Decontamination of human xenotransplantable tumor with mouse hepatitis virus by implantation in nude rat: a case report

A human tumor xenograft contaminated with mouse hepatitis virus (MHV) was implanted in a nude rat in order to decontaminate the tumor line. The decontamination failed in the first trial, but succeeded in the second trial. The difference between the two trials was the duration of implantation of the tumor in the nude rat, i.e., 12 days in the first and 24 days in the second trial. Duration of implantation might be a factor in the decontamination of transplantable tumors infected with MHV by passaging in the nude rat.

The nucleocapsid protein of coronavirus mouse hepatitis virus interacts with the cellular heterogeneous nuclear ribonucleoprotein A1 in vitro and in vivo

The nucleocapsid (N) protein of mouse hepatitis virus (MHV) and the cellular heterogeneous nuclear ribonucleoprotein A1 (hnRNP-A1) are RNA-binding proteins, binding to the leader RNA and the intergenic sequence of MHV negative-strand template RNAs, respectively. Previous studies have suggested a role for both N and hnRNP-A1 proteins in MHV RNA synthesis. However, it is not known whether the two proteins can interact with each other. Here we employed a series of methods to determine their interactions both in vitro and in vivo. Both N and hnRNP-A1 genes were cloned and expressed in Escherichia coli as glutathione S-transferase (GST) fusion proteins, and their interactions were determined with a GST-binding assay. Results showed that N protein directly and specifically interacted with hnRNP-A1 in vitro. To dissect the protein-binding domain on the N protein, 15 deletion constructs were made by PCR and expressed as GST fusion proteins. Two hnRNP-A1-binding sites were identified on N protein: site A is located at amino acids 1 to 292 and site B at amino acids 392 to 455. In addition, we found that N protein interacted with itself and that the self-interacting domain coincided with site A but not with site B. Using a fluorescence double-staining technique, we showed that N protein colocalized with hnRNP-A1 in the cytoplasm, particularly in the perinuclear region, of MHV-infected cells, where viral RNA replication/transcription occurs. The N protein and hnRNP-A1 were coimmunoprecipitated from the lysates of MHV-infected cells either by an N- or by an hnRNP-A1-specific monoclonal antibody, indicating a physical interaction between N and hnRNP-A1 proteins. Furthermore, using the yeast two-hybrid system, we showed that N protein interacted with hnRNP-A1 in vivo. These results thus establish that MHV N protein interacts with hnRNP-A1 both in vitro and in vivo.

Macrophage infiltration, but not apoptosis, is correlated with immune-mediated demyelination following murine infection with a neurotropic coronavirus

Mice infected with mouse hepatitis virus strain JHM (MHV-JHM) develop a chronic demyelinating encephalomyelitis that is in large part immune mediated. Potential mechanisms of immune activity were assessed using an adoptive transfer system. Mice deficient in recombinase-activating gene function (RAG1(-/-)), defective in B- and T-cell maturation, become persistently infected with MHV but do not develop demyelination. Adoptive transfer of splenocytes from mice immunized to MHV into RAG1(-/-) mice infected with an attenuated strain of the virus results in the rapid and progressive development of demyelination. Most striking, adoptive transfer resulted, within 5 to 6 days, in extensive recruitment of activated macrophages/microglia to sites of demyelination within the spinal cord. Clearance of virus antigen occurred preferentially from the gray matter of the spinal cord. Apoptotic cells were identified in both the gray and white matter of the central nervous system (CNS) from RAG1(-/-) mice before and after adoptive transfer, with a moderate increase in number, but not distribution, of apoptotic cells following the development of demyelination. These results suggest that apoptosis following MHV-JHM infection of the murine CNS is not sufficient to cause demyelination. These results, showing that macrophage recruitment and myelin destruction occur rapidly after immune reconstitution of RAG(-/-) mice, suggest that this will be a useful system for investigating MHV-induced demyelination.

