The selective distribution of LYVE-1-expressing endothelial cells and reticular cells in the reticulo-endothelial system (RES).

LYVE-1, a receptor molecule for hyaluronan, is expressed in the lymphatic endothelium, blood sinus endothelium, and certain macrophage lineages. The present immunohistochemical study revealed a broader distribution of LYVE-1 in vascular endothelial cells of the murine lung, adrenal gland, and heart as well as the liver and spleen. In addition, sinus reticular cells-including sinuslining cells-in the medulla of the lymph node also intensely expressed LYVE-1. Ultrastructurally, immuno-gold particles for LYVE-1 were localized on the entire length of plasma membrane in all cell types. Most of these LYVE-1-expressing cells had previously been classified as the reticuloendothelial system (RES) specialized for eliminating foreign particles. An LPS stimulation decreased the LYVE-1 expression in macrophages but elevated the expression at mRNA and protein levels in the liver and lung, major organs for the elimination of blood-born waste substances. LYVE-1-expressing endothelial cells in these organs participated in the endocytosis of exogenous particles, and the uptake ability was conspicuously enhanced by the LPS challenge. Although the expression of the degrading enzyme, hyaluronidase, was generally low in the LYVE-1-expressing cells, they were topographically associated with a dense distribution of macrophages possessing hyaluronidase activities in each tissue. These findings suggest that the LYVE-1-expressing cells might be involved in the uptake of hyaluronan and other waste products as well as foreign particles circulating in the blood and lymph while participating in the subsequent degradation in relay with adjacent macrophage populations.

Morphological Analysis of Reticuloendothelial System in Capuchin Monkeys (Sapajus spp.) after Meso-2,3-Dimercaptosuccinic Acid (DMSA) Coated Magnetic Nanoparticles Administration.

Magnetic nanoparticles can be used for numerous in vitro and in vivo applications. However, since uptake by the reticuloendothelial system represents an obstacle for the achievement of nanoparticle diagnostic and therapeutic goals, the aim of the present study was to evaluate the uptake of dimercaptosuccinic acid coated magnetic nanoparticles by reticuloendothelial system phagocytic cells present in lymph nodes, spleen, and liver tissue and how the presence of these particles could have an impact on the morphology of these organs in capuchin monkeys (Sapajus spp.). Animals were intravenously injected with dimercaptosuccinic acid coated magnetic nanoparticles and euthanized 12 hours and 90 days post-injection. Organs were processed by transmission electron microscopy and histological techniques. Samples of spleen and lymph nodes showed no morphological changes. Nevertheless, liver samples collected 90 days post-administration showed slight morphological alteration in space of Disse. Moreover, morphometrical analysis of hepatic mitochondria was performed, suggesting a clear positive correlation between mitochondrial area and dimercaptosuccinic acid coated magnetic nanoparticles administration time. The present results are directly relevant to current safety considerations in clinical diagnostic and therapeutic uses of magnetic nanoparticles.

Characterization of sinusoidal endothelial cells of the liver and bone marrow using an intravital lectin injection method.

The vascular endothelia express a variety of structural and biological phenotypes. We used an intravital injection method of plant derived lectins (Lycopersicon esculentum lectin (LEL), Ricinus communis Agglutinin-I (RCA-I), Ulex europaeus Agglutinin-I (UEA-I) and Concanavalin A (ConA)) to elucidate the morphology and function of the sinusoidal endothelium of the liver and bone marrow. All four lectins stained the sinusoidal endothelia of the liver and bone marrow in a patchy granular pattern which differed from the uniform and smooth staining pattern of non-sinusoidal vessels in other organs. By transmission electron microscopy, the granular pattern was identified as internalization of these lectins and subsequent accumulation within the endothelial cells, suggesting their active endocytosis. The endocytosis of these lectins emphasizes the fact that sinusoidal endothelial cells of the liver and bone marrow belong to the reticuloendothelial system (RES), a cell system characterized by internalization of foreign material. We introduce this intravital lectin injection as a useful technique to discriminate sinusoidal endothelial of the liver and bone marrow from other vascular endothelia.

Re-evaluation of the reticulo-endothelial system.

