The marginal zone and marginal sinus in the spleen of the gerbil. A light and electron microscopy study

The spleen of the adult gerbil (M. unguiculatus) is characterized by the absence of venous sinuses and ellipsoid sheaths. The follicle (white pulp) is separated from the surrounding red pulp by a distinct marginal zone. The cell types in the marginal zone are common to both the follicle and red pulp. Separating the marginal zone from the follicle is a vascular channel of capillary dimension, the marginal sinus. A number of terminal segments of the arterial vessels within the follicle were observed to form a direct connection with the marginal sinus. Ultrastructurally, discontinuities were evident within the walls of the marginal sinus that would permit passage of both cellular and plasma components from the marginal sinus to either marginal zone or the follicle.     

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.     

Circulatory pathways in the sinusal spleen of the dog, studied by scanning electron microscopy of microcorrosion casts

Scanning electron microscopy of microcorrosion casts was used to visualize circulatory pathways in the sinusal spleen of dog. The examination of contracted versus dilated organs and variations of the volume of material injected gave an indication of flow dynamics. Minimal injections of material into contracted spleens produced filling of mainly the fastest routes for flow, whereas injections into dilated spleens primarily filled slower routes. This procedure yielded a more complete, three-dimensional picture of the arterial, intermediate, and venous pathways as a whole, and of the relative amounts of flow through different arterial routes. Evidence of flow from capillary lumina out into ellipsoid sheaths was plentiful in casts from dilated spleens, but rare in casts from contracted organs. The pattern of flow within and out of the marginal sinus has been elucidated: A circumferential filling occurs first, followed by a flow that radiates outward into the marginal zone and red pulp. Venous sinuses filled via two routes in addition to the generally accepted path from the reticular meshwork via fenestrations in sinus walls. First, many venous sinuses extending out from the marginal sinus and surrounding marginal zone originated as open-ended tubes continuous with the reticular spaces of the marginal sinus or marginal zone. Second, direct connections of arterial capillaries with venous sinuses in the red pulp were found. Evidence indicating that some mechanism is controlling the flow via these routes is discussed. The strikingly different arrangement of venous sinuses in the subcapsular region is demonstrated.     

Functional structure of the carpal and ventral vibrissae of the squirrel (Sciurus vulgaris)

A study is made of the histology, distribution and ultrastructure of nerve-organs in the carpal and ventral sinus hairs of the squirrel Sciurus vulgaris L. These sinus hairs were found to be typical tactile hairs. Their situation on the inner surfaces of the forelimbs, and on the ventral body wall is assumed to be useful during climbing. Five different types of nerve end-organs were found:
1. Ring-shaped end-organs, especially in the ring sinus, associated with certain cells in connectivetissue and in many cases also anchored to the hair follicle.
2. Merkelcells in the basal cell layer of the outer root sheath at the level of the ring sinus.
3. Lanceolate end-organs between the glassy membrane and the connective tissue of the ringwulst and betweenthese in the upper part of the ring sinus.
4. Encapsulated end-organs in the cavernous sinus.
5. Free thin nerveendings.     

Structure of the sinus hair follicle in the big-clawed shrew,Sorex unguiculatus

The structural features of sinus hair follicles in Sorex unguiculatus were studied by macroscopic dissection, serial section light microscopy and electron microscopy. The shrew has about 540 sinus hairs regularly arranged on the snout. The maxillary nerves innervating them are extremely thick, while the optic nerves are very thin. Thus the follicle must be one of the most important sense organs in this animal. In the follicle the ring sinus is well-developed and the trabeculae of the cavernous sinus are reduced in number and thickness. The ring bulge is not a unified structure but a pair of bodies which consist of head, stalk and attachment plaque. It is characterized by the presence of numberous thick collagen fibrils (400 nm) and appears to be mechanically rigid. Lanceolate nerve terminals, free endings, Merkel cells with nerve terminals and unmyelinated fibers are observed, but encapsulated endings are lacking in and around the follicles. Straight lanceolate terminals on the posterior side of the follicle are thick and three-sided in cross section, while those on the anterior side are thin and two-sided. Free endings are located on the anterior side of the follicle. These and other findings are discussed on the basis of the assumption that the Sorex sinus hair follicle is more specialized as a vibrating system than in other mammals.     

