Reticuloepithelial Cells Research Articles

Density of lymphocytes in cortex and medulla substance of thymus particles of white rats in normal conditions and under influence of heavy metal salts during three months

The consumption of clean water is the most relevant today, but natural water is delivered to our homes through plastic, iron and galvanized pipes. Metal ions, which are part of the pipe material, can get into drinking water and affect the human body, in particular the thymus. That is why the aim of the work was to determine the density of large, medium and small lymphocytes in the cortex and medulla of the thymus lobules of outbred white male rats of reproductive age when consuming small doses of heavy metal salts with water for three months. The study was conducted on 40 outbred white male rats of reproductive age, which were divided into 4 groups: 1 group – control animals that consumed distilled water; 2 group of animals that consumed aqueous solutions – CuSO4·5H2O at a dose of 0.247 mg/dm3; 3 group – aqueous solution of ZnSO4·7H2O at a dose of 1.505 mg/dm3; group 4 – aqueous solution of FeSO4·7H2O at a dose of 0.5 mg/dm3. Histological, electron microscopic and morphometric research methods were used to study the density of large, medium and small lymphocytes in different zones of the thymus lobules. It was found that in the control group of rats, the density of large lymphocytes is the highest in the subcapsular zone, and the lowest in the medulla. The density of medium lymphocytes is the lowest in the subcapsular zone. The density of small lymphocytes is the lowest in the medulla, and the highest in the cortico-medullary zone. When using CuSO4·5H2O salts with drinking water for three months, there were no significant changes in the density of lymphocytes compared to the control group, except for a slight decrease in the density of large lymphocytes in the cortex of the thymus lobules. The density of lymphocytes in the third group of animals that consumed zinc salts (ZnSO4·7H2O) with drinking water changes significantly: the density of large lymphocytes in the subcapsular zone decreases by 2.3 times, in the cortico-medullary zone it increases by 4.7 times, and in the medulla it increases by 2.7 times; the density of medium lymphocytes decreases in the subcapsular zone by 2 times; the density of small lymphocytes decreases by 1.5 times in the subcapsular zone, in the cortex and cortico-medullary zone – decreases by 1.2 times, and in the medulla by 1.1 times. When using FeSO4·7H2O salts with drinking water for three months, no special changes in the density of lymphocytes were noted: a decrease in the density of large lymphocytes in the subcapsular zone by 1.5 times and by 1.3 times in the cortex was observed; the density of medium lymphocytes decreases by 1.2 times in the cortex, and the density of small lymphocytes decreases by 1.2 times in the subcapsular zone and cortex, and increases by 1.2 times in the medulla, compared to the control group of animals. Ultrastructural changes in the structure of lymphocytes and reticuloepithelial cells were not detected when heavy metal salts were consumed with water. Thus, the study showed that the most toxic for the body are zinc salts (ZnSO4·7H2O), the consumption of which with drinking water in small doses for three months led to significant changes in the density of lymphocytes, compared to the control group experimental animals.

Applications of EMbedding and backscattered scanning electron microscopy for morphological and functional assessment of the thymus forcedly removed in children with congenital heart defects during the first weeks of life

Thymectomy in a number of clinical situations is an unavoidable step of cardiac surgical treatment of congenital heart defects, but the issue of its effects on development of immunity in early ontogenesis remains open. There is still debates among scientists about the risk of immune deficiency states in children who underwent thymectomy at an early age. One may see completely different opinions, both in domestic and foreign publications. A tool for resolving this issue may be provided by morpho-functional studies of the removed thymic tissue by means of modern scanning electron microscopy techniques. The objective of our study was to assess the possibilities of EMbedding and backscattered scanning electron microscopy for morphological and functional evaluation of the thymus, which was forcedly removed in the infant patients with congenital heart defects over the first weeks of life. The thymus of a newborn infant (postnatal day 27) with congenital heart disease: ventricular septal defect was examined using EMbedding and backscattered scanning electron microscopy imaging after embedding in epoxy resin. The mass of thymus gland was 15.7 g, the dimensions of thymus were: transverse, 3.4 cm; longitudinal, 4.1 cm; thickness, 1.7 cm; volume, 12.4 cm3. The study showed ability of EMbedding and backscattered scanning electron microscopy in morphological and functional assessment of thymus gland considered the central organ of the immune system. Step-bystep visualization from low to high magnifications, from tissues to cells and intracellular structures, as well as layer-by-layer examination of thymic cortex, medulla, interlobular septa and vessels, allows you to effectively assess the functionality of the thymus. This research method is sufficient for scientific research of the forcedly removed thymus since it enables us to visualize its microanatomy, allowing cell phenotyping at different layers of the thymus, studying intercellular interactions of thymocytes with reticulo-epithelial cells, subtle features of Hassall’s bodies and, finally, the process of T lymphocytes’ release from thymus gland.

