Remodeling of pineal epithelium in the fetal rat as delineated by immunohistochemistry of laminin and cadherin

Epithelial remodeling in the rat pineal during fetal development was immunohistochemically analyzed by using antibodies for laminin and cadherin as molecular markers of basal lamina and intercellular junctions, respectively. The proliferation and differentiation of pinealocytes were also investigated in relation to the advance of epithelial remodeling. The pineal anlage of embryonic day 16 is completely covered by basal lamina immunolabeled for laminin. After embryonic day 17, local dissolution of the basal lamina occurs on the epithelial folds, which develop predominantly in the rostral pineal wall. Some pineal cells migrate through these interruptions and form cellular aggregations outside the basal lamina. Cadherin immunostaining reveals focal dissolution of intercellular junctions in epithelial regions protruding into the pineal lumen. Dissolution of the basal lamina and intercellular junctions accompanied by cellular migration into the stromal tissue or into the pineal lumen continues until birth. The distribution of mitotic cells immunolabeled for BrdU is homogeneous throughout the organ during the fetal period, whereas that of differentiating pinealocytes immunoreactive for synaptophysin shows striking regional heterogeneity in close correlation with the remodeling of the pineal epithelium. The migrating cell populations located either outside the basal lamina or inside the pineal lumen are more liable to become synaptophysin-positive than the rest of the epithelium. These results suggest that epithelial remodeling in the fetal pineal is induced, at least in part, by epithelial infolding and that this remodeling promotes the differentiation of pinealocytes.

Apoptosis of neutrophils and their elimination by Kupffer cells in rat liver

The fate of neutrophils in the peripheral circulation is poorly understood. In this study, the role of Kupffer cells in eliminating aged and apoptotic neutrophils was investigated. Liver, spleen, lung, and blood samples from Wistar rats were examined by light and electron microscopy, the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling (TUNEL) method, and immunohistochemistry after the intravenous injection of OK-432, a streptococcal preparation. Neutrophils were trapped predominantly in the periportal and midzonal regions of hepatic lobules and were in contact with endothelial cells and Kupffer cells, or were surrounded by Kupffer cells. The trapping of neutrophils peaked after 6 hours. Apoptotic neutrophils, with or without buds, were found in the lumen of hepatic sinusoids as early as 6 hours, reached maximal levels after 12 hours, and represented greater than 60% of the total number of neutrophils in the liver. The presence of apoptotic neutrophils was correlated with the degree of neutrophil phagocytosis. Double-staining showed that TUNEL-positive neutrophils were phagocytosed or encircled by ED1- or ED2-positive Kupffer cells. In contrast, apoptosis and phagocytosis of neutrophils were rare in the spleen, lung, and peripheral blood. These results suggested that the appearance of apoptotic neutrophils in the hepatic sinusoids and their rapid clearance by Kupffer cells occurs after the invasion of bacteria (i.e., bacteremia or bacteriotoxemia) or the release of inflammatory mediators into the blood stream. These findings have important implications for the regulation of neutrophil homeostasis, the limitation of inflammation and tissue injury, and provide insight into the physiological removal of circulating, senescent neutrophils.

