Cytotoxic T cell-resistant variants are selected in a virus-induced demyelinating disease

C57BI/6 mice infected with mouse hepatitis virus, strain JHM (MHV-JHM) develop a chronic demyelinating encephalomyelitis. Infectious virus can be isolated only from symptomatic mice. In C57BI/6 mice, two CD8+ T cell epitopes within the MHV-JHM surface glycoprotein were previously identified. Here, we show that mutations in the RNA encoding the immunodominant of the epitopes are present in nearly all virus samples isolated from these mice. Mutations are not present in sequences flanking this epitope or in other CD8+ or CD4+ T cell epitopes. Furthermore, analysis of five peptides corresponding to variant epitopes in direct ex vivo cytotoxicity assays showed that each mutation caused a loss of epitope recognition. These results suggest that escape from CD8+ T cell recognition is necessary for enhanced virus replication and development of clinical disease in these MHV-JHM-infected mice.

Effect of adoptive transfer of CD4, CD8 and B cells on recovery from MHV3-induced immunodeficiencies

A chronic viral infection can occur when the host fails to mount an effective immune response to clear the virus. Mouse hepatitis virus type 3 (MHV3) appears to be an excellent model for the study of the relationship between viral-induced immunodeficiency and chronic disease development. (C57BL/6 x A/J)F1 mice surviving acute hepatitis develop a chronic disease characterized by T- and B-cell immunodeficiencies, viral persistence in various organs including the brain, spleen and thymus, and death within 3 months postinfection (p.i.). We have reported that T- or B-cell deficiencies, observed in MHV3 chronically infected (C57BL/6 x A/J)F1 mice, can be partially or totally thwarted by adoptive transfer of CD4+, CD8+ and/or B cells, at 15 days p.i. in mice surviving the acute phase of the disease. Adoptive transfer of syngeneic CD4+ and/or CD8+ allowed a partial restoration of the T-cell deficiencies, as characterized by thymic atrophy, decrease in splenic T cells, and in all thymocyte subpopulations. B-cell immunodeficiency, as defined by a decrease in splenic B cells, as well as in the bone marrow pre-B- and B-cell compartments, and the occurrence of abnormally larger forms of bone marrow pre-B and B cells, were partially thwarted by B-cell treatment only. Splenic B cells and the bone marrow B-cell compartment, respectively, returned partially or totally to normal values, whereas the pre-B-cell compartment remained depleted in infected mice treated with B cells. Levels of all immunoglobulin classes returned to normal values in MHV3 chronically infected mice when treated with CD4+ in combination with CD8+ cells. All T- and/or B-cell treatments, however, were sufficient to thwart the process of the chronic disease, and favoured the survival of mice for up to 6 months p.i.

Generation of antiviral CD11ahigh T cells in CD4+ T cell-depleted mice and adult thymectomized mice after mouse hepatitis virus infection

The mechanism of CD11ahighCD8+ T cell induction after mouse hepatitis virus infection, which has been suggested to play a key role in the elimination of infectious virus from the spleen in C57BL/6 mice, was studied. In CD4+ T cell-depleted mice, CD11ahighCD8+ T cells were induced in the spleen and spleen cells showed virus-specific cytotoxic T lymphocyte activity after mouse hepatitis virus infection. The same results were obtained in adult thymectomized mice. These results indicate that CD11ahighCD8+ T cells can be generated after mouse hepatitis virus infection in the absence of either CD4+ T cells or the thymus.

Hepatic pathology resulting from mouse hepatitis virus S infection in severe combined immunodeficiency mice

Mouse hepatitis virus (MHV) is a pervasive pathogen that causes morbidity and mortality in mouse colonies worldwide. Although it is not a major cause of mortality in immunocompetent mice, infections from MHV strains of lower virulence can be fatal to athymic nude mice. The histopathologic features and alterations of serum biochemical parameters resulting from infection with a low-virulence MHV strain in severe combined immunodeficiency (scid) mice has not been well described. Thus we recently studied the disease caused by MHV-S in scid mice after intranasal inoculation. Mouse hepatitis virus infection in scid mice, which have severe defects of B and T cells, may be highly lethal, resulting in immediate mortality. However, our results indicate that scid mice survived for an average of 12 to 14 days after infection with doses of MHV up to 10(7) PFU/mouse. The virus caused a significant increase in serum enzyme activities and bilirubin concentration associated with histologically demonstrable hepatocellular injury at postinoculation days 3, 4, and 8. Furthermore, virus was detected in mouse liver homogenates and nasal and bronchial lavage specimens. These results provide valuable information regarding the histopathologic and biochemical consequences of MHV-S infection in scid mice.

Thymus involution induced by mouse hepatitis virus A59 in BALB/c mice

Mouse hepatitis virus A59 (MHV-A59) infection of adult BALB/c mice induced a severe, transient atrophy of the thymus. The effect was maximal at 1 week after infection, and thymuses returned to normal size by 2 weeks after infection. There was no effect of glucocorticoids, since thymus atrophy was also found in adrenalectomized, infected mice. In infected thymus, immature CD4+ CD8+ lymphocytes were selectively depleted, and apoptosis of lymphocytes was increased. The MHV receptor glycoprotein MHVR was detected on thymus epithelial cells but not on T lymphocytes. In a small number of stromal epithelial cells, but in very few lymphocytes, the viral genome was detectable by in situ hybridization. These observations suggested that MHV-A59-induced thymic atrophy results not from a generalized lytic infection of T lymphocytes but rather from apoptosis of immature double-positive T cells that might be caused by infection of a small proportion of thymus epithelial cells or from inappropriate secretion of some factor, such as a cytokine.

