Structure of sinuses in the human lymph node

Summary A casting technique has been employed to display in three dimensions, the lymphatic microcirculation within the human lymph node. The casting compound filled the marginal sinus, and diffusely permeated the cortical lymphoid parenchyma. However, deep within the lymph node in the medullary region, the medium remained within the limits of the sinus walls. The casts showed well-defined channels appearing similar to vessels. These converged into larger vessels, which drained into efferent lymphatics leaving the node at the hilus.Electron microscopic examination showed that the outer wall of the marginal sinus and the trabecular side of trabecular sinuses had an intact, continuous endothelium with a basement membrane. However, gaps were present in the inner wall of the marginal sinus, as well as in the parenchymal wall of the trabecular sinus. In the medulla, the sinuses were lined by endothelial cells which appeared similar to macrophages. The sinus lining was incomplete and possessed numerous perforations. These observations indicated that sinus walls adjacent to connective tissue served as a barrier to cell movement, but those adjacent to a large lymphoid cell population had gaps, with cells in apparent transit between sinus lumen and parenchyma.     

Ultrastructure of the DNA-synthesizing cells of the sinoatrial node in mouse embryos according to electron microscopic autoradiographic data

By means of electron microscopic autoradiography with 3H-thymidine a study was made of the differentiation degree of DNA synthesizing muscle cells in the sinoatrial node (SAN) of the heart conductive system of the 18 day old mouse embryos. Clear myocytes (CM), predominating in the SAN at this stage, are irregular in shape, with interdigitating protrusions. Nuclei are clear, spherical or ellipsoidal. One hour following 3H-thymidine injection, about 6% of CM display labeled nuclei; this index is considerably lower than in working ventricular myocardium. Like unlabeled myocytes, CM being in phase S contain sparse, randomly located thin myofibrilles. In some areas of the sarcoplasm, only myofilament bundles and Z-disk material can be seen. The number of CM myofibrilles is always considerably less than in the working ventricular myocytes. Accumulations of intermediate (8--11 nm) filaments are present. Mitochondria with a few cristae are not numerous. The sarcoplasmic reticulum and Golgi apparatus being relatively well developed, multivesicular bodies, centrioles, and occasional cilia are often seen. Near the centrioles (basal bodies), striated filamentous bundles are found sometimes showing periodic dense lines separated by 50--70 nm. Specialized contacts between CM are rare, being presented only by desmosomes and primitive intercalated discs. Besides CM, sparse small dark cells occur filled with myofibrilles and mitochondria. In the peripheral regions of the node "transitional" cells are seen. The SAN of the 18 day old embryo mouse heart grown due to proliferation of CM with a poorly developed myofibrillar apparatus.     

Langerhans cells in the lymph node: mirror section and immunoelectron microscopic studies

Cells immunostained with antibodies against both OKT-6 and S-100 protein were observed only in superficial and hilar lymph nodes draining tissues with predominantly squamous epithelia. In contrast, in mesenteric lymph nodes and the spleen, only S-100 protein-positive, but OKT-6-negative cells were found. We suspect that the S-100 and OKT-6-positive cells might be Langerhans cells (LC) and the S-100-positive, OKT-6-negative cells, interdigitating reticulum cells (IDC). We further postulate that the LC in superficial and hilar lymph nodes might migrate from squamous epithelia, with which contact is required for the formation of Birbeck granules.     

Tissue nature of the lining of the lymph node sinuses]

The lymphatic nodes of intact albino rats were investigated electron microscopically. It was shown that the lymphatic sinuses were restricted by a layer of flattened cells; the basal membrane was absent. Certain distinctions in the structure of the cell lining sinuses and the reticular cells comprising the reticular base of the lymphoid tissue of the lymphatic node were found. The structure of the "sinus network" strands is shown. The structure of the cells of the sinuses lining is shown to be identical to the structure of cells of the vascular endothelium. It suggests the endothelial nature of the lining of the lymphatic node sinuses.     

Structural changes in the lymph node sinuses in acute blood loss]

By means of light and scanning electron microscopy sinuses of the popliteal lymph nodes have been studied in 50 Wistar male rats. After modelling of an acute hemorrhage in the animals (in 15, 120 min and 1 day) volume of the medullary and marginal sinuses increases essentially, while blood stream intensity decreases in peripheral tissues. Amount of fenestrae in the sinusal lining decreases, that is, perhaps, caused by edema of cytoplasm in the lining cells and accompanied with formation of numerous cytoplasmic protrusions into the sinusal lumen. In 3 days the blood stream level in the peripheral tissues restores, structural organization of the littoral cells in the lymphatic sinuses normalizes. The data obtained demonstrate that during the first day after the acute hemorrhage decrease of hematolymphatic exchange intensity in lymph nodes and enhancement of transitory lymph flow in them take place.     

