Dynamics of changes in cell composition in the lymphoid tissue of somatic lymph nodes during total overheating of the body

At total overheating a manifested macrophagal reaction is observed in the rat somatic lymph nodes. Concentration of autoantigens in tissues increases, that results in transformation of small lymphocytes towards lymphoblasts and plasma cells. When manifested disorders of hemo- and lymphocirculation are present, eosinophils and mast cells, being tissue regulators of microcirculation and wall permeability of blood capillaries and lymphatic sinuses++., increase in number.     

Structural organization of the compensation process in the lymph nodes in venous stasis

Transmission and scanning electron microscopy was used to study the structural organization of the lymph nodes during venous congestion. At the early period (1 h of venous congestion) one could see an increased number of the fenestrated cells in the venous part of the capillary whereas at the later period (after 6 h to 3 days) a rise of the microvesicular transport via endotheliocytes of the arterial part of the capillary and via fenestras of the venous part. Within 7 to 14 days one could see activation of the microvesicular transport via the indicated parts of the capillary. At all the stages of venous congestion the fluid contained by the parenchyma of the lymph node penetrates via fenestras and intercellular fissures to the marginal sinus, while only via fenestra to the cerebral sinuses.     

High endothelial venules of the lymph nodes express Fas ligand.

Fas (CD95, APO-1) is widely expressed on lymphatic cells, and by interacting with its natural ligand (Fas-L), Fas induces apoptosis through a complex caspase cascade. In this study we sought to survey Fas-L expression in vascular and sinusoidal structures of human reactive lymph nodes. Immunohistochemical Fas-L expression was present in all paracortical high endothelial venules (HEVs), in cells lining the marginal sinus wall, and in a few lymphocytes, but only occasionally in non-HEV vascular endothelium. In the paracortical zone over 60% of all vessels and all paracortical HEVs showed Fas-L expression, whereas in the medullary zone less than 10% of the blood vessels were stained with Fas-L. Normal vessels outside lymph nodes mostly showed no Fas-L expression. We show that in human reactive lymph nodes Fas-L expression is predominantly present in HEVs. Because the circulating lymphocytes gain entry to nodal parenchyma by transendothelial migration through HEVs, the suggested physiological importance of Fas-L expression in these vessels lies in the regulation of lymphocyte access to lymph node parenchyma by possibly inducing Fas/Fas-L mediated apoptosis of activated Fas-expressing lymphoid cells. The Fas-L expressing cells in the marginal sinus might have a similar function for cells accessing the node in afferent lymph.     

Interaction of lymphocytes and high endothelial venules in irradiated lymph nodes

After total-body exposure to various doses of ionizing radiation, the ability of lymphocytes to interact specifically with high endothelial venules of rat cervical and mesenteric lymph nodes was analyzed in frozen sections. Following a radiation dose of 1.5 Gy, high endothelial venules remained intact and the binding of unirradiated lymphocytes to the venules was enhanced relative to unirradiated controls. At radiation doses above 5.0 Gy, damage to high endothelial venules was observed histologically as well as assessed functionally. There was a significant decrease in specific lymphocyte-venule binding and a significant increase in nonspecific binding. These findings suggest that radiation-induced damage to high endothelial venules might play a role in radiation-induced immunosuppression by interfering with the normal passage of lymphocytes from the blood into lymph nodes via a specific interaction between lymphocytes and high endothelial venules.     

The unique ultrastructure of high-endothelial venules in inguinal lymph nodes of the pig

Lymph nodes in pigs are unique in their inverted structure, with the medulla in the periphery and the cortex in central areas. Furthermore, in this species most migrating lymphocytes do not use the classical route via efferent lymphatics to leave the lymph node. High-endothelial venules (HEV) are the entry sites for lymphocytes and in pigs probably also the exit site for recirculating lymphocytes. Therefore, the blood vessels and especially the HEV of the pig superficial inguinal lymph node were investigated as to whether morphological peculiarities could be found in the vascular system, using vascular casting, transmission- and scanning electron microscopy. A thin layer of capillary network surrounded the periphery of the lymph node and HEV branched acutely. The endothelial cells of HEV possessed well developed cytoplasmic organelles, interdigitated with each other, and demonstrated local cell-cell contacts. There were unusual cells bridging the adluminal wall of HEV. These cells were called intravascular bridging cells. They were characterized by an often invaginated nucleus, few pinocytotic vesicles, many microvilli on the surface, wide, flat, cytoplasmic processes like a pseudopod, Weibel-Palade bodies and local cell-cell contacts with endothelial cells. The pseudopod-like processes ramified over the endothelial junctions and covered lymphocytes. Lymphocytes were seen in different phases of migration between endothelial cells and in the intercellular junctions. The previous functional studies on the peculiar route of lymphocyte recirculation in pig lymph nodes are extended by these morphological data, showing a unique structure of HEV in pigs.     