By injecting lithium carmine (Lit-car) into living animals, Ribbert (1904) and Kiyono (1914) showed that specific staining occurred in some cells in various organs. Kiyono termed those cells "histiocytes" which consisted of free amoeboid cells and cells of reticulo-endothelium. Aschoff (1924) introduced the concept 'reticulo-endothelial system (RES)' for the collection of cells having in common the property of vital staining. Van Furth (1972) proposed the term "mononuclear phagocyte system (MPS)" advocated that RES be replaced by MPS. As a consequence we presently suffer from a "reticulo-endothelial confusion", based on the delusion that cells other than macrophages are not members of the RES. The point that most clearly illustrates this is the fact that the Lit-car-laden cells in the body are named macrophages in modern textbooks of histology. To clarify the confusion, we re-examined the vital staining at light and electron microscopic levels and analyzed the scavenger cells using biochemical methods. Injected Lit-car was actively endocytosed by sinusoidal endothelial cells in the liver and reticular cells in the sinus of lymph nodes. Of note, uptake of the dye was comparatively much lower in macrophages/monocytes. Our findings indicate the existence of scavenger endothelial cells and reticular cells in blood and lymphatic circulations respectively. We name these two systems "the scavenger RES" collectively.

The role of zinc in pre- and postnatal mammalian thymic immunohistogenesis.

Mammalian thymic histogenesis can be morphologically divided into three consecutive stages: a) epithelial, b) lymphopoietic or lympho-epithelial, and 3) differentiated cellular microenvironmental, with formation of Hassall's bodies (HBs). Immunomorphological changes characteristic of human thymic involution begin during or soon after the first year after birth, and continue progressively throughout the entire life span. The 3% to 5% annual reduction in the number of cells of the human thymic microenvironment continues until middle age, when it slows down to less than 1% per year. According to the extrapolation of these results, total loss of thymic reticulo-epithelial (RE) tissue and the associated thymocytes should occur at the age of 120 years in humans. The marked reduction of the thymic cellular microenvironment is a well- controlled physiological process and is presumably under both local and global regulation by the cells of the RE meshwork and by the neuroendocrine axis, respectively. In humans, the age related decline of facteur thymique serique (FTS) levels in blood begins after 20 years of age and FTS completely disappears between the 5th and 6th decade of life. In contrast, serum levels of thymosin-alpha 1 and thymopoietin seem to decline earlier, starting as early as 10 years of age. The influences of a variety of other hormones on the involution of the thymus have also been characterized: testosterone, estrogen, and hydrocortisone treatment results in marked involution, cortisone and progesterone administration have a slight to moderate effect while use of desoxycorticosterone has no effect. The experimental administration of thyroxin yielded dose dependent results: low doses resulted in thymic hypertrophy, higher doses produced a slight hypertrophy, while the highest employed doses caused thymic atrophy. The atrophy was of apicnotic type, very different from that detected after treatment with corticoid hormones. Thymus transplantation experiments indicate that age-related, physiological thymic involution has been genetically preprogrammed. Grafting of the thymus from one week old C3H leukemic strain mice into 6 month old hosts resulted in changes in thymic weight and involution patterns that were synchronous in all recipients, in direct correlation with the glands in the donor, but not in the host. These data strongly suggest that the stimulus for thymus cell proliferation and differentiation is genetically determined within the organ implant. Since the thymus is the primary T-lymphopoietic organ during mammalian ontogenesis, its age-related involution with typical immunomorphological alterations can be held responsible only for the decline in antigen-specific T lymphocyte immune functions. Thymic involution and diminished T lymphocyte proliferation can be partially restored by thymic tissue transplantation or use of thymic hormones. The only partial reconstitution of CD4+ T helper lymphocyte subset after antineoplastic chemotherapy and bone marrow transplantation represents a significant, therapy complicating, clinical problem. After high-dose chemotherapy, restoration of thymus dependent CD4+ T lymphocyte genesis was reported only in children. Our radiation, stem cell transplantation, and hormone treatment experiments in animals strongly suggest age and time dependent regeneration of the cytoarchitecture of the thymic cellular microenvironment, as well as intrathymic lymphopoiesis. The human body's zinc pool undergoes progressive reduction, resulting in low zinc plasma levels and a negative crude zinc balance in older rodents, as well as humans. Previous research suggests that the diminished bioavailability of zinc in older mammals may represent one of the major factors for the involution of the thymus and consequent cellular immunological dysfunction. In PBMCs, zinc induces several cytokines, predominantly IL-1, IL-6 and TNF-alpha, and therefore, has an immense immunoregulative capacity. (ABSTRACT TRUNCATED)

Reticulo-endothelial stroma of the head-kidney from the seawater teleost gilthead seabream (Sparus aurata L.): an ultrastructural and cytochemical study.

