Mouse hepatitis virus

Inoculation of mice with most neurotropic strains of the coronavirus mouse hepatitis virus results in an immune response-mediated demyelinating disease that serves as an excellent animal model for the human disease multiple sclerosis. Recent work has shown that either virus-specific CD4(+) or CD8(+) T cells are able to mediate demyelination and also that the antibody response is crucial for clearing infectious virus. Another exciting advance is the development of recombinant coronaviruses, which, for the first time, will allow genetic manipulation of the entire viral genome.     

Mouse pancreas involvement in murine hepatitis virus infection]

After intraperitoneal inoculation with mouse hepatitis virus (MHv) into mice, the excretory cells of the pancreas showed a marked vacuolar degeneration concomitantly with hepatitis. MHV-specific antigen was evidenced in the cytoplasm of infected cells. Electron microscopy revealed a number of virions within the matrix, spaces of the endoplasmic reticulum and areas of focal cytoplasmic necrosis. The virus titer of the pancreas was equal or superior to that of the liver at least in early stage of infection.     

Mouse hepatitis virus S in weanling Swiss mice following intranasal inoculation

Three-week-old outbred mice were inoculated intranasally with a mildly pathogenic strain of mouse hepatitis virus (MHV-S). Tissues were analyzed for distribution of infectious virus, lesions, and viral antigen at intervals up to 49 days after inoculation. Sera were tested for neutralizing antibody to MHV-S. Within the first week of infection, virus was isolated from lung and brain of most mice and liver of one mouse, but not from blood, spleen, or intestine. Microscopic lesions consisted of mild olfactory mucosal necrosis, neuronal necrosis of olfactory bulbs and tracts, lymphoplasmacytic infiltrates and vacuolation in the brain, mild nonsuppurative pulmonary perivascular lymphocyte infiltration, focal interstitial pneumonia, and focal necrotizing hepatitis. The presence and distribution of MHV antigen, as determined by indirect immunofluorescence, correlated with virus recovery and acute lesions. No virus or antigen was demonstrable beyond day 7. Serum antibody was first detected on day 10, and titers peaked on day 28 after infection.     

Sexual transmission of hepatitis C virus and its relation with hepatitis B virus and HIV.

OBJECTIVE--To determine the extent of transmission of hepatitis C virus in sexual partners of intravenous drug misusers and to examine the relation between the prevalences of HIV, hepatitis B virus, and hepatitis C virus infections in homosexual men and intravenous drug misusers and their sexual partners. DESIGN--Serum samples collected between 1984 and 1988 were tested for hepatitis B virus markers and antibodies against hepatitis C virus by enzyme linked immunosorbent assay (ELISA) and for HIV antibody by enzyme immune analysis and western blotting. SETTING--Large referral university hospital with an external AIDS clinic in the metropolitan area of Barcelona, Spain. SUBJECTS--243 Intravenous drug misusers, 143 of their regular heterosexual partners, and 105 homosexual men. MAIN OUTCOME MEASURES--Prevalences of hepatitis C virus, hepatitis B virus, and HIV infections. RESULTS--In all, 178 of the 243 (73%) intravenous drug misusers, 16 out of 143 (11%) of their partners, and 17 of the 105 (16%) homosexual men had antibodies against hepatitis C virus. The presence of hepatitis C virus infection was unrelated to sex, age, the presence of HIV or hepatitis B virus infections, or the Centers for Disease Control stage of HIV. In sexual partners of intravenous drug misusers there were strong correlations between the presence of hepatitis C virus infection and that of HIV (p = 0.001) and hepatitis B virus (p = 0.013) infections. CONCLUSIONS--Intravenous drug misusers have a high risk of acquiring hepatitis C virus, hepatitis B virus, and HIV infections, but the presence of hepatitis C virus infection seems to be unrelated to the presence of the other two viruses. Homosexual men have a high prevalence of HIV and hepatitis B virus infections with a low prevalence of hepatitis C virus infection, the presence of which is not related to that of the other two infections. Conversely, heterosexual partners of intravenous drug misusers have low prevalences of the three virus infections, but the presence of hepatitis C virus infection correlates significantly with the presence of HIV and hepatitis B infections. The rate of sexual transmission of hepatitis C virus seems to be low, even in partners of people known to be seropositive for this virus.     