Mouse hepatitis virus type 3 infection provokes a decrease in the number of sinusoidal endothelial cell fenestrae both in vivo and in vitro

Fenestrations of hepatic endothelial cells play an active role as a sieving barrier allowing extensive exchange between the blood and liver parenchyma. Alteration of these structures may be induced in the course of various pathological events and provoke important perturbations of liver function. We demonstrate here that sinusoidal endothelial cells are permissive for mouse hepatitis virus 3 (MHV3) in vivo and in vitro and that this infection leads to a striking decrease in the number of fenestrae. The disappearance of these structures observed under scanning electron microscopy or in cryofracture preparations in vivo and in vitro cannot be reversed by the action of cytochalasin B on the microfilament network. The decrease in the porosity seems to be related directly to the productive infection of the endothelial cells, because it was not observed in A/J mice resistant to the virus and in susceptible BALB/c mice immunized with a thermosensitive mutant in which no viral replication occurs. In conclusion, a viral infection of liver endothelial cells may cause extensive loss of the fenestrations and thus lead to important functional pertubations.

Interleukin-12 gene expression after viral infection in the mouse

Interleukin-12 is a lymphokine that triggers gamma interferon secretion by various cells and differentiation of T-helper lymphocytes towards the Th1 subtype. Since viruses are potent inducers of gamma interferon production and elicit immune responses most probably mediated by Th1 cells, like B-cell immunoglobulin G2a secretion, we analyzed interleukin-12 message expression after infection of mice with lactate dehydrogenase-elevating virus, mouse hepatitis virus, and mouse adenovirus. Our results indicated that the message for the p40 component of interleukin-12 was transiently increased shortly after infection. Interleukin-12 was expressed mainly by macrophages. Therefore, production of interleukin-12 might constitute the initial event that would determine the subsequent characteristics of the immune response elicited by viral infections.

Demyelination induced by murine coronavirus JHM infection of congenitally immunodeficient mice

Mouse hepatitis virus JHM (JHMV or MHV-4) induces demyelination in rodents and has been studied as a model for the human disease, multiple sclerosis (MS). As is proposed in MS, the mechanism of subacute demyelination induced by JHMV appears to be primarily immunopathological, since demyelination in JHMV-infected mice is abrogated by immunosuppressive doses of irradiation and restored by adoptive transfer of splenocytes. Thy-1+ cells play a critical role in transmitting disease to these recipient mice. To further characterize cells which may mediate JHMV-induced immunopathology, we inoculated congenitally immunodeficient mice with JHMV. By 12 days post-inoculation, both immunocompetent C57BL/6J controls and athymic nude C57BL/6 mice had severe paralysis and demyelination. In marked contrast, C57BL/6 mice with the severe combined immune deficiency (SCID) mutation had little or no paralysis or demyelination. Adoptive transfer of immune spleen cells from nude mice to infected SCID mice produced paralysis and demyelination. These findings suggest that a cell population present in immunocompetent C57BL/6J and nude mice but absent or non-functional in irradiated and SCID mice is essential for JHMV-induced demyelination. Identification of cells which mediate demyelination in this experimental system may have implications for our understanding of coronavirus pathogenesis and human demyelinating diseases.

Impairment of bone marrow pre-B and B cells in MHV3 chronically-infected mice

Mouse hepatitis virus type 3 (MHV3) appears to be an excellent model for the study of the relationship between viral-induced immunodeficiency and the development of chronic disease. Animal surviving acute hepatitis develop a chronic disease characterized by viral persistency in various organs, by a humoral immunodeficiency, and eventually die within the next three months postinfection. To verify if B cell immunodeficiency occurs during the chronic disease, percentage and absolute number of bone marrow B lineage cell subpopulations were recorded at various times postinfection (p.i.) in pathogenic L2-MHV3-infected (C57BL/6 x A/J) F1 mice. Absolute numbers of B (cmu+smu+) cells decreased as early as three days p.i. up to 15 days p.i., and then gradually returned toward normal values in L2-MHV3-infected mice during the chronic disease. In contrast, pre-B (cmu+smu-) cells were less significantly decrease during the chronic disease. In addition, abnormally enlarged cells (> 13 microns) were detected either in bone marrow pre-B or B cells from L2-MHV3-infected mice.

