Disorganisation of intermediate filament structure in alcoholic and other liver diseases.

The distribution of Mallory body antigens JMB1 and 2 was examined in 82 human fresh diagnostic needle liver biopsies and 28 necropsies by the indirect immunoperoxidase technique using 2 monoclonal antibodies (anti-JMB1 and 2) against Mallory bodies. The JMB1 antigen was detectable in bile duct epithelium and in hepatocytes of histologically normal livers. It was also found in all Mallory bodies in various hepatic disorders. This antigen was markedly increased in the cytoplasm of all liver cells in acute alcoholic hepatitis superimposed on alcoholic cirrhosis, in most cases of acute alcoholic hepatitis, and in severe fatty infiltration of the liver with or without Mallory body formation. Mallory bodies contained this antigen but the cytoplasm of Mallory body containing cells lacked JMB1. In normal liver the JMB2 antigen was localised on the cytoplasmic intermediate filament network of hepatocytes and bile duct epithelium; and almost all Mallory bodies also contained this antigen but the adjacent cytoplasm of these cells lacked JMB2. In severe alcoholic liver disease these antigens could not be detected in large zones of hepatocytes even when these hepatocytes did not contain Mallory bodies. It is evident that there is disorganisation of intermediate filament constituents in severe alcoholic liver disease.     

Serum vitamin A deficiency and increased intrahepatic expression of cytokeratin antigen in alcoholic liver disease

The clinical and histologic significance of cytokeratin antigen expression in various intrahepatic locations was assessed in 57 patients with alcoholic liver disease as part of a large Veterans Administration Cooperative Study of Alcoholic Hepatitis. Cytokeratin antigen was demonstrated in fixed, paraffin-embedded liver tissue by an avidin-biotin peroxidase method using a mixture of two different monoclonal antibodies, AE1 (acidic; 48, 50 and 56.5 kD) and AE3 (basic; 52, 56, 58 and 65 to 67 kD). In contrast to the normal liver, in which only bile duct epithelium was positive, this antibody mixture stained both bile ducts and hepatocytes in pathologic livers. Serum levels of vitamin A showed a significant inverse correlation with the amount of cytokeratin antigen (scale: 0 to 3) in hepatocytes without Mallory bodies (p = 0.001), in Mallory body-containing hepatocytes (p less than 0.0001) and in bile ducts (p = 0.0074). Increased amount of cytokeratin antigen in each of these locations, in turn, correlated directly with the histologic severity of the liver disease. Histologic severity (fibrosis, parenchymal degeneration/necrosis, hepatocyte regeneration and inflammation) was significantly higher in patients when either Mallory bodies (p less than 0.0001) or cytokeratin antigen (p = 0.0021) was present in hepatocytes. Demonstration of cytokeratin antigen in hepatocytes which contained Mallory bodies correlated positively (p = 0.03) with clinical severity of the liver disease as determined by high serum bilirubin and prolonged prothrombin time (Maddrey's discriminant function).(ABSTRACT TRUNCATED AT 250 WORDS)     

Expression of Ley antigen as a phenotypic marker of apoptosis in alcoholic hepatitis

Apoptosis is a type of cell death which is clearly distinguishable from necrosis in its morphological and biochemical features. To clarify the role of apoptosis in alcoholic liver injury, we investigated the expression of apoptosis-related Le^y antigen by immunohistochemistry in liver samples from patients who suffered from alcoholic liver diseases. Liver biopsy samples were taken from 20 patients who drank more than 80 g ethanol per day on average. Indirect immunohistochemical staining was carried out using anti-cytokeratin (CAM 5.2) and anti-Le^y (BM-1/JIMRO) antibodies. To examine the relationship between Mallory bodies and apoptosis, double staining was performed using both antibodies. In alcoholic hepatitis, many Mallory bodies were stained with anti-cytokeratin antibody in hepatocytes of the centrilobular area. Le^y antigen was also detected in hepatocytes in the same area. Immunohistochemical double staining showed that some of the hepatocytes containing Mallory bodies were stained with anti-Le^y antibody. Few hepatocytes expressing Le^y antigens, however, were observed in other types of alcoholic liver diseases including steatosis, fibrosis and cirrhosis. From these results, it is concluded that apoptosis is also involved in alcoholic hepatitis and that hepatocytes containing Mallory bodies may be eliminated by apoptosis.     