The nucleocapsid protein of murine hepatitis virus type 3 induces transcription of the novel fgl2 prothrombinase gene

Using a set of parental and recombinant murine hepatitis virus strains, we demonstrate that the nucleocapsid protein induces transcription of the novel fgl2 prothrombinase gene and elevated procoagulant activity in those strains that produce fulminant hepatitis. Chinese hamster ovary cells cotransfected with a construct expressing nucleocapsid protein from susceptible strains and with a luciferase reporter construct containing the fgl2 promoter showed a 6-fold increase in luciferase activity compared with nontransfected cells or cells cotransfected with a construct expressing nucleocapsid protein from resistant strains. Two deletions found at coding sites 111-123 and 1143-1145 of structural domains I and III, respectively, of the nucleocapsid gene may account for the differences between pathogenic and nonpathogenic strains. Preliminary mapping of the fgl2 promoter has defined a region from -372 to -306 upstream from the ATG translation initiation site to be responsive to nucleocapsid protein. Hence, mapping of genetic determinants in parental and recombinant strains demonstrates that the nucleocapsid protein of strains that induce fulminant hepatitis is responsible for transcription of the fgl2 prothrombinase gene. These studies provide new insights into the role of the nucleocapsid gene in the pathogenesis of viral hepatitis.

Interference of natural mouse hepatitis virus infection with cytokine production and susceptibility to Trypanosoma cruzi

Mouse hepatitis virus (MHV) infection can have a pronounced impact on several investigation areas. Reports on natural MHV outbreaks are rare and most studies have been conducted by deliberately infecting mice with MHV laboratory strains that cause moderate to severe disturbances to the immune system. We have investigated the effects of a natural acute outbreak of MHV in our otherwise specific-pathogen-free (SPF) inbred mouse colonies, and of enzootic chronic MHV infection on cytokine production and resistance to the intracellular pathogen Trypanosoma cruzi. We found that BALB/c and/or C57BL/6 SPF mice that had been injected with T. cruzi blood trypomastigotes from recently MHV-contaminated (MHV+) mice developed significantly higher parasite blood counts, accelerated death, and showed higher IL-10 production by spleen cells than their counterparts whose T. cruzi inoculum was derived from MHV-negative (MHV-) donors. Interferon-gamma (IFN-gamma) production by MHV+ and MHV- mice was not significantly different. In contrast, T. cruzi infection of chronically MHV-infected mice did not result in major changes in the course of infection when compared with that observed in mice from MHV- colonies, although a trend to higher parasitaemia levels was observed in BALB/c MHV+ mice. Nevertheless, both BALB/c and C57BL/6 T. cruzi-infected MHV+ mice had diminished IFN-gamma production to parasite-antigen stimulation in comparison with similarly infected MHV- mice. Interleukin-10 (IL-10) production levels by spleen cells did not differ between chronic MHV+ and MHV- mice, but IFN-gamma neutralization by monoclonal antibody treatment of anti-CD3-stimulated spleen cell cultures showed higher levels of IL-10 synthesis in MHV+ BALB/c mice.

Inhibition of nitric oxide synthase-2 reduces the severity of mouse hepatitis virus-induced demyelination: implications for NOS2/NO regulation of chemokine expression and inflammation

Infection of C57BL/6 mice with mouse hepatitis virus strain V5A13.1 (MHV-V5A13.1) results in an acute encephalitis followed by a chronic, progressive demyelinating disease with clinical and histological similarities to the human demyelinating disease Multiple Sclerosis (MS). Studies were undertaken to evaluate the contribution of NOS2 generated NO in demyelination in MHV-infected mice. MHV-infected animals were treated daily with either 8 mg of aminoguanidine (AG), a selective inhibitor of NOS2 activity, or PBS by intraperitoneal (i.p.) injection. MHV-infection of mice resulted in 20% mortality in both groups with surviving mice clearing virus below levels of detection, as measured by plaque assay, by day 12 postinfection (p.i.). A significant decrease in the severity of clinical disease was observed in AG-treated animals as compared to mice receiving PBS at days 7 and 12 p.i. (P< or =0.001 and 0.003, respectively) however, by day 21 p.i. AG-treated mice exhibited the same severity of clinical disease as control animals. Examination of brain and spinal cords from infected mice revealed a pronounced reduction in the severity of inflammation at day 7 p.i. in mice treated with AG as compared to control mice. By day 12 p.i. there was a significant decrease (P< or =0.02) in the severity of demyelination in AG-treated mice as compared to control animals yet both PBS and AG treated mice had a similar degree of demyelination by day 21 p.i. Analysis of chemokine mRNA transcripts by RNase protection assay revealed that AG-treated mice had significantly lower levels (P < or = 0.007) of transcripts for the C-C chemokine monocyte chemoattractant protein-1 (MCP-1) at day 7 p.i. as compared to control animals. By day 12 p.i., AG-treated mice and control mice had similar levels of chemokine transcripts. Together, these data suggest that inhibition of NOS2/NO slows the progression of MHV-induced demyelination. One potential mechanism by which this may occur is through controlling inflammation through modulation of chemokine expression in the CNS.

