Elimination of mouse hepatitis virus from a breeding colony by temporary cessation of breeding

During quarantine in a Trexler-type isolator, high mortality was noted among offspring in a breeding colony of C.B.-17 scid/+ mice. Histology and immunohistochemistry on tissues of surviving weanlings confirmed mouse hepatitis virus infection (MHV). Since MHV infection is reported to be acute and self limiting, elimination of infection was attempted by cessation of breeding for a 15-week period. F1 mice born thereafter were seropositive for MHV at 3 to 4 weeks old and seronegative 4 weeks later, attributed to decay of maternally-derived antibodies. F2 mice were seronegative for MHV at 3 to 9 weeks old. No deaths occurred in any litters. These results suggest that MHV can be eliminated from a colony by temporary cessation of breeding, as evidenced by seronegative progeny through the F2 generation.

Experimental neuropathology of chronic demyelination induced by a JHM virus variant (DS)

A small plaque variant of JHM virus has a markedly reduced ability to kill mice following intracerebral inoculation. Spinal cords of mice surviving 13 to 16 months following acute infection with this variant were examined ultrastructurally. Multiple subpial areas of demyelination in the anterior and lateral white matter were found in five of 13 mice. The lesions had more gliosis, fewer oligodendrocytes, and less remyelination than has been described following other infections with JHM virus. No conclusive evidence of active demyelination or viral-like particles was found. The pathogenesis of the lesions observed may be due to a persistent, attenuated infection of oligodendrocytes or to immunologic processes. These lesions were similar to chronic multiple sclerosis plaques. Therefore, this variant should prove to be a useful tool for studying the long-term effects of viral-induced demyelinating diseases.

Altered splenic T cell function of BALB/cByJ mice infected with mouse hepatitis virus or Sendai virus

Mouse hepatitis virus and Sendai virus are among the most common viruses naturally infecting laboratory mice. Concanavalin A-stimulated in vitro proliferative responses of splenocytes were examined after infection of BALB/cByJ mice with the JHM strain of mouse hepatitis virus (MHV-JHM) or Sendai virus. Mice were exposed to these viruses by presumed natural routes (per os or intranasally). Immunodepression was marked but transient among BALB/cByJ mice exposed to MHV-JHM. Among mice exposed to Sendai virus and examined over a 21-day period, spleen cells from only one mouse, sacrificed 10 days postinoculation, exhibited a severely impaired ability to respond to concanavalin A. Lymphokine production by spleen cells from control and infected mice was then assessed. IL 2 was either absent or present at very low levels in culture supernates of concanavalin A-unresponsive spleen cells from MHV-JHM-infected mice. Spleen cells from the single Sendai virus-infected mouse also produced very low levels of IL 2. In contrast, IL 1 was detected in supernatants of all spleen cell cultures derived from control, MHV-JHM-infected, or Sendai virus-infected mice. There was not a clear correlation between concanavalin A responsiveness and the ability of spleen cells to produce interferon-gamma. These results stress the importance of using laboratory mice of known microbiological status for immunologic experiments.

Effect of mouse hepatitis virus infection on combination therapy of P388 leukemia with cyclophosphamide and pyrimidinones

At least three marked differences were noted in the results compared from two parallel experiments using identical protocols with virus-free mice and mouse hepatitis virus (MHV) infected mice inoculated with P388 leukemia. First, the therapeutic effect of cyclophosphamide (CY), a cytotoxic antitumor drug, was apparently augmented in MHV-infected mice. A 162% increase of life span (ILS) was obtained in MHV-infected mice compared to a 100% ILS in uninfected mice. Second, the experimental error in terms of the range of animal survival time was much larger with MHV-infected mice than with uninfected mice. In MHV-infected mice, the therapeutic effect of the combination treatment with CY and pyrimidinone was not statistically different from that of the treatment with CY alone. In uninfected mice, the effects of the combination therapy at all doses of pyrimidinone were statistically more effective than that of CY treatment alone.

Host age and genotypic effects on enterotropic mouse hepatitis virus infection

Intestinal lesions due to infection with an enterotropic strain of mouse hepatitis virus (MHV-Y) were found to be more severe and wide-spread in BALB/cByJ and Cr1:CD-1(ICR) mice than in SJL mice inoculated at 1 week of age, using nonparametric ranking analysis. Lesions and viral antigen were limited largely to the bowel, but also occurred in the liver and brain of some mice. BALB/cByJ mice developed a particularly high prevalence of brain infection, resulting in mortality after the enteric phase of infection had ceased. MHV-Y antigen was present in neurons, glia and vascular endothelium in a vascular distribution. Cr1:CD-1(ICR) pups inoculated with MHV-Y at 4 or 7 days of age developed severe typhlocolitis, enteritis and encephalitis with moderate mortality. Pups infected at 2 or 3 weeks of age had mild intestinal lesions with minimal alteration of mucosal architecture, no encephalitis and no mortality. These results demonstrate that host age and genotype influence the course of enterotropic mouse hepatitis virus, as has been shown previously with non-enterotropic, respiratory-type strains of mouse hepatitis virus.

