Bile duct ligation in rats induces biliary expression of cytokine-induced neutrophil chemoattractant

BACKGROUND & AIMS

Bile duct obstruction causes neutrophilic inflammation of the liver and leads to hepatic fibrosis. In obstructive liver disease, the localization of neutrophils in portal tracts suggests that cells within this region produce neutrophil chemoattractants. In this study, we investigated whether bile duct obstruction in rats induces portal expression of cytokine-induced neutrophil chemoattractant (CINC).

METHODS

Rats underwent bile duct ligation for 3 hours to 8 days. CINC regulation was examined in vivo at various intervals by immunohistochemistry, ribonuclease protection, and in situ hybridization. CINC production was also investigated in cell culture, in response to putative stimuli from obstructed liver.

RESULTS

Bile duct ligation caused neutrophilic infiltration of the liver within 3 hours. CINC was also rapidly induced, with specific expression identified in biliary cells. Rat intrahepatic biliary cells produced CINC constitutively in culture; when exposed to cholestatic bile, they showed a 12-fold increase in CINC secretion. The effect of bile was not attributable to toxicity or to dissolved cytokines or endotoxin. Mechanical strain, designed to mimic the stretching of biliary cells during obstruction, did not induce CINC.

CONCLUSIONS

Biliary cells contribute to hepatic inflammation during cholestasis by producing neutrophil chemoattractants. A major stimulus to biliary chemoattractant production in vivo may be bile itself.

Simian immunodeficiency virus (SIV)-specific CTL are present in large numbers in livers of SIV-infected rhesus monkeys

The immunopathogenesis of AIDS-associated hepatitis was explored in the SIV/rhesus monkey model. The livers of SIV-infected monkeys showed a mild hepatitis, with a predominantly CD8+ T lymphocyte infiltration in the periportal fields and sinusoids. These liver-associated CD8+ T cells were comprised of a high percentage of SIV-specific CTL as defined by MHC class I/Gag peptide tetramer binding and Gag peptide epitope-specific lytic activity. There was insufficient viral replication in these livers to account for attracting this large number of functional virus-specific CTL to the liver. There was also no evidence that the predominant population of CTL were functionally end-stage cells trapped in the liver and destined to undergo apoptotic cell death in that organ. Interestingly, we noted that liver tetramer-binding cells showed an increased expression of CD62L, an adhesion molecule usually only rarely expressed on tetramer-binding cells. This observation suggests that the expression of specific adhesion molecules by CTL might facilitate the capture of these cells in the liver. These results demonstrate that functional SIV-specific CD8+ T cells are present in large numbers in the liver of chronically SIV-infected monkeys. Thus, the liver may be a trap for virus-specific cytotoxic T cells.

Critical contribution of liver natural killer T cells to a murine model of hepatitis

Natural killer T (NKT) cells constitute a distinct subpopulation of T cells with a unique antigen specificity, prompt effector functions, and an unusual tissue distribution. NKT cells are especially abundant in the liver, but their physiological function in this organ remains unclear. In the present study, we examined the possible contribution of NKT cells to a murine model of hepatitis induced by i.v. injection of Con A. CD1-deficient mice lacking NKT cells were highly resistant to Con A-induced hepatitis. Adoptive transfer of hepatic NKT cells isolated from wild-type mice, but not from FasL-deficient gld mice, sensitized CD1-deficient mice to Con A-induced hepatitis. Furthermore, adoptive transfer of hepatic mononuclear cells from wild-type mice, but not from CD1-deficient mice, sensitized gld mice to Con A-induced hepatitis. Upon Con A administration, hepatic NKT cells rapidly up-regulated cell surface FasL expression and FasL-mediated cytotoxicity. At the same time, NKT cells underwent apoptosis leading to their rapid disappearance in the liver. These results implicated FasL expression on liver NKT cells in the pathogenesis of Con A-induced hepatitis, suggesting a similar pathogenic role in human liver diseases such as autoimmune hepatitis.

The Long Evans Cinnamon (LEC) rat develops hepatocellular damage in the absence of antimicrosomal antibodies

Long Evans Cinnamon (LEC) rats are an inbred strain with a mutation affecting a copper transporter. As a result, hepatic copper levels rise and the rats spontaneously develop hepatitis that is fatal in about 40% of the rats. The rats that die have been reported to develop anti-microsomal antibodies, most frequently against protein disulfide isomerase (PDI), prior to the onset of liver damage. The association between the presence of antibodies and death of the LEC rats, along with the detection of antibodies prior to the detection of liver damage suggested that the antibodies may have a role in the pathogenesis of liver damage. The objective of this study was to more clearly delineate the temporal relationship between antibody production and the onset of liver damage and copper accumulation. Serum was screened for the presence of anti-microsomal antibodies by immunoblotting. Liver damage was assessed by serum biochemistry and histological examination on rats between 6 and 12 weeks of age (four per group). Copper accumulation in the liver was determined by biochemistry and histological examination. Evidence of liver damage was detectable by serum biochemistry and histopathology by 11.5 weeks. Copper was rarely detected in hepatocytes, although it was detected in macrophages. Sera from only one of seven rats with evidence of liver damage had detectable anti-microsomal protein antibodies. The protein recognized was not PDI. The development of anti-microsomal autoantibodies did not precede the development of significant liver damage, suggesting that they play only a secondary role, if any, in the pathogenesis of hepatitis in this rat strain.

Immune-mediated cholangiohepatitis in neonatally thymectomized mice: the role of T cells and analysis of T-cell receptor Vbeta usage

We have previously reported the induction of immune-mediated cholangiohepatitis following injection of a hybrid recombinant proteins containing the E2 of the pyruvate dehydrogenase (PDC-E2) and the branched-chain keto-acid dehydrogenase (BCOADC-E2) to neonatally thymectomized (Tx) A/J mice. Further, we demonstrated that intrahepatic infiltrating mononuclear cells could transfer pathology to other Tx mice. To further our observations, we examined intrahepatic infiltrating mononuclear cells by flow cytometry and used cell transfer experiments to identify the phenotype involved. Interestingly, following immunization of neonatally Tx A/J mice and immunization with the bihybrid molecule, the number of CD3+infiltrating mononuclear cells were significantly higher (77.8%) compared with the control group. There was a small although not significant increase among intrahepatic infiltrating mononuclear cells and splenic cells of Vbeta 5.1,5.2+, Vbeta7+and Vbeta17+. In addition, Vbeta14+cells accounted for 20.4% of the infiltrating T-cells (P<0.01 vs. the control group). In further experiments, CD3+, CD4+or CD8+cells were isolated and removed from intrahepatic infiltrating mononuclear cells and subpopulations of mononuclear cells transferred to Tx mice. Both CD3+CD4+cells and CD3+CD8+cells are required for development of the lesion, and the damage is mediated by CD3+Vbeta14+cells.

Liver-infiltrating T lymphocytes are attracted selectively by IFN-inducible protein-10

We have demonstrated that interferon-inducible protein-10 (IP-10) is produced in hepatocytes surrounded by infiltrative mononuclear cells in chronic hepatitis. To clarify the role of IP-10 in hepatitis, we examined the chemoattractive activity of IP-10 on liver-infiltrating lymphocytes in experimental animal models of hepatitis. IP-10 was specifically induced in the livers of mice treated intravenously (i.v.) with Con A, while monocyte chemotactic protein-1 (MCP-1) showed a much lower level of induction and neither RANTES nor macrophage inflammatory protein-1alpha (MIP-1alpha) was detected. The liver-infiltrating lymphocytes in Con A-induced hepatitis were attracted only by IP-10, and not by other chemokines such as RANTES, MCP-1 and MIP-1alpha. The chemoattractive effect of IP-10 was dose-dependent and was neutralized by monoclonal antibodies to IP-10. The specific effect of IP-10 on liver-infiltrating lymphocytes was also seen on those obtained from rat livers with fulminant hepatitis induced by sequential treatment with killed Propionibacterium acnes (P. acnes) and LPS. Peripheral blood lymphocytes were slightly attracted by IP-10 as well as RANTES and MIP-1alpha, while hepatic resident lymphocytes were not. On the other hand, thioglycolate-elicited peritoneal macrophages did not respond to IP-10, although they did show a response to RANTES, MCP-1 and MIP-1alpha. These results indicated that IP-10 is a specific chemoattractant for T lymphocytes in the inflammatory liver tissues and may play a specific role in the development of hepatitis.

