Binding properties of mechanically and enzymatically isolated hepatocytes for IgG and C3

Expression of ECM proteins fibulin-1 and -2 in acute and chronic liver disease and in cultured rat liver cells

Fibulin-2 has previously been considered as a marker to distinguish rat liver myofibroblasts from hepatic stellate cells. The function of other fibulins in acute or chronic liver damage has not yet been investigated. The aim of this study has been to evaluate the expression of fibulin-1 and -2 in models of rat liver injury and in human liver cirrhosis. Their cellular sources have also been investigated. In normal rat liver, fibulin-1 and -2 were both mainly present in the portal field. Fibulin-1-coding transcripts were detected in total RNA of normal rat liver, whereas fibulin-2 mRNA was only detected by sensitive, real-time quantitative polymerase chain reaction. In acute liver injury, the expression of fibulin-1 was significantly increased (17.23-fold after 48 h), whereas that of fibulin-2 was not modified. The expression of both fibulin-1 and -2 was increased in experimental rat liver cirrhosis (19.16- and 26.47-fold, respectively). At the cellular level, fibulin-1 was detectable in hepatocytes, "activated" hepatic stellate cells, and liver myofibroblasts (2.71-, 122.65-, and 469.48-fold over the expression in normal rat liver), whereas fibulin-2 was restricted to liver myofibroblasts and was regulated by transforming growth factor beta-1 (TGF-beta1) in 2-day-old hepatocyte cultures and in liver myofibroblasts. Thus, fibulin-1 and -2 respond differentially to single and repeated damaging noxae, and their expression is differently present in liver cells. Expression of the fibulin-2 gene is regulated by TGF-beta1 in liver myofibroblasts.

Antibody-dependent enhancement of hepatitis C virus infection

Hepatitis C virus (HCV) often causes a persistent infection associated with hypergammaglobulinemia, high levels of antiviral antibody and circulating immune complexes, and immune complex disease. We previously reported that only a limited neutralizing activity to vesicular stomatitis virus or HCV pseudotype is generated in animals immunized with recombinant HCV envelope proteins and chronically infected HCV patient sera. Interestingly, when some of these neutralizing sera were diluted into a range of concentrations below those that reduced virus plaque number, an increase in pseudotype plaque formation was observed. Purified HCV E2-specific human monoclonal antibodies were used to further verify the specificity of this enhancement, and one- to twofold increases were apparent on permissive Huh-7 cells. The enhancement of HCV pseudotype titer could be inhibited by the addition of a Fc-specific anti-human immunoglobulin G Fab fragment to the virus-antibody mixture prior to infection. Treatment of cells with antibody to Fc receptor I (FcRI) or FcRII, but not FcRIII, also led to an inhibition of pseudotype titer enhancement in an additive manner. Human lymphoblastoid cell line (Raji), a poor host for HCV pseudotype infection, exhibited a four- to sixfold enhancement of pseudotype-mediated cell death upon incubation with antibody at nonneutralizing concentrations. A similar enhancement of cell culture-grown HCV infectivity by a human monoclonal antibody was also observed. Taken together, antibodies to viral epitopes enhancing HCV infection need to be taken into consideration for pathogenesis and in the development of an effective vaccine.

Localization of the sulfate/anion exchanger in the rat liver

Although the sulfate/anion transporter (sat-1; SLC26A1) was isolated from a rat liver cDNA library by expression cloning, localization of sat-1 within the liver and its contribution to the transport of sulfate and organo sulfates have remained unresolved. In situ hybridization and immunohistochemical studies were undertaken to demonstrate the localization of sat-1 in liver tissue. RT-PCR studies on isolated hepatocytes and liver endothelial and stellate cells in culture were performed to test for the presence of sat-1 in these cells. In sulfate uptake and efflux experiments, the substrate specificity of sat-1 was evaluated. Sat-1 mRNA was found in hepatocytes and endothelial cells. Sat-1 protein was localized in sinusoidal membranes and along the borders of hepatocytes. The canalicular region and bile capillaries were not stained. Sulfate uptake was only slightly affected by sulfamoyl diuretics or organo sulfates. Sulfate efflux from sat-1-expressing oocytes was enhanced in the presence of bicarbonate, indicating sulfate/bicarbonate exchange. Estrone sulfate was not transported by sat-1. Sat-1 may be responsible for the uptake of inorganic sulfate from the blood into hepatocytes to enable sulfation reactions. In hepatocytes and endothelial cells, sat-1 may also supply sulfate for proteoglycan synthesis.

Cellular localization of hepatic cytochrome 1B1 expression and its regulation by aromatic hydrocarbons and inflammatory cytokines

