bluuebunny/crossref_metadata_2025 huggingface dataset:
Immunohistology of lymphoid and non‐lymphoid cells in the thymus in relation to T lymphocyte differentiation
Authors: Van Ewijk W.
Published: February 2005

The present paper reports the distribution of lymphoid and non‐lymphoid cell types in the thymus of mice. To this purpose, we employed scanning electron microscopy and immunohistology. For immunohistology we used the immunoperoxidase method and incubated frozen sections of the thymus with (1) monoclonal antibodies detecting cell‐surface‐differentiation antigens on lymphoid cells, such as Thy‐1, T‐200, Lyt‐1, Lyt‐2, and MEL‐14; (2) Mococlonal antibodies detecting the major histocompatibility (MHC) antigens, H‐2K, I‐A, I‐E, and H‐2D; and (3) monoclonal antibodies directed against cell‐surface antigens associated with cells of the mononuclear phagocyte system, such as Mac‐1, Mac‐2, and Mac‐3. The results of this study indicate that subsets of T lymphocytes are not randomly distributed throughout the thymic parenchyma; rather they are localized in discrete domains.

Two major and four minor subpopulations of thymocytes can be detected in frozen sections of the thymus: (1) the majority of cortical thymocytes are strongly Thy‐1+ (positive), strongly T‐200+, variable in Lyt‐1 expression, and strongly Lyt‐2+; (2) the majority of medullary thymocytes are weakly Thy‐1+, strongly T‐200+, strongly Lyt‐1+, and Lyt‐2− (negative); (3) a minority of medullary cells are weakly Thy‐1+, T‐200+, strongly Lyt‐1+, and strongly Lyt‐2+; (4) a small subpopulation of subcapsular lymphoblasts is Thy‐1+, T‐200+, and negative for the expression of Lyt‐1 and Lyt‐2 antigens; (5) a small subpopulation of subcapsular lymphoblasts is only Thy‐1+ but T‐200− and Lyt−; and (6) a small subpopulation of subcapsular lymphoblasts is negative for all antisera tested. Surprisingly, a few individual cells in the thymic cortex, but not in the medulla, react with antibodies directed to MEL‐14, a receptor involved in the homing of lymphocytes in peripheral lymphoid organs. MHC antigens (I‐A, I‐E, H‐2K) are mainly expressed on stromal cells in the thymus, as well as on medullary thymocytes. H‐2D is also expressed at a low density on cortical thymocytes. In general, anti‐MHC antibodies reveal epithelial‐reticular cells in the thymic cortex, in a fine dendritic staining pattern. In the medulla, the labeling pattern is more confluent and most probably associated with bone‐marrow‐derived interdigitating reticular cells and medullary thymocytes. We discuss the distribution of the various lymphoid and non‐lymphoid subpopulations within the thymic parenchyma in relation to recently published data on the differentiation of T lymphocytes.
Contribution of thymus lymphocytes to the peripheral lymphoid tissues and the effect of antigen on the rate of cell exit from the thymus
Authors: Scollay Roland , Shortman Ken
Published: February 2005

Some of the important questions concerning the development of T cells in the thymus can be answered by a study of the different thymocyte subpopulations and a comparison of their properties with those of the cells exported to the peripheral lymphoid tissues. What is the relationship between cortical and medullary thymocytes? Why do most cortical cells die? Which subpopulation gives rise to thymus migrants? How many cells are exported from the thymus? Are the exported cells fully mature? Are any of these functions affected by antigen stimulation or other peripheral events? In this paper we review the background to some of these questions and focus on the effect of peripherally administered antigen on the export of cells from the thymus. Experimental data are presented which suggest that the overall rate of emigration is not grossly affected by large doses of intravenous protein antigens. Nor is there any obvious qualitative change, at least in terms of the size of the cells released. The possibility of changes in the specificity of the exported cells is discussed, but as yet there are no data which throw light on this point.
T‐Cell development in the absence of a thymus: The number, the phenotype, and the functional capacity of T lymphocytes in nude mice
Authors: Chen Wei‐Feng , Scollay Roland , Shortman Ken , Skinner Margot , Marbrook John
Published: February 2005

A small but definite proportion of T‐lymphocyte‐like cells have been reported in nu/nu (nude) mouse spleen despite the congenital absence of a thymus in these animals. We have determined the number and the characteristics of such cells using flow cytometry. The level of T‐like cells increased with age. In 4‐month‐old nu/nu CBA spleen, 14% of all cells expressed some Thy 1 antigen. However, only 4% expressed mature T‐cell levels, and only the 2% with the highest Thy 1 also showed a normal distribution of Ly 1 and Ly 2 antigens. These T‐like cells were slightly larger than normal nondividing T lymphocytes.

We have assessed the total functional capacity of T‐like cells in nu/nu CBA spleen using a high‐cloning‐efficiency limit‐dilution culture system. Almost all precursor cells capable of forming clones when stimulated with concanavalin A in the presence of irradiated spleen cells and growth factors, and almost all precursors of those clones that were cytolytic in a lectin‐mediated tumor‐cell‐lysis assay, were within this 2% subpopulaton of nu/nu spleen cells with mature T‐cell markers. Increased levels of purified interleukin 2 failed to induce further precursor function, indicating that maturation of pre‐T cells was not obtained. However the nu/nu spleen cells bearing mature T‐cell markers displayed only 10‐30% of the cloning efficiency of normal splenic T cells. The majority of nu/nu spleen T‐like cells, even within this phenotypically “normal” subset, appeared to be nonfunctional.