The cellular nature of genetic susceptibility to a virus

Using peritoneal macrophage cultures it was found that both PRI mice and their macrophages in culture were susceptible to mouse hepatitis virus and that C(3)H mice and macrophages were resistant. All F(1) macrophages and some back-cross cell cultures were susceptible. The degeneration of F(1) and back-cross macrophages obtained either from adult mouse peritoneal exudate or newborn mouse liver, occurred more slowly than PRI macrophages. Segregation of susceptibility occurred in the first back-cross generation. Tests of three back-cross generations from susceptible mice yielded about one-quarter of the mice shown to be susceptible either by direct test or test of their macrophages. A clear correlation between susceptibility in vivo and in vitro was established both in the test of the percentage segregation and in tests of individual back-cross mice. A small series of tests, however, indicated that 50 per cent of the back-cross mice had the genetic capacity to transmit susceptibility. Thus a hypothesis of two genes for susceptibility, although not excluded, may yield to a hypothesis of a single dominant gene, incompletely expressed. Resistant cells were converted into susceptible cells by ingestion of a relatively large particle containing a heat-stable substance. This susceptibility, although complete, was temporary. The nature of the factor causing the change has been discussed.

The role of IL-10 in mouse hepatitis virus-induced demyelinating encephalomyelitis

Interleukin 10 (IL-10) is an important anti-inflammatory cytokine. To examine its role in virus-induced encephalomyelitis, IL-10-deficient (IL-10 -/-) mice were infected with a neurotropic strain of mouse hepatitis virus (JHMV). JHMV-infected IL-10 -/- mice, compared to IL-4 -/- and syngeneic C57BL/6 mice, exhibited increased morbidity and mortality. Virus was cleared from the CNS of all groups of mice with equal kinetics by day 9 postinfection and the lack of either IL-4 or IL-10 did not alter the distribution of viral antigen, suggesting a lack of correlation between viral replication and the increased clinical disease in IL-10 -/- mice. In moribund IL-10 -/- mice, a moderate increase in mononuclear cell infiltration was correlated with increased expression of tumor necrosis factor-alpha, interferon-gamma, and inducible nitric oxide synthase mRNAs. In the small percentage of IL-10 -/- mice that survived, no differences in either demyelination or inflammation were observed. Together, these results suggest that IL-10 is not required for viral clearance, and although it appears to be one of the mechanisms responsible for inhibiting the extent of inflammation in the CNS during acute JHMV infection, it has little role in the eventual resolution of CNS inflammatory responses.

Dynamic regulation of alpha- and beta-chemokine expression in the central nervous system during mouse hepatitis virus-induced demyelinating disease

Infection of C57BL/6 mice with the V5A13.1 strain of mouse hepatitis virus (MHV-V5A13.1) results in an acute encephalomyelitis and chronic demyelinating disease with features similar to the human demyelinating disease multiple sclerosis. Chemokines are a family of proinflammatory cytokines associated with inflammatory pathology in various diseases. The kinetics and histologic localization of chemokine production in the central nervous system of MHV-infected mice were examined to identify chemokines that contribute to inflammation and demyelination. Transcripts for the chemokines cytokine-response gene-2 (CRG-2), regulated on activation, normal T cell expressed and secreted (RANTES), macrophage-chemoattractant protein-1 and protein-3 (MCP-1, MCP-3), macrophage-inflammatory protein-1beta (MIP-1beta), and MIP-2 were detected in the brains of MHV-infected mice at 3 days postinfection (p.i.), and these transcripts were increased markedly in brains and spinal cords at day 7 p.i., which coincides with the occurrence of acute viral encephalomyelitis. By day 35 p.i., RANTES, CRG-2, and MIP-1beta were detected in brains and spinal cords of mice with chronic demyelination. CRG-2 mRNA expression colocalized with viral RNA and was associated with demyelinating lesions. Astrocytes were the predominant cell type expressing CRG-2 mRNA. These observations suggest a role for chemokines, notably CRG-2, in the initiation and maintenance of an inflammatory response following infection with MHV, which is important in contributing to demyelination.