Contribution of immune response to the hepatic fibrosis induced by porcine serum

To investigate whether hepatic fibrosis induced by porcine serum in rats is caused by an immune reaction to porcine serum, rats that were immunologically tolerant exclusively to porcine serum were subjected to the repeated injection of porcine serum over a long period. This porcine serum-tolerant group consisted of 15 Wistar rats that had been injected intraperitoneally with porcine serum twice a week from the first postnatal day for 18 weeks. The control group consisted of 16 Wistar rats, aged 8 weeks, that were injected intraperitoneally with porcine serum twice a week for 10 weeks. Livers were fixed and examined by light microscopy. The serum of each rat was subjected to indirect enzyme-linked immunosorbent assay (ELISA) to measure the level of antibody to porcine albumin. In addition, immunohistochemical staining for ED1 was performed on untreated normal and porcine serum-induced fibrotic rat livers to examine the distribution of macrophages and their precursors, the monocytes. All rats in the tolerant group showed an extremely low antibody level (x = 68.27 +/- 4.53), and none (0/15) developed hepatic fibrosis. The majority of rats in the control group showed a very high antibody level (x = 1242.19 +/- 201.15); 75 percent (12/16) developed hepatic fibrosis. Data indicate that, despite the prolonged, repeated injections of porcine serum, if an immune response to porcine serum does not occur, the rats do not develop hepatic fibrosis. The porcine serum-tolerant rats developed hepatic fibrosis after 4 weeks of CCl4 treatment, indicating that injection of porcine serum into neonatal rats did not cause anergy of fibrogenesis, thereby preventing the animal from developing hepatic fibrosis. In normal rat liver, ED1-positive cells, which include nearly all Kupffer cells, were located pre-dominantly in the periportal area. In fibrotic rat liver, ED1-positive cells aggregated prominently in the newly formed and advanced connective tissue septa developed mainly between the neighboring central veins, and in fibrotic parts of the liver capsule. Aggregation of ED1-positive cells was rarely observed in nonfibrotic parts of the liver capsule. The difference between normal and fibrotic rat liver in distribution of EDl-positive cells suggests an involvement of macrophages in fibrogenesis and septum formation. In conclusion, our study showed a significant contribution by the immune response to porcine serum antigens leading to porcine serum-induced rat hepatic fibrosis--processes in which macrophages may be important. This study may lead to an understanding of the mechanism responsible for this form of experimental hepatic fibrosis.

Contribution of immune response to the hepatic fibrosis induced by porcine serum

To investigate whether hepatic fibrosis induced by porcine serum in rats is caused by an immune reaction to porcine serum, rats that were immunologically tolerant exclusively to porcine serum were subjected to the repeated injection of porcine serum over a long period. This porcine serum-tolerant group consisted of 15 Wistar rats that had been injected intraperitoneally with porcine serum twice a week from the first postnatal day for 18 weeks. The control group consisted of 16 Wistar rats, aged 8 weeks, that were injected intraperitoneally with porcine serum twice a week for 10 weeks. Livers were fixed and examined by light microscopy. The serum of each rat was subjected to indirect enzyme-linked immunosorbent assay (ELISA) to measure the level of antibody to porcine albumin. In addition, immunohistochemical staining for ED1 was performed on untreated normal and porcine serum-induced fibrotic rat livers to examine the distribution of macrophages and their precursors, the monocytes. All rats in the tolerant group showed an extremely low antibody level (x = 68.27 +/- 4.53), and none (0/15) developed hepatic fibrosis. The majority of rats in the control group showed a very high antibody level (x = 1242.19 +/- 201.15); 75 percent (12/16) developed hepatic fibrosis. Data indicate that, despite the prolonged, repeated injections of porcine serum, if an immune response to porcine serum does not occur, the rats do not develop hepatic fibrosis. The porcine serum-tolerant rats developed hepatic fibrosis after 4 weeks of CCl4 treatment, indicating that injection of porcine serum into neonatal rats did not cause anergy of fibrogenesis, thereby preventing the animal from developing hepatic fibrosis. In normal rat liver, ED1-positive cells, which include nearly all Kupffer cells, were located pre-dominantly in the periportal area. In fibrotic rat liver, ED1-positive cells aggregated prominently in the newly formed and advanced connective tissue septa developed mainly between the neighboring central veins, and in fibrotic parts of the liver capsule. Aggregation of ED1-positive cells was rarely observed in nonfibrotic parts of the liver capsule. The difference between normal and fibrotic rat liver in distribution of EDl-positive cells suggests an involvement of macrophages in fibrogenesis and septum formation. In conclusion, our study showed a significant contribution by the immune response to porcine serum antigens leading to porcine serum-induced rat hepatic fibrosis--processes in which macrophages may be important. This study may lead to an understanding of the mechanism responsible for this form of experimental hepatic fibrosis.

