Nuclear receptor CAR (NR1I3) is essential for DDC-induced liver injury and oval cell proliferation in mouse liver

The liver is endowed with the ability to regenerate hepatocytes in response to injury. When this regeneration ability is impaired during liver injury, oval cells, which are considered to be postnatal hepatic progenitors, proliferate and differentiate into hepatocytes. Here we have demonstrated that 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) activates the nuclear receptor constitutive active/androstane receptor (CAR), resulting in proliferation of oval cells in mouse liver. Activation of CAR by DDC was shown by hepatic nuclear CAR accumulation and cytochrome P450 (CYP)2B10 mRNA induction after feeding a 0.1% DDC-containing diet to Car(+/+) mice. After being fed the DDC diet, Car(+/+), but not Car(-/-) mice, developed severe liver injury and an A6 antibody-stained ductular reaction in an area around the portal tract. Oval cell proliferation was confirmed by laser capture microdissection and real-time PCR; mRNAs for the two oval cell markers epithelial cell adhesion molecule and TROP2 were specifically induced in the periportal region of DDC diet-fed Car(+/+), but not Car(-/-) mice. Although rates of both hepatocyte growth and death were initially enhanced only in DDC diet-fed Car(+/+) mice, growth was attenuated when oval cells proliferated, whereas death continued unabated. DDC-induced liver injury, which differs from other CAR activators such as phenobarbital, occurred in the periportal region where cells developed hypertrophy, accumulated porphyrin crystals and inflammation developed, all in association with the proliferation of oval cells. Thus, CAR provides an excellent experimental model for further investigations into its roles in liver regeneration, as well as the development of diseases such as hepatocellular carcinoma.     

Overexpression of transforming growth factor-alpha causes liver enlargement and increased hepatocyte proliferation in transgenic mice.

Transforming growth factor-alpha (TGF-alpha) expression is associated with hepatocyte DNA replication both in vivo and in culture. Our previous work using TGF-alpha transgenic mice showed that constitutive overexpression of this growth factor in the liver causes hepatic tumors in 75 to 80% of the animals at 12 to 15 months of age. To understand the cellular events by which TGF-alpha overexpression leads to abnormal liver growth, we examined hepatocyte proliferative activity in young and old TGF-alpha transgenic mice and hepatocyte ploidy in normal, dysplastic, and neoplastic livers of these animals. At 4 weeks of age, transgenic mice had higher liver weights and liver weight/body weight ratios than non-transgenic mice of the same age and hepatocyte proliferative activity, measured by 3H-thymidine incorporation after 3- and 7-day infusion, proliferating cell nuclear antigen staining, and mitotic index determination, was 2 to 3 times higher than in controls. In both transgenic and non-transgenic mice hepatocyte proliferation declined with age but the decrease was much more pronounced in control animals, so that at 8 months of age, hepatocyte replication was 8 to 10 times higher in transgenic animals. Surprisingly, however, transgenic and non-transgenic mice at this age had similar liver weight/body weight ratios. Labeling studies done in 3-month-old animals revealed that hepatocyte turnover was much faster in transgenic than in control animals, suggesting that a homeostatic compensatory mechanism involving cell death tended to restore normal liver weight/body weight ratios in older transgenic mice. Ploidy analyses showed that at 4 weeks of age transgenic mice had a higher proportion of diploid and tetraploid hepatocytes and that the hepatocellular tumors which developed in TGF-alpha transgenic mice at 13 months of age contained a higher fraction of diploid hepatocytes than that present in adjacent tissue or in dysplastic livers. The results demonstrate that constitutive overexpression of TGF-alpha causes increased hepatocyte proliferation and liver enlargement in young animals and is associated with a delay in the establishment of hepatic polyploidy. These findings as well as the response of transgenic mice to partial hepatectomy show that constitutive overexpression of TGF-alpha initially caused increased but regulated hepatocyte proliferation which in older animals was compensated in part by a faster cell turnover. At 8 to 10 months of age, proliferative activity may become constitutive in some TGF-alpha expressing hepatocytes.(ABSTRACT TRUNCATED AT 400 WORDS)     

Hepatitis resulting from liver-specific expression and recognition of self-antigen

