The Effect of Acyclovir on the Acute and Latent Murine Gammaherpesvirus-68 Infection of Mice

Mice inoculated intranasally with murine gammaherpesvirus-68 were used to evaluate the efficacy of acyclovir (ACV) in the treatment of acute and latent infections. Effectiveness was measured by infectious virus assay of the lung (site of active replication) and infectious centre assay of spleen cells (site of latency). Intraperitoneal administration of ACV at 6-h intervals starting soon after inoculation was more effective in reducing infectious virus in the lung than was treatment with 12-hourly injections commencing 3 days post-infection. Further, ACV treatment during acute infection resulted in an approximately 10-fold reduction in the number of infectious centres in the spleen as compared to placebo-treated animals. However, once latency was established, ACV treatment was not effective in reducing the number of infectious centres in the spleen. This is the first report demonstrating that ACV can be used to minimize the replication of murine gammaherpesvirus in mice at the site of primary infection, resulting in a reduction in the number of latently infected spleen lymphocytes.

The delayed hypersensitivity T cell and its interaction with other T cells

In this review Tony Nash and Philip Gell consider mainly recent work on the delayed hypersensitivity (DH) T cell (TDH) in mice, using viruses as infectious agents to probe the nature of DH and its relationship to protection.

Semliki Forest virus strongly reduces mosquito host defence signaling

The Alphavirus genus within the Togaviridae family contains several important mosquito-borne arboviruses. Other than the antiviral activity of RNAi, relatively little is known about alphavirus interactions with insect cell defences. Here we show that Semliki Forest virus (SFV) infection of Aedes albopictus-derived U4.4 mosquito cells reduces cellular gene expression. Activation prior to SFV infection of pathways involving STAT/IMD, but not Toll signaling reduced subsequent virus gene expression and RNA levels. These pathways are therefore not only able to mediate protective responses against bacteria but also arboviruses. However, SFV infection of mosquito cells did not result in activation of any of these pathways and suppressed their subsequent activation by other stimuli.

Expansion and activation of NK cell populations in a gammaherpesvirus infection

NK cells are an important component of the innate immune response to many virus infections. In particular, they play a major role in control of alpha and beta herpesvirus infections in humans and mice and there is evidence for a protective role in Epstein-Barr virus infection. MHV-68 has been widely used to study gammaherpesvirus pathogenesis and provides a tractable means of investigating the role of NK cells in gammaherpesvirus infections. We have shown that, following MHV-68 infection of mice, the NK cell population is expanded and activated and capable of cytotoxic killing in vitro. However, depletion of NK cells prior to MHV-68 infection did not affect viral loads in vivo. To investigate the possibility that MHV-68 was downregulating NK cell activity in vivo and evading the NK cell response, we infected NK cell-depleted mice with the related virus, MHV-76, which lacks a 9.5 kb region of the genome known to be involved in modulating the host immune response. Infection of NK cell-depleted mice with MHV-76 did not result in increased viral loads indicating that genes within this region do not encode products which modulate NK cell activity.

The m4 gene of murine gammaherpesvirus modulates productive and latent infection in vivo

Murine gammaherpesvirus 68 (MHV-68) infection of mice represents a viable small-animal model for the study of gammaherpesvirus pathogenesis. MHV-76 is a deletion mutant of MHV-68, which lacks four MHV-68-specific genes (M1 to M4) and eight viral tRNA-like sequences at the 5' end of the genome. These genes are implicated in latency and/or immune evasion. Consequently, MHV-76 is attenuated in the acute phase of in vivo infection with respect to MHV-68. Little is known about the role of M4 in viral infection, except that it is expressed as an immediate-early/early transcript during lytic replication of MHV-68 in vitro. To elucidate the contribution M4 makes to in vivo pathogenesis, we created a novel MHV-76 mutant (MHV-76inM4), in which the region of MHV-68 coding for M4 and accompanying putative promoter elements were inserted into the 5' region of the MHV-76 genome. The growth of MHV-76inM4 in vitro was indistinguishable from that of MHV-76 and MHV-68. However, virus titers from MHV-76inM4-infected BALB/c mice were significantly increased with respect to MHV-76 at early times in the lung. In addition, at days 17 and 21 postinfection, there was a significant elevation in latent viral load in splenocytes of MHV-76inM4-infected mice compared to MHV-76. Like MHV-76-infected mice, MHV-76inM4-infected mice display no evidence of overt splenomegaly, a finding characteristic of MHV-68 infection. M4 expression in vivo was detectable during productive infection in the lung and during the establishment of latency in the spleen, but in general M4 was not detectable during long-term latency (day 100 postinfection).

Analysis of a novel strain of murine gammaherpesvirus reveals a genomic locus important for acute pathogenesis

Infection of mice by murine gammaherpesvirus 68 (MHV-68) is an excellent small-animal model of gammaherpesvirus pathogenesis in a natural host. We have carried out comparative studies of another herpesvirus, murine herpesvirus 76 (MHV-76), which was isolated at the same time as MHV-68 but from a different murid host, the yellow-necked mouse (Apodemus flavicollis). Molecular analyses revealed that the MHV-76 genome is essentially identical to that of MHV-68, except for deletion of 9,538 bp at the left end of the unique region. MHV-76 is therefore a deletion mutant that lacks four genes unique to MHV-68 (M1, M2, M3, and M4) as well as the eight viral tRNA-like genes. Replication of MHV-76 in cell culture was identical to that of MHV-68. However, following infection of mice, MHV-76 was cleared more rapidly from the lungs. In line with this, there was an increased inflammatory response in lungs with MHV-76. Splenomegaly was also significantly reduced following MHV-76 infection, and much less latent MHV-76 was detected in the spleen. Nevertheless, MHV-76 maintained long-term latency in the lungs and spleen. We utilized a cosmid containing the left end of the MHV-68 genome to reinsert the deleted sequence into MHV-76 by recombination in infected cells, and we isolated a rescuant virus designated MHV-76(cA8+)4 which was ostensibly genetically identical to MHV-68. The growth properties of the rescuant in infected mice were identical to those of MHV-68. These results demonstrate that genetic elements at the left end of the unique region of the MHV-68 genome play vital roles in host evasion and are critical to the development of splenic pathology.