Langerhans cells in the lymph node: mirror section and immunoelectron microscopic studies.

Cells immunostained with antibodies against both OKT-6 and S-100 protein were observed only in superficial and hilar lymph nodes draining tissues with predominantly squamous epithelia. In contrast, in mesenteric lymph nodes and the spleen, only S-100 protein-positive, but OKT-6-negative cells were found. We suspect that the S-100 and OKT-6-positive cells might be Langerhans cells (LC) and the S-100-positive, OKT-6-negative cells, interdigitating reticulum cells (IDC). We further postulate that the LC in superficial and hilar lymph nodes might migrate from squamous epithelia, with which contact is required for the formation of Birbeck granules.     

A scanning electron microscopic study of SV40 infected cells.

The surface of the SV40-infected African green monkey kidney (AGMK) cells was studied morphologically by scanning electron microscopy. In 24 hr post infection (p.i.), the cell surface was covered with slightly elongated microvilli. The microvilli increased in number. In 96 hr.p.i. most of the cells showed SV40-specific cytopathic effects (CPE). Nuclear swellings and the elongation of microvilli were eminent. Microvilli were observed projecting with high densities especially on the nuclear portions of the cell surfaces. Features suggesting cytoplasmic vacuolization were also observed in some cells. Spherical particles viewed in some of the cells at the late stage of infection were considered SV40 virions. Their origin was also discussed.     

Changes in the surface and cytoskeletal apparatus of the endotheliocytes of the rat aorta during division (based on scanning electron microscopic data)

Endothelium of the abdominal aorta of 32 KWR-line rats was exposed to freeze injury. En face preparations were made to look for endothelial cells (EC) on different stages of mitosis. Specimens were dried by critical point technique, and the grid was placed on their surface. Then specimens were investigated in succession with light and scanning electron microscopes. The cytoskeleton of EC was investigated on detergent-extracting preparations. It is shown that the end of phase S of the cell cycle and the beginning of prophase are characterized with the lifting of the nuclear-containing zone. Fine microvilli appear on the EC surface during prophase. The cytoskeleton becomes more structured and polarized. During metaphase, EC becomes spherical, its microvilli are shortened. Fine cytoplasmic shoots are seen to extend from the cell poles to the substratum. The density of the fibrillar structures swiftly rise. During anaphase the EC surface is covered with blebs. During late telophase the surface of dividing EC becomes flatter. Their nuclei are connected with rare bundles of fibrillar structures. Mechanisms of EC surface changes during mitosis and the role of cytoskeletal elements are discussed.     

Blood vascular network of the rat lymph node: tridimensional studies by light and scanning electron microscopy

Many aspects of the blood vascular network of the lymph node are unknown, and others need confirmation. We have studied the blood vasculature of rat peripheral lymph nodes by means of carbon perfusion and vascular cast corrosion techniques. At the hilus of the node, an artery gives off arterioles running in medullary cords towards the cortex. Some reach the peripheral cortex directly, branching there into slender cortical vessels. Other arterioles enter the periphery of the deep cortex units, and then head towards the peripheral cortex. Upon reaching it, they curve part way above the center of the deep cortex units and provide slender branches to the overlying peripheral cortex. Dense plexuses of capillaries arise from arterioles in the medullary cords, in the periphery of the deep cortex units, and in the outermost stratum of the extrafollicular zone of the peripheral cortex. In the cortex, the draining high endothelial venules are restricted to the extrafollicular zone and to the periphery of the deep cortex units. At the cortico-medullary junction, these peculiar venules transform into regular medullary venules which form the hilar veins. In contrast, the folliculo-nodules and center of the deep cortex units are little vascularized by a loose capillary network, while no vessels occur in the subsinus layer. These features of the node vascular network are of interest in relation to the node architecture.     