Cytochrome P450 1B1 (CYP1B1) is an activator of several xenobiotics and is induced in the liver upon experimental exposure to aromatic hydrocarbons. Since its cellular localization and regulation are incompletely clarified, Cyp1B1 expression and inducibility by 9,10-dimethyl-1,2-benzanthracene (DMBA) and inflammatory cytokines were investigated in different rat liver cell populations in vitro and in the liver during hepatocellular injury. Expression of Cyp1B1 was studied by Northern blot analysis in hepatic stellate cells (HSCs), myofibroblasts (MFs), Kupffer cells (KCs), and hepatocytes at various time points of primary cultures and in acutely damaged rat liver (carbon tetrachloride model). Enzyme inducibility was assessed by incubation of cells with DMBA as well as, in the case of HSCs, with tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor beta1 (TGFbeta1). Cyp1B1 messengers were expressed at high levels by HSCs and MFs, whereas constitutive expression was not detectable in KCs or in hepatocytes. Cyp1B1-specific mRNA were expressed at highest levels in HSCs at an early stage of activation (2 days after plating) and were diminished upon further activation. DMBA strongly enhanced Cyp1B1 gene expression in HSCs, MFs, and in hepatocytes at day 3 of primary cultures, but not in hepatocytes at day 1, or in KCs. The inflammatory cytokine TNF-alpha enhanced the Cyp1B1 gene expression in HSCs, either when administered alone or in addition to DMBA, while TGFbeta1 did not affect Cyp1B1 expression, even after DMBA induction. We conclude that HSCs and MFs seem to be the major cellular sources of hepatic Cyp1B1 expression and that the constitutive expression of the Cyp1B1 gene and the responsiveness to DMBA stimulation differ between mesenchymal and parenchymal liver cells, indicating a cell-specific regulation of Cyp1B1 gene expression. Interestingly, TNF-alpha is a potent stimulator of the Cyp1B1 gene in HSCs and acts in concert with DMBA.

Liver cell uptake and degradation of soluble immunoglobulin G immune complexes in vivo and in vitro in rats

Immune complexes were formed between dinitrophenylated human serum albumin (DNP-HSA) and polyclonal rabbit immunoglobulin G (IgG) anti-DNP antibodies at antibody excess. The antigen was labelled with isotope (125I-tyramine-cellobiose) or fluorochrome, (6-[fluorescein-5-(and-6)-carboxamido] hexanoic-acid, succinimidyl ester). The radiolabelled antigen, native or antibody complexed, was given intravenously to rats. Radioactivity was measured in various organs at 1 hour following injection. The liver was the main site for removal of the antigen as well as of the immune complexes. Within the liver, immune complexes were mainly associated with nonparenchymal liver cells, the total recovery from Kupffer cells being about 10 times greater than from the liver endothelial cells. The uncomplexed radiolabelled antigen was readily degraded by both cells types. After IgG complexing, the degradation decreased, both in Kupffer cells and in liver endothelial cells. In vitro experiments with isolated liver cells, showed that IgG complexing increased antigen uptake to about the same extent in Kupffer cells and in liver endothelial cells. The degradation of both antigen and immune complexes was less efficient in vitro than in vivo. Immune complex uptake in vitro was shown also by confocal fluorescence microscopy in Kupffer cells and in liver endothelial cells. Also in vitro, only minor uptake was found in the hepatocytes. We conclude that both liver endothelial cells and Kupffer cells are involved in the hepatic handling of soluble IgG immune complexes, but we found no evidence for substantial uptake by hepatocytes.

Autoantibody against a 78 kDa membrane protein of HepG2 cell in the sera of patients with alcoholic liver diseases

Sera from 14 normal control subjects, 30 patients with alcoholic liver diseases (fatty liver, n = 8; hepatitis, n = 13; liver cirrhosis, n = 9), 7 controls with chronic hepatitis B, and 8 controls with chronic hepatitis C were masured for their concentrations of antibodies against HepG2 membrane protein by a binding assay utilizing 125I-labeled protein A. When the cut-off level was set as the mean value plus 2 SD of normal control subjects, the incidence of positivity was 75%, 69.2%, and 77.8% in patients with alcoholic fatty liver, alcoholic hepatitis, and alcoholic cirrhosis, respectively. Both the mean serum antibody values and the positive incidence were significantly higher in patients with alcoholic liver diseases than in either the normal controls or in the control patients with chronic hepatitis. Sodium dodecylsulfate polyacrylamide gel electrophoresis of 125I-labeled HepG2 membrane protein precipitated with IgG from patients with alcoholic liver diseases revealed an immunoreactive band at a molecular weight of 78,000 daltons (gp78). The antibody activity remained after immunoabsorption by human liver-specific lipoprotein (LSP) but decreased when HepG2 cells were pre-treated with trypsin or neuraminidase. Consequently, gp78 appears to be a glycoprotein distinct from LSP, and is specifically recognized by IgG from patients with alcoholic liver diseases. This assay may provide a new system to measure autoantibody to hepatocytes in alcoholic liver diseases.

Expression of von Willebrand factor in normal and diseased rat livers and in cultivated liver cells

Von Willebrand factor (vWf) is an adhesive glycoprotein known to play an important role in hemostasis and in tissue injury. Because the latter process resembles hepatic fibrogenesis, we studied the tissue distribution of vWf in diseased livers. In normal rat liver vWf was strongly expressed in the vascular endothelium and as small spots or fiber-like structures in the hepatic parenchyma. During acute liver injury, pronounced staining was observed within the area of necrosis. In fibrotic livers vWf deposits were distributed predominantly at the scar-parenchyma interface but also within the septum and in sinusoidal lining cells. Testing different liver cell populations in vitro demonstrated that vWf gene expression was limited to endothelial cells (ECs) and, therefore, the latter cell population might represent the vWf-positive cells detected in vivo. The distribution of vWf within fibrotic septa suggests that vWf becomes a component of the extracellular matrix (ECM) in fibrotic livers.

