The Discovery of Endoplasmic Reticulum Storage Disease. The Connection between an H&E Slide and the Brain.

The revolutionary evolution in science and technology over the last few decades has made it possible to face more adequately three main challenges of modern medicine: changes in old diseases, the appearance of new diseases, and diseases that are unknown (mostly genetic), despite research efforts. In this paper we review the road travelled by pathologists in search of a method based upon the use of routine instruments and techniques which once were available for research only. The application to tissue studies of techniques from immunology, molecular biology, and genetics has allowed dynamic interpretations of biological phenomena with special regard to gene regulation and expression. That implies stepwise investigations, including light microscopy, immunohistochemistry, in situ hybridization, electron microscopy, molecular histopathology, protein crystallography, and gene sequencing, in order to progress from suggestive features detectable in routinely stained preparations to more characteristic, specific, and finally, pathognomonic features. Hematoxylin and Eosin (H&E)-stained preparations and appropriate immunohistochemical stains have enabled the recognition of phenotypic changes which may reflect genotypic alterations. That has been the case with hepatocytic inclusions detected in H&E-stained preparations, which appeared to correspond to secretory proteins that, due to genetic mutations, were retained within the rough endoplasmic reticulum (RER) and were deficient in plasma. The identification of this phenomenon affecting the molecules alpha-1-antitrypsin and fibrinogen has led to the discovery of a new field of cell organelle pathology, endoplasmic reticulum storage disease(s) (ERSD). Over fifty years, pathologists have wandered through a dark forest of complicated molecules with strange conformations, and by detailed observations in simple histopathological sections, accompanied by a growing background of molecular techniques and revelations, have been able to recognize and identify arrays of grotesque polypeptide arrangements.

Morphologic and immunohistochemical characterization of granulomas in the nucleotide oligomerization domain 2-related disorders Blau syndrome and Crohn disease.

BACKGROUND: Blau syndrome (BS) and Crohn disease (CD) are both characterized by granulomatous inflammation and related to nucleotide oligomerization domain 2 (NOD2) mutations. OBJECTIVE: This study aimed to define the morphologic and immunohistochemical characteristics of granulomas in patients with NOD2-related BS and CD. METHODS: Granuloma-containing biopsy specimens from 6 patients with BS and 7 pediatric patients with CD carrying NOD2 mutations or single nucleotide polymorphisms were studied for morphology, cellular composition, and cytokine expression by using hematoxylin and eosin staining and immunohistochemistry. RESULTS: Biopsy specimens from patients with BS typically showed polycyclic granulomas with large lymphocytic coronas, extensive emperipolesis of lymphocytes within multinucleated giant cells (MGCs), MGC death, and fibrinoid necrosis and fibrosis. In contrast, biopsy specimens from patients with CD showed simple granulomas with subtle/absent lymphocytic coronas, sclerosis of the surrounding tissue, and polymorphonuclear cells. Findings found to be similar in all granulomas were as follows: CD68 and HLA-DR expression by epithelioid cells, monocyte-macrophage lineage cells and MGCs, increased lymphocytic HLA-DR expression, increased CD4(+)/CD8(+) T-cell ratio, and CD20(+) B lymphocytes evenly distributed within and around granulomas. In both patient groups prominent IFN-γ expression was found in and around granulomas, and TNF-α and IL-23 receptor expression was moderate. IL-6, IL-17, and TGF-ß expression was prominent in granulomas from patients with BS but sporadic in granulomas from patients with CD. IL-10 expression was absent. CONCLUSION: Granulomas from patients with BS and granulomas from patients with NOD2-associated CD show distinct morphologic features and cytokine expression patterns, suggesting that the T(H)17 axis might be involved in the pathogenesis of BS, whereas T(H)1 is important in both patients with BS and patients with CD.

Patent hepatic ciliated foregut remnant resulting in an umbilicobiliary sinus tract, with gallbladder agenesis, in an 8-wk-old male French Bulldog.

Hepatic ciliated foregut remnants or cysts are congenital abnormalities resulting from retention of embryonic ciliated foregut within the liver. These structures are rarely reported in the human medical literature and have not been reported in the veterinary literature previously, to our knowledge. We describe here a case of an 8-wk-old male French Bulldog with a congenital patent hepatic ciliated foregut remnant resulting in an umbilicobiliary sinus tract. The dog also had concurrent gallbladder agenesis. The patient had yellow fluid discharging from the umbilicus, mimicking a patent urachus. Surgical exploration, removal, and histology provided a conclusive diagnosis of a hepatic foregut remnant and therapeutic resolution of the clinical signs. The histologic appearance of a hepatic foregut remnant is classical, namely a duct composed of 4 layers: an inner ciliated epithelial lining, loose connective tissue, smooth muscle, and a fibrous capsule.

