Reticuloepithelial Cells Research Articles

Induction of apoptosis in mouse thymocytes by cyclosporin A: in vivo study.

We investigated the in vivo effect of cyclosporin A (CsA) on mouse thymus and thymocytes. Administration of CsA (10 mg/kg of body weight) was found to induce a marked reduction in the size, weight and consistency of the thymus. These modifications were associated with thymic reticulo-epithelial cells (TREC) and thymocyte damage. Some of the damaged thymocytes displayed characteristic of cells undergoing apoptosis. Ultrastructural study of thymocytes and thymic tissue, as well as DNA electrophoresis of thymocytes, showed chromatin condensation, cellular shrinkage, and nuclear fragmentation in oligonucleosomal fragments. DNA labeling with propidium iodide (PI) of thymocytes from CsA treated mice cultured for 24 hrs showed an increased number of apoptotic nuclei. Furthermore, flow cytometric analysis using monoclonal antibodies (mAbs) specific for thymocyte subsets confirmed that CsA induces a large decrease in the relative number of mature single positive (SP) CD4+CD8- and CD8+CD4- thymocytes expressing high densities of CD3 and T cell receptor ab (TCR alpha beta) surface molecules, but also a decrease in the absolute number of the other thymocyte subsets. These results suggest that CsA causes macroscopic and ultrastructural modifications of the thymus, associated with an active process of cell death in mouse thymocytes in vivo. In line with these results we formulate a hypothesis concerning the stage of T-cell development at which CsA induces apoptosis.

Dynamic Changes in the Intermediate Filaments of the Epithelial Cells During Development of the Chicken's Bursa of Fabricius

The development of bursal follicles and the differentiation of the follicle-associated epithelium and interfollicular epithelium were studied immunohistochemically using monoclonal anti-vimentin and anti-cytokeratin antibodies. In 10-day-old embryos the entodermal and cloacal epithelia coexpressed vimentin- and cytokeratin-intermediate filaments. Both undifferentiated and differentiated bursal surface epithelium simultaneously expressed vimentin- and cytokeratin-intermediate filaments during the entire period of embryogenesis. Vimentin expression in reticuloepithelial cells was related to bursal cell differentiation but was not linked to immune function. Sequential loss of vimentin from interfollicular epithelium, follicle-associated epithelium, and reticuloepithelial cells may reflect sequential acquisition of maturity in these three compartments. The presence of cytokeratin-intermediate filaments suggested that follicle-associated epithelium was not of mesenchymal origin. Testosterone treatment did not influence the vimentin and cytokeratin filament expression in the epithelial cell.

Changes in the thymus and spleen of the turtle Mauremys caspica after testosterone injection: A morphometric study

To confirm a possible role of sex hormones in governing the seasonal variations affecting the reptilian lymphoid organs, a morphometric analysis was carried out on the thymus and spleen of turtles, Mauremys caspica, intraperitoneally injected with a single dose of testosterone propionate (TP) at the third week of June when physiological levels of testosterone are low. At 4 and 6 weeks, control turtles show an apparent lymphocyte mobilization both from thymus and spleen with a decrease in the percentage of thymic cortex, numbers of cortical lymphocytes, and mitotic index, but increased numbers of medullary lymphocytes. In the thymic cortex of treated turtles, there is a decrease in the same parameters but they occur in the first 2 weeks, whereas the medullary lymphocytes also undergo reduction at 4 and 6 weeks. In addition, the number of reticuloepithelial cells per area unit decreases at 2 weeks in the thymic cortex of treated turtles. These results are discussed from the point of view of a biphasic effect of testosterone on turtle lymphoid organs: In the first weeks, the changes observed could be attributed to the high levels of testosterone; after 4 and 6 weeks, variations are dependent both on long-term effects of testosterone and on those induced by the high values of corticosterone occurring in summer.