BACKGROUND: Head-kidney, considered the major fish lympho-haemopoietic tissue, consists of cells of the different haemopoietic series supported by a network of stromal cells whose morphofunctional properties have not been established. We report the ultrastructure and cytochemical features of the reticulo-endothelial stroma of the head-kidney from the seawater teleost gilthead seabream (Sparus aurata L.). METHODS: Samples of head-kidney were processed for electron microscopic study. Some of the samples were incubated for acid and alkaline phosphatase, peroxidase, glucose-6-phosphatase, or ATPase. RESULTS: The reticulo-endothelial stroma of gilthead seabream head-kidney consists of sinusoidal cells (endothelial and adventitial cells) and reticular cells (macrophage-type reticulum and fibroblast-like reticular cells). Transcytosis vesicles and rounded medium electron-dense granules were observed in the cytoplasm of the endothelial cells. The adventitial cells partially covered the outside surface of the endothelial cells and were joined by desmosomes. The macrophage-type reticulum cells were characterized by their cytoplasmic processes and acid phosphatase positive lysosomes. The fibroblast-like reticular cells were joined by desmosomes and formed an extensive network between the haemopoietic parenchyma. They were peroxidase negative and acid and alkaline phosphatase, glucose-6-phosphatase, beta-glucuronidase, and ATPase positive. CONCLUSIONS: The ultrastructural and cytochemical features of the reticulo-endothelial stroma of the gilthead seabream head-kidney are similar to those of mammalian bone marrow, suggesting phylogenetic analogies between both tissues.

Two distinct types of reticular cells in the pig sheathed artery.

The morphology of reticular cells of the sheathed arteries, in the red pulp of pig spleen, was studied by using transmission electron microscopy; and their histochemical reactivity with periodic acid-thiocarbohydrazide-silver proteinate (PA-TCH-SP). The phagocytic ability was evaluated by injecting colloidal carbon into the splenic artery. Reticular cells of the sheathed arteries were classified as type I and type II cells. Type I cells have a nucleus with scanty chromatin, and the cytoplasm reacts positively to PA-TCH-SP. The PA-TCH-SP-positive granules are considered to be subunits of beta-glycogen particles based on their morphological features. Type II cells have a nucleus with abundant chromatin and are not stained by PA-TCH-SP. Both types of reticular cells are connected with reticular fibers. Results of the colloidal carbon injection showed that type I reticular cells did not ingest carbon particles during the time frame of the experiment, whereas type II reticular cells are phagocytic and ingested carbon.

Ultrastructural and morphometrical studies on the reticular framework and reticular fibers in the reticuloendothelial system of rats.

The reticular framework and reticular fibers in the thymus, cervical lymph node, spleen and bone marrow of Wistar rats were studied by transmission electron microscopy and morphometrical method. The reticular framework was usually observed in these organs as a common structure that consisted mainly of the slender cytoplasmic processes of the fibroblastic reticular cells interconnected with tight junction. Ultrastructurally, the reticular fibers were a mixture of collagen fibrils and amorphous materials, and were almost completely ensheathed by the cytoplasm of fibroblastic reticular cells. Such characteristic structure of the reticular fibers was found not only in the thymus, lymph node and spleen, but also in the bone marrow where it has not been clearly demonstrated previously. Morphometrical analysis revealed that the content of collagen fibrils in the reticular fiber in the lymphoid tissues (the thymus, lymph node and splenic white pulp) was much greater than that in the hematopoietic tissues (the bone marrow and splenic red pulp). Based on these evidences, it was reasonably considered that the reticular framework and reticular fiber ensheathed by the cytoplasm of the fibroblastic reticular cells were the most representative common structure in the reticuloendothelial system (RES) and played some important roles in the functions of RES.

