Differential effects of 1-naphthaleneacetic acid, indole-3-acetic acid and 2,4-dichlorophenoxyacetic acid on the gravitropic response of roots in an auxin-resistant mutant of arabidopsis, aux1

BACKGROUND/AIMS: Gallbladder mucus itself has been recognized to play an important role in gallstone development. Despite the diverse mechanisms of stone induction and the differences in stone composition, there is a quantitative increase in the epithelial mucus production period before stone formation. As brown pigment stones are found frequently in gallstone disease, we conducted a study on gallbladders with brown pigment stones or combination stones with a brown periphery to evaluate the mucin content in the gallbladder epithelium in comparison to gallbladders with cholesterol stones and those without stones. METHODS: Gallbladder specimens were fixed in 10% formalin immediately after cholecystectomy and then embedded in paraffin. The specimens were sectioned for periodic acid-Schiff-alcian blue (PAS-AB, pH 2.5) double stain to evaluate the intra-epithelial mucin content. The PAS-AB index was calculated as a proportion of the PAS-AB-positive mucin area to the total epithelial area, using a computerized image analyzer. RESULTS: Evaluation of the PAS-AB index on the lining epithelia of gallbladders showed that it was 32.43 +/- 9.96% in gallbladders with brown stones, which is significantly (p < 0.001) higher than in gallbladders with cholesterol stones (15.63 +/- 6. 75%) and gallbladders without stones (9.55 +/- 4.77%). CONCLUSION: The results show that gallbladders with brown stones contain more abundant mucin than gallbladders with cholesterol stones or those without stones. They also suggest that the gallbladder epithelium per se might play a more important role in stone formation in those with brown stones than in those with cholesterol stones.     

Characterization of apomucin expression in intrahepatic cholangiocarcinomas and their precursor lesions: an immunohistochemical study

To date, seven apomucins have been characterized and their expression in malignant and premalignant lesions is under evaluation. In this study, we examined the expression of MUC1, MUC2, MUC3, and MUC5/6 apomucins in cholangiocarcinoma (CC) and biliary epithelial dysplasia. We used 14 liver samples from patients with hepatolithiasis and CC, 11 with hepatolithiasis showing biliary epithelial dysplasia, 31 with CC alone (19 hilar, 10 peripheral, and 2 unclassifiable), and 14 with combined hepatocellular-cholangiocellular carcinoma (HC-CC) and immunohistochemically characterized the expression profiles of apomucins. Nondysplastic biliary epithelial cells in the intrahepatic large bile ducts constantly expressed MUC3 apomucin. MUC5/6 and MUC3 apomucin expression was widespread in dysplastic biliary epithelial cells in hepatolithiasis, although the latter was reduced or absent in dysplastic foci. CC extensively expressed MUC1 apomucin and focally expressed MUC2 apomucin. In addition, CC of the hilar type, including those with hepatolithiasis, frequently expressed MUC3 apomucin (68% and 57%, respectively), whereas those of the peripheral type infrequently expressed MUC3 apomucin (10%) (P < .01). MUC5/6 apomucin was more frequently expressed in well-differentiated (89%), compared with poorly differentiated CC (42%) (P < .01). Cholangiocellular elements of combined HC-CC frequently expressed MUC1 apomucin, although they rarely expressed MUC2 and MUC3 apomucin and infrequently expressed MUC5/6 apomucin. The frequent and aberrant expression of "gastric type" MUC5/6 apomucin in biliary epithelial dysplasia, as well as in CC, suggests that biliary epithelial cells gain a gastric apomucin phenotype during carcinogenesis. MUC3 apomucin expression in CC is a marker that suggests that CC arises in the intrahepatic large bile ducts.     

Case report: secondary biliary cirrhosis possibly related to congenital hepatic fibrosis. Evidence for decreased number of portal branch veins and hypertrophic peribiliary vascular plexus

A 30-year-old man with presinusoidal portal hypertension was transplanted for cryptogenic cirrhosis. On the explanted liver, few intrahepatic stones, biliary cirrhosis, chronic cholangitis of the large bile ducts and a peculiar proliferation of small dilated bile ducts at the periphery of the portal tracts led to the diagnosis of secondary biliary cirrhosis and cholangitis, possibly linked to ductal plate malformation, including congenital hepatic fibrosis associated with a minor form of Caroli's disease. Ex vivo portogram and histology showed the paucity of portal vein branches and the hypertrophy of the peribiliary vascular plexus. This hypertrophy, which has been reported in livers with presinusoidal hypertension, is another indirect argument to suggest the diagnosis of congenital hepatic fibrosis.     