The hepatic inflammatory response after acetaminophen overdose: role of neutrophils

Acetaminophen overdose induces severe liver injury and hepatic failure. There is evidence that inflammatory cells may be involved in the pathophysiology. Thus, the aim of this investigation was to characterize the neutrophilic inflammatory response after treatment of C3Heb/FeJ mice with 300 mg/kg acetaminophen. A time course study showed that neutrophils accumulate in the liver parallel to or slightly after the development of liver injury. The number of neutrophils in the liver was substantial (209 +/- 64 PMN/50 high-power fields at 12 h) compared to baseline levels (7 +/- 1). Serum levels of TNF-alpha and the C-X-C chemokines KC and MIP-2 increased by 28-, 14-, and 295-fold, respectively, over levels found in controls during the injury process. In addition, mRNA expression of MIP-2 and KC were upregulated in livers of acetaminophen-treated animals as determined by ribonuclease protection assay. However, none of these mediators were generated in large enough quantities to account for neutrophil sequestration in the liver. There was no upregulation of Mac-1 (CD11b/ CD18) or shedding of L-selectin on circulating neutrophils. Moreover, an anti-CD18 antibody had no protective effect against acetaminophen overdose during the first 24 h. These results indicate that there is a local inflammatory response after acetaminophen overdose, including a substantial accumulation of neutrophils in the liver. Because of the critical importance of beta2 integrins for neutrophil cytotoxicity, these results suggest that neutrophils do not contribute to the initiation or progression of AAP-induced liver. The inflammation observed after acetaminophen overdose may be characteristic for a response sufficient to recruit neutrophils for the purpose of removing necrotic cells but is not severe enough to cause additional damage.

A novel murine anti-human Fas mAb which mitigates lymphadenopathy without hepatotoxicity

Defects in Fas-mediated apoptosis are implicated in autoimmune diseases including rheumatoid arthritis (RA). Although induction of Fas-mediated apoptosis could have therapeutic effects on these diseases, it might cause deleterious effects in liver as Fas ligand or an agonistic anti-murine Fas antibody Jo2 causes severe hepatic injury in mice. We report here on the interesting characteristics of the newly obtained anti-Fas mAb, HFE7A, which cross-reacts with the Fas molecules of various species ranging from human to mouse and mitigates autoimmune symptoms without hepatotoxicity in mice. The administration of HFE7A to mice induced apoptosis in the thymocytes, although administration of HFE7A to mice or to marmosets did not induce any sign of hepatitis. The effect of HFE7A on liver is different from that of anti-murine Fas antibody Jo2, which causes acute and lethal hepatic injury to mice. Administration of HFE7A reduced lymphadenopathy and abnormal T cells in MRL-gld/gld mice. HFE7A induced apoptosis in synovial cells prepared from RA patients. Surprisingly, HFE7A protected mice from fulminant hepatitis induced by Jo2. Therefore, HFE7A is a potential therapeutic antibody not only for autoimmune diseases including RA but also for fulminant hepatitis.

Protective effects of soyasapogenol A on liver injury mediated by immune response in a concanavalin A-induced hepatitis model

The present study was carried out to analyze the effects of soyasapogenol A on the liver injury mediated by the immune response in concanavalin A-induced hepatitis in mice. Soyasapogenol A reduced the number of infiltrating inflammatory cells in the liver and significantly lowered the elevated level of plasma tumor necrosis factor-alpha (TNF-alpha) 2 h after concanavalin A treatment, and then markedly reduced the elevated plasma alanine aminotransferase activity and decreased the number of apoptotic bodies in the liver parenchymal cells but not in the sinusoidal cells at 24 h. Since the effect of soyasapogenol A on the elevated plasma TNF-alpha level was not appreciable compared to the preventive effect of soyasapogenol A on the elevated plasma alanine aminotransferase level, these results suggest that soyasapogenol A directly prevents apoptosis of hepatocytes, and secondly, inhibits the elevation of plasma TNF-alpha, which consequently resulted in the prevention of liver damage in the concanavalin A-induced hepatitis model.

Prophylactic DNA vaccine for hepatitis C virus (HCV) infection: HCV-specific cytotoxic T lymphocyte induction and protection from HCV-recombinant vaccinia infection in an HLA-A2.1 transgenic mouse model

DNA vaccines express antigens intracellularly and effectively induce cellular immune responses. Because only chimpanzees can be used to model human hepatitis C virus (HCV) infections, we developed a small-animal model using HLA-A2.1-transgenic mice to test induction of HLA-A2.1-restricted cytotoxic T lymphocytes (CTLs) and protection against recombinant vaccinia expressing HCV-core. A plasmid encoding the HCV-core antigen induced CD8(+) CTLs specific for three conserved endogenously expressed core peptides presented by human HLA-A2.1. When challenged, DNA-immunized mice showed a substantial (5-12 log(10)) reduction in vaccinia virus titer compared with mock-immunized controls. This protection, lasting at least 14 mo, was shown to be mediated by CD8(+) cells. Thus, a DNA vaccine expressing HCV-core is a potential candidate for a prophylactic vaccine for HLA-A2.1(+) humans.

Treatment of concanavalin A-induced hepatitis in mice with low molecular weight heparin

BACKGROUND/AIMS

Heparin has been noted to inhibit inflammation independent of its known anti-coagulant activity. In the present study, we examined the ability of heparin and low molecular weight heparin to prevent immune-mediated, concanavalin A-induced liver damage.

METHODS

Mice were pretreated with either heparin or low molecular weight heparin (Fragmin) prior to their inoculation with concanavalin A (10 mg/kg). Liver enzymes, liver histology, and the serum levels of tumor necrosis factor-a, interleukin-6, and interleukin-10 were examined in the control and treated mice.

RESULTS

The histopathologic damage in the liver, and the concanavalin A-induced release of aminotransferases, tumor necrosis factor-a, and interleukin-6 were significantly inhibited in mice pretreated with low molecular weight heparin, whereas the serum levels of the anti-inflammatory cytokine interleukin-10 were increased (p<0.01). Interestingly, maximal inhibition was obtained with low low molecular weight heparin doses (5 and 1 microg/mouse, p<0.001), while higher doses were less effective. Concanavalin A-induced liver injury was not prevented by pretreatment of the mice with heparan sulphate (p<0.001), which although it is structurally similar to heparin possesses neither anti-inflammatory nor anti-coagulant properties.

CONCLUSIONS

This study demonstrates the efficacy of low molecular weight heparin in preventing immune-mediated liver damage in mice.

Propionibacterium acnes induces acute TNFalpha-mediated apoptosis of hepatocytes followed by inflammatory T-cell-mediated granulomatous hepatitis in mice

The CD3+/TCRalphabeta+ T-cell-mediated hepatic inflammation induced by Propionibacterium acnes could be divided into an acute and a chronic phase. The acute phase occurred within 72 h after injection and displayed hepatic apoptosis. Anti-TNFalpha antibody inhibited both the P. acnes-induced hepatic apoptosis and lymphocyte infiltration seen in this phase, indicating the involvement of this cytokine. Thereafter, a chronic phase was manifested from days 7 to 14 after injection. It was characterized as granulomatous inflammation admixed with apoptosis of infiltrating lymphocytes and some hepatocytes. Immunohistochemical staining showed that the infiltrating lymphocytes displayed TNFalpha, TNF type I receptor and a variety of cytokines including IL-1beta, IL-4, IL-6, IL-10, IFNgamma or IL-12. Interestingly, in naive mice, the arteries in the liver constitutively expressed IFNgamma. Its expression appeared to be substantially increased at 48 h, decreased at 72 h, and increased again on day 14 after P. acnes injection. Furthermore, Fas or FasL was only detected on the lymphocytes within the granuloma. We conclude that P. acnes can induce a TNFalpha-mediated acute hepatic apoptosis which subsequently progress to a T-cell-mediated granulomatous hepatitis with increased expression of multiple cytokines and Fas/FasL.