C1 esterase inhibitor gene expression in rat Kupffer cells, peritoneal macrophages and blood monocytes: modulation by interferon gamma

Kupffer cells (KC) represent the main part of the tissue macrophages. Beside phagocytosis of particulate material, involvement of KC in immunological and inflammatory reactions has been supposed. As C1 esterase inhibitor (C1-INH) is a serine protease inhibitor involved in such processes, the aim of this work was to study C1-INH synthesis in KC and, by comparison, in peritoneal macrophages (PM) and blood monocytes (MC) of the rat. C1-INH synthesis was studied on the protein level by biosynthetic labeling, immunoprecipitation, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis, and on the RNA level by Northern blotting of total RNA or by in situ hybridization. KC were found to express C1-INH gene spontaneously. C1-INH synthesis represents 1.3 +/- 0.2% of total protein synthesis at day 1 of culture and the absolute amount each cell synthesis remains constant during the whole time in culture. Transcripts of C1-INH were detected both in freshly isolated and in cultured KC. In contrast, spontaneous C1-INH gene expression was not detectable in freshly isolated PM, but only in cultured PM. In MC, C1-INH was not detectable at any time, whatever. Treatment of the cells with interferon gamma increased C1-INH synthesis in KC and in PM and caused an induction of C1-INH synthesis in MC. The results suggest that constitutive C1-INH synthesis is a functional marker for mature tissue macrophages.

Synthesis of cellular fibronectin by rat liver fat-storing (Ito) cells: regulation by cytokines

Fibronectins are multifunctional extracellular matrix glycoproteins that seem to play a pacemaker role in liver fibrogenesis. The expression of cellular fibronectin by rat liver fat-storing cells in primary culture and their modulation by cytokines was studied. Cellular fibronectin was localized in the cytoplasm and on the surface of cultured fat-storing cells as well as in extracellular matrix fibrils by indirect immunofluorescence. Immunoprecipitation of endogenously labeled fibronectin using type specific antibodies showed the synthesis and secretion of cellular fibronectin by fat-storing cells in vitro. ED1 positive sequences specific for cellular fibronectin and absent in plasma fibronectin were detected within the total RNA of fat-storing cells. Cellular fibronectin synthesis was severalfold enhanced in "activated" vs. "resting" fat-storing cells. Treatment of fat-storing cells with transforming growth factor beta 1 resulted in a dose dependent increase of fibronectin synthesis. In contrast, interferon gamma inhibited the synthesis of fibronectin. The stimulation of fibronectin synthesis by transforming growth factor beta 1 and the inhibition by interferon gamma might be of importance for pathophysiology and therapy of liver fibrogenesis.

Endocytosis of soluble IgG immune complex and its transport to lysosomes in hepatic sinusoidal endothelial cells

Both Kupffer cells and sinusoidal endothelial cells are engaged in the hepatic uptake of soluble IgG immune complex (IgG-IC) through Fc-receptors on their surface. Hepatocytes have also been reported to take up IgG-IC. It remains unclear, however, whether the endothelial cell degrades IgG-IC and whether the hepatocyte participates in IgG-IC clearance. In this study, normal mice received a single intravenous injection of soluble immune complex preformed in antigen excess, i.e. bovine serum albumin (BSA) anti-BSA-mouse-IgG complex (BABIgG) or BSA anti-BSA-mouse-F(ab')2 complex (BABF(ab')2), or BSA alone. An immunoperoxidase study for BSA showed that from 1 to 120 min after injection only BABIgG was ingested by both endothelial cells and Kupffer cells but not by hepatocytes. The staining intensity of BABIgG was maximal at about 15 min and decreased subsequently. Endocytosis of BABIgG occurred through coated pits in the endothelial cells. Within a few minutes, endocytosed BABIgG was found in tubulovesicular structures and large vesicles. The occasional large vesicles were shown to be lysosomes by simultaneous demonstration of BABIgG with acid phosphatase. BABIgG was not found on either of the endothelial and hepatocellular surfaces facing the space of Disse or in hepatocytes. These results indicate that soluble IgG-IC is endocytosed by sinusoidal endothelial cells and degraded in the lysosomes and that the participation of hepatocytes in the clearance of IgG-IC is improbable.

Tenascin gene expression in rat liver and in rat liver cells. In vivo and in vitro studies

Tenascin is a major glycoprotein constituent of the extracellular matrix with a strong affinity to fibronectin; its distribution is believed to be temporarily and spatially limited. Tenascin gene expression is increased during wound healing processes. As repair mechanisms in chronic liver diseases resemble wound healing we studied tenascin gene expression in rat liver and in isolated rat liver cells. In normal rat liver a tenascin specific antiserum stains sinusoidal cells with fiber-like prolongations, which at the same time are desmin-positive (ITO-cells). In the CCl4-acutely-damaged liver a strong tenascin staining is detected in cells located among the mononuclear cells of the inflammatory infiltrates in the areas of necrosis and in cells of the sinusoids. In CCl4-chronically-damaged liver a strong tenascin staining is demonstrable in the connective tissue septa. In both cases, many of the tenascin-positive cells can be identified as desmin-positive by means of the double-staining fluorescence technique. The wall of larger vessels is always tensacin-negative. The staining pattern obtained with a fibronectin-specific antiserum is somewhat comparable with that of tenascin but the vessel wall was positive. hepatocytes, Kupffer cells, ITO-cells and endothelial cells were isolated from rat liver and studied for their capacity to express the tenascin gene. Biosynthetically labeled tenascin was immunoprecipated from supernatants and cell lysates obtained from cultured ITO-cells and to a much lesser extent from intracellular lysates obtained from endothelial cells; its synthesis in ITO-cells increased during the time in culture. Tenascin was also identified immuno-cytochemically in increasing amount in ITO-cells in culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of the gene of the alpha-smooth muscle-actin isoform in rat liver and in rat fat-storing (ITO) cells