Mesangial cells of the lamprey, Lampetra japonica, store vitamin A

Structure and vitamin A-storage of the mesangial cells in the lamprey kidney are documented using the gold chloride method, fluorescence histochemistry and electron microscopy. Abundant lipid droplets in the cytoplasm of the mesangial cells release intense, but quickly fading vitamin A-fluorescence under a fluorescence microscope and react with gold chloride. Characteristic tubular invaginations of the plasma membrane which usually occur in the lamprey smooth muscle cells are observed in these cells. We discuss similarities of the lamprey mesangial cells with hepatic stellate cells in the lamprey and mammals, such as vitamin A-storage, blood flow-regulation and proliferative potential. To the best of our knowledge, this is the first report on and proof of vitamin A-storage in mesangial cells, providing evidence for a vitamin A-storing cell lineage in vertebrates.

Expression of neuron-specific enolase in the pineal organ of the domestic fowl during post-hatching development

Immunohistochemistry for neuron-specific enolase (NSE) revealed that NSE is localized in both a limited number of pinealocytes and intrinsic afferent neurons in the pineal organ of the domestic fowl. Furthermore, a computer-assisted three-dimensional imaging technique allowed to clarify the reverse distributional pattern of both elements: NSE-positive pinealocytes displayed a dense distribution especially in the vesicular portion of the gland, whereas NSE-immunoreactive nerve cells were mainly found in the pineal stalk. The number of NSE-positive intrinsic neurons in the pineal organ of chickens decreased rapidly after hatching, with a concentration of these elements in the basal portion (stalk) of the pineal organ. On the other hand, immunoreactive pinealocytes increased remarkably in the end-vesicle of the organ with age, followed by a gradual expansion toward the proximal portion. Thus, the spectacular increase in NSE-positive pinealocytes and the progressive reduction of reactive neurons occurred in parallel during the course of post-hatching development. NSE-immunoreactive pinealocytes displayed morphological characteristics of bipolar elements, endowed with an apical protrusion into the pineal lumen and a short basal process at younger stages, whereas multipolar types of NSE-positive pinealocytes were predominantly found in the adult domestic fowl. These results indicate that in the pineal organ of the domestic fowl (1) the ontogenetic expansion of NSE-immunoreactive pinealocytes is paralleled by a regressive afferent innervation, (2) the NSE-positive pinealocytes transform from a bipolar (columnar) type to a multipolar type during post-hatching development, and (3) these ontogenetic changes in the NSE-immunoreactivity and morphology of pinealocytes may reflect the development of a neurosecretory-like capacity of the organ.

Expression of neuron-specific enolase in the developing rat retina as revealed by immunocytochemistry

Expression of neuron-specific enolase (NSE) in retinal neurons was immunocytochemically investigated during the development of the rat retina. At embryonic day 14 (E14), the first immunoreaction of NSE was identified in the pigment epithelium. NSE-positive ganglion cells occurred at the inner surface of the retina by E15. Horizontal cells and photoreceptor cells became stainable for NSE in the outer portion of the neuroblastic layer as early as E17. At E20, when the majority of ganglion cells were intensely positive for NSE, immunoreactive amacrine cells first appeared at the outer surface of the developing inner plexiform layer. It was not until postnatal day 7 (P7) that NSE-positive bipolar cells occurred in the middle of the inner nuclear layer. At this stage, most of the photoreceptor cells located in the outer nuclear layer were immunolabeled, whereas the ectopic photoreceptor cells in the inner nuclear layer were devoid of immunoreaction. Most identifiable retinal neurons became strongly immunostained for NSE by P14. Our results indicate that the NSE expression of retinal neurons occurs just after their migration to the final location and prior to establishing the synaptic structures. In this paper, the characteristic sequence in which different types of retinal neurons exhibit NSE immunoreaction is discussed in the light of certain autoradiographic data on the sequence of retinal cell genesis.