Active participation of CCR5(+)CD8(+) T lymphocytes in the pathogenesis of liver injury in graft-versus-host disease

We examined the molecular pathogenesis of graft-versus-host disease-associated (GVHD-associated) liver injury in mice, focusing on the role of chemokines. At the second week after cell transfer in the parent-into-F1 model of GVHD, CD8(+) T cells -- especially donor-derived CD8(+) T cells -- infiltrated the liver, causing both portal hepatitis and nonsuppurative destructive cholangitis (NSDC). These migrating cells expressed CCR5. Moreover, macrophage inflammatory protein-1alpha (MIP-1alpha), one of the ligands for CCR5, was selectively expressed on intralobular bile duct epithelial cells, endothelial cells, and infiltrating macrophages and lymphocytes. Administration of anti-CCR5 antibody dramatically reduced the infiltration of CCR5(+)CD8(+) T lymphocytes into the liver, and consequently protected against liver damage in GVHD. The levels of Fas ligand (FasL) mRNA expression in the liver were also decreased by anti-CCR5 antibody treatment. Anti-MIP-1alpha antibody treatment also reduced liver injury. These results suggest that MIP-1alpha-induced migration of CCR5-expressing CD8(+) T cells into the portal areas of the liver plays a significant role in causing liver injury in GVHD; thus, CCR5 and its ligand may be the novel target molecules of therapeutic intervention of hepatic GVHD.

A critical role for antigen-specific Th1 cells in acute liver injury in mice

A novel liver injury model was established in mice by targeting of OVA-containing liposomes into the liver, followed by adoptive transfer of OVA-specific Th1 cells. Combined treatment of mice with OVA-containing liposomes and Th1 cell transfer caused an increase in serum transaminase activity that was paralleled with an elevation of serum IFN-gamma levels. In sharp contrast, OVA-specific Th2 cell transfer resulted in an increase of serum IL-4 levels, but did not induce liver injury. Neither NK, NK T, nor CD8+ T cells were required for the Th1-induced liver injury. The liver injury was blocked by anti-IFN-gamma mAb and anti-TNF-alpha mAb, but not by anti-Fas ligand mAb. The Fas/Fas ligand independency was also demonstrated using Fas-deficient lpr mice. These findings indicate that Th1 cells are the major effector cells in acute liver injury.

The mouse interferon-gamma transgene chronic hepatitis model (Review)

Acute hepatitis models are widely used for the evaluation of drugs for liver disease or for basic research on hepatitis. However, it is difficult to produce similar liver conditions to human chronic hepatitis with an acute hepatitis model. The interferon-gamma (IFN-gamma) transgenic mouse, which carries the mouse IFN-gamma gene, strongly expresses the IFN-gamma gene in the liver and develops chronic hepatitis from the age of 6-10 weeks. We found that the hepatitis in this mouse reflects human chronic hepatitis at least in the following points, i) infiltration by lymphoid cells into the portal areas and necroinflammation in the lobules, and ii) expression of Fas antigen and Fas ligand mRNAs in the liver. Furthermore, the induction of CPP32-like protease activity in the transgenic mouse liver suggests the involvement of this protease activity in the development of chronic hepatitis.

Cx32 mRNA in rat liver: effects of inflammation on poly(A) tail distribution and mRNA degradation

Previous studies showed that the expression of connexin 32 (Cx32), the polypeptide subunit component of the major hepatic gap junction, is reduced in liver by changes in mRNA stability during bacterial lipopolysaccharide (LPS)-induced inflammation. In this study, we examined the distribution of Cx32 mRNA poly(A) tail lengths during LPS-induced inflammation, because this is considered the first step in the degradation of many mRNAs. During LPS treatment the first detectable change in Cx32 mRNA was a gradual shortening of its poly(A) tail, which reached a final size of approximately 20 nucleotides. However, the poly(A) tail did not disappear entirely before the bulk of Cx32 mRNA was degraded. Treatment with actinomycin D, which blocks the degradation of Cx32 mRNA after LPS administration, resulted in the appearance of a completely deadenylated mRNA, which otherwise could not be detected. On the contrary, treatment with cycloheximide resulted in a decrease in the stability of Cx32 mRNA without an apparent change of the poly(A) tail size. The effect of cycloheximide on Cx32 mRNA stability seems to be due indirectly to the induction of an inflammatory response by this drug. These results suggest that, similar for many mRNAs, shortening of the poly(A) tail is one of the first steps in the degradation of Cx32 mRNA during inflammation.

Alleviation of lipopolysaccharide-induced acute liver injury in Propionibacterium acnes-primed IFN-gamma-deficient mice by a concomitant reduction of TNF-alpha, IL-12, and IL-18 production

The present study was designed to investigate the role of IFN-gamma in LPS-induced liver injury following priming with Propionibacterium acnes. At 1 week after priming BALB/c mice with P. acnes, a large number of macrophages (Mphi) and lymphocytes predominantly infiltrated the portal area, resulting in the intrahepatic formation of granulomas consisting of epithelioid and lymphoid cells. In comparison, in IFN-gamma gene-disrupted BALB/c mice (IFN-gamma knockout mice), the number of infiltrated Mphi was decreased, with a significant reduction in the number and size of granulomas. Subsequent elicitation with a low dose of LPS induced massive hepatic necrosis in wild-type BALB/c mice, with a marked increase in the serum levels of TNF-alpha, IL-12, and IL-18 and subsequently of alanine transferase. In contrast, IFN-gamma knockout mice developed scattered focal necrosis of the liver with significantly lower levels of serum alanine transferase as well as drastic decreases in TNF-alpha, IL-12, and IL-18 production. The administration of an anti-IFN-gamma neutralizing mAb at the eliciting phase significantly alleviated liver injury and reduced serum IL-12 and IL-18 levels. Thus, endogenously produced IFN-gamma is involved in the pathogenesis of this liver injury model by regulating Mphi infiltration and granuloma formation in the priming phase as well as cytokine production in the eliciting phase.

Involvement of Fas/Fas ligand system-mediated apoptosis in the development of concanavalin A-induced hepatitis

Concanavalin A (Con A)-induced hepatitis is an experimental hepatitis model in which hepatic injury is caused by the action of cytokines produced by T cells. Using IFN-gamma-deficient mice, we previously demonstrated that IFN-gamma plays a central role in Con A-induced hepatitis. Here, we show that development of the disease is completely suppressed in gld/gld mice, in which Fas ligand is defective. In contrast, suppression of the disease in Ipr/Ipr mice was incomplete, since a small amount of the fas mRNA was produced in these mice. The data indicate that activation of the Fas/Fas ligand system is a necessary step in the development of Con A-induced hepatitis. Furthermore, we found that not only fas but also caspase-1 expression was reduced in IFN-gamma-deficient mice. Since caspase-1 is an integral component of Fas signal transduction, these observations suggest that IFN-gamma-induced activation of both fas and caspase-1 expression causes enhancement of hepatocyte apoptosis resulting in the development of hepatitis.

Role of P-selectin cytoplasmic domain in granular targeting in vivo and in early inflammatory responses

P-selectin is an adhesion receptor for leukocytes expressed on activated platelets and endothelial cells. The cytoplasmic domain of P-selectin was shown in vitro to contain signals required for both the sorting of this protein into storage granules and its internalization from the plasma membrane. To evaluate in vivo the role of the regulated secretion of P-selectin, we have generated a mouse that expresses P-selectin lacking the cytoplasmic domain (DeltaCT mice). The deletion did not affect the sorting of P-selectin into alpha-granules of platelets but severely compromised the storage of P-selectin in endothelial cells. Unstored P-selectin was proteolytically shed from the plasma membrane, resulting in increased levels of soluble P-selectin in the plasma. The DeltaCT-P-selectin appeared capable of mediating cell adhesion as it supported leukocyte rolling in the mutant mice. However, a secretagogue failed to upregulate leukocyte rolling in the DeltaCT mice, indicating an absence of a releasable storage pool of P-selectin in the endothelium. Furthermore, the neutrophil influx into the inflamed peritoneum was only 30% of the wild-type level 2 h after stimulation. Our results suggest that different sorting mechanisms for P-selectin are used in platelets and endothelial cells and that the storage pool of P-selectin in endothelial cells is functionally important during early stages of inflammation.