Extrahepatic peribiliary glands express alpha-amylase isozymes, trypsin and pancreatic lipase: an immunohistochemical analysis

We examined expression of alpha-amylase isozymes (pancreatic and salivary), trypsin and pancreatic lipase on the epithelium of extrahepatic peribiliary glands immunohistochemically using 53 autopsied normal extrahepatic bile ducts. Three parts of the extrahepatic bile duct (common bile duct, intrapancreatic bile duct and bile duct at the ampulla of Vater) were examined in each case. Histologically, the extrahepatic bile duct harbored branched tubular glands (extrahepatic peribiliary glands). Extrahepatic peribiliary glands were few in the common bile duct and intrapancreatic bile duct and numerous in the bile duct at the ampulla of Vater. Immunohistochemically, pancreatic alpha-amylase was expressed in the epithelium of extrahepatic peribiliary glands in 42 cases (79%). Salivary alpha-amylase was expressed in the epithelium of the glands in 38 cases (72%). Trypsin was expressed in the epithelium of the glands in 32 cases (60%). Pancreatic lipase was expressed in the epithelium of the glands in 45 cases (85%). The immunoreactivity of these enzymes was granular and located in the supranuclear cytoplasm (corresponding to the Golgi apparatus) of the epithelium of the glands. We confirmed the specificity of the immunoreactivity of these enzymes with various methods. These results suggest that extrahepatic peribiliary glands produce alpha-amylase isozymes, trypsin and pancreatic lipase and secrete these enzymes into lumens of the extrahepatic bile duct. The secreted enzymes may play an important role in the physiology of the extrahepatic bile duct and bile.     

Enhanced apoptosis relates to bile duct loss in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is characterized by an immune-mediated destruction of intrahepatic small bile ducts. Apoptosis, a unique pattern of cell death, has been suggested to be responsible for the biliary destruction in PBC. To address this issue, we attempted to detect the apoptosis of biliary epithelial cells by in situ nick-end labeling and by the expression of apoptosis-related proteins using immunohistochemistry in patients with various hepatobiliary diseases, including PBC. The data was noteworthy for several reasons. First, apoptosis was occasionally detected on biliary cells in all liver specimens; however, the positive rate was high in PBC and relatively low in other livers. Strong expression of CD95 was frequently observed in the epithelial cells of the injured bile ducts of PBC, which accompanied high intensity CD95 ligand-expressing mononuclear cells. Perforin and granzyme B immunoreactivities were occasionally found on the bile ducts in control liver diseases as well as PBC, but granzyme B-positive biliary cells were prominent in PBC. In contrast, Lewis Y expression, as detected using BM-1 antibody, was consistently present in the injured bile ducts of PBC. These data suggest that apoptosis, via the perforin/granzyme B pathway, may be associated with the degrading fraction of cell cycle regulation in the small-sized biliary tree under physiological and pathological liver conditions. Moreover, enhanced apoptosis, mediated by CD95/CD95 ligand interaction, may contribute to the bile duct injury and loss observed in PBC.     

Topometry of normal intrahepatic bile ducts

This paper focuses on practical problems which may also prove to be of theoretical importance, by presenting a method of establishing an exact topometry of the intrahepatic bile ducts. Measurements were made on corrosive casts of the intrahepatic bile ducts from 13 human livers. On the basis of the topometric results presented it is possible to construct an adequate model by means of plastic tubes and to use it for the study of bile flow.     

Hepatic peribiliary cysts: multiple tiny cysts within the larger portal tract, hepatic hilum, or both

PURPOSE: To describe characteristic imaging features of hepatic peribiliary cysts. MATERIALS AND METHODS: Four patients with hepatic cysts in which the radiologic (n = 3) or histologic (n = 1) findings were consistent with peribiliary cysts of the liver (multiple small cysts seen exclusively in the larger portal tract, hepatic hilum, or both at gross examination and dilatations of extramural peribiliary gland at histologic examination) underwent computed tomography (CT) and ultrasound (US). In three patients, CT was performed after drip infusion of cholangiographic contrast material. RESULTS: Contrast material-enhanced CT clearly depicted many tiny cysts along the larger portal veins up to the third- or fourth-order branch (n = 3). US depicted multiple cysts in the echogenic portal tract definitely (n = 2) or equivocally (n = 2). On cholangiographic contrast-enhanced CT scans, cystic areas were located adjacent to or surrounding the bile ducts, and the possibility of biliary dilatation, communication, or both was disproved. CONCLUSION: Hepatic peribiliary cysts can be diagnosed with US and enhanced CT, especially with CT performed after administration of cholangiographic contrast material.     