Expression of MHC class I genes in mouse hepatitis virus (MHV-A59) infection and in multiple sclerosis

Our studies revealed that virus induced demyelination as well as human inflammatory demyelination involves upregulation of class I MHC genes and surface expression of antigens encoded by these genes. Induction involves the action of an intermediate soluble factor/s which is at present unknown. These findings suggest that MHC class I restricted, cytotoxic T lymphocyte (CTL) reactions, against self or foreign antigens may play a role in these conditions. These findings may help to elucidate the mechanism of coronavirus-induced demyelination as well as the pathogenesis of multiple sclerosis.

In vivo and in vitro models of demyelinating disease, XXIII: Infection by JHM virus of athymic rats

Wistar Lewis (WL), Long Evans (LE) and other rat strains develop complete resistance to CNS disease when inoculated intracerebrally with 5 x 10(4) PFU/ml of murine hepatitis JHM virus (JHMV) after the 10th day of age (1). Immunosuppression of WL rats following onset of the age-related resistance demonstrated that cyclosporin A (CsA) was partially able to abrogate resistance. Studies on nude (rnu/rnu) rats, their heterozygous (rnu/+) litter mates and genetically related LE rats showed that rnu/+ and LE animals became completely resistant to JHMV before the age of weaning, whereas some rnu/rnu rats, challenged as late as 70 days of age, developed disease symptoms, albeit after a long latent period. These observations indicated that the cellular immune system plays an important role in suppressing the viral disease process in the CNS. When the infection of nude rats was initiated on or after the 15th day of life, the histological lesions were generally small and present in both grey and white matter but were seldom seen in the spinal cord. By contrast in rnu/+, LE and WL rats with late-onset disease symptoms, only the demyelinating-type white matter lesions were present. Mononuclear infiltrates, evident throughout the CNS, of nude rats were sometimes massive near the meningies and within ventricular spaces. JHMV RNA was detectable by dot-blotting analysis in the CNS of both paralysed and asymptomatic rnu/rnu and rnu/+ rats. In-situ hybridization with cDNA probes for JHMV RNA showed that neurons in the hippocampus and cerebellum, as well as cells in the white matter, were frequently infected. The present data indicate that in the rat T cells have an important function in maintaining resistance to the JHMV-related CNS disease. However, even without a functional T cell compartment after 15 days of age nude rats did not develop an acute encephalitis, suggesting that an age-dependent, non-immunological mechanism is also involved in restricting the spread of infection.

Effect of inapparent murine hepatitis virus infections on macrophages and host resistance

Inapparent infections of mice with murine hepatitis virus (MHV) altered host resistance to experimental infection with a second virus, encephalomyocarditis virus (EMC), reduced the protective effects of exogenously administered interferon against EMC infections, and it altered macrophage ectoenzyme phenotypes in two macrophage populations. Resident peritoneal macrophages from mice experimentally infected with one of two strains of MHV also demonstrated altered ectoenzyme phenotypes. These data demonstrate that inapparent infections with MHV alter several host resistance and macrophage parameters and directly demonstrate that effects of inapparent MHV infection on macrophage parameters can be reproduced experimentally.

Effect of exogenous mouse interferon on murine fulminant hepatitis induced by mouse hepatitis virus type 2

We investigated the effect of exogenous mouse alpha- + beta-interferon produced by mouse L cells on the growth of mouse hepatitis virus type 2 (MHV-2) in the liver, the development of liver cell necrosis, and survival in murine fulminant hepatitis induced by MHV-2. Murine fulminant hepatitis was induced in 4-week-old male ICR mice by intraperitoneal inoculation of MHV-2. Mouse interferon (10(3) IU/mouse/day) was intraperitoneally injected every day. Exogenous mouse interferon suppressed both the growth of MHV-2 in the liver tissue and development of liver cell necrosis, and prolonged the survival. It was also found that the earlier mouse interferon was administered, the greater was the prolongation of survival.

Enterotropic mouse hepatitis virus infection in nude mice

The cause of emaciation and diarrhea in athymic nude mice was found to be hyperplastic typhlocolitis resulting from infection with enterotropic mouse hepatitis virus (MHV). The disease was reproduced in experimentally-inoculated nude mice using intestinal homogenates from affected mice and cell culture-derived virus. Material derived from an experimental mouse was passed into neonatal Swiss mice and caused acute typhlocolitis. Virus failed to grow in NCTC-1469 cells and 17Cl-1 cells, which are normally permissive for MHV, but grew to low titer in a mouse rectal carcinoma cell line, CMT 93. These results show that an enterotropic strain of MHV can cause chronic enteric disease in athymic nude mice. The pattern of infection differs markedly from the more common MHV wasting syndrome in nude mice caused by non-enteric strains of MHV.