Mallory bodies and liver diseases

Abstract   Mallory bodies are cytoplasmic inclusions in hepatocytes consisting of abnormal keratins, ubiquitin and several proteins (p62, heat shock proteins) involved in the unfolded protein response. They are morphologic hallmarks of alcoholic and nonalcoholic steatohepatitis but may also be associated with metabolic and toxic liver cell injury and hepatocellular neoplasms. Mallory bodies can be experimentally produced in mouse liver by chronic intoxication with griseofulvin or 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC). Mallory body formation is associated with derangement of the keratin intermediate filament cytoskeleton of the hepatocyte. The analysis of Mallory body composition and particularly their experimental induction in animal models and in tissue culture cells disclosed a major role of oxidative stress in the underlying liver cell injury.     

Immunological and biochemical characterization of the keratin-related component of Mallory bodies: a pathological pattern of hepatocytic cytokeratins

Mallory bodies induced by long-term griseofulvin feeding in mouse liver were isolated and analyzed by one- and two-dimensional gel electrophoresis and reaction of the separated polypeptides with cytokeratin antibodies using the blotting technique. Comparison with normal intermediate filament cytoskeletons from mouse hepatocytes revealed that Mallory bodies contain two polypeptides: Component II (Mr: 55,000; apparent isoelectric point values: 6.45, 6.1, 5.9) and component III (Mr: 48,000; apparent isoelectric point values: 5.7, 5.5, 5.43, 5.38, 5.2) which appear to be similar, if not identical, to liver cytokeratins A and D, respectively. By contrast, component I of Mallory bodies (Mr: 65,000; apparent isoelectric point values: 5.4, 5.38, 5.2) was not found in appreciable amounts in normal hepatocytes. Component II was positive in immunoreaction with antibodies to murine hepatocyte keratins A and D as well as epidermal prekeratin. Component III showed reaction with the antibodies to murine hepatocyte keratins A and D but not with those raised against epidermal prekeratins. By contrast, the unusual component I reacted with antibodies to murine hepatocyte keratin D and to epidermal prekeratins. The results prove that cytokeratin polypeptides are major constituents of Mallory bodies and suggest that the pattern of liver cytokeratin polypeptides is altered during the toxic treatment and/or Mallory body formation.     

Mallory bodies in alcoholic liver disease: identification of cytoplasmic filament/cell membrane and unique antigenic determinants by monoclonal antibodies.

Polyclonal and monoclonal antibodies have been produced to Mallory body protein (MBP) extracted from isolated Mallory bodies (MBs). The polyclonal antibodies reveal a unique determinant in MBs. The first monoclonal antibody (anti-JMB1) detects a second unique determinant (JMB1) in MBs which is not detectable in normal hepatocytes. The second monoclonal antibody (anti-JMB2) shows that MBs contain another determinant which is associated with the cell and nuclear membranes and a cytoplasmic filament system of normal hepatocytes and bile duct epithelium; this antigen is not detectable in the cell membranes or cytoplasmic filament systems of hepatocytes which contain MBs. The third monoclonal antibody (anti-JMB3) reacts only with an antigen (JMB3) in mesenchymal cells of alcoholic cirrhotic liver and its significance, at this time, is unclear. It is suggested that the metabolism of JMB1, JMB2, and JMB3 antigens is deranged in hepatocytes damaged by alcohol. It is concluded that the antigenic structure of MBs is more complex than hitherto realised and that all of these antigens are distinct from prekeratin (a component of epidermal cell intermediate filaments).     

Heat shock protein 70 expression,keratin phosphorylation and Mallory body formation in hepatocytes from griseofulvin-intoxicated mice

Background  

Keratins are members of the intermediate filaments (IFs) proteins, which constitute one of the three major cytoskeletal protein families. In hepatocytes, keratin 8 and 18 (K8/18) are believed to play a protective role against mechanical and toxic stress. Post-translational modifications such as phosphorylation and glycosylation are thought to modulate K8/18 functions. Treatment of mouse with a diet containing griseofulvin (GF) induces, in hepatocytes, modifications in organization, expression and phosphorylation of K8/18 IFs and leads, on the long term, to the formation of K8/18 containing aggregates morphologically and biochemically identical to Mallory bodies present in a number of human liver diseases. The aim of the present study was to investigate the relationship between the level and localization of the stress inducible heat shock protein 70 kDa (HSP70i) and the level and localization of K8/18 phosphorylation in the liver of GF-intoxicated mice. The role of these processes in Mallory body formation was studied, too. The experiment was carried out parallely on two different mouse strains, C3H and FVB/n.     