We conclude that the absence of a thymus leads to qualitative, as well as quantitative, deficiencies in the T‐cell population, and various interpretations are discussed.
The migration of lymphocytes across specialized vascular endothelium: VIII. Physical and chemical conditions influencing the surface morphology of lymphocytes and their ability to enter lymph nodes
Authors: Ford W. L. , Allen T. D. , Pitt M. A. , Smith M. E. , Stoddart R. W.
Published: February 2005

The introductory review amplifies the finding that simply holding lymphocytes in vitro reversibly compromises their ability to enter lymph nodes from the blood, although entry into the spleen is unaffected. The differential migration of T and B lymphocytes from the blood, lymphocyte traffic in athymic rats, and the secretion of a sulphated glycoconjugate by high endothelial cells in lymph nodes are also discussed.

Original data are presented concerning the effects of varying the conditions under which lymphocytes are held in vitro (time, temperature, medium, centrifugation) on their ability to enter lymph nodes and also on their surface morphology. In general, conditions that reduced the number of microvilli and induced surface blebbing also tended to affect the delicate function of crossing specialized vascular endothelium; but there was no simple relationship between morphology and migratory behavior. The localization of lymphocytes to the bone marrow was augmented by holding them in vitro, and this effect was greater after holding at room temperature (RT) than at 0°C, in contrast to impaired entry into lymph nodes. Small amounts of heparin (10 units) injected along with lymphocytes significantly reduced early localization in lymph nodes. These findings have practical implications for the design of lymphocyte traffic experiments and are relevant to the mechanism of lymphocyte attachment to vascular endothelium, since the well‐known effect of trypsinizing lymphocytes can be reproduced by maintenance in vitro.
Localization of lymphocyte subpopulations in peripheral lymphoid organs: Directed lymphocyte migration and segregation into specific microenvironments
Authors: Rouse Robert V. , Reichert Roger A. , Gallatin W. Michael , Weissman Irving L. , Butcher Eugene C.
Published: February 2005

The distribution of lymphocytes in the peripheral lymphoid organs is controlled by recirculatory and microenvironmental factors. Specific interactions between recirculating lymphocytes and high endothelial venules in various lymphoid sets and subsets in those organs. Separate endothelial determinants on peripheral node and Peyer's patch endothelium along with complementary lymphocyte receptors mediate this organ specificity. B and T cells also exhibit nonrandom organization within lymphoid tissues; after entry via high endothelial venules they segregate into their respective domains, which appear to be determined by distinct types of nonlymphoid stromal cells. Antigenic stimulation results in changes in lymphocyte phenotype as well as in the lymphoid microenvironment. The response to most complex antigens is the formation of germinal centers (GC) composed primarily of proliferating B cells; the phenotype of the few T cells therein is supportive of the GC as a site of B‐T interaction. The phenotype of the B cells in GCs suggest a role for GCs in immunoglobulin class switching and the determination of subsequent homing specificity.
Functional anatomy of germinal centers
Authors: Nieuwenhuis P. , Opstelten D.
Published: February 2005

This year we celebrate the first centennial of the discovery of germinal centers by Flemming in 1884. The present paper reviews and adds new data to the functional anatomy of a germinal center. Emphasizing its reactive nature, we first describe a germinal center reaction and then deal with its infrastructural aspects and constituent cell populations, both lymphoid and nonlymphoid. Elements involved in the de novo formation of a germinal center, like antigen, T cells, and the mysterious germinal‐center‐precursor cell, are discussed. Next, attention is paid to the requirements for lymphoid cells to migrate into germinal centers, and novel features of germinal‐center‐seeking cells are presented. Subsequently, we discuss kinetic aspects of the high proliferative activity in a germinal center; and finally a description of the functional capacities of germinal‐center‐derived cells, such as B memory cells and IgM‐antibody‐forming cell precursors, completes this picture of present‐day knowledge of the germinal center, a structure which has yet to reveal its last secrets.
Gut‐ and bronchus‐associated lymphoid tissue
Authors: Bienenstock John , Befus Dean
Published: February 2005

Bronchus‐associated and gut‐associated lymphoid tissues (BALT and GALT) have both functional and morphologic similarities and are involved in seeding lung, gut, and other mucosal sites with predominantly IgA‐containing B cells. Both types of lymphoid tissue are engaged in the regulation and the controlled amplification of immune responses, which vary from positive mucosal responses in both mucosae and peripheral tissues to local mucosal responses and systemic tolerance. Their further involvement in provision of cells destined to reside in the epithelial compartment of the body appears likely but requires further investigation. Their role in the provision of precursors of mucosal mast cells must also be explored further, but some participation in this event appears likely. The mucosa‐associated lymphoid tissue (MALT) system appears to be integrated with the systemic immune system but may be considered as separate from it in several functional ways.
The hematopoietic stroma
Authors: Weiss Leon , Sakai Hidetaka
Published: February 2005