Temperature-dependent genotype-by-genotype interaction between a pathogenic fungus and its hyperparasitic virus

The outcome of host-parasite interactions may depend not only on the genotypes of the species involved but also on environmental factors. We used the fungus Cryphonectria parasitica, the causal agent of chestnut blight, and its hyperparasitic virus, Cryphonectria hypovirus-1 (CHV1), to test for genotype-by-genotype-by-environment interactions in a host-parasite system. In C. parasitica, infection with CHV1 induces a hypovirulent phenotype with reduced virulence toward the chestnut tree (Castanea spp.) and thus controls chestnut blight in many European regions. In contrast, uninfected virulent C. parasitica have nearly eradicated the American chestnut in North America. We applied a full factorial design and assessed the fungal growth and sporulation of four C. parasitica strains, uninfected and infected with each of the four known CHV1 subtypes, at 12°, 18°, 24°, and 30°C. We found a significant (P ≤ .00001) genotype-by-genotype-by-environment interaction, demonstrating the potential for a selection mosaic. As a consequence, different host and parasite genotypes would be selected under different climatic conditions, affecting the coevolutionary dynamics of the host-parasite interaction and the course of chestnut blight epidemics. Genotype-by-genotype-by-environment interactions are essential to take into account when designing biological control strategies.     

Mouse hepatitis virus immunofluorescence in formalin- or Bouin's-fixed tissues using trypsin digestion

Mouse hepatitis viral antigens were demonstrated by immunofluorescence in formalin- and Bouin's-fixed tissues processed routinely for histopathology followed by partial digestion with trypsin. Staining was superior in tissues fixed in formalin and was not diminished in tissue sections from paraffin blocks stored at room temperature as long as 2 years. The relative ease of this procedure and the commercial availability of reagents makes this a useful technique for the definitive diagnosis of mouse hepatitis virus infection.     

Mouse hepatitis virus 3 replication in T and B lymphocytes correlate with viral pathogenicity

Viral pathogenicity may be regulated by host defense mechanisms at the virus-immune cell interaction level. The immune system plays an important role in the outcome of acute disease induced by the mouse hepatitis virus type 3 (MHV3) virus. The lymphoid cells act as effectors in the virus elimination as well as targets for viral replication. In order to demonstrate a correlation between MHV3 pathogenicity and viral replication in lymphocytes, genetically-determined resistant A/J and susceptible C57BL/6 mice were infected with pathogenic (L2-MHV3) or nonpathogenic (YAC-MHV3) viral strains. Pathogenicity and histopathologic studies have revealed that lymphoid organs such as thymus and spleen, showed injuries or atrophy in susceptible mice infected with L2-MHV3. No histopathologic lesions in the lymphoid organs occurred in C57BL/6 mice infected with YAC-MHV3 or A/J mice infected with both viruses. The mechanisms involved in the lymphoid injuries were studied regarding viral replication in the lymphoid organs and cells in infected mice. Results indicate that cell depletion in lymphoid organs is caused by a complete viral replication in lymphoid cells. Thy1.2+ and surface IgM+ lymphoid cells from susceptible C57BL/6 mice infected with L2-MHV3 were permissive to viral replication and to subsequent cell lysis. No cell lysis, however, occurred in lymphoid cells from C57BL/6 mice infected with YAC-MHV3 and A/J mice infected with both virus strains. In vitro studies, with purified T and B cell populations were performed to determine the mechanism effecting susceptibility or resistance to viral-induced cell lysis occurring in such cells. A blockade, probably occurring at the viral RNA polymerase activity level, prevents viral replication in resistant cells between the stages of fixation of the virus at the cell-surface receptor and the viral protein translation. These experiments indicate that an intrinsic virus-specific resistant mechanism occurs in lymphoid cells that plays a major role in the viral pathogenicity.     