Mesoderm differentiation in early amphibian embryos depends on the animal cap

Embryos of Ambystoma mexicanum from the late morula to the late blastula stage were dissected and cultivated in varying combinations. The marginal zone (presumptive mesoderm) when isolated together with the vegetal region differentiated to notochord after dissection from early blastulae, but did not differentiate to other tissues. When isolated from middle to late blastulae, in addition myoblasts and mesenchyme were formed. The marginal zone isolated together with the animal region (presumptive ectoderm) differentiated to notochord, muscle, mesenchyme, renal tubules and mesothelium irrespective of the stage of dissection. Combination of isolated animal and vegetal regions did lead to the induction of mesodermal organs. The experiments suggest that further steps in the differentiation of mesodermal organs after the induction of mesoderm by the vegetalizing factor depend on factors from the animal region, which are involved in pattern formation.     

B cells are crucial for both development and maintenance of the splenic marginal zone

The splenic marginal zone is a unique compartment that separates the lymphoid white pulp from the surrounding red pulp. Due to the orchestration of specialized macrophages and B cells flanking a marginal sinus, this compartment plays an important role in uptake of blood-borne Ags and it gives the spleen its specialized function in antibacterial immunity. In this study, we demonstrate that both development and maintenance of this marginal zone is highly dependent on the presence of B cells. Spleens from B cell-deficient mice were found to lack both metallophilic and marginal zone macrophages as well as mucosal addressin cellular adhesion molecule-1+ sinus lining cells. Using an inducible Cre/loxP-driven mouse model in which mature B cells could be partially depleted by removal of the B cell receptor subunit Igalpha, we could show that the integrity and function of an established marginal zone was also dependent on the presence of B cells. This was confirmed in a transgenic model in which all B cells were gradually depleted due to overexpression of the TNF family member CD70. The loss of all cellular subsets from the marginal zone in these CD70 transgenic mice was effectively prevented by crossing these mice on a CD27(-/-) or TCRalpha(-/-) background, because this prohibited the ongoing B cell depletion. Therefore, we conclude that B cells are not only important for the development, but also for maintenance, of the marginal zone. This direct correlation between circulating B cells and the function of the spleen implies an increased risk for B cell lymphopenic patients with bacterial infections.     

Marginal zone bridging channels as a pathway for migrating macrophages from the red towards the white pulp in the rat spleen

The spleen of (PvG/c X DA)F1 rats, intravenously injected with carbon, was investigated. Large heavily carbon-laden (LHC) macrophages, which were found only in the red pulp at 30 min, appeared along marginal zone bridging channels (MZBC) from the red pulp towards the white pulp side successively during 1-6 h after carbon injection. After this time, they appeared in the periarterial lymphatic sheaths (PALS) near MZBC and then in the deeper PALS along the arteries by 5-10 days. Frequently, they were found in rows from MZBC into the white pulp. These findings suggest migration of LHC macrophages from the red towards the white pulp trough MZBC. Possible migration of LHC macrophages through MZBC was observed for a long period--at least 3 months examined. LHC macrophages came together preferentially in PALS and in and around the germinal centers consisting of large pyroninophilic lymphoblastoid cells. Occasionally, possible migration of LHC macrophages from regions around sinuses crossing the marginal zone vertically (vertical sinus) was also observed. Sinuses accompanied by LHC macrophages often ran parallel in close association with MZBC, particularly at sites of MZBC near the red pulp.     

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.     