Induction and persistence of immune-mediated cholangiohepatitis in neonatally thymectomized mice

The availability of recombinant autoantigens allows the experimental study of the relationships between primary biliary cirrhosis (PBC) and mitochondrial antigens. We took advantage of these recombinant autoantigens and attempted to induce autoimmune cholangitis by immunizing neonatally thymectomized (NTx) lipopolysaccharide (LPS)-treated A/J mice, known to be prone to organ-specific autoimmune diseases. We employed a recombinant protein containing a dual-headed molecule that coexpresses the immunodominant epitope of the E2 subunits of the pyruvate dehydrogenase complex and the branched-chain keto-acid dehydrogenase complex. We report herein that an immune-mediated cholangiohepatitis was induced by such immunization and the concurrent injection of LPS into NTx mice. The incidence of cholangitis was 79% in the NTx, immunized, LPS group compared to 14% in the NTx, nonimmunized, LPS group. The histopathology ranged from mild to severe and included bile duct damage, focal hepatic necrosis, and endotheliitis, but no granulomas. Moreover, almost all such lesions persisted for 12 weeks after the discontinuation of immunization and LPS injections in the NTx mice. Interestingly, we were successful (89%) in transferring the cholangiohepatitis by injection of liver infiltrating mononuclear cells from the NTx, immunized, LPS mice into congenic nonimmunized NTx mice; such lesions could not be transferred with spleen cells. Although the pathology is not typical of PBC, this model offers a unique venue for the study of immune-mediated hepatobiliary injury.

Failure to induce organ-specific autoimmunity by breaking of tolerance: importance of the microenvironment

Peripheral tolerance is considered to be a safeguard against autoimmunity. Using a TCR-transgenic mouse system displaying peripheral tolerance against a liver-specific MHC class I Kb antigen, we investigated whether the breaking of tolerance would result in autoimmunity. Reversal of tolerance was achieved by simultaneous challenge with cells expressing the Kb autoantigen and IL-2. Tolerance could not be broken with IL-2 alone or when Kb- and IL-2-expressing cells were applied to different sites of the mice. However, despite the presence of activated autoreactive T cells that were able to reject Kb-positive grafts no autoaggression against the Kb-positive liver was observed. These results indicate that breaking of tolerance per se is not sufficient to cause liver-specific autoimmunity. However, when in addition to breaking tolerance the mice were infected with a liver-specific pathogen, autoaggression occurred. Thus, in this system at least two independent steps seem to be required for organ-specific autoimmunity: reversal of peripheral tolerance resulting in functional activation of autoreactive T cells and conditioning of the liver microenvironment which enables the activated T cells to cause tissue damage.

Immunohistochemical characterization of the lesions of feline progressive lymphocytic cholangitis/cholangiohepatitis

The histopathological features of liver biopsies from 20 cats with progressive lymphocytic cholangitis/cholangiohepatitis are reported. These biopsies were subject to immunohistochemical investigation for expression of CD3, CD79. Major Histocompatibility Complex (MHC) Class II molecules, and feline IgG, IgM and IgA. Livers from five normal cats, which were also examined showed constitutive expression of MHC Class II by sinusoidal Kupffer cells and bile duct epithelium, in addition to a population of portal, and bile duct inter-epithelial, CD3+ T lymphocytes. In liver biopsies from cats with the active phase of lymphocytic cholangitis/cholangiohepatitis (n = 11), the portal lymphocytes were predominantly CD3+ T cells that infiltrated bile duct epithelium and periportal hepatic parenchyma, CD79+ B lymphocytes formed distinct aggregates or follicles within the regions of T-cell infiltration. Low numbers of plasma cells were present, and these predominantly expressed IgA. MHC Class II was expressed by Kupffer cells, infiltrating T and B lymphocytes and macrophages. There was membrane and cytoplasmic Class II expression by bile duct epithelium, some vascular endothelium, and fibroblasts within areas of fibrosis. In liver biopsies from cats with chronic lymphocytic cholangitis/cholangiohepatitis (n = 9), there was less in flammation, but the composition of the infiltrates was similar to that in the active phase of disease. The findings provide further evidence for an immune mediated pathogenesis in progressive lymphocytic cholangitis/cholangiohepatitis.

In vivo evidence for a functional role of both tumor necrosis factor (TNF) receptors and transmembrane TNF in experimental hepatitis

The significance of tumor necrosis factor receptor 1 (TNFR1) for TNF function in vivo is well documented, whereas the role of TNFR2 so far remains obscure. In a model of concanavalin A (Con A)-induced, CD4+ T cell-dependent experimental hepatitis in mice, in which TNF is a central mediator of apoptotic and necrotic liver damage, we now provide evidence for an essential in vivo function of TNFR2 in this pathophysiological process. We demonstrate that a cooperation of TNFR1 and TNFR2 is required for hepatotoxicity as mice deficient of either receptor were resistant against Con A. A significant role of TNFR2 for Con A-induced hepatitis is also shown by the enhanced sensitivity of transgenic mice overexpressing the human TNFR2. The ligand for cytotoxic signaling via both TNF receptors is the precursor of soluble TNF, i.e. transmembrane TNF. Indeed, transmembrane TNF is sufficient to mediate hepatic damage, as transgenic mice deficient in wild-type soluble TNF but expressing a mutated nonsecretable form of TNF developed inflammatory liver disease.

Contribution of Fas ligand to T cell-mediated hepatic injury in mice

BACKGROUND & AIMS

Fas has been implicated in liver damage. The aim of this study was to investigate the role of its ligand to induce hepatocyte death and liver damage in T cell-dependent hepatitis.

METHODS

Fas ligand-mediated lysis of primary hepatocytes from C57BL/6 wild-type, Fas ligand-deficient gld, and Fas-deficient lpr mice and concanavalin A-induced hepatitis in these mice were assessed.

RESULTS

Freshly isolated hepatocytes from wild-type or gld mice, but not those from lpr mice, were susceptible to Fas ligand-mediated lysis. When concanavalin A was intravenously administered into wild-type mice, they developed acute hepatic injury with massive degenerative changes in hepatocytes. In contrast, both gld and lpr mice had lower aminotransferase levels with milder histological changes. Reverse-transcription polymerase chain reaction and flow cytometric analysis showed that Fas ligand was induced in the liver shortly after the concanavalin A injection and was predominantly expressed on intrahepatic T cells. Administration of monoclonal antibody neutralizing mouse Fas ligand could reduce the aminotransferase increase.

CONCLUSIONS

The results indicate that Fas ligand plays a role in the T cell-dependent hepatitis induced by concanavalin A administration.

Suppression of concanavalin A-induced hepatitis in IFN-gamma(-/-) mice, but not in TNF-alpha(-/-) mice: role for IFN-gamma in activating apoptosis of hepatocytes

Con A-induced hepatitis (Con A-hepatitis) is a hepatitis model in which hepatic injury is supposed to be caused by cytokines from activated T cells. To elucidate the pathogenesis of this disease, we analyzed the roles of IFN-gamma and TNF-alpha using deficient mice of these cytokines. Development of hepatitis was reduced significantly in IFN-gamma(-/-) mice, while susceptibility of TNF-alpha(-/-) mice was not changed. Interestingly, apoptotic cell death was observed in the affected livers of control or TNF-alpha(-/-) mice, but not in those of IFN-gamma(-/-) mice. Fas mRNA expression was increased in the livers of hepatitis mice, but less abundantly in those of IFN-gamma(-/-) mice. Since apoptosis of liver cells was rarely observed in Con A-treated lpr/lpr mice, involvement of the Fas-Fas ligand system in this apoptotic process was suggested. These observations suggest that IFN-gamma plays a central role in Con A-hepatitis by activating Fas-induced apoptosis of liver cells.