Analysis of the heterogeneity within bovine pineal gland by immunohistochemistry and in situ hybridization

In the present study, we demonstrate a cortical and medullary arrangement of parenchymal cells in the bovine pineal gland by using antibodies for neuron-specific enolase, synaptophysin, and hydroxyindole O-methyltransferase (HIOMT) as markers of pinealocytes, and glial fibrillary acidic protein (GFAP) as a marker of interstitial (glial) cells. Furthermore, by means of probes specific for HIOMT mRNA, we have examined possible differences in melatonin synthesis between the cortex and the medulla. Immunoreactive pinealocytes for each antigen investigated are more densely distributed in the cortex than in the medulla. In the cortex, GFAP-positive interstitial cells have large intenselystained somata endowed with several long, thin cytoplasmic processes, whereas in the medulla, they display smaller, less intensely labeled perikarya from which numerous fine short processes emerge. Golgi staining has confirmed these morphological differences between the interstitial cells in the cortex and those in the medulla. An analysis using confocal laser microscopy together with in situ hybridization for HIOMT mRNA has shown that the expression of mRNA transcripts in the cortex is more intense than that in the medulla. The expression of the HIOMT gene in a cluster of cells in the medial habenular nucleus is lower than that in pinealocytes of the pineal organ proper.

Morphometric analysis of infiltrating cells that adhere to the sinusoidal wall and migrate into the space of disse in the orthotopically transplanted rat liver

To reveal the kinetics of infiltrating cells in the hepatic parenchyma after the liver transplantation, we identified the cell type (macrophages, monocytes, agranular lymphocytes, large granular lymphocytes, and neutrophils) and localization on toluidine blue-stained sections of perfusion-fixed liver grafts in rejecting and tolerant combinations and performed quantitative analysis of the density of each cell species infiltrating inside and outside the sinusoid at days 4 and 7. The number of total infiltrating cells per unit square became 9 times as high as that of an untreated liver at day 4 and 30 times as high at day 7. Macrophages accounted for a large part of the infiltrating cells both in and around the sinusoid: 72% of intrasinusoidal infiltrating cells and 88% of extrasinusoidal ones at day 4; 73% of intrasinusoidal ones and 93% of extrasinusoidal ones at day 7. The ratio of extrasinusoidal cell to intrasinusoidal cell of macrophages was 9:91 at day 4 and 34:66 at day 7, much higher than ratios of other infiltrating cells. This fact means that macrophages show a marked tendency to migrate out of the sinusoid in the liver graft. The proportion of macrophages to total infiltrating cells dropped at day 4 and went up again at day 7, while that of monocytes showed a reverse pattern. Histologically, immature macrophages, possibly derived from recipient monocytes, coexisted with vacuolated donor macrophages in the sinusoid at day 4, but the latter cells were diminished at day 7. These data indicate that transformation of recipient monocytes into macrophages in the sinusoid and subsequent extrasinusoidal migration of newly formed macrophages occur soon after the cell influx into the liver graft begins at day 4. The present study has revealed that macrophages, especially those migrating into the space of Disse, will be closely related to the pathogenesis of the liver transplantation.

Light and electron microscopic analysis of liver sinusoids during hepatocarcinogenesis with 2-acetylaminofluorene in rats

To clarify the sequential changes and morphological differences of the sinusoidal structures between hepatocellular carcinoma (HCC) and hepatocellular adenoma (HA), we examined morphological changes of sinusoidal cells and related structures such as basement membrane during hepatocarcinogenesis in the rat. During continuous feeding of carcinogenic diets containing 2-acetylaminofluorene to rats, HA appeared at the 8th week in the peripheral area and then extended toward the centrolobular area. The appearance of HCC was recognized at the 27th week. In the HA lesion, the morphology of sinusoidal cells and related structures was basically the same as that of normal liver except for a slight thickening of the basement membrane and a decreased amount of vitamin A-lipid droplets of stellate cells. In HCC, the fenestrations of endothelial cells disappeared and the basement membrane became continuous, thick and often multilayered. Stellate cells contained almost no vitamin A-lipid droplets and were associated with abundant collagen fibers. Kupffer cells and pit cells were not seen inside the sinusoid. All these features of the sinusoids in HCC resembled the morphological characteristics of the capillary. The present study has revealed that HCC possesses sinusoid structures distinct from those of HA. This suggests that HCC may not derive directly from HA but may develop newly within the HA.