Murine gammaherpesvirus-68 infection causes multi-organ fibrosis and alters leukocyte trafficking in interferon-gamma receptor knockout mice

Murine gammaherpesvirus-68 (MHV-68) infection in interferon-gamma receptor knockout mice (IFN-gammaR(-)/(-)) results in splenic fibrosis and excessive loss of splenocytes. In our present study we found that MHV-68 infection in IFN-gammaR(-)/(-) mice also resulted in fibrosis and atrophy of the mediastinal lymph nodes, interstitial pulmonary fibrosis and fibrotic changes in the liver. Atrophy and cellular depletion of the spleen in IFN-gammaR(-)/(-) was not the result of increased cell death. The loss of splenocytes in IFN-gammaR(-)/(-) mice, which was most evident on day 23 after infection, correlated with an increase in the number of leukocytes in peripheral blood. At the peak of leukocytosis, on day 23 after infection, peripheral blood cells from infected IFN-gammaR(-)/(-) mice were unable to traffic through the fibrosed spleens of IFN-gammaR(-)/(-) mice but were able to enter the spleens of wild-type mice. This indicates that leukocytosis was in part the result of emigration of cells from the spleen and their subsequent exclusion of re-entry at the height of fibrosis. Significant cytokine and chemokine changes were observed in spleens of IFN-gammaR(-)/(-) mice. IFN-gamma, tumor necrosis factor-alpha (TNF-alpha ), TNF-beta, interleukin-1beta (IL-1beta), transforming growth factor-beta1 (TGF-beta1), lymphotactin, and MIP-1beta were elevated on day 14 after infection whereas chemokines IP-10 and MIG were significantly reduced. These changes suggest a role for dysregulated cytokines and chemokines in severe organ-specific fibrosis with implications for immune-mediated fibrotic disorders.

Natural history of murine gamma-herpesvirus infection

Murine gamma-herpesvirus 68 (MHV-68) is a natural pathogen of small rodents and insectivores (mice, voles and shrews). The primary infection is characterized by virus replication in lung epithelial cells and the establishment of a latent infection in B lymphocytes. The virus is also observed to persist in lung epithelial cells, dendritic cells and macrophages. Splenomegaly is observed two weeks after infection, in which there is a CD4+ T-cell-mediated expansion of B and T cells in the spleen. At three weeks post-infection an infectious mononucleosis-like syndrome is observed involving a major expansion of Vbeta4+CD8+ T cells. Later in the course of persistent infection, ca. 10% of mice develop lymphoproliferative disease characterized as lymphomas of B-cell origin. The genome from MHV-68 strain g2.4 has been sequenced and contains ca. 73 genes, the majority of which are collinear and homologous to other gamma-herpesviruses. The genome includes cellular homologues for a complement-regulatory protein, Bcl-2, cyclin D and interleukin-8 receptor and a set of novel genes M1 to M4. The function of these genes in the context of latent infections, evasion of immune responses and virus-mediated pathologies is discussed. Both innate and adaptive immune responses play an active role in limiting virus infection. The absence of type I interferon (IFN) results in a lethal MHV-68 infection, emphasizing the central role of these cytokines at the initial stages of infection. In contrast, type II IFN is not essential for the recovery from infection in the lung, but a failure of type II IFN receptor signalling results in the atrophy of lymphoid tissue associated with virus persistence. Splenic atrophy appears to be the result of immunopathology, since in the absence of CD8+ T cells no pathology occurs. CD8+ T cells play a major role in recovery from the primary infection, and also in regulating latently infected cells expressing the M2 gene product. CD4+ T cells have a key role in surveillance against virus recurrences in the lung, in part mediated through 'help' in the genesis of neutralizing antibodies. In the absence of CD4+ T cells, virus-specific CD8+ T cells are able to control the primary infection in the respiratory tract, yet surprisingly the memory CD8+ T cells generated are unable to inhibit virus recurrences in the lung. This could be explained in part by the observations that this virus can downregulate major histocompatibility complex class I expression and also restrict inflammatory cell responses by producing a chemokine-binding protein (M3 gene product). MHV-68 provides an excellent model to explore methods for controlling gamma-herpesvirus infection through vaccination and chemotherapy. Vaccination with gp150 (a homologue of gp350 of Epstein-Barr virus) results in a reduction in splenomegaly and virus latency but does not block replication in the lung, nor the establishment of a latent infection. Even when lung virus infection is greatly reduced following the action of CD8+ T cells, induced via a prime-boost vaccination strategy, a latent infection is established. Potent antiviral compounds such as the nucleoside analogue 2'deoxy-5-ethyl-beta-4'-thiouridine, which disrupts virus replication in vivo, cannot inhibit the establishment of a latent infection. Clearly, devising strategies to interrupt the establishment of latent virus infections may well prove impossible with existing methods.

Regression of a murine gammaherpesvirus 68-positive b-cell lymphoma mediated by CD4 T lymphocytes

Murine gammaherpesvirus 68-infected S11 cells were injected subcutaneously into nude mice. Adoptively transferred restimulated lymphocytes consistently elicited the regression of S11 tumors. CD4 T lymphocytes were most effective in preventing tumor formation, and immunohistochemistry highlighted populations of CD4 T cells in regressing tumors.

Murine gammaherpesvirus M11 gene product inhibits apoptosis and is expressed during virus persistence

The murine gammaherpesvirus (MHV-68) M11 gene encodes a protein with BH1 domain homology to Bcl-2. We found that the M11 gene product (MHVBcl-2) protected murine epithelial cells from TNF-alpha induced apoptosis. M11 was transcribed during early lytic infection in vitro. During early infection of mice, M11 message was detected in spleen and lung along with lytic cycle messages. During persistence, lytic cycle gene expression was undetectable but M11 RNA was still present. This suggests that MHVBcl-2 promotes virus survival by protecting not only productively infected but also persistently infected cells from apoptotic death.