Anatomical Study of Thymus at Different Stages of Development in Pati Duck of Assam

Background: The study on Thymus of Pati duck of Assam is of great value in regard to normal academic and vaccine production. The aim of the study was to evaluate the gross and histo-morphological examination of thymus of Pati duck at different age group. Methods: The present studies were conducted on 36 numbers of Pati duck of Assam of irrespective of sex at different stages of development. The ducks were divided into six groups viz., day old, 15th day, 4th week, 8th week, 16th week and 24th week of age. For histomorphological studies, tissue samples were fixed in 10% NBF and then processed as per the standard technique andprocedure of Luna (1968). The paraffin blocks were sectioned in Shandon Finesse microtome at 5 micrometer (µm) thickness and the tissue sections were stained with Mayer’s Haematoxylin and Eosin staining technique for Cellular details, Van Gieson’s method for collagen fibres, Gomori’s method for reticular fibres, Hart’s and Verhoeff’s method for elastic fibers and Bielchowsky’s method for axis cylinder and dendrites. Result: The thymus, a primary lymphoid organ of Pati duck of Assam was arranged in two long chains on either side of the neck embedded in the sub dermal connective tissue as chains of lobes connected to each other by connective tissue. The thymus of Pati duck consisted of a capsule made up of connective tissue fibres and cells from which trabeculae entered the parenchyma dividing that organ into a number of incomplete lobules. The unique structure of the thymus, the Hassall’s corpuscles, was formed by the hypertrophied reticulo-epithelial cells and was very common in the medulla.

ОБМЕН РНК В СЕКРЕТОРНЫХ СТРОМАЛЬНЫХ ЭПИТЕЛИОЦИТАХ МОЗГОВОГО ВЕЩЕСТВА ТИМУСA В ДИНАМИКЕ ЭМБРИОГЕНЕЗА БЕЛОЙ КРЫСЫ

Currently, the thymus is considered as a polyfunctional organ that performs immunological, lympho- cytopoietic and endocrine functions, the performance of which is closely related to the differentiation of T-lymphocytes under the influence of hormones secreted by reticuloepithelial cells of the stroma. In this regard, the article describes the processes of syhthetic activity of RNA in the nuclei of stroticuloepithelial cells of the thymic medulla in the dynamics of embryogenesis of the white rat. According to the results of a quantative cytophotometric study, indicators of the RNA level in the nucleoli of the medulla epithelial stromal cells have been obtained. It was revealed that the synthesis of thymopoetines, which provide the processes of differentiation of immune competent T-lymphocytes of the thymus gland, begins on the 15th day of embryogenesis Subseguently, the secretory activity of RNA in the nucleoli of reticuloepithelial cells increases in waves in the form of two peaks on the 17 and 19 days of embryogenesis. By the time the fetus is born, on day 21. there is consistently high and uniform level of thymopoetines, which determine the thymus as a finally differentiated immunocompetential organ that provides the mechanismes of cellular immunity.