Mucin gene expression in biliary epithelial cells

BACKGROUND/AIMS: In recent years considerable advances have been made in our knowledge of human mucin genes. Although analysis of their genomic organization is still in progress, the pattern of their expression in different human mucosae is now fairly well established. However, little is known about their expression in the biliary tree. In this study we determined the pattern of expression of the different human mucin genes in gallbladder biliary epithelial cells, intrahepatic bile ducts and liver. METHODS: Two complementary methods were used: Northern-blot and in situ hybridization analyses. The experiments were performed with eight probes corresponding to MUC1, MUC2, MUC3, MUC4, MUC5AC, MUC5B, MUC6 and MUC7. RESULTS: Our results revealed a strong mRNA expression of MUC3, MUC6 and MUC5B, a weak expression of MUC1, MUC5AC and MUC2, and no expression of MUC4 and MUC7. Surprisingly, MUC3, which was the gene which was most expressed in the biliary tree, was also found in hepatocytes, suggesting another function for the MUC3 protein than that of a secreted mucin. CONCLUSIONS: We conclude that MUC3, MUC6 and MUC5B were the main mucin genes expressed in biliary epithelial cells.     

Regulation of bicarbonate-dependent ductular bile secretion assessed by lumenal micropuncture of isolated rodent intrahepatic bile ducts

While intrahepatic bile duct epithelial cells secrete bile through transport of ions and water, the physiological mechanisms regulating ductular bile secretion are obscure, in part because of the lack of suitable experimental models. We report here the successful micropuncture of the lumen of isolated intrahepatic bile ducts and direct measurements of ductular ion secretion. Intact, polarized bile duct units (BDUs) were isolated from livers of normal rats by enzymatic digestion and microdissection. BDUs were cultured and mounted on a microscope in bicarbonate-containing buffer, and the lumens were microinjected with 2',7'-bis(2-carboxyethyl)-5-(and -6)carboxyfluorescein (BCECF)-dextran. Lumenal pH was measured by ratio imaging of BCECF fluorescence using digitized video fluorescent microscopy. After 36 hr in culture, the ends of BDUs sealed, forming closed compartments. After lumenal microinjection of BCECF-dextran, fluorescence was stable at the pH-insensitive wavelength, indicating no dye leakage. Serial changes in pH of extralumenal buffers containing pH-gradient collapsing ionophores allowed us to establish reliable standard curves relating fluorescence ratio to lumenal pH (r = 0.99; P < 0.001). By this approach, the basal pH inside the lumen of BDUs was 7.87 +/- 0.08 units (n = 9), 0.47 unit higher (P < 0.001) than the bathing buffer pH. Addition of 100 microM forskolin increased (P = 0.02) the lumenal pH from 7.78 +/- 0.06 to 7.97 +/- 0.06 units (n = 5); the forskolin effect was completely abolished by incubation of BDUs in HCO3-/CO2-free buffer. Moreover, forskolin caused a 50-fold increase in cAMP levels in BDUs. The observations are consistent with cAMP-dependent, active lumenal HCO3- secretion by BDUs. Furthermore, they demonstrate the suitability of the BDU model for studying regulatory and mechanistic aspects of ductular bile secretion.     

An approach for treating the hepatobiliary disease of cystic fibrosis by somatic gene transfer

Cystic fibrosis (CF) is an inherited disease of epithelial cell ion transport that is associated with pathology in multiple organ systems, including lung, pancreas, and liver. As treatment of the pulmonary manifestations of CF has improved, management of CF liver disease has become increasingly important in adult patients. This report describes an approach for treating CF liver disease by somatic gene transfer. In situ hybridization and immunocytochemistry analysis of rat liver sections indicated that the endogenous CFTR (cystic fibrosis transmembrane conductance regulator) gene is primarily expressed in the intrahepatic biliary epithelial cells. To specifically target recombinant genes to the biliary epithelium in vivo, recombinant adenoviruses expressing lacZ or human CFTR were infused retrograde into the biliary tract through the common bile duct. Conditions were established for achieving recombinant gene expression in virtually all cells of the intrahepatic bile ducts in vivo. Expression persisted in the smaller bile ducts for the duration of the experiment, which was 21 days. These studies suggest that it may be feasible to prevent CF liver disease by genetically reconstituting CFTR expression in the biliary tract, using an approach that is clinically feasible.     