Rta of murine gammaherpesvirus 68 reactivates the complete lytic cycle from latency

Herpesviruses are characterized as having two distinct life cycle phases: lytic replication and latency. The mechanisms of latency establishment and maintenance, as well as the switch from latency to lytic replication, are poorly understood. Human gammaherpesviruses, including Epstein-Barr virus (EBV) and human herpesvirus-8 (HHV-8), also known as Kaposi's sarcoma-associated herpesvirus (KSHV), are associated with lymphoproliferative diseases and several human tumors. Unfortunately, the lack of cell lines to support efficient de novo productive infection and restricted host ranges of EBV and HHV-8 make it difficult to explore certain important biological questions. Murine gammaherpesvirus 68 (MHV-68, or gammaHV68) can establish de novo lytic infection in a variety of cell lines and is also able to infect laboratory mice, offering an ideal model with which to study various aspects of gammaherpesvirus infection. Here we describe in vitro studies of the mechanisms of the switch from latency to lytic replication of MHV-68. An MHV-68 gene, rta (replication and transcription activator), encoded primarily by open reading frame 50 (ORF50), is homologous to the rta genes of other gammaherpesviruses, including HHV-8 and EBV. HHV-8 and EBV Rta have been shown to play central roles in viral reactivation from latency. We first studied the kinetics of MHV-68 rta gene transcription during de novo lytic infection. MHV-68 rta was predominantly expressed as a 2-kb immediate-early transcript. Sequence analysis of MHV-68 rta cDNA revealed that an 866-nucleotide intron 5' of ORF50 was removed to create the Rta ORF of 583 amino acids. To test the functions of MHV-68 Rta in reactivation, a plasmid expressing Rta was transfected into a latently infected cell line, S11E, which was established from a B-cell lymphoma in an MHV-68-infected mouse. Rta induced expression of viral early and late genes, lytic replication of viral DNA, and production of infectious viral particles. We conclude that Rta alone is able to disrupt latency, activate viral lytic replication, and drive the lytic cycle to completion. This study indicates that MHV-68 provides a valuable model for investigating regulation of the balance between latency and lytic replication in vitro and in vivo.

Herpes virus latency in sensory ganglia--a comparison with endogenous neuronal gene expression

Central to infection by a majority of DNA viruses is the expression of encoded proteins that modify cell cycle. Viruses such as SV40 and Adenovirus viruses encode proteins that interact directly, or indirectly, with key cell cycle proteins such as CBP300 and the retinoblastoma gene product. However, neurons do not have a cell cycle as we generally describe it and this is also reflected in the difficulty in obtaining immortalised neuronal cultures. The replication strategies of viruses that infect post-mitotic cells such as neurons may be different from infection of other somatic cells. The life cycle for viral latency or slow infection of neurons appears to involve silencing or restricting expression of the viral genome until such times as dictated by the environment. These signals from the environment usually reflect cell stress, otherwise the cell appears to tolerate the existence of the virus genome. We will review the genomic structure of alphaherpesviruses in neurons and transcriptional control mechanisms that may regulate expression. Where appropriate we will contrast and compare virus and endogenous neuronal gene expression.

2'-Deoxy-5-ethyl-beta-4'-thiouridine inhibits replication of murine gammaherpesvirus and delays the onset of virus latency

The antiviral thionucleoside analogue 2'-deoxy-5-ethyl-beta-4'-thiouridine (4'-S-EtdU) was shown to be a more potent inhibitor of gammaherpesvirus infection than acyclovir. This compound inhibits replication of murine herpesvirus (MHV)-68 in the lungs of mice when given 3 days post-infection. However, as with other nucleoside analogues, it was unable to prevent the establishment of latency, despite delaying the onset of latent infection in the spleen. In contrast, virus persistence in the lung was inhibited following drug treatment, although persistence was re-established in mice when treatment was suspended after 12 days. These data suggest that 4'-S-EtdU is a highly effective inhibitor of murine gammaherpesvirus replication and as such provides a powerful tool to study the pathogenesis of this virus in vivo.

The role of endogenous interleukin-12 in resistance to murine cytomegalovirus (MCMV) infection and a novel action for endogenous IL-12 p40

Biologically active interleukin-12 (IL-12), comprising a 40 kDa subunit (p40) covalently linked to a 35 kDa subunit (p35), is produced in response to a range of infectious stimuli. Here, we demonstrate that mice deficient in either IL-12 p40 (p40-/-) or IL-12 p35 (p35-/-) are susceptible to murine cytomegalovirus (MCMV) infection in terms of survival (Balb/c p35-/-) and viral clearance (Balb/c p35-/- and Balb/c p40-/-), and this susceptibility may be correlated to a deficiency in serum interferon-gamma (IFN-gamma) levels. These data support a role for endogenous IL-12 in controlling MCMV infection. The IL-12 p40 subunit is produced in excess of IL-12 p35, and to date the function of the excess endogenous p40 has been assumed to be one of IL-12 antagonism, as demonstrated by experiments with exogenous p40 both in vivo and in vitro. We show that Balb/c p35-/- alone are significantly compromised in survival of a sublethal infection and in clearance of virus from the spleen. These mice produce a very early IFN-gamma spike (8 h after infection) and an aberrant tumor necrosis factor-alpha (TNF-alpha) spike (day 2 after infection). MCMV infection has revealed an altered Balb/c p35-/- phenotype compared with Balb/c p40-/-, and this indicates that endogenous p40 may have an activity independent of and additional to IL-12 antagonism in vivo.

Type I interferons and IRF-1 play a critical role in the control of a gammaherpesvirus infection

The murine gammaherpesvirus 68 (MHV-68) is an ideal model system for the study of interactions between gammaherpesviruses and their hosts. Intranasal infection of mice with MHV-68 results in replication of the virus in the lung epithelium followed by latent infection of B cells. Resolution of productive MHV-68 infection depends on the adaptive immune system, but little is known about the role of innate immune mechanisms and the early interaction between the host and the virus. In this report, we have used mice that are deficient in components of the early defence system, the common type I interferon (IFN) receptor (IFN R), the transcriptional activator IRF-1, and the inducible nitric oxide synthase, to investigate the contribution of these mechanisms to control of MHV-68 infection. We show that while wild-type mice are highly resistant to infection with MHV-68, mice unresponsive to type I IFNs (IFN-alpha/beta R(-/-) ) are highly susceptible to the virus. At high multiplicities of infection (m.o.i. ; 4 x 10(6) PFU), 80-90% of IFN-alpha/beta R(-/-) mice succumb to infection, and at low m.o.i. (4 x 10(3) PFU), 50% mortality rates occur. Both high and low doses of virus lead to 100- to 1000-fold higher lung virus titres in IFN-alpha/beta R(-/-) mice than are found in wild-type mice and result in systemic dissemination of the virus. Latently infected cells are detectable in the spleens of IFN-alpha/beta R(-/-) mice earlier than in wild-type mice, and the numbers of latently infected cells are 10-fold higher in the IFN-alpha/beta R(-/-) mice during the acute phase of infection. We find IRF-1 has a critical role in protection from fatal disease, whereas inducible nitric oxide synthase does not appear to be important. The results indicate that innate immune mechanisms are critical for the early control of MHV-68 and may play a role in the establishment of latency.

Behavioural changes in the rat following infection with varicella-zoster virus

Following the establishment of a chronic varicella-zoster virus infection in the rat, behavioural allodynia and hyperalgesia were observed in the injected, but not the contralateral hind limb up to 33 days post-infection. This model may prove useful in investigating mechanisms involved in the establishment of post-herpetic neuralgia.

