Large granular lymphocytes (LGLs) differ from other lymphocytes in their recirculation pattern and are distributed preferentially in nonlymphoid organs such as the liver and lung. The liver-associated LGLs adhere strongly to the sinusoidal endothelium and show a natural killer (NK) cytotoxicity against incoming metastatic tumor cells; this reaction occurs very rapidly because, in contrast to the immune response, it does not require complex processes in the lymphoid tissue. They have been extensively studied morphologically in terms of pit cells. LGLs have two characteristic cell organelles which participate in the NK cytolysis, i. e., dense granules and rod-cored vesicles. The former are lysosomes derived from multivesicular bodies and contain pore-forming proteins. The latter are the secretory vesicles exclusively seen in LGLs and are markedly increased in number when the NK function is augmented by biological response modifiers. These two structures are believed to be exocytosed in the space between LGL and the conjugated tumor cell. The microenvironment of the liver sinusoids, which includes Kupffer cells, endothelial cells and other lymphocytes, is considered to regulate the function of the liver-associated LGLs. Liver-associated LGLs, as well as Kupffer cells, are intrinsically involved in the defense system of the liver under various physiological and pathological conditions.

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Blood vascular casts of the rat adrenal glands were observed with a scanning electron microscope. The cortical capillary plexus drains, through the corticomedullary venous radicles, into the subcortical veins continuous with the medullary collecting veins. The medullary capillary plexus drains into the corticomedullary venous radicles, subcortical veins and medullary collecting veins. No portal vessel was noted between the cortical and medullary capillaries. These findings indicate that the cortical blood rich in glucocorticoids preferentially and continuously flows into the corticomedullary venous radicles, subcortical veins and medullary collecting veins all three of which are fenestrated in type, and also suggest that the vascular route from the cortical capillaries to the medullary collecting veins functions as a substitute for the portal system, controling the biosynthesis of catecholamines in the adrenal medulla. The vascular bed of the accessory adrenal gland (extra-adrenal cortical or chromaffin body) is sometimes annexed to that of the adrenal gland. On rare occasions, the vascular beds of the extra-adrenal cortical and chromaffin bodies fuse with each other. Additional scanning of tissue samples confirmed the direct drainage of cortical capillaries into the medullary veins and also the endothelial fenestrations of these capillaries and veins.

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A new monoclonal antibody (JK-199) was found to react with basement membranes on paraffinembedded tissue sections without prior enzyme digestion. JK-199 was shown to react with isolated type IV collagen treated by any of four different fixatives —PLP, 4% formalin, modified Zamboni's (0.2% picric acid, 4% paraformaldehyde in 0.1M phosphate buffer, pH 7.4) or Bouin's—applied for 6h at room temperature and incubated at 60°C for 30min to simulate routine tissue processing. None of the fixatives was able to alter the reactivity of JK-199 with isolated type IV collagen. In the human placenta, specific and intense staining of basement membranes was demonstrated on paraffin sections fixed with any of the four fixatives. In human skin, basement membranes were fully demonstrated on paraffin sections fixed by PLP fixative or by 4% formalin, but only partially on sections fixed by picric acidcontaining fixatives. Optimal results, i. e., with the least non-specific or incomplete staining, were obtained on PLP-fixed paraffin-embedded tissues. In PLP-fixed paraffin sections of the kidney, skeletal muscle, and small intestine, all basement membranes were stained intensely by this antibody (JK-199) at the expected locations. The results indicate that JK-199 may be widely applicable for the analysis of basement membrane kinetics, including developmental precesses or pathological conditions.