The thymus in fish: Development and possible function in the immune response

With the exception of Agnatha, fish possess the functional equivalent of the thymus gland found in higher vertebrates. As in other vertebrates, this gland originates from the pharyngeal pouches and ontogenically is the first lymphoid organ to be infiltrated with lymphoid cells. Histology of the structure may differ from one species to another but the cellular component is basically similar. The (paired) gland is surrounded by an epithelial capsule. Within the gland a framework of reticulo-epithelial cells supports the lymphocytes. The age-related involution process, which characterizes the thymus of higher vertebrates, does not necessarily occur in fish. Nevertheless, thymus growth and function may be modulated by those factors that induce its involution such as aging, season, sexual maturity, and stress. The major role played by the thymus in the immune response of higher vertebrates is presumed to occur in fish. Thymus-derived cell dependent immune reactions have been demonstrated in fish. The cells that mediate these functions are designated as T-like cells. So far, cell surface markers equivalent to those of mammalian T lymphocytes have not been characterized. The T lymphocyte specificities are supposed to be acquired within or via the thymic microenvironment. Unfortunately, there is limited data concerned with the cytological and physiological basis of the maturation of thymus-derived cells. Direct involvement of the fish thymus in defense mechanisms has not been investigated extensively. The gland appears to be weakly protected because of its superficial location and is easily exposed to pathogens. Neoplasia is the main pathologic condition reported in the thymus of fish, with little else having been published regarding thymic pathology.

Immunocytochemical Localization of the Glucocorticoid Receptor in Rat Brain, Pituitary, Liver, and Thymus with Two New Polyclonal Antipeptide Antibodies*

The intracellular localization of the glucocorticoid receptor (GR) was studied in male rat brain, pituitary, liver, and thymus. Two new polyclonal anti-GR antibodies, GR 57 and GR 59, raised against two synthetic peptides (346-357 and 245-259) that correspond to unique regions of the amino-terminus of human GR were used. Vibratome sections (30-50 microns) of perfused brain and frozen sections (6-8 microns) of pituitary, liver, and thymus fixed in paraformaldehyde were incubated in preimmune serum, immunoserum, epitope-purified immunoserum, or peptide-absorbed immunoserum of either GR 57 or GR 59 and immunostained by the avidin-biotin peroxidase method. GR immunoreactivity (GR-ir) was primarily nuclear in brain, pituitary, liver, and thymus sections from intact rats. Adrenalectomy caused nuclear GR-ir to decrease and cytoplasmic GR-ir to increase. When adrenalectomized rats were treated with corticosterone (100 micrograms and 1 mg) or dexamethasone (1 microgram, 100 micrograms, and 1 mg), GR-ir was again predominantly nuclear. One microgram of corticosterone failed to cause nuclear GR-ir when administered to adrenalectomized rats. Immunoreactive neurons and glial cells were extensively distributed, with varied intensity, throughout the rat forebrain. The areas include cortex, septum, hippocampus, amygdala, thalamus, and hypothalamus. Cells with the strongest GR-ir were located in the caudate putamen, paraventricular, arcuate, and central amygdala nuclei, areas CA1-CA2 of the hippocampus, and laminae 4 and 5 of the cortex. In the pituitary, cells of the anterior and posterior lobes were GR immunoreactive, while those in the intermediate lobe were not. Hepatocytes of the liver and thymocytes and reticuloepithelial cells of the thymus were GR immunoreactive. The results show that GR can be localized immunocytochemically in numerous rat tissues using antipeptide polyclonal antibodies and correlated with the results of biochemical and ligand receptor studies.

Historical perspective: The bursa of Fabricius and its influence on B-cell development, past and present

The bursa of Fabricius has a history and a future. The history included its description by Hieronymus Fabricius and the discovery in the 1950s of its pivotal role in humoral immunity. The apparent obligate role of the bursa in B-cell development was modified by research in the 1960s and 1970s which described the synthesis of immunoglobulin in bursaless birds and led to the concept of extra bursal sites. Then in the 1980s, supported by the research of the past 25 years and the new technology, the obligate role of the bursa in orchestrating the V-gene repertoire-antibody diversity was revealed. Microenvironmental studies in the 1970s and 1980s announced the importance of bursal epithelium, secretory dendritic cells, and other reticuloepithelial cells in interpreting the ontogeny of B-cell differentiation. The past history of the bursa will be remembered for its contribution to present and future research and the present and future will be promising if the experiences of the past are not forgotten.

