In normal rat liver, Kupffer cells were unequivocally identified using peroxidase cytochemistry by light microscopy in semithin plastic sections. The Kupffer cell population was found to constitute 31% of the sinusoidal cells and by morphometry and serial sectioning, a mean absolute number of 14 to 20 X 10(6) Kupffer cells per g liver was calculated. The mean distribution of Kupffer cells in the liver lobules was 43% in the periportal, 28% in the midzonal and 29% in the central area of the lobule. Administration of latex particles labeled only 64% of all Kupffer cells, and in particular centrally located cells, showed a lower activity of latex uptake, even at overloading doses. Furthermore, the latter cells were of smaller size than periportal Kupffer cell profiles. The mean number and distribution of latex-labeled Kupffer cells did not change over a period of 3 months, indicating a long lifetime for these resident macrophages. This slow population turnover was supported by the observed small mitotic index, 0.06% after a 6 hr arrest by vinblastine, and by the small [3H]thymidine labeling index which did not change over a period of 3 weeks after administration of the label. It is proposed that the Kupffer cell population, under physiologic conditions, is a long-living and self-renewing population, the kinetics of which substantially differ from those of other sinusoidal cell types.

This article describes the cytoskeleton associated with fenestrae and sieve plates of rat liver sinusoidal endothelial cells. Fenestrae control the exchange between the blood and parenchymal cells. We present evidence indicating that several agents that change the fenestrae and sieve plates also cause changes in the cytoskeleton. Cultured liver endothelial cells (LECs) were slightly fixed and treated with cytoskeleton extraction buffer. Detergent-extracted whole mounts of cultured cells were prepared for either scanning electron microscopy (SEM) or transmission electron microscopy (TEM). Extracted cells show an integral intricate cytoskeleton; sieve plates and fenestrae are delineated by cytoskeleton elements. Fenestrae are surrounded by a filamentous, fenestrae-associated cytoskeleton with a mean filament thickness of 16 nm. Sieve plates are surrounded and delineated by microtubuli, which form a network together with additional branching cytoskeletal elements. The addition of ethanol to cultured cells enlarged the diameter for these fenestrae-associated cytoskeleton rings by 5%, whereas serotonin treatment reduced the diameter by 20%. These observations indicate that the fenestrae-associated cytoskeleton probably changes the size of fenestrae after different treatments. After treatment with cytochalasin B the number of fenestrae increased. However, cytochalasin B did not change the structure of the fenestrae-associated cytoskeleton ring, but disperses the microtubuli. In conclusion, LECs have a cytoskeleton that defines and supports sieve plates and fenestrae. Fenestrae-associated cytoskeleton is a dynamic structure and plays a role in maintaining and regulating the size of fenestrae after different treatments. Therefore, the fenestrae-associated cytoskeleton controls the important hepatic function of endothelial filtration.

Considerable numbers of large granular lymphocytes (LGL) were isolated from rat liver by a simple method consisting of sinusoidal lavage at elevated (50 cm water column) perfusion pressure. This method gave a yield comparable with the enzymatic dissociation method commonly used for the isolation of nonparenchymal liver cells, but was shorter in time and had the advantage of avoiding the potentially harmful effects of the dissociating enzymes. The isolated LGL were highly cytotoxic against YAC-1 lymphoma cells and this cytolytic activity was blocked by treatment of the effector cells with an antibody against natural killer cells (anti-asialo GM1). We characterized the hepatic LGL as nonphagocytic, nonadherent, peroxidase-negative and acid phosphatase-positive cells which could be enriched in the low-density fraction of a Percoll gradient. At the light microscopic level, they showed characteristic azurophilic granules which corresponded to strongly osmiophilic granules with a specific morphology in electron microscopy. It is concluded that these LGL are identical to the "pit cells" which were formerly described by electron microscopy in situ as normal components of the liver sinusoids and which are easily recognized by their fine structure. It is also proposed that the liver may represent one of the major natural killer organs.

Partial hepatectomy and a single intravenous injection of zymosan were used to provoke expansion of the Kupffer cell population in rat liver. The number of Kupffer cells per microscopic field increased exponentially for 4 to 5 days after either stimulation. During this exponential growth phase, high mitotic activity of Kupffer cells was observed. The rate of mitosis, based on counts of cells arrested in metaphase by vinblastin, was compared with the increase in total cell population. During the first 3 days after partial hepatectomy, local proliferation was sufficient to explain the increase in population since the mean potential doubling time was 1.3 days compared to an observed doubling time of 3.7 days. During the first 3 days after zymosan stimulation, observed doubling time was 4.3 days compared with the mean potential doubling time of 5.2 days which led to the conclusion that growth is largely due to local proliferation of Kupffer cells. In both experimental situations, extrahepatic recruitment of "resident-type" macrophages was required during the last 2 days of the growth phase, since mitotic activity became too low to explain the observed growth. Proliferating Kupffer cells had characteristics of mature resident macrophages and were, therefore, considered to be different from elicited "exudate-type" cells, such as monocytes.

The high mortality of colon cancer is to a large extent caused by the frequent occurrence of liver metastasis. This is remarkable, because the liver harbors two distinct cell populations that can eliminate invading cancer cells, namely hepatic natural killer (