Migration pathways of recirculating murine B cells and CD4+ and CD8+ T lymphocytes

Migration pathways of B cell and CD4+ and CD8+ T cell subsets of murine thoracic duct lymphocytes (TDL) were mapped. Per weight, the spleen accumulated more TDL than any other organ, regardless of lymphocyte subset. Spleen autoradiographs showed early accumulations of TDL in marginal zone and red pulp. Many TDL exited the red pulp within 1 hr via splenic veins. The remaining TDL entered the white pulp, not directly from the adjacent marginal zone but via distal periarterial lymphatic sheaths (dPALS). From dPALS, T cells migrated proximally along the central artery into proximal sheaths (pPALS) and exited the white pulp via deep lymphatic vessels. B cells left dPALS to enter lymphatic nodules (NOD), then also exited via deep lymphatics. T cells homed to lymph nodes more efficiently than B cells. Lymphocytes entered nodes via high-endothelial venules (HEV). CD4+ TDL reached higher absolute concentrations in diffuse cortex than did CD8+ T cells. However, CD8+ TDL moved more quickly through diffuse cortex than did CD4+ TDL. B cells migrated from HEV into NOD. Both T and B TDL exited via cortical and medullary sinuses and efferent lymphatics. A migration pathway across medullary cords is described. All TDL subsets homed equally well to Peyer's patches. T TDL migrated from HEV into paranodular zones while B cells moved from HEV into NOD. All TDL exited via lymphatics. Few TDL entered zones beneath dome epithelium. All subsets were observed within indentations in presumptive M cells of the dome epithelium.     

Morphology and distribution of cystic cavities in the normal murine thymus

Summary The normal murine thymus was examined by lightand electron microscopy to determine the distribution and morphology of extracellular cystic cavities. Most cavities were confined to the cranial half of each gland, situated at the junction between cortex and medulla. They varied in size and shape, and gave rise to narrow channels that coursed to the capsular surface of the gland. Large cavities could be divided into three zones. A short cranial zone exhibited gland-like features, consisting of cells lining a clear lumen. A central zone was lined by a diverse population of cells. Some possessed secretory granules, while others exhibited an apical ciliated border. Lining cells interdigitated with each other and were joined laterally by intercellular junctions. The lumen of the central zone contained lymphocytes and macrophages in an amorphous extracellular matrix. The caudal zone of each cavity had an attenuated and incomplete cellular lining, communicating directly with the surrounding thymic parenchyma. Thymic cavities may represent the initial part of the efferent lymphatic system of the gland, beginning in the tissue spaces at the corticomedullary junction. Selected cells could then enter and interact with the luminal contents in the central zone of the cavity. Ciliated cells may then propel lymphocytes and secretions into the narrow channels radiating from the uppermost part of the chamber, leaving a cell-free lumen in this region. These cavities may function in sequestering lymphocytes, macrophages and thymic secretions before their exit from the gland.     

Ultrastructure of the tubular nephron of the lizard Podarcis (= Lacerta) Taurica

The proximal, intermediate, and distal convoluted tubules of the neprhon of Podarcis (= Lacerta) taurica were examined by electron microscopy. Proximal tubule cells have large, apical cytoplasmic protrusions and microvilli interpreted to function in urate secretion. Adjacent cells are bound apically by tight junctions and desmosomes but interdigitate in their basal region. This situation is repeated in the other tubules with significant differences in intercellular space width. The basal surfaces bear numerous cytoplasmic processes. The intermediate tubule has proximal and distal segments each with dark, ciliated, and light cells, the cuboidal dark cells with dense cytoplasm constituting the main bulk of the wall. As the cells of the proximal and distal segments resemble those of the proximal and distal convoluted tubules, respectively, the intermediate tubule is considered as a transition region. The ciliated cell body has two broad processes extending from the lumen, one to the basement membrane and one to a foot process of a light cell. The light cell is surrounded by dark and ciliated cells. It does not reach the lumen, but contacts the basement membrane through a process running below a ciliated cell to form a mushroom-shaped structure in tubule cross-section, the light cell process forming the stalk and a ciliated cell the cap. The cilia probably propel the glomerular filtrate towards the distal convoluted tubule. This latter tubule has initial, middle, and terminal zones, all nonciliated but with different lumen widths and cell shapes.     