Murine gamma-herpesvirus 68 glycoprotein 150 protects against virus-induced mononucleosis: a model system for gamma-herpesvirus vaccination

Murine gamma-herpesvirus 68 (MHV-68) is a model for the study of the pathogenesis of gamma-herpesviruses. Epstein-Barr virus (EBV) is a highly related gamma-herpesvirus that causes significant disease in humans. The major membrane antigen gp350 of EBV is a candidate vaccine antigen for protection against EBV-related disease. An MHV-68 glycoprotein, gp150, has significant homology to EBV gp350. We have therefore used the MHV-68 gp150 to model the potential efficacy of EBV gp350 in protecting from virus-associated disease. A recombinant vaccinia virus expressing MHV-68 gp150 was constructed. This recombinant vaccinia virus was used to infect mice via the subcutaneous route. This vaccination resulted in production of MHV-68-neutralising antibodies. Mice were then challenged intra-nasally with MHV-68. MHV-68-associated mononucleosis was virtually abrogated in immunised mice. However, mice did establish MHV-68 latency. The results suggest that gp350 may be effective as an immunogen to prevent EBV-associated infectious mononucleosis in humans that are EBV-seronegative.

Substance use among adolescents with juvenile rheumatoid arthritis

OBJECTIVE

To determine the prevalence of substance use among adolescents with juvenile rheumatoid arthritis and to assess available opportunities for rheumatologists to identify high risk teens.

METHODS

Fifty-two teens (mean age 13.9 years, 86% female) completed questionnaires regarding substance use (alcohol, tobacco, marijuana, and other illicit substances), functional disability, and frequency of health care contacts.

RESULTS

Alcohol use was reported by 30.7% of teens, including 23.5% of those for whom methotrexate was prescribed; 15.4% reported tobacco use in the last year, and 13.4% reported other illicit substance use in their lifetime, although most use was experimental. No teen reported marijuana use. The majority reported regular contact with their rheumatologist but only 26.9% were ever interviewed alone.

CONCLUSION

Many teens with juvenile rheumatoid arthritis, including those prescribed methotrexate, used substances, especially alcohol. When rheumatologists see adolescents, particularly in situations where methotrexate may be prescribed, a clinical setting conductive to confidentially, physician comfort in asking about sensitive topics such as substance abuse, and referral relationships with skilled adolescent health and substance abuse counseling providers are essential.

The PI capsid region of Theiler's virus controls replication in mouse glial cell cultures

The GDVII strain of Theiler's virus is virulent. The DA strain is avirulent and can persist and initiate lesions of inflammatory demyelination in the CNS of susceptible strains of mice. Other, resistant strains of mice clear the infection. Replication of the GDVII and DA strains of Theiler's virus and their genetic recombinants R2, R3 and R4 were compared in mixed glial cell cultures derived from the mouse CNS. Differences were observed in the early rate of viral production. These mapped to the P1 capsid region of the viral genome. Viruses with GDVII P1 sequences produced virus and spread more rapidly than viruses with DA P1 sequences. GDVII virus infected greater numbers of cells than DA virus. Both strains of virus rapidly replicated at least to the level of translation in astrocytes (GFAP+), macrophage/microglial cells (F4/80+), oligodendrocytes (O4+) and bipotential precursor (A2B5+) cells. Early in infection many A2B5+ and GFAP+ cells were infected and destroyed. In contrast, O4+ cells were relatively resistant to cell-death. The cultures survived and produced virus over 14 days of study, at which time all 4 cell-type were present in the culture but < 1% of all the cells, the majority of which were O4+, expressed viral protein. Most of these infected O4+ cells retained a healthy morphology with extensive sheets of cytoplasm, suggesting that Theiler's virus infection of mature oligodendrocytes was non-destructive.

Investigation of the role of delayed-type-hypersensitivity responses to myelin in the pathogenesis of Theiler's virus-induced demyelinating disease

The contribution of autoimmune responses to the pathogenesis of Theiler's virus-induced demyelinating disease was investigated. Delayed-type hypersensitivity responses to myelin were examined in both symptomatic and asymptomatic mice at different times post-infection, in order to determine whether autoreactivity correlates with the development of demyelination. The results indicate that although autoimmune responses probably do not play a major role in the initiation of demyelination at early times post-infection, autoreactivity to myelin antigens dose eventually develop in symptomatic animals, perhaps through the mechanism of epitope spreading. Autoimmunity to myelin components is therefore an additional factor that may contribute to lesion progression in chronically diseased animals.

Immunological control of murine gammaherpesvirus infection is independent of perforin

Perforin-mediated cytotoxic T cell killing has been suggested to be of importance in the control of noncytopathic virus infections, based on studies with lymphocytic choriomeningitis virus (LCMV). We examined the role of perforin in a mouse model of gammaherpesvirus infection using transgenic perforin-deficient mice. Previous work from this laboratory has shown that CD8 T cells are essential for the resolution of the acute lung infection and control of latently infected B cells in murine gamma-herpesvirus 68 infection. The absence of perforin did not significantly affect the kinetics of either the lytic lung infection or the latent spleen infection. Lymphocytes from both perforin-deficient and control mice secreted comparable levels of IFN-gamma, IL-10 and IL-6. In addition, lymphocytes from both strains had similar levels of CD3epsilon-dependent cytotoxic activity in the spleen, draining lymph nodes and bronchoalveolar lavage. These data indicate that the lack of perforin has little affect on the ability of mice to control an experimental gammaherpesvirus infection.

Immune response to murine cell lines of glial origin transplanted into the central nervous system of adult mice

Temperature-sensitive simian virus 40 (SV40) T antigen-transformed central nervous system (CNS)-derived murine cell lines were used to analyse the host response to transplantation in the mouse adult brain. The cell lines were shown to be susceptible to immune recognition in vitro by cytotoxic effector cells indicating that tissue-specific privilege was not in operation. Histological examination at time points post-implantation showed characteristic responses similar to those seen during graft rejection. Astrocytosis and up-regulation of major histocompatibility complex (MHC) class I and MHC class II activation of resident microglia and recruitment of macrophages were observed in both allogeneic and syngeneic hosts 10 days post-implantation suggesting a trauma-induced response. However, the response in allogeneic hosts was more widespread and evident when the syngeneic responses had returned to normal levels. Evidence of T-cell infiltration was also more pronounced in the allogeneic hosts. Despite quite extensive host reactions to these cellular grafts at early time-points the implants appeared to survive in the host CNS long after the responses had abated and could be detected at the maximum time-point studied of 40 days.