Fat storing cells (FSCs) in the liver represent the main site of vitamin A deposition in the body. These cells are considered to play an important role during scar formation and fibrogenesis in the liver. The putative descent of FSCs from the fibroblastic or from the myofibroblastic system have not been determined yet by morphological or immunohistochemical studies. To further define the origin of these liver cells, we analysed the pattern of expression of three structural proteins: vimentin, desmin and the alpha-smooth muscle (SM)-actin isoform in FSCs of the rat liver, in smooth muscle cells (SMCs) from the aorta and in rat skin fibroblasts. FSCs were studied by immunohistochemical methods immediately after isolation, at days 3 and 7 after plating. FSC-gene-expression was also analysed by Northern blot analysis of total RNA extracted from cells in culture at days 3 and 7 after isolation. Arterial SMCs and skin fibroblasts were studied in a similar way. For comparison, isolated rat hepatocytes and Küpffer cells (Kc) were studied. Of freshly isolated FSCs, 100% were vimentin-positive, 50% were desmin-positive, but all were alpha-SM-actin negative. Three days after isolation, FSCs were clearly positive for vimentin and desmin and weakly alpha-SM-actin-positive, as demonstrated by indirect immunofluorescence as well as by the immunoperoxidase technique. Desmin, alpha-SM-actin and vimentin staining was further increased at day 7 after isolation, and alpha-actin specific transcripts in FSC-RNA were clearly detectable at day 7 after isolation. Passaged arterial SMCs were vimentin- and alpha-SM-actin-positive, but desmin-negative and fibroblasts were only vimentin-positive.(ABSTRACT TRUNCATED AT 250 WORDS)

Lymphocytes from hepatic inflammatory infiltrate kill rat hepatocytes in primary culture. Comparison with peripheral blood lymphocytes

In the last few years it has become possible in the liver to isolate lymphocytes from inflammatory infiltrates and to culture them in vitro. Most of the lymphocyte clones obtained are CD 8+ cytotoxic cells, but interactions between these lymphocytes and hepatocytes in primary culture have not been analysed previously. In this study, cloned human T lymphocytes from liver biopsies and from the peripheral blood of patients with chronic hepatitis B or primary biliary cirrhosis, after phenotypical and functional characterization into CD 8+ or CD 4+ cytotoxic lymphocytes, were activated in an antigen-independent fashion by adding either anti CD 3 or anti CD 2/R-3 monoclonal antibodies to the cell suspension. The activated cells were then coincubated with rat hepatocytes in primary culture. The killing capacity of the activated lymphocytes was monitored by light and electron microscopy and by measurement of lactic dehydrogenase (LDH)-release into the culture medium. It was found that cytotoxic CD 8+, but not CD 4+ helper lymphocytes very effectively killed hepatocytes. The killing effect was dependent on the time of cocultivation and on effector-target (E/T) ratio. Total breakdown of the hepatocyte monolayer was achieved after 10-20 h coculture and at an E/T ratio of 10 to 1. As LDH-release in the culture medium reached about 80% of the total LDH-content, most of the hepatocytes were lysed by activated lymphocytes. Cytotoxic activity of clones obtained from different biopsies was comparable with that of clones from peripheral blood. Hepatocytes in primary culture seem to be very sensitive to the killing capacity of activated cytotoxic lymphocytes.

Rabbit hepatocytes in primary culture: preparation, viability and use in studies of propranolol metabolism

Isolated hepatocyte cultures have become a frequently used model system for investigating drug metabolism. Although rat and hamster hepatocytes are frequently used for this purpose, metabolism in these species differs in many respects from human metabolism. A species with a metabolism more closely resembling that of humans might be more useful. Our in vivo experiments demonstrated that the metabolism of propranolol in the rabbit is more similar to that in humans than in rats or hamsters. We therefore examined the usefulness of rabbit parenchymal liver cells for studies of propranolol metabolism. A detailed method is presented for their preparation and culture, along with data on their viability, structure and protein synthesizing capability. One- or two-day-old hepatocyte cultures were exposed to 10 mumol/L 3H-propranolol from 30 min to 2 hr; metabolites were identified by gas chromatography-mass spectrometry and quantitated by high-performance liquid chromatography. Propranolol metabolism was linear over 1 hr, with 15% of the substrate metabolized during this time. The cytochrome P-450 pathways, which result in ring oxidation and side-chain oxidation, were expressed in a reproducible fashion similar to that found in vivo in humans. The arylhydrocarbon hydroxylase inhibitor alpha-naphthoflavone (100 mumol/L) inhibited side-chain oxidation of propranolol by 90% without affecting ring oxidation. In contrast, chlorpromazine (100 mumol/L) was shown to inhibit ring oxidation of propranolol by 85% without affecting side-chain oxidation. Cimetidine (250 mumol/L) inhibited both pathways by about 50%.(ABSTRACT TRUNCATED AT 250 WORDS)