Culture of human endometrial cells under polarizing conditions

Glandular epithelial and stromal cells were isolated from human endometrial biopsies and cultured in a dual-chambered system (Millicell; Millipore, Bedford, Ma., USA) that provides access of the medium to both sides of a membrane coated with reconstituted basement membrane material (Matrigel; Collaborative Research Inc., Bedford, Ma., USA). Examination by electron microscopy revealed that the epithelial cells formed a polarized cuboidal-columnar monolayer on the Matrigel surface. The cells exhibited apical microvilli, basal nuclei, and numerous cytoplasmic structures consistent with a well-differentiated cytoplasm; they were joined basally by interdigitating processes and apically by tight junctions and desmosomes. In contrast, epithelial cells cultured in parallel on plastic dishes were flattened, had fewer microvilli and cytoplasmic structures, and no junctional complexes.     

The role of M cells in the protection of mucosal membranes

 The mucosa-associated lymphoid tissues continuously take up antigenic matter from the lumen to generate immune responses or to maintain immune tolerance. This antigen sampling is performed by highly specialised epithelial cells, the membranous (M) cells of the dome epithelia. M cells possess a unique ultrastructure and lie in close contact to lymphoid cells. They endocytose soluble and solid substances, including entire microorganisms, at their apical membrane, transport these in vesicles to their basolateral membrane and exocytose them to the intercellular space. This review summarises the structural and functional peculiarities of M cells in different species and at the different sites of lymphoid tissue along the digestive and respiratory tracts. Specialisations of M cells for antigen uptake and transport comprise the composition of their apical membrane and its glycocalyx, a modified cytoskeleton as compared to enterocytes and a pocket-like invagination of the basolateral membrane populated by lymphocytes and macrophages. Besides ultrastructural characteristics, histochemical markers are listed that are currently available for detecting M cells by light microscopy. The origin, differentiation and distribution of M cells and other epithelial cell types of the dome epithelium are outlined. As M cells are used as entry sites by various pathogens and, in the future, might be employed for the oral application of vaccines and drugs, the clinical relevance of M cells in health and disease is discussed. Accepted: 4 August 1997     

The Harderian gland of the Cheesman's gerbil (Gerbillus cheesmani ) of the Kuwaiti desert

The Harderian gland is a large orbital structure. Several functions have been ascribed to the gland such as lubrication of the eye, a source of pheromones, thermoregulartory lipids and photoprotective secretions and a part of the retinal-pineal axis. In the present study, the Harderian gland of the Cheesman's gerbil, Gerbillus cheesmani, is described for the first time. The gland is located around the posterior portion of the eyeball. The gland is compound tubular, surrounded by a thin connective tissue capsule. Only one secretory epithelial cell type was recognized, characterized by the presence of lipid vacuoles and cytoplasmic slashes in high numbers; the former being more concentrated towards the apical part while the latter being more concentrated towards the central and basal parts. Some of the cytoplasmic slashes contained electron dense filamentous structures. Similar structures were observed in the lipid vacuoles. Thus, a functional relationship between the cytoplasmic slashes and the lipid vacuoles is suggested. A unique structure was observed, termed dome-like cells, located between the epithelial cells and the basement membrane. These cells were characterized by the extensive presence of pleomorphic mitochondria and compact lamellae of granular endoplasmic reticulum (GER) in the form of finger prints. The gland was found to be actively secreting porphyrins as well as lipids. Cellular debris was also seen in the tubular lumina. Myoepithelial cells with their spindle shape and elongated nuclei were evident between the basement membrane and the secretory epithelium. Sparse interstitial tissue was observed in-between the gland tubules of both male and female gerbils. Macrophages, dendritic melanocytes and lymphocytes are the most represented cellular components of the interstitium. Further studies are required to investigate the function of the dome-like cells as well as the role of lymphocytes in the rodents Harderian gland.     