Cell-mediated immune responses to liver membrane protein in canine chronic hepatitis

Peripheral blood mononuclear cells from dogs with chronic inflammatory liver disease and dogs with noninflammatory liver diseases were evaluated for proliferative responses to pokeweed mitogen and canine liver membrane protein. Dogs with chronic hepatitis were selected based on histopathological evidence of periportal lymphocytic infiltrates with or without neutrophilic infiltrates, fibrosis and necrosis. Incorporation of tritiated thymidine was assessed 72 hours after addition of liver membrane protein or pokeweed mitogen. Peripheral blood mononuclear cell proliferation in response to liver membrane protein was significantly higher in chronic hepatitis dogs compared to control dogs. Eight of 12 dogs with chronic hepatitis and 2 of 7 dogs with noninflammatory liver disease had proliferative responses to liver membrane protein greater than 2 standard deviations above the mean of the control group. These data support the hypothesis that immune-mediated processes are involved in canine chronic hepatitis, but did not determine whether this is a primary disorder or occurred secondary to liver destruction.

The appearance of unusual phenotypic cells (CD4+ Mac-1+ class II+) in the liver of (NZW x BXSB)F1 mice is possibly an animal model for autoimmune hepatitis

The male (NZW x BXSB)F1 (W/BF1) mouse, a murine model for autoimmune diseases, shows hepatosplenomegaly with lymphoid cell infiltration in the liver by 20 weeks of age. The majority of infiltrating cells are T cells, B cells and plasma cells, as seen in autoimmune hepatitis. Together with the increase in serum glutamate pyruvate transaminase (GPT) levels, anti-dsDNA antibody (Ab) and circulating immune complex (CIC) levels increase with age. These findings are compatible with those of autoimmune hepatitis in humans. In addition, a unique finding in this mouse is the accumulation of CD4+ Mac-1+ Class II+ cells in the sinusoidal space. The cells have the capacity to proliferate and differentiate into macrophages in vitro, indicating that they are the precursors of macrophages. This W/BF1 mouse provides a useful tool for not only analyzing the pathogenesis of autoimmune hepatitis but also establishing a new therapeutic strategy for it. In addition, we discuss the significance of the appearance of abnormal cells in autoimmune-prone mice.

Tumor necrosis factor receptor p55 is essential for intrahepatic granuloma formation and hepatocellular apoptosis in a murine model of bacterium-induced fulminant hepatitis

Accumulating evidence implicates tumor necrosis factor (TNF) and Fas systems in liver injury, although the interaction between these two systems remains to be investigated. In this study, we examined Propionibacterium acnes-primed TNF receptor p55-deficient (TNFRp55-/-) or Fas-deficient MRL/MpJ Lpr/Lpr mice challenged with lipopolysaccharide (LPS). Priming with P. acnes caused mononuclear cell infiltration into the hepatic lobules and granuloma formation in the livers of TNFRp55 wild-type mice. Subsequent LPS challenge caused massive liver injury and a marked increase in transaminase levels, leading to acute lethality in control wild-type mice. In contrast, the same treatment caused few pathological changes in livers of TNFRp55-/- mice, and all animals survived. P. acnes and subsequent LPS challenge induced granuloma formation and apoptotic changes, respectively, in livers of MRL/MpJ Lpr/Lpr mice. However, liver injury was 50% of that in control MRL/MpJ +/+ mice, suggesting some role of the Fas-Fas ligand system in this liver injury model. On the other hand, an agonistic anti-Fas antibody caused massive apoptosis and hemorrhagic changes of the liver without any priming with P. acnes, leading to death in both TNFRp55-/- and control wild-type mice. These results suggest that TNFRp55 but not Fas was involved in P. acnes-induced granuloma formation as well as subsequent LPS-induced liver injury and that TNFRp55 and Fas independently induced apoptosis of hepatocytes in vivo.

Experimental hepatitis and role of cytokines

Activated T lymphocytes appear to be responsible for liver damage in chronic active hepatitis and autoimmune liver disease. We described three experimental mouse models of T cell dependent liver injury. D-galactosamine (GalN)-sensitized mice challenged with either T cell activating anti-CD3 monoclonal antibody (mAb) or with the superantigen staphylococcal enterotoxin B (SEB) developed severe liver injury characterized by internucleosomal DNA fragmentation as well as by histological hallmarks of hepatocyte apoptosis, both preceding the increase of plasma transaminases. Administration of the T cell mitogen concanavalin A (Con A) to unsensitized mice also resulted in hepatic apoptosis and the ensuing necrosis. Anti-CD3 mAb as well as SEB or Con A induced the release of systemic tumor necrosis factor (TNF), interferon gamma (IFN gamma), and various other cytokines. Passive immunization against TNF or pretreatment with immunosuppressive drugs such as cyclosporin A, FK 506 or dexamethasone protected mice from liver injury. T lymphocytes were identified as effector cells of Con A in vivo i) by proof of resistance of athyrnic nude mice against Con A and ii) by restoration of susceptibility in nude by lymphocyte transfer from control mice. Moreover, antibody-dependent depletion of CD4+ T cells fully protected against Con A, whereas depletion of CD8+ T cells failed to prevent liver injury. These results indicated that cytokines released following T helper cell activation rather than cytotoxic T cells mediated liver injury. We recently found that IFN gamma is also a critical mediator of Con A-induced hepatic damage. In conclusion, these T cell-dependent models of inflammatory liver injury allow the investigation of basic principles of hepatic disorders associated with T cell activation and infiltration as well as pharmacological in vivo studies for the development of hepatoprotective drugs.

Susceptibility of experimental autoimmune hepatitis in transgenic mice overexpressing the c-H-ras gene

Results from a recent study of ours have demonstrated the significant role of the wild-type ras gene in the development of hepatocellular carcinoma in rasH2 mice having prototype human c-H-ras genes. Chronic cell death and regeneration have been considered to work as co-carcinogens with wild-type ras gene overexpression in this model. To elucidate a role of gene overexpression in the occurrence of chronic inflammation, we tried to induce inflammation in the liver of rasH2 mice by immunizing them with the supernatant of a freshly prepared syngenic liver homogenate. Immunization resulted in a dense inflammatory infiltrate in the portal tract and focal necrosis with spots of fatty or foamy degeneration in the transgenic mouse liver; however, these observations were less frequently observed in non-transgenic mouse liver. Monocytes, granulocytes and plasma cell infiltration were observed in the livers of transgenic mice. An immunohistochemical study showed that CD3-positive lymphocytes also infiltrated the liver. The inflammatory infiltrate was still present in the transgenic liver 24 weeks after the last injection, but little infiltrate was observed at the same time in non-transgenic mice. No hepatic tumours could be produced over the 6 months duration of the study and the results are only preliminary. However, these results do suggest that overexpression of wild-type ras is partially responsible for the occurrence of autoimmune chronic hepatitis.

Differential pathogenesis of lethal mousepox in congenic DBA/2 mice implicates natural killer cell receptor NKR-P1 in necrotizing hepatitis and the fifth component of complement in recruitment of circulating leukocytes to spleen

Innate resistance of C57BL/6 (B6) mice to lethal mousepox is controlled by multiple genes. Previously, four resistance genes were localized to specific subchromosomal regions and transferred onto a susceptible DBA/2 (D2) background by serial backcrossing and intercrossing to produce congenic strains. Intraperitoneally inoculated ectromelia virus was uniformly lethal and achieved similar titers in B6 and D2 mice but elicited differential responses in liver, spleen, and circulating blood leukocytes. The distribution of these response phenotypes in congenic strains linked control of phenotypes with specific subchromosomal regions. D2.R1 mice, which carried a differential segment of chromosome 6, exhibited a B6 liver response and intermediate spleen and circulating leukocyte responses. D2.R2 and D2.R4 mice, which carried differential segments of chromosomes 2 and 1, respectively, exhibited a D2 liver response, a B6 spleen response, and an intermediate circulating leukocyte response. The localization of control of liver response phenotypes to chromosome 6 implicates cells that express natural killer (NK) cell receptor NKR-P1 alloantigens. The localization of control of spleen and circulating leukocyte responses to chromosomes 1, 2, and 6 implicates NK cells, the fifth component of complement, and a gene near the selectin gene complex in recruitment of circulating leukocytes to spleen.