Mycoplasma gallisepticum infection triggered histopathological changes, oxidative stress and apoptosis in chicken thymus and spleen

Previous studies mainly focused on the inflammatory responses caused by Mycoplasma gallisepticum (MG) in the chicken respiratory mucosa, setting the stage for chronic infection and disease manifestation. However, the underlying mechanism is still unknown. Spleen and thymus are important immune organs, which play a critical role in eliciting protective immune responses to ensure healing process and elimination of harmful stimuli. In the present study, the effects of MG infection on chicken spleen and thymus were investigated. The results showed that MG infection reduced antioxidant activities and induced oxidative stress in the spleen and thymus tissues. Histological examination showed normal morphology of chicken spleen and thymus in control group compared to MG infection group. In contrast, increased number of necrotic and nuclear debris, lymphocytolysis, prominent reticuloepithelial cells and loose arrangement of cells in the spleen and thymus were seen in MG-infected chickens. Ultrastructural analysis indicated nuclear and mitochondrial damage including mitochondrial swelling, deformation of nuclear membrane and congestion of chromatin material in MG infection group. The mRNA and protein expression of apoptosis-related genes were significantly upregulated in the spleen and thymus of MG-infected chickens compared to control group. Moreover, Terminal deoxynucleotidyl transferase–mediated dUTP nick endlabeling (TUNEL) assay results suggested that MG infection increased the number of positive-stained nuclei in the spleen and thymus. Meanwhile, the mRNA expression of mitochondrial dynamics in the spleen and thymus were altered by MG infection. In summary, these results showed that MG induced oxidative stress and apoptosis, which could be the possible causes associated with the immune damage, structural impairment and disease pathogenesis of MG infection.

Thymic Hassall's corpuscles in Nandanam chicken - light and electronmicroscopic perspective (Gallus domesticus).

The present study was aimed to study the light and electron microscopic studies of thymic Hassall’s corpuscles was done in various age groups of Nandanam Chicken ranging from day-old to forty weeks. Hassall’s corpuscles are special, unique structures present in thymic medulla and also in the cortex of all the age groups of Nandanam chicken (from hatch to forty weeks) in the present study. Size of the Hassall’s corpuscles in the medulla is larger than the ones present in the cortical region of thymus. The Hassall’s corpuscles are made up of structureless eosinophilic mass surrounded by concentrically arranged reticuloepithelial cells. Under electron microscope, the Hassall’s corpuscles were composed of reticuloepithelial cells interconnected by many desmosomes. The epithelial cells had abundance of cytoplasmic fibrils and desmosomes with few mitochondria and ribosomes. The nucleus was oval or round which was slightly indented. The centre of the Hassall’s corpuscles was appeared either solid or cystic. The cystic corpuscles had cell debris within the cyst lumen.

Morphogenesis of human fetal thymus during weeks 22–27 of development

Distinctive features of human fetal thymus morphogenesis in early ontogeny in the case of uncomplicated pregnancy have been characterized. A steady increase of thymus dimensions and weight occurred concomitantly to differentiation of morphofunctional zones within the organ. Cell differentiation in the subcapsular and inner cortical zones of the thymus lobes was manifested as changes in parameters of expression of T-lymphocyte antigens CD1, CD2, and CD3 and ultrastructural features of reticuloepithelial cells (REC) type I and II forming a microenvironment for lymphocytes. RECs of the medullar zone formed a glomerular syncytium with desmosomal interepithelial contacts by week 22 of fetal development. Small lymphocytes predominated among thymocytes (66%). Hassall's corpuscles, the structural correlates of morphological and functional maturity, predominated in the fetal thymuses during developmental weeks 25-27.

Experimental pathology of T-2 toxicosis and mycoplasma infection on performance and hepatic functions of broiler chickens

