Thymic medullary regions are formed in neonatal mice as islet-like structures, which increase in size over time and eventually fuse a few weeks after birth into a continuous structure. The ...development of medullary thymic epithelial cells (TEC) is dependent on NF-κB associated signaling though other signaling pathways may contribute. Here, we demonstrate that Stat3-mediated signals determine medullary TEC cellularity, architectural organization and hence the size of the medulla. Deleting Stat3 expression selectively in thymic epithelia precludes the postnatal enlargement of the medulla retaining a neonatal architecture of small separate medullary islets. In contrast, loss of Stat3 expression in cortical TEC neither affects the cellularity or organization of the epithelia. Activation of Stat3 is mainly positioned downstream of EGF-R as its ablation in TEC phenocopies the loss of Stat3 expression in these cells. These results indicate that Stat3 meditated signal via EGF-R is required for the postnatal development of thymic medullary regions.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
T-cell development is under the tight control of thymic microenvironments. Conversely, the integrity of thymic microenvironments depends on the physical presence of developing thymocytes, a ...phenomenon designated as âthymic crosstalkâ. We now show, using three types of immunodeficient mice, i.e. CD3(epsilon) transgenic mice, RAG(null) mice and RAG(null)-bone-marrow-transplanted CD3(epsilon) transgenic mice, that the control point in lymphoid development where triple negative (CD3(â),CD4(â),CD8(â)) thymocytes progress from CD44(+)CD25(â) towards CD44(â)CD25(+), influences the development of epithelial cells, critically inducing the extra, third dimension in the organization of the epithelial cells in the cortex. This tertiary configuration of the thymic epithelium is a typical feature for the thymus, enabling lymphostromal interaction during T-cell development. Crosstalk signals at this control point also induce the formation of thymic nurse cells. Moreover, our data indicate that establishment of a thymic cortex is a prerequisite for the development of the thymic medulla. Thus, differentiating thymocytes regulate the morphogenesis of thymic microenvironments in a stepwise fashion.
We describe a novel murine progenitor cell population localised to a previously uncharacterised region between sebaceous glands and the hair follicle bulge, defined by its reactivity to the thymic ...epithelial progenitor cell marker MTS24. MTS24 labels a membrane-bound antigen present during the early stages of hair follicle development and in adult mice. MTS24 co-localises with expression of α6-integrin and keratin 14, indicating that these cells include basal keratinocytes. This novel population does not express the bulge-specific stem cell markers CD34 or keratin 15, and is infrequently BrdU label retaining. MTS24-positive and -negative keratinocyte populations were isolated by flow cytometry and assessed for colony-forming efficiency. MTS24-positive keratinocytes exhibited a two-fold increase in colony formation and colony size compared to MTS24-negative basal keratinocytes. In addition, both the MTS24-positive and CD34-positive subpopulations were capable of producing secondary colonies after serial passage of individual cell clones. Finally, gene expression profiles of MTS24 and CD34 subpopulations were compared. These results showed that the overall gene expression profile of MTS24-positive cells resembles the pattern previously reported in bulge stem cells. Taken together, these data suggest that the cell-surface marker MTS24 identifies a new reservoir of hair follicle keratinocytes with a proliferative capacity and gene expression profile suggestive of progenitor or stem cells.
Intrathymic lipid-laden multilocular cells (LLMC) are known to express pro-inflammatory factors that might regulate functional activity of the thymus. However, the phenotype of age-associated ...intrathymic LLMC is still controversial. In this study, we evaluated LLMC density in the aging thymus and better characterized their distribution, ultrastructure and phenotype. Our results show an increased density of LLMC in the thymus from 03 to 24 months of age. Morphologically, intrathymic LLMC exhibit fibroblastoid fusiform, globular or stellate shapes and can be found in the subcapsular region as well as deeper in the parenchyma, including the perivascular area. Some parenchymal LLMC were like telocytes accumulating lipids. We identified lipid droplets with different electrondensities, lipofuscin granules and autolipophagosome-like structures, indicating heterogeneous lipid content in these cells. Autophagosome formation in intrathymic LLMC was confirmed by positive staining for beclin-1 and perilipin (PLIN), marker for lipid droplet-associated proteins. We also found LLMC in close apposition to thymic stromal cells, endothelial cells, mast cells and lymphocytes. Phenotypically, we identified intrathymic LLMC as preadipocytes (PLIN+PPARγ2+), brown adipocytes (PLIN+UCP1+), macrophages (PLIN+Iba-1+) or pericytes (PLIN+NG2+) but not epithelial cells (PLIN- panCK+). These data indicate that intrathymic LLMC are already present in the young thymus and their density significantly increases with age. We also suggest that LLMC, which are morphologically distinct, establish direct contact with lymphocytes and interact with stromal cells. Finally, we evidence that intrathymic LLMC correspond to not only one but to distinct cell types accumulating lipids.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Early in ontogeny, the secondary lymphoid organs become populated with numerous cells of mesodermal origin which forms both the lymphoid and stromal elements. The critical receptor/ligand ...interactions necessary for lymphoid organogenesis to occur are for the most part unknown. Although lymphotoxin-α (LTα ) has been shown to be required for normal lymph node, Peyer's patch, and splenic development, it is unclear if soluble LTα 3, and/or cell-bound lymphotoxin-α β (LTα β ) mediate these developmental events. Here we report that blocking LTα β /lymphotoxin-β receptor (LTβ R) interaction in vivo by generating mice which express a soluble LTβ R-Fc fusion protein driven by the human cytomegalovirus promoter results in an array of anatomic abnormalities affecting both the spleen and Peyer's patches, but not the lymph nodes. These results demonstrate that surface LTα β ligand plays a critical role in normal lymphoid organ development.
