Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “thymic selection”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 505 records · Page 28Linked to original sources
PubMed1989

A role for the thymic epithelium in the selection of pre-T cells from murine bone marrow.

A rat thymic epithelial cell line IT45-R1 has been previously described as secreting soluble molecules that in vitro chemoattract rat hemopoietic precursor cells. The development of such an in vitro migration assay was based on the ability of cells to migrate across polycarbonate filters in Boyden chambers. In the present paper, by using the same strategy, we studied murine bone marrow cells capable of migrating in vitro toward IT45-R1 conditioned medium. The responding cells were shown to represent a minor bone marrow subpopulation characterized by a low capacity to incorporate tritiated thymidine in vitro (less than 10% of control). Moreover, this cell subset was considerably impoverished with respect to granulocyte-macrophage CFU (less than 7% of control) and pluripotent hemopoietic stem cells (less than 12% of control). Potential generation of T cells of donor-type in the lymphoid organs of irradiated recipients was measured by using C57BL/Ka Thy-1.1 and Thy-1.2 congenic mice. Thy-1.1 irradiated mice were injected intrathymically or intravenously with the selectively migrated cell subset of Thy-1.2 donor-type bone marrow cells. The use of an i.v. transfer route allowed us to show that these cells possess thymus-homing and colonization abilities. In a time-course study after intrathymic cell transfer, these migrated cells were able to generate Thy-1.2+ donor-type thymocytes represented by all cortical and medullary cell subsets in a single wave of repopulation from day 20 to day 30 after transfer, with a peak around days 23 to 25. The degree of repopulation closely resembled that seen with unfractionated bone marrow cells in terms of absolute numbers of donor cells per thymus (82% of control, 22 x 10(6) Thy-1.2+ cells) as well as in percent donor cells per thymus (105% of control). Thy-1.2+ cells were also detected in the lymph nodes and the spleens of reconstituted recipient mice. Taken together, these results support the idea that the supernatant of the established thymic epithelium IT45-R1 induces the migration of a murine bone marrow subset that contains hemopoietic stem cells already committed to the lymphoid lineage (i.e., pre-T cells).

Animals↗
PubMedDate not supplied

Influence of antigen processing on thymic T-cell selection.

The design of a specific blocking peptide for the immunosuppressive therapy of an autoimmune disease requires the identification of peptides of an autoantigen that are physiologically processed in vivo and bind to MHC-encoded membrane glycoproteins. However, knowledge of how an antigen is physiologically processed by antigen-presenting cells (APC) in vivo, particularly in the thymus, is lacking. It is also unknown whether the processing of an antigen by different APC in the thymus can influence thymic T-cell selection. This is an important consideration for attempts to delete or inactivate autoreactive T cells that elicit autoimmune disease. To address these issues, we investigated the processing of biosynthetically labelled recombinant human insulin (rHI), a model autoantigen, injected into mice and characterized the insulin peptides associated with MHC class II molecules on thymic epithelial cells and dendritic cells. These APC were found to differ in the way they process insulin. The detection of MHC-class-II-bound insulin peptides on the surface of the epithelial cells but not the dendritic cells correlated with their capacity to either present or not present insulin to T cells, respectively. Thus, antigen processing may control the appearance of different peptide-MHC class II complexes on thymic APC that mediate positive and negative selection, and thereby influence the development of the T-cell repertoire. Our findings could have important bearing on the future design of synthetic blocking peptides that reduce or eliminate the onset of autoimmune disease.

Animals↗
PubMed1983

Glucocorticoid binding properties of mouse thymic lymphosarcoma cell populations selected for resistance to the cytolytic effects of glucocorticoids in vivo.

Thirteen independently derived murine thymic lymphosarcoma lines were assayed for various aspects of sensitivity to glucocorticoid-induced cytolysis. All tumor lines were sensitive to cytolysis, as evidenced by profound tumor regression after pharmacologic doses of cortisol. All tumor lines contained about 20,000 high-affinity, dexamethasone binding sites/cell. Between 55 and 88% of these presumptive receptor sites underwent nuclear translocation during a 30-minute incubation at 37 degrees C. Dissociation constants (Kd) for the dexamethasone-receptor complex were between 1.5 and 3.6 nM in all cases. Kd for the triamcinolone acetonide-receptor complex were determined for a few tumor lines and were between 0.5 and 0.9 nM. Cytolysis-resistant subpopulations were selected by prolonged glucocorticoid treatment of BALB/c pi mice bearing tumors from seven of the lymphosarcoma lines. All seven resistant subpopulations contained about 20,000 high-affinity, dexamethasone binding sites/cell. Between 57 and 80% of these presumptive receptor sites underwent nuclear translocation under standard assay conditions. No resistant variants exhibited significantly reduced dexamethasone binding or nuclear translocation properties.

Animals↗
PubMed1989

Definition of the thymic generative lineage by selective expression of high molecular weight isoforms of CD45 (T200).

Selective expression of CD45 isoforms distinguishes naive and memory T cells in peripheral blood. Paradoxically, although the most recent thymic emigrants are CD45R+ CD45 p180-, the majority of thymocytes are CD45 p180+. Speculating that the small subset of thymocytes selectively expressing only the high molecular weight isoforms of CD45 constitute the thymic generative lineage giving rise to peripheral T cells, we characterized the phenotypic and functional properties of CD45 p180- thymocytes. All cells bearing CD45 p180 were removed by rigorous depletion or all CD45R+ thymocytes were removed in a parallel depletion. CD45R- thymocytes were essentially the same in phenotype and CD4/CD8 subset distribution as unfractionated thymus, and dissimilar to naive peripheral blood lymphocyte (PBL) T cells. In contrast, CD45 p180- thymocytes, mainly CD45R+, were CD1- CD38- pgp 1+, corresponding closely to the phenotype of naive CD45R+ PBL T cells. This subset is enriched in CD4+ or CD8+ single positives, includes a high proportion of CD4-8- thymocytes which are predominantly CD3-, and appears to have a medullary location. Approximately 40%-50% of CD45 p180- thymocytes expressed a high density of CDw29 (4B4), which in the periphery is expressed at high density only on CD45 p180+ memory T cells and at low density on CD45R+ naive T cells. However, the expression of high density CDw29 in the absence of CD45 p180 indicates a close resemblance to fetal lymphocytes and suggests an essential role for CDw29 in both the least and the