Liver membrane antibodies (LMA) recognize a 26-kD protein on the hepatocellular surface

Sera from 82 patients with chronic inflammatory liver diseases and from patients with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA) and Hashimoto's thyroiditis were studied by immunoblotting against purified liver plasma membranes (LPM) and soluble liver protein (SLP) fractions from different species after previous separation by SDS-PAGE. Eighteen of 19 sera with LMA of IgG type in immunofluorescence assay and six LMA-negative sera (three sera from patients with RA) showed antibodies of the IgG or IgM classes against a protein with a molecular weight of 26 kD which was present in LPM and SLP fractions from rats, rabbits, pigs and humans. The reaction with 26-kD liver protein did not correlate with other known autoantibody-antigen systems. All sera were negative in the 26-kD region with liver mitochondria, liver microsomes and soluble proteins of kidney (with one exception), heart and gut from the rat. The 26-kD protein was purified by affinity chromatography on immobilized anti-26-kD protein antibodies from patients, eluted from the 26-kD band of immunoblots. Studies with purified 26-kD liver protein and with SLP as antigens after separation in two-dimensional electrophoresis confirmed that patient serum and experimental rabbit antiserum react with the same protein. Eluted patient antibodies and rabbit antisera showed a linear fluorescence pattern on isolated hepatocytes from rat and rabbit. The data indicate that one of the target antigens of LMA is a species-nonspecific 26-kD protein located on the hepatocellular surface.

Fat-storing (Ito) cells of rat liver synthesize and secrete apolipoproteins: comparison with hepatocytes

Fat-storing cells of the liver store most of the vitamin A of the body. Vitamin A is present in a few large fat droplets within the cell. The aim of our study was to investigate apolipoprotein biosynthesis in isolated fat-storing cells from rat liver during the time in culture. Isolated rat hepatocytes were studied for comparison. Proteins were biosynthetically labeled and further identified by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Apoproteins in culture supernatants were identified by density gradient ultracentrifugation and by one- and two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of aliquots of the gradient. Rat plasma was processed in the same way and used for comparison. Fat-storing cells synthesized and secreted apoprotein E, apoprotein A-I, apoprotein A-IV, and low amounts of apoprotein C. The synthesis of these proteins increased during the culture time, reaching a maximum at the fifth day after isolation. The proteins were identified mostly as apoproteins of high-density lipoprotein. Hepatocytes synthesized and secreted apoproteins of all classes of lipoproteins. The distribution of high-density lipoprotein apoproteins was similar to that of fat-storing cells but hepatocytes produced larger amounts of the apoproteins.

Murine tissue macrophages synthesize and secrete amyloid proteins different to amyloid A (AA)

We recently demonstrated that serum amyloid A (SAA) gene expression can be induced in extrahepatic sites with exception of the brain. Furthermore we demonstrated that tissue macrophages express SAA-gene constitutively and that SAA-gene expression can be increased by endotoxin. Until now the protein corresponding to the SAA-specific mRNA contained in macrophages has not been identified. We compared proteins precipitated from endogenously labelled samples by three antisera against amyloid A (AA) raised in different laboratories. Radiolabelled samples were derived from murine hepatocyte cultures, from cell-free translation of acute phase liver RNA or hepatocytes RNA and from peritoneal macrophages as well as Kupffer cells. All three antisera recognize a protein of 12.5 kDa Mr produced by hepatocytes (SAA), and a major protein of 14.3 kDa Mr contained in the cell-free translation products; this is the precursor of the mature SAA as demonstrated by cleavage experiments with canine pancreas microsomal enzymes. The antisera also recognize two proteins--a major one of 14.5 kDa Mr and a second of 12.5 kDa Mr contained in the supernatants and cell lysates of liver and peritoneal macrophages. New antisera raised against the two proteins do not recognize any protein, either of hepatocyte or of cell-free translation samples; they specifically precipitate two proteins from macrophage samples with the same molecular mass as that of the proteins precipitated by the anti SAA antisera. Murine acute phase sera do not react with the new antisera. However, amyloid deposits of amyloidotic mice specifically react with the new antisera. We describe two new components of murine amyloid produced by tissue macrophages.

Antigenical alterations of hepatocyte membrane in rats after long-term administration of ethanol and carbon tetrachloride

The presence of IgG over the hepatocyte's surfaces in ethanol- and/or carbon tetrachloride-pretreated rats was demonstrated as a very thin lineal fluorescent deposition around the membrane. The percentage of parenchymal IgG-positive liver cells ranged between 15 and 100% in all animals of treated groups. This suggests that ethanol may induce hepatic injury mediated by IgG autoantibodies which may be a response to an antigenical determinant present in hepatocytes altered by ethanol and/or carbon tetrachloride treatment.