Light and electron microscopic studies of the paracortical post-capillary high-endothelial venules

Summary The light and electron microscopic structure of the high-endothelial postcapillary venules of lymph nodes were studied in the mouse, rat, guinea pig, and rabbit. The venules were most frequently found in the mouse and rat. In all species, they reached their highest degree of differentiation in the paracortical area. The morphology in the light microscope was identical in all four species. The venules in the rat and mouse were surrounded by a cuff of concentrically-arranged lymphocytes, which was rarely seen in the guinea pig and rabbit.The ultrastructure of the high-endothelial cells in all four species was very complex; a prominent Golgi apparatus was present which often occupied large parts of the cytoplasm. Coated and uncoated vesicles originating in the Golgi apparatus often permeated the cytoplasm. These vesicles emptied their contents into the extracellular space after fusion with the plasma membranes.Numerous lymphocytes traversed vessel walls. During their passage, they were always located between, not inside the high-endothelial cells.     

Histochemical studies of high-endothelial venules of lymph nodes and peyer's patches in the mouse

Summary The histochemistry and DNA turnover of postcapillary high-endothelial venules in lymph nodes and Peyer's patches have been investigated. Autoradiographic studies showed that the cells are long lived. They exhibit a distinct metachromatic reaction that is indicative of a moderate amount of RNA. They are PAS positive due to the presence of glycogen. Considerable amounts of mucopolysaccharides are not found inside the cells. The reactions for lactate dehydrogenase, NADH-tetrazolium reductase and unspecific esterase are strong. The intensities of the reactions are comparable to those of the epithelium of the intestinal villus and of reticular cells and definitely stronger than that of other endothelial cells. Tests for acid phosphatase, alkaline phosphatase, succinic dehydrogenase, glucose-6-phosphate dehydrogenase and NADPH-tetrazolium reductase showed that these enzymes are either absent or present in small amounts.     

Diurnal dynamics of spatial-temporal organization of lymph nodes

Experiments, performed on CBA mice demonstrate that all the parameters of lymph nodes of various localization possess a diurnal rhythmicity. Certain lympho-endocrine connections participate in realization of the regional peculiarities of the diurnal rhythms via regulation of redistribution of streams of the migrating lymphoid cells, that form the lymph node structures. There are certain differences in endogenous glucocorticoids action, depending on the level of the motor activity, that determines level of the mast cells activation, value of lymph-formation and blood stream intensity in the drained region. Concrete examples of the diurnal spatial-time organization of functional steps are described in inguinal, mesenteric and bifurcational lymph nodes.     

Microanatomical organization and cytoarchitectonics of lymphoid tissue in the mesenteric lymph nodes under conditions of experimental total hyperthermia

Microanatomical organization and cell composition of the rat mesenteric lymph nodes have been studied under conditions of experimental total hyperthermia. Possibilities of the compensatory-adaptive reactions of the lymphoid tissue have been determined. Disturbances of microhemo-++- and lymphocirculation in the lymph nodes in different time after hyperthermia are accompanied with accumulation of mast cells and eosinophils in various zones of the node; they normalize certain physiological parameters of microcirculation and permeability of the metabolic microvessel walls. In 30 days after a single total overheating of the rat organism, the microanatomical organization changes in the lymph nodes investigated are manifested as atrophy of B-dependent zones and further volumetric increase of the paracortical zone. Therefore, it is possible to think about a decreasing intensity of the humoral immunity and increasing intensity of the cellular one.     

Transport function of lymph nodes in body antiorthostatic posture

The spontaneous contractile activity of isolated lymph nodes and the lymph flow from intestine lymphatic vessel in antiorthostatic posture of rats with an inclination angle of 30 degrees during 7-14 days, was decreased. Contractions of the rat lymph nodes in response to actions of adrenaline, acetylcholine and histamine were diminished. There are changes of biochemical components of lymph and blood plasma with simultaneous decrease of the blood plasma volume. It is concluded that the lymphatic system on antiorthostatic posture plays the compensatory role with the purpose of stabilization of homeostasis in the brain.     