Fulminant hepatic failure in murine hepatitis virus strain 3 infection: tissue-specific expression of a novel fgl2 prothrombinase

Activation of the immune coagulation system has been implicated in the pathogenesis of fulminant liver failure caused by murine hepatitis virus strain 3 (MHV-3). The recent discovery of the fgl2 gene, which encodes for MHV-3-induced prothrombinase (fgl2 prothrombinase), allows for fundamental studies to determine the molecular basis for fulminant liver failure. Transcription of the fgl2 gene and translation of the protein it encodes were examined in the liver and other organs of susceptible mice following MHV-3 infection. No constitutive expression of the fgl2 gene or the fgl2 prothrombinase was detected. Within 12 to 24 h of MHV-3 infection, however, fgl2 gene transcripts were detected in large amounts in the liver, spleen, and lungs, all of which are rich in reticuloendothelial cells, but were only focally present in small amounts in the kidney and brain. There was sequential detection of fgl2 prothrombinase in the liver, where it was localized specifically to the endothelium of intrahepatic veins and hepatic sinusoids; this was allowed by fibrin deposition, which resulted in confluent hepatocellular necrosis. These results provide further evidence for the role of the selective expression of this novel fgl2 prothrombinase in the pathogenesis of MHV-3-induced fulminant liver failure.

Expression of a recombinant monoclonal antibody from a bicistronic mRNA

The variable regions of the murine monoclonal antibody A1, which effectively neutralizes the infection of susceptible cells by the murine hepatitis virus strain JHM, were cloned, sequenced, and expressed in mammalian cells as a functional recombinant antibody. To accomplish the concurrent synthesis of both antibody chains, the light- and heavy-chain-coding regions were inserted into a bicistronic expression cassette based on the encephalomyocarditis virus internal ribosomal entry site. The strategy of combining both coding regions in one bicistronic mRNA allows for the rapid isolation of cell clones expressing high levels of recombinant antibody.

Nitric oxide synthase type II expression by different cell types in MHV-JHM encephalitis suggests distinct roles for nitric oxide in acute versus persistent virus infection

Intranasal inoculation with mouse hepatitis virus strain JHM (MHV-JHM) results in acute meningoencephalitis. We found NOS II mRNA expression in brains of acutely infected animals on days 5 through 7 after infection. In situ hybridization and immunohistochemistry demonstrated NOS II message and protein in infiltrating macrophages. Persistent infection with MHV-JHM results in chronic demyelinating encephalomyelitis. NOS II mRNA was detected in persistently infected spinal cords. In situ hybridization and immunohistochemistry showed expression of NOS II in astrocytes in and around demyelinated lesions. These results suggest the role of NO release in acute versus persistent infection with this virus, and its contribution to the resulting pathology, may be different.

Human carcinoembryonic antigen and biliary glycoprotein can serve as mouse hepatitis virus receptors

Receptors for murine coronavirus mouse hepatitis virus (MHV) are members of the murine carcinoembryonic antigen (CEA) gene family. Since MHV can also infect primates and cause central nervous system lesions (G. F. Cabirac et al., Microb. Pathog. 16:349-357, 1994; R. S. Murray et al., Virology 188:274-284, 1992), we examined whether human CEA-related molecules can be used by MHV as potential receptors. Transfection of plasmids expressing human carcinoembryonic antigen (hCEA) and human biliary glycoprotein into COS-7 cells, which lack a functional MHV receptor, conferred susceptibility to two MHV strains, A59 and MHV-2. Domain exchange experiments between human and murine CEA-related molecules identified the immunoglobulin-like loop I of hCEA as the region conferring the virus-binding specificity. This finding expands the potential MHV receptors to primate species.

Patterns of oligodendrocyte pathology in coronavirus-induced subacute demyelinating encephalomyelitis in the Lewis rat

Intracerebral infection of rats with JHM coronavirus induces a chronic inflammatory demyelinating disease, which in many respects mimicks the pathology of multiple sclerosis. We investigated the patterns of demyelination and oligodendrocyte pathology in this model. In early stages of the disease infection of oligodendrocytes was associated with a downregulation of expression of mRNA for proteolipid protein in the absence of myelin destruction. When demyelinating lesions were formed infected oligodendrocytes were destroyed by necrosis, whereas oligodendrocytes that did not contain detectable virus antigen or RNA were in part dying by apoptosis. At this stage of the disease remyelination of the lesions was pronounced. At later stages after infection virus antigen was nearly completely cleared from the lesions. In spite of the lack of detectable virus, ongoing demyelination and unspecific tissue destruction occurred, and oligodendrocytes were mainly destroyed by apoptosis. These late lesions revealed only minimal central remyelination, but they were frequently repaired by Schwann cells. Our studies suggest that the mechanisms of myelin destruction in this model of virus-induced demyelination are complex and that the patterns of tissue damage may change during the course of the disease.