Dexamethasone and hydrocortisone enhance the in vitro migration of prethymic stem cells to thymus supernatant.

The migration of prethymic stem cells from the bone marrow to thymus supernatant was examined in a blind well migration assay following treatment with glucocorticoids (GCS). To study the in vivo effects of GCS, time release pellets containing dexamethasone (DEX) were implanted subcutaneously in young adult CBA/J mice for 7, 14 and 21 days. After seven and 21 days of DEX treatment, enhanced migration of bone marrow lymphoid cells to thymus supernatant occurred. To study the in vitro effects of GCS on prethymic stem cell migration, bone marrow cells were incubated for one or six hours in media containing dexamethasone (DEX), hydrocortisone (HCS), or medium alone. After a six-hour incubation with GCS, significantly more bone marrow cells migrated toward thymus supernatant in vitro than bone marrow cells incubated in medium alone. The enhanced migration of cells to thymus supernatant seen in this assay may reflect a feedback mechanism whereby bone marrow cell migration is enhanced to restore the thymic lymphocyte reserves depleted following treatment with GCS.     

Ontogeny of acquired immunological tolerance to H-2 alloantigens

The ontogeny of mixed lymphocyte reaction and cell-mediated lymphocytotoxicity (CML) responsiveness was studied in mice that had been neonatally tolerized by the injection of 15 × 10⁶ semiallogeneic bone marrow and spleen cells, and compared to that of unprimed littermates. Spleen cells from primed mice did not develop reactivity towards the tolerizing antigen but did develop reactivity towards third-party alloantigens. Similarily, thymus cells from primed mice also failed to develop CML reactivity towards the tolerizing antigen. Thymus cell mixed lymphocyte reactivity, which was demonstrable in neonates before the tolerizing injection, declined rapidly between 2 and 4 days of age, compared to that of controls. Thus neonatal tolerance was shown to operate at least at a thymic, and perhaps pre-thymic level; measurement of the levels of chimeric cells in the thymus and bone marrow favored the latter interpretation.     

The effects of thymus supernatant on the thymus homing ability of aged murine bone marrow cells.

This study examined the effect of thymus supernatant on the ability of bone marrow cells from senescent mice to home to the thymus. An in vitro and an in vivo assay were employed. The in vitro assay used a blind well migration of aged bone marrow cells to thymus supernatant across a membrane with 5-microns pores. The in vitro assay measured the ability of aged bone marrow to repopulate the thymus of an irradiated host. Our results support previous reports that the bone marrow from old mice has a greatly reduced ability to migrate to thymus supernatant and to repopulate the thymus of an irradiated host. Further, we found that a brief treatment of the old bone marrow with thymus supernatant significantly improved its thymus homing ability both in vitro and in vivo.     

Stress-induced alterations in the programmed natural cycles of post-natal lymphoid organ development in C57BL/6 mice: Evidence for a regulatory feedback relationship between bone marrow and thymus

This study investigated some effects of weaning and immobilization stress in C57BL/6 mice aged 22-68 days, i.e., over a period including activation of the hypothalamus-pituitary-adrenal (HPA) axis and puberty. Specifically, the study evaluated the evolution, over the referred age interval, of a set of variables (body, thymus, spleen and axillary lymph nodes weights, the proportion of lymphoid cells in the bone marrow, the relative chemoattraction capacity of thymic supernatants for lymphoid cells and the migratory capacity of bone marrow lymphoid cells) in either weaned mice or weaned mice subjected to immobilization stress, compared to "non-stressed" unweaned mice. Cyclic patterns, observed for most variables in unweaned mice, were especially pronounced in two cases: the relative migratory capacity of bone marrow lymphoid cells collected at different ages towards neonatal thymic supernatant, and the relative chemoattraction capacity of thymic supernatants of different ages as tested against a sample of bone marrow lymphoid cells from mice aged 35 days. Weaning stress tended to intensify the involution stages of the cycles in thymus, spleen and lymph node weight, but increased the relative proportion of lymphoid cells in the bone marrow cell population. Both types of exogenous stress tended to affect cycle phase, i.e., cycle peaks and troughs were shifted in time. Correlations were observed between patterns seen in the thymus and bone marrow, suggesting the existence of an autoregulatory feedback loop governing pre-T cell migration and bone marrow/thymus homeostasis. These results also suggest that exogenous stress acts as a non-programmed regulator, modulating the naturally programmed cyclic patterns.     