Effect of persistent mouse hepatitis virus infection on MHC class I expression in murine astrocytes

Neurotropic strains of mouse hepatitis virus (MHV) have been used extensively for the study of viral pathogenesis in the central nervous system (CNS), serving as models for human neurological diseases such as multiple sclerosis (MS). MHV strains A59 and JHMV both cause acute and chronic encephalomyelitis and demyelination in susceptible strains of mice and rats. In acute disease, CNS damage is most likely the result of lytic infection in neurons and oligodendrocytes, and death can be prevented by the adoptive transfer of Class I-restricted CD8+ T cells. However, in later stages of the disease induced by some MHV strains, virus tends to be restricted to astrocytes in a nonlytic infection, and the immune response appears to contribute to CNS damage. These data lead us to suggest that the astrocyte may play a central role in the neuropathogenesis of MHV infection. Consistent with this possibility, A59 has been reported to induce the expression of Class I molecules of the major histocompatibility complex (MHC) in glial cells following infection in vivo and in vitro. In this communication, we have examined the influence of persistent infection by both A59 and JHMV on MHC Class I expression in primary murine astrocytes. Persistence was characterized by the presence of intracellular viral antigen and mRNA in the absence of detectable infectious virus particles. Under these conditions, JHMV, but not A59, inhibited constitutive expression of the H-2 Kb molecule, with the magnitude of inhibition increasing with postinfection time. A59 was not able to induce Class I during persistence, presumably due to the lack of infectious virus particles. Class I expression was restored by the addition of gamma-interferon (IFN-gamma) to astrocytes persistently infected with either A59 or JHMV. Thus, Class I inhibition is not a permanent consequence of JHMV persistence, and persistence does not interfere with normal signalling pathways for Class I induction.

Transcription and translation of proinflammatory cytokines following JHMV infection

Infection with JHMV results in the transcriptional activation of two host cell genes encoding proinflammatory cytokines, tumor necrosis factor (TNF)-alpha and interleukin (IL)-1 beta. Analysis of irradiated mice showed that IL-1 beta mRNA accumulation in the central nervous system was predominantly derived from the mononuclear infiltrate. By contrast, accumulation of TNF-alpha mRNA was unaffected by immunosuppression, suggesting that resident cells were the source of this cytokine. Infected mice were treated with anti-TNF antibody to determine if TNF-alpha contributed to either the encephalomyelitis or demyelination associated with JHMV infection. Surprisingly, neither the cellular infiltrate nor demyelination were affected. In vitro analysis showed that IL-1 beta but not TNF was secreted from JHMV infected macrophages. The absence of TNF secretion is due to a block in translation of the TNF mRNA which accumulates during infection.

Antiviral activity of interferon gamma in vivo during mouse hepatitis virus infection

A/J mice became resistant to experimental MHV3 infection after immunization with UV-inactivated MHV3 (0% mortality, 0/10). Depletion of interferon (IFN) gamma-producing CD4+ T lymphocytes with monoclonal antibodies to CD4+ led to susceptibility to virus infection (60% of mortality, 6/10). The resistance to MHV3 infection of CD4+ T lymphocyte-depleted-A/J mice was restored by treatment with 1000 U of IFN gamma on days -1, 0, 1, 2, 3 and 4 (10% of mortality, 1/10). The low virus titers observed in resistant mice (controls or CD4+ depleted plus IFN gamma treated) were cleared 6 days after infection and the virus titers observed among susceptible mice (CD4+ depleted) increased gradually and peaked on day 6, when the animals died. Previous data, taken together with the direct evidence presented in this paper, provide strong evidence supporting the concept of an in vivo antiviral role of IFN gamma through a central action on the mechanisms of resistance to MHV3 infection.

Methods for studying antiviral functions of macrophages and mononuclear phagocytes

Methods to check the antiviral activities of mononuclear phagocytes or macrophages are described. Two types of antiviral activities are defined. The intrinsic antiviral activity is determined as the outcome of virus replication in the macrophage per se whereas the extrinsic antiviral activity refers to the ability to reduce virus production in other surrounding cells that are normally permissive. The interpretation of the data are discussed.

Microcytic anemia and changes in ferrokinetics as late after-effects of glucan administration in murine hepatitis virus-infected C57BL/10ScSnPh mice

Mild microcytic anemia (without changes in mean corpuscular hemoglobin concentration, MCHC) was discovered 6-14 weeks after a single s.c. administration of 4 mg of particulate glucan to C57BL/10ScSnPh mice serologically positive for murine hepatitis (MHV). The anemia was associated with granulocytosis, decreased body weight and spleen hypertrophy. The overall intensity of erythropoiesis was measured by 59Fe-incorporation into the heme of erythropoietic organs. The localization of erythropoiesis became markedly redistributed--heme production was suppressed in the bone marrow while a several-fold increase was recorded for the spleen. A new steady state was also discovered in ferrokinetics: an iron pool localized away from the blood, erythropoietic organs and the liver was significantly elevated, and hypoferremia was detected. Anemia and wasting of mice were not observed in the same mouse strain free of MHV. A single administration of particulate glucan resulted in late impairment of red blood cell formation in the C57BL/10ScSnPh mouse strain infected with the mouse hepatitis virus. The anemia shares a number of features with those observed for the anemia of chronic diseases.