Fifty years of impact on liver pathology: a history of the Gnomes.

Professional societies play a major role in medicine and science. The societies tend to be large with well-developed administrative structures. An additional model, however, is based on small groups of experts who meet regularly in an egalitarian model in order to discuss disease-specific scientific and medical problems. In order to illustrate the effectiveness of this model, the history and practices are examined of a long-standing successful example, the International Liver Pathology Group, better known as the Gnomes. The history shows that groups such as the Gnomes offer a number of important benefits not available in larger societies and nurturing such groups advances science and medicine in meaningful ways. The success of the Gnomes' approach provides a road map for future small scientific groups.

The amazing universe of hepatic microstructure.

An informal review is presented by the author of his 50 years of involvement in practice and research in hepatopathology. Some background for the author's attitude and meandering pathway into his professional career serves as introduction to a short discussion of the main topics of his interest and expertise. Histogenesis of liver cancer was the theme of early work for a Ph.D. thesis, the results of which were lost into oblivion due to local rules and circumstances, but were rescued three decades later. His conclusions about the cells of origin of liver cancer remain concordant with the newer concepts in the field after nearly half a century. Studies in the field of chronic hepatitis became a long saga, involving the first classification of this syndrome by "the Gnomes" in 1968, histochemical investigations of viral antigens, lymphocyte subsets and adhesion molecules, and a quarter century later, the creation of a new classification presently in use. Cholestasis was a broadening field in diagnostic entities and involved the study of liver lesions, comprising pathways of bile regurgitation (including reversed secretory polarity of hepatocytes) and so-called ductular reaction. The latter topic has a high importance for the various roles it plays in modulating liver tissue of chronic cholestasis into biliary cirrhosis, and as the territory of hepatic progenitor cells, crucial for liver regeneration in adverse conditions and in development of liver cancer. Study of the embryology of intrahepatic bile ducts helped to clarify the strange appearance of the ducts in "ductal plate configuration" in several conditions, including some forms of biliary atresia with poor prognosis and all varieties of fibrocystic bile duct diseases with "ductal plate malformation" as the basic morphologic lesion.

Keratin 19 marks poor differentiation and a more aggressive behaviour in canine and human hepatocellular tumours.

BACKGROUND: The expression of Keratin 19 (K19) was reported in a subset of hepatocellular carcinomas (HCCs). K19 positive HCCs are associated with an increased malignancy compared to K19 negative HCCs. No suitable mouse models exist for this subtype of HCC, nor is the incidence of K19 expression in hepatocellular neoplasia in model animals known. Therefore, we compared the occurrence and tumour behaviour of K19 positive hepatocellular neoplasias in dog and man. RESULTS: The expression of hepatocellular differentiation (HepPar-1), biliary/progenitor cell (K7, K19), and malignancy (glypican-3) markers was semi-quantitatively assessed by immunohistochemistry. The histological grade of tumour differentiation was determined according to a modified classification of Edmondson and Steiner; the staging included intrahepatic, lymph node or distant metastases. Four of the 34 canine hepatocellular neoplasias showed K19 positivity (12%), of which two co-expressed K7. K19 positive tumours did not express HepPar-1, despite the histological evidence of a hepatocellular origin. Like in human HCC, all K19 positive hepatocellular neoplasias were glypican-3 positive and histologically poorly differentiated and revealed intra- or extrahepatic metastases whereas K19 negative hepatocellular neoplasias did not. CONCLUSIONS: K19 positive hepatocellular neoplasias are highly comparable to man and occur in 12% of canine hepatocellular tumours and are associated with a poorly differentiated histology and aggressive tumour behaviour.

Clinicopathological study on cholangiolocellular carcinoma suggesting hepatic progenitor cell origin.