The stroma of the hematopoietic tissues includes a number of diverse cell types, i.e., bone‐lining cells and related capsular and trabecular structures, epithelial‐reticular cells and other epithelial cells, reticular cells, macrophages, and antigen‐presenting cells. These stromal cells possess a variety of mechanical and metabolic functions. They support and confine the hematopoietic tissues and their vasculature. They regulate the migrations of blood and hematopoietic cells. Stromal cells contribute to the microenvironment that induces the differentiation of stem cells into the several blood‐cell lines. The nature of the interactions of stromal and hematopoietic cells depends upon long‐ and short‐range humoral factors, and upon such cell‐surface compounds as immunoglobulins and major histocompatability antigens. Blood cells themselves, as neutrophils and lymphocytes, play regulatory roles in hematopoiesis along with stromal cells. Moreover, certain stromal cells, such as macrophages, originate as blood cells and have migratory phases. Distinctions between blood cells, their derivatives, and stromal cells may therefore be difficult to draw.
The anatomy of peripheral lymphoid organs with emphasis on accessory cells: Light‐microscopic immunocytochemical studies of mouse spleen, lymph node, and peyer's patch
Authors: Witmer Margit D. , Steinman Ralph M.
Published: February 2005

Antigen, lymphocytes, and accessory cells interact within peripheral lymphoid organs to generate immunity. Two cell types have been studied for accessory function in culture: mononuclear phagocytes and nonphagocytic Ia‐rich dendritic cells. The monoclonal antibodies which have been used to study isolated murine macrophages (MØ) and dendritic cells (DC) include α‐macrophage (F4/80, M1/70), α‐dendritic cell (33D1), α‐Fc receptor (2.4G2), and α‐Ia (B21‐2) reagents. In this paper, the antibodies have been used to stain accessory cells in cryostat sections of mouse spleen, lymph node, and Peyer's patch. Each organ is known to contain subregions that are rich in either macrophages, B cells, or T cells. We found that the accessory cells in each subregion had a different phenotype. (1) Macrophage‐rich regions: Macrophages that lined the site of antigen delivery (marginal zone of spleen, around afferent lymphatics of node, and below the epithelium of Peyer's patch) were stained with M1/70 but not with F4/80. F4/80 was abundant on macrophages in other sites: spleen red pulp, node medulla, and around Peyer's patch efferent lymphatics. (2) B‐lymphocyte‐rich follicles: Follicular dendritic cells, which retain immune complexes extracellularly, are concentrated on the outer aspect of the germinal center. This region stained strongly with α‐Fc receptor antibody 2.4G‐2, but not with M1/70, F4/80, or 33D1. (3) T areas: The interdigitating cells of T areas have been linked to isolated dendritic cells. Irregular Ia‐rich cells were distributed uniformly in the T areas of each organ. However, staining with 33D1 was not detected and was restricted to foci of nonphagocytic cells at the spleen red/white pulp junction. F4/80, M1/70 or 2.4G2 also did not stain the T area, except for the region close to splenic central arteries. Therefore the principal surface markers and location of the candidate accessory cells in murine lymphoid organs are M1/70+ macrophages at the site of antigen entry; F4/80+ macrophages around regions of lymphocyte efflux; germinal center dendritic cells, which may be rich in 2.4G2; and Ia‐rich interdigiting cells in the T area.
Antigen processing and presentation by macrophages
Authors: Allen Paul M. , Unanue Emil R.
Published: February 2005

The classical macrophage is one of the most important cells involved in presenting antigen to helper T cells, because of its ability to regulate its expression of Ia molecules and to encounter and process particulate and soluble antigens. We have summarized in this report studies examining the handling by macrophages of two different antigens, the bacteria Listeria monocytogenes and the protein hen egg white lysozyme (HEL). The purpose was to identify potential sources of immunogenic peptides. Presentation of Listeria required an intracellular processing stage sensitive to lysosomotropic drugs. The Listeria required internalization and processing, after which immunogenic molecules were recognized by T cells on the macrophage surface. Metabolic studies showed that Listeria‐derived peptides were released by macrophages that had phagocytosized the bacteria. The release of these peptides was a temperature‐dependent process, unaffected by inhibiting lysosomal catabolism by treatment with chloroquine. Listeria‐derived peptides were also detected on the surface of the macrophage. These peptides behaved like integral membrane proteins, some of which persisted for at least 24 hr at the macrophage surface. When tested for immunogenicity, the released peptides were very weakly immunogenic. The membrane‐associated peptides alone could not stimulate Listeria‐specific T cells, but could be reprocessed by additional macrophages and subsequently stimulate the T cells. A defined antigen system using HEL‐specific T‐cell hybridomas was used to examine the processing of HEL. Presentation of HEL required a choloroquine‐sensitive intracellular processing stage. In examining two T‐cell hybridomas, a differential requirement for antigen processing was determined. The immunogenicity of released HEL from HEL‐pulsed macrophages was also tested, and no “processed” antigen was detected capable of directly stimulating T cells; however, native HEL was released from the macrophage and could be processed and presented by other macrophages.
Cells of the fetomaternal interface: Their role in the maintenance of viviparous pregnancy
Authors: Lala P. K. , Kearns M. , Colavincenzo V.
Published: February 2005