Pathological changes in the spleens of gamma interferon receptor-deficient mice infected with murine gammaherpesvirus: a role for CD8 T cells

Murine gammaherpesvirus is a natural rodent pathogen which causes a primary infection in the lungs and establishes a persistent infection in B lymphocytes. During the primary infection, large amounts of gamma interferon (IFN-gamma) are produced by spleen, mediastinal, and cervical lymph node cells. To investigate the role of IFN-gamma in control of the virus infection, mice lacking the cellular receptor for IFN-gamma (IFN-gamma R-/- mice) were infected with murine gammaherpesvirus 68 (MHV68). IFN-gamma R-/- mice showed no difference from wild-type mice in the titers of infectious virus in the lungs or in the rate of clearance of the lung infection. In the spleen, however, clear differences were observed. By 14 days postinfection, spleens from IFN-gamma R-/- mice were pale, shrunken, and fibrous. Histological examination showed that there was an early (day 10) infiltration of granulocytes followed by widespread destruction of splenic architecture (days 14 to 17). A marked decrease in the number of splenic B cells and CD4+ and CD8+ T cells occurred. These changes were accompanied by a 10- to 100-fold greater load of latently infected cells in IFN-gamma R-/- mice than in wild-type mice at 14 to 17 days postinfection, but this was reduced to the levels found in wild-type mice by 21 days postinfection. Treatment of the mice with the antiviral drug 2'-deoxyl-5-ethyl-beta-4'-thiouridine from 6 days postinfection did not prevent the occurrence of these changes. The changes were, however, completely reversed by depletion of CD8+ T cells prior to and during the primary infection. Depletion of CD4+ T cells also reversed the major pathological and virological changes, although in this case there was evidence of some histological changes. Thus, the lack of IFN-gamma receptor had profound consequences in spleens of MHV68-infected mice. The possible mechanisms involved in these changes are discussed.

Genetic content and preliminary transcriptional analysis of a representative region of murine gammaherpesvirus 68

Murine gammaherpesvirus 68 (MHV-68) is a relatively recently discovered pathogen of wild rodents and provides a unique opportunity to explore in detail the interactions of a gammaherpesvirus with its natural host. It may also provide a much needed small animal model for human gammaherpesviruses. As a step in the detailed analysis of virus gene structure and expression we have sequenced over 20 kb of the MHV-68 genome and mapped gene transcripts by Northern blot hybridization. The region we chose to analyse contains several conserved gene blocks as well as some less well conserved genes and allowed us to estimate the relationship of this virus to other herpesvirus family members. Of particular interest is the fact that none of the characteristic Epstein-Barr virus (EBV) genes is present at this genomic locus although MHV-68 does have one gene encoding a membrane glycoprotein, 9p150, which shows similarities to the major membrane glycoprotein of EBV. Our results further confirm that MHV-68 is a gammaherpesvirus marginally more closely related to a cluster of gammaherpesviruses including herpesvirus salmiri than to EBV. Northern analysis shows that the temporal regulation of expression is broadly similar to that of other herpesviruses in this region of the genome. We also show that like other gammaherpesviruses, MHV-68 splices its homologue of the EBV transcriptional activator gene BMRF1.

Characterisation of the immune response in a neural xenograft rejection paradigm

We have looked at both donor and host MHC expression in a neural xenograft rejection paradigm. Grafts of either mouse corpus callosum or an SV40 large T transformed astrocytic cell line were placed in the mid-brain of neonatal rats. Three weeks later graft rejection was induced by the application of a skin graft of the same donor origin. MHC expression in the neural graft and the host brain was examined histologically four and ten days after the animals had received a skin graft. Donor MHC expression was detected in the corpus callosal grafts at both time points and preceded host MHC expression and the lymphocytic infiltrate. The grafts of the transformed cell line could not be induced to express MHC antigens under the experimental protocol used nor were they rejected. The migratory patterns of the transformed cells were compared to the well characterised migration patterns of astrocytes from the corpus callosal grafts.

Absence of splenic latency in murine gammaherpesvirus 68-infected B cell-deficient mice

Murine gammaherpesvirus 68 (MHV-68) is a natural pathogen of mice which causes an acute lung infection and establishes a latent infection in B lymphocytes. In this paper we describe the infection in transgenic B cell-deficient (muMT) mice, to determine whether a latent infection can be established in a mouse lacking circulating B lymphocytes. Little difference was observed in the acute lung infection, although there was a slight delay in virus clearance in the muMT mice. This indicates that antiviral antibody is of little importance in the resolution of the lung infection. Neither free nor latent virus could be detected in the spleen in the muMT mice. In addition, these mice did not develop MHV-68-induced splenomegaly. These data suggest that within the lymphoid compartment B lymphocytes are the sole reservoir for MHV-68 infection in vivo, confirming earlier work which identified B cells as the site of latent infection based on cell fractionation studies. In addition, our study shows that CD4-driven lymphocyte expansion leading to splenomegaly is dependent on the presence of MHV-68-infected B cells in the spleen. Although no free virus was detected (using conventional biological assays) in the lung after the resolution of the acute infection, MHV-68 genome was detected in the lungs of both control and muMT mice by PCR analysis. This suggests that cells in the lung may act as a reservoir of latent virus which is independent of the B lymphocyte infection.

Characterization of tumor cell lines derived from murine gammaherpesvirus-68-infected mice

Cell lines were derived from mice with murine gammaherpesvirus-68 (MHV-68)-associated lymphoproliferative disease. Four were of an ambiguous phenotype and were MHV-68 negative. One, S11, was a B lymphocyte that contained MHV-68 genomes in both linear and episomal forms and released virus. The line was clonable and grew into tumors in nude mice. This is the first naturally occurring MHV-68-positive B-cell line to be generated, and it will be an invaluable tool for the study of MHV-68 latency.