Differentiation of functionally active mouse T lymphocytes from functionally inactive bone marrow precursors. IV. Recovery of T-cell function from bone marrow precursors in a histo-incompatible environment.

Regeneration of T-cell activities in vivo or in vitro from mouse bone marrow precursors differentiating in the presence of an allogeneic thymus was investigated. The data indicated that T-depleted bone marrow cells fail to affect long-term reconstitution of allogeneic recipients unless a pool of rapidly maturing T-precursor cells is also removed (post-thymic pool). Animals reconstituted with pre-thymic bone marrow stem cells become stable chimaeras in which cells capable of generating an in vitro CML response to host antigens, as well as cells capable of suppressing that response, could be demonstrated. Similar data (CML directed against the H-2 antigens of the 'host' thymus feeder layer and cells capable of inhibiting that response) were obtained when pre-thymic bone marrow cells were grown in vitro on allogeneic thymus feeder cells. When cytotoxic T-lymphocyte precursor (CTLp) and helper (CTLh) cells were separately investigated, a restriction in their co-operation for an anti-host response was observed when precursor cells differentiated in an allogeneic environment. Only CTLp and CTLh differentiating in the presence of the same allogeneic thymus source (whether in vivo or in vitro) could co-operate to generate CTL directed to H-2 antigens of that thymus source.     

Immunological aspects of aging: early changes in thymic activity

Age related changes in immune function are preceded by changes in thymic function. One index of thymic function is the ability of the thymus to induce the differentiation of bone marrow pre-T cells into active T cells. Movement of precursors of PHA-responsive T cells into the thymus ceases prior to adolescence in long-lived, autoimmune disease resistant mice as determined by studies utilizing chromosome markers in parabiotic mice. The cause for this age-dependent, cell traffic phenomenon is not known, but it would appear that an extrathymic regulatory mechanism may be operating, since these precursor T cells have the capacity to migrate into the thymus, and even a grafted, involuting thymus is capable of accepting precursor T cells, under extraordinary conditions. Results indicate that shortly after adolescence, immature T cell precursors of PHA-responsive cells in the thymus, and perhaps the periphery, are the sole source of PHA-responsive T cells. T cell migration and maturation is discussed in relation to thymic hormones and the thymic-neuroendocrine regulatory axis.     

Conditioning of Nude bone marrow increases in vitro migration to thymus supernatant.

The thymus must be continuously seeded by cells termed prothymocytes in order to maintain normal T-cell development (Scollay et al. 1986). Using parabiotic studies, the source of prothymocytes appears to be either from the fetal liver or the adult bone marrow (Roderwald et al. 1992). The ability of the body to distinguish self from non-self and mount a functionally mature immune response is dependent upon the intrathymic education of these cells. Therefore, it is apparent that successful migration of prothymocytes into the thymus is an inescapable event in the development and maintenance of the immune system. Utilization of the athymic Nude mouse is a valuable asset in the elucidation of the mechanisms influencing the migration of bone marrow cells into the thymus. Its aberration enables investigators to examine the effect of thymic factors on cells previously devoid of thymic influence. In an attempt to understand the migration of normal prothymocytes into the thymus, we analyzed the in vitro migration of athymic bone marrow cells towards newborn thymus supernatant. Adult athymic murine bone marrow cells were incubated in either thymus supernatant or media and allowed to migrate toward one or the other. Similar control experiments were performed using CBA adult mice. Results indicate that athymic bone marrow migration towards both supernatant and media can be restored to control levels after incubation in thymus supernatant.     

Prothymocyte seeding in the thymus

A major gap in our understanding of T lymphocyte development is the process of stem cell differentiation into T lymphocyte precursors. An important question is whether bone marrow-derived stem cells become committed to T lymphoid lineage within the bone marrow, or whether this occurs once cells have entered the microenvironment of the thymus. Attempts to identify a haemapoietic precursor of thymocytes in mice, a "prothymocyte", have involved cell transfer experiments involving isolated and selected populations of bone marrow stem cells, as well as transformed or continuous cell lines representing early stage in mouse T cell development. Current information on the properties of stem cells which can seed the thymus is reviewed in this paper, and the possibility that progenitor T cells may be identified by their expression of receptor(s) which localise them into the thymus is considered.     