Liver-specific immune reactivity in response to aberrant expression of antigen on the surface of hepatocytes is thought to be a major factor in development of autoimmune hepatitis (AIH). Persistent inflammation develops when these antigens are not eliminated and/or responses are not appropriately regulated. We have developed transgenic mice (OVA-HEP), which express chicken ovalbumin on the surface of hepatocytes. These mice are tolerant to ovalbumin, develop normally and have shown no evidence of liver or other disease up to 2 years of age. Adoptive transfer of na?ve ovalbumin-specific T cells into OVA-HEP transgenic mice led to liver-specific inflammation in a dose dependent manner. This hepatic necroinflammation was dependent upon CD8(+) Valpha2 OVA-specific T cells, was limited to the liver, and was augmented by OVA-specific CD4(+) T cell help; but did not result from adoptive transfer of ovalbumin-specific CD4 T cells alone. The response was self-limited but persistent inflammation developed after repeated transfer of antigen-specific T cells. This model of T cell recognition of antigen on hepatocytes may be used to understand many liver-specific aspects of the immune response in autoimmune hepatitis.     

A mouse model of hepatocellular carcinoma: ectopic expression of fibroblast growth factor 19 in skeletal muscle of transgenic mice

Most mouse models of hepatocellular carcinoma have expressed growth factors and oncogenes under the control of a liver-specific promoter. In contrast, we describe here the formation of liver tumors in transgenic mice overexpressing human fibroblast growth factor 19 (FGF19) in skeletal muscle. FGF19 transgenic mice had elevated hepatic alpha-fetoprotein mRNA as early as 2 months of age, and hepatocellular carcinomas were evident by 10 months of age. Increased proliferation of pericentral hepatocytes was demonstrated by 5-bromo-2'-deoxyuridine incorporation in the FGF19 transgenic mice before tumor formation and in nontransgenic mice injected with recombinant FGF19 protein. Areas of small cell dysplasia were initially evident pericentrally, and dysplastic/neoplastic foci throughout the hepatic lobule were glutamine synthetase-positive, suggestive of a pericentral origin. Consistent with chronic activation of the Wingless/Wnt pathway, 44% of the hepatocellular tumors from FGF19 transgenic mice had nuclear staining for beta-catenin. Sequencing of the tumor DNA encoding beta-catenin revealed point mutations that resulted in amino acid substitutions. These findings suggest a previously unknown role for FGF19 in hepatocellular carcinomas.     

Role of transforming growth factor beta 1 on hepatic regeneration and apoptosis in liver diseases.

AIMS--To investigate the effects of transforming growth factor beta 1 (TGF-beta 1) on regeneration and induction of apoptosis of liver cell and bile duct in various liver diseases. METHODS--Formalin fixed paraffin wax sections of 18 liver tissue samples were obtained by needle biopsy, surgery, or necropsy; these included six liver cirrhosis, three obstructive jaundice; five fulminant hepatitis, one subacute hepatitis, and three normal liver. Expression of TGF-beta 1, apoptosis related Le(y) antigen, Fas antigen, a receptor for tumour necrosis factor, and biotin nick end labelling with terminal deoxynucleotidyl transferase mediated dUTP (TUNEL) for locating DNA fragmentation, was investigated histochemically. RESULTS--TGF-beta 1 was expressed in areas of atypical bile duct proliferation, where bile duct continuously proliferated from liver cells. In occlusive jaundice and fulminant hepatitis, TUNEL was positive in nuclei and cytoplasm of metaplastic cells which formed incomplete bile ducts, and these cells appeared to extend from TGF-beta 1 expressing liver cells. Fas antigen was found only on the cell membrane of proliferated bile duct in fulminant hepatitis, which differed from TGF-beta 1 and TUNEL positive areas. Le(y) antigen was expressed in liver cell and bile duct at the areas with atypical bile duct proliferation, but its coexpression with TUNEL was rare. CONCLUSIONS--TGF-beta 1 plays a role in the arrest of liver cell regeneration and atypical bile duct proliferation, and in areas of rapidly progressing atypical bile duct proliferation, such as in fulminant hepatitis or bile retention. Apoptosis appears to be induced by TGF-beta 1. This phenomenon may account for the inadequate hepatic regeneration that occurs with liver disease.     