大鼠纹状体边缘区内神经降压肽和生长抑素免疫阳性反应的分布

用免疫组织化学方法研究了大鼠纹状体边缘区中神经降压肽和生长抑素免疫阳性反应的分布。神经降压肽和生长抑素免疫阳性纤维和胞体散在分布于纹状体中,但在边缘区中分布密集,形成一条明显的带,带的宽度和位置和边缘区一致。边缘区中可见神经降压肽和生长抑素免疫阳性胞体。本研究证明纹状体边缘区中存在密度较高的神经降压肽和生长抑素免疫阳性纤维和胞体,并推测和边缘区的学习记忆功能有关     

Elimination of phagocytic cells in the spleen after intravenous injection of liposome-encapsulated dichloromethylene diphosphonate

Summary Dichloromethylene diphosphonate can be used for temporary elimination of macrophages in the spleen when administered after entrapment in liposomes. No comparable effect on the macrophages of the spleen was observed with free dichloromethylene diphosphonate or in the case of empty liposomes. Marginal metallophils on the boundary between white pulp and marginal zone as well as macrophages in the marginal zone and red pulp disappeared from the spleen within one day and remained largely absent for about a week. After this time cells reappeared slowly, and at approximately four weeks after injection their presence in the spleen did not differ from that in control animals. Marginal metallophils and macrophages in the spleen were demonstrated by use of enzyme-histochemical methods and by their capacity to ingest carbon particles.     

Homology and evolution of the orbitotemporal venous sinuses of humans.

The orbitotemporal venous sinuses accompany the intracranial branches of the stapedial artery. These sinuses are large in primitive primates and drain the extensive territories supplied by the stapedial artery as well as the brain. The orbit is drained by a wide cranio-orbital sinus which empties into the postglenoid emissary vein. Also emptying into the postglenoid vein is the petrosquamous sinus. The latter diverts cerebral blood from the transverse sinus and also drains the temporalis muscle. Emptying into both the cranio-orbital and petrosquamous sinuses are meningeal tributaries, which drain the cranial side wall and the dura mater. The relatively small sinus communicans runs in the angle between the petrosal bone and the cranial side wall. It commences at the postglenoid vein and connects the distal end of the petrosquamous sinus to the pterygoid venous plexus. In humans, the orbitotemporal sinus system is greatly modified. Its remnants persist for the most part as "middle meningeal veins." The system no longer drains the orbit, the temporal fossa, or the brain. The petrosquamous sinus becomes attenuated or obliterated along part or all of its length. The postglenoid vein vanishes. The cranio-orbital sinus is reduced in diameter and its connection to the orbit is feeble or absent. During development, the posterior end of the cranio-orbital sinus migrates inferiorly along the sinus communicans. In most individuals, this migration ceases at the foramen spinosum, site of the emissary vein of the sinus communicans. Meningeal tributaries are relatively large in humans, and drain principally into the cranio-orbital sinus or sphenoparietal sinus. The sphenoparietal sinus is an evolutionary novelty restricted to hominoids and is frequently developed in only Homo and Pongo.     

In-vivo effects of lipopolysaccharide on lymphoid and non-lymphoid cells in the mouse spleen

In mice marginal metallophils are located at the periphery of the white pulp along the inner border of the marginal sinus. These cells have a weak phagocytic capacity but their function is still unclear. In the present study evidence is given that marginal metallophils migrate from the periphery of the follicle towards the follicle centres after administration of at least 7 micrograms lipopolysaccharide (LPS). This migration is most significant after 24 and 48 h and appears to be a specific effect of LPS. In the follicle centre marginal metallophils take up cell debris and may become tingible body macrophages. The similarity between these two cell types is discussed. The possible effects of several other polyclonal B-cell mitogens on marginal metallophils have also been studied. Dextran sulphate also induces migration of marginal metallophils but this compound triggers a migration and accumulation of these cells at the periphery of the follicles.     

Ontogeny of reticular framework of white pulp and marginal zone in human spleen: immunohistochemical studies of fetal spleens from the 17th to 40th week of gestation