This experiment was conducted using 192 day-old Ross 308 chicks, divided into 4 groups of 4 replicate consisting 48 birds. Group I was fed a control diet, Group II was fed control diet supplemented with 0.5 ppm T-2 toxin for 5 weeks, Group III was fed control diet supplemented with 8 × 108 cfu/mL of Mycoplasma gallisepticum, and group IV was fed control diet supplemented by T-2 toxin and Mycoplasma gallisepticum. Body weight and feed conversation ratio (FCR), relative organ weights, clinical signs, biochemical characteristics, and gross and histopathological lesions were recorded in the experimental groups at the end of the second and fifth weeks of age. Body weight and relative weights of bursa of Fabricius, thymus, and spleen decreased and FCR increased significantly (P ≤ 0.05), but the relative weights of liver and kidney showed no significant decrease (P ≤ 0.05) in the serum total proteins, albumin, and increase in aspartate aminotransferase and alanine transaminase were observed in T-2 toxin and T-2 accompanied with Mycoplasma fed birds when compared to the control group. Liver was enlarged, friable, and yellowish discoloration with distended gall bladder was noticed. Lymphoid organs such as bursa of Fabricius, thymus, and spleen were atrophied in group II and group IV throughout the study. Microscopically, liver showed vacuolar degeneration of hepatocytes, with increased Kupffer cell activity, bile duct epithelial hyperplasia, and infiltration of inflammatory cells. Kidney showed vacuolar degeneration of tubular epithelium along with pyknotic nuclei. Lymphoid organs showed lymphocytolysis and depletion with prominent reticuloepithelial cells. Proventriculus revealed desquamation of villous epithelial cells and lymphoid infiltration in submucosa. Heart showed mild hemorrhage with infiltration of inflammatory cells. Lung showed edema and inflammatory cells in the bronchioles. Trachea showed desquamation and erosions of mucosa. Proliferation of mucosal glands with increased mucous secretion was obvious. Air sacs showed thickening with presence of inflammatory cells and edema.

EMF radiation at 2450 MHz triggers changes in the morphology and expression of heat shock proteins and glucocorticoid receptors in rat thymus.

Electromagnetic fields (EMFs) can act as inducers or mediators of stress response through the production of heat shock proteins (HSPs) that modulate immune response and thymus functions. In this study, we analyzed cellular stress levels in rat thymus after exposure of the rats to a 2.45 GHz radio frequency (RF) using an experimental diathermic model in a Gigahertz Transverse Electromagnetic (GTEM) chamber. In this experiment, we used H&E staining, the ELISA test and immunohistochemistry to examine Hsp70 and Hsp90 expression in the thymus and glucocorticoid receptors (GR) of 64 female Sprague–Dawley rats exposed individually to 2.45 GHz (at 0, 1.5, 3.0 or 12.0 W power). The 1 g averaged peak and mean SAR values in the thymus and whole body of each rat to ensure that sub-thermal levels of radiation were being reached. The thymus tissue presented several morphological changes, including increased distribution of blood vessels along with the appearance of red blood cells and hemorrhagic reticuloepithelial cells. Levels of Hsp90 decreased in the thymus when animals were exposed to the highest power level (12 W), but only one group did not show recovery after 24 h. Hsp70 presented no significant modifications in any of the groups. The glucocorticoid receptors presented greater immunomarking on the thymic cortex in exposed animals. Our results indicate that non-ionizing sub-thermal radiation causes changes in the endothelial permeability and vascularization of the thymus, and is a tissue-modulating agent for Hsp90 and GR.

Histogenesis and Morphogenesis of Hassall's Corpuscles in Human Fetuses: A Light Microscopic Study

Twenty-eight healthy fetuses between 11-40 weeks were selected to study the histological and morphological growth of Hassall's corpuscles. We were found that Hassall's corpuscle appreciated earliest at 14th weeks and seen as two to three cells nest in area having degenerated tissues. Later, as the age of fetus advanced the size and shape of Hassall's corpuscles rapidly increasing by additions of more apoptotic cells and aggregation of reticulo-epithelial cells. Near 28th week these corpuscles showed spurt of growth and initially corpuscles were distant from each other, they started to come together e.g. reducing inter-corpuscular distance. In late stage (near term) these corpuscles fused together giving variable shapes and sizes.