Alpha- and gamma-interferon (IFN alpha, IFN gamma) but not interleukin-1 (IL-1) modulate synthesis and secretion of beta 2-microglobulin by hepatocytes

Soluble serum beta 2-microglobulin has been thought to result from membrane shedding by activated T-lymphocytes. This hypothesis could explain the increase of beta 2-microglobulin serum levels during virally induced mononucleosis, but not elevated levels as observed in other virally induced and in malignant diseases. In this paper we demonstrate that beta 2-microglobulin is a true secretory protein, and that its synthesis in hepatocytes is modulated by IFNs but not by IL-1. While the 45,000 MW HLA antigen can be found only in cell lysates, beta 2-microglobulin is shown to be secreted also into the culture medium like other secretory proteins (e.g. albumin-factor B-complement C3). Furthermore, interferon alpha (IFN alpha) as well as interferon gamma (IFN gamma) directly stimulate, in a dose- and time-dependent manner, beta 2-microglobulin synthesis by human hepatoma cells (Mz-Hep-1 and PLC/PRF5) and murine hepatocyte primary cultures. The increase of beta 2-microglobulin production induced by interferons is demonstrated at both the protein and the RNA level, indicating that interferon acts at a pretranslational level. The interferon effect on beta 2-microglobulin synthesis is specific since synthesis of secretory proteins like complement C3 or albumin, and of a structural protein like actin, remains unchanged. In contrast to IFN, IL-1, the main mediator of acute phase response, does not change beta 2-M biosynthesis rate. These data indicate that (i) beta 2-microglobulin is a secretory protein, (ii) IFNs but not IL-1 can mediate increased beta 2-M serum levels, and (iii) the liver may be its primary source.

Interleukin 6, the third mediator of acute-phase reaction, modulates hepatic protein synthesis in human and mouse. Comparison with interleukin 1 beta and tumor necrosis factor-alpha

Interleukin 6 (IL6) is the new definition of a group of cytokines previously named according to their biological activity, e.g. B cell stimulatory factor 2 (BSF-2), hybridoma plasmocytoma-growth factor (HGF), interferon-beta 2 (IFN-beta 2), hepatocyte stimulating factor (HSF). It has recently been suggested that IL6 may represent the major mediator of acute-phase protein response whereas IL1 beta and TNF-alpha could play a minor role. We compared the effect of the three cytokines on hepatic protein synthesis by performing in vitro as well as in vivo experiments. Human hepatoma cells (PLC/PRF5) were exposed to each cytokine separately for 20 h, and the effect was then studied at the protein and RNA level. All three cytokines reduced albumin and increased C3 and ceruloplasmin biosynthesis. The cytokines induced the same effect at the RNA level indicating that the modulation was pretranslational. The effect of the cytokines was specific since actin gene expression was not changed; furthermore the effect was blocked by specific antibodies against the cytokines. The effect of the single cytokines was dose and time dependent, and quantitatively comparable. None of the cytokines was able to alter alpha 1-anti-trypsin synthesis. In vivo experiments with mice showed that IL1 beta and TNF-alpha both induce serum amyloid A (SAA) mRNA in the mouse liver and increase factor B (Bf) gene expression. Human recombinant IL6 induced SAA gene expression and it also had a weak positive effect on Bf gene expression after i.p. injection. These data demonstrate that the three cytokines studied are quantitatively and qualitatively comparable, and that all three are probably involved in acute-phase protein response.

Differences of liver membrane antibody frequency in alcoholic liver disease. Detection of IgG and IgA classes using radioimmunoassay

The presence of liver membrane antibody in IgG and IgA was investigated by radioimmunoassay using isolated rabbit hepatocytes as target cells. This technique was more sensitive than the immunofluorescent method. IgG liver membrane antibodies were positive in 24% of patients with alcoholic liver disease. IgA liver membrane antibodies were detected in 58% of patients with alcoholic liver disease, whereas they were detected only in 21% of those with nonalcoholic liver disease, except for cases of autoimmune chronic active hepatitis. In alcoholic liver disease, IgA liver membrane antibodies were detected at a high frequency in a group of patients with alcoholic hepatitis and active cirrhosis (94%) as compared with that of fatty liver, hepatic fibrosis, and inactive cirrhosis (42%). These results suggest that alcoholic liver disease is characterized in part by a humoral immune response of IgA liver membrane antibodies.

Methods for quantitating HLA gene product expression in the liver during hepatitis B virus infection

HLA antigens play an important role in the immunological responses to transplanted organs and in tumor surveillance and antiviral immunity. In several liver diseases qualitative and quantitative changes in the HLA gene product expression can be found on hepatocytes, bile duct epithelium and sinusoidal lining cells and these changes may affect the efficacy of the immune system in recognizing an exogenous antigen. In this paper we describe methods for quantitating the changes in HLA antigen expression occurring in the liver during various phases of hepatitis B virus infection and the way in which we have attempted to identify possible mechanisms leading to chronicity.

Localization of Fc receptors on liver sinusoidal endothelium. A histological study by electron microscopy

The localization of Fc receptors for IgG on mouse liver sinusoidal endothelium was studied in tissue sections by light and electron microscopy using peroxidase-antiperoxidase IgG complexes as ligands. Light microscopy revealed that Fc receptors were continuously present along the sinusoidal wall, but absent on the endothelium of the central vein and that of the portal area blood vessels. Electron microscopy revealed Fc receptors on both the luminal and basal aspects of the plasma membrane, far more being present on the former, on the walls of cytoplasmic fenestrae, and abundantly on the walls of coated pits and vesicles of sinusoidal endothelial cells. Fc receptors were found more frequently on sinusoidal endothelial cells than on Kupffer cells. Fat-storing cells lacked the receptors and hepatocytes showed an ambiguous result which was considered to be nonspecific.