In situ nucleic acid hybridization of cytokines in primary biliary cirrhosis: predominance of the Th1 subset

Primary biliary cirrhosis (PBC) is an autoimmune liver disease characterized by destruction of the intrahepatic bile ducts. It is generally believed that cellular immune mechanisms, particularly involving T cells, result in this bile duct damage. The relative strength of Th1 and Th2 responses has recently been proposed to be an important factor in the pathophysiology of various autoimmune diseases. In this study, we have attempted to identify the Th subset balance in PBC, by detection of cytokines specific to the two T-cell subsets, i.e., interferon gamma (IFN-gamma) for Th1 cells and interleukin-4 (IL-4) for Th2 cells. We analyzed IFN-gamma and IL-4 messenger RNA (mRNA) positive cells in liver sections from 18 patients with PBC and 35 disease controls including chronic active hepatitis C, extrahepatic biliary obstruction (EBO), and normal liver, using nonisotopic in situ hybridization and immunohistochemistry. Mononuclear cells expressing IFN-gamma and IL-4 mRNA were aggregated in inflamed portal tracts in PBC livers, but were rarely present in extrahepatic biliary obstruction, alcoholic fibrosis, or normal liver sections. The IFN-gamma and IL-4 mRNA positive cells in PBC livers were detected in significantly higher numbers than in control livers (P < .01). Moreover, IFN-gamma mRNA expression was more commonly detected than IL-4 expression in PBC livers, and the levels of IFN-gamma mRNA expression were highly correlated with the degree of portal inflammatory activity. IFN-gamma mRNA-positive cells were detected primarily around damaged bile ducts that were surrounded by lymphoid aggregates. The data indicate that Th1 cells are the more prominent T-cell subset in the lymphoid infiltrates in PBC.     

Intrabiliary growth of metastatic colonic adenocarcinoma: a pattern of intrahepatic spread easily confused with primary neoplasia of the biliary tract

Because of its propensity to spread along epithelial surfaces, colonic adenocarcinoma can mimic other neoplasms. For example, colonic adenocarcinoma can grow along the surface of the urinary bladder and can simulate primary bladder neoplasia, and metastatic colonic adenocarcinoma can grow along alveolar walls and can mimic primary lung neoplasia. Intraepithelial spread along bile ducts, however, is not a well-recognized behavior of hepatic metastases. Indeed, dysplastic change in the epithelium lining the biliary tract is sometimes used to discriminate primary biliary neoplasms from metastatic adenocarcinoma. We report on eight cases of colonic adenocarcinoma metastatic to the liver that demonstrated prominent spread throughout the biliary tree along intact basement membranes. Morphologically, this pattern closely resembled high-grade dysplasia (i.e., carcinoma in situ) of the extrahepatic and intrahepatic bile ducts. Clinically, two of the tumors were mistaken for primary biliary neoplasia because of the common radiologic finding of intrabiliary masses with distended bile ducts. A definite diagnosis of metastatic carcinoma was established by careful attention to the medical history, thorough evaluation of the morphologic features, and histologic comparison with the primary colon cancer. For patients with a history of colonic adenocarcinoma, consideration of a liver metastasis is appropriate even when certain histologic and radiographic features point to a neoplasm of biliary origin.     

A clinicopathologic study of primary cholesterol hepatolithiasis

BACKGROUND/AIMS: We conducted the present study in order to clarify the clinicopathologic features of primary cholesterol hepatolithiasis and compare them with those in primary calcium bilirubinate hepatolithiasis. MATERIALS AND METHODS: We reviewed the clinicopathologic features of 24 patients with primary cholesterol hepatolithiasis. The clinical symptoms were mild, and the median duration of symptoms was 5 years. RESULTS: In 22 patients complete stone clearance was obtained using percutaneous cholangioscopic lithotomy, partial hepatectomy, or their combination. The patients showed excellent clinical outcome (median follow-up period, 6 years) despite the absence of bilioenteric drainage. Stones have recurred in 4 patients, who remain asymptomatic. The histopathologic findings in 7 hepatectomized patients were compared with those in 7 patents with calcium bilirubinate hepatolithiasis. The inflammatory changes around the stone-containing duct, i.e., wall thickening, fibrosis, sludge formation, and glandular hyperplasia, were significantly milder in the cholesterol hepatolithiasis patients (p < 0.01 or p < 0.05). CONCLUSIONS: These clinical and histopathologic findings indicate that primary cholesterol hepatolithiasis should be regarded as a different clinical entity from calcium bilirubinate hepatolithiasis which has a close relationship with bile stasis and bacterial infection as etiological factors.     