Keratin 8 and 18 hyperphosphorylation is a marker of progression of human liver disease

Keratin 8 and 18 (K8/18) phosphorylation plays a significant and site-specific role in regulating keratin filament organization, association with binding proteins, and modulation of cell cycle progression. Keratin hyperphosphorylation correlates with exposure to a variety of stresses in cultured cells and in mouse models of liver, pancreatic, and gallbladder injury, and it is found in association with mouse and human Mallory bodies. We asked whether K8/18 phosphorylation correlates with human liver disease progression by analyzing liver explants and biopsies of patients with chronic noncirrhotic hepatitis C virus (HCV) or cirrhosis. We also examined the effect of HCV therapy with interleukin-10 on keratin phosphorylation. Using site-specific antiphosphokeratin antibodies we found keratin hyperphosphorylation on most K8/18 sites in all cirrhotic liver explants tested and in most liver biopsies from patients with chronic HCV infection. Immunofluorescence staining of precirrhotic HCV livers showed focal keratin hyperphosphorylation and limited reorganization of keratin filament networks. In cirrhotic livers, keratin hyperphosphorylation occurred preferentially in hepatic nodule cells adjacent to bridging fibrosis and associated with increased stress kinase activation and apoptosis. Histological and serological improvement after interleukin-10 therapy was accompanied by normalization of keratin hyperphosphorylation on some sites in 7 of 10 patients. In conclusion, site-specific keratin phosphorylation in liver disease is a progression marker when increased and a likely regression marker when decreased.     

丙,丁和庚型RNA病毒所致肝炎的免疫病理和组织病理特点及临床意义

目的探讨由ＲＮＡ病毒引起的丙型肝炎（ＨＣ）、丁型肝炎（ＨＤ）和庚型肝炎（ＨＧ）的免疫病理和组织病理不同特点及临床意义。方法　采用双重ＰＡＰ方法检测ＨＣ肝组织ＨＣＶ－ＮＳ５;采用直接酶标法检测ＨＤ肝组织ＨＤＡｇ;采用链霉菌抗生物素蛋白－过氧化酶法（ＳＰ）检测ＨＧ肝组织ＨＧＶ－ＮＳ５。同时常规苏木素伊红染色。结果在免疫病理表达中,阳性信号的位置、形态和阳性肝细胞在肝小叶的分布及周围淋巴细胞的浸润等在ＨＣ、ＨＤ和ＨＧ三者中有较明显的差异。在组织病理变化中,汇管区淋巴细胞聚集或淋巴滤泡形成、胆管损伤、脂肪性变、Ｍａｌｌｏｒｙ小体、多核巨肝细胞和玫瑰花结等在 ＨＣ、ＨＤ和 ＨＧ三者中也有较明显的差异。结论ＲＮＡ病毒所引起的ＨＣ、ＨＤ和ＨＧ在免疫病理表达和组织病理变化有可鉴别诊断的不同特点,为临床防治和预后判断提供了依据。     

Mallory bodies in a patient with type Ia glycogen storage disease

Mallory bodies were determined by light microscopy and confirmed by electron microscopy in the liver of a 37-yr-old woman with type Ia glycogen storage disease. They were found mainly in the swollen hepatocytes of the centrilobular region in the liver associated with periportal and centrilobular pericellular fibrosis. Ultrastructurally, the shape of small circular structures found in the Mallory body was similar to that of the circularly disorganized rough endoplasmic reticulum seen around the Mallory body. Although Mallory bodies are seen in several liver diseases other than alcoholic liver injury, there has been only one report of finding them in the liver in type I glycogen storage disease.     