Requirement of Galphai in thymic homing and early T cell development

Demonstration of thymic homing dependent on Galphai proteins is one of the keys to determine whether thymic entrance of blood-borne progenitors is a highly selective process. The present study provides compelling evidence of an indispensable role for Galphai proteins in this process. Absence of either Galphai2 or Galphai3 significantly abrogated thymic homing, with an effect of Galphai3 being greater than that of Galphai2. Pertussis toxin treatment that blocks both Galphai2 and Galphai3 almost completely blocked thymic seeding in the thymus. Null mutation of Galphai3 also hindered bone marrow cell development and thus reduced production of pre-thymic progenitors. In contrast, Galphai2 exhibited a more prominent role than Galphai3 in guidance of CD4-CD8--double negative (DN) 1 cell migration and early thymic differentiation. The Galphai-deficiency-induced defects might be compensated for in part via augmented function of thymic stromal cells so that a nearly normal output of mature T cells could be maintained in these Galphai-deficient mice. These studies underscore the importance of Galphai in regulating thymic homing and pre-thymic and early thymocyte differentiation.     

Restraint and sound stress reduce the in vitro migration of prethymic stem cells to thymus supernatant.

Murine bone marrow cells were examined in an in vitro assay to determine whether stress modulates the migration of prethymic stem cells to thymus supernatant. Adult CBA/J mice were either restraint or sound stressed for two hours daily for five days. Bone marrow cells were removed and migrated toward newborn thymus supernatant in an in vitro migration assay in blind well chambers. Bone marrow cells from animals which had been stressed for five days showed a significant decrease in the percent migration to thymus supernatant when compared to bone marrow cells from age-matched control mice. This suggests that either a smaller proportion of precursor cells are available in the bone marrow for migration to the thymus or the number of cells remains the same but these cells are less responsive to chemoattractive factors in the supernatant, thus causing them to migrate at a decreased rate.     

Effect of cortisone and X-irradiation on cellular depletion and regeneration in the thymus of mice: experimental discrimination between thymus lymphocyte precursors in the bone marrow and in the thymus.

The effect of cortisone treatment on the ability of bone marrow cells to repopulate X-irradiated thymus was investigated. In one experimental series, groups of mice were treated first with cortisone and then irradiated with or without bone marrow protection. Mice treated with either cortisone or radiation alone served as controls. During an initial, bone marrow independent phase of thymus regeneration, cortisone had a stronger inhibitory effect on the cellular regeneration of the organ than irradiation. On the other hand, during a subsequent bone marrow dependent phase, thymus regeneration was impaired by radiation exposure but not by cortisone treatment. In another experimental series, irradiated mice were transplanted with bone marrow cells in different numbers from syngeneic donors which had either been treated with cortisone or were left untreated. Twenty days later the cell number was consistently larger in the thymus of animals which has been transplanted with cortisone treated bone marrow than in the animals transplanted with untreated bone marrow. It is concluded that the thymus lymphocyte precursors in the bone marrow and the early precursors of thymocytes in the thymus differ with regard to their sensitivity to cortisone and radiation and, therefore, may represent two distinct cell types.     

Altered lymphocyte recognition repertoire during ageing. III. Changes in MHC restriction patterns in parental T lymphocytes and diminution in T suppressor function.

Irradiated C57BL/6 and (C57BL/6 X C3H)F1 mice have been reconstituted with bone marrow prepared from young (2 month) or aged (24 month) C57BL/6 donors. Indirect examination of the T cell receptor for H-2d alloantigens on H-2b splenocytes of these reconstituted mice, using the suppression of the H-2b anti-H-2d response induced by (H-2b X H-2d)F1 anti-(H-2b anti-H-2d) suppressor cells, suggests that the allo-receptor repertoire derived from bone marrow of aged mice is different from that of T cells derived from young bone-marrow precursors. These observations were supported by direct evidence, from rosette formation with murine erythrocytes, for changes in the T cell receptor of these different (radiation-chimaera) sources of H-2b-T cells. Along with these subtle changes in the allo-receptor repertoire of T cells derived from bone marrow of aged mice grown in irradiated F1 hosts, there is a decrease (compared with mice reconstituted with bone marrow from young donors) in the apparent frequency of T cells recognizing antigen in association with the new MHC-restricting elements in these parent F1 chimaeras. Analysis of those cell subsets reported to be involved in the regulation of MLC responses suggests that some of the differences observed between T cell differentiation from bone-marrow stem cells of young or aged donors may in part be explained by a diminution in the production from bone marrow of aged mice of those cells important for homeostasis within the immune system.     