Ultrastructure of the jugular body of Rana pipiens

Summary The jugular bodies in adult Rana pipiens, are surrounded by a capsule of mesothelium and connective tissue, and their parenchyma consists of cell cords arranged in a sinusoidal network. The cell cords are formed by irregular reticular cells, showing numerous filaments and joined together by zonulae adhaerents. The intercellular spaces are filled by reticular fibres and free cells. These latter are small and medium lymphocytes, lymphoblasts, and developing and mature plasma cells. Additionally, free macrophages, neutrophils and acidophils also occur. Sinusoidal blood vessels show thin walls with numerous filaments and pinocytotic vesicles. They exhibit a discontinuous basement membrane, and tight junctions frequently occur between endothelial cells. Occasionally, lymphatic vessels are found and the innervation is principally vasomotor, although nerve endings appear remarkably near reticular cells and lymphocytes. The jugular bodies of adult R. pipiens are plasma cell and antibody-forming organs, whose functional significance is discussed in relation to their ultrastructural organization.     

Deep splenic lymphatic vessels in the mouse: a route of splenic exit for recirculating lymphocytes

A study of pathways of lymphocyte migration through mouse spleen revealed lymphatic channels closely following arteries in trabeculae and white pulp. Because there is no detailed record of the layout of deep splenic lymphatics in the mouse, or other species, we present our observations in this paper, relating our findings to normal migratory pathways of lymphocytes through the spleen. Lymphatics draining the spleen are so inconspicuous that they often are not mentioned in anatomical discussions. The data presented clearly demonstrate 1) the existence and layout of deep lymphatic vessels in the mouse spleen, and 2) that migrating lymphocytes exit white pulp via these lymphatic vessels. CD4+ and CD8+ T cell subsets migrated proximally along the central artery from distal (dPALS) to proximal periarterial lymphatic sheaths (pPALS) and exited via deep lymphatic vessels that originate there. B cells migrated from dPALS to enter lymphatic nodules (NOD), thus segregated from T cells. B cells then migrated toward and exited via deep lymphatics. The appearance of labelled lymphocytes in lymph coincided with their disappearance from white pulp compartments. Labelled T cells were observed in splenic lymphatics as early as 1 hr after intravenous infusion but took, on average, about 6 hr. B cells took somewhat longer. Thus T and B cells entered and left white pulp through shared pathways, but took divergent intermediate routes through dedicated zones, pPALS for T cells, NOD for B cells.     

Incorporation of 3H-uridine into the large decidual cells of rats and their differentiation

The antimesometrial part of rat's decidua of the 9th day of gestation was divided into three zones. Cells of either zone display their own morphological and cytochemical properties. Different rates of 3H-uridine incorporation were observed in the cytoplasm and the nucleus in cells of either zone during 5, 30, 60 and 240 minutes after precursor injection. The largest member of silver grain accumulation was observed in the karyoplasm and nucleolus of cells of the transitional zone. The nucleus of basal zone cells had the smallest intensity of 3H-uridine incorporation. The nuclei of the epithelial zone cells are characterized by a lower intensity of 3H-uridine incorporation than those of the transition zone. The intensity to cytoplasmic accumulation of silver grains raised from cells of the basal zone up to cells of the epithelial zone. The largest quantity of cytoplasmic radioactivity was observed 240 minutes after 3H-uridine injection.     

Tissue architecture: the ultimate regulator of epithelial function?

The architecture of a tissue is defined by the nature and the integrity of its cellular and extracellular compartments, and is based on proper adhesive cell-cell and cell-extracellular matrix interactions. Cadherins and integrins are major adhesion-mediators that assemble epithelial cells together laterally and attach them basally to a subepithelial basement membrane, respectively. Because cell adhesion complexes are linked to the cytoskeleton and to the cellular signalling pathways, they represent checkpoints for regulation of cell shape and gene expression and thus are instructive for cell behaviour and function. This organization allows a reciprocal flow of mechanical and biochemical information between the cell and its microenvironment, and necessitates that cells actively maintain a state of homeostasis within a given tissue context. The loss of the ability of tumour cells to establish correct adhesive interactions with their microenvironment results in disruption of tissue architecture with often fatal consequences for the host organism. This review discusses the role of cell adhesion in the maintenance of tissue structure and analyses how tissue structure regulates epithelial function.     