CIITA activates the expression of multiple genes involved in antigen presentation and it is believed to be required for both constitutive and IFNγ-inducible expression of these genes. To understand ...the role of CIITA in vivo, we have used gene targeting to generate mice that lack CIITA. CIITA-deficient (−/−) mice do not express conventional MHC class II molecules on the surface of splenic B cells and dendritic cells. In addition, macrophages resident in the peritoneal cavity do not express MHC class II molecules upon IFNγ stimulation nor do somatic tissues of mice injected with IFNγ, in contrast with wild-type mice. The levels of Ii and H-2M gene transcripts are substantially decreased but not absent in CIITA (−/−) mice. The transcription of nonconventional MHC class II genes is, however, not affected by CIITA deficiency. A subset of thymic epithelial cells express MHC class II molecules. Nonetheless, very few mature CD4 T cells are present in the periphery of CIITA (−/−) mice despite MHC class II expression in the thymus. Consequently, CIITA (−/−) mice are impaired in T-dependent antigen responses and MHC class II–mediated allogeneic reponses.
In the normal mouse spleen, two distinct populations of dendritic cells (DC) are present that differ in microanatomical location. The major population of marginal DC is found in the "marginal zone ...bridging channels" and extends into the red pulp. The interdigitating cells (IDC) are localized in the T cell areas in the white pulp. The aim of the present study was to characterize these two splenic DC populations with regard to their phenotype, in vivo phagocytic function, and turnover. Both marginal DC and IDC are CD11c+ and CD13+, but only IDC are NLDC-145+ and CD8alpha+. Notably, both populations, when freshly isolated, express the macrophage markers F4/80, BM8, and Mac-1. To study the phagocytic capacity of these cells, we employed the macrophage "suicide" technique by injecting liposomes loaded with clodronate i.v. Marginal DC, but not IDC, were eliminated by this treatment. Phagocytosis of DiI-labeled liposomes by DC confirmed this finding. The two DC populations differed significantly with regard to their turnover rates, as studied in a transgenic mouse model of conditional depletion of DC populations with high turnover. In these mice, marginal DC were completely eliminated, but the IDC population remained virtually intact. From these data we conclude that the marginal DC population has a high turnover, in contrast to the IDC population. Taken together, the present results indicate that marginal DC and IDC represent two essentially distinct populations of DC in the mouse spleen. They differ not only in location, but also in phenotype, phagocytic ability, and turnover.
This study describes abnormalities of the thymus in mice in which the
Stat3 gene has been specifically disrupted behind the keratin 5 promoter. In these mice, virtually all of the thymic epithelial ...cells (TEC) were deficient for Stat3 activation. Adult mutant mice developed severe thymic hypoplasia, which included alterations in the cortical TEC architecture that coincided with the loss of thymocytes. Even during the asymptomatic period of preadolescence, these mice exhibited a higher susceptibility of the thymus to suboptimal doses of dexamethasone or γ-irradiation, while their thymocytes per se were no more sensitive than controls. These results indicate that Stat3 in TEC plays an essential role in maintaining thymic architecture and thymocyte survival.
The development and maintenance of thymic microenvironments depends on sustained crosstalk signals derived from developing thymocytes. However, the molecular basis for the initial phase in the ...lymphoid dependent development of thymic epithelial cells (TECs) remains unclear. Here we show that similarly to regular thymocytes, developing B cells enforced to express the Notch ligand Delta-like-1 (DLL1) efficiently induce the non-polarized, three-dimensional (3D) meshwork architecture of cortical TECs in fetal thymic organ culture. Moreover, the DLL1-overexpressing B cells induce well-developed distinct medullae. Such medullae also arose in lobes reconstituted with Rag2
−/− thymocytes overexpressing DLL1. Our present findings thus strongly suggest that Notch signaling from thymocytes to TECs induces TEC development at an early phase of thymic organogenesis. The present approach using non-T lineage cells for the in vitro construction of thymic environments may also provide a novel tool for thymus regeneration and T cell production in immunocompromised individuals.
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