Hepatic over-expression of TGF-beta1 promotes LPS-induced inflammatory cytokine secretion by liver cells and endotoxemic shock

Transforming growth factor-beta (TGF-beta) is an important suppressor of inflammation. However, TGF-beta has also been found to promote secretion of inflammatory cytokines, and transgenic mice, which constitutively express TGF-beta in liver, have been found to be more susceptible to endotoxemia. To approach this apparent paradox, we investigated the role of hepatic TGF-beta1 in endotoxemia by utilising inducible TGF-beta1-transgenic mice that express TGF-beta1 under control of the C-reactive protein promoter. In contrast to non-transgenic littermates, administration of lipopolysaccharide (LPS) induced strongly increased expression of TGF-beta and acute phase proteins in the TGF-beta1-transgenic mice. Hepatic TGF-beta1-expression in the transgenic mice started an inflammatory cytokine cascade, marked by increased and prolonged secretion of TNF-alpha and IL-6 by hepatocytes. The inflammatory response of the TGF-beta1-transgenic mice to LPS was associated with high rates of mortality due to endotoxemic shock, marked by systemic hypotension and hypothermia. Endotoxemic shock was primarily mediated by TNF-alpha and IL-6, since inhibitory antibody to TNF-alpha or, more effectively, to IL-6 could reduce mortality in these mice. In conclusion, while TGF-beta-signalling to immune cells may suppress inflammatory effector function, TGF-beta-signalling to liver cells seems to promote LPS-stimulated secretion of inflammatory cytokines and to predispose for lethal endotoxemic shock.     

Evolution of neoplastic development in the liver of transgenic mice co-expressing c-myc and transforming growth factor-alpha.

We have previously shown that co-expression of c-myc and transforming growth factor (TGF)-alpha as transgenes in mouse liver results in major enhancement of neoplastic development in this organ as compared with expression of either of these transgenes alone. In this report we describe in detail the progression from liver cell dysplasia to hepatocellular carcinomas (HCCs) occurring in the liver of c-myc/TGF-alpha and c-myc transgenic mice. Despite morphological similarities in the sequence of events between the two transgenic lines, the dramatic acceleration, extent, and severity of hepatic lesions in c-myc/TGF-alpha mice clearly demonstrated the synergistic effects of this transgenic combination. Although c-myc/TGF-alpha and c-myc females displayed longer latency and lower tumor incidence, the pathological changes were the same as those seen in the male mice, including the formation of HCCs, which are absent in TGF-alpha single-transgenic females. Tumors in single- and double-transgenic mice showed induction of the endogenous c-myc and TGF-alpha and, most frequently, unchanged or decreased epidermal growth factor receptor, further indicating the collaborative role of c-myc and TGF-alpha in providing a selective growth advantage to tumor cells independently of the epidermal growth factor receptor levels. To identify possible tumor precursors, we focused particularly on the dysplastic changes preceding and accompanying the appearance of preneoplastic and neoplastic lesions in the double-transgenic mice. Early on, these changes were characterized by the appearance of large dysplastic hepatocytes, mostly pericentrally, expressing high levels of TGF-alpha and uPA, as well as TGF-beta 1, particularly in apoptotic cells. After a short period of replication and expansion into the liver parenchyma, as well as penetration into the central veins, these cells underwent apoptotic cell death while preneoplastic and neoplastic lesions were forming. The peritumorous tissues also contained small dysplastic hepatocytes and oval-like cells, similar to those found in the tumors. Transplantation of the transgenic liver tissues harboring only dysplasia with or without vascular lesions onto nude mice was able to yield HCCs composed of small diploid cells, suggesting that initiated cells are generated during the early dysplastic phase and can progress to HCC. It is therefore likely that large dysplastic hepatocytes undergo apoptosis, which may be closely associated with the up-regulation of TGF-beta 1 and uPA, whereas other cells evolve into the precursor population for HCC. Due to the simultaneous presence of c-myc, TGF-alpha, and dysplasia in premalignant human liver diseases, our transgenic mouse system appears to be an appropriate model for studying human hepatocarcinogenesis.     