An immune system capable of discriminating between self and nonself evolved in nature long before the appearance of the viviparous mode of pregnancy, which brings maternal cells into a direct physical contact with genetically disparate cells of fetal origin. In the hemochorial type of placentation, the former include cells of the maternal immune system. This article briefly reviews the possible mechanisms that may protect the semiallogeneic conceptus in nature, with special reference to the role of the cells at the fetomaternal interface. We also present some new data on the antigenicity of pre‐ and postimplantation trophoblast cells and the immunobiology of decidual cells. Systemic changes in the maternal immune system appear to represent homeostatic responses to the presence of a semiallogeneic conceptus, unrelated to its protection; mechanisms for this protection must reside locally at the fetomaternal interface. We find that the lack of immunogenicity of the outer (trophoblast) cells of the preimplantation blastocyst can be explained by a transient disappearance of the major histocompatibility (MHC) antigens on their cell surface. However, following implantation and the formation of the placenta, class 1 MHC antigens reappear on certain classes of trophoblast cells, i.e., labyrinthine and spongiotrophoblast cells of the murine placenta. Similarly, cytotrophoblast cells of the early human placenta exhibit the presence of class 1 MHC antigens. An absence of class 2 MHC antigens despite the presence of class 1 antigens cannot entirely explain the lack of trophoblast immunogenicity. A local immunosuppression mediated by trophoblast cells themselves as well as maternal cells of hemopoietic origin in the decidua remain as a strong possibility. Typical decidual cells appear to play a central role in the maintenance of pregnancy because of their numerous functions: nutritive, endocrine, and immunoregulatory. Our studies reveal that they are descendants of bone‐marrow‐derived precursors, have unique surface markers recognizable with monoclonal antibodies nonreactive with other hemopoietic cell lineages, and have the ability to abrogate mixed lymphocyte reactions in vitro in a genetically unrestricted manner. Further studies directed at the cells of the fetomaternal interface should provide a better insight into the mode of survival of the nature's most commonplace allograft.
Influence of colchicine and vinblastine on the intracellular migration of secretory and membrane glycoproteins: II. Inhibition of secretion of thyroglobulin in rat thyroid follicular cells as visualized by radioautography after 3H‐fucose injection
Authors: Wild G. , Bennett G.
Published: February 2005

Young (40 gm) rats were given a single intravenous injection of colchicine (4.0 mg) or vinblastine (2.0 mg). At 10 min after colchicine and 30 min after vinblastine administration, the rats were injected with 3H‐fucose. Control rats received 3H‐fucose only. All rats were sacrificed 90 min after 3H‐fucose injection and their tissues processed for radioautography.

In thyroid follicular cells of control animals, at this time interval, 57% of the total label was associated with colloid and secretory vesicles in the apical cytoplasm while 27% was localized in the Golgi apparatus and neighboring vesicles. In experimental animals, the proportion of label in colloid and apical vesicles was reduced by more than 69% after colchicine and more than 83% after vinblastine treatment. The proportion of label in the Golgi region, on the other hand, increased by more than 125% after colchicine and more than 179% after vinblastine treatment. Within the Golgi region, the great majority of the label was associated with secretory vesicles which accumulated adjacent to the trans face of the Golgi stacks. It is concluded that the drugs do not interfere with passage of newly synthesized thyroglobulin from the Golgi saccules to nearby secretory vesicles, but do inhibit intracellular migration of these vesicles to the cell apex. In most cells the number of vesicles in the apical cytoplasm diminished, but this was not always the case, suggesting that exocytosis may also be partially inhibited. The loss of microtubules in drug‐treated cells suggests that the microtubules may be necessary for intracellular transport of thyroglobulin.
Influence of colchicine and vinblastine on the intracellular migration of secretory and membrane glycoproteins: III. Inhibition of intracellular migration of membrane glycoproteins in rat intestinal columnar cells and hepatocytes as visualized by light and electron‐microscope radioautography after 3h‐fucose injection
Authors: Bennett G. , Carlet E. , Wild G. , Parsons S.
Published: February 2005

In the first paper of this series (Bennett et al., 1984), lightmicroscope radioautographic studies showed that colchicine or vinblastine inhibited intracellular migration of glycoproteins out of the Golgi region in a variety of cell types. In the present work, the effects of these drugs on migration of membrane glycoproteins have been examined at the ultrastructural level in duodenal villous columnar cells and hepatocytes.

Young (40 gm) rats were given a single intravenous injection of colchicine (4.0 mg) or vinblastine (2.0 mg). At 10 min after colchicine and 30 min after vinblastine administration, the rats were injected with 3H‐fucose. Control rats received 3H‐fucose only. All rats were sacrificed 90 min after 3H‐fucose injection and their tissues processed for radioautography.