A scanning electron microscopic study of the luteo-follicular complex

Summary As observed by SEM, the repair of an ovulated mammalian follicle is accompanied by a sequence of morphogenetic processes. In the initial phase, a mass of cells and coagulated fluids forms at the site of rupture. Shortly thereafter, connective cells, recruited from the adjacent and subjacent connective tissue stroma begin to proliferate and to migrate over this mass such that in the rabbit, the entire site of disruption is covered by a layer of connective cells by approximately 2 days following ovulation. Coincident with the migration of the connective tissue, superficial cells from undisturbed lateral and basal areas of an ovulated follicle also proliferate and begin to migrate over the newly established connective tissue matrix. By approximately 4 days following ovulation in the rabbit, the surface of an ovulated follicle is repopulated by elements of the superficial epithelium. The formation of the underlying corpus luteum (corpora luted) involves characteristic morphological changes as granulosa cells transform into steroid secreting luteal cells. The luteal cells become organized into cords of cells which usually surround capillary vessels. When examined by SEM, the smooth-surfaced endoplasmic reticulum of the luteal cell is quite apparent and is observed to form a three-dimension network of anastomosing tubules which are continuous with the nuclear membrane. Variations in the appearance of the surface of the ovary which directly overlies corpora lutea were observed when the mouse, rat and rabbit were compared. The regression of corpora lutea involves the infiltration of the luteal mass by connective tissue and both degeneration and vacuolization of the luteal cells. The regressing corpus luteum is a honey-comb-like structure in which each space is occupied by a degenerating luteal cell.This work was supported by grants from the National Institutes of Health, Public Health Service (to J.V.B., no. HD-04274), and from Consiglio Nationale delle Ricerche (C.N.R., contracts nos. CT 76.01288.04 and CT 77.01921.4)     

Cytophotometric and electron microscopic studies of chronic human skin lymphomas. II. Research on lymph node involvement

Results of electron microscopic and cytophotometric studies of biopsy material from lymph nodes of patients with cutaneous lymphomas with low degree of malignancy are discussed, with special reference to early diagnostic criteria of the disease. Specific characteristics of tumor tissue involve the presence of atypical lymphocytes with marginal condensed chromatin extrusions of nuclear material, deep invaginations of the nuclear membrane, nuclear pockets, excess of the mean DNA content per nucleus above the diploid standard level, more than 5% of nuclei being in the hyperdiploid area. Electron microscopic and cytophotometric methods allowed to diagnose the tumor injury of lymph nodes, when the traditional histological techniques revealed no signs of malignancy.     

Surface configuration of mesothelial cells in effusions. A comparative light microscopic and scanning electron microscopic study.

Surface configuration of mesothelial cells identified by light microscopy (LM) has been studied by scanning electron microscopy (SEM). It has been shown that mesothelial cells may have a variable SEM appearance. The surfaces of a small proportion of mesothelial cells are covered by regular microvilli (MV) and show openings of the pinocytotic vesicles. The surfaces of the majority of these cells are covered by vesicles or blebs. An intermediate population of mesothelial cells, i.e., cells displaying side-by-side blebs and MV, has also been observed. The latter cells no longer display pinocytotic vesicles. Occasional mesothelial cells have smooth surfaces. It has been shown by LM and transmission electron microscopy that cells with blebs are viable and capable of mitotic activity. It is concluded that mesothelial cells, detached from their epithelial setting, lose microvilli and pinocytotic vesicles and acquire surface blebs. The possible relationship between mesothelial cells and macrophages based on surface features has been discussed.     

Change in the mitochondria of the left heart ventricle in the intact rabbit during the course of the day (based on scanning electron microscopic data)

The myocardium of the left ventricle of intact rabbit was investigated by scanning electron microscopy during 24 hours, namely at 0, 6 a.m., noon and 6 p.m. It was discovered that the mitochondria reach the maximal volume at 6 p.m. and the minimal at 6 a.m. The qualitative differences in the mitochondria at different periods of the day are described. A correlation was established between the swelling of the mitochondria and some indices of heart function.     

rRNA sequence-based scanning electron microscopic detection of bacteria

A new scanning electron microscopic method was developed for gaining both phylogenetic and morphological information about target microbes using in situ hybridization with rRNA-targeted oligonucleotide probes (SEM-ISH). Target cells were hybridized with oligonucleotide probes after gold labeling. Gold enhancement was used for amplification of probe signals from hybridized cells. The hybridized cells released a strong backscatter electron signal due to accumulation of gold atoms inside cells. SEM-ISH was applied to analyze bacterial community composition in freshwater samples, and bacterial cell counts determined by SEM-ISH with rRNA-targeted probes for major phyla within the domain Bacteria were highly correlated to those by fluorescent in situ hybridization (FISH). The bacterial composition on surface of river sediment particles before and after cell dispersion treatment by sonication was successfully revealed by SEM-ISH. Direct enumeration of bacterial cells on the surface of sonicated sediment particles by SEM-ISH demonstrated that members of Cytophaga-Flavobacterium existed tightly on the surface of particles. SEM-ISH allows defining the number and distribution of phylogenetically defined cells adherent to material surfaces, which is difficult in FISH, and it gives new insight into electron microscopic studies of microorganisms in their natural environment.