A target role for mast cell in the prevention and therapy of hepatic fibrosis

Hepatic fibrosis is a common pathological process of chronic hepatic disease. Despite the extensive studies, the pathophysiological mechanisms in hepatic fibrosis remain unclear. Mast cell has a variety of physiological and pathological functions through the production of heparin, histamine, neutrophil chemoattractants, immunoregulatory cytokines, and mast cell-specific serine proteases tryptase and chymase. The survival and proliferation of mast cell are dependent upon stem cell factor. More recently, the data have suggested that mast cell has been associated with hepatic fibrosis in many chronic liver diseases. However, to what extent the mast cell effects the hepatic fibrosis remains to be clarified. Several therapeutic approaches to inhibit mast cell activation have already demonstrated some clinical utility in tissue fibrosis or inflammatory diseases such as the use of mast cell stabilizers, inhibitors of tryptase or chymase, blockade of stem cell factor and anti-IgE therapy. The article introduces the hypothesis that mast cell has a central role when it is affected by its activation state in the progression of hepatic fibrosis, thus new therapeutic strategies for treatment of hepatic fibrosis are suggested by this hypothesis. Considering the important role of mast cell and the development of these tangible therapeutic approaches in hepatic fibrosis will enable us to target any types of chronic liver diseases, which appears to be a more reasonable or a promising strategy.     

Immunosuppressive functions of hepatic myeloid-derived suppressor cells of normal mice and in a murine model of chronic hepatitis B virus

The immunosuppressive state of tumour-bearing hosts is attributable, at least in part, to myeloid-derived suppressor cells (MDSC). However, the role of MDSC in physiological conditions and diseases other than cancer has not been addressed. As the liver is a tolerogenic organ, the present study attempted to localize and assess functions of hepatic MDSC in a normal liver and in a murine model of chronic hepatitis B virus (HBV) infection. MDSC was identified in the liver of normal mice and HBV transgenic mice (TM) as CD11b(+) Gr1(+) cells by dual-colour flow cytometry. Highly purified populations of MDSC and their subtypes were isolated by fluorescence-activated cell sorting. The functions of MDSC and their subtypes were evaluated in allogenic mixed lymphocyte reaction (MLR) and hepatitis B surface antigen (HBsAg)-specific T cell proliferation assays. Normal mice-derived liver MDSC, but not other myeloid cells (CD11b(+) Gr1(-) ), suppressed T cell proliferation in allogenic MLR in a dose-dependent manner. Alteration of T cell antigens and impaired interferon-γ production seems to be related to MDSC-induced immunosuppression. In HBV TM, the frequencies of liver MDSC were about twice those of normal mice liver (13·6±3·2% versus 6·05±1·21%, n=5, P<0·05). Liver-derived MDSC from HBV TM also suppressed proliferative capacities of allogenic T cells and HBsAg-specific lymphocytes. Liver MDSC may have a critical role in maintaining homeostasis during physiological conditions. As liver MDSC had immunosuppressive functions in HBV TM, they may be a target of immune therapy in chronic HBV infection.     

Transforming growth factor-beta1 protein, proliferation and apoptosis of oval cells in acetylaminofluorene-induced rat liver regeneration

Administering of 2-acetylaminofluorene (2-AAF) before a two-thirds partial hepatectomy (PHx) results in suppression of hepatocyte proliferation and stimulation of oval cell proliferation. The objectives of this study was to examine the oval cell behaviour and associated transforming growth factor-beta1 (TGF-beta1) protein expression by combining 2-AAF with selective hepatic damage caused by PHx. We also studied the temporal relationship between TGF-beta1 expression, and proliferation and apoptosis of oval cells. Oval cells emerged from the portal areas and became more numerous with time fanning out into the periportal and midzonal hepatic parenchyma. Both smooth muscle actin (SMA) and TGF-beta1 immunostain revealed that TGF-beta1-positive cells were SMA-positive hepatic stellate cells (HSCs). Coinciding with the proliferation of oval cells, an increase expression of TGF-beta1 produced by SMA-positive HSCs was observed, thereafter apoptosis of oval cells reached its peak. This result implicated that TGF-beta1 produced by HSCs is intimately associated with proliferation and apoptosis of oval cells, and plays a role in the cessation of oval cell activation and remodeling of liver parenchyma in 2-AAF induced liver regeneration.     

Transgenic mice expressing cyclooxygenase-2 in hepatocytes reveal a minor contribution of this enzyme to chemical hepatocarcinogenesis