The long road to the thymus: the generation,mobilization, and circulation of T-cell progenitors in mouse and man

The majority of T cells develop in the thymus. T-cell progenitors in the thymus do not self-renew and so progenitor cells must be continuously imported from the blood into the thymus to maintain T-cell production. Recent work has shed light on both the identity of the cells that home to the thymus and the molecular mechanisms involved. This review will discuss the cells in the bone marrow and blood that are involved in early thymopoiesis in mouse and man. Understanding the pre-thymic steps in T-cell development may translate into new therapeutics, especially in the field of hematopoietic stem cell transplantation.     

Transplantation of retrovirally transduced bone marrow prevents autoimmune disease in aged mice by peripheral tolerance mechanisms

Transplantation of bone marrow (BM) engineered to express self-antigen has been shown to protect 100% of young mice from myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE), with thymic clonal deletion as a tolerance mechanism. Here, we asked whether aged mice can also be tolerised following transplantation with self-antigen-engineered BM and whether castration-induced thymus regrowth can enhance this outcomes. Then, 50% of aged mice were protected from EAE regardless of castration-induced thymus regrowth. EAE-free and diseased mice demonstrated MOG-specific lymphocyte proliferation and antibody production regardless of castration-induced thymus regrowth, consistent with lack of intrathymic deletion of self-antigen-reactive T cells. Although low chimerism levels ( < 4%) were observed, EAE-free mice showed significantly higher chimerism levels in lymphocytes in peripheral lymphoid organs compared with thymus. CD4⁺CD25⁺ regulatory T cells were elevated in lymph nodes of EAE-free mice. We conclude that transplantation of self-antigen expressing BM protects 50% of aged mice and castration-induced thymic regrowth had no effect on outcomes. Peripheral tolerance mechanisms are implicated since protection is associated with higher chimerism levels in peripheral T and B lymphocytes and with elevated regulatory T cells.     

Transplantation of retrovirally transduced bone marrow prevents autoimmune disease in aged mice by peripheral tolerance mechanisms

Transplantation of bone marrow (BM) engineered to express self-antigen has been shown to protect 100% of young mice from myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE), with thymic clonal deletion as a tolerance mechanism. Here, we asked whether aged mice can also be tolerised following transplantation with self-antigen-engineered BM and whether castration-induced thymus regrowth can enhance this outcomes. Then, 50% of aged mice were protected from EAE regardless of castration-induced thymus regrowth. EAE-free and diseased mice demonstrated MOG-specific lymphocyte proliferation and antibody production regardless of castration-induced thymus regrowth, consistent with lack of intrathymic deletion of self-antigen-reactive T cells. Although low chimerism levels (?相似文献   

Human thymus in health and disease: Recent advances in diagnosis and biology

The thymus is the crucial tissue where thymocytes develop from hematopoietic precursors that originate from the bone marrow and differentiate to generate a repertoire of mature T cells able to respond to foreign antigens while remaining tolerant to self-antigens. Until recently, most of the knowledge on thymus biology and its cellular and molecular complexity have been obtained through studies in animal models, because of the difficulty to gain access to thymic tissue in humans and the lack of in vitro models able to faithfully recapitulate the thymic microenvironment. This review focuses on recent advances in the understanding of human thymus biology in health and disease obtained through the use of innovative experimental techniques (eg. single cell RNA sequencing, scRNAseq), diagnostic tools (eg. next generation sequencing), and in vitro models of T-cell differentiation (artificial thymic organoids) and thymus development (eg. thymic epithelial cell differentiation from embryonic stem cells or induced pluripotent stem cells).     