An outbreak of Candida parapsilosis prosthetic valve endocarditis

The histologic features of normal and hyperplastic epithelia of the extra-glandular excretory ducts of human minor salivary glands were studied, and their pathologic significance evaluated. Normal duct epithelium consisted of two layers: inner columnar cells, and basal cubical or squamous cells. A few goblet cells were present among the inner cells. Hyperplasia of the duct epithelia occurred focally or entirely, and was classified into the following histologic types: (1) simple hyperplasia, and (2) metaplastic hyperplasia, which were divided into (a) mucous cell hyperplasia, (b) oncocytic hyperplasia and (c) squamous cell hyperplasia. Squamous cell hyperplasia was subdivided into (i) acanthotic type and (ii) reserve cell-like type with or without dysplasia. Simple or metaplastic epithelial hyperplasia of the extra-glandular excretory ducts of minor salivary glands may be induced by chronic inflammation or other types of irritation, and proliferating cells of such regenerating tissue sometimes exhibit features reminiscent of a neoplastic process. Furthermore, it is suggested that metaplastic epithelial hyperplasia of the excretory minor salivary gland ducts could be the site of origin of tumor development, i.e., some oral squamous cell carcinomas may arise from primary lesions in the hyperplastic epithelium of the extraglandular excretory minor salivary gland ducts.     

Effect of contact lens wear on the conjunctival mucous system

Biopsy specimens from the upper tarsal conjunctiva of 20 contact lens wearers with a clinically evident increase in mucus and ten non-lens wearing subjects were examined by light microscopy and scanning and transmission electron microscopy to determine the effect of contact lens wear on the mucous cell system(s). Three types of crypts associated with mucous secretion were found in all specimens: those with intracellular openings (type I, 0.1 to 0.2 mum) associated with non-goblet mucous secretory cells; those with small intercellular openings (type II, 1 to 2 mum) usually associated with goblet cells, and those with intraepithelial and intrastromal crypts with large intercellular openings (type III, 10 to 60 mum) lined with goblet and non-goblet mucous secretory cells. Contact lens wearers had increased numbers of non-goblet cells with mucous secretory vesicles lining the surface of the conjunctiva and the epithelial infoldings of type III crypts than did the normal subjects. We conclude that increased mucous secretion in contact lens wearers is associated with an increased number of cells and number of secretory vesicles involved in the non-goblet cell mucous system.     

Developmental mucin gene expression in the human respiratory tract

The epithelial surface of the respiratory tract is coated with a protective film of mucus secreted by epithelial goblet and submucosal gland cells. Histology of the airway mucosa and composition of secretions during the second trimester of fetal life are known to differ from the normal adult in that these secretions show similarities with those of hypersecretory disorders. To provide information regarding cell-specific expression of mucin genes and their relation to developmental patterns of epithelial cytodifferentiation, we studied the expression of eight different mucin genes (MUC1-MUC4, MUC5AC, MUC5B, MUC6, MUC7) in human embryonic and fetal respiratory tract using in situ hybridization. These investigations demonstrated that MUC4 is the earliest gene expressed in the foregut at 6.5 wk, followed by MUC1 and MUC2 from 9. 5 wk of gestation in trachea, bronchi, epithelial tubules, and terminal sacs before epithelial cytodifferentiation. In contrast, MUC5AC, MUC5B, and MUC7 are expressed at later gestational ages concomitant with epithelial cytodifferentiation. During this developmental stage, MUC1 and MUC4 mRNAs are located in goblet and ciliated cells, whereas MUC2 mRNAs are located in basal and goblet cells. MUC5AC expression is confined to goblet cells. In the submucosal glands, MUC2 mRNAs are located in both mucous and serous cells, whereas MUC5B and MUC7 mRNAs are expressed in mucous and in serous cells, respectively. These data suggest distinct developmental roles for MUC1, MUC2, MUC4, MUC5AC, MUC5B, and MUC7 in the elongation, branching, and epithelial cytodifferentiation of the respiratory tract during ontogenesis. Distinct patterns of mucin gene expression are also likely to play an important role in regulating appropriate epithelial cell proliferation and cytodifferentiation in adult airway mucosa as it is indicated by aberrant expression in hypersecretory disorders.     