Cellular distribution of prothymosin alpha and parathymosin in rat thymus and spleen.

By means of immunohistochemical methods, we have investigated the cellular distribution of prothymosin alpha and parathymosin in rat thymus and spleen, using specific antibodies raised against thymosin alpha-1 and against parathymosin. We observed prothymosin alpha immunoreactivity in lymphoid cells both in thymus and spleen. In the thymus, prothymosin alpha staining was more marked in cortex than in medulla. In the spleen, prothymosin alpha was found in lymphocytes of the periarteriolar lymphatic sheaths and was especially prominent in the germinal centers. Parathymosin immunoreactivity in the thymus was mainly localized in the medulla; positive cells were reticuloepithelial cells from the thymic reticulum and the blood barrier. Thymocytes were negative. In spleen, parathymosin was found in reticular cells arranged in a ring between the periarteriolar lymphatic sheath and the marginal zone. Our results do not support an exclusive role for these peptides as immune system hormones or cytokines.

In vitro morphological characterization of the bursal reticuloepithelial (REp) cells of chicken

The REp cells of the bursa follicle medulla of chicken were isolated in vitro. Culture of the REp cells was maintained over a period of 10 days and the cells were observed at 3 and 10 days by means of transmission electron microscopy (TEM) and immunofluorescence. The use of an anticytokeratin monoclonal antibody confirmed their epithelial nature. TEM observations showed the presence of desmosomes and tonofilaments, which are characteristic of epithelial cells. Furthermore, to some extent the cells regenerated in vitro the network they form in vivo. Though the growth rate becomes slower with time, the features of the REp cells do not significantly change.

Reappraisal of histogenesis in the bursal lymphoid follicle of the chicken

The development of the bursal follicle and the appearance of the follicle-associated epithelial (FAE) cell and the reticuloepithelial (REp) cell were studied. The stages of development of the bursal follicle were observed by light and electron microscopy; an anticytokeratin monoclonal antibody was also used. At the beginning of follicle development, a mesenchymal cell cluster is observed in the tunica propria; the cluster becomes wedged in a niche of the surface epithelium, and gradually it is completely surrounded by the epithelium itself, which closes under the clump of mesenchymal cells. The epithelial cells lying upon the mesenchymal clump become necrotic, and a number of mesenchymal cells bulge out, forming the FAE cells. The epithelial cells that have closed under the mesenchymal nodule become stratified and form the REp cells; they become star-shaped because the medullary-lymphoid cells grow between them. Finally, the cortex is formed, possibly as a result of the migration of medullary cells before they peripheralize. It is concluded that FAE cells are not specialized epithelial cells, as they do not react to an anticytokeratin monoclonal antibody; on the contrary, they are formed by mesenchymal stemcells that bulge into the lumen and change their character after moving into the epithelium. The REp cells appear in the follicular primordium shortly after the bursal follicle begins to develop; the pronounced reactivity of the REp cells to an anticytokeratin monoclonal antibody supports the hypothesis of their epithelial origin.

Influence of the thymus on steroidogenesis by rat ovarian cells in vitro.

Thymic hormones and factors have been shown to modulate the function of other endocrine glands including the gonads. Absence of the thymus during development results in ovarian dysgenesis characterized by a decrease in the number of follicles and corpora lutea, bringing about severe changes in reproductive function. To examine whether thymic secretions might affect ovarian activity, whole dispersed ovarian cells obtained from immature rats pretreated with pregnant mare serum gonadotrophin were exposed to a thymus fraction of approximately 28 kDa and also to the media from incubated thymuses (TIM) and the conditioned media from cultured thymic reticuloepithelial cells (TCM). The thymic fraction caused a dose-dependent decrease in human chorionic gonadotrophin (hCG)-stimulated production of progesterone, oestradiol and testosterone, but had no effect on their synthesis in the absence of hCG. Similarly, hCG-induced production of these steroids was decreased by TIM and TCM. Progesterone secretion was the most markedly affected. These results suggest: (1) that the thymus contains a factor with a molecular weight of approximately 28 kDa which interacts with hCG in ovarian cells, (2) that the thymus can release active substances which modify steroid secretion by the ovary in vitro and (3) that the reticuloepithelial cells of the thymus are involved in the secretion of factors which modulate the stimulation by hCG of steroidogenesis in ovarian cells.