Immunoglobulin on the surface of isolated hepatocytes is associated with antibody-dependent cell-mediated cytotoxicity and liver damage

Hepatocytes isolated from patients with chronic liver disease are often covered by immunoglobulin. The aim of the present study was to establish whether this surface immunoglobulin (SIg) mediates liver cell damage. Freshly isolated hepatocytes from percutaneous liver biopsy of 16 patients with chronic active hepatitis (CAH) (6 HBsAg positive), 3 with HBsAg-positive chronic lobular hepatitis (CLH), 5 with HBsAg-positive chronic persistent hepatitis (CPH) and 12 with minor histological abnormalities (MHA) (5 HBsAg positive) were divided into two aliquots. One was studied for the presence of membrane-bound immunoglobulin and the third component of complement by direct immunofluorescence and the other was incubated, in an allogeneic cytotoxic assay, with peripheral blood mononuclear cells prepared from healthy volunteers as a source of effectors for antibody-dependent cell-mediated cytotoxicity (ADCC). Liver biopsies were scored for portal and parenchymal inflammatory activity. The percentage of SIg positive hepatocytes was significantly higher in patients with CAH (median 52.5%) than in patients with CLH/CPH (20.5%) or in patients with MHA (1%). Percentages of SIg-positive liver cells were significantly correlated with total liver biopsy scores and with both portal or parenchymal scores considered independently. SIg were found to belong to the IgG class in all groups of patients. When hepatocytes were cultured with normal human lymphocytes, allogeneic cytotoxicity values were significantly higher in patients with CAH (median 34%) than in patients with CLH and CPH (18%) or in those with MHA (12%). Percentage cytotoxicity was positively correlated with total biopsy scores and with portal activity but not with parenchymal activity, suggesting that ADCC might play a damaging role mainly in the portal areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Sinusoidal endothelial cells from guinea pig liver synthesize and secrete cellular fibronectin in vitro

Endothelial liver cells were obtained from guinea pig by enzymatic digestion and centrifugal elutriation. Cells were cultured on gelatin and fibronectin pretreated culture vessels. Endothelial cells were characterized by phase-contrast microscopy, electron microscopy and the presence of Factor VIII-related antigen. Fibronectin secretion was determined in cell-free supernatants by a sensitive and specific ELISA and localized on fixed cultured cells by immunofluorescence. [35S]Methionine endogeneously labeled fibronectin was immunoprecipitated from supernatants and cellular lysates and displayed on sodium dodecyl sulfate polyacrylamide slab gel electrophoresis. After attachment to the culture vessel, one day after plating, endothelial cells start to produce fibronectin as measured by ELISA and demonstrated by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Secretion of fibronectin increases as cells proliferate to form a confluent monolayer. By immunofluorescence, fibronectin is visualized inside permeabilized cells and as a fibrillar network on the cell surface. Underneath the cell bodies, fibronectin-positive material is present as short strands. From supernatants and cellular lysates, fibronectin is immunoprecipitated with an apparent Mr of about 235,000 obviously larger than plasma fibronectin with an Mr of 220,000, which behaves electrophoretically like fibronectin isolated from early hepatocyte cultures. As endothelial cells incorporate [3H]fucose in fibronectin, whereas hepatocytes do not, we conclude that endothelial cells in contrast to hepatocytes produce cellular fibronectin. Endothelial cells, therefore, are probably the cellular source of the fibronectin present in the space of Disse. The significance of this finding with respect to fibrotic liver disease is discussed.

Liver membrane autoantibodies in chronic active hepatitis. Studies on mechanically and enzymatically isolated rabbit hepatocytes

Target antigens relevant for immune reactions in inflammatory liver diseases should be expressed on the hepatocellular membrane. Using mechanically or enzymatically isolated rabbit hepatocytes, we evaluated the influence of cell integrity on the detection of membrane-expressed antigens by sera from patients with chronic hepatitis and by murine monoclonal antibodies. Our results provide evidence that target antigens of liver membrane autoantibodies (LMA) as well as liver kidney microsomal antibodies (LKM) are not expressed on the hepatocellular membrane of viable and intact isolated rabbit hepatocytes. However, LMA were detected in the sera of 56% of patients with autoimmune chronic active hepatitis using mechanically isolated hepatocytes. These findings underline the diagnostic relevance of the autoantibodies. It is suggested that LMA are directed against constituents of the cytoskeleton. Therefore, it seems to be unlikely that this antibody is causally involved in the pathogenesis of autoimmune liver diseases.

Expression of Ia-antigens on guinea pig Kupffer cells. Studies with monoclonal antibodies

The expression of the Ia-antigen on guinea pig Kupffer cells was studied employing two monoclonal antibodies against two different determinants of the Ia-molecule. The study was performed in situ on liver sections and on isolated highly purified Kupffer cells kept in culture up to 6 days. The influence of guinea pig hepatocyte culture supernatant and of supernatants of phytohemoagglutinin (PHA)-stimulated human peripheral blood lymphocytes (PBL) on the Ia expression was measured. Immunofluorescence staining of cryostat sections revealed that the monoclonal antibodies used are able to detect Ia-antigens on liver macrophages in situ. The in vitro studies strongly suggest that all Kupffer cells are able to express Ia-antigens. The expression of Ia-antigens on Kupffer cells decreased during the culture time and was no longer detectable on day 5. At this time, incubation of the cell cultures with PBL conditioned medium induced the reexpression of Ia-antigens. Supernatants from guinea-pig hepatocyte cultures did not have any negative influence on the expression of the Ia-antigen on Kupffer cells in vitro. These data support the hypothesis that liver macrophages have the potential to behave immunologically as accessory cells and might contribute to local immune responses in acute as well as chronic states of liver diseases.

