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

Recruitment of dendritic cells to pathological niches in inflamed liver

The liver is a specialized organ for host defense and immunity. Recruitment of dendritic cells (DCs) is crucial to host defense in a granulomatous liver disease in mice. In response to danger signals, DC precursors are mobilized de novo into the circulation. Myeloid DC (mDC) precursors are recruited to perisinusoidal spaces and activated to form granulomas. Recruited mDCs subsequently extravasate into Disse's space and migrate to the portal area to induce portal tract-associated lymphoid tissue (PALT). Some mDCs are remobilized into draining hepatic lymph nodes (LNs) to prime antigen-specific CD4+ helper T cells. Kupffer cell-derived CCL3/MIP-1alpha attracts mDC precursors to the sinusoidal granulomas, whereas PALT composed cell-derived CCL21/SLC attracts activated mDCs to the T-cell zone of PALT. Inflammatory cytokines modulate this sinusoid-portal migration through IL-1R/TLR signaling. Recruited mDCs themselves also produce several chemokines and cytokines that modulate T-cell responses. A unique trafficking of circulating mDC precursors within the inflammation-associated, newly formed compartments ("pathological niches") is strictly regulated by both homeostatic and inducible chemokines and determines the final efficiency of the immunity in this organ.

Regulation by chemokines of circulating dendritic cell precursors, and the formation of portal tract-associated lymphoid tissue, in a granulomatous liver disease

We have studied the recruitment and roles of distinct dendritic cell (DC) precursors from the circulation into Propionibacterium acnes-induced granulomas in mouse liver. During infection, F4/80(-)B220(-)CD11c(+) DC precursors appeared in the circulation, migrated into the perisinusoidal space, and matured within newly formed granulomas. Recruited DCs later migrated to the portal area to interact with T cells in what we term "portal tract-associated lymphoid tissue" (PALT). Macrophage inflammatory protein 1alpha attracted blood DC precursors to the sinusoidal granuloma, whereas secondary lymphoid organ chemokine (SLC) attracted mature DCs to the newly identified PALT. Anti-SLC antibody diminished PALT expansion while exacerbating granuloma formation. Therefore, circulating DC precursors can migrate into a solid organ like liver, and participate in the granulomatous reaction in response to specific chemokines.

Pretelangiectasis and telangiectasis of the bovine liver: a morphological, immunohistochemical and ultrastructural study

Forty-five livers from conventionally slaughtered Holstein-Friesian steers with telangiectasis were studied by histochemical methods, immunolabelling for fibronectin, laminin and type IV collagen, and transmission electron microscopy. None of the previously described changes in telangiectasis (necrosis, hepatitis, thromboembolism, dilatation of the space of Disse by glycogen extruded from hepatocytes and reduced density of the perisinusoidal reticulin framework) were evident. Pretelangiectasis (sinusoidal dilatation) and telangiectasis (blood-filled cavities) were characterized by sinusoidal barrier alterations, leading to sinusoidal capillarization; and there was progressive formation of a true basement membrane and perisinusoidal fibrosis. Comparison of bovine liver telangiectasis and human peliosis hepatis suggests that they have a similar pathogenesis. It is suggested that a primary alteration of the sinusoidal barrier is responsible for an increased deposition of basement membrane components (fibronectin, laminin, type IV collagen) in the perisinusoidal region, and fibrosis. These are likely to render the exchange of oxygen and substrates between blood and hepatocytes more difficult and to produce haemodynamic imbalances, leading to hepatocyte atrophy and eventually to sinusoidal disruption.

A pathological study of the perisinusoidal unit of the liver in acute African swine fever

African swine fever is an acute haemorrhagic disease of pigs which may serve as a model for the study of the pathogenesis of other viral haemorrhagic fevers. This paper describes an ultrastructural study of the sequence of lesions produced in the perisinusoidal functional unit of the liver of pigs inoculated with the Malawi '83 strain of African swine fever virus, which is classified as haemadsorbing and highly virulent. Virus replication was observed in Kupffer cells and monocytes from three days after inoculation, in hepatocytes and fat-storing cells at five and seven days after inoculation, and in sinusoidal endothelial cells at seven days after inoculation. Further observations included intravascular coagulation, which peaked at five days after inoculation, and fibroblast and myofibroblast transformation of fat-storing cells at seven days after inoculation. These results suggest that activated cells of the mononuclear phagocyte system may play a major role in this sequence of lesions and the possible role of the cytokines that may be released by these cells is discussed.