Bone marrow origin of mucosal mast cells

Infection with the intestinal parasite Nippostrongylus brasiliensis stimulates an accumulation of mucosal mast cells (MMC) in the villi of the small intestine of normal but not athymic or W/Wv anemic mice. W/Wv mice are congenitally deficient in both MMC and skin and connective tissue mast cells (CTMC). Athymic mice have normal or elevated numbers of CTMC but are severely deficient in MMC. CTMC derive from the bone marrow. To determine the origin of MMC, athymic and W/Wv mice were given various hematopoietic or lymphoid tissues from normal littermate or beige mice and the MMC response to N. brasiliensis infection was evaluated. The MMC defect in athymic mice was repaired by grafts of thymus cells, thymus gland, or spleen cells, but not by bone marrow cells or anti-Thy 1-treated bone marrow or spleen cells. The MMC and CTMC defects of W/Wv mice were repaired by grafts of bone marrow, spleen cells, or anti-Thy 1-treated bone marrow or spleen cells. Neither the MMC nor the CTMC defect in W/Wv mice was repaired by grafts of thymus cells or thymus glands. These results indicate the following, MMC, like CTMC, derive from the bone marrow and not from the thymus. MMC require a thymic influence for development. Athymic mice possess bone marrow precursors for both MMC and CTMC but lack a thymus-dependent component necessary for MMC development. W/Wv mice lack both MMC and CTMC mast cell precursors but possess the thymus-dependent component required for MMC development.     

Age-related thymic involution is mediated by Fas on thymic epithelial cells

Age-related thymic involution, which is linked to senescence of the immune system, was found to be mediated by the death receptor Fas. The thymus of aged Fas(-/-) mice exhibited an intact structure and the normal differentiation of thymocytes. Both thymocytes and thymic epithelial cells (TECs) were sensitive to Fas-mediated apoptosis, and in vivo stimulation of wild-type thymocytes with anti-CD3 mAb was shown to induce apoptosis in TECs in a Fas-dependent manner. In addition, thymopoiesis continued uninterrupted in aged Fas(-/-) mice that had been lethally irradiated and reconstituted with bone marrow cells derived from wild-type mice, while age-related thymic involution was observed in irradiated wild-type mice reconstituted with bone marrow cells from either Fas(-/-) or wild-type mice. The results indicate that Fas on TECs plays a key role in age-related thymic involution.     

Development of cytotoxic T lymphocyte precursors in the absence of the thymus

Reconstitution of adult thymectomized and lethally irradiated C3H or (C 3 H × DBA/2) F₁ mice with syngeneic adult bone marrow cells or 18 to 20-day-old fetal liver cells resulted almost regularly in the generation of large numbers of cytotoxic T lymphocyte precursors (CTLP) against trinitrophenylated C3H cells and three types of allogeneic stimulator and target cells. The responses against 2,4,6- trinitrophenylated cells were restricted and in so far typical for cytotoxic T lymphocytes. The failure of bone marrow cells from athymic C 3 H mice to reconstitute significant cytotoxic activity indicated that the CTLP had developed from “cytotoxic T lymphocyte preprogenitors” (CTLPP) which were derived from the donor and which had already been under thymic influence. The stem cell preparations in themselves contained frequencies of mature CTLP far too low to account for the reactivity and CTLP frequencies in the reconstituted mice. This fact implied that the CTLPP proliferated extensively and/or matured in the recipient in the absence of the thymus. Individual mice failed to respond to one or more of these stimulator cells. The failure of individual mice to respond was randomly expressed for the four specificities even when the mice were reconstituted with the same stem cell preparation suggesting that CTLPP with defined specificity and low frequency (about 1/10⁸ in fetal liver) were contained in the stem cell preparation and transferred randomly into the irradiated recipients. This would imply that one CTLPP gives rise to 5 × 10³–20 × 10³ CTLP within 5 weeks. The data suggest that the peripheral pools, at least of certain T cell subclasses, may be maintained largely by post-thymic proliferation of CTLPP.     

Recruitment of adult thymic progenitors is regulated by P-selectin and its ligand PSGL-1

The molecular mechanisms that direct the migration of early T lymphocyte progenitors to the thymus are unknown. We show here that P-selectin is expressed by thymic endothelium and that lymphoid progenitors in bone marrow and thymus bind P-selectin. Parabiosis, competitive thymus reconstitution and short-term homing assays indicated that P-selectin and its ligand PSGL-1 are functionally important components of the thymic homing process. Accordingly, thymi of mice lacking PSGL-1 contained fewer early thymic progenitors and had increased empty niches for prothymocytes compared with wild-type mice. Furthermore, the number of resident thymic progenitors controls thymic expression of P-selectin, suggesting that regulation of P-selectin expression by a thymic 'niche occupancy sensor' may be used to direct progenitor access.