Granuloma formation in the liver of Balb/c mice intoxicated with carbon tetrachloride

Hepatic granulomas induced by a single or several subcutaneous injections of carbon tetrachloride (CCl4) in Balb/c mice were examined electronmicroscopically and immunocytochemically. Stellate cells (fat-storing cells; lipocytes; Ito cells) were identified by the detection of cytoplasmic desmin, while T-lymphocytes and monocytes/macrophages were identified with monoclonal antibodies Thy 1.2 and MOMA-2, respectively. Following pericentral necrosis induced with CCl4, clear foci containing lymphocytes, monocytes, macrophages and perisinusoidal stellate cells occurred in the surrounding hepatic parenchyma on day 5. These clear foci developed to granulomas with increasing numbers of macrophages and stellate cells. Mitotic and apoptotic figures in randomly distributed macrophages, and direct contacts between macrophages and stellate cells were frequently seen within the granulomas. The stellate cells were characterized by a well-developed granular endoplasmic reticulum and Golgi complex. Collagen fibrils were closely applied to the stellate cells and connective tissue septa extended between neighboring granulomas and/or the pericentral necrotic areas after several injections of CCl4. CCl4-induced hepatic granulomas provide a model for investigating paracrine and/or autocrine modulation within a well-organized microenvironment during progressive hepatic inflammation and fibrosis.

Intralobular heterogeneity of perisinusoidal stellate cells in porcine liver

The aim of the present investigation was to elucidate the intralobular heterogeneity of the perisinusoidal stellate cells (fat-storing cells, lipocytes) in the porcine liver. Their three-dimensional structure, desmin immunoreactivity and vitamin-A storage were studied by use of the Golgi silver, immunocytochemical and gold chloride methods. In order to locate the stellate cells, the hepatic lobules were divided into 10 zones. The stellate cells were readily identified in Golgi preparations by their striking dendritic appearance with branching processes encompassing the sinusoids. The stellate cells in the centrolobular zones were conspicuously dendritic with longer processes in comparison to those emitted by periportal elements. Such arborizations were studded with numerous thorn-like microprojections. Desmin immunoreaction in the periportal zones was stronger than that in the centrolobular zones. Vitamin-A storage in the stellate cells was well developed in zones 2-4, but reduced gradually toward the central region. The perisinusoidal stellate cells display marked heterogeneity in morphology and function based on their zonal location in the hepatic lobule.

Tissue kallikrein in the rat pineal gland: an immunocytochemical study

Tissue kallikrein in the rat pineal gland was immunocytochemically investigated with the aid of specific antiserum against rat urinary kallikrein. We also compared the tissue kallikrein immunoreactivity of the pineal gland with that of the submandibular gland and kidney, which have been well established as tissue kallikrein-synthesizing organs. The cytoplasm of pinealocytes from both the superficial and the deep portion of the gland exhibited specific immunolabeling for tissue kallikrein, but the immunoreaction was weaker than that observed in exocrine organs. Two types of tissue kallikrein-immunoreactive pinealocytes were distinguished; the first predominant type displayed moderate immunostaining, whereas a small number of cells, the second type, were so intensely labeled that their cytoplasmic processes were clearly outlined. The results of the present study suggest the existence of different types of pinealocytes and a potential physiological role of tissue kallikrein in the rat pineal gland.

Role of mesenchymal cell populations in porcine serum-induced rat liver fibrosis

The role of liver mesenchymal cell populations in porcine serum-induced rat liver fibrosis were studied morphologically and immunohistochemically. Five-week-old rats were intraperitoneally injected with porcine serum twice a week and examined at various intervals between 3 and 24 wk after the initial injection. At an early phase, numbers of fibroblasts and extracellular matrix increased in the walls of central veins and in portal and capsular connective tissues. In the walls of central veins, the number of "second-layer cells" (i.e., the fibroblasts located at the second layer of the wall) increased. Connective tissue septa, accompanying some fibroblasts, extended from these interstitial tissues into the hepatic parenchyma, and their foremost edges came into direct contact with the perisinusoidal stellate cells. The sinusoids adjacent to the newly formed septa collapsed and later disappeared; this process resulted in the formation of hepatic limiting plates along the septa. At a more advanced stage, the interstitial fibroblasts and septal cells-which were derived from interstitial fibroblasts and the stellate cells-increased and became multilayered, constructing three-dimensional cell networks. These networks, together with increased collagen fibrils and elastic fibers, constitute the fibrotic dense connective tissue. In the control rat, smooth muscle cells were positive on vimentin, desmin and smooth muscle-alpha-actin staining. The stellate cells, second-layer cells, capsular and portal fibroblasts were shown to be vimentin and desmin positive and smooth muscle-alpha-actin negative. In the fibrotic liver, septal(fibroblastic) cells were vimentin and desmin positive and smooth muscle-alpha-actin negative. We conclude that not only the perisinusoidal stellate cells but also the interstitial fibroblasts, including the second-layer cells, play substantial role in the development of porcine serum-induced septal fibrosis in rat liver.