Keratin species in type II pneumocytes in culture and during lung injury

A detailed understanding of alveolar epithelial cell transitions during remodeling after lung injury requires the identification of specific markers. We have developed a panel of monoclonal antibodies against species of the intermediate filament protein, keratin. These individual species are recognized markers of the state of differentiation of various epithelial cells. These and complementary protein analytic methods have been applied to studies of isolated, enriched Type II pneumocyte preparations as well as to normal and injured lung tissues. Monoclonal antibody 24A3, initially raised against Morris hepatoma 7777 keratins, decorated a filament network in isolated cultured rat Type II pneumocytes by indirect immunofluorescence; it reacts by 2-dimensional polyacrylamide gel immunoblot procedures with an acidic, 46,000-dalton keratin. Monoclonal antikeratin antibodies AE1 and AE3, raised against human epidermal keratins, reacted poorly with isolated Type II cells; however, AE3 reacted by immunoblot technique with the 55,000-dalton keratin subclass. The bronchial epithelium reacted intensely with 24A3 as well as with a mix of AE1 plus AE3 in ethanol-fixed, paraffin-embedded sections of normal and injured rat lung. Alveolar regions of normal lung reacted poorly with all 3 antibodies, however, as visualized by light microscopy. At the same time, very large, presumptive epithelial cells in the alveolar regions stained intensely with 24A3 3 days after intratracheal instillation of bleomycin, whereas thin cells lining the alveoli in injured regions were intensely reactive 14 days after bleomycin treatment. These elongated cells may represent Type II pneumocytes in the process of converting to Type I cells.     

Appearance of hepatocytelike cells in the interlobular bile ducts of human liver in various liver disease states.

Among 1,098 liver biopsy specimens obtained from patients with various liver diseases characterized by liver injury, 58 epithelial cells whose cytoplasms stained positively by the periodic acid-Schiff stain (digested with diastase) were recognized in the interlobular bile ducts of 37 specimens from 36 patients. Light microscopic study revealed that the cytoplasms of these cells were clear or stained weakly eosinophilic on hematoxylin and eosin staining and that the cell limits were distinct. From their reaction with periodic acid-Schiff stain and from electron microscopic observation it was clear that these cells contained an abundance of glycogen and were located among the normal bile duct cells surrounded by basement membrane. On electron microscopy, these cells had microvilli of equal sizes on their luminal surfaces and many irregularly sized microvilluslike cell membrane projections on their basal surfaces. They rested on basement membrane with basal spaces. These cells varied in size from 25.0 to 452.2 microns 2 (mean = 212.2 microns 2). In contrast, the sizes of normal bile duct cells and hepatocytes ranged from 20.0 to 69.3 microns 2 (mean = 34.2 microns 2) and from 113.0 to 860.3 microns 2 (mean = 447.0 microns 2), respectively. Immunohistochemical study with antiserum to cytokeratin 19, albumin and alpha 1-antitrypsin on serially cut frozen sections showed that some of these cells expressed markers of bile duct cells and hepatocytes. Some cells expressed only the markers of hepatocytes. Computer graphic three-dimensional reconstruction clearly demonstrated that these cells were located sparsely (but sometimes in groups) among normal interlobular bile duct cells, without any connection to the surrounding parenchymal hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)     

The development of the intrahepatic bile ducts in man: a keratin-immunohistochemical study

The development of the intrahepatic bile ducts in man was studied using an immunohistochemical technique on 56 liver specimens ranging in age from 6 weeks of gestation to 8 months after birth. On paraffin sections, two monoclonal anticytokeratin antibodies (CAM 5.2 and KL-1) that normally stain both hepatocytes and bile duct cells and two polyclonal anticytokeratin antisera that in normal adult liver stain bile ducts only were applied. For immunohistochemical staining of cryostat sections (only available from 14 weeks of gestation on), four monoclonal antibodies specifically directed against individual cytokeratin polypeptides 7,8, 18 and 19 were used. Adult human hepatocytes contain cytokeratin 8 and 18 whereas bile duct cells also express cytokeratin 7 and 19 in addition to cytokeratin 8 and 18. On paraffin sections, primitive hepatocytes were stained with monoclonal antibodies CAM 5.2 and KL-1 from 6 weeks of gestation on. On cryostat sections, they were positive with monoclonal antibodies anticytokeratin 8 and 18 from the earliest time point examined (14 weeks). From 9 weeks of gestation on, portal vein branches were surrounded by a layer of cells showing a stronger positive reaction with monoclonal antibodies CAM 5.2 and KL-1 on paraffin sections and with monoclonal antibodies anti-cytokeratin 8 and 18 on cryostat sections (only available from 14 weeks on). This layer, referred to as the ductal plate, first appeared around large portal vein branches close to the hilum and subsequently around more peripheral branches. The duct plates became duplicated over variably long segments of their perimeter, lumina appeared and tubular structures were formed. The latter gradually became incorporated in the connective tissue surrounding the portal vein, resulting in the appearance of individualized bile ducts. Ductal plate cells were stained by both polyclonal anticytokeratin antisera on paraffin sections. On cryostat sections (available from 14 weeks of gestation on), they were immunoreactive for cytokeratin 19 but negative with the monoclonal antibody directed against cytokeratin 7 until 20 weeks of gestation. From then on, weakly positive staining for cytokeratin 7 was detected, but staining intensity subsequently increased and reached the level observed in adult liver at 1 month after birth. At birth, the smallest branches of the portal vein were still surrounded by a discontinuous ductal plate. We conclude that intrahepatic bile duct cells develop from hepatocytes around branches of the portal vein.(ABSTRACT TRUNCATED AT 400 WORDS)     