The hepatitis B virus and its DNA polymerase: The prototype three-D virus

Summary The hepatitis B virus (HBV), the causal agent of serum hepatitis, has a diameter of 42 nm and is comprised of an outer surface coat and a 27 nm core. A unique DNA-dependent DNA polymerase is associated with the core of the virus. The core also houses a circular DNA that contains both double-stranded and single-stranded regions. In the endogenous reaction, the DNA polymerase repairs the single-stranded gaps of the viral DNA. The surface protein of the virus, called hepatitis B surface antigen, contains both lipid and carbohydrate, and is often present in particulate form in the blood of infected patients. In Asia and Africa HBV infection is associated with subsequent development of primary hepatocellular carcinoma. Although most patients recover completely from acute illness, the hepatitis B virus may cause chronic infection. Recently, a virus similar to human HBV was discovered in woodchucks. HBV has not yet been propagated in a cell culture system and the mode of replication of this unusual virus in hepatocytes is still moot. Although reliable therapy has not yet been provided, the problem of this world-wide infection has led to many interesting approaches to both vaccine production and anti-viral chemotherapy.     

Morphogenesis of hepatitis B virus and its subviral envelope particles

After cell hijacking and intracellular amplification, non-lytic enveloped viruses are usually released from the infected cell by budding across internal membranes or through the plasma membrane. The enveloped human hepatitis B virus (HBV) is an example of virus using an intracellular compartment to form new virions. Four decades after its discovery, HBV is still the primary cause of death by cancer due to a viral infection worldwide. Despite numerous studies on HBV genome replication little is known about its morphogenesis process. In addition to viral neogenesis, the HBV envelope proteins have the capability without any other viral component to form empty subviral envelope particles (SVPs), which are secreted into the blood of infected patients. A better knowledge of this process may be critical for future antiviral strategies. Previous studies have speculated that the morphogenesis of HBV and its SVPs occur through the same mechanisms. However, recent data clearly suggest that two different processes, including constitutive Golgi pathway or cellular machinery that generates internal vesicles of multivesicular bodies (MVB), independently form these two viral entities.     

Mouse susceptibility to mouse hepatitis virus infection is linked to viral receptor genotype.

We have reported that the receptor for mouse hepatitis virus (MHV) expressed in MHV-susceptible BALB/c mice (MHVR1) has 10 to 30 times the virus-binding activity of the MHV receptor expressed in MHV-resistant SJL mice (MHVR2) (N. Ohtsuka, Y. K. Yamada, and F. Taguchi, J. Gen. Virol. 77:1683-1992, 1996). This fact indicates the possibility that the difference in MHV susceptibility between BALB/c and SJL mice is determined by the virus-binding activity of the receptor. To test this possibility, we have examined MHV susceptibility in mice with the homozygous MHVR1 gene (R1/R1 genotype), mice with the MHVR1 and MHVR2 genes (R1/R2 genotype), and mice with the homozygous MHVR2 gene (R2/R2 genotype) produced by cross and backcross mating between BALB/c and SJL mice. All 63 F2 and backcrossed mice with the MHVR1 gene (R1/R1 and R1/R2) were susceptible to MHV infection, and all 57 with the homozygous MHVR2 gene (R2/R2) were resistant. We have also examined the MHV receptor genotypes of several mouse strains that were reported to be susceptible to MHV infection. All of those mice had the MHVR1 gene. These results suggest the possibility that the viral receptor determines the susceptibility of the whole animal to MHV infection.     

Susceptibility of human hepatitis delta virus RNAs to small interfering RNA action

In animal cells, small interfering RNAs (siRNA), when exogenously provided, have been reported to be capable of inhibiting replication of several different viruses. In preliminary studies, siRNA species were designed and tested for their ability to act on the protein expressed in Huh7 cells transfected with DNA-directed mRNA constructs containing hepatitis delta virus (HDV) target sequences. The aim was to achieve siRNA specific for each of the three RNAs of HDV replication: (i) the 1,679-nucleotide circular RNA genome, (ii) its exact complement, the antigenome, and (iii) the less abundant polyadenylated mRNA for the small delta protein. Many of the 16 siRNA tested gave >80% inhibition in this assay. Next, these three classes of siRNA were tested for their ability to act during HDV genome replication. It was found that only siRNA targeted against HDV mRNA sequences could interfere with HDV genome replication. In contrast, siRNA targeted against genomic and antigenomic RNA sequences had no detectable effect on the accumulation of these RNAs. Reconstruction experiments with nonreplicating HDV RNA sequences support the interpretation that neither the potential for intramolecular rod-like RNA folding nor the presence of the delta protein conferred resistance to siRNA. In terms of replicating HDV RNAs, it is considered more likely that the genomic and antigenomic RNAs are resistant because their location within the nucleus makes them inaccessible to siRNA-mediated degradation.