Identification and characterization of murine gammaherpesvirus 68 gp150: a virion membrane glycoprotein

Murine gammaherpesvirus 68 (MHV-68) is a naturally occurring virus of murid rodents which displays pathobiological characteristics similar to those of other gammaherpesviruses, including Epstein-Barr virus (EBV). However, unlike EBV and many other gammaherpesviruses, MHV-68 replicates in epithelial cells in vitro and infects laboratory strains of mice and therefore provides a good model for the study of gammaherpesviruses. Studies of sequences around the center of the MHV-68 genome identified a gene (designated BPRF1 for BamHI P fragment rightward open reading frame 1) whose putative product had motifs reminiscent of a transmembrane glycoprotein. All other gammaherpesviruses have a glycoprotein in this genomic position, but the BPRF1 gene showed sequence homology with only the EBV membrane antigen gp340/220. Biochemical analysis showed that the product of BPRF1 was a glycoprotein present on the surface of infected cells, and immunoelectron microscopy showed that it was present in the virus particle. In addition, antibodies to the BPRF1 product raised by using a bacterial fusion protein neutralized the virus in the absence of complement. The predominant molecular weights of the protein were 150,000 and 130,000. Pulse-chase analysis and endoglycosidase-H digestion showed that the 130,000-molecular-weight form was a precursor of the 150,000-molecular-weight form, and cell surface labelling showed that the 150,000-molecular-weight form alone was on the cell surface. We therefore named the protein gp150. Since gp150 is the first virion-associated glycoprotein and neutralizing determinant of MHV-68 to be characterized, it provides a valuable tool for the future study of virus-host interactions.

Identification and characterization of murine gammaherpesvirus 68 gp150: a virion membrane glycoprotein

Murine gammaherpesvirus 68 (MHV-68) is a naturally occurring virus of murid rodents which displays pathobiological characteristics similar to those of other gammaherpesviruses, including Epstein-Barr virus (EBV). However, unlike EBV and many other gammaherpesviruses, MHV-68 replicates in epithelial cells in vitro and infects laboratory strains of mice and therefore provides a good model for the study of gammaherpesviruses. Studies of sequences around the center of the MHV-68 genome identified a gene (designated BPRF1 for BamHI P fragment rightward open reading frame 1) whose putative product had motifs reminiscent of a transmembrane glycoprotein. All other gammaherpesviruses have a glycoprotein in this genomic position, but the BPRF1 gene showed sequence homology with only the EBV membrane antigen gp340/220. Biochemical analysis showed that the product of BPRF1 was a glycoprotein present on the surface of infected cells, and immunoelectron microscopy showed that it was present in the virus particle. In addition, antibodies to the BPRF1 product raised by using a bacterial fusion protein neutralized the virus in the absence of complement. The predominant molecular weights of the protein were 150,000 and 130,000. Pulse-chase analysis and endoglycosidase-H digestion showed that the 130,000-molecular-weight form was a precursor of the 150,000-molecular-weight form, and cell surface labelling showed that the 150,000-molecular-weight form alone was on the cell surface. We therefore named the protein gp150. Since gp150 is the first virion-associated glycoprotein and neutralizing determinant of MHV-68 to be characterized, it provides a valuable tool for the future study of virus-host interactions.

Murine gammaherpesvirus-induced splenomegaly: a critical role for CD4 T cells

Murine gammaherpesvirus (MHV-68) causes an acute respiratory infection followed by a latent infection in B lymphocytes. In the first 2-3 weeks after infection mice develop a marked splenomegaly, where the spleen cell number increases by 2-3 fold. Cytofluorimetric analysis during splenomegaly revealed an increase in numbers of B lymphocytes and of both CD4+ and CD8+ T lymphocytes. The largest increase relative to uninfected spleens was in the CD8+ population. The number of latently infected cells in the spleen peaked at day 10 post-intraperitoneal infection, then declined to 1/10(6)-1/10(7) cells per spleen. Depletion of CD4+ T lymphocytes prevented the splenomegaly and greatly reduced the peak infective centre level, while having no effect on the long-term of latently infected cells. Given the similarity between MHV-68-induced splenomegaly and Epstein-Barr virus-induced infectious mononucleosis, these data highlight the usefulness of MHV-68 as a mouse model for the study of gammaherpesvirus immunology and pathobiology.

A Salmonella typhimurium htrA live vaccine expressing multiple copies of a peptide comprising amino acids 8-23 of herpes simplex virus glycoprotein D as a genetic fusion to tetanus toxin fragment C protects mice from herpes simplex virus infection

Multiple tandem copies of an immunogenic epitope comprising amino acids 8-23 of glycoprotein D of herpes simplex virus (HSV) were expressed as C-terminal fusions to tetanus toxin fragment C (TetC) in different Salmonella typhimurium live vaccine strains. Expression of the longer fusions was best in strains harbouring a lesion in htrA, a stress protein gene. SL3261, an aroA strain, did not effectively express the longer fusions. Mice immunised with an S. typhimurium C5 htrA mutant expressing fusions with two or four copies of the peptide made an antibody response to both the peptide and TetC, whereas constructs expressing one copy of the peptide only elicited antibody to TetC. A non-immunogenic octameric fusion underwent rearrangements in vivo resulting in a predominantly monomeric fusion. In contrast, the S. typhimurium SL3261 aroA vaccine expressing the TetC-tetrameric fusion did not elicit antibody to the peptide. Sera from mice immunised with a single dose of the dimer and tetramer fusions in the htrA strain neutralised HSV in vitro, and the mice were protected from HSV infection as measured by a reduction in virus load in the ear pinna. We have previously shown that mice vaccinated with salmonella expressing TetC are protected against tetanus toxin and virulent salmonella challenge. These results suggest that it may be possible to develop a multivalent vaccine against salmonellosis, tetanus and HSV.

Theiler's murine encephalomyelitis virus 3D RNA polymerase: its expression in the CNS and the specific immune response generated in persistently infected mice

Intracerebral inoculation of the neurotropic murine picornavirus, Theiler's murine encephalomyelitis virus (TMEV), results either in an acute encephalitis (GDVII strain) or in the establishment of a persistent infection with the development of demyelinating lesions (BeAn strain). In this article, the expression of the viral RNA polymerase was studied in the central nervous system of both acutely and persistently infected mice and in infected cells in tissue culture. Similar numbers of acutely infected glial cells (80-85%) expressed both viral polymerase and structural proteins in vitro while a much smaller proportion of persistently infected glial cells (0.6-0.9%) expressed these proteins. Following infection of mice with GDVII, many cells in the brain were found to express polymerase. However, in the spinal cord of mice persistently infected with BeAn, very few cells were found to express the polymerase while many more cells showed the presence of viral structural proteins. This suggests that a restriction in viral replication, possibly at the level of polymerase expression, may be a feature of the persistent infection. However, enough polymerase was expressed to maintain a polymerase-specific antibody response in a number of infected animals as late as 21 months post-infection. Mechanisms that may be involved in the establishment and maintenance of TMEV persistence are discussed with reference to these findings.