Treatment of intrahepatic gallstone

The postoperative outcomes in patients with hepatolithiasis are greatly affected by the presence of residual stones. One hundred and seventeen patients with hepatolithiasis treated in our clinic were analysed. The indication of hepatectomy for hepatolithiasis was determined by the degree of stricture of intrahepatic bile duct. The rate of residual stones was reduced from 54.5% to 14.5% by the introduction of choledochoscopical lithotomy. Thus, pre- and postoperative choledochoscopical examination and lithotomy are shown to play an important role in treatment of the patients with hepatolithiasis.     

Intestinal parasites in the vendors and consumers of street food. A study conducted in the Dakar area

To determine the origin and nature of mucinlike material in fine-needle aspiration (FNA) smears of the breast in noncancerous breast lesions, we studied breast FNA smears from four patients. All smears contained epithelial cells floating in a mucinlike background, which raised suspicion for mucinous (colloid) carcinoma. Mucicarmine stain was performed on one smear from each case. Subsequent tissue biopsy specimens were studied using mucicarmine, periodic acid-Schiff with and without diastase, and alcian blue stains at pH 2.7 and 0.9 on selected tissue sections. Correlation of the cytologic and histologic findings of each lesion was performed. The mucinlike background in all four FNA smears stained strongly with mucicarmine. Corresponding biopsy specimens revealed pseudoangiomatous hyperplasia in the first case, fibroadenoma and atypical ductal hyperplasia in the second, benign phyllodes tumor in the third, and fibroadenoma in the fourth. Each lesion in cases 1 to 3 was associated closely with fibrocystic changes. In case 4, cystic changes were located within the fibroadenoma. On tissue sections of all four cases, the cyst contents and 10% to 50% of normal lobule and duct contents stained with mucicarmine, indicating that the cyst contents were the most probable source of mucin in the FNA smears. The presence of pools of mucicarmine-positive material in FNA smears of the breast is not an exclusive feature of mucinous carcinoma; mucicarmine-positive mucin can arise from benign cystic changes as well as from normal lobules and ducts.     

Identification of bipotential progenitor cells in human liver development

Intermediate filament proteins have been reported to be expressed in a cell lineage-specific manner during morphogenesis. We studied the expression of cytokeratin (CK)14, CK19, and vimentin and of the hepatocyte-specific HepPar1 antigen during the development of human liver. Nineteen fetal livers (gestational ages 4 to 40 weeks), 3 normal infant livers, and 3 normal adult livers were studied by immunoperoxidase staining of paraffin sections with monoclonal anti-CK19, anti-vimentin, and HepPar1 antibodies and polyclonal anti-CK14 antibodies. Double-immunostaining for CK14 and CK19 as well as bile duct cytokeratin and HepPar1 antigen was also done. CK19 and HepPar1 antigen were the first markers detected in immature progenitor cells of the liver primordium at 4 weeks' gestation. During subsequent liver development, the progenitor cells expressed HepPar1 antigen, CK14, and CK19, from 8 to 14 weeks' gestation. As hepatocyte differentiation progressed, expression of HepPar1 antigen increased, and CK14 and CK19 were abrogated from hepatoblasts at 14 to 16 weeks' gestation. In contrast, as progenitor cells transformed into ductal plate cells, CK19 expression increased and persisted in differentiated bile ducts, whereas CK14 and HepPar1 antigen were lost. Vimentin was detected in ductal plate and biliary epithelial cells from 9 to 36 weeks' gestation, but not in hepatoblasts or hepatocytes. Double-immunostaining confirmed coexpression of CK14 and CK19 in the progenitor cells for a short time (8 to 14 weeks' gestation) during early development. Double immunostaining for bile duct CK and HepPar1 antigen clearly demonstrated the divergence of the hepatocyte and bile duct epithelial cell lineages. Our findings suggest that hepatic progenitor cells differentiate in steps marked by the acquisition or loss of specific phenotypic characteristics. Commitment of the HepPar1+CK19+ progenitor cells to either hepatocyte or bile duct epithelial cell lineages results in increased expression of one marker and loss of the other marker. These characteristics clearly identify bipotential hepatic progenitor cells in the developing human liver.