The enveloping of intercellular collagenous fibrils by reticular cell processes in postnatal development of rat lymph nodes.

In the lymph nodes of adult rats reticular fibers are known to be covered by the processes of reticular cells. This study aims to visualize the sequence of the envelopment of reticular fibers by reticular cells during development. Rat popliteal lymph nodes of one to twenty-three days after birth were examined by electron microscopy. At the earliest stages, collagenous protofibrils were found in the intercellular space between studded mesenchymal cells. The protofibrils clustered around the plasma membrane of immature reticular cells and then became arranged into microfibrils of 30-40 nm in diameter. Bundles of the fibrils which might be called reticular fibers were surrounded by processes of more than one reticular cell. Then the reticular fiber came to be enclosed by the cytoplasmic process of a single reticular cell. Finally at 16-23 days after birth, the reticular fiber was completely ensheathed by the thick cytoplasmic process of a single reticular cell closed with a junctional complex. Throughout these periods, basal lamina-like materials existed between the reticular fiber and cytoplasmic process. Clumps of fibrils were rarely in contact with leukocytes, including lymphocytes. Immature elastic fibers appeared among collagenous fibrils of the reticular fiber when the fiber came to be enclosed by processes of some reticular cells. It was shown that the enclosure of the reticular fiber by the reticular cell did not result from physical pressure due to the increase of the number of lymphocytes, but the reticular cell actively enclosed the reticular fiber.(ABSTRACT TRUNCATED AT 250 WORDS)

Localization of interferon-induced lupus inclusions demonstrated by computer image reconstruction of monensin-treated Daudi cells.

A structural analysis of cells that contained the interferon-alpha-induced lupus inclusions (LI) was performed using a high-voltage electron microscope to determine the exact cellular location of LI and their association with normal cell organelles. LI were induced in the human B lymphoblastoid cell line, Daudi, by culturing with the pure recombinant human leukocyte interferon, IFLrA. Just prior to harvesting, a portion of the cells was treated with monensin to selectively swell the Golgi apparatus, and thereby simplify their identification using the electron microscope. Organellar associations between LI and the outer nuclear envelope and Golgi apparatus were identified in stereopairs of 1-micron sections prepared from both cells that were not treated with monensin and those that were treated with monensin. Serial 0.25-micron sections of the monensin-treated cells were prepared, and seven arbitrarily chosen cells were examined. Each of these cells contained a single LI, and it formed throughout an endoplasmic-reticulum region that made contact with both the outer nuclear envelope and the Golgi vesicles. Reconstruction of a cell by computer from the digitized negatives of serial sections clearly illustrated these relationships. This study reports the first determination of the association between LI and the Golgi apparatus. It also identifies the presence of only one LI in every cell, and the routine association of the LI with both the outer nuclear envelope and the Golgi apparatus. The unique cell location of LI formation suggests their functioning in membrane biogenesis, the trafficking of proteins to the plasma membrane or to cytoplasmic vesicles, or the processing of proteins for secretion.

Male lupus: prevalence of IgA deficiency, 7S IgM and abnormalities of reticuloendothelial system Fc-receptor function.

Serological studies conducted on sera from a group of 31 male SLE patients revealed a 32% prevalence of 7S IgM and a 9.7% prevalence of IgA deficiency. Previous reports using similar methods indicated a higher (43-50%) prevalence of 7S IgM than was found in studies involving predominantly females with SLE (15-18%), and an overall prevalence of IgA deficiency ranging from 0.95% to 4.6%. Males resembled females in the prevalence of Fc-receptor specific reticuloendothelial system dysfunction, correlating with levels of circulating immune complex-like material and disease activity.

In vitro morphological characterization of the bursal reticuloepithelial (REp) cells of chicken.

The REp cells of the bursa follicle medulla of chicken were isolated in vitro. Culture of the REp cells was maintained over a period of 10 days and the cells were observed at 3 and 10 days by means of transmission electron microscopy (TEM) and immunofluorescence. The use of an anticytokeratin monoclonal antibody confirmed their epithelial nature. TEM observations showed the presence of desmosomes and tonofilaments, which are characteristic of epithelial cells. Furthermore, to some extent the cells regenerated in vitro the network they form in vivo. Though the growth rate becomes slower with time, the features of the REp cells do not significantly change.