Synergism between hepatic injuries and a nonhepatotropic reovirus in mice. Enhanced hepatic infection and death

Reovirus type 1, after intravenous inoculation in the adult mouse, is secreted via bile into the intestine in an infectious form. Although reovirus type 1 is rapidly removed from systemic circulation by the liver and the lung, very few hepatocytes express reovirus antigen during infection. In intestinal cells, reovirus replicates selectively in the crypts. This site preference may be due to active cell proliferation in the crypts. We hypothesized that the state of the cell may affect virus replication and tested this hypothesis by using chemical and surgical means to increase hepatic mitotic activity. Adult mice were treated with carbon tetrachloride or surgical trauma, inoculated with reovirus type 1 intravenously, and subsequently killed. Virus antigen was identified using a highly specific immunohistochemical technique. Liver sections were stained using immunoperoxidase with specific rabbit antireovirus antibody. Hepatotoxin and surgical trauma increase reovirus antigen detection in both Kupffer cells and hepatocytes. Only the sequential administration of CCl4 and virus caused mortality at doses sublethal for each alone. These data demonstrate a synergism between hepatic injury and reovirus which results in a significant increase in the magnitude of viral infection and contributes to mortality. Such synergism may be important in idiopathic liver disease.

Ultrastructure and quantitative composition of isolated endothelial cells of rat liver

Isolated endothelial cells (n 110; 350-540 microns3 in volume) of the sinusoid of rat liver were found to differ from in situ endothelial cells by their rounded shape with the nucleus usually in the centre and fenestrae of the sieve plates across the entire cytoplasm. Their volume density is 0.2814 (SE 0.0085). Some of them tend to form complex, ramified structures as well as clefts and vacuoles up to 1 micron in size. Dense bodies are other structures quite often seen in endothelial cells (Vv 0.0189, SE 0.0085). Mitochondria, on the other hand, are extremely rare (Vv 0.0023, SE 0.0009). Both the preservation and relocation of sieve structure after isolation may probably be due to the cytoskeleton which in vivo causes changes of size and number of endothelial cell fenestrae under physiological and pathological conditions.

The liver as a self-organizing system. I. Theoretics of its representation

The liver is described as a composite system consisting of a set of operative creodic microunits open to a continuous flow of matter, energy and informations. Its dynamics depend on two interactive and interrelated subsystems with actions described as homopoiesis and homeorhesis, making it an autoisodiasostic system. The system's emergent (equifinal) or emergence states, operative potential, diffusion and reaction phenomena and compensation states are also formally described. For readers not familiar with the language of general system theory, of system dynamics and of categorical analysis, a glossary of some terms is provided.

Glutathione synthesis and export in experimental liver cirrhosis induced by thioacetamide: relations to ultrastructural changes

Micro-and macronodular experimental liver cirrhosis was induced in female rats by administration of 0.03% thioacetamide (TAA) in drinking water for 3 or 6 months, respectively. The glutathione (GSH) status (content, synthesis, export) and ultrastructural changes of liver were investigated 14 d after withdrawal of TAA. The hepatic level of GSH was increased after 6 months TAA treatment. The levels of oxidized glutathione (GSSG) were not changed after 3 months or 6 months TAA administration. The GSH synthesis was not disturbed in the cirrhotic livers; only the ratio between the 2 synthesizing enzymes was changed in macronodular liver cirrhosis. The plasma GSH content was reduced in both cases, independent of the stage of liver cirrhosis. The electron microscopic studies on cirrhotic rat livers revealed a series of characteristic structural changes, such as disorganization and total lack of the microvilli border, appearance of basement membrane-like deposits within the narrowed space of Disse, disappearance of the highly porous endothelial cell lining and partly an intensively detoriated blood supply within the pseudolobules. It is suggested that all these changes may contribute to a disturbance of the GSH export from the hepatocytes into the blood. It is very likely, however, that the alterations of the sinusoidal cell surface play the most important role. 1. The GSH/GSSG redox potential is shifted in favour of the reduced form in this cirrhosis model. This shift seems to be connected with later stages of cirrhogenesis. 2. A GSH export disturbance is responsible for the decreased plasma GSH level in liver cirrhosis.

The ability of cultivated human skin fibroblasts to store vitamin A. A contribution to the cytogenesis of the Ito cells of the liver

Cultivated skin fibroblasts were fed with retinol palmitate in a dosage of 100,000, 200,000, or 300,000 I.U. In dependence on the dosage a remarkable uptake and storage of vitamin A can be observed in vitro (27.2, 53.0 or 60.7% of the fibroblasts). Distinctly retinol palmitate storing cells have lost their typical fibroblast-like appearance and are transformed into cells which are comparable to the Ito cells of the liver from the cytomorphological point of view.