UNLABELLED: Cholangiolocellular carcinoma (CLC), a subtype of cholangiocellular carcinoma (CC), is thought to originate from the ductules/canals of Hering, where hepatic progenitor cells (HPCs) are located. We investigated the clinicopathological features of 30 CLCs and their relationship to HPCs. We evaluated the expression of hepatocytic markers (hepatocyte paraffin-1, canalicular polyclonal carcinoembryonic antigen, and CD10), biliary/HPC markers (keratin [K]7, K19, and neural cell adhesion molecule), the adenosine triphosphate binding cassette transporters: multidrug resistance protein 1, multidrug resistance-associated protein (MRP)1, MRP3, and breast cancer resistance protein, using immunohistochemistry and electron microscopy. In addition, gene expression profiling of CLC was performed and compared with the profile of hepatocellular carcinoma (HCC) with or without HPC features (K19 expression). In surrounding nontumoral tissue, K7-positive and K19-positive HPCs/ductular reaction were observed. More than 90% of the tumor was composed of CLC areas that showed small monotonous and/or anastomosing glands, strongly positive for K7 and K19. Especially at the tumor boundary, all cases showed a HCC-like trabecular area characterized by canalicular CD10/polyclonal carcinoembryonic antigen expression, and submembranous K7 expression, similar to intermediate hepatocytes. K7-positive/K19-positive HPCs were also seen. Out of 30 cases, 19 showed papillary and/or clear glandular formation with mucin production, representing CC areas. These three different areas showed transitional zones with each other. We observed an increased expression of MRP1, MRP3, and breast cancer resistance protein in the tumor. Electron microscopy findings in HCC-like trabecular areas confirmed the presence of HPCs and intermediate hepatocytes. HPC markers, K7, K19, prominin-1, receptor for stem cell factor c-kit, octamer-4 transcription factor, and leukemia inhibitory factor were upregulated (P < 0.05), while albumin was downregulated in CLC (P = 0.007) toward K19-negative HCCs. Comparison of CLC with K19-positive HCCs indicated a high homology. CONCLUSION: All these findings highly suggest a progenitor cell origin of CLC.

Mineralization of alpha-1-antitrypsin inclusion bodies in Mmalton alpha-1-antitrypsin deficiency.

BACKGROUND: Alpha-1-antitrypsin (AAT) deficiency (AATD) of Z, Mmalton, Siiyama type is associated with liver storage of the mutant proteins and liver disease. The Z variant can be diagnosed on isoelectric focusing (IEF) while Mmalton and Siiyama may be missed or misdiagnosed with this technique. Therefore, molecular analysis is mandatory for their characterization. In particular, that holds true for the Mmalton variant as on IEF profile it resembles the wild M2 subtype. METHODS: This is a retrospective analysis involving review of medical records and of liver biopsy specimens from a series of Mmalton, Z and Siiyama Alpha-1-antitrypsin deficiency patients. The review has been implemented by additional histological stains, electron microscopic observations and 3-D modeling studies of the sites of the mutations. RESULTS: Z, Mmalton and Siiyama liver specimen contained characteristic intrahepatocytic PAS-D globules. The globules differed in the three variants as only Mmalton cases showed dark basophilic precipitates within the AAT inclusions. The precipitates were visualized in haematoxylin-eosin (H.E.) stained preparations and corresponded to calcium precipitates as demonstrated by von Kossa staining. On immunohistochemistry, ZAAT inclusions were stained by polyclonal as well as monoclonal noncommercial anti-AAT antibody (AZT11), whilst Mmalton and Siiyama inclusion bodies remained negative with the monoclonal anti-Z antibody. 3-D protein analysis allowed to predict more severe misfolding of the Mmalton molecule as compared to Z and Siiyama that could trigger anomalous interaction with endoplasmic reticulum chaperon proteins, namely calcium binding proteins. CONCLUSIONS: Mmalton AAT inclusion bodies contain calcium precipitates inside them that allow the differential diagnosis with Siiyama and ZAAT inclusions in routine histological sections. The study has confirmed the specificity of the monoclonal AZT11 for the Z mutant. Thus, the combination of these two features is crucial for the distinction between the three variants and for predicting the genotype, whose confirmation would definitely require molecular analysis. Our study provides new data on the pathomorphogenesis of Mmalton inclusion bodies whose mineralization could play a central role in disease pathogenesis of Mmalton that is distinct from the Z and Siiyama variants. Calcium is known to be a major effector of cell death either via the increased intracellular concentration or the alteration of homeostasis.

[Cystic diseases of the liver. From embryology to malformations]. / Maladies kystiques du foie. De l'embryologie aux malformations.