In duodenal villous columnar cells, 3H‐fucose labeling of the apical plasma membrane was reduced by 51% after colchicine and by 67% after vinblastine treatment; but there was little change in labeling of the lateral plasma membrane. Labeling of the Golgi apparatus increased. This suggests that labeled glycoproteins destined for the apical plasma membrane were inhibited from leaving the Golgi region, while migration to the lateral plasma membrane was not impaired. In hepatocytes, labeling of the sinusoidal plasma membrane was reduced by 83% after colchicine and by 85% after vinblastine treatment. Labeling of the lateral plasma membrane also decreased, although not so dramatically. Labeling of the Golgi apparatus and neighboring secretory vesicles increased. This indicates that the drugs inhibited migration of membrane glycoproteins from the Golgi region to the various portions of the plasma membrane. Accumulation of secretory vesicles at the sinusoidal front suggests that exocytosis may also have been partially inhibited. In both cell types, microtubules almost completely disappeared after drug treatment. Microtubules may, therefore, be necessary for intracellular transport of membrane glycoproteins, although the possibility of a direct action of these drugs on Golgi or plasma membranes must also be considered.
Ultrastructural and cytochemical observations on 5‐fluorouracil‐induced cleft‐palate development in hamster
Authors: Shah Ravindra M. , Wong David T. W. , Suen Roger S. K.
Published: February 2005

Sequential alterations in 5‐fluorouracil‐treated hamster fetal palate were studied by light and electron microscopy and by acid phosphatase cytochemistry. At an early stage in 5‐fluorouracil‐treated fetuses, when the palatal shelves were vertical, lysosomes first appeared in cells of the prospective fusion epithelium and then in the cells of subjacent mesenchyme. In contrast to controls, increasing numbers of both the epithelial and mesenchymal cells of the vertical palate showed lysosomal injury in 5‐fluorouracil‐treated fetuses as development progressed. Subsequently, the basal lamina in the vertical palate showed alterations, characterized initially by disturbances in lamina lucida, by fingerlike extensions of lamina densa, and ultimately by its complete breakdown. At a later stage, when shelves became horizontal, the lysosomes were absent in both the epithelial and mesenchymal cells, and the basal lamina continuity was restored. Unlike controls, however, 5‐fluorouracil‐treated horizontal shelves never contacted one another. Instead, the epithelia of the horizontal shelves underwent stratification. It appears that premature formation of lysosomes in palatal epithelial and mesenchymal cells following 5‐fluorouracil treatment disrupts normal cytodifferentiation and affects the integrity of the basal lamina; both effects are associated with cleft‐palate development.
The nasopalatine ducts and associated structures in the rhesus monkey (Macaca mulatta): Topography, prenatal development, function, and phylogeny
Authors: Zingeser Maurice R.
Published: February 2005

Morphological and developmental characteristics of the rhesus monkey nasopalatine duct system and associated primary palatal structures are described along with functional and phylogenetic considerations. Examination of five adult palates and coronal sections of 13 fetal palates together with dissections of a sixth adult specimen and of a 119‐day‐old fetal palate reveal that the lateral lobes of the tripartate incisive papilla cover clefts leading into the ducts. The ducts pierce the bony palate to enter the nasal fossae in proximity to the incisive suture. The ontogenetic stability of the duct path reflects the retention of ancient duct and primitive choanae relationships and functionally maintains an optimal oral odorant‐to‐receptor channel.

Sixteen timed pregnancy specimens (35–100 days) provided histological material for documenting rostral nasopalatal development. Duct primordia, identified at 35 days, had by 40 days formed the medial duct walls (conjoined septum‐papilla from the primary medial palatal component), the lateral duct walls (maxillary processes), and the rostral walls (fused maxillary‐intermaxillary components). The caudal walls derive from the fusion of palatal shelves with the papilla (45 days), thus distinguishing primary and secondary fusion modes. Duct epithelial maturation occurs between 70 and 100 days.

The absence of a vomeronasal system is attributed to reduction of olfaction in reproductive behavior, while the presence of the coevolved nasopalatine ducts is linked to the persistence of epiglottal‐velar valving. The ducts serve as oral food‐odor conduits in otherwise functionally separated respiratory and digestive tracts.
Cellular composition and organization of ductal buds in developing rat mammary glands: Evidence for morphological intermediates between epithelial and myoepithelial cells
Authors: Ormerod E. Jane , Rudland Philip S.
Published: February 2005

In the developing rat mammary gland, terminal end buds (TEBs), lateral buds and alveolar buds represent the major sites of morphogenetic activity and cellular differentiation. The morphology and cellular composition of these buds from 20‐to 22‐day‐old rats and cycling rats have been studied by immunocytochemical and electron microscopic techniques. The mammary buds are composed of a heterogeneous collection of cells including epithelial and myoepithelial cells, irregular loosely adherent cells, and occasional large clear cells. The irregular, loosely packed cells or cap cells are mainly situated around the periphery of the TEBs and lateral buds. “Chains” of irregularly shaped cells also extend from the peripheral cap cell layer to the center of the TEB; and, where they converge on lumina, they display microvilli and junctional complexes. At the tips of the end buds, the cap cells are of undifferentiated appearance; however, similar cells situated toward the subtending mammary ducts show a gradation in ultrastructure to that of myoepithelial cells. This change is accompanied by an increase in the amounts of immunoreactive myosin and keratin seen within the cells and a 200‐fold increase in the thickness of the basement membrane. In contrast, the peripheral cells of the alveolar buds are more closely packed, contain a greater number of myofilaments, and show increased staining with antisera to myosin. We suggest that the undifferentiated cap cells do not represent a discrete cell type, since they show transitional forms to myoepithelial cells within the subtending mammary ducts, and that the tendency toward the myoepithelial phenotype is predominant in the more differentiated structures, the alveolar buds.
Changes in the fine structure of rat visceral yolk‐sac placenta during prolonged pregnancy
Authors: Jollie William P.
Published: February 2005

