; however, HPMPC was as effective as DHPG at one-fifth the DHPG dose. Moreover, when a single dose (100 mg/kg) of HPMPC was administered 24 h prior to MCMV infection, it suppressed virus replication at seven and 14 days post-infection, thus resulting in a significant prolongation of life. PMEA was effective against opportunistic HSV-1 infections, but appeared to be less effective than HPMPC against MCMV infections. These results indicate that MAIDS can be used as a model for evaluating antivirals in an immunocompromised host, and suggest that both PMEA and HPMPC may be useful in the treatment of opportunistic CMV and HSV-1 infections.

Analysis of the role of antibody-dependent cellular cytotoxic antibody activity in murine neonatal herpes simplex virus infection with antibodies to synthetic peptides of glycoprotein D and monoclonal antibodies to glycoprotein B.

The role of antibody in neonatal herpes simplex virus (HSV) infection remains controversial. A battery of well-characterized monoclonal antibodies to HSV glycoprotein B (gB), and polyclonal antibodies against synthetic peptides of predicted epitopes of HSV glycoprotein D (gD) were used to determine in vitro functional activity and association with protection against lethal infection in a murine model of neonatal HSV disease. Antiviral neutralization activity of HSV was not associated with antibody-dependent cellular cytotoxicity (ADCC) activity to HSV-infected cells in vitro. In a model of high dose challenge (10(4) PFU), protection was not afforded by any antibody alone, but was by antibody plus human mononuclear cells, and highly associated with ADCC functional activity (P less than 0.001). In a low dose challenge model, neutralizing activity of antibody alone was associated with protection in vivo (P less than 0.001). Of the nine neutralizing epitopes of gD in vitro, eight were predicted surface regions. Four of the five epitopic sites of gD (2-21, 267-276, 288-297, and 303-312) that were determined to be important targets of ADCC and in vivo protection were also predicted to be surface regions. The only exception was the antiserum to region 52-61 which was predicted to be buried and also showed these activities. ADCC as well as neutralizing antibody activity are important in protection against neonatal HSV infection.

Cloning and molecular characterization of the murine herpesvirus 68 genome

Murine herpesvirus 68 (MHV-68) is a naturally occurring herpesvirus of small free-living rodents. In order to facilitate the molecular characterization of the virus genome, a library of cloned restriction fragments has been produced and restriction enzyme cleavage maps deduced for the enzymes BamHI, EcoRI and HindIII. The MHV-68 genome comprises a region of unique DNA of approximately 118 kbp which is flanked by variable numbers of a 1.23 kb repeat unit. The organization of the MHV-68 genome is, therefore, most similar to that of the lymphotropic gamma 2 group of herpesviruses which include herpesvirus saimiri and herpesvirus ateles.

Murine herpesvirus 68 is genetically related to the gammaherpesviruses Epstein-Barr virus and herpesvirus saimiri

Short nucleotide sequence analysis of seven restriction fragments of murine herpesvirus 68 (MHV-68) DNA has been undertaken and used to determine the overall genome organization and relatedness of this virus to other well characterized representatives of the alpha-, beta- and gammaherpesvirus subgroups. Nine genes have been identified which encode amino acid sequences with greater similarity to proteins of the gammaherpesvirus Epstein-Barr virus (EBV) than to the homologous products of the alphaherpesviruses varicella-zoster virus and herpes simples virus type 1 or the betaherpesvirus human cytomegalovirus. In addition, the genome organization of MHV-68 is shown to have an overall collinearity with that of the gammaherpesviruses EBV and herpesvirus saimiri. In common with these viruses, dinucleotide frequency analysis of MHV-68 coding sequences reveals a marked reduction in CpG dinucleotide frequency thus implicating a dividing cell population as the site of latency in vivo.

Protection against murine neonatal herpes simplex virus infection by lymphokine-treated human leukocytes.

One-week-old mice were protected against a uniformly lethal herpes simplex virus (HSV) infection by IL-2 alone, but especially by the addition of human mononuclear cells (MC) plus IL-2. The dose response of IL-2 was biphasic. The addition of MC from cord blood did not enhance IL-2-mediated survival. Because the effect of IL-2 alone, or IL-2 plus MC, was ablated by anti-IFN-gamma and human neonates have an IFN-gamma production defect, the protective effect of MC plus human IFN-gamma (HuIFN-gamma) was tested. MC from adults cultured for 5 days in HuIFN-gamma afforded protection. At least 1 x 10(6) HuIFN-gamma-treated MC were required with increasing survival to 1 x 10(7) MC. The effector cell activity was ablated by adherence, silica, L-leucine methyl ester treatment or treatment with Leu-M3 plus C (all macrophage markers), and OKT4 plus C treatment (CD4 marker). Use of Leu-11, Leu-7, OKT3, or OKT8 plus C did not inhibit protection and excluded NK or T cell participation. In addition to survival, the ability to produce anti-HSV antibody was reconstituted. For the first time protection was afforded by human cord blood MC after treatment with HuIFN in vitro. We have identified an IFN-gamma-driven protection system against murine neonatal HSV infection mediated by human adult- or cord blood-derived CD4-positive macrophages. Protection is associated with enhanced effector cell function and reconstitution of the neonatal antibody production defect.