Interleukin 10 suppresses experimental chronic, granulomatous inflammation induced by bacterial cell wall polymers

BACKGROUND AND AIMS

Interleukin 10 (IL10) inhibits monocyte/macrophage and T lymphocyte effector functions. This study examined the effect of systemically administered IL10 on acute and chronic granulomatous enterocolitis, hepatitis, and arthritis in a rat model.

METHODS

Lewis rats were injected intramurally with streptococcal peptidoglycan-polysaccharide (PG-APS) polymers. Beginning 12 hours before PG-APS injection, rats were treated daily with subcutaneous murine recombinant IL10 or vehicle for three or 17 days.

RESULTS

IL10 attenuated acute enterocolitis in a dose dependent fashion (p < 0.01). Protective effects were more profound in the chronic granulomatous phase with decreased enterocolitis and markedly inhibited leucocytosis, hepatic granulomas, and chronic erosive arthritis (p < 0.001). IL10 downregulated tissue IL1, IL6, tumour necrosis factor alpha, and interferon gamma gene expression, consistent with the in vitro effects of IL10 on PG-APS-stimulated splenocytes. Caecal IL1 protein concentrations and IL2 and interferon gamma secretion by in vitro stimulated mesenteric lymph nodes were downregulated in IL10 treated animals.

CONCLUSIONS

These results indicate that exogenous IL10 can inhibit experimental granulomatous inflammatory responses and suggest that IL10 treatment could be an effective new therapeutic approach in human disorders such as Crohn's disease, rheumatoid arthritis, and sarcoidosis.

Midzonal necrosis of the liver after concanavalin A-injection

Concanavalin A (Con A) can induce an immune-mediated hepatitis. Since direct evidence of immune mechanism for this hepatitis is lacking, we employed adoptive transfer to study the mechanism of Con A-induced hepatitis. Intravenous administration of Con A (20 mg/kg) to Balb/c mice was accompanied by elevations of serum alanine aminotransferase (ALT) levels and midzonal necrosis with lymphocyte infiltration in the liver. None of the Balb/c nu/nu mice showed biochemical or pathologic hepatic abnormalities with the same dose of Con A. In the area of midzonal necrosis, CD4-positive T lymphocytes appeared at 24 hr after injection, and then both CD4-positive and CD8-positive T lymphocytes were found at the margin of zonal necrosis at 48 hr. Pretreatment with carrageenan, a potent inhibitor of macrophages, prevented these biochemical and pathologic changes. Mononuclear cells infiltrating in the liver of Balb/c mice 24 hr after priming with Con A were harvested and injected into Balb/c nu/nu mice injected with Con A 24 hr previously. Serum ALT levels elevated and the same pathologic changes observed in Con A-treated Balb/c mice were observed. These changes were not observed when the splenic cells from Con A-treated Balb/c mice were transferred to Con A-treated nude mice. These results suggest that Con A-induced hepatic injury is mediated by macrophages and T lymphocytes sensitized by Con A or its metabolites.

TNF-alpha gene expression in the liver of the IFN-gamma transgenic mouse with chronic active hepatitis

Cytokine gene expression in the liver of transgenic mouse which specifically expresses interferon-gamma gene (IFN-gamma) was measured using polymerase chain reaction analysis. IFN-gamma mRNA was found to be expressed in the transgenic mouse liver along with TNF-alpha mRNA. Messenger RNAs of CD4 and CD8, maturation markers of T cells, were expressed in both normal and transgenic mouse livers, indicating the presence of resident T cells. The level of CD4 and CD8 expression was slightly elevated in the transgenic mouse case, indicating an increased number of CD4+ and/or CD8+ T cells, but the lack of the activation marker IL-2 mRNA suggested a nonactivated state. TGF-beta 1 mRNA was expressed in both normal and transgenic mouse livers without any increase in the latter, and therefore does not appear to be involved in the development of chronic active hepatitis in this transgenic mouse. Since TNF-alpha is a terminal mediator of liver injury in several animal liver injury models, its high expression, presumably a result of the IFN-gamma which is transcribed from the introduced gene, might be involved in the development of chronic active hepatitis in this transgenic mouse.

Autoimmune hepatitis. Definition--classification--histopathology--immunopathogenesis

Autoimmune hepatitis (AIH) is a distinct form of acute and chronic inflammatory liver disease in which immune reactions against host antigens are found to be the major pathological mechanism. If left untreated it carries an unfavourable prognosis, and the diagnosis should be made as soon as possible. The diagnostic approach has been greatly facilitated by the establishment of a panel of marker autoantibodies, which do not define distinct therapeutic groups of AIH, but do allow a subgrouping based on differences in patient populations, some clinical features and prognosis. The characterization of organ-specific components of the liver cell surface as targets of cellular and humoral autoimmune reactions give new insights into the pathogenesis of the disease, even though the primary event triggering the disease remains to be defined. The most important disease-promoting factor seems to be a genetically determined background for autoimmunity. Without this different environmental factors, including viruses, toxins, cytokines and drugs, are only able to induce transient autoimmune phenomena and not autoimmune disease. The histopathology of AIH is in keeping with the present pathogenetic concept. Although there is no pathognomonic feature distinguishing this type of hepatitis from virus-induced forms, some distinct morphological lesions are regarded as characteristic. Clinical research on AIH has benefited greatly from observations of experimental AIH in mice. Recognition of the critical role of autoreactive T-lymphocytes in the pathogenesis and the observation of spontaneous recovery from AIH in the animal model associated with antigen-specific and antigen-non-specific T-cell suppression have made basic contributions to our improved understanding of the natural course of AIH in humans.

Critical involvement of interferon gamma in the pathogenesis of T-cell activation-associated hepatitis and regulatory mechanisms of interleukin-6 for the manifestations of hepatitis

A single intravenous injection of concanavalin A (Con A) induces T-cell activation and an acute hepatitis in mice. This study investigated the role of interferon gamma (IFN-gamma) in the pathogenesis of this hepatitis model. Striking increases in the plasma levels of various cytokines, including tumor necrosis factor (TNF), interleukin-2 (IL-2), and IFN-gamma, were detected before the increase in plasma aminotransferase levels induced by Con A injection. TNF levels peaked within 2 hours, whereas IFN-gamma levels peaked at 6 hours after Con A injection. In contrast to a sharp peak of TNF levels, high IFN-gamma levels were detected for a more prolonged period. Passive immunization with anti-IFN-gamma monoclonal antibody (MAb) conferred a dose-dependent protection against liver injury in this model. This protection was observed when anti-IFN-gamma MAb was administered at least 30 minutes before Con A injection but not when given 1 hour after Con A injection. The protection from Con A-induced hepatitis was also induced by administration of rIL-6 before Con A injection. rIL-6 treatment induced significant albeit incomplete inhibition of IFN-gamma and TNF production, whereas this regimen did not affect IL-2 production. Despite striking protective effects of rIL-6 or anti-IFN-gamma MAb, comparable levels of cellular (both T cell and polymorphonuclear cell) infiltration were detected in liver sections from animals untreated, or treated with either rIL-6 or anti-IFN-gamma MAb. Moreover, electron microscopic examination showed that infiltrating T cells exhibited a blastoid appearance in all groups. These results indicate that IFN-gamma plays a critical role in the development of Con A-induced acute hepatitis and suggest that IL-6 administration can regulate the manifestation of hepatitis through mechanisms including the reduced production of inflammatory cytokines such as IFN-gamma.