Hermansky-Pudlak syndrome: case report and clinicopathologic review.

The Hermansky-Pudlak syndrome is an autosomal recessive disorder consisting of the triad of albinism, a bleeding diathesis, and ceroid deposition within the reticuloendothelial system. In this study of a patient with Hermansky-Pudlak syndrome, we demonstrate the presence of ceroid within dermal macrophages. Electron microscopic studies suggest that melanosomes may be a substrate for the formation of ceroid in the skin. A review of the clinical and pathophysiologic features of this disorder is presented.

Mechanisms of splenic control of murine malaria: cellular reactions of the spleen in lethal (strain 17XL) Plasmodium yoelii malaria in BALB/c mice, and the consequences of pre-infective splenectomy.

The splenic response in lethal 17XL Plasmodium yoelii murine malaria is vigorous, displaying marked phagocytosis, erythropoiesis, lymphopoiesis, plasmacytopoiesis, and, from day 3 of infection, increasing levels of parasitized erythrocytes. There is also a pronounced response of newly characterized fibroblastic stromal cells which branch and fuse with one another, forming extensive, complex, irregular, syncytial membranous sheets which provide a variety of barriers. Hence, I term these barrier cells (BC), and their fusion results in barrier-forming complexes (BFC). BC form adherent surfaces, trapping parasitized erythrocytes and monocytes-macrophages, facilitating phagocytosis. They envelop single plasma cells, erythrocytes, erythroblasts, lymphocytes, reticulocytes, monocytes-macrophages, or clusters of them. They surround blood vessels, forming blood-spleen barriers. They are insinuated into the circumferential reticulum at the periphery of white pulp, isolating white pulp. They form channels in red pulp, directing blood flow. They are associated with collagen. There appear to be several sources of BC. They may originate by activation of established reticular cells which form the filtration beds, by activation of reticular cells covering the pulp surface of capsule and trabeculae, and as a major source in this malaria, from circulating progenitors entering the splenic pulp from the vasculature. In non-lethal malaria, these barrier systems protect splenic reticulocytes from parasitization. In the lethal 17XL malaria they do not, and there follows a considerable increase in parasitization in the spleen with a corresponding increase in active macrophages. Large-scale parasitization and parasite recycling through the great stores of splenic reticulocytes in the lethal malaria, and the failure of parasitization of these splenic reticulocytes reserves on the non-lethal malaria, suggests that the actions of the spleen aggravate the lethal malaria and ameliorate the non-lethal. This is supported by the finding that non-lethal malaria is aggravated and lethal malaria ameliorated by splenectomy.

Reticular meshwork of the spleen in rats studied by electron microscopy.

The reticular meshwork of the rat spleen, which consists of both fibrous and cellular reticula, was investigated by transmission electron microscopy. The fibrous reticulum of the splenic pulp is composed of reticular fibers and basement membranes of the sinuses. These reticular fibers and basement membranes are continuous with each other. The reticular fibers are enfolded by reticular cells and are composed of two basic elements: 1) peripheral basal laminae of the reticular cells, and 2) central connective tissue spaces in which microfibrils, collagenous fibrils, elastic fibers, and unmyelinated adrenergic nerve fibers are present. The basement membranes of the sinuses are sandwiched between reticular cells and sinus endothelial cells and are composed of lamina-densalike material, microfibrils, collagenous fibrils, and elastic fibers. The presence of these connective tissue fibrous components indicates that there are connective tissue spaces in these basement membranes. The basement membrane is divided into three parts: the basal lamina of the reticular cell, the connective tissue space, and the basal lamina of the sinus endothelial cell. When the connective tissue space is very small or absent, the two basal laminae may fuse to form a single, thick basement membrane of the splenic sinus wall. The fibrous reticulum having these structures is responsible for support (collagenous fibrils) and rebounding (elastic fibers). The cells of the cellular reticulum--reticular cells and their cytoplasmic processes, which possess abundant contractile microfilaments, dense bodies, hemidesmosomes, basal laminae, and a well-developed, rough-surfaced endoplasmic reticulum, and Golgi complexes, which are characteristic of both fibroblasts and smooth muscle cells--are considered to be myofibroblasts. They may play roles in splenic contraction and in fibrogenesis of the fibrous reticulum. The contractile ability may be influenced by the unmyelinated adrenergic nerve fibers that pass through the reticular fibers. The three-dimensional reticular meshwork of the spleen consists of sustentacular fibrous reticulum and contractile myofibroblastic cellular reticulum. This meshwork not only supports the organ but also contributes to a contractile mechanism in circulation regulation, in collaboration with major contractile elements in the capsulo-trabecular system.