Evaluation of the role of exogenous pathogens on the incidence of embryo loss during early pregnancy in mice

The mating of CBA/j female mice (H2k) by DBA/2j male mice (H2d) typically results in an elevated incidence of spontaneous embryo loss thus providing an ideal genetically controlled laboratory model for the study of the factors causing early embryo loss during pregnancy. There is now considerable data on the cells and factors involved in fetal resorption but little is known about the events which activate this process. While the activation of the maternal response to the fetal implant could have endogenous or genetic origins, a role for exogenous factors including microbial pathogens could also be involved. In order to investigate these possibilities, the reproductive success of CBA/j female x DBA/2j male matings in a conventional animal care facility were compared with matings in a specific pathogen free (SPF) animal facility. All animals housed under these conditions were routinely screened by immunoassay and culture, for the presence of a number of viral and bacterial pathogens of mice. The incidence of spontaneous embryo loss in specific pathogen free CBA female mice mated by DBA and other male strains was found to be virtually identical to that of CBA female mice infected with multiple viral pathogens and housed under otherwise identical conditions (non-SPF). However, the numbers of implantation per pregnancy was significantly greater in an SPF facility. Therefore, exposure of mating mice to exogenous viral and bacterial pathogens did not appear to alter the overall incidence of spontaneous embryo resorption. It was concluded that the immunomodulatory effects of infection by common murine pathogens neither augmented nor reduced post-implantation embryo losses.

Critique of the toxicology and carcinogenesis studies of iodinated glycerol in F344/N rats and B6C3F1 mice

Carter-Wallace conducted a detailed audit and evaluation of the data available from the carcinogenicity studies with iodinated glycerol conducted in the B6C3F1 mouse and the F344/N rat by the National Toxicology Program (NTP). We conclude that there is no evidence of carcinogenicity of the compound in either the B6C3F1 mouse or the F344/N rat.

B cells induce apoptosis via a novel mechanism in fibroblasts infected with mouse hepatitis virus

B cells from nonimmune mice mediate the cytolysis of fibroblasts infected with the coronavirus, mouse hepatitis virus (MHV), strain A59. In this investigation, we report that splenic B cells and a B cell hybridoma induced the fragmentation of MHV-infected target cell DNA into a nucleosomal ladder pattern, characteristic of apoptosis. To determine the mechanism by which B cells mediated this killing event, we used criteria previously established for the killing of target cells by cytotoxic T lymphocytes (CTLs) and compared this B-cell-mediated killing to lymphocytic choriomeningitis virus (LCMV)-specific CTL killing of LCMV-infected target cells. Unlike CTL-mediated cytotoxicity, B cells efficiently lysed and induced the fragmentation of the DNA in their target cells in the presence of EGTA, arguing against a Ca(2+)-dependent granule exocytosis model for killing. In addition, paraformaldehyde-fixed B cells were able to kill MHV-infected targets. We were unable to detect TNF-alpha-associated cytotoxicity via bioassay with nonimmune effector B cells against the TNF-sensitive cell line, LM, or the TNF-alpha-resistant subline, L929.w, infected with MHV. Serine esterase inhibitors (benzamidine hydrochloride and N alpha-p-tosyl-L-arginine methyl ester) blocked CTL-induced 51Cr release and DNA fragmentation. In contrast, the inhibitors did not block the B-cell-induced 51Cr release, but did cause an inhibition in the fragmentation of the DNA of the target cell. These data indicate that B cells are capable of inducing the lysis and DNA fragmentation of MHV-infected target cells similar to CTL-induced apoptosis. However, we show that the mechanism(s) by which these processes are induced by B cells is distinct from CTL-mediated cytotoxicity.

In vitro and long-term in vivo immune dysfunction after infection of BALB/c mice with mouse hepatitis virus strain A59

Mouse hepatitis virus (MHV) is a pervasive pathogen in most mouse colonies worldwide. Infection with this virus, which is often inadvertent and unrecognized, has previously been correlated in numerous anecdotal reports with immune modulation seriously affecting the outcome of biomedical experiments. Studies using experimental models to examine the effects of MHV infection have demonstrated that the virus can both stimulate and depress immune function in vitro. We have used intranasal infection of MHV-susceptible BALB/c mice with MHV strain A59 to examine the effects of this virus on lymphoid tissue composition as well as immune function both in vitro and in vivo. We observed that the thymus, spleen, and lymph nodes underwent a transient period of marked cellular depletion. During that time, the percentages of T and B cells in the spleen remained normal. However, within 1 week after inoculation, splenic lymphoid cell proliferation was significantly decreased in response to the T-cell stimuli, concanavalin A and anti-CD3 monoclonal antibody. This continued through day 35 but was resolved by 102 days postinoculation. Notably, at days 35 and 102, mice infected with MHV-A59 were unable to reject skin grafts at a rate comparable to normal animals. These results support a basis for in vitro and, importantly, long-term in vivo immune dysfunction after infection with MHV.

Hepatic cytochrome P450 and related drug biotransformation during an outbreak of mouse hepatitis virus in a colony of Swiss BALB/c mice

Mouse hepatitis is a common highly infectious virus of the Coronaviridae family that commonly infects laboratory colonies of BALB/c mice. In a natural outbreak of this disease in our institution we demonstrated that mouse hepatitis virus appears to have little or no effect on the levels of cytochrome P450 or on the activities of ethoxyresorufin O-dealkylase and benzyloxy resorufin O-dealkylase in hepatic microsomes. Antibody titers for the virus were elevated in all mice tested and were negative in a control uninfected group. In a number of studies carried out over a period of months during the active outbreak we did not observe lower levels of cytochrome P450 in comparison with infectious free periods. Although the activation of host defence mechanisms and infections are well known to diminish the cytochrome P450 enzyme system in the liver, these results indicate that during a period of confirmed active infection with mouse hepatitis virus there was no evidence of an impairment in drug biotransformation enzymes.