Induction of autoimmune hepatitis and autoantibodies to liver antigens by neonatal thymectomy in mice

We examined development of autoimmune hepatitis in neonatally thymectomized C3H/HeN mice and tried to characterize the nature of liver antigens recognized by the autoantibodies at the molecular level. Autoantibodies to crude liver proteins detected by ELISA were found in 12(67%) of 18 mice thymectomized 2 days after birth. However, autoantibodies were not detected in mice thymectomized 7 days after birth. The autoantibodies mainly consisted of IgG and reached the maximum level 8 weeks after birth. Hepatic inflammation, mononuclear cell infiltration in the portal area, was seen in 5 (28%) of 18 mice thymectomized 2 days after birth, but not in mice thymectomized 7 days after birth. Most infiltrating cells were Thy-1+ lymphocytes. The serum autoantibody level to crude liver proteins in mice with hepatitis was much higher than that in mice without hepatitis. We fractionated crude liver proteins by a Sepharose 6B column and examined the reactivity against the autoantibodies. The autoantibodies of three of five mice with hepatitis reacted with th approximately 150kD liver proteins other than liver-specific protein (LSP). By Western immunoblotting of SCS-PAGE using LSP and fractionated liver proteins, we found that the molecular weights of the target antigens were 52kD in LSP and 150kD (strong band), 138, 128, 120 and 110kD (weak band) in fractionated liver proteins other than LSP. This 150-kD target molecule in crude liver proteins was found only in liver. These results indicate that hepatitis and autoantibodies to liver proteins are induced spontaneously by neonatal thymectomy in mice, and the candidates of autoantigen in this hepatitis model are 52-kD protein in LSP and 150-kD liver proteins different from LSP. Still more, we regard the 150-kD molecule as a new autoantigen related to hepatitis.

Anti-liver membrane protein antibodies in dogs with chronic hepatitis

Serum from 21 dogs with chronic hepatitis was evaluated for anti-liver membrane protein (anti-LMP) antibodies by an enzyme-linked immunosorbent assay. Ten of the 21 dogs had anti-LMP antibody concentrations greater than 2 SD above the mean value for the 10 healthy control dogs; titers ranged from 1:40 to greater than 1:1,600. Anti-LMP-positive dogs were not restricted by breed, had higher alanine amino transferase activity and total bilirubin concentration, and more severe liver lesions when compared with anti-LMP-negative dogs. This study provided evidence of humoral autoantibodies in dogs with chronic hepatitis, but it did not determine if the autoantibodies were primary or secondary.

Role of metabolism in cocaine-induced immunosuppression in splenocyte cultures from B6C3F1 female mice

Cocaine has been reported to directly suppress the in vitro immune responses at very high concentrations. In the present study, the possible role of metabolism in cocaine-induced immunosuppression was investigated in splenocyte cultures isolated from B6C3F1 female mice. Since cocaine can be metabolized by both esterase and P-450 monooxygenase, we studied the direct effects of cocaine, benzoylecgonine and norcocaine on the in vitro T-dependent antibody response to SRBC. Direct exposure to cocaine only produced a modest (30%) but nonsignificant suppression of the antibody response, while benzoylecgonine, a primary product of metabolism by the esterase pathway, was devoid of activity. In contrast, direct exposure to norcocaine, the initial product of N-demethylation by the P-450 pathway, produced significant suppression at concentrations greater than or equal to 10 microM. Similar results were observed in studies measuring LPS and Con A mitogenicity. Furthermore, a significant suppression was observed when splenocytes were preincubated for 1 h with 1 mM cocaine in the presence of liver S-9 fractions isolated from phenobarbital-induced mice. Meanwhile, no suppression was obtained when splenocytes were preincubated in the presence of untreated S-9 fractions. To characterize the mechanism of our results, the capacity of both untreated and phenobarbital-induced microsomes to produce formaldehyde from cocaine was compared. The N-demethylation of cocaine was NADPH-dependent and phenobarbital-induced microsomes produced approx. 6-times higher amounts of formaldehyde, indicating a greater portion of cocaine could be metabolized through the P-450 pathway to its toxic metabolites. Finally, because benzoylecgonine shares with cocaine the presence of a methyl group on the tropane nitrogen, we also compared the ability of N-demethylation from cocaine and benzoylecgonine in mouse liver microsomes. Our results indicated that benzoylecgonine could not be demethylated as determined by a failure to generate any formaldehyde. These results offer further support that the N-demethylation pathway is a critical step to cause its immunotoxicity.

Occurrence of autoimmune antibodies to liver microsomal proteins associated with lethal hepatitis in LEC rats: effects of TJN-101 ((+)-(6S,7S,R-biar)- 5,6,7,8-tetrahydro-1,2,3,12-tetramethoxy-6,7-dimethyl-10,11- methylenedioxy-6-dibenzo[a,c]cyclooctenol) on the development of hepatitis and the autoantibodies

Long Evans Cinnamon (LEC) rats, that spontaneously develop hepatitis, were found to possess autoantibodies to liver microsomal proteins (anti-LM) before the development of hepatitis. Anti-LM antibody was assumed to appear in association with the lethal hepatitis in the LEC rats. Thus, the purpose of this study was to investigate the effects of an anti-hepatitis drug on the development of hepatitis and the occurrence of the antibody in LEC rats. Mortality, blood biochemical parameters and the titer of serum anti-LM antibody were measured. In control LEC rats, 4 of 8 rats died before 20 weeks of age. In rats treated with TJN-101 ((+)-(6S,7S,R-biar)-5,6,7,8-tetrahydro-1,2,3,12-tetramethoxy -6,7-dimethyl-10,11 - methylenedioxy-6-dibenzo[a,c]cyclooctenol), 4 of 7 rats died of hepatitis, but the time of death was delayed by 7-10 weeks compared to the control rats. The titer of the anti-LM antibody increased 3-7 weeks before death in the non-survivors in control and TJN-101-treated rats, supporting the idea that anti-LM antibody occurs in association with acute lethal hepatitis.

Chronic active hepatitis in mice caused by Helicobacter hepaticus

Helicobacter infections cause chronic gastroenteritis in humans and several animal species. We recently discovered a new Helicobacter (H. hepaticus) that is the etiological agent of a unique chronic active hepatitis in mice. Natural infection appeared to be acquired early in life in enzootically infected colonies. Liver lesions arose as focal necrosis and focal nonsuppurative inflammation by 1 to 4 months of age in susceptible mouse strains. By 6 to 8 months, extensive liver involvement included hepatocytomegaly, bile ductular (oval cell) hyperplasia, and cholangitis. There was an age-related increase in proliferating cell nuclear antigen hepatocyte nuclear labeling index. The bacteria were usually found within bile canaliculi as determined by ultrastructural evaluation of liver lesions, the Steiner modification of the Warthin-Starry stain and immunohistochemistry with a rabbit antibody to Helicobacter pylori. Naturally infected mice showed an age-related increase in serum IgG antibodies to Helicobacter hepaticus proteins. The disease was experimentally reproduced by intraperitoneal injection of liver suspensions from affected livers or bacteria cultivated in vitro. The earliest lesions of the experimental disease appeared 4 weeks after injection. The course of spontaneous and experimental infection was slow and insidious and resulted in high titers of antibodies to bacterial proteins. This chronic bacterial infection represents a new model of chronic liver disease.

Impaired T and B cell subpopulations involved in a chronic disease induced by mouse hepatitis virus type 3

A chronic viral infection can occur when the host immune system fails to detect the viruses. Mouse hepatitis virus type 3 (MHV3) seems to be an excellent model for the study of the relationship between viral-induced immunodeficiency and the development of chronic disease. Animals that survive acute hepatitis develop a chronic disease characterized by viral persistency in various organs, including the brain, spleen, and thymus, and they eventually die within the next 3 mo postinfection (p.i.). To verify whether T and B cell immunodeficiency occurs either in the acute or chronic phase of the disease, the percentage and absolute number of splenic T and B lymphocytes, thymic T, or bone marrow B-lineage cell subpopulations were recorded at various times p.i. in pathogenic L2-MHV3-infected and nonpathogenic YAC-MHV3-infected (C57BL/6 x A/J) F1 mice. Splenic T and B cells were depleted as early as 48 h p.i., and maintained at low levels for up to 3 mo until death of mice. Such depletions resulted from thymic depletion in all T cell subpopulations, and in B (cytoplasmic micro-chain+ and surface micro-chain+) lymphocytes only in the bone marrow of pathogenic L2-MHV3-infected mice. In vitro studies of purified thymic stromal cells have produced a nonproductive L2-MHV3 replication with a low viral transmission to complexed thymocytes. However, pre-B and B cells have supported a productive viral replication, generating abnormal forms, which leads to cell lysis. These results are discussed in relation to viral persistency in the brain and lymphoid cells, which results from a chronic impairment of cellular and humoral immune mechanisms that are involved in the viral elimination process.