Cystic diseases of the liver which are in most cases hereditary, are related to an embryonic disorder know as ductal plate malformation. These diseases correspond to partial or total arrest of remodeling of the ductal plate, leading to more or less complete persistence of the excess of embryonic biliary structures. The ductal plate malformation may concern different segments of the intrahepatic biliary tree (segmental bile ducts, interlobular bile ducts and the smallest bile duct ramifications) leading to various pathoclinical entities. Caroli's disease is characterized by persistent dilated large intrahepatic bile ducts and appears to be the result of a factor acting during the early period of bile duct embryogenesis. Congenital hepatic fibrosis is characterized by ductal plate malformations of more distal, interlobular, bile ducts, and could be due to a factor that acts later on during bile duct development. This disorder may be isolated or associated with malformations of large, segmental, intrahepatic bile ducts. Von Meyenburg complexes and autosomal dominant polycystic liver disease are related to ductal plate malformation of more peripheral interlobular bile ducts and caused by a factor intervening in the later phase of bile duct embryogenesis. The genetic or non genetic factors leading to these ductal plate malformations are unknown.

Ductal plates in hepatic ductular reactions. Hypothesis and implications. II. Ontogenic liver growth in childhood.

This article discusses the processes of bile duct growth and new lobule formation in the liver during childhood in the light of the ductal plate (DP) hypothesis. Unlike in other organs in which tubular elongation and branching ends with the creation of the organ-specific terminal differentiation products, in the liver a steadily enlarging parenchymal mass needs to establish continuity of its canalicular network with the existing bile duct system. The hypothesis suggests that this occurs by DP formation, like in the embryonic liver, and further assumes that pathological ductular reactions (DRs) induced by cholestasis or hypoxia are amplified equivalents of similar mechanisms operating at low level during liver growth. The concept is confronted with data on porcine liver growth, since swine and non-swine liver growth is thought to be comparable. Relative bile acid load may be the driving force for establishment of new canaliculo-ductular connections, supported in zones of relative hypoxia by hypoxia-inducible factor 1 alpha secreted by hepatocytes. The latter mechanism is at the base for induction of appropriate vascular changes in selected sinusoids, resulting in the development of portal inlet venules and additional draining central veins. The process gives rise to the formation of new single lobules by formation of new portal tracts or to the transformation of single lobules in compound lobules by development of new vascular septa. The concept of postnatal DP formation is important in the elucidation of several unexplained findings in adult liver diseases.

Ductal plates in hepatic ductular reactions. Hypothesis and implications. III. Implications for liver pathology.

This article discusses on the basis of the ductal plate hypothesis the implication of the concept for several liver abnormalities. The occurrence of ductal plates (DP) during liver growth in childhood would explain the paraportal and parenchymal localizations of von Meyenburg complexes in postnatally developed parts of the liver, and their higher incidence in adulthood versus childhood. It partly clarifies the lack of postnatal intrahepatic bile duct development in Alagille syndrome and the reduced number of portal tracts in this disease. Ductular reactions (DRs) in DP configuration are the predominant type of progenitor cell reaction in fulminant necro-inflammatory liver disease, when lack of sufficient parenchymal regeneration results in liver failure. The concept of dissecting DRs explains the micronodular pattern of advanced biliary and alcoholic cirrhosis. The concept explains the DP patterns of bile ducts in several cases of biliary atresia, with implications for diagnosis and prognosis. The hypothesis also has an impact on concepts about stem/progenitor cells and their niche.

Ductal plates in hepatic ductular reactions. Hypothesis and implications. I. Types of ductular reaction reconsidered.

This article focuses on the observation that most hepatic ductular reactions (DRs) have ductal plate (DP)-like patterns. Considering old and recent data, it hypothesizes that in DR, dedifferentiation of hepatocytes in ductular metaplasia may lead to the de novo development of liver stem/progenitor cells (LPCs). The three recognized types of DR are reconsidered, and an additional fourth type, DR type 2B, is added. In DR type 1 whose pattern differs from DP, the pre-existing cholangiocytes multiply and adjust the ductal structure in response to micro-environmental changes induced by oedema and inflammation. This DR fails to establish new canaliculo-ductular connections. DRs types 2A, 2B and 3 represent progenitor cell-based reactions in DP configuration which establish canaliculo-ductular connections similar to DPs in embryonic and foetal liver development. DR type 2A occurs in periportal areas in chronic cholestatic and inflammatory diseases and is interpreted as a reaction of LPCs, which either pre-exist or derive from dedifferentiated hepatocytes. DR type 2B occurs in centrolobular areas and zones of parenchymal hypoxia, is induced by hypoxia and corresponds to "ductular metaplasia" like type 2A with a presumably similar cellular origin. DR type 3 relates to the well-recognized activation of LPCs that reside in the canals of Hering. All DRs in DP configuration play a role in progression of fibrosis in chronic liver diseases.