Localization and ultrastructure of the Kupffer cells in orthotopically transplanted liver grafts in the rat

Kupffer cells play an important role in the acceptance or rejection of liver grafts. We examined the ultrastructure of the Kupffer cells in transplanted rat livers, from an early to a late stage where the graft is accepted, using a DA-to-PVG combination. Two days after surgery, endocytic activity of the Kupffer cells had increased, as evidenced by worm-like structures and many endocytic vacuoles. There was often close apposition to the monocytes or lymphocytes. By day 4, infiltration of mononuclear cells into the sinusoids was readily noticeable. By day 7, several Kupffer cells had migrated into the space of Disse through the openings in endothelial linings. The number of Kupffer cells reached a maximum at 14 days. They were located mostly outside the sinusoid, adhering to the hepatocytes. At this point in time, however, the Kupffer cells contained few endocytic vacuoles and phagolysosomes, in contrast to those at 2 days. The number and location of Kupffer cells became almost normal at 2 months. The present results indicate that Kupffer cells are highly activated before mononuclear cell infiltration becomes manifest in the sinusoid, and that when a rejecting reaction reaches a peak, they are usually located extrasinusoidally and show a morphologically immature profile.

Liver units in three dimensions: I. Organization of argyrophilic connective tissue skeleton in porcine liver with particular reference to the "compound hepatic lobule"

Liver units were investigated in pig livers by means of histologic serial tracing, physical model building, and computer-aided three-dimensional imaging. Observations of the argyrophilic connective tissue skeleton were based mainly on the celloidin-embedded serial sections treated with silver impregnation. The parenchymal mass that clothed the initial segments of hepatic venous radicles was demarcated by fibrous septa which formed isolable units with two basic patterns: the simple hepatic lobule (SHL) and the compound hepatic lobule (CHL). Both lobule types presented regular limiting structures circumscribing each unit. Three-dimensional studies revealed that 25% of the lobules in a section belonged to the SHL type and 75% to the CHL type, the latter being predominant among the surface lobules. When considered in only two dimensions, however, the SHL-like lobules constituted the majority. Polygonal analysis disclosed that the pentagonal lobule was the most typical, instead of the "hexagonal" or "classic" lobule. The CHLs represented a multiaxial unit containing a system of venous tributaries in accordance with intralobular septation, whereas the SHLs were found with one axial vessel having a dendritic tendency at the incipient end; some SHLs were drained eccentrically by separate vessels into a sublobular vein. It was observed that, in dividing CHLs, whereas particular sinosoids were transformed into portal twigs, other sinusoids were changed into central venous tributaries. Fibrous deposition occurred along the septal-line sinusoids, bringing into view the septum-initiating plane. Fibroconnective tissue was supplied from the portal area and central (sublobular) adventitia, where portal triad structures and adventitial arterioles, respectively, were included. The findings of the present study facilitate the understanding of several characters of the lobules that have been reported previously, or occasionally postulated, such as the portal-central bridging tendency, the intralobular arterioles or ductules, the translobular artery or portal vein, the "portal-portal" or "portal-central" anastomoses, and the apposition of pericentral zone close to periportal zone. Based on differences in argyrophilia of sinusoidal reticulum, in proportion of lobule types, and in vasculature, the anatomic heterogeneity of liver unit was demonstrable in zonality, regionality, and locality.