The antigenic heterogeneity of the reticular framework of the white pulp (WP) and marginal zone (MZ) is well documented in the human adult spleen. The ontogeny of the WP and MZ of human fetal spleens was examined with special reference to the heterogeneity of the reticular framework. In the spleen of the 17th gestational week (gw), α-smooth muscle actin (α-SMA)-positive reticulum cells were scattered around the arterioles. From the 20th to 23rd gw, α-SMA-positive reticulum cells increased in number and began to form a reticular framework. An accumulation of T and B lymphocytes occurred within the framework, and a primitive WP was observed around the arterioles. At the 24th gw, antigenic diversity of the reticular framework was observed, and T and B lymphocytes were segregated in the framework. T lymphocytes were sorted into the α-SMA-positive reticular framework, and the periarteriolar lymphoid sheath (PALS) was formed around the arteriole. B lymphocytes aggregated in eccentric portions to the PALS and formed the lymph follicle (LF). The reticular framework of the LF was α-SMA-negative. MZ appeared in the α-SMA-positive reticular framework around the WP at the 26th gw. The PALS, LF, and MZ developed with gestational time. The reticular framework of the PALS, LF, and MZ is thus heterogeneous in the fetal spleen, and the development of the heterogeneity is related to the ontogeny of the PALS, LF, and MZ. This work was supported, in part, by the Open Translational Research Project, Advanced Medical Science Center, Iwate Medical University.     

Localization and transport of lipids in the avian ovarian follicular layers and the structural relationship of theca and granulosa to the basement membrane

We describe the localization of lipids in the wall and superficial ooplasm of the largest avian ovarian follicles by the use of different fixatives and light and electron microscopy. We demonstrate that each yolk globule is always accompanied by one or more highly osmiophilic and sudanophilic alcohol insoluble yolk masses, which we have called satellite yolk. Together with the protein containing yolk globule it forms an integral morphological part of a compartmentalized, bipartite yolk system. Cytochemical, histoautoradiographic, biochemical, and light and electron microscopical aspects of satellite yolk were studied. At the start of satellite yolk formation in the 3–4 mm diameter follicle (when the oocyte begins to yellow) the distribution of the microcirculation of the follicle wall becomes printed on the underlying superficial ooplasm of the oocyte. The oocyte then presents so-called yolk mountains (containing satellite yolk), only localized below the thecal capillary sinus and not below the efferent and radially perforating thecal veins (black hole regions). We also describe the structural continuity between the thecal intercellular spaces and the microvilli-associated extracellular spaces of the granulosa cells via the basement membrane. The thecal cells present centripetal extensions into the basement membrane and the basement membrane material extends centripetally into the granulosa microvillar channels. Therefore, at least two cellular barriers are crossed when fat or fat precursors are transported from the thecal capillary sinus to the ooplasm.     

Formation of the Neural Plate and the Mesoderm in Normally Developing Embryos of Xenopus laevis

Normally developing embryos of Xenopus were fixed at various stages between the blastula and early tail bud stage, and their serial sections were examined. The marginal belt of the blastula was characterized by abundance of cells with RNA-rich peripheral cytoplasm called mesoplasm. At the early gastrula stage, the marginal belt was folded into two layers giving rise to mesodermal material and marginal ectoderm. During gastrulation, the mesodermal material, which consisted of RNA-rich cells, spread to enclose the blastocoel and the endoderm, and a large part of it was shifted to the dorsal side of the embryo. It gradually established the mesodermal layer. The notochord was formed on the dorsal lip of the blastopore by involution, separately from preformed mesodermal material. The RNA-rich cells in the marginal ectoderm became columnar, forming a broad belt in the marginal zone. This belt was deformed and shifted to the dorsal side during gastrulation, eventually establishing the neural plate showing quantitative differentiation along the head-tail axis. Possible mechanisms involved in the formation of the neural plate and mesoderm were discussed with reference to the organizer and the mesoplasm.     