Light and electron microscopic studies of postcapillary venules in developing human fetal lymph nodes.

Developing lymph nodes from 30 human fetuses with crownrump lengths (CRL) of 38 mm (8.7 wk) to 245 mm (26 wk) were studied by light and electron microscopy. Blood vessels that appear to be postcapillary venules (PCV) are present in nodes of 47 mm CRL and older fetuses. These venules first appear in nodes whehn the nodal population of lymphocytes is sparse. In these early nodes PCV are distributed randomly and consist of a low endothelium, underlying basal lamina and incomplete pericyte sheath. Early nodal PCV are distinguised from other nodal blood vessels by the presence of lymphocyte diapedesis and several luminal lymphocytes. In the late stages of nodal development PCV are the more common non-capillary blood vessel and appear in the parenchyma near the periphery of the node. Late nodal PCV are generally characterized by a cuboidal endothelium that is rich in Golgi apparatus, lysosomes and Weibel-Palade bodies. The lumen and wall of late nodal PCV contain lymphocytes. The relationship between the development of the parenchyma of fetal nodes and the appearance and activity of PCV, the passage of lymphocytes through the PCV wall and the fine structure of developing PCV are described. It is suggested that the lymphocytes that first appear in developing nodes, and the majority of the lymphocytes found in late nodes, migrate to the node via the blood vascular system and enter the nodal parenchyma by passing across PCV endothelium.     

Structural and ultrastructural changes of lymph nodes in primary lymphoedema

Optical and electronmicroscopic investigations of the inguino-iliac lymph nodes and lymphatic vessels of the lower limb suggested a pathogenic role of lymph node structural alterations in primary lymphoedema. Most of the investigated lymph nodes showed an extensive fibrosis frequently associated with lipomatosis ectasy of medullary sinuses, a.o., estimated as primary lesions appearing on a genetically propensic ground or by developmental anomalies. Alteration of the lymphatic vessel intima, proliferation, muscle hypertrophy, subintimal fibrohyalinosis, a.o., occurred in consequence of the impeded lymphatic drainage by the primary lymph node fibrosis.     

Volume flow and wall shear stress quantification in the human conjunctival capillaries and post-capillary venules in vivo

Understanding the mathematical relationships of volume blood flow and wall shear stress with respect to microvessel diameter is necessary for the study of vascular design. Here, for the first time, volume flow and wall shear stress were quantified from axial red blood cell velocity measurements in 104 conjunctival microvessels of 17 normal human volunteers. Measurements were taken with a slit lamp based imaging system from the post capillary side of the bulbar conjunctiva in microvessel diameters ranging from 4 to 24 micrometers. The variation of the velocity profile with diameter was taken into account by using a profile factor function. Volume flow ranged from 5 to 462 pl/s with a mean value of 102 pl/s and gave a second power law best fitting line (r=0.97) deviating significantly from the third power law relation with diameter. The estimated wall shear stress declined hyperbolically (r=0.93) from a maximum of 9.55 N/m(2) at the smallest capillaries, down to a minimum of 0.28 N/m(2) at the higher diameter post capillary venules. The mean wall shear stress value for all microvessels was 1.54 N/m(2).     

Morpho-functional changes in the lymph nodes during fever reaction]

Lymph nodes (mesenteric, popliteal, cervical) of rabbits in fever reaction of different duration have been studied in our work. As a whole morpho-functional changes in lymph nodes in fever reaction indicate the increase of their functional activity: hyperplasia of lymphatic substance with the growth of lymphocytes number and slightly differentiated lymphoid cells in follicles and paracortical zone, hyperplasia of pulposus bands, the signs of macrophagal reaction and plasmatization of lymph nodes are to be observed and all these create prerequisites for the increase of tensity of cellular and humoral immunity. Simultaneously the signs of destruction of cellular elements--lymphocytolysis in the porta tract and the growth of number of PAS-positive cells in the parenchyma of the nodes take place.     

Ultrastructural organization of capillary endotheliocytes of the popliteal and iliac lymph nodes in the rat

The popliteal and iliac lymph nodes have different regional specialization. The former belong to somatic lymph nodes, while the latter get lymph also from internal organs; this explains certain differences in their structural-functional organization. Some objective quantitative data have been obtained that characterize ultrastructure of blood capillaries in the rat popliteal and iliac lymph nodes under normal conditions of the organism's functioning. They demonstrate essential differences in the level of transendothelial transport and, hence, functional activity of these organs.