Structure of the inguinal lymph nodes after extirpation of the pancreas

Swiching off the external and internal secretion of the pancreas by means of extirpation of the organ demonstrates a progressive hypoplasia of the immunocompetent tissue in the inguinal lymphatic nodes. The involution is determined by decreasing number of small, middle and large lymphocytes in the cortical part of the node. Together with the decreasing number of the lymphatic nodules, by the 20th-60th days after the operation the germinative centers become poor in middle, large lymphocytes and in lymphoblasts. Among the cells mentioned, mitotic activity is decreased. Hence, thymus-dependent, but to a greater extent, thymus--independent zones of the lymphatic nodes are subjected to involution.     

Distribution of myoepithelial cells and basement membrane proteins in the resting, pregnant, lactating, and involuting rat mammary gland

Using antisera to specific proteins, the localization of the rat mammary parenchymal cells (both epithelial and myoepithelial), the basement membrane, and connective tissue components has been studied during the four physiological stages of the adult rat mammary gland, viz. resting, pregnant, lactating, and involuting glands. Antisera to myosin and prekeratin were used to localize myoepithelial cells, antisera to rat milk fat globule membrane for epithelial cells, antisera to laminin and type IV collagen to delineate the basement membrane and antisera to type I collagen and fibronectin as markers for connective tissue. In the resting, virgin mammary gland, myoepithelial cells appear to form a continuous layer around the epithelial cells and are in turn surrounded by a continuous basement membrane. Antiserum to fibronectin does not delineate the basement membrane in the resting gland. The ductal system is surrounded by connective tissue. Only the basal or myoepithelial cells in the terminal end buds of neonatal animals demonstrate cytoplasmic staining for basement membrane proteins, indicating active synthesis of these proteins during this period. In the secretory alveoli of the lactating rat, the myoepithelial cells no longer appear to form a continuous layer beneath the epithelial cells and in many areas the epithelial cells appear to be in contact with the basement membrane. The basement membrane in the lactating gland is still continuous around the ducts and alveoli. In the lactating gland, fibronectin appears to be located in the basement membrane region in addition to being a component of the stroma. During involution, the alveoli collapse, and appear to be in a state of dissolution. The basement membrane is thicker and is occasionally incomplete, as also are the basket-like myoepithelial structures. Basement membrane components can also be demonstrated throughout the collapsed alveoli.     

Ontogeny of reticular cells in the ileal Peyer's patch of sheep and goats.

The ontogeny of reticular cells in the ileal Peyer's patch of sheep from 70 days gestational age was studied by light and electron microscopy and by enzyme histochemistry. Small to medium-sized lymphocytes were seen in the lamina propria at 97 days, when the stroma was essentially still mesenchymal. By 110 days, the stromal cells in the dome/follicle primordia had differentiated into reticular fibroblasts, whose processes and fibers were seen to surround groups of lymphocytes. With advancing age the number and size of primordia increased, and proliferation was obvious among the lymphocytes. Processes of reticular cells increased in number and penetrated between individual lymphocytes of the groups. Coarser desmosome-like contacts were seen between the reticular cells from 115 days onwards. A central light area in the follicle was apparent from 130 days onwards. The fine structure of the stromal cells in this light follicle center developed towards but never became similar to that of follicular dendritic cells in a typical germinal center. The fine interdigitating end branches of the stromal cells were less numerous, and the dense homogeneous material present in between the end branches was not observed in the ileal Peyer's patch follicle. Instead, small particles and vesicles were seen between the various cell types of the light center and were not restricted to the intercellular spaces between the stromal cells. In the dark peripheral zone of the follicle, the stromal cells retained more immature features. The follicle became bordered by a capsule at an early stage. This capsule was formed by multiple layers of flattened fibroblasts separated by small amounts of intercellular material only. The alkaline phosphatase, Mg(2+)-dependent adenosine triphosphatase and 5' nucleotidase reactivities of the follicular dendritic cells in the ileal Peyer's patch were similar to those of early prenatal primary follicles of sheep lymph nodes. This study indicates that the stromal cells of the ileal Peyer's patch are mesenchymal in nature and different from those of germinal centers and the epithelial stromal cells of bursa Fabricii of birds.     