Visceral yolk‐sac membranes were obtained surgically from viable rat fetuses which had been retained experimentally in utero in lactating animals for as long as 3 days beyond delivery of their littermates. They were examined with the electron microscope. The fine structure of the yolk‐sac placental membrane (i.e., the tissues separating vitelline capillary lumina from the uterine cavity) remained unimpaired during the delay period. Progressive changes included a decrease in the height of the endodermal epithelium, but a thickening of the basement membrane underlying it by repeated replication of the subepithelial basal lamina and an increase in collagen fiber content in the reticular lamina. Transcytosis across the endothelium of the capillaries of the peripheral vitelline circulation remained unchanged throughout the delay period; endocytosis of materials, presumably maternal serum proteins, from the uterine cavity into the apices of the endodermal epithelium, however, decreased with time. At the oldest stage (26 days post‐coitum) most endocytosed materials had been stored for hydrolysis in large subapical vacuoles which were identified as secondary lysosomes; and evidence of uptake from the uterine lumen was essentially absent. Accordingly, placental transport of protein by the visceral yolk sac of the rat can be regarded as a perinatal process. The action of an elaborately developed and well‐preserved Golgi apparatus in both cellular mechanisms, viz., digestion of maternal proteins and protein transfer, was inferred.
The tracheobronchial epithelium of the bonnet monkey (Macaca radiata): A quantitative ultrastructural study
Authors: Wilson Dennis W. , Plopper Charles G. , Hyde Dallas M.
Published: February 2005

Since there are major differences between the airway epithelium of man and that of common laboratory species, the tracheobronchial epithelium of the bonnet macaque was characterized to evaluate its usefulness as a model for study of human conducting airways. This study compared the light microscopic, scanning electron microscopic, and ultrastructural appearance of epithelium from the posterior membranous and anterior cartilaginous trachea and mainstem bronchus. Population densities, epithelial volumetric densities, and frequency distributions of cross‐sectional areas of nuclei were determined for cell types present on electron micrographs. Four epithelial cell types were distinguished by ultrastructural criteria. Basal cells were 31% of the population and were similar to those described in other species. Ciliated cells were also similar to those of other species and composed 41% of the population; their nuclei were larger than those of other cell types. Mucous goblet cells had large numbers of secretory granules with electron‐dense cores and a lucent periphery. They were only 8% of the population by nuclear count but composed 20% of the epithelial volume. The fourth cell type had multiple small vesicles containing small amounts of granular material and was termed a “small mucous granule cell.” Small mucous granule cells (16% of the population) were present in greater numbers than mucous goblet cells but were a smaller proportion of the epithelial volume (8%). While population densities of cell types determined from transmission electron micrographs did not vary between sample sites, scanning electron microscopy demonstrated longitudinal streaks of secretory cells in the posterior trachea suggesting that regional differences in epithelial organization exist. We conclude that the macaque extrapulmonary airway epithelium differs from published descriptions of laboratory rodents in both cell types present and relative abundance of those cell types. Although detailed quantitative studies of human extrapulmonary airways are not available, the primate airways resemble those of man in both the types of cells present and the complexity of pseudostratification.
Endocytosis in nonciliated epithelial cells of the ductuli efferentes in the rat
Authors: Hermo L. , Morales C.
Published: February 2005

The nonciliated cells lining the ductuli efferentes presented three distinct cytoplasmic regions. The apical region contained, in addition to cisternae of endoplasmic reticulum and mitochondria, two distinct membranous elements. The tubulovesicular system consisted of dilated tubules connected to the apical plasma membrane and subjacent distended vesicular profiles. The apical tubules, not connected to the cell surface, consisted of numerous densely stained tubules of small size which contain a compact, finely granulated material. The supranuclear region, in addition to a Golgi apparatus and ER cisternae, contained dilated vacuoles, pale and dense multivesicular bodies, as well as numerous dense granules identified cytochemically as lysosomes. The basal region contained the nucleus and many lipid droplets. The endocytic activity of these cells was investigated using cationic ferritin (CF) and concanavalin‐A‐ferritin (Con‐A‐ferritin) as markers of adsorptive endocytosis; and native ferritin (NF), concanavalin‐A‐ferritin in the presence of α‐methyl mannoside, and horseradish peroxidase or albumin bound to colloidal gold for demonstrating fluid‐phase endocytosis. These tracers were injected separately into the rete testis, and animals were sacrificed at various time intervals after injection. At 1 min, CF or Con‐A‐ferritin were seen bound to the apical plasma membrane, to the membrane of microvilli, and to the membrane delimiting elements of the tubulovesicular system. Between 2 and 5 min, these tracers accumulated in the densely stained apical tubules and at 15 in min the dilated vacuoles. Between 30 min and 1 hr, the tracers appeared in multivesicular bodies of progressively increasing density, whereas at 2 hr and later time intervals, many dense lysosomal elements became labeled. The tracers for fluid‐phase endocytosis showed a distribution similar to that for CF or Con‐A‐ferritin except that they did not bind to the apical plasma membrane, microvilli, or membrane delimiting the tubulovesicular system. At no time interval were any of the tracers observed in the abluminal spaces. Thus, the nonciliated epithelial cells of the ductuli efferentes are actively involved in fluid‐phase and adsorptive endocytosis, both of which result in the sequestration of endocytosed material within the lysosomal apparatus of the cell.
Muscle fiber termination at the tendon in the frog's sartorius: A stereological study
Authors: Eisenberg Brenda R. , Milton Richard L.
Published: February 2005