Selective binding of biotinylated albumin to the lymphoid microvasculature

Chemically modified albumin binds to the surface of microvascular endothelia lining the vessel wall in several tissues. In this paper, we report that following their biotinylation, ovalbumin (bioOVA) and bovine serum albumin (BSA) [biotinyated albumin (bioAlb)] showed heterogeneous binding to distinct vascular subsets in different lymphoid tissues. The binding of bioAlb could be demonstrated both by fluorescent and enzymohistochemical techniques. In the spleen, the reaction was restricted to the red pulp sinuses whereas the white pulp vessels (including the central arteriole) and the marginal sinus were negative for bioAlb binding. In lymph nodes, the strongest labeling was observed in the medullary sinuses. In the thymus, the most prominent labeling of capillaries was restricted to the corticomedullary area where it was found to be less intense compared with the splenic reaction. The splenic reactivity of bioAlb in the mouse was defined using antibodies against endothelial cell subsets in distinct vascular beds in the red pulp and marginal zone, respectively. The bioAlb-binding elements of the splenic red pulp sinus architecture corresponded to the display of hyaluronan receptor stabilin-2 and subset-specific marker IBL-9/2 while they differed from the expression pattern of both the complementary red pulp sinus subset and the marginal sinus-lining cells expressing MAdCAM-1 antigen, respectively. Similar red pulp sinus-restricted reactivity could be demonstrated in the human, rat, and guinea pig. The use of bioAlb may thus offer a reliable probe for the histological identification of select microvascular endothelia in lymphoid tissues.     

On the histology and histochemistry of the snout and vibrissae of the common shrew (Sorex araneus L.)

Summary The structure of the snout and tactile hair system of the common shrew (Sorex araneus) and the distribution of cholinesterase and alkaline phosphatase activity were studied. The structure of the vibrissae is exceptional compared with that of other mammals studied. Differences are the attachment system of hair follicle to the capsule, the impossibility of dividing the blood sinus clearly into cavernous sinus and ring sinus, the lack of continuous ring-wulst, clear constriction in the outer root sheath at the neck of hair follicle and some specialized structures connected with this. Alkaline phosphatase was not found in the nervous structures of the vibrissae but cholinesterase activity occurs at least in two different structures upon or in the outer root sheath of the hair follicle. The role of these structures and the significance of vibrissae to the shrew is discussed.     

Splenic marginal zone dendritic cells mediate the cholera toxin adjuvant effect: dependence on the ADP-ribosyltransferase activity of the holotoxin

The in vivo mechanisms of action of most vaccine adjuvants are poorly understood. In this study, we present data in mice that reveal a series of critical interactions between the cholera toxin (CT) adjuvant and the dendritic cells (DC) of the splenic marginal zone (MZ) that lead to effective priming of an immune response. For the first time, we have followed adjuvant targeting of MZ DC in vivo. We used CT-conjugated OVA and found that the Ag selectively accumulated in MZ DC following i.v. injections. The uptake of Ag into DC was GM1 ganglioside receptor dependent and mediated by the B subunit of CT (CTB). The targeted MZ DC were quite unique in their phenotype: CD11c(+), CD8alpha(-), CD11b(-), B220(-), and expressing intermediate or low levels of MHC class II and DEC205. Whereas CTB only delivered the Ag to MZ DC, the ADP-ribosyltransferase activity of CT was required for the maturation and migration of DC to the T cell zone, where these cells distinctly up-regulated CD86, but not CD80. This interaction appeared to instruct Ag-specific CD4(+) T cells to move into the B cell follicle and strongly support germinal center formations. These events may explain why CT-conjugated Ag is substantially more immunogenic than Ag admixed with soluble CT and why CTB-conjugated Ag can tolerize immune responses when given orally or at other mucosal sites.     

Video-Assisted Implantation of a Left Ventricular Lead and Intrathoracic Tunneling to a Right-Sided CRT-D Device

We describe two cases in which a biventricular implantable cardioverter defibrillator for cardiac resynchronization therapy had to be placed on the right side due to unsuitability of the left subclavian vein. Endocardial implantation of a left ventricular lead through the coronary sinus was previously attempted but was unsuccessful. Implantation of the epicardial left ventricular pacing lead was performed through video-assisted thoracic surgery on the left side. The connector end of the left ventricular pacing lead was tunnelized through the anterior mediastinum into the right pleural space. The right-sided pocket was then opened. A tunnel was created from the pocket to the thoracic wall, and the pleural space was entered over the second rib. The lead was retrieved from the right pleural space and connected with the Cardiac resynchronization therapy-device (CRT-D). Both procedures and postoperative periods were uneventful. Intrathoracic left-to-right tunneling of an epicardial left ventricular lead by video-assisted thoracic surgery is feasible and safe. It provides an alternative to subcutaneous tunneling.