Ultrastructural characteristics of lymphokine-activated killer cells of the rat in comparison with natural killer cells

Lymphokine-activated killer (LAK) cells with a broad spectrum of tumor cell killing have been reported to be related to natural killer (NK) cells morphologically and phenotypically. We here examine the ultrastructural characteristics of LAK cells of the rat, comparing them to those of normal and OK-432-activated NK cells. Results show that, five days after the culturing of spleen lymphocytes with human recombinant interleukin-2, there were induced LAK cells, which were large granular lymphocytes and had a cytotoxic capacity against NK-resistant P-815 tumor cells. They were larger in size than NK cells and richer in cell organelles such as ribosomes, rough endoplasmic reticulum, a Golgi apparatus, granules and vesicles. The granules of LAK cells were shown to be related to multivesicular bodies as those of NK cells; they included multivesicular bodies, fully dense granules and intermediate forms between them. The average numbers and sizes of the granules and the proportion of multivesicular bodies and intermediate forms among the total granules were greater in LAK cells than in NK cells. The density of the small vesicles packed in multivesicular bodies and intermediate forms was much higher in LAK cells. At the contacting surface of the LAK cells bound to the target cells, exocytosis of multivesicular bodies was shown to occur. We recognized here two populations of LAK cells with different types of vesicles, one containing rod-cored vesicles and the other a new type of vesicles termed "demilune-cored vesicles". The latter vesicles were the same in size as the rod-cored ones and contained a dense core located eccentrically. Between these two populations of LAK cells, there was no difference concerning the profile of the dense granules. The present study indicates that, although LAK and NK cells share several ultrastructural features, the former show markedly enriched cell organelles, which indicate an accelerated metabolism of the cell for continuous proliferation.

Perisinusoidal stellate cells of the liver: important roles in retinol metabolism and fibrosis

In mammals, liver perisinusoidal stellate cells play an important role as a main store of body retinol (vitamin A). This fat-soluble vitamin is essential for vision, and regulates differentiation and growth of many cell types during embryonal development as well as in adult tissues. Thus, many cell types require a continuous supply of retinol. The storage of retinol (as retinyl esters) in stellate cells ascertains ample access of retinol to such cells also during periods with a low dietary intake. In lower vertebrates such as fish, vitamin A-storing stellate cells are found not only in the hepatic lobule, but also in the connective tissues of organs like intestine, kidney, ovaries, testes, and gills. Extrahepatic vitamin A-storing stellate cells are found in higher vertebrates when excessive doses of vitamin A are administered. It is not clear at present whether these cells also play a role in retinol metabolism under normal conditions. Stellate cells proliferate in a fibrotic liver, and they have been found to synthesize connective tissue compounds such as collagen. It was recently demonstrated that stellate cells are the principal cellular source of collagen and other extracellular substances in normal as well as fibrotic livers. Therefore, stellate cells, which seem to be a specialized type of pericyte, have a central role in the pathological changes observed during the development of liver fibrosis.

Localization of hydroxyindole O-methyltransferase-synthesizing cells in bovine epithalamus: immunocytochemistry and in-situ hybridization

Hydroxyindole O-methyltransferase (HIOMT)-immunoreactive cells and melatonin synthesis were demonstrated in bovine epithalamus (including the pineal gland) with monoclonal antibodies and cRNA probes to HIOMT. The HIOMT-immunoreactive product was present in the cytoplasm of pinealocytes. All identifiable pinealocytes were clearly labeled in the pineal gland. The expression of the HIOMT gene was first identified in pinealocyte cytoplasm by in-situ hybridization (ISH). The distribution of the hybridization-positive cells in the pineal gland was compatible with that revealed by immunocytochemistry using the monoclonal antibody to HIOMT. In addition, HIOMT transcripts were found in the medial habenular nucleus, and the habenular and posterior commissure; they may correspond to S-antigen-immunoreactive cells demonstrated in the same regions of the hamster and the mouse. In these regions, the hybridization-positive cells did not exhibit HIOMT-immunoreactivity; thus, cells devoid of immunoreactivity may synthesize but rapidly transport the newly synthesized proteins. These results indicate (1) that the conversion of N-acetylserotonin into melatonin takes place in the cytoplasm of pinealocytes, (2) that some epithalamic cells in the habenular area may synthesize melatonin, and (3) that melatonin may act as a chemical messenger in centrally directed processes, as shown by using S-antigen immunocytochemistry.