The force produced within skeletal muscle fibers is transmitted to the bone via a myotendinous junction. This junctional region was examined by light and electron microscopy in the sartorius muscles of three Rana temporaria. The muscle fibers tapered and inserted at an angle of about 25° with the connective tissue fascia near the bone. The composition of the structures within the last 100 μm of the fiber was analyzed morphometrically. The T‐system, terminal cisternae, and caveolae were the same as in the central region of the muscle fiber. However, the mitochondrial content was higher and the volume of longitudinal sarcoplasmic reticulum was lower than elsewhere in the fiber. The membrane at the end of the fiber had extensive villiform processes interdigitating with the tendon. The surface area of the membrane around the villiform processes was estimated with point‐counting techniques and calculated from the stereological equations appropriate for partially anisotropic structures. The extra membrane involved in the myotendinous junction was about 32 times that of the cross‐sectional area of the fiber. Part of this additional membrane contained specialized adherens junctions through which the contractile proteins of the muscle are anchored to collagen. The increased area at the myotendinous junction presumably provides greater mechanical strength than a flat termination. The high values of membrane capacitance and specific resistance measured electrophysiologically at the end of the fiber also can be attributed to the characteristics of the terminal membrane structure.
Architectural design and fiber‐type distribution of the major elbow flexors and extensors of the monkey (cynomolgus)
Authors: Roy Roland R. , Bello Maureen A. , Powell Perry L. , Simpson Don R.
Published: February 2005

Because the architectural and biochemical properties of a skeletal muscle dictate its force, velocity, and displacement properties, the major extensors (triceps brachii) and flexors (biceps brachii, brachialis, and brachioradialis) of the elbow in a primate (cynomolgus, monkey) were studied. Functional cross‐sectional areas (CSA) were calculated from muscle mass, mean fiber length (normalized to a 2.20 μm sarcomere length), and angle of fiber pinnation measurements from each muscle. Fiber‐type distributions were determined and used as a gross index of the biochemical capacities of the muscle. The extensor group had a shorter mean fiber length (31 vs. 47 mm), a larger CSA (13 vs. 8 cm2), and a higher overall percentage of slow‐twitch fibers (47 vs. 26%). Consequently, the elbow extensors had a relatively greater potential for force production and force maintenance than the flexors. In contrast, the flexors were designed to optimize their length‐velocity potentials; i.e., they had relatively long fibers and a higher fast‐twitch fiber composition than the extensors. These morphologic differences between antagonistic muscle groups should be considered when evaluating the motor control mechanisms regulating reciprocal movements about the elbow.
Mitochondrial reorganization during resumption of arrested meiosis in the mouse oocyte
Authors: Van Blerkom Jonathan , Runner Meredith N.
Published: February 2005

Correlated nuclear and cytoplasmic reorganizations during the 14 hr of reactivated meiosis in vivo and in vitro were examined in the laboratory mouse. Observations of living oocytes by differential interference contrast microscopy, and by fluorescent microscopy with nontoxic mitochondrial and DNA‐specific probes, enabled us to determine that the major cytoplasmic reorganization involved two mitochondrial translocations associated with two stages of nuclear maturation. These observations were confirmed at the fine structural level by parallel transmission electron microscopy. Mitochondria translocate to the perinuclear region during formation of the first metaphase spindle and subsequently disperse during abstriction of the first polar body. Determinations of frequency of maturation in more than 2,900 normal oocytes, and in more than 1,100 oocytes in which germinal vesicle breakdown was reversibly inhibited, indicated that mitochondrial redistributions are a normal and probably necessary feature of reactivated meiosis in the laboratory mouse. We suggest that these two rapid translocations serve to concentrate mitochondria for localized activities that require elevated levels of adenosine triphosphate.
Morphometric analysis of the pineal complex of the golden hamster over a 24‐hour light: Dark cycle: I. The superficial pineal in untreated and optically enucleated animals
Authors: Dombrowski Teresa A. , McNulty John A.
Published: February 2005

Morphometric analysis of the superficial pineal gland of intact and blinded golden hamsters was conducted at both the light and electron microscopic level. The volume of the superficial gland was estimated to be 151 × 106 μm3, comprising 90–94% of the total pineal parenchymal tissue. Analysis of structural rhythms in animals maintained under a 14:10 L:D cycle showed significant 24‐hr variations in values for pinealocyte nuclei, nucleoli, rough and smooth endoplasmic reticulum, Golgi bodies, dense bodies, and dense‐cored vesicles. Peak values for these structures generally occurred at the light:dark interface. These results provide morphological correlates for known rhythmic variations in the synthesis of pineal‐gland products. Superficial pineals examined 8 weeks following optic enucleation exhibited a decrease in the volume of pinealocyte nuclei and cytoplasm, while nucleolar size and the amounts of smooth and rough endoplasmic reticulum, Golgi bodies, dense bodies and dense‐cored vesicles were enhanced. The latter changes are interpreted as indications of increased synthetic activity by the superficial pineal gland in response to light deprivation.
Morphometric analysis of the pineal complex of the golden hamster over a 24‐hour light: Dark cycle: II. The deep pineal in untreated and optically enucleated animals
Authors: Dombrowski Teresa A. , McNulty John A.
Published: February 2005