Biosynthesis of the third (C3), eighth (C8), and ninth (C9) complement components by guinea pig hepatocyte primary cultures

In the present report guinea pig hepatocyte primary cultures were established in order to study the synthesis of the eighth (C8) and ninth (C9) complement component. As reference-protein, the third complement component (C3) was measured antigenetically and hemolytically. Synthesis of C8 and C9 was determined by means of the hemolytic activity of the culture supernatant harvested every 24 h during a 6-day incubation period in vitro. The data to be reported demonstrated that the hepatocytes are able to synthesize spontaneously and secrete C8 and C9; in their culture medium a hemolytic activity of about 15-25 X 10(8) em/10(6) cells/24 h for C8 and of 25-90 x 10(8) em/10(6) cells/24 h for C9 were found. The same hepatocyte cultures produced 2500-6000 micrograms/10(6) cells/24 h of C3. Hemolytic C3 activity was also found in the culture media. The synthesis of C8 and C9 could be reversibly inhibited by addition of 30-50 micrograms cycloheximide per ml of culture medium. The kinetics of synthesis show a slight decrease after the first day of culture and a recovery in the following days up to a rate that is two- to threefold higher than that of the first day. The data suggest that hepatocytes could contribute to the production of C8 and C9 present in the plasma.

Mechanically isolated hepatocytes are unsuitable to detect antibodies directed against plasma membrane determinants

The ultrastructural morphology of mechanically and enzymatically isolated hepatocytes was compared. Plasma membrane integrity was evaluated by electron microscopy, both in the absence and in the presence of ruthenium red, which stains cell coat glycoproteins and makes it possible to identify even partially permeable cells, and by indirect immunofluorescence using experimental antibodies directed against epithelial submembranous components (prekeratin, actin). In order to evaluate the antigenic integrity of the hepatocellular plasma membrane after the isolation procedures, an immuno-electronmicroscopical technique (Staph. pA-colloidal gold) was applied using the IgG fraction from two liver-kidney microsomal antibody (LKM) positive sera, known to react with both plasma membranes and smooth endoplasmic reticulum (SER). Enzymatic procedure made it possible to isolate hepatocytes with a good preservation of both plasma membranes and subcellular organelles. Ruthenium red staining was confined to plasma membranes, thus indicating the preservation of both cell-coat glycoproteins and plasma membrane. Most cells were negative after exposure to experimental antibodies. After exposure to LKM positive sera colloidal gold was strictly confined to the plasma membrane. On the other hand, mechanically isolated hepatocytes showed wide interruptions of the plasma membrane and gross alterations of subcellular organelles. Most cells were stained by ruthenium red, thus confirming the plasma membrane permeability. In addition, a linear peripheral positivity was found in the vast majority of the cells tested with anti-prekeratin and anti-actin antibodies. LKM-colloidal gold complexes were found at the level of both residual plasma membrane and SER.(ABSTRACT TRUNCATED AT 250 WORDS)

Infection of murine hepatocyte cultures by herpes simplex virus (HSV) 1 and 2

A study was undertaken of the interaction between liver cells and Herpes Simplex Virus (HSV) in vitro. Hepatocytes were obtained from HSV-resistant (C57/B16) and from HSV-susceptible (BALB/c, A/J, C3H) mouse strains and cultured according to standard methods. Each culture was infected with several strains of HSV-type 1 or of HSV-type 2, respectively. The multiplicity of infection was 5. The cytopathic effect was evaluated by light- and electron-microscopy. The number of infectious particles was determined using rabbit kidney or Vero cell cultures. All evaluations were made at different time intervals after infection. No difference concerning the replication rate of HSV-1 and 2 in isolated hepatocytes from resistant and susceptible mouse strains was detected. However, a marked difference was observed with respect to the production of infectious particles: HSV-1 exhibited a good multiplication rate, whereas no production of virus particles was observed with HSV-2. The data show that mice hepatocytes fail to bear the genotype for resistance to HSV infections.

Electron microscopic observations on primary hepatocyte cultures infected with herpes simplex virus types I and II

The replication cycle of the Herpes simplex virus (HSV) strains I and II has so far been described mainly in established proliferative cell cultures. Most of the biochemical data and ultrastructural cell changes regarding the virus-cell interaction have been obtained from 'permissive' cells which allow almost unrestricted viral multiplication. It seems obvious, however, that the in vivo viral infections are not represented adequately by these experiments. In order to achieve a more realistic view of the ultrastructural events during HSV infection of adult tissue, cell cultures were prepared from adult mouse and rat livers and infected with several HSV strains. Established 'permissive' cell lines (BHK and RK cells), served as controls. Although the main principles of viral attachment, replication and release of viral particles, were similar in hepatocytes and proliferating cells, marked differences were observed regarding the better preservation of the nuclear structures, the lower replication rate of viruses, the hypertrophy of the endoplasmic reticulum, and the changes in the Golgi apparatus. Summarizing, it can be stated that hepatocytes infected by HSV in cell culture display the well known general features of adult cells infected by viruses in vivo.