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Eight-week-old female C57B1/6 mice were injected with endotoxin LPS and/or other antigens into the left hind footpad, and then the number of lymph follicles in the draining popliteal lymph nodes was examined. In untreated mice each popliteal node contained 10-12 lymph follicles at both 8 and 15 weeks of age. Animals given 50μg of LPS at 8 weeks of age showed an increase in the number of lymph follicles 3 weeks later, but this number returned to normal levels by 15 weeks after the LPS injection. After a 2-μg-LPS injection at 23 weeks of age, the number of lymph follicles in the draining lymph node was unchanged, but that in animals given the 2-μg-injection 15 weeks after the 50-μg-LPS injection was significantly increased. In animals receiving 2 Lf of diphtheria toxoid, instead of the 2-μg-LPS, at 15 weeks after a 50-μg-LPS injection, the number of lymph follicles per draining node was within the normal range. In one group of mice, the initial injection of 50-μg-LPS at 8 weeks of age was followed by injections every third week of several kinds of antigens which had been shown to be ineffective in inducing follicle formation. Here, the number of lymph follicles in the draining popliteal node was kept to significantly increased levels at 25 weeks of age.
The present results suggest that, while most lymph follicles normally developing in the lymph node are maintained for a long time under normal conditions, many lymph follicles induced by antigenic challenge have a limited life span and undergo atrophy unless they are periodically activated by additional antigenic stimuli, and that atrophied follicles finally become unable to respond to antigenic stimulation. It is also suggested that antigenic materials which trigger the formation of lymph follicles in the primary challenge can evoke follicle formation more efficiently in the secondary challenge.

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We describe the three-dimensional organization of the microvasculature of human palatine tonsils as revealed by the vascular corrosion casting/scanning electron microscope method and light microscopy of sections. The tonsillar arteries travel in the connective tissue septa and give off many branches. They further branch into arterioles which in turn enter the follicle and the interfollicular region. These arterioles, giving off capillaries en route, reach the subepithelial region where they break up into sinusoidal capillaries. The subepithelial capillary network overlying the follicle protrudes hemispherically towards the crypt, while that overlying the interfollicular region has many switch-back loops of capillaries projected towards the crypt. The subepithelial sinusoids gather into the high endothelial venules (HEVs) which, collecting capillaries in the follicle and the interfollicular region en route, course down into the interfollicular region alongside the follicle. The HEVs surround the lateral and basal surfaces of the follicle and ultimately lead into the ordinary veins in the septa. The subepithelial sinusoids seem to be involved in taking up immunoglobulins secreted by plasma cells and any other substances released by lymphocytes and/or macrophages as well as supplying the tissues with necessary oxygen and nutrients. That the HEVs are downstream to the subepithelial sinusoids suggests that some substances which are taken up into the sinusoids and transported to the postcapillary venules induce differentiation of HEVs and maintain them.

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The periurethral glandular complex of the male water buffalo consists of a prostate body (not always present), a disseminate prostate and paired bulbourethral glands. The epithelium contains two types of columnar secretory cells and occasional basal cells. Type I secretory cells produce glycoprotein with a wide range of terminal sugars, these cells dominate in the cranial region of the periurethral glandular complex, whereas Type II secretory cells elaborate a mixture of carboxylated and sulphated sialomucin and prevail in the caudal portions of the periurethral glandular complex. At the ultrastructural level, Type I cells display a characteristic localization of organelles: a round nucleus in the basal portion, a Golgi apparatus and rough endoplasmic reticulum in the middle third, and secretory granules in the apical portion. Type II cells possess the ultrastructure of typical mucous cells. Following perfusion fixation of the epithelium, modifications of the lateral plasmalemmata are very obvious forming apicolateral secretory canaliculi, an intercellular channel system and a basolateral labyrinth. Nerve fibers surround the glandular basal lamina. Occasionally axons, probably of cholinergic nature, penetrate the basal lamina, then terminate in the intercellular clefts or form intraepithelial neuroglandular contacts.

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Bone marrow cells isolated from long bones of a ddY mouse were cultured on sperm whale dentin and examined by light, scanning and transmission electron microscopy. The osteoclasts in vitro showed essentially the same ultrastructures as in vivo.
The distribution of actin in the osteoclasts was examined by an indirect immunofluorescent antibody method, which revealed a wide ring-shaped area under the fluorescence microscope.
Transmission electron microscopy showed that the ring-shaped area corresponded to the clear zone. The clear zone and resorption lacunae were examined by a double illuminating method to determine the relationship between the clear zone and the lacunae, which could be divided into three types. The distribution and function of the clear zone are discussed.

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The periodontal ligament-cementum interface of rat first molars was investigated by electron microscopy. Evidence supporting cementoblast phagocytosis of collagen fibrils of the periodontal ligament was found. In addition, collagen-containing vacuoles were frequently observed within cementoblasts in association with an acid phosphatase activity. The presence of acid phosphatase activity in these vacuoles suggested that intracellular degradation of collagen was occurring.
Our results showed that cementoblasts exhibited collagen phagocytic activity and suggest that cementoblasts may play an important role in the physiological remodeling and metabolic breakdown of the collagen at the periodontal ligament-cementum interface.