Lymphocyte recognition elements on the VP1 protein of Theiler's virus

Theiler's virus is a murine picornavirus that persists in the central nervous system in susceptible mouse strains, and gives rise to immune mediated demyelinating disease. Antiviral CD4 T cells are necessary to protect from overwhelming virus replication in the acute phase of the disease, and are thought to act by stimulating the antibody response. The present study used overlapping synthetic peptides to map the location of epitopes recognized by CD4 T cells. One T-cell epitope was identified between amino acids 33-47 of VP1, which was recognized by virus-reactive T cells. 'Cryptic' epitopes were also present within VP1 at positions 153-167, 166-180, 225-239 and 233-247. A linear B-cell epitope was identified in the C-terminal region 225-276. Immunization of CBA mice with inactivated virus, but not peptides containing VP1 B- or T-cell epitopes, reduced the virus titre in the CNS in the acute phase of the disease.

Experimental herpes simplex virus type 1 (HSV-1) infection of the spinal cord and dorsal root ganglia

Host factors determining the outcome of herpes simplex virus type 1 (HSV-1) infection within neurons are poorly understood. This paper aims to identify regional differences in the behaviour of HSV-1 within the nervous system as an approach to investigating the role of the host environment in determining the outcome of infection. We describe a mouse model of HSV infection focused on motor neurons of the spinal cord, resulting from intramuscular injection (i.m.) and compare this with the behaviour of virus within sensory neurons following scarification of virus on to skin. Viral antigen was detectable immunohistochemically by 2 days in both models and disappeared by 9-11 days. The time course of acute infection was reflected in the i.m. group by quantitative plaque assay for virus. Inflammation and cell destruction occurred in both models, but clinical features and histological destruction were greater in the group infected via the intramuscular route. In the sensory ganglia, a latent state from which virus could be reactivated by explanation, was established with LATS expression detectable in many neurons at 35 days post-infection (p.i.), but not in non-neuronal cells. Expression of latency associated transcript (LATS) was detected in motor neutrons in spinal cords at 35 days p.i. providing evidence for establishment of a LATS-positive latent state at this site, and continued to be detectable up to 6 months post-infection. In addition, LATS was detected in white matter at late times, suggesting a non-neuronal site of latency. In contrast to the behaviour in sensory ganglia, induced reactivation from spinal cords, by explanation and nerve section, was a very rare event. We have shown that a LATS-positive latent state can be established within motor neurons of the CNS, but that there are regional differences in the biology and outcome of infection between the CNS and peripheral nervous system. We propose that this may be a useful model to study reproducibly, the behaviour of HSV-1 in a CNS environment and, by comparison with sensory ganglion infection, to explore host factors which may underlie these regional differences. The relevance of this model for using HSV-1 as a therapeutic vector for motor neurons is also discussed.

Lymphoproliferative disease in mice infected with murine gammaherpesvirus 68

Murine gammaherpesvirus is a natural pathogen of wild rodents. In the laboratory it establishes an infection of epithelial cells and persists in B lymphocytes in a latent form. Inbred mice chronically infected with the virus develop a lymphoproliferative disease (LPD) similar to that seen in patients infected with Epstein-Barr virus. The frequency of LPD over a period of 3 years was 9% of all infected animals, with 50% of these displaying high grade lymphomas. The incidence of LPD was greatly increased when infected mice were treated with cyclosporin A. The majority of mice used in the experiments were BALB/c, although lymphomas were detected in mice on other genetic backgrounds, ie, CBA and B10Br. Lymphomas were associated with both lymphoid and nonlymphoid tissues (liver, lung, and kidney). In all cases of lymphomas studied thus far, there was a mixed B cell (B220+ve) and T cell (CD3+ve) phenotype. The B cells were light chain restricted, indicative of a clonal origin. Variable numbers of virus genome-positive cells were detected by in situ hybridization in and around the lymphomas. In contrast, no lytic antigen-positive cells were detected, indicating that genome-positive cells were either latently infected or undergoing an abortive infection. These observations suggest that murine gammaherpesvirus-infected mice may be an important model to study the pathogenesis of LPD associated with other gammaherpesviruses, such as Epstein-Barr virus.

Characterization of murine gammaherpesvirus 68 glycoprotein B (gB) homolog: similarity to Epstein-Barr virus gB (gp110)

Murine gammaherpesvirus 68 (MHV-68) is a natural pathogen of murid rodents and displays similar pathobiological characteristics to those of the human gammaherpesvirus Epstein-Barr virus (EBV). However, in contrast to EBV, MHV-68 will replicate in epithelial cells in vitro. It has therefore been proposed that MHV-68 may be of use as a model for the study of gammaherpesviruses, EBV in particular, both in vitro and in vivo. The EBV homolog of herpes simplex virus glycoprotein B (gB), termed gp110, is somewhat unusual compared with those of many other herpesviruses. We therefore decided to characterize the homolog of gB encoded by MHV-68 (termed MHV gB) to observe the properties of a gammaherpesvirus gB produced in epithelial cells and also to test the relatedness of MHV-68 and EBV. The MHV gB-coding sequence was determined from cloned DNA. The predicted amino acid sequence shared closest homology with gammaherpesvirus gB homologs. Biochemical analysis showed that MHV gB was a glycoprotein with a molecular weight of 105,000. However, the glycans were of the N-linked, high-mannose type, indicating retention in the endoplasmic reticulum. In line with this, MHV gB was localized to the cytoplasm and nuclear margins of infected cells but was not detected on the cell surface or in virions. Additionally, anti-MHV gB antisera were nonneutralizing. Thus, the MHV gB was unlike many other herpesvirus gBs but was extremely similar to the EBV gB. This highlights the close relationship between MHV-68 and EBV and underlines the potential of MHV-68 as a model for EBV in epithelial cells both in vitro and in vivo.

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.

Antioxidant status in asthma

Reduced levels of glutathione peroxidase (GSH-Px) have been observed in adults with asthma. This study examines the antioxidant status in children with asthma compared with a control group in a cross-sectional analysis. Red blood cell GSH-Px, superoxide dismutase (SOD), and plasma concentrations of retinol, vitamin C, alpha tocopherol, and cholesterol were measured in 37 subjects (26 males) with stable controlled asthma. Thirty-five subjects (20 males) without eczema, hayfever, or recurrent respiratory symptoms were used as a control group. Children with asthma had significantly reduced red blood cell GSH-Px activity compared with controls [median (inter-quartile range) for asthma group, 10.25 (9.25-11.91); for control group, 11.75 (10.34-12.26) IU/g Hb; P = 0.006]. There were no significant differences in activity of SOD or vitamin C, retinol, or alpha tocopherol/cholesterol ratio. The reduction in GSH-Px activity may have therapeutic and etiological implications for asthma. The effects of disease activity and treatment on antioxidant status needs for further study.