Polymorphism of Hassall′s corpuscles in thymus of human fetuses

Background:Hassall's corpuscles (HC) are commonly used as diagnostic features for identifying human thymus and are still present in thymuses undergoing fatty degeneration in young adults. However, few studies have been performed on human fetuses.Aim:A cross-sectional study was done, to study the morphology of HC in human fetuses.Materials and Methods:Twenty-eight thymuses were collected from fetuses of gestational age ranging from 11 to 40 weeks. Thymuses were processed by paraffin embedding methods and hematoxylin and eosin staining.Results:The size of HC varied from very small (100 microns) to very large corpuscles (> 900 microns). A high level of polymorphism was also observed, from round to unusual or odd shapes corpuscles. The degenerated reticulo-epithelial cells represented the starting point in HC formation. The growth of HC was rapid, especially near 28 weeks, and the level of HC polymorphism was significantly greater after 28 weeks of gestation. In advanced stages of gestation, the increase in size of some corpuscles reduced the spaces between them, and some patterns strongly supported the hypothesis that some HC had fused in a single and larger corpuscle.Conclusion:The rapid rise in number and size of HC around 28 weeks of gestation would fit with their role in the negative selection process of thymocytes.

Morphological and immunohistochemical characterisation of the thymus in juvenile turbot (Psetta maxima, L.)

We performed structural and immunohistochemical studies on the thymus of juvenile turbot (Psetta maxima L.) in order to define its cellular composition. The thymic stroma was mainly composed of two subpopulations of reticulo-epithelial cells (RECs). RECs immunoreactive to anti-actin antibody were distributed through the organ, while RECs that were cytokeratin-immunopositive were located in the outer zone of the thymus. The parenchyma of the thymus was composed of several cell types such as lymphocytes/thymocytes, lymphoblasts, melano-macrophages and to a lesser extent of nurse-like cells, immunoglobulin positive (Ig+) cells, mucous cells, rodlet cells and neuroendocrine cells. CD3ε+ lymphocytes were mainly located in the outer zone. On the other hand, Ig+ cells were observed in the transitional region between the inner and outer zones of the thymus. The neuroendocrine cells were large and exhibited immunoreactivity to neuropeptide Y and vasoactive intestinal polypeptide. They were located in the inner zone of the thymus in close association with lymphoblasts and lymphocytes/thymocytes. This work provides useful information on the structure and cellular composition of the thymus of turbot, identifying several immunomarkers that allow the identification of different cell types, providing the basis for further studies on the immune response of turbot against diseases.

Role of Nigella sativa in ameliorating chloramphenicol induced tissue damage in rats

Nigella sativa ascribed to have many medicinal properties. The study aimed to investigate whether N. sativa oil could decrease the side effects induced by the antibiotic, chloramphenicol. Rats were assigned into the following: The control group (first group); the second and the third groups which were orally administrated chloramphenicol for 21 days at a dose of 86 mg/kg body weight. Then the third group was treated with N. sativa oil for 30 days at a dose of 13.5 mg/ 150 g; the forth group was synergistically administrated both chloramphenicol and N. sativa for 21 days. Administration of N. sativa oil was extended to 30 days more in this group. There was a decrease in erythrocyte, hemoglobin and hematocrit with a progressive increase of leukocyte count in drug treated group. A decrease in neutrophils and lymphocyte with an increase in nucleated immature red cells as well as myeloblasts and myelocytes. On the other hand, N. sativa showed a time dependent improvement in blood parameters. A gradual decrease in the counts of immature stages was realized with the administration of N. sativa. Pathological changes in spleen included splenomegaly, lymphocytic depletion, enlargement of the marginal zone, wide trabeculae, reticular cells, pyknotic nuclei and cells in different stages of megakaryopoiesis. A marked depletion in cortical lymphocytes, disturbed lobular pattern, increased reticuloepithelial cells and dilated blood vessels in the thymus of group 2. N. sativa showed only a slight improvement of the damaged spleen tissues, while a time dependent repair in thymic tissue and both the cellular and humoral immunity was observed. In conclusion, N. sativa had an obvious protective effect and decreased the side effects of chloramphenicol. Key words: Nigella sativa, chloramphenicol, pathological changes.

Immunohistochemical evidences showing the presence of thymulin containing cells located in involuted thymus and in peripheral lymphoid organs.