The pattern of proteins synthesized in the liver is profoundly modified upon infection of susceptible mice with mouse hepatitis virus 3

Susceptible BALB/c mice, after experimental infection with mouse hepatitis virus 3 (MHV3), revealed virus titres in the liver that increased gradually to a peak of 8 x 10(5) PFU/g of tissue after 3 days' infection, when the mice died of acute hepatitis. BALB/c mice were infected with MHV3, subsequently labelled in vivo with 35S-methionine, and then the liver preparations from both infected and non-infected animals were subjected to two-dimensional gel electrophoresis. Comparisons of the patterns by computer image analysis revealed 17 gene products which increased, and 8 gene products which decreased, upon virus infection in their two-dimensional gel spot intensity. We conclude that during MHV3 infection of a susceptible strain of mice, a major modification in protein synthesis occurs. The pattern alterations were not related to the virus gene products but were mostly endogenous mouse proteins. Whether these proteins are a result of a defence attempt by the animal, or are dictated by the virus in order to prevent a protective response from happening, remains to be shown.

Modification of the amount of cholesterol in hepatic steatosis induced in susceptible and resistant mice infected with MHV3: a biochemical and ultrastructural study

A mouse hepatitis virus-3 strain subcultured in our laboratory is a unique experimental model in which to study virus-induced liver steatosis. This strain produces massive lipid deposition not only in sensitive adult BALB/c mice but also (though less extensive) in virus-resistant adult A/J mice. Biochemical determinations have shown that this steatosis is characterized by an increased amount of neutral lipids (sterols and triglycerides) in infected livers of BALB/c mice and by a smaller increase in those of A/J mice. However, the relative percentage of cholesterol and triglycerides is similar in both strains. Liver phospholipid content was significantly decreased in both strains of mice. To discriminate between cytoplasmic and membrane cholesterol content in different types of liver cells, an ultrastructural study was performed with filipin, a specific cholesterol marker. This study shows on one hand an important increase in the cholesterol in the hepatocytes of BALB/c mice and a smaller increase in those of A/J mice, in agreement with biochemical data. However, marked cholesterol decrease and abnormal cholesterol distribution were observed in the endothelial liver cells of infected BALB/c mice. This decreased cholesterol content probably led to higher fluidity of these membranes, which could be related to the important drop in the number of endothelial cell fenestrae observed after mouse hepatitis virus-3 infection. Because in A/J infected mice neither a decrease in the amount and distribution of cholesterol nor decreased fenestration were observed in endothelial liver cells, these findings could be correlated with the resistance of these mice to the infection.

Effect of eicosanoids on induction of procoagulant activity by murine hepatitis virus strain 3 in vitro

The development of hepatitis secondary to murine hepatitis virus strain 3 (MHV-3) infection correlates with the induction of macrophage procoagulant activity (PCA). 16,16 dimethyl prostaglandin E2 (dmPGE2) has previously been shown to inhibit the development of disease in this model and in parallel, inhibit induction of PCA, a macrophage effector molecule which has previously been shown to correlate with resistance/susceptibility to MHV-3 infection. These studies were undertaken to determine if inhibition of PCA was a specific property of dmPGE2 or if this property was shared by other eicosanoids including prostacyclin (PGI2), PGF2a and leukotriene B4 (LTB4). Furthermore, using the recently developed anti-PCA monoclonal antibody 3D4.3 (IgG2ak) which reacted with and inhibited functional PCA, studies were then undertaken to determine the mechanism by which PCA was inhibited by dmPGE2 (transcriptional, post-transcriptional or post-translational). Treatment with dmPGE2 resulted in inhibition of PCA induction compared with vehicle control over a range of 10(-12) to 10(-6) M. Utilizing the monoclonal antibody 3D4.3, it was demonstrated by Western immunoblot and immunofluorescence studies that although PCA was functionally inhibited by dmPGE2, it was still antigenically expressed as proteins of molecular weights 74 and 70 kd. Treatment of macrophages with PGI2, PGF2a or LTB4 failed to inhibit or augment PCA induction to MHV-3 stimulation at all concentrations tested (10(-12) to 10(-6) M). These results suggest that inhibition of PCA by dmPGE2 is a specific property of this eicosanoid and that its actions occur at a post-translational level.

Hygromycin B therapy of a murine coronaviral hepatitis

Hepatitis caused by mouse hepatitis virus (MHV-A59), a murine coronavirus, is accompanied by direct infection and replication of virus within the liver. We demonstrate here that the aminoglycoside hygromycin B is able to eliminate MHV-A59 infection from mouse peritoneal macrophages and cultured liver cells in vitro and is also able to reduce levels of virus replication and necrotic liver foci in vivo.