Effect of interferon-γ on the abnormality of T cell activation in NZB mice

It is known that New Zealand black (NZB) mice have a defect in the autoantigen recognition mechanism by T cells. The present study was carried out to examine whether the defect could be improved by normalizing the self Ia molecule expression on thymic reticuloepithelial cells (TRC) by using interferon-γ (IFN-γ). Syngeneic mixed lymphocyte reaction (SMLR) was used as an indicator of the mechanism of autoantigen recognition. In the reaction, T cells separated from the thymus were used as responders, and machrophages separated from the spleen were used as stimulators. When the responders were cultured with TRC, in which self Ia molecule expressions had been enhanced by IFN-γ, for activation, the low level of SMLR in NZB mice was elevated close to the normal level. It was suggested, therefore, that IFN-γ could normalize the defective autoantigen expression on TRC in NZB mice and improve the abnormal T cell activation against autoantigens.

Involution of the bursa of Fabricius in ducks

SummaryOn the involution of the bursa of Fabricius of the duckThe morphological and structural aspects of the functional aspects of the involution were studied light‐ and electronmicroscopically in ducks 90 to 150 days old. The first involutionary changes were observed in the interfollicular connective tissue around day 100. Following this, cells left the periphery of the follicles; they were connected with collagen fibers and positioned themselves between the lymphocytes of the cortex that became thinner before it disappeared.On day 135 the medulla lost its lymphocyte content through wide ducts which opened directly into the lumen of the bursa. On day 150 the bursa experienced a massive overgrowth; almost all follicles had disintegrated and only small groups of cells remained which consisted principally of reticuloepithelial cells and some lymphocytes.Cysts were not observed during the involution of the bursa.

Development and histogenesis of the thymus in dog. A light and electron microscopical study

The development of the thymus was studied with histological, transmission electron microscopic (TEM) and histochemical methods in 100 dog fetuses (beagle), between day 19 of gestation and day 21 after birth. Thymus development could be divided in three stages: 1/Formation of epithelial palisades; 2/ Initiation of lymphopoiesis; 3/ Differentiation of the medulla and Hassall's bodies (HB). The epithelial anlagen were seen at day 23 of gestation showing the characteristic palisade structure of the endodermally derived epithelium. Ten days later the beginning of lymphoiesis and the reticularization of the epithelial cells could be seen. The first HB could be found at day 38 when cortical-medullary differentiation is recognized. The histochemical observation demonstrated a rich content of PAS positive coarse granules in the cytoplasm of reticulo-epithelial (RE) cells. On the other hand, the HB showed a diffuse PAS positive reaction. The ultrastructural investigations demonstrated the presence of desmosomes connecting RE cells to one another. Desmosomes were not found between RE and lymphocytes. The growth of the developing thymus into the mesenchymal matrix resulted in the lobulation of the organ by connective tissue cells and fibers. The first mast cells were seen at day 35 of gestation, most abundantly in the interlobular connective tissue (ICT) although a few were present in the cortex and somewhat more in the medulla, near the HB. At the end of development small groups of neutrophil cell precursors appeared in the ICT and the cortex. Cysts were not present up to day 21 after birth.

Progestin receptor in the thymus of ovariectomized immature rats.

By using the synthetic progestin promegestone (R5020), the location and characteristics of progestin receptors in the thymic cytosols from immature ovariectomized oestrogen-treated rats were determined. Tritiated promegestone bound to the cytosol with high affinity (dissociation constant (Kd) = 2.0 +/- 0.3 nmol/l; promegestone greater than progesterone greater than oestradiol greater than corticosterone testosterone) and low capacity (number of binding sites (Bmax) = 143.0 +/- 13.5 fmol/mg protein). These values were appropriate for progestin receptors. However, an extremely high dose of dexamethasone (10 mumol/l; 1000-fold excess over [3H]promegestone) slightly inhibited the specific binding. Progestin receptors were predominantly located in the reticuloepithelial (RE)-cell fraction, with few in the thymocyte T-cell fraction. The receptor level was raised (24.9 +/- 11.3 (S.E.M.) to 143.0 +/- 13.5 fmol/mg protein) with increased doses of oestrogen (0-30 micrograms) administered in vivo. Using sucrose density gradient ultracentrifugation it was found that the thymic progestin receptor had a sedimentation coefficient of 9S under low-salt conditions. These results clearly suggest that the thymus of the immature female rat contains a specific progestin receptor which is mainly located in the RE cells.