The deep pineal gland of golden hamsters was morphometrically analyzed and quantitatively compared with the superficial pineal under a 14:10 lighting regime and following blinding. The deep pineal comprised 6–10% of the total pineal parenchymal tissue. Pinealocytes of the deep gland were smaller than the cells of the superficial pineal and showed a greater percent volume of Golgi bodies, rough endoplasmic reticulum, and dense‐cored vesicles. Twenty‐four‐hour rhythms in nucleoli and Golgi bodies were found in deep pinealocytes. These rhythms were out of phase with comparable rhythms in the superficial pineal gland, suggesting that distinct subpopulations of pinealocytes are present within the respective parts. Blinding resulted in decreased nuclear and nucleolar volume, while the amount of smooth endoplasmic reticulum, Golgi bodies, dense bodies, and dense‐cored vesicles increased significantly. Marginal increases were seen in mitochondria and lipid droplets. The greater abundance of those organelles involved in synthesis and secretion suggests enhanced cellular activity after blinding. Many of the morphological responses are similar to alterations in the pinealocytes of the superficial pineal following optic enucleation.
A light and fluorescence cytochemical and electron microscopic study of granule‐containing cells in the intrapulmonary ganglia of Pseudemys scripta elegans
Authors: Scheuermann D. W. , De Groodt‐Lasseel M. H. A. , Stilman C.
Published: February 2005

In the lung of the red‐eared turtle, large numbers of intramural ganglia located in the intraparenchymal connective tissue are demonstrated. Numerous cells in close proximity to the principal ganglionic neurons displayed a bright blue‐white formaldehyde‐induced fluorescence. Microspectrofluorometric analysis revealed the presence of dopamine (DA) in all cells measured. Subsequent light histochemcial staining of the fluorescent sections showed the DA‐containing cells to display argentaffinity. Electron microscopy of serial sections revealed cells characterized by dense‐cored vesicles corresponding to the intensely formaldehyde‐induced fluorescent cells. The argentaffin technique performed directly on ultrathin sections selectively stained the dense‐cored vesicles. After fixation with glutaraldehyde followed by dichromate, x‐ray microanalysis showed the chromium to be incorporated into the dense granules. Cholinergic‐type nerve endings formed axosomatic synaptic contacts with the DA‐containing cells, which can therefore be considered as intrinsic postganglionic elements. No efferent synapses from the granule containing cells to the principal ganglionic neurons could be observed. The granule‐containing cells occurred solitarily and in clusters, partially invested with satellite cells, and usually located near fenestrated capillaries; they displayed cytoplasmic processes and indicated emiocytotic granule release. Adjacent granule‐containing cells were separated by spaces about 20 nm wide, gradually widening to form intercellular channels with apically projecting microvilli and primary cilia. It is concluded that the intrapulmonary granule‐containing cells of the red‐eared turtle belong to the APUD system. Furthermore, morphologically these cells appeared to possess a special sensory apparatus which designates them as paraneurons. The possible physiological significance of these intrapulmonary granule‐containing cells is discussed.
The three‐dimensional architecture of the elastic‐fiber network in canine hepatic portal system
Authors: Crissman Robert S. , Guilford William
Published: February 2005

The architectural arrangement of the elastic‐fiber network in the wall of canine hepatic portal veins was observed with the scanning electron microscope (SEM). Selective NaOH sonication digestion and autoclaving were used to expose and isolate the networks of elastic fibers from six selected regions of the hepatic portal vessels from seven healthy dogs. Elastic stains of adjacent segments prepared for light microscopy demonstrated that the elastic fibers were concentrated in two areas within the intact portal wall. The innermost area corresponded to the internal elastic lamina (IEL) of the tunica intima, the internal muscular layer, and the connective tissue layer of the tunica media. The second area was in the tunica adventitia. SEM specimens revealed two sleeves of elastic fiber networks which corresponded to the above regions. Small scattered bundles of radially oriented elastic fibers spanned the gap between the two sleeves. Each tunica had a different architectural arrangement of elastic fibers. The IEL had circumferentially oriented fibers which branched and anastomosed to form a continuous network on the innermost surface. The architecture of the IEL was the most variable between the different regions. The network of the IEL was the most “open” in the caudal region (splenic vein) and became “denser” toward the liver. The large elastic fibers inthe tunica media were oriented at approximately right angles to the primary fibers of the IEL. These longitudinally oriented fibers anastomosed with adjacent longitudinal fibers to form a continuous network. In the tunica adventitia, thick, longitudinally oriented fibers of the continuous network fused together to form incomplete layers of fibers. The architecture of the elastic‐fiber network in the canine hepatic portal vein was compared to that previously described in the systemic canine saphenous vein.