Primary sclerosing cholangitis complicated by amyloid A amyloidosis: complete regression of the nephrotic syndrome by liver transplantation.

Secondary amyloidosis may complicate chronic inflammatory conditions and mostly presents as a renal disease with nephrotic syndrome or renal insufficiency. Its prognosis is largely affected by control of the underlying disease. We report a patient with primary sclerosing cholangitis, who developed cirrhosis over a 4-year period. Therapy with steroids and azathioprine was necessary for symptom control. Despite this treatment, she developed secondary amyloidosis with nephrotic syndrome 4 years after the initial presentation. The inflammatory process in the bile ducts was considered the cause of amyloid A amyloidosis. To control the nephrotic syndrome, liver transplantation was performed with the removal of the diseased liver and bile duct system. Liver transplantation was followed by a progressive and complete disappearance of the nephrotic syndrome. This is the first report describing the occurrence of amyloid A amyloidosis in primary sclerosing cholangitis, and the reversal of a secondary amyloidosis-induced nephrotic syndrome as a result of liver transplantation.

Preneoplastic lesions in human hepatocarcinogenesis.

The early stages of hepatocarcinogenesis in human chronic liver diseases are characterized by the emergence of preneoplastic lesions of which some will eventually develop into hepatocellular carcinoma (HCC). Basic studies on the genetic and epigenetic alterations of these preneoplastic lesions may eventually lead to new therapeutic strategies. Clinicopathological studies are also important in order to determine optimal management of patients with a preneoplastic lesion. This article aims to provide a comprehensive review of the current concepts of preneoplastic lesion in chronic liver diseases. The microscopical small-cell dysplastic focus is the smallest morphologically recognizable precursor lesion of HCC and therefore is a logical target of study to elucidate the earliest events in hepatocarcinogenesis. In contrast, large-cell dysplasia is not a precursor lesion, but appears to be of clinical value because of its good predictive value for development of HCC. Dysplastic nodules (DNs) are macroscopically recognizable precursor lesions of HCC and high-grade DNs (HGDNs) have a risk of malignant transformation. Detection of DNs and correct differentiation from small HCC (<2 cm) is sometimes difficult, especially when only imaging techniques are used. Additional clinicopathological studies on identification and optimal treatment of DNs are necessary. Molecular studies on HGDNs and small HCCs may yield much information on the genetic mechanisms involved in the transition from severe dysplasia to early malignancy. In contrast, currently available data indicate that (large) regenerative nodules do not represent a distinct step in hepatocarcinogenesis. Animal models will be helpful in the further unravelling of human HCC development, provided that studies are performed on models that are good representatives of human hepatocarcinogenesis. We propose three criteria by which good mimickers can be identified.

Diagnostic and pathogenetic implications of the expression of hepatic transporters in focal lesions occurring in normal liver.

Hepatocellular adenoma and focal nodular hyperplasia (FNH) are benign liver tumours. The differential diagnosis of these lesions and of well- to moderately differentiated hepatocellular carcinomas is often difficult but is very important in view of their different treatment. Although neither type of lesion is connected to the biliary tree, FNHs are cholestatic, whereas this is rarely the case for hepatocellular adenomas. This suggests that hepatocellular uptake and secretion of bile constituents is different in FNHs compared to adenomas. We therefore evaluated the expression and localization of hepatic transporters in hepatocellular adenomas, different types of FNH and well- to moderately differentiated hepatocellular carcinomas in non-cirrhotic liver and compared them with normal liver, using real-time RT-PCR and (semi-)quantitative immunohistochemistry. The parenchymal expression of the uptake transporter OATP2/8 (OATP1B1/3) was minimal or absent in adenoma, while there was strong and diffuse expression in FNH. We observed diffuse parenchymal expression of the basolateral export pump MRP3 in adenomas, while only reactive bile ductules and adjacent cholestatic hepatocytes were MRP3-positive in FNH. The MRP3/OATP2/8 expression pattern of atypical FNHs resembled that of adenomas, suggesting that both types of lesion are related. Most hepatocellular carcinomas showed decreased expression of one or more of the canalicular transporters (MDR1, MDR3, BSEP). The differences in transporter expression profile between FNHs and adenomas are most likely pathogenetically important and may explain why only FNHs are cholestatic. The finding that each type of focal lesion in non-cirrhotic liver has a specific transporter expression pattern may be useful in the establishment of a correct diagnosis by imaging or on needle biopsy.