Microcirculatory pathways in normal human spleen, demonstrated by scanning electron microscopy of corrosion casts.

Confusion regarding microcirculatory pathways in normal human spleen has arisen due to extrapolation from pathological material and from other mammalian spleens, not to mention difficulties in tracing intricate three-dimensional routes from the study of thin sections or cut surfaces of tissue. We examined microcirculatory pathways in normal human spleens freshly obtained from organ transplant donors. A modified corrosion casting procedure was used to obtain an open view of vessels and their connections. Our results demonstrate: 1) "arteriolar-capillary bundles" within lymphatic nodules and extensive branching of arterioles in the marginal zone (MZ); 2) the marginal sinus around lymphatic nodules; 3) the peri-marginal cavernous sinus (PMCS) outside the MZ or immediately adjacent to the nodule itself; the PMCS receives flow via ellipsoid sheaths and MZ, or directly from arterial capillaries, and drains into venous sinuses; 4) fast pathways for flow into venous sinuses via ellipsoid sheaths; 5) arterial capillary terminations in the reticular meshwork of the red pulp or MZ ("open" circulation); direct connections to venous sinuses also occur ("closed" circulation), although rarely; and 6) numerous open-ended venous sinuses in the MZ, allowing a large proportion of the splenic inflow to bypass the red cell filtration sites in the reticular meshwork and at venous sinus walls.

Characteristics of histiocytic lesions in the reticuloendothelial system of NZB mice.

The so-called Potter's lesion, previously described as preneoplastic in the lymph nodes of C58 mice, develops frequently in autoimmune NZB mice. These lesions were characterized in the present study by bands or sheets of pale-staining histiocytic cells in the cortex and medulla of the lymph node, and multiple small nodules of the same cells were found in the red pulp of the spleen and the liver. Electron microscopically, the cells had pleomorphic cytoplasm with long processes, electron-dense bodies, abundant mitochondria, and a characteristic labyrinth structure with many C-type viruses. Mac-1 antigen, IgG-Fc receptor, ferritin, and ACPase activity were identified on these cells. Intraperitoneally-injected iron colloids were found in the lesions of the spleen and liver but not in those of the lymph nodes. The lymph node lesions appeared when the mice were about 3 months of age and enlarged until the mice were around 10 months old, after which they gradually receded and were replaced by small vessels and fibroblastic cells. These data indicate that the lesions represent reactive hyperplasia of the macrophage system and may have no direct association with the development of malignant lymphoma in NZB mice.

Apotransferrin receptors and the delivery of iron from cultured human blood monocytes.

A study was done to find out whether apotransferrin receptors are involved in the release of iron from reticuloendothelial cells. To this end, human macrophages which had been obtained by culturing blood monocytes for 7 days were incubated with either diferric or apotransferrin at the physiological pH of 7.4 or at an acidic pH (6.0). While specific diferric transferrin receptors (Kd 1.3 X 10(-8) M) were demonstrated at pH 7.4, no apotransferrin receptors were found. In contrast, both diferric receptors (Kd 2.1 X 10(-8) M) and apotransferrin receptors (Kd 6.8 X 10(-9) M) were found at pH 6.0. The findings of specific apotransferrin binding at acidic pH fits in with the current understanding of iron uptake by cells, in which the iron-transferrin complex is endocytosed and the iron is released at acidic pH. The present results suggest that the apotransferrin remains attached to its receptor in the endocytosed vesicle at this acidic pH but that it becomes detached at the cell surface where the pH is neutral. No evidence was found to indicate that iron is transported out of macrophages via apotransferrin receptors at the physiological pH.