Thymulin is a well-characterized thymic hormone that exists as a nonapeptide coupled to equimolar amounts of Zn2+. Thymulin is known to have multiple biological roles, including T cell differentiation, immune regulation, and analgesic functions. It has been shown that thymulin is produced by the reticulo-epithelial cells of the thymus, and it circulates in the blood from the moment of birth, maintain its serum level until puberty diminishing thereafter in life. To study the localization of this hormone, we prepared polyclonal and monoclonal antibodies against the commercial peptide and utilized immunocytochemical techniques for visualization. The results indicate that thymulin stains the thymic reticular cells, the outer layers of Hassall's corpuscles and a large round cellular type, which is keratin-negative and does not show affinity for the common leukocyte antigen (CD-45). In mice, this thymulin-positive cell remains in the thymus throughout life and even appears in relatively increased numbers in old involuted thymi. It also appears in thymus-dependent areas of the spleen and lymph nodes, demonstrating that at least one of the thymus cells containing this peptide can be found in peripheral lymphoid tissue.

Immunohistochemical evidences showing the presence of thymulin containing cells located in involuted thymus and in peripheral lymphoid organs

Thymulin is a well-characterized thymic hormone that exists as a nonapeptide coupled to equimolar amounts of Zn2+. Thymulin is known to have multiple biological roles, including T cell differentiation, immune regulation, and analgesic functions. It has been shown that thymulin is produced by the reticulo-epithelial cells of the thymus, and it circulates in the blood from the moment of birth, maintain its serum level until puberty diminishing thereafter in life. To study the localization of this hormone, we prepared polyclonal and monoclonal antibodies against the commercial peptide and utilized immunocytochemical techniques for visualization. The results indicate that thymulin stains the thymic reticular cells, the outer layers of Hassall's corpuscles and a large round cellular type, which is keratin-negative and does not show affinity for the common leukocyte antigen (CD-45). In mice, this thymulin-positive cell remains in the thymus throughout life and even appears in relatively increased numbers in old involuted thymi. It also appears in thymus-dependent areas of the spleen and lymph nodes, demonstrating that at least one of the thymus cells containing this peptide can be found in peripheral lymphoid tissue.

Thymic reticulo-epithelial cells

The reticulo-epithelial (RE) cellular network of the thymic stromal cellular microenvironment plays a vital role in neuroendocrine regulation and lymphoid cell homing and development. Transmission electronmicroscopic observations have confirmed that there are four functional subtypes of medullar RE cells: undifferentiated; squamous; villous; and cystic. Immunocytochemical observations have shown that the secreted thymic hormones, thymosin α1 and thymopoietin (and its short form, thymopentin or TP5), are both produced by RE cells. Thymic RE cells also produce numerous cytokines, including IL-1 and -6, G-CSF, macrophage-CSF and GM-CSF that likely are important during the various stages of thymocyte activation and differentiation. The coexistence of pituitary hormone and neuropeptide secretion, such as growth hormone, prolactin, adrenocorticotopic hormone and thyroid-stimulating hormone, among many others, and the production of a number of interleukins and growth factors, as well as the expression of receptors for all, by the same RE cell, is an unique molecular biological phenomenon. The thymic RE cell network represents an important cellular and humoral microenvironment in the neuroendocrine homeopathic regulatory mechanisms of the multicellular organism.

A stromal myoid cell line provokes thymic erythropoiesis between 16th to 20th weeks of intrauterine life.

The thymus provides an optimal cellular and humoral microenvironment for cell line committed differentiation of haematopoietic stem cells. The immigration process requires the secretion of at least one peptide called thymotaxine by cells of the reticulo-epithelial (RE) network of the thymic stromal cellular microenvironment. The thymic RE cells are functionally specialised based on their intrathymic location and this differentiation is modulated by various interaction signals of differentiating thymocytes and other non lymphatic haematopoietic stem cells. To study the role of another cell line in fetal thymic haematopoietic proliferation and differentiation in different stages of development: the stromal myoid cells. Fifteen cases of fetal thymic specimens (4th to 8th weeks: five cases 16th to 20th weeks: five cases and 28th to 32nd weeks: five cases respectively) were studied. Tissue paraffin samples were stained immunohistochemically using (i) a monoclonal antibody recognising alpha-smooth muscle actin, a contractile microfilament expressed exclusively by smooth muscle cells, myofibroblasts and related cells, (ii) a monoclonal antibody glycophorin C recognising the erythropoietic cells. Histology-Embryology Department of Democritus University of Thrace (Alexandroupolis) over ten year period (1991-2001). The number of alpha-smooth muscle actin-positive cells significantly increased during the late second and third trimester of gestation. In the above period a relevant increase in the number of glycophorin C positive cells were observed. Our data suggest that a myoid cell line is involved in the formation of an appropriate microenvironment for homing and proliferation of erythropoietic cells.