Cyclooxygenase-2 (COX-2) has been associated with cell growth regulation, tissue remodeling, and carcinogenesis. Ectopic expression of COX-2 in hepatocytes constitutes a nonphysiological condition ideal for evaluating the role of prostaglandins (PGs) in liver pathogenesis. The effect of COX-2-dependent PGs in chronic liver disease, hepatitis, fibrosis, and chemical hepatocarcinogenesis, has been investigated in transgenic (Tg) mice that express human COX-2 in hepatocytes and in Tg hepatic human cell lines. We have used three different complementary approaches: i) diethylnitrosamine (DEN)-induced chemical hepatocarcinogenesis in COX-2 Tg mice, ii) DEN/phenobarbital treatment of human COX-2 Tg hepatocyte-like cells, and iii) COX-2 Tg hepatocyte-like cells implants in nude mice. The data suggest that PGs produced by COX-2 in hepatocytes promoted mild hepatitis in 60-week-old mice, as assessed by histological examination, but failed to contribute to the development of liver fibrogenesis after methionine- and choline-deficient diet treatment. Moreover, liver injury, collagen content, and hepatic stellate cell activation were equally severe in wild-type and COX-2 Tg mice. The contribution of COX-2-dependent PGs to the development of DEN-induced hepatocarcinogenesis was evaluated in Tg mice, Tg hepatocyte-like cells, and nude mice and the analysis revealed that COX-2 expression favors the development of preneoplastic foci without affecting malignant transformation. Endogenous COX-2 expression in wild-type mice is a late event in the development of hepatocellular carcinoma.     

Hepatic progenitor cell represents a transitioning cell population between liver epithelium and stroma

Following an acute injury, the liver may maintain its structure and function through mitotic division of mature hepatocytes (i.e. hepatic regeneration). However, the regeneration ability of hepatocytes can be impaired in chronic liver diseases including chronic viral infection and alcohol abuse. Hepatic progenitor cells/oval cells (HPCs/OCs), capable of differentiation into both hepatocytes and cholangiocytes, occur and proliferate during chronic injury. Unfortunately, a use of HPCs for clinical therapy is blocked by the difficulty of exact identity of HPCs in liver. Focusing on the links between phenotype of HPCs and real stem cells originating from fetal liver or bone marrow (BM), the recent studies of HPCs neglect functional analysis and the close relationship between activation of HPCs and extracellular matrix (ECM) remodeling. It is currently widely accepted that mesenchymal-epithelial transition (EMT) and epithelial-mesenchymal transition (MET) play important roles not only in liver development but also in healing of chronic injured adult liver. Co-expression of epithelial/mesenchymal and HPCs markers has been demonstrated in cells undergoing EMT/MET. These cells led to hepatic regeneration after transplanted into rats with chronic liver injury. Notably, there is an increased expression of mesenchymal markers in HPCs after exposure to transforming growth factor-beta1 (TGF-β1). Based on these evidences, we hypothesize that HPCs represent a transitioning cell population undergoing EMT/MET, both parenchymal and mesenchymal cells of liver may be the direct sources of HPCs.     

Loss of keratin 19 favours the development of cholestatic liver disease through decreased ductular reaction

Keratins (K) are cytoprotective proteins and keratin mutations predispose to the development of multiple human diseases. K19 represents the most widely used marker of biliary and hepatic progenitor cells as well as a marker of ductular reaction that constitutes the basic regenerative response to chronic liver injury. In the present study, we investigated the role of K19 in biliary and hepatic progenitor cells and its importance for ductular reaction. K19 wild‐type (WT) and knockout (KO) mice were fed: (a) 3,5‐diethoxycarbonyl‐1,4‐dihydrocollidine (DDC); (b) cholic acid (CA); (c) a choline‐deficient, ethionine‐supplemented (CDE) diet; or (d) were subjected to common bile duct ligation (CBDL). The bile composition, liver damage, bile duct proliferation, oval cell content and biliary fibrosis were analysed. In untreated animals, loss of K19 led to redistribution of the K network in biliary epithelial cells (BECs) but to no obvious biliary phenotype. After DDC feeding, K19 KO mice exhibited (compared to WTs): (a) increased cholestasis; (b) less pronounced ductular reaction with reduced ductular proliferation and fewer oval cells; (c) impaired Notch 2 signalling in BECs; (d) lower biliary fibrosis score and biliary bicarbonate concentration. An attenuated oval cell proliferation in K19 KOs was also found after feeding with the CDE diet. K19 KOs subjected to CBDL displayed lower BEC proliferation, oval cell content and less prominent Notch 2 signal. K19 deficiency did not change the extent of CA‐ or CBDL‐induced liver injury and fibrosis. Our results demonstrate that K19 plays an important role in the ductular reaction and might be of importance in multiple chronic liver disorders that frequently display a ductular reaction. Copyright © 2015 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.     

The development of proliferating ductular structures in liver disease. An immunohistochemical study.