Mallory bodies--immunohistochemical detection by antisera to unique non-prekeratin components.

Mallory bodies (MBs) were prepared in 95% pure form from a case of human chronic alcoholic liver disease. A protein referred to as Mallory body protein (MBP), was isolated from MB by reduction and alkylation which gave one band an SDS-polyacrylamide electrophoresis. Antisera were raised to both purified MBs and MBP in rabbits and a goat. Both antisera, after absorption with spleen cells, specifically reacted immunohistochemically with MBs in frozen sections from patients with alcoholic liver disease. They also reacted with small granular structures in hepatocytes which are interpreted as a precursor or degradation product of MBs. The anti-MB serum also stained MBs in trypsinised paraffin sections in the immunoperoxidase procedure. Neither antisera reacted with normal liver or skin, and the reactivity of anti-MB and MBP sera for MBs was not abolished by absorption with prekeratin; these results indicate that MBs contain unique antigenic determinants not present in prekeratin. It is concluded that MBs are not simply composed of intermediate filament proteins.     

Primary biliary cirrhosis: modalities of injury and death in biliary epithelium

BACKGROUND/AIM: Despite the number of studies on primary biliary cirrhosis, contrasting data remain concerning modalities of cholangiocyte death. Liver biopsies obtained from 40 patients with anti mitochondrial antibody-positive primary biliary cirrhosis, at various stages of the disease, were examined, and special attention was paid to the expression of subcellular damage and evidence of apoptosis. METHODS: Liver sections were stained with haematoxylin/eosin or Sirius red. Ductular mass was evaluated on sections after cytokeratin 7 staining. Apoptosis was evaluated on haematoxylin/eosin stained material or after processing for terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling assay. In 16 patients, part of the biopsy was processed for electron microscopy. Twenty histologically normal liver biopsies were used for control purposes. RESULTS: According to Scheuer's classification, 29 patients were classified as stage I-II, and 11 as stage III-IV. A strong staining of bile ducts was evident after immunohistochemistry for cytokeratin 7, often associated with ductular metaplasia in lobular zone 1. Cytokeratin 7-positive cells occupied 3.0+/-1.3% of liver mass as compared to 0.25+/-0.03% in controls. Ductular metaplasia accounted for 1.4+/-0.07% of all cytokeratin 7-positive cells. Regardless of staging, apoptotic bodies were seen only exceptionally in epithelial wall of bile ducts, whereas cholangiocyte damage leading to extensive lytic necrosis appeared responsible for most of the bile duct mass loss, as also confirmed by ultrastructural studies. A few terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling-positive nuclei were occasionally associated with the inflammatory infiltrate and evidence of apoptosis in hepatocytes was frequent, especially in zone 1. CONCLUSION: Regardless of staging, lytic necrosis and not apoptosis accounts for most of the bile duct loss in primary biliary cirrhosis. Furthermore, ductular metaplasia appears as a late event with highly variable pattern being observed between patients.     

Amniotic epithelial cell–derived cholangiocytes in experimental cholestatic ductal hyperplasia