The intracellular distribution of cell organelles in natural killer cells during the cytolysis of bound tumor cells, with special reference to the rod-cored vesicles

The secretory function of the natural killer (NK) cells has been considered to be essential for cytolytic activity against their target cells. In this study, the distribution and spatial relationship of various cell organelles which participate in the secretory process, i.e., Golgi apparatus, vesicles, granules and microtubules, were examined ultrastructurally in non-treated and OK-432-activated rat NK cells bound to the tumor cells, with special reference to the rod-cored vesicles which are the most characteristic structure of the NK cells. Rod-cored vesicles and their closely related structures, "empty" vesicles, were derived from the end portion of the Golgi trans cisternae and became accumulated in the central area which was surrounded by the Golgi apparatus, nucleus and contact surface. Some of the vesicles appeared to be further transported to the contact area along the microtubules extending from the centrioles toward the bound targets. The access of the vesicles to the contact surface occurred at that portion where subplasmalemmal actin lattice was thin. The distribution of the dense granules and multivesicular bodies was similar to that of the vesicles, but the area of their occurrence was a little wider. At the outer aspect of the Golgi apparatus was situated the endoplasmic reticulum from which transitional vesicles came to the inner or cis cisternae of the apparatus. The present observations indicate that the cell organelles of the conjugated NK cells are purposefully arranged in the cytoplasm in such order that the generated rod-cored vesicles and "empty" ones are efficiently directed toward the bound tumor cells.

Stomatocytic or discoidal erythrocyte ghosts containing only spectrin

We extracted Triton-treated erythrocyte ghosts with 2 M KCl (Triton/KCl/ghosts), and then with 1.2 M KBr at pH 5.5 (Triton/KCl/KBr ghosts). Triton/KCl/KBr ghosts were very similar in shape to untreated ghosts, Triton ghosts and Triton/KCl ghosts under a phase-contrast microscope at various pH vales and salt concentrations, despite having lost most of their phospholipids and proteins, except for spectrin. Negatively stained Triton ghosts, Triton/KCl ghosts and Triton/KCl/KBr ghosts appeared similar to each other, but the regularity of the spectrin network structure decreased somewhat in that order. Triton/KCl/KBr ghosts were stabilized by adding both actin and band 4.1, but not by adding either alone. These and previous findings strongly suggest that the spectrin network is visible and the simplest inframembrane structure.

Differentiation of crypt epithelium in human palatine tonsils: the microenvironment of crypt epithelium as a lymphoepithelial organ

The differentiation of the keratinocytes of the human palatine tonsils were studied by means of light and electron microscopy and immunohistochemistry using a polyclonal (K) and two monoclonal antikeratin antibodies (PKK1, PKK2). In the surface epithelium, the basal cells, cuboidal or columnar in shape, undergo progressive terminal differentiation and are transformed into the flattened cells of the upper layers. K reacts with both the basal and spinous layers, while PKK1 and PKK2 mark exclusively the basal layer. In the neck portion of the crypt, cavities containing one or aggregated lymphocytes with amorphous substances are observed in the spinous layer. The cavities are surrounded by elongated cytoplasmic processes of transformed epithelial cells bearing surface microvilli. These transformed epithelial cells display intense PKK1- and PKK2-positive reactions, whereas other conventional polygonal cells in the vicinity remain PKK1- and PKK2-negative as do those in the surface epithelium. In the deep portion of the crypt, where numerous lymphocytes invade the epithelium, the epithelial cells are transformed into star-shaped reticulum cells showing PKK1- and PKK2-positive reactions. The extended and branched cytoplasmic processes interconnect with one another constituting a complex network of reticulum cells, the well known reticulation of the crypt epithelium. Ten-nm filaments are usually oriented parallel to the longitudinal axis of transformed epithelial cells. Our observations suggest that the cell-shape transformation, i.e., from conventional polygonal epithelial cells into epithelial reticulum cells, occurs when the epithelial cells are in close contact with the infiltrating lymphocytes, and that this transformation is accompanied by a change in keratin phenotype.