Changes in the specific cytochemical properties of rat decidual cells during differentiation

The antimesometrial part of rat's decidua of 8-9 day of gestation was divided into three parts: epithelial, transition and basal zones. Cells of either zone have their own morphological and cytochemical features. Cells of the epithelial zone are characterized by synthesis of tissue specific antigens and fat (fatty acids). Cells of the transition zone synthesize glycogen. Acid mucopolysaccharides are located in the basal zone only. Decidual cells do not synthesize cholesterol. Con A receptors are localized on the surface of cells of the basal and transition zones and disappear from the surface of epithelial zone cells. It is concluded that differentiation of large decidual cells of the antimesometrial part of rat's decidua are accompanied by a significant change in cytochemical features of cell precursors the synthesis of acid mucopolysaccharides and glycogen stops, while tissue specific antigens and fat (fatty acids) start their syntheses, Con A receptor disappear.     

Differentiation of lens fibers in explanted embryonic chick lens epithelia

Central regions of explanted lens epithelia from 6-day-old chick embryos were maintained in tissue culture for 4 weeks to determine the extent to which lens fiber differentiation would progress in vitro. Cellular outgrowth from the explants created 3 distinct zones; namely, a thick central zone, a thicker annular zone and a flattened peripheral zone. Cells of the central and annular zones underwent morphological and biochemical changes which correspond to the differentiation of lens fibers in vivo. The mean cell length increased a minimum of 25-fold. The nuclei in the longer cells became pycnotic; DNA remained in the nuclei but accumulated single-strand breaks. The cytoplasm became filled with a homogeneous granular matrix. Organelle density decreased, but microtubules persisted, mostly along surface membranes; free ribosomal clusters were present. There were occasional desmosomes and infoldings of cell membranes. The proportion of ribosomal RNA synthesized decreased relative to the total RNA synthesized, especially in the central zone. Finally, the proportion of delta crystallin synthesized increased to 40–50% of the newly synthesized protein. These data suggest that the transformation of lens epithelial cells into fibers results from a programmed differentiation which can take place in tissue culture.     

Qualitative and quantitative morphologic study of Peyer's patches of the mouse after neonatal thymectomy and hydrocortisone injection

Peyer's patches in normal adult mice, neonatally thymectomized mice and mice injected with hydrocortisone were studied qualitatively and quantitatively by light microscopy. The patch was divided into germinal center, follicular area, parafollicular area and dome area. In normal mice, the volumetric ratio of the germinal center to the entire patch was 30.9%; that of the follicular area, 33.3%; that of the parafollicular area, 27.7%; and that of the dome area, 8.2%. Thymus-dependent small lymphocytes were 40% of small lymphocytes in the patch. Out of the total thymus-dependent small lymphocytes in the patch, 13% were included in the germinal center; 19%, in the follicular area; 62%, in the parafollicular area; and 6%, in the dome area. Hydrocortisone-sensitive small lymphocytes were 65% of the total small lymphocytes in the patch, the germinal center contained 9%; the follicular area, 84%; the parafollicular area, 2%; and the dome area, 5%. The epithelium over the dome area was invaded by numerous small lymphocytes. Forty-eight percent of lymphocytes within the epithelium over the dome were thymus-dependent and 67% were hydrocortisone-sensitive. It is concluded that Peyer's patch may be considered as a peripheral lymphatic tissue, functionally as well as morphologically.     

