A sensitive radioimmunoassay for the determination of antibodies to mouse hepatitis virus

A Th1 cell line (3E9.1) from resistant A/J mice inhibits induction of macrophage procoagulant activity in vitro and protects against MHV-3 mortality in vivo

Induction of immune coagulants has been implicated in the pathogenesis of murine hepatitis virus strain 3 (MHV-3)-induced fulminant hepatic necrosis. Previous work from our laboratory has shown that the induction of procoagulant activity (PCA) correlates with the resistance/susceptibility to disease in inbred and recombinant inbred (RI) strains of mice. Macrophages from susceptible, but not resistant, strains of mice expressed increased levels of PCA in response to MHV-3 stimulation. T lymphocytes, however, had a marked regulatory role in the final expression of macrophage PCA. CD3+ CD4+ CD8- lymphocytes from RI H-2 compatible susceptible mice were able to instruct macrophages from susceptible mice to express significantly augmented levels of PCA, whereas CD3+ lymphocytes from RI H-2 compatible MHV-3-immunized resistant mice were able to suppress induction of PCA. In this present study, T-cell lines were derived from draining popliteal lymph nodes from resistant A/J mice, which had been immunized with MHV-3. All T-cell lines showed marked proliferation to MHV-3 and MHV-JHM which was major histocompatibility complex (MHC) restricted. All cell lines were CD3+, four of these were CD4+ and one was CD8+. All of the CD4+ cell lines produced IL-2 and two produced interferon-gamma (IFN-gamma), consistent with the Th1 cytokine profile. One cell line (3E9.1) was able to inhibit the induction of macrophage PCA through production of a soluble factor although cell-to-cell contact could not be excluded. This CD4+ T-cell line conferred protection to infected and susceptible AXB8 mice. These results demonstrate that the existence of a Th1 subpopulation of cells with a regulatory effect on macrophage PCA induction in MHV-3-infected mice contributes to the resistance of the A/J strain of mice to MHV-3 infection.

Monoclonal antiprothrombinase (3D4.3) prevents mortality from murine hepatitis virus (MHV-3) infection

The induction of monocyte/macrophage procoagulant activity (PCA) has been implicated in the pathogenesis of murine hepatitis virus strain 3 (MHV-3) infection and disease. Previously, we have shown that induction of PCA by MHV-3 correlated with resistance/susceptibility to infection in different mouse strains. In this study, all BALB/cJ mice that were infected with 10(3) plaque-forming units of MHV-3 developed severe liver disease and died within 96-120 h. Examination of the livers of these animals showed marked hepatic necrosis, deposition of fibrin, and cellular expression of PCA by direct immunofluorescence staining in areas of necrosis as well as in hepatic sinusoids. Splenic mononuclear cells recovered from these mice expressed high concentrations of PCA with time after infection. Infusion into mice of a high-titered monoclonal antibody that neutralized PCA (3D4.3) attenuated the development of hepatic necrosis and enhanced survival in a dose-dependent manner. All of the animals receiving 100 micrograms, and 44% and 22% of the animals that received 50 and 25 micrograms per day, respectively, survived for 10 d and made a full recovery. Administration of the antibody resulted in a dose-dependent reduction in fibrin deposition, PCA expression as detected by direct immunofluorescence staining and by a functional assay. In animals treated with high concentrations of antibody, titers of antibody to PCA fell from 87 +/- 15 micrograms/ml to 100 +/- 7 ng/ml during the active phase of the disease, consistent with sequestration due to binding of the immunoglobulin to cells expressing PCA. Surviving animals, when rechallenged with MHV-3, had a 40% mortality, consistent with the known rates of metabolism of immunoglobulin. This further suggested that protection was by a passive mechanism. The results reported here demonstrate that a neutralizing antibody to PCA protects animals from fulminant hepatitis and death associated with MHV-3 infection, and supports the notion that PCA is a potent inflammatory mediator that plays a pivotal role in the pathogenesis of liver injury resulting from MHV-3 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.

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.

Expression of macrophage procoagulant activity in murine systemic lupus erythematosus

To explore the induction of monocyte/macrophage procoagulant activity in autoimmune disease, the BXSB murine model of systemic lupus erythematosus was studied. Splenic macrophage procoagulant activity rose coincident with age and the development of glomerulonephritis from 38 +/- 6 mU/10(6) macrophages at 1 mo to a maximum of 29,000 +/- 15,000 mU at 4 mo. Macrophages from 1-mo-old mice could be induced to express a 1,000-fold increase in monocyte/macrophage procoagulant activity when incubated with lymphocytes or lymphocyte supernatants from 5-mo-old mice. Plasma from 5-mo-old but not from 1-mo-old mice was able to induce the production of the lymphokine by cells from 1-mo-old animals. This lymphokine was not interleukin 1,2, or gamma interferon. We conclude that induction of monocyte/macrophage procoagulant activity parallels disease development in the male BXSB mouse, is dependent on the interaction between lymphocytes and plasma factors, and may be important in mediation of injury in lupus nephritis.

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.

The effect of mouse hepatitis virus infection on the microcirculation of the liver

Mouse hepatitis virus type 3 infection results in strain-dependent liver disease. The effects of mouse hepatitis virus type 3 on the microcirculation of the liver in both fully susceptible (Balb/cJ) and fully resistant (A/J) mice were studied. In Balb/cJ mice, 6 to 12 hr following infection, abnormalities in liver blood flow were observed which consisted of granular blood flow in both terminal hepatic and terminal portal venules. In addition, sinusoidal microthrombi were present predominantly in periportal areas. By 24 to 48 hr, liver cell edema and small focal lesions were prominent. At 48 hr, thrombi and hepatocellular necrosis were widespread, and blood was shunted from damaged areas into patent sinusoids. In sharp contrast to these abnormal findings, normal streamlined blood flow was present in the resistant A/J animals at all time points following infection. Since large amounts of virus were demonstrated by immunofluorescene in and by recovery and growth from livers of both resistant and susceptible strains, the presence of the virus per se cannot explain the abnormalities observed.