The correlation between portal myofibroblasts and development of intrahepatic bile ducts and arterial branches in human liver.

BACKGROUND/AIMS: The development of the intrahepatic bile ducts most likely requires interactions between epithelial and mesenchymal cells. In view of the epithelial-mesenchymal interactions between portal myofibroblasts (pMFs) and biliary epithelial cells in adult diseases of the bile ducts, we investigated the presence and function of pMFs during the development of intrahepatic bile ducts, as well as the development of intrahepatic branches of the hepatic artery. METHODS: We performed haematoxylin-eosin-stainings and immunohistochemistry for alpha-smooth-muscle actin, cytokeratin 19 and vimentin on serial sections of 45 fetal and postnatal liver biopsies. RESULTS: The mesenchyme of portal tracts in the ductal plate stage devoid of a hepatic artery branch, contained numerous and diffusely scattered pMFs. Portal tracts with a hepatic artery branch were always larger than those without and showed a decreasing number of pMFs. In the remodeling stage, all portal tracts contained a hepatic artery branch, and pMFs were restricted to the periductal mesenchyme. These periductal pMFs disappeared after full incorporation of the bile duct. CONCLUSION: Our findings strongly suggest interactions between pMFs and epithelial cells of the developing bile ducts. The development of the intrahepatic arterial branches always precedes the incorporation of the tubular segments of the ductal plate.

Progenitor cells in diseased human liver.

Hepatic progenitor cells are immature epithelial cells that reside in the smallest ramifications of the biliary tree in human liver. These cells are capable of differentiating toward the biliary and the hepatocytic lineages and represent the human counterpart of the oval cells in murine liver. An increased number of progenitor cells (referred to as "activation") and differentiation of the same toward hepatocytes or bile duct epithelial cells, or both, is a component of virtually all human liver diseases. The extent of progenitor cell activation and the direction of differentiation are correlated with the severity of the disease and the type of mature epithelial cell (hepatocyte or bile duct epithelial cell), respectively, that is damaged. Analogous to findings in animal models of hepatocarcinogenesis, human hepatic progenitor cells most likely can give rise to hepatocellular carcinoma. The factors that govern human hepatic progenitor cell activation and differentiation are beginning to be identified.

Hepatic stellate cell/myofibroblast subpopulations in fibrotic human and rat livers.

BACKGROUND/AIMS: Hepatic stellate cells (HSC) are commonly considered the precursor population of septal myofibroblasts (MF) in cirrhosis. We studied the distribution and expression profile of mesenchymal (myo)fibroblast-like populations in fibrotic and cirrhotic liver, in an attempt to elucidate their possible interrelationships. METHODS: Fibrotic/cirrhotic livers (from 22 human explants and from two rat models: carbon tetrachloride intoxication, bile duct-ligation) were studied by means of immunohistochemistry (single and double immunostaining) with antibodies raised against desmin, alpha-smooth muscle actin (alpha SMA), glial fibrillary acidic protein (GFAP), neural-cell adhesion molecule (N-CAM), synaptophysin, neurotrophins, neurotrophin receptors and alpha B-crystallin (ABCRYS). RESULTS: Septal MF showed the same expression profile as portal MF, in human and rat, being alpha SMA/ABCRYS/brain-derived nerve growth factor/GFAP-expression, with additional N-CAM- and desmin-expression in rat portal/septal MF. Perisinusoidally located HSC stained with all tested markers, MF at the septal/parenchymal interface showed an expression profile, intermediate between the profiles of HSC and portal/septal MF. CONCLUSIONS: In advanced fibrosis and in cirrhosis, regardless of cause or species, three distinct mesenchymal (myo)fibroblast-like liver cell subpopulations can be discerned: portal/septal MF, interface MF and perisinusoidally located HSC. The fact that septal MF share more characteristics with portal MF than with HSC might suggest descent.