Nuclear localization of gold labeled-hydrocortisone-bovine serum albumin conjugate injected intravenously into the hormone-target cells of rat.

We have suggested in a previous study using 2-nm colloidal gold labeled-testosterone-bovine serum albumin (testosterone-BSA-gold) that 2-nm gold labeled-steroid hormone-BSA conjugates would be a useful tool for analyzing the mechanism of steroid hormone action (39). In this study, we examined whether hydrocortisone-BSA conjugate (hydrocortisone-BSA) showed a similar distribution to radiolabeled hydrocortisone in vivo, by injecting 2-nm colloidal gold labeled-hydrocortisone-BSA (hydrocortisone-BSA-gold) into the rat tail vein. The hydrocortisone-BSA-gold with silver enhancement became visible as silver deposits under electron microscopy in the nuclei of hepatocytes and hepatic stellate cells but not in Kupffer cells in the liver, and in the thymocytes and thymic reticuloepithelial cells in the thymus of a rat killed 2 h postinjection. The percentage of nuclei showing deposits in the non-target cells, the epithelial cells of the seminal vesicle, was similar to the value in the seminal vesicle of a control rat injected with BSA labeled with 2-nm colloidal gold as reported previously. In the hepatocytes and thymocytes of a control rat not injected, the percentages of nuclei showing deposits were similar to those in the rat injected with testosterone-BSA-gold or BSA-gold as reported previously, but lower than those in the rat injected with hydrocortisone-BSA-gold. These results suggest that hydrocortisone-BSA-gold is useful for the morphological study of hydrocortisone target cells, and imply that BSA conjugated with hydrocortisone can enter the target cell nuclei of the rat. The present study further indicates that the fate of gold labeled-steroid hormone-BSA conjugates may be decided at the cell membrane level.

Evidence that secretory products of the reticulo-epithelial cells of the rat thymus modulate the secretion of gonadotrophins by rat pituitary cells in culture

It is now well accepted that the endocrine system can be strongly influenced by the immunological status of the body. This laboratory has provided documented evidence that the rat thymus produces a biologically active secretion, with a molecular weight of approximately 30 kDa, that augments the gonadotrophin-releasing hormone (GnRH) stimulated secretion of gondotrophins by isolated pituitary cells in culture. To determine the cells of origin of the factor involved, the reticulo-epithelial cells from the thymus were incubated in vitro to provide media for the examination of possible effects on the secretion of gonadotrophins by the rat pituitary. The enrichment of the culture with reticulo-epithelial cells was confirmed using anticytokeratins antibodies. It was found that the addition of such conditioned medium increased the secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH), with a greater effect on the former. The increment in gonadotrophin secretion was time- and dosedependent. This same conditioned medium also potentiated the effect of GnRH on the cultured pituitary cells. The fractionation of thymic-conditioned medium using selective molecular membrane filters, provided evidence that the active factor or factors involved in the enhanced secretion of gonadotrophins are larger than 10 kDa MW. Present findings show that thymic reticulo-epithelial cells are responsible for this activity.

Ultrastructural localisation of NADPH-diaphorase in the chick thymic medulla.

Nicotinamide-adenine-dinucleotide phosphate-diaphorase positive cells in the chick thymus were studied at the electron-microscopic level. The formazan, a marker for the enzyme nitric oxide synthase, labelled cystic, undifferentiated, endocrine-like and myoid cells in the medulla. Some lymphoid and reticulo-epithelial cells were also lightly labelled. The reaction product was predominantly bound to the membranes of the endoplasmic reticulum in all the cells labelled and also to the nuclear envelope and outer membrane of mitochondria. The Golgi apparatus and the plasma membrane were free of the reaction product.