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The d-segment of the rat penile bone at 14 weeks is composed of an outer zone of atrophy, a middle zone of hypertrophy and an inner zone of ossification. Hypertrophic chondrocytes in the middle zone generally present a few secretory vesicles and a poorly developed Golgi apparatus and rough endoplasmic reticulum, suggesting a serious decrease in the secretion of territorial matrix substances. Instead, most of the cells contain prominent glycogen lakes, lipid droplets and/or fine cytoplasmic filaments. These and other findings indicate that the chondrocytes are in a resting state.
In the calcified layer of the zone, and in addition to the hypertrophic or degenerating chondrocytes, another type of cell is recognizable. These sometimes remain viable through the process of cartilage degeneration and may be liberated from the besieging calcified interterritorial matrix and from their own lacuna by chondroclasts. These surviving cells are more similar in ultrastructure to bone cells than to the adjacent chondrocytes, surrounded by the lamina limitans characteristic of the resting osteocytes. However, they are directly covered by a typical territorial matrix inside the lamina limitans and do not extend slender cell processes into the calcified matrix beyond the lamina limitans, and the territorial matrix is never calcified even after calcification of the interterritorial matrix. The cells, therefore, are regarded as belonging to the chondrocytes.

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The immunocytochemical localization of amelogenins in the developing deciduous tooth germs of 6-month-old human fetuses was investigated by the protein A-gold method using an antiserum against porcine 25K amelogenin. The inner enamel epithelial cells and underlying matrix showed no amelogenin-like immunoreactivity. Distinct immunoreactivity was initially shown by fine fibrils found beneath the intact basal lamina of preameloblasts at the early differentiation stage. At the late differentiation stage, amelogenin-like immunoreactivity was shown by a fine granular material within the extracellular matrix as well as by the Golgi apparatus, secretory granules, lysosomal structures, coated vesicles, and coated pits of preameloblasts with a disrupted basal lamina. At the formative stage, the localization of immunoreactivity in secretory ameloblasts was similar to that in preameloblasts during the late differentiation stage. However, immunopositive coated vesicles and coated pits were only found at the early stage of matrix formation. The calcified enamel matrix and stippled material showed intense immunoreactivity. Immunocytochemical labeling of the enamel matrix appeared as a gradient, decreasing from the enamel surface to the dentinoenamel junction. No maturation stage of ameloblasts existed in the tooth germs examined. In predentin and dentin, amelogeninlike immunoreactivity was occasionally detected on odontoblasts and their processes, but odontoblasts and cells of the stratum intermedium contained no immunoreactive elements. These findings confirmed that the secretory ameloblast in the human deciduous tooth germ is responsible for the synthesis and secretion of enamel proteins.

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Pieces of tissue containing dorsal raphe nuclei of fetal rat brains were transplanted into the anterior eye chambers of adult rats. The differences between the developmental patterns of catecholaminer gic and serotonergic neurons —especially the extension of their axonal processes— in the grafts were immunohistochemically examined using tyrosine hydroxylase (TH) and serotonin antisera.
At an early stage after transplantation (3 days), TH-positive neurons appeared in grafts that had and had not been pretreated with a monoamine oxidase inhibitor (MAOI, Nialamide), while serotonin-positive neurons were demonstrated only in the grafts that had undergone MAOI pretreatment. Morphological differences in the growth pattern in the experimental milieu between the TH and serotonin neurons were also demonstrated: at this early stage, the somata of the TH neurons were multipolar and stellate shaped and possesed several distinct processes, while the serotonin neurons were ovoid shaped and lacked such processes.
One week to 1 month after transplantation, the number of TH-positive fibers gradually increased, but their distribution was restricted to the area surrounding the cell bodies of the TH neurons in the graft.
However, the processes of the serotonin neurons formed a dense plexus in the graft, and a small number of these fibers extended into the host iris 1 week after transplantation. By one month after the operation, the density of the serotonin fibers had gradually increased throughout the graft, and protruding serotonin fibers formed a network of varicose fibers in the host uveal tissue. The present results suggest that the regrowth pattern of the dopaminergic and serotonergic neurons in the grafts of the raphe nuclei show characteristic structural differences at various stages after transplantation.

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