"Natural" presentation of human papillomavirus type-16 E7 protein to immunocompetent mice results in antigen-specific sensitization or sustained unresponsiveness

We have used a mouse model that utilizes the exclusively epithelial nature of human papillomavirus (HPV) infections to investigate the in vivo immune response to the E7 protein of human papillomavirus type-16. A keratinocyte cell line expressing E7 protein has been established and grafted onto syngeneic mice using a transplantation technique that permits the reformation of a differentiated epithelium on a granulation tissue bed. In this way viral antigens may be presented to the immune system in a way comparable to natural infection. A delayed-type hypersensitivity (DTH) response was studied post grafting by intradermal challenge with recombinant E7 protein. A significant response to E7 has been demonstrated in this way; however, priming with a low amount of HPV-16 E7 antigen induces immunological unresponsiveness, as measured by a loss of DTH reactivity to the protein, and persistence of keratinocytes expressing E7. Lymphocytes from mice exhibiting DTH reactivity have been shown to proliferate when stimulated with purified recombinant E7 protein in vitro, while immunoperoxidase staining of tissue from the sites of immunologically-induced inflammation has defined the cell infiltrate to be phenotypically characteristic of DTH. The observations reported here have important implications for vaccine strategy.

Study of the mechanisms by which CD4+ T cells contribute to protection in Theiler's murine encephalomyelitis

Theiler's murine encephalomyelitis virus (TMEV) is a picornavirus which causes a biphasic central nervous system (CNS) disease in certain strains of mice. Lytic virus replication within the CNS causes acute damage at early times post-infection, with the surviving animals developing a chronic CNS demyelinating disease. This damage is thought to result both from direct viral damage and from an immunopathological CD4+ T-cell mediated delayed-type hypersensitivity response to virus. By contrast, CD4+ T cells have a vital protective role at early times post-infection, as mice specifically depleted of CD4+ T cells of this subset prior to infection with TMEV die within 3-5 weeks. In an investigation of how CD4+ T cells act to mediate protection in TMEV-infected mice, we show that CD4+ cell-depleted animals, which fail to make a significant antiviral antibody response, could be protected by passive transfer of neutralizing antibodies. However, surviving animals had high levels of persisting virus in the CNS and they developed very severe symptoms of chronic demyelinating disease. The appearance of infectious virus was not due to selection of neutralizing antibody-resistant viral variants. These results demonstrate that the key protective role of CD4+ T cells in TMEV-infected mice is to provide help for antibody production by B cells at early times post-infection, but that other CD4+ cell-dependent mechanisms must contribute to control of virus replication, and are of importance in determining the levels of virus subsequently persisting in the CNS, and hence the severity of the chronic demyelinating disease.

Virus-cell interactions in the nervous system and the role of the immune response

The outcome of a viral infection within the nervous system depends on a complex interplay between the virus, its target cell and the immune system. Recent research has elucidated a variety of mechanisms involved in these interactions and their role in the production of disease.

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.

Interactions of murine gammaherpesvirus 68 with B and T cell lines

Murine gammaherpesvirus is a natural pathogen of wild rodents. We have established that in vivo the virus persists in B lymphocytes in a latent form and therefore has similar biological properties to Epstein-Barr virus and related gamma-I-herpesviruses. In this report we have established a persistent infection in mouse myeloma (B) cells (NSO cell line), but not in mouse thymoma (T) cells (BW 5147 cell line). The virus persists indefinitely in myeloma cells, without any apparent cytopathic effect, but with the production of infectious virus. We demonstrate that ACV abolishes the productive infection, but large numbers of cells harbor the virus in a latent form, as determined by an infectious center assay. Analysis of the viral DNA has shown that during a persistent infection linear virus genomes predominated, with low levels of circular DNA also present. Treatment of cells with ACV results in a significant reduction of linear genomes, but has no effect on the level of circular DNA molecules. These data provide further evidence to support our earlier observations on B cells as the site of latency and provides an in vitro model with which to study the molecular basis of MHV-68 latency/persistence.

Delayed-type hypersensitivity response to the human papillomavirus type 16 E7 protein in a mouse model

To study the immune response to human papillomavirus type 16, a mouse model was developed using a mouse keratinocyte cell line expressing the E7 protein. This line was grafted onto syngeneic mice to form a differentiated epithelium, thus closely mimicking the natural infection. A delayed-type hypersensitivity response could be demonstrated after intradermal challenge with a vaccinia virus recombinant expressing the E7 protein. This response appeared to be specific for the E7 polypeptide and was mediated by CD4+ cells.

Murine gammaherpesvirus 68 establishes a latent infection in mouse B lymphocytes in vivo

Murine gammaherpesvirus 68 (MHV-68) is able to persist in spleen cells of infected mice. To determine the cell type harbouring persistent virus, spleen cells from infected animals were separated into immunoglobulin (Ig)-positive (B cell-enriched), Ig-negative (T cell-enriched) and plastic-adherent (macrophage-enriched) fractions. These cells were co-cultivated with permissive BHK-21 cells in an infectious centre assay. The consistent recovery and enrichment of infectious centres in the Ig-positive fraction clearly demonstrates that B cells are a major site of virus persistence/latency. This observation indicates that MHV-68 is biologically similar to Epstein-Barr virus and other members of the B cell lymphotropic gammaherpesvirus 1 subgroup.

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.

Relative role of B and T lymphocytes in pathogenesis of a murine herpes virus

Pathogenesis of a murine herpes virus was investigated in inbred strains (BALB/c, CBA, AKR and C57BL/10) of mice. After intranasal inhalation, virus was found to replicate primarily in the lungs, followed by haematogenous spread to the target organs (adrenal glands and ganglia). AKR (H-2k) were found to be most susceptible to virus infection while CBA (H-2k) mice appeared to be relatively resistant. Infection of B-cell depleted BALB/c mice resulted in detection of lower lung virus titres in B-cell depleted animals as compared to normal intact mice. Moreover, 3 of 12 normal mice in untreated group died of virus infection while deaths did not occur in the B-cell depleted group. Results of T-cell subset depletion experiments in BALB/c mice revealed maximum mortality in the group depleted of both Lyt-2+ and L3T4+ subpopulations. Infectious virus titres were also higher in lungs of T-cell depleted animals.