Proliferation of bile ductules or ductular hepatocytes occurs in a variety of liver diseases. The origin of these ductular structures and the mechanism of their proliferation are controversial. Using cytokeratin as marker for ductular structures, liver diseases in which ductular proliferation was a consistent and prominent feature were studied. Paraffin-embedded sections of livers (five cases each) with acute or chronic obstruction of extrahepatic bile ducts, primary biliary cirrhosis (stage II), drug-induced cholestatic liver disease, liver allograft rejection, vicinity of metastatic carcinoma, and massive hepatic necrosis were studied by immunohistochemical methods using three kinds of antiserum against cytokeratin polypeptides of different molecular weights. Bile ductules in diseases involving bile ducts and ductular hepatocytes in massive hepatic necrosis were closely associated with hepatocytes at the limiting plate or with injured hepatocytes. These findings suggest that hepatocytes play an important role in the proliferation of ductular structures or may represent their origin.     

Liver portal fibrosis in dioxin receptor-null mice that overexpress the latent transforming growth factor-beta-binding protein-1

Mice lacking aryl hydrocarbon (dioxin) receptor (AhR) had variable degree of hepatic fibrosis and altered liver architecture. Transforming growth factor-beta (TGF-beta), a major profibrogenic molecule in the liver, is localized to the extracellular matrix by its association to the latent TGF-beta-binding protein-1 (LTBP-1). Very recently, LTBP-1 has been shown to be negatively regulated by the AhR. Embryonic fibroblasts from AhR-null (AhR(-/-)) mice overexpress LTBP-1 and secrete four times more active TGF-beta than wild-type fibroblasts. To test whether TGF-beta and LTBP-1 overexpression colocalize within the fibrotic nodule of AhR(-/-) liver, we have characterized this hepatic portal fibrosis using collagen protein staining, immunohistochemistry and in situ hybridization. LTBP-1 mRNA and protein were overexpressed in the fibrotic region and colocalized with other indicators of fibrosis such as collagen and fibronectin and the fibroblast marker proteins alpha-actin and vimentin. TGF-beta protein also colocalized with fibrosis, although in contrast, TGF-beta mRNA expression, rather than restricted to the fibrotic compartment, was present throughout the hepatic parenchyma and exhibited similar levels in wild-type and AhR(-/-) mice. These results suggest that LTBP-1 targets TGF-beta to specific areas of the liver and that the AhR could be a negative regulator of liver fibrosis, possibly through the control of LTBP-1 and TGF-beta activities.     

Transforming growth factor-beta1 released from the spleen exerts a growth inhibitory effect on liver regeneration in rats

Several previous reports indicated that partial hepatectomy (PH) when combined with splenectomy enhances the regenerative capacity of the liver, most probably due to the removal of unknown inhibitory factors released from the spleen. Transforming growth factor (TGF)-beta1 is a major antiproliferative factor for the hepatocytes, and the role of splenic TGF-beta1 in liver regeneration is yet to be clarified. The splenic expression of TGF-beta1 and its secretion into the portal circulation from the spleen were evaluated in a standardized two-thirds hepatectomy model in rats. Rats in the control group underwent only the hepatectomy, while splenectomy was added in the splenectomy group. The hepatocyte proliferation rate was assessed by proliferating cell nuclear antigen (PCNA) immunostaining, and the results were compared with the TGF-beta1 kinetics in the portal blood. Significant increase in PCNA index and decrease in portal TGF-beta1 level were noticed in the splenectomy group at 48 hours after PH compared with the control group. Both TGF-beta1 protein and mRNA expression level in the spleen were strongest at 48 hours after PH and coincided with the peak of the plasma TGF-beta1 level. TGF-beta type II receptor (TbetaR-II) expression in the liver after PH was assessed immunohistochemically. The expression of TbetaR-II decreased at 12 hours and returned to preoperative level at 24 hours after PH in both groups. The changes of TbetaR-II expression were similar in both groups, and the significant difference was not observed at 48 hours after PH. Namely, splenectomy did not alter the expression of TbetaR-II in remnant liver at the peak of hepatocytes proliferation. In conclusion we found that TGF-beta1 was produced and secreted by the spleen during the early phase of liver regeneration and removal of the spleen enhanced proliferation of hepatocytes. Splenectomy thus may exert a salutary effect in selected patients with jeopardized regenerative capacity of the liver.