Murine experimental autoimmune hepatitis: nonspecific inflammation due to adjuvant oil

Experimental autoimmune hepatitis (EAH) has been induced in several strains of mouse by immunization with liver cytosol plus Freund's complete adjuvant. Our goal was to validate EAH in female C57Bl/6 mice and to compare the ability of immunization with liver cytosol and hepatocyte plasma membranes in Freund's complete (CFA) or incomplete (IFA) adjuvants to induce EAH. Control mice received Hank's balanced salt solution (HBSS), alone or an emulsion of HBSS in either CFA or IFA. The severity of hepatitis in coded liver sections was compared. EAH-like lesions were found not only in mice immunized with liver antigens in CFA or IFA but also in mice injected with either CFA or IFA. Mice injected with HBSS alone showed no hepatitis. These results indicate that immunization with neither liver nor mycobacteria cell wall antigens is required for induction of EAH-like lesions and suggest that the EAH in C57Bl/6 mice may be a nonspecific inflammatory response to adjuvant oil.

T cell activation-associated hepatic injury: mediation by tumor necrosis factors and protection by interleukin 6

This study investigates the molecular mechanisms underlying the induction of and protection from T cell activation-associated hepatic injury. When BALB/c mice were given a single intravenous injection of concanavalin A (Con A) (> or = 0.3 mg/mouse), they developed acute hepatic injury as assessed by a striking increase in plasma transaminase levels within 24 h. Histopathologically, only the liver was injured while moderate infiltration of T cells and polymorphonuclear cells occurred in the portal areas and around the central veins. The induction of hepatic injury was dependent on the existence as well as the activation of T cells, as untreated BALB/c nu/nu mice or BALB/c mice pretreated with a T cell-specific immunosuppressive drug, FK506, failed to develop disease. Significant increases in the levels of various cytokines in the plasma were detected before an increase in plasma transaminase levels. Within 1 h after Con A injection, tumor necrosis factor (TNF) levels peaked, this being followed by production of two other inflammatory cytokines, interleukin 6 (IL-6) and IL-1. Passive immunization with anti-TNF but not with anti-IL-1 or anti-IL-6 antibody, conferred significant levels of protection. Moreover, administration of rIL-6 before Con A injection resulted in an IL-6 dose-dependent protection. A single administration of a given dose of rIL-6 completely inhibited the release of transaminases, whereas the same regimen induced only 40-50% inhibition of TNF production. More than 80% inhibition of TNF production required four consecutive rIL-6 injections. These results indicate that: (a) TNFs are critical cytokines for inducing T cell activation-associated (Con A-induced) hepatitis; (b) the induction of hepatitis is almost completely controlled by rIL-6; and (c) rIL-6 exerts its protective effect through multiple mechanisms including the reduction of TNF production.

Distinguishing between acute and symptomatic chronic hepatitis B virus infection

BACKGROUND/AIMS

Differentiating between an acute hepatitis B (AH-B) infection and an acute exacerbation of a chronic hepatitis B (CH-B) infection can present a problem for the clinician. The only current serological method of distinguishing between acute and symptomatic chronic hepatitis B virus (HBV) infection is the immunoglobulin M antibody to hepatitis B core antigen (anti-HBc) assay, which can be problematic. Therefore, in an attempt to better distinguish between acute and chronic HBV infection, sera from 26 patients with AH-B and 53 patients with CH-B were compared in a variety of experimental immunoassays.

METHODS

Experimental assays have been designed to detect free antibody to hepatitis B e antigen (anti-HBe), hepatitis B e antigen (HBeAg)/anti-HBe immune complexes (ICs), and hepatitis B surface antigens (HBsAg)/antibody to hepatitis B surface antigen (anti-HBs) in the presence of excess antigen. An additional assay was developed to detect a novel anti-HBc specificity, designated antibody to woodchuck hepatitis virus (anti-HBcW), which cross-reacts with the core antigen of the woodchuck hepatitis virus.

RESULTS

Sera from patients with CH-B showed significantly higher levels of free anti-HBe, HBeAg/anti-HBe ICs, and HBsAg/anti-HBs ICs compared with AH-B patient sera. Furthermore, patients with CH-B consistently produced high titer anti-HBcW, whereas patients with AH-B produced little or no anti-HBcW antibody.

CONCLUSIONS

The serology of AH-B infection and symptomatic CH-B infection can be distinguished using a variety of experimental immunoassays in addition to the immunoglobulin M anti-HBc assay.

Remission of experimental autoimmune hepatitis is associated with antigen-specific and non-specific immunosuppression

Experimental autoimmune hepatitis (EAH) is an animal model for autoimmune hepatitis. The disease is T cell-mediated and runs a subacute course, with maximal disease activity around week four after disease induction and a slow ensuing recovery. The aim of the present study was to investigate the immunoregulatory mechanisms that may account for recovery in EAH. It was found that T cell reactivity to liver antigens preceded histological disease, but at the peak of disease activity this T cell response was already suppressed. Active and antigen-specific suppression could be demonstrated, as irradiated splenocytes from animals at the beginning of recovery from EAH were able to suppress in vitro the T cell response to liver antigens by 42%. The response to an irrelevant antigen was suppressed by 16%, showing additional antigen non-specific suppression in vitro. The response to an in vivo immunization with an unrelated microbial antigen (tetanus toxoid) at the peak of disease was markedly reduced (by 90%). These data demonstrate in vitro and in vivo immunosuppression associated with the overcoming of and recovery from EAH. They stress the importance of immunoregulatory cycles in the control of autoimmune hepatitis.

Immunosuppression with cyclosporine during the incubation period of experimental woodchuck hepatitis virus infection increases the frequency of chronic infection in adult woodchucks

The immunosuppressive agent cyclosporine was given to adult woodchucks during acute experimental infection with woodchuck hepatitis virus (WHV). All 17 woodchucks given WHV alone or with a vehicle resolved the infection (i.e., zero chronicity), but when cyclosporine was given throughout the incubation and acute phases of infection (0-12 or 14 weeks; n = 12), the rate of chronic infection increased to 92%. When cyclosporine was given only during the incubation period (0-4 weeks; n = 10) or only during the acute phase of infection (2-12 weeks; n = 9), the rates increased to 50% and 55%, respectively. However, when the drug was given after the acute phase (8-18 weeks; n = 9), the chronic infection rate (11%) did not differ from that in untreated and vehicle controls. Immune responses inhibited by cyclosporine are important in resolution of acute WHV infection and occur mainly during the first 8 weeks. Immunosuppression of these responses for even short intervals during incubation (e.g., 0-4 weeks) increases the risk of chronicity.

Autoantibodies in experimental autoimmune hepatitis

Experimental autoimmune hepatitis (EAH) can be induced in mice by immunization with syngeneic soluble liver antigens in complete Freund's adjuvant. It has previously been shown that autoreactive T cells play an important role in this animal model of autoimmune hepatitis. We have studied the occurrence of liver autoantibodies in EAH. Characteristic autoantibodies appeared several weeks after disease induction and antibody titres continued to rise when histological and biochemical signs of disease activity had already regressed. Autoantibodies in EAH seemed to recognize autoantigens other than those present in autoimmune chronic active hepatitis patients. We conclude that autoantibodies arise in experimental autoimmune hepatitis but that these autoantibodies do not play a critical role in the pathogenesis of the disease.