The effect of dioctyltin dichloride on the thymus and T-cell differentiation in the rat.

Various industrial and environmental chemicals have been shown to have a profound effect on thymus and thymus dependent functions (Seinen and Willems, 1976; Vos, 1977; Miller, 1983). Recently, particular attention has been paid to the selective effect of dioctyltin compounds on the thymus. These materials are used extensively in the plastics industry, in particular, during the heat/light stabilisation process in the manufacture of PVC items intended to come into contact with drugs and food stuffs. In 1976 Seinen and Willems reported that dioctyltin dichloride (DOTC) caused a severe reduction of thymic weight in weanling rats after exposure to diets containing 50 or 150 ppm DOTC. Subsequent work in our laboratories indicated that 6–8 week old PVG strain rats were equally sensitive to DOTC. Animals exposed to 75 ppm DOTC via their diet developed overt thymic atrophy after 2 wks exposure (Fig. 1), almost complete atrophy was evident after 4 wks exposure and by 8 wks the thymic remnant consisted almost entirely of brown fat. Body weight gain and food intake were not influenced by the feeding regime and animals showed no signs of abnormal behaviour or appearance. Examination of plastic embedded thymic sections from DOTC treated rats revealed a marked depletion of cortical thymocytes, a concurrent loss of the cortico-medullary junction and an apparent increase in the number of vacuolated reticulo-epithelial cells (RECs).

Specific binding of 17β-estradiol in the human thymus

Many observations suggest that estrogenic preparations can depress cell-mediated immune reactions. Since cell-mediated immunity is thymus-dependent, the estrogen-binding properties of human and mouse thymus tissue were studied with the use of an aqueous two-phase separation system. A high-affinity and low-capactiy estrogen binding was found in human thymus tissue from six prepubertal children of both sexes and two grown women. A similar specific binding was found in the mouse thymus and in the human, uterus. The association constant (Ka) for the binding in the human thymus was 16.01 ± 8.98 × 109M−1. The human uterus, which is known to possess estrogen receptors, had Ka values in the same range. The binding seems to be located in the reticuloepithelial cells of the thymus. Data suggest that the human thymus is a target organ for estrogens, which may influence lymphocyte function during therapy.

Identification of thymostimulin secreting cells in calf thymus by immunoperoxidase method.

An anti- thymostimulin (TS) serum was tested on calf thymus to study the localization of the hormonal factor. The immunoperoxidase method was applied to tissue fixed in Bouin's fluid and embedded in paraffin, or to tissue fixed in paraformaldehyde and embedded in Epon for semi-thin sections. Immuno-reactivity was shown, with DAB- Fluka , in reticulo-epithelial cells in the medulla, and between the cortex and the medulla, while with DAB-Sigma reactivity was found in the cortex as well. The external cells of Hassall's corpuscles were also reactive. Myoid cells were not reactive. In semi-thin sections a weak reactivity was noted at the periphery of a few lymphocytes. Comparison with the localization of other thymic factors, and the possibility of a functional cycle of the epithelial cells synthesizing one or more factors are discussed.

Estrogen-responsive creatine-kinase in the reticulo-epithelial cells of rat thymus.