Virus-induced central positional nystagmus in mice

Geotropic direction-changing nystagmus in lateral body positions was observed in 4-week-old BALB/c mice after intracerebral injection with a temperature-sensitive mutant of mouse hepatitis virus. The positional nystagmus was detected already 2 days after infection and it lasted half a year at least. The nystagmic responses of the semicircular canals were also evaluated before and after infection. They were unaltered during the disease, which was clinically manifested by general weakness, ataxia and tremor. Histopathological examination 2 weeks after infection revealed demyelination in various parts of the CNS.

Acute and chronic changes in the microcirculation of the liver in inbred strains of mice following infection with mouse hepatitis virus type 3

The acute and chronic effects of mouse hepatitis virus type 3 on the microcirculation of the liver in both semisusceptible C3HeB/FeJ and fully resistant A/J mice were studied. In the C3HeB/FeJ mice, abnormalities of microcirculatory flow were noted as early as 12 hr after infection and by 24 hr, localized avascular foci appeared. Disturbances were characterized by granular blood flow, sinusoidal microthrombi, distortion of sinusoids by edematous hepatocytes and necrotic lesions. Following the acute infection, Day 10, two patterns of chronic disease were observed. Eighty percent of the mice developed chronic granulomatous hepatitis whereas in the remaining 20% a more severe chronic aggressive hepatitis was observed which was characterized by ongoing hepatocellular necrosis and a marked mononuclear cell infiltrate. In both cases, in vivo microcirculatory abnormalities were found predominantly around visible lesions. Onset of the microcirculatory abnormalities was found to be concomitant with a rise in monocyte related procoagulant activity. Procoagulant activity rose acutely and remained elevated throughout the chronic phase but was higher in animals with severe disease. In contrast to the above, normal blood flow and histology were seen in the resistant A/J mice at all times following infection, and procoagulant activity remained at basal levels despite active viral replication as demonstrated by immunofluorescence studies and recovery of infectious virus. These observations suggest a role for monocyte procoagulant activity in the development of microcirculatory abnormalities following mouse hepatitis virus type 3 infection which may be important in the pathogenesis of the disease.

Host genetic regulation of acute MHV-4 viral encephalomyelitis and acute experimental autoimmune encephalomyelitis in (BALB/cKe x SJL/J) recombinant-inbred mice

In the present report we provide the strain distribution patterns of susceptibility to acute mouse hepatitis virus type-4 (MHV-4) encephalomyelitis, acute experimental allergic encephalomyelitis (EAE) and vasoactive amine sensitivity (VAAS) for 9 (CXJ) recombinant-inbred strains between BALB/cKe (C) and SJL/J(J) mice. We confirm that susceptibility to MHV-4 is not linked to the H-2 complex, and that all strains susceptible to acute EAE have both a responder H-2 haplotype (H-2s or H-2d) and induced (B. pertussis) VAAS. In addition, we provide evidence that susceptibility to acute EAE induction is controlled by an additional presently unmapped locus and that an EAE-like histopathological disease does not usually follow MHV-4 infection intracerebrally in animals susceptible to MHV-4, acute EAE and induced VAAS.

Natural resistance of mice to mouse hepatitis virus type 3 infection is expressed in embryonic fibroblast cells

Mouse hepatitis virus 3 (MHV3) infection in mice varies according to the mouse strain used; they may show resistance, semi-susceptibility (paralysis) or full susceptibility (lethal acute hepatitis). In order to study the mechanism of inborn resistance, viral infection was carried out in primary cultures of embryonic fibroblasts originating from various mouse strains exhibiting different sensitivities to MHV3 infection. Virus-induced cytopathic effects and cell membrane antigens as well as virus replication and interferon synthesis were studied. Persistent infection was induced in four out of six primary embryonic fibroblast cultures and in six of six secondary cultures. Two primary embryonic fibroblast cultures from susceptible strains underwent total lysis. A high yield of virus was obtained, as tested by viral titres and cell membrane antigen detection. No significant difference in virus production or in interferon synthesis was observed in fibroblast cultures of the various mouse strains tested. Cytopathic effects characterized by cell lysis were related, however, to phenotypes in vivo. This effect was lost after a single trypsinization of the culture. In addition, resistance to virus-induced cell lysis was inhibited by actinomycin D treatment. These results indicate that the intrinsic resistance of fibroblasts is effective not against virus replication but against virus-induced cell lysis. Such a cellular control mechanism may be an important factor for resistance in vivo.