FINE STRUCTURE OF THE MYOEPITHELIUM OF THE ECCRINE SWEAT GLANDS OF MAN

The secretory coils of glutaraldehyde-osmium tetroxide-fixed and Epon-Araldite-embedded eccrine sweat glands from the palms of young men were studied with the electron microscope. The myoepithelial cells lie on the epithelial side of the basement membrane and abut other epithelial elements directly. The irregularly serrated base of the cell has dense thickenings along the plasma membrane which alternate with zones bearing pits; the smooth apical surface lacks dense thickenings, is studded with pits, and conjoined to secretory cells by occasional desmosomes. Masses of myofilaments, 50 A in diameter, fill most of the cell and are associated with irregular dense zones. In cross-section the arrangement of the myofilaments seems identical with that of the I band of striated muscle, and the dense zone has typical Z band structure. A few microtubules and cytoplasmic cores bearing profiles of the endoplasmic reticulum, filamentous mitochondria, and glycogen granules penetrate the fibrillar masses and run parallel to the oriented myofilaments. In the perinuclear zone, Golgi membranes, rough- and smooth-surfaced elements of the endoplasmic reticulum, mitochondria, glycogen, microtubules, lipid, pigment, and dense granules are variable components in the cytoplasm. The interrelationships of the myoepithelial cells with the secretory cells suggest that the former may act as regulators, controlling the flow of metabolites to the secretory epithelium.     

FETAL RAT INTESTINAL ABSORPTION OF HORSERADISH PEROXIDASE FROM SWALLOWED AMNIOTIC FLUID

Horseradish peroxidase (HRP) injected into amniotic fluid is swallowed by rat fetuses and within 3–6 h reaches the gut lumen. This macromolecular protein is then absorbed by the columnar lining cells via a system of apical cytoplasmic tubules formed by invaginations of the plasma membrane. From cytoplasm subjacent to the brush border HRP is transported, within vacuoles, to the supranuclear region, where some is retained for at least 18 h, and to interepithelial spaces. Extracellular enzyme is then found throughout the epithelial basement membrane and between connective tissue cells of the mucosal and submucosal layers Finally, HRP can be detected within lumina of blood and lymphatic capillaries, strongly suggesting that it is transported from the intestine to the circulation.     

Thyroxine-induced gill resorption in the axolotl (ambystoma mexicanum)

Normal gill structure and thyroxine induced resorptive changes were studied in Ambystoma mexicanum. The gill is normally composed of a mesenchymal core covered with a multilayered epithelium. The general architecture is simpler than that of the teleost and elasmobranch, but the vascular arrangement is analogous. There are three basic cell types in the epithelium: a characteristic epithelial cell containing tonofibrils and mucus, a ciliated cell with an ultrastructure similar to that of the chloride cell, and the mucin-filled Leydig cell. The basal lamella and mesenchymal tissue appear typical of amphibians. Cytologic changes during thyroxine induced gill resorption varied with cell type. Some epithelial cells demonstrated a cytoplasmic response with swelling of mitochondria and rough endoplasmic reticulum and late, lytic nuclear changes, while others remained viable and went on to cornify. Ciliated cells showed early changes in nuclear chromatin pattern followed by rapid, progressive dilatation of endoplasmic reticulum. Leydig cells sustained variable changes leading to collapse of the perinuclear mucus, and cells of this type were absent in mature epidermis. Early basement membrane changes included widening and reduplication of the adepidermal membrane followed by morphologic fraying of collagen plies. There is no cytologic evidence to suggest that autolysis plays a major role in gill tissue dissolution. Resorption involved the maintenance of structural integrity in the face of diminishing physical dimensions. The epithelium became cornified, the basement lamellae dissolved, and the mesenchymal tissue was resorbed through action of macrophages in an orderly distal to proximal direction.     

On the source of uterine 'luminal fluid' proteins in the mouse

Examination by light-, transmission electron- and scanning electron-microscopy showed that flushing the lumen of the mouse uterus with small volumes of fluid damaged the endometrium by rupturing and removing luminal epithelial cells, splitting the epithelial basement membrane and connective tissue stroma, and rupturing and leaching stromal cells and blood vessels. The damage increased with increasing progestation of the uterus and between Days 4 and 5 of pregnancy. I conclude that many so-called 'luminal fluid' proteins originate from luminal and stromal cells, intercellular fluid and blood and that apparent changes in luminal fluid protein content during early pregnancy may largely reflect alterations in the extent and type of damage produced by flushing, as a consequence of changes in the physical state of the uterus induced by hormones and the presence of blastocysts.