We have evaluated the presence of the so-called "estrogen-induced protein" (IP) in the thymus of immature rat. IP is one of the earliest proteins synthesized in response to estrogen in rat uterus and has recently been identified as the BB-isozyme of creatine-kinase (J. Biol. Chem. 256 (1981) 5741). Estrogen-exposed tissues were labelled with [35S]methionine and the soluble proteins separated by SDS-polyacrylamide gel electrophoresis followed by fluorography. It was observed that estrogen stimulated the labelling of a thymic protein with electrophoretic mobility identical to that of uterine IP. The effect was dose-related and specific for estrogen receptor ligands. Thymic IP, like that of the uterus, was immunoprecipitated equally well by either anti-IP antiserum from rat uterus or anti-BB-creatine-kinase antiserum from rat brain. After purification by ion-exchange and affinity chromatography, there was a parallel increase in the extent of recovery of IP and BB-creatine-kinase activity in both the thymus and the uterus. Using the immunohistochemical peroxidase-antiperoxidase method with anti-IP serum, the immune-reaction product was localized in a few cells identified as reticulo-epithelial cells. The thymocytes were always free of any reaction product. These data demonstrate that the reticulo-epithelial cells of rat thymus are a target for estrogens.

Dihydrotestosterone regulation of thymocyte function in the rat—mediation by serum factors

We have previously reported that reticuloepithelial cells of rat thymic tissue contain specific, high-affinity estrogen (E) and dihydrotestosterone (DHT) receptors which are not present in thymocytes, and that stimulation of the concanavalin A (Con A) sensitive thymocyte population is by means of a thymic serum substance depressed by estradiol. To ascertain if a serum substance modulated by DHT could also effect a thymocyte population, we incubated thymocytes in vitra for 3 days in the presence of the mitogens Con A or phytohaemagglutinin (PHA) + tissue culture media+ 20% specific rat serum preparations and pulse labelled with tritiated thymidine. Rat serum samples were prepared from control, castrate, thymectomized (Tx) and castrate-Tx animals as well as from similar groups of animals treated in vitro for 3 days with physiological doses of DHT. It was found that there was a significant enhancement of thymocyte blastogenesis in cultures incubated with castrate rat serum + Con A or PHA vs control serum cultures ( P < 0.001). Direct replacement of DHT either to normal or castrate sera in vitro at physiological concentrations did not alter the level of thymocyte blastogenesis from normal or castrate controls. Sera prepared from castrate animals treated with DHT at physiological concentrations did not depress the blastogenic response, but sera from animals treated with testosterone were successful in depressing the blastogenic response to noncastrate levels. Sera prepared from Tx animals were stimulatory on thymocyte blastogenesis when PHA were utilized ( P < 0.02) and this stimulation was depressed in sera from animals treated in vivo with DHT. Sera prepared from Tx or castrate-Tx animals were not able to stimulate thymocyte blastogenesis when Con A was utilized but were stimulatory when prepared from castrate-Tx animals pretreated in vivo with DHT. It is hypothesized that Con A sensitive thymocytes are depressed by a thymic serum factor under the control of E and that both Con A and PHA sensitive thymocytes are depressed by a serum factor possibly of extrathymic origin that is under the control of DHT. A tentative hypothesis for the regulation of thymocytes by gonadal steroid hormones is presented.

Thymic epithelial genotype influences the production of recombinant leukemogenic retroviruses in mice.

By using T1 oligonucleotide fingerprinting and mapping techniques, we analyzed the genomic structure of retroviruses produced by thymocytes and splenocytes of reciprocal bone marrow-and thymus-grafted chimeras. We found that the genetic factor(s) derived from NZB mice that suppresses the development of thymic leukemia in (AKR X NZB)F1 mice also prevents the formation of recombinant leukemogenic viruses and the expression of preleukemic changes in the (AKR X NZB)F1 thymocytes. The NZB mouse gene or genes appeared to exert this suppressive effect by acting on the thymic reticuloepithelial cells and not on the thymic lymphocytes of (AKR X NZB)F1 hybrids. Prospective studies with thymic epithelial grafts from young mice showed that the AKR thymic epithelium could mediate the formation and expression of leukemogenic recombinant viruses and preleukemic changes in thymocytes that lead to the development of thymic leukemia, whereas the (AKR X NZB)F1 thymic epithelium was deficient in this regard. Our results also confirmed a previous observation that during in vivo generation of recombinant leukemogenic viruses, the acquisition of polytropic virus-related sequences in the 3' portion of the p15E gene and the U3 region and in the 5' part of the gp70 gene can occur independently.