Characterization of brain-infiltrating mononuclear cells during infection with mouse hepatitis virus strain JHM

The eradication of infectious virus from the central nervous system (CNS) following infection with the neurotropic JHM strain of mouse hepatitis virus (JHMV) is thought to be immune-mediated. Furthermore, a significant decrease of infectious virus coincides with the appearance of prominent inflammatory infiltrates in the brain and spinal cord. In the present study, mononuclear cells infiltrating the brain during JHMV infection were isolated and characterized. While all subsets of immune cells were present, there appeared to be a temporal relationship between the peak incidence of CD8+ T cells (40% of total isolated cells) and reduction of virus at day 7 post-infection. Cells with the natural killer (NK) phenotype (at least 30%) were also present throughout infection. These data suggest that CD8+ T cells and NK cells are prominent among cells which infiltrate the brain during JHM virus infection and may have important roles in reduction of virus within the CNS.

Persistent MHV (mouse hepatitis virus) infection reduces the incidence of diabetes mellitus in non-obese diabetic mice

The frequency of diabetes mellitus was compared in non-obese diabetic mice before and after inadvertent exposure of the colony to mouse hepatitis virus infection. Prior to exposure, diabetes prevalence and cumulative diabetes incidence in 7-month-old mice was 65% and 25% in females and males, respectively. Diabetes incidence/quarter revealed a seasonal pattern with peaks in winter. After mouse hepatitis exposure, the diabetes incidence in the colony decreased and testing for mouse hepatitis antibody in blood samples revealed a persistent infection. In the offspring of mice delivered by caesarean section, the diabetic incidence increased sharply from a nadir of 36% to 95% and from 9% to 65% in females and males, respectively. In individual mice, diabetes resistance was strongly correlated to high titres of mouse hepatitis virus antibody. The results of this inadvertent viral infection demonstrate that a diabetes-susceptible genotype is strongly modulated by environmental factors. Investigators studying this diabetes model should strive for specific pathogen-free colony status and a high incidence of diabetes before attempting to investigate therapeutic modalities.

Protective effect of OK-432 (streptococcal preparation) on murine fulminant hepatitis following mouse hepatitis virus infection

The effects of OK-432 (streptococcal preparation) on murine fulminant hepatitis were investigated. Hepatitis was induced by injection of mouse hepatitis virus type 2 (MHV-2) at a strength of either 1 x 10(3) or 1 x 10(4) plaque-forming units (PFU). Mice without OK-432 treatment died within 5 days, whereas mice preinoculated with OK-432 showed survival rates of 50% (1 x 10(3) PFU) or 10% (1 x 10(4) PFU) after 60 days. Survival time was not prolonged if OK-432 was injected after MHV-2. Examined histologically, mice not treated with OK-432 showed severe haemorrhagic necrosis of the liver, often panlobular. Treated mice showed less necrosis; the least necrosis was observed in those injected with OK-432 before MHV-3. In those mice injected first with OK-432 and then with 1 x 10(3) PFU of MHV-2 that survived 7 days, autopsy showed a very slight and focal hepatic necrosis, with follicular infiltration by lymphocytes and macrophages. Mitogenic reaction of spleen cells was remarkably less than normal in mice with MHV-2 injection. However, mice injected with OK-432 before MHV-2 (same treatment as mice showing high survival rates) showed relatively high reactivity in comparison with mice not treated with OK-432.

Disparate mechanisms of induction of procoagulant activity by live and inactivated bacteria and viruses

This study describes the dose response, time course, and lymphocyte requirements of procoagulant activity (PCA) induction following stimulation of thioglycolate-elicited BALB/c peritoneal macrophages with live and inactivated bacteria (Bacteroides fragilis, Escherichia coli, and Staphylococcus aureus) and murine hepatitis virus type 3 (MHV-3). Induction of PCA by MHV-3 was significantly more rapid and the maximal PCA achieved was significantly greater than by the three bacterial species studied. In relation to induction of PCA by bacteria, the PCA response was more rapid and of greater magnitude with S. aureus and E. coli than with B. fragilis. MHV-3 induced an augmented PCA response at all concentrations of virus studied in a dose-dependent fashion, whereas higher titers of live bacteria (greater than 10(7) CFU/ml) inhibited PCA, suggesting the production of an inhibitory factor. Significant PCA induction was observed when macrophages were incubated with bacteria or virus in the absence of lymphocytes. At low titers of B. fragilis (10(3) CFU/ml), addition of lymphocytes greatly augmented PCA production, whereas at higher titers (10(7) CFU/ml), the addition of lymphocytes only slightly augmented the PCA response. In contrast, MHV-3 induction of PCA was enhanced by the addition of lymphocytes at all concentrations of virus studied, suggesting a lymphocyte-dependent process. Heat-inactivated bacteria were as effective as live bacteria in inducing PCA, suggesting that induction of PCA by bacteria requires only a bacterial surface component. In contrast, UV-inactivated MHV-3 did not induce PCA, suggesting that viral replication is a necessary step in PCA induction. These results suggest that the cellular and metabolic requirements for induction of PCA differ among viral and bacterial pathogens and may partly explain their differences in pathogenicity.

[The antiviral activity of amiksin and its effect on the interferon status in hepatitis in mice]

A single administration of amixin followed by oral infection with mouse hepatitis virus provided protection of 40%-50% animals for 72 hours and normalized the interferon status. In parallel with decreasing level of virus-induced endogenous interferon the interferon-inhibiting activity of lymphocytes of the infected animals increased and approached normal levels.

