The blood hepatocytic barrier: a light microscopical, transmission- and scanning electron microscopic study

The hepatic stellate (Ito) cell: its role in human liver disease

The hepatic stellate (Ito) cell lies within the space of Disse and has a variety of functions. Stellate cells store vitamin A in characteristic lipid droplets. In the normal human liver, the cells can be identified by the presence of these lipid droplets; in addition, many stellate cells in the normal liver express alpha-smooth muscle actin. In acute liver injury, there is an expansion of the stellate cell population with increased alpha-smooth muscle actin expression; stellate cells appear to play a role in extracellular matrix remodelling after recovery from injury. In chronic liver injury, the stellate cell differentiates into a myofibroblast-like cell with marked expression of alpha-smooth muscle actin and occasional expression of desmin. Myofibroblast-like cells have a high fibrogenic capacity in the chronically diseased liver and are also involved in matrix degradation. In vitamin A intoxication, hypertrophy and proliferation of the stellate and myofibroblast-like cells may lead to non-cirrhotic portal hypertension, fibrosis and cirrhosis. In liver tumours, myofibroblast-like cells are involved in the capsule formation around the tumour and in the production of extracellular matrix within it. The transition of stellate cells into myofibroblast-like cells is regulated by an intricate network of intercellular communication between stellate cells and activated Kupffer cells, damaged hepatocytes, platelets, endothelial and inflammatory cells, involving cytokines and nonpeptide mediators such as reactive oxygen species, eicosanoids and acetaldehyde. The findings suggest that the stellate cell plays an active role in a number of human liver diseases, with a particular reactivity pattern in fibrotic liver disorders.

Hepatic sinusoidal endothelium: Ulex lectin binding

The sinusoidal endothelial cells of human liver can be identified by light and electron microscopy, but there appear to be no specific immunocytochemical markers of these cells. Among specific markers available for vascular endothelial cells in general, Ulex europaeus I lectin (UEA I) is the most sensitive. In the present study, 37 liver biopsies were examined for UEA I binding and for Factor VIII related antigen (F VIII RAg) to determine if sinusoidal endothelial cells were positive. The material included normal liver, biopsies from patients with cirrhosis and biopsies in a variety of other liver diseases. Three embryonal human livers were also included in the immunocytochemical analysis. Eleven oesophageal rings obtained at mechanical transection for variceal bleeding in cirrhotic patients were used as control tissue. Sinusoidal endothelial cells of normal liver did not stain with UEA I, but six of seven with alcoholic cirrhosis and only one of 25 non-cirrhotic liver specimens (a case of acute hepatitis with bridging necrosis) were positive. In two of the six cirrhoses the sinusoidal endothelial cells were stained for F VIII RAg as well. Embryonal sinusoidal endothelial cells were stained with UEA I but were negative for F VIII RAg. The results of the study confirm that sinusoidal endothelial cells of normal adult human liver are phenotypically different from those lining blood vessels in other sites. In cirrhosis, positive staining may be related to the transformation of hepatic sinusoids into true capillaries and thus be a marker of the severity of physiological disturbance in the liver.

Light microscopical demonstration and zonal distribution of parasinusoidal cells (Ito cells) in normal human liver

The parasinusoidal cells of the liver (Ito cells) were demonstrated light microscopically in autopsy specimens fixed in formalin and stained with Oil red O after dichromate treatment. The method allows examination of large samples containing numerous acini. Quantitative assessment showed a zonal gradient with 6.3 and 7.7 parasinusoidal cells per 62.5 X 10(3) micron2 in zone 1 and 3, respectively.

The concept of the "perisinusoidal functional unit" of the liver--importance to pathological processes

Non-hepatocytes account for 30 per cent of cells in the liver, with sinusoid-coating endothelial and Kupffer cells being the most common types. In addition, there are some scattered pit cells in the wall. Ito cells (perisinusoidal cells, lipocytes) are located in the Disse space. In this paper a review is given of structural and functional changes of cells in response to pathological conditions with reference to the importance of such changes due to diseases of the liver and the organism in large. Cooperation and interaction among non-hepatocytes, the vascular pole of hepatocytes, and Disse space as the site of reaction are summarised under the concept of the "Perisinusoidal Functional Unit", and the concept is explained in greater detail by examples (lipoprotein catabolism, processes of phagocytosis, vitamin A storage, virus infections, accumulation of pathological substances, fibrosis, and capillarization).