Aim: Bile duct paucity, ductopenia, is a feature of end-stage chronic cholangiopathies such as primary biliary cirrhosis. The limited proliferative ability of cholangiocytes after specific injury is thought to be the principal cause of ductopenia, although the detailed mechanisms involved are unclear. It has been reported that human amniotic epithelial cells (AEC) express differentiation markers of hepatic parenchymal cells, suggesting a resemblance of AEC to hepatic progenitor cells. The aim of the present study was to develop a mouse model of experimental cholestasis to assess the capability of mouse AEC to trans-differentiate into cholangiocytes. Methods: Enhanced green fluorescent protein (EGFP)-transgenic C57BL/6 pregnant female mice were used as the source of AEC. At 11.5 gestational days, 1 x 10(5) AEC were isolated from EGFP-transgenic mouse embryos and transferred into C57BL/6 mice. Chronic cholestasis was induced by 0.1%alpha-naphthylisothiocyanate (ANIT) feeding immediately after the transfer of AEC. The proliferation of cholangiocytes in the livers was assessed morphologically and immunohistochemically (cytokeratin 7; CK7). The proliferative activity was also quantified immunohistochemically by proliferating cell nuclear antigen (PCNA) protein expression. EGFP of transferred AEC was confirmed by fluorescent laser microscopy and immunofluorescent staining for EGFP. Also, Notch2 and Hes1 expression was evaluated to examine the roles of the differentiation markers in this process. Results: Marked proliferation of cholangiocytes was observed in ANIT-fed mice confirmed by quantitative CK7 (3-4 fold vs control) and PCNA (11-20 fold vs control) staining. EGFP and CK7 double positive cells in interlobular bile ducts were confirmed in the livers of AEC-transferred recipients. Positivity of EGFP was further confirmed by the immunofluorescent staining for EGFP. Moreover, both Notch2 and Hes1 expression was confirmed in the proliferative bile duct in this model. Conclusions: Significant ductular proliferation was observed in ANIT-fed mice. EGFP-positive cholangiocytes were confirmed in this chronic cholestasis model. AEC transfer was able to contribute to the repopulating of proliferating cholangiocytes under cholestasis, suggesting AEC might be a candidate cell source for stem cell administration in future clinical applications to re-model interlobular bile ducts.     

Changes of integrin expression in rat hepatocarcinogenesis induced by 3'-Me-DAB

AIM:To investigate the expression of integrins in rats liver during 3'-Me -DAB induced hepatocarcinogenesis and to find out the relationship between integrins and liver cancer metastasis.METHODS:The expressions of integrins alpha(1), alpha(2), alpha(3) and alpha(5) and epidermal keratin (EK) were observed by immunohisto chemical PAP method.RESULTS:In the normal liver tissues, hepatocytes express integrins alpha(1) and alpha(5) and in the bile duct epithlium, EK. In liver cirrhosis, hepatocytes highly express integrins alpha(1), alpha(2), alpha(3) and alpha5and in hyperplastic bile duct epithelium, integrins alpha(1), alpha(5) and EK. Expression of integrins alpha(1), alpha(2), alpha(3) and alpha(5) were obviously decreased in the preneoplastic nodules and primary carcinoma but expressions of integrins alpha(1) and alpha(5) in metastasis in the lung and diaphragma were higher than those in primary carcinoma.CONCLUSION:Integrins alpha(1) and alpha(5) may play a major role in chemically induced hepatocarcinogenesis and metastasis in rats.     

Monoclonal antibodies against antigens expressed on human hepatocellular carcinoma cells

Monoclonal antibodies with selectivity for human hepatoma cell lines were produced by immunizing BALB/c mice with human hepatoma cell lines, HA22T/VGH or Hep 3B, and fusing sensitized mouse spleen cells with mouse myeloma cells. Two monoclonal antibodies recognizing antigens present only on human hepatoma cell lines were investigated. The monoclonal antibody IB1 was found to react with 3 of 9 hepatoma cell lines. Monoclonal antibody 9B2 reacted with all nine hepatoma cell lines. None of the other 20 cell lines tested was bound by IB1 and 9B2. The immunoperoxidase staining of monoclonal antibodies on frozen sections of paired hepatoma and normal liver tissues from the same individuals were studied. Antibody IB1 reacted with 3 of 13 hepatoma tissues, but with none of the normal liver and other tissues, and antibody 9B2 was reactive with antigens appearing on the bile canalicular domain of hepatoma and normal liver tissues. The antibody 9B2 stained no normal tissues with the exception of proximal tubules of kidney. Radioimmunoprecipitation tests identified two antigens reacting with 9B2. The major antigen had an apparent molecular weight of 140,000 and a minor one of 130,000. Therefore, antibody IB1 seems to be specific for antigens present on a group of human hepatoma cells and may be useful for classification and diagnosis of human hepatomas. Antibody 9B2 is quite specific to human liver cells and may be used to provide clues for the characterization of tumor cell lines, identification of metastatic tumors with hepatocytic origin, and study of the structure and function of bile canaliculi.