In vivo analysis of glial cell phenotypes during a viral demyelinating disease in mice

C57 BL/6N mice injected intracranially with the A59 strain of mouse hepatitis virus exhibit extensive viral replication in glial cells of the spinal cord and develop demyelinating lesions followed by virus clearing and remyelination. To study how different glial cell types are affected by the disease process, we combine three-color immunofluorescence labeling with tritiated thymidine autoradiography on 1-micron frozen sections of spinal cord. We use three different glial cell specific antibodies (a) to 2',3' cyclic-nucleotide 3' phosphohydrolase (CNP) expressed by oligodendrocytes, (b) to glial fibrillary acidic protein (GFAP) expressed by astrocytes, and (c) the O4 antibody which binds to O-2A progenitor cells in the rat. These progenitor cells, which give rise to oligodendrocytes and type 2 astrocytes and react with the O4 antibody in the adult central nervous system, were present but rare in the spinal cord of uninfected mice. In contrast, cells with the O-2A progenitor phenotype (O4 + only) were increased in number at one week post viral inoculation (1 WPI) and were the only immunostained cells labeled at that time by a 2-h in vivo pulse of tritiated thymidine. Both GFAP+ only and GFAP+, O4+ astrocytes were also increased in the spinal cord at 1 WPI. Between two and four WPI, the infected spinal cord was characterized by the loss of (CNP+, O4+) oligodendrocytes within demyelinating lesions and the presence of O-2A progenitor cells and O4+, GFAP+ astrocytes, both of which could be labeled with thymidine. As remyelination proceeded, CNP immunostaining returned to near normal and tritiated thymidine injected previously during the demyelinating phase now appeared in CNP+ oligodendrocytes. Thus O4 positive O-2A progenitor cells proliferate early in the course of the demyelinating disease, while CNP positive oligodendrocytes do not. The timing of events suggests that the O-2A progenitors may give rise to new oligodendrocytes and to type 2 astrocytes, both of which are likely to be instrumental in the remyelination process.

Induction of MHC class I antigens on glial cells is dependent on persistent mouse hepatitis virus infection

H-2 class I antigens, but not class II antigens, were detected on the surface of glial cells persistently infected with mouse hepatitis virus strain A59 (MHV-A59) as late as 90 days post-infection. Uninfected glial cells remained negative for H-2 class I and class II surface antigens. We have previously shown that conditioned media from infected glial cell cultures (supernatants) contain a factor unrelated to infectious virus and capable of inducing H-2 class I antigens on uninfected glial cells. The synthesis of this factor appears to be dependent on production of infectious virus since the H-2 inducing activity could not be detected 3 days following the addition of neutralizing antibodies to the cultures. This suggests that H-2 inducing activity contains an unstable component, the synthesis of which is dependent on continual virus production. Persistent MHV infection and H-2 class I antigen expression may play a role in MHV-induced demyelination.

Muramyl peptides confer hepatoprotection against murine viral hepatitis

The hepatoprotection induced by synthetic muramyl peptides was investigated using a model of lethal murine mouse hepatitis MHV-3 virus infection. MDP and a nonpyrogenic analog, Murametide, inhibited the steep elevation of serum transaminases induced by MHV-3 irrespective of whether the immunomodulators were administered before or after the infection. A significant proportion of MDP or Murametide-treated animals, in contrast to controls, survived the MHV-3 infection. The histopathological examination of the liver revealed marked necrosis of the hepatic parenchymal cells and infiltration of the inflammatory cells in controls but not in MDP-treated animals.

Evidence from microcorrosion casts and measurements of red cell velocity

Hepatitis has been considered, classically, as a diffuse hepatocellular necrosis, and little attention has been paid to the relationship of lesions to the microvasculature. In livers of mice (Balbc/J) infected with murine hepatitis virus (MHV-3), microcorrosion casts showed spherical cavities where casting compound was unable to fill sinusoids. At 48 hr postinfection such "lesions" had a mean diameter of 83 micron +/- 26 (SD) and their number/mm2 (at the surface of casts) was 0.95 +/- 1.3. Blind-ended sinusoids formed a distinct boundary between perfused and nonperfused areas, and concave impressions at their ends indicated cells blocking the lumen. In vivo microscopy of transilluminated livers in infected mice showed localized rounded areas without flow, corresponding to lesions seen in casts. RBC velocity measurements in sinusoids adjacent to lesions demonstrated that velocities fall from normal values to zero over a narrow border zone. Beginning with the most proximal sinusoid with visible flow and moving outward from the lesion to the second and third sinusoids, mean RBC velocities (micron/sec, +/- SD) were 17.4 +/- 6.7, 33.9 +/- 8.7, 66.6 +/- 27.3, respectively; this last value was not significantly different from velocities in normal liver (69.2 +/- 30.6). Transmission electron microscopy of livers of infected mice confirmed the presence of sinusoidal lumens blocked by protruding lining cells, RBCs, platelets, swollen hepatocytes, and cellular debris. This study demonstrates that the lesions are focal in origin, microvascular blockage leading to gradually increasing necrosis in all directions.

Delayed-type hypersensitivity response in the central nervous system during JHM virus infection requires viral specificity for protection

The JHM strain of mouse hepatitis virus (JHMV) elicits an I-A-restricted delayed-type hypersensitivity (DTH) response mediated by a Thy-1+, Lyt-1+, and CD4+ T cell. Adoptive transfer of these polyclonal CD4+ T cells from immunized mice prevents death in lethally infected recipients without significantly reducing virus titer in the central nervous system (CNS). These observations raise the possibility that the recruitment of mononuclear cells into the CNS may play a critical role in survival from a lethal CNS infection. Transient DTH response to nonviral antigens induced an accumulation of monocytes in the CNS that was maximal at 48 h post-challenge and virtually resolved by 5 days post-challenge. By contrast the induction of prolonged DTH responses resulted in the accumulation of a large number of monocytes that persisted in the CNS for at least 5 days post-challenge. Neither type of DTH reaction suppressed virus replication or prevented death from concomitant lethal JHMV infection.

Blastogenesis of large granular lymphocytes in nonlymphoid organs

High numbers of large granular lymphocytes (LGL) accumulate in the livers and peritoneal cavities of mice during the course of viral infection. Accumulation of natural killer (NK) cells at day 3 postinfection (p.i.) was shown to be radiation-sensitive, implying that proliferation was required for this response. Accumulation occurred in splenectomized mice, indicating that the spleen, known to be an organ for mature NK cell proliferation, was not the major source for liver and peritoneal NK/LGL. Significant percentages (greater than 25%) of the LGL found in the liver and peritoneal cavity following viral infection or interferon induction with poly-inosinic:poly-cytidylic acid were defined morphologically as blasts (large cells with prominent nucleoli and intensely basophilic cytoplasms containing azurophilic granules). Most blast LGL at day 3 p.i. were sensitive to administration of anti-asialo GM1 serum in vivo, were Lyt-2-, and were enriched in populations that lysed NK cell-sensitive targets in vitro, indicating that these were NK/LGL. At day 3 p.i., leukocytes from the liver and peritoneal cavity incorporated 3H-thymidine and bound to and killed NK cell-sensitive targets in single-cell cytotoxicity assays. These data suggest that NK/LGL undergo at least one round of division in the liver and peritoneal cavity during viral infection. In contrast, blast LGL at day 7 p.i. were resistant to in vivo treatments with anti-asialo GM1 serum, were Lyt-2+, and were enriched in populations of cells that killed virus-infected histocompatible targets, indicating that they were cytotoxic T lymphocytes (CTL). These results suggest that both NK/LGL and CTL/LGL are capable of blastogenesis and presumed proliferation at sites of virus infection, providing a means for the in situ augmentation of a host's cell-mediated antiviral defenses.

[Antiviral activity of amiksin incorporated into liposomes]

The results of a comparative study of the antiviral activity of amyxin (tilorone) without liposomes and incorporated into liposomes on the model of experimental enteral hepatitis of mice are presented. The use of amyxin in liposomes was shown to prolong interferon production and to provide significant 60% protection of the animals. The possible mechanism of increasing the antiviral effectiveness of amyxin upon its incorporation into liposomes, enteral administration and subsequent enteral infection of mice with hepatitis virus is discussed. It is assumed that use of amyxin in liposomes may increase its effectiveness in prevention of human hepatitis A.

[Effect of low-molecular interferon inducers in experimental hepatitis in mice]

Among low molecular interferon inducers preparations were selected which were capable of inducing interferon (IFN) synthesis after oral administration and advantageous for further clinical use. The dynamics of interferon production was studied after oral administration of three national low molecular interferon inducers. The selected preparations: a synthetic inducer, amiksin, and 2 natural compounds (gossypol derivatives), kagocel-1 and PXL-6, stimulated high levels of interferon production (from 10,000 to 20,000 IU/ml) in the intestinal tract of the animals 4 hours after induction and protected the animals from hepatitis virus of mice (the Meshcherin strain) after oral administration 24 hours before infection (35-55%). Amiksin and PXL-6 produced significant protection (p less than 0.01 or 0.001)--40 or 50%, respectively, when administered 4 hours before virus infection.

Intranasally administered alpha/beta interferon prevents extension of mouse hepatitis virus, strain JHM, into the brains of BALB/cByJ mice

Intranasally administered alpha/beta interferon blocked extension of the coronavirus, mouse hepatitis virus, strain JHM (MHV-JHM), from the nose to the brain of BALB/cByJ mice following intranasal inoculation with the virus. Two hundred units of alpha/beta interferon were administered intranasally to BALB/cByJ mice daily over a five day period. The mice were exposed intranasally to 10(3) median tissue culture infectious doses of MHV-JHM on the third day of interferon treatment. Two days after virus exposure, the proportion of mice with MHV in nasal turbinates was reduced from 10 of 10 in the untreated group to 7 of 10 in the interferon-treated group, and mean titers in virus-containing noses were lower in the interferon-treated group. Five days after virus exposure, the proportion of mice with infectious virus in the brain was significantly lower in the interferon-treated group (1 of 10 mice) than in the untreated group (10 of 10 mice). Systemic infection, as measured by presence and concentration of virus in the spleen, was not affected by intranasal interferon treatment. These results suggest that intranasally administered interferon protects against local extension of MHV-JHM from nose to brain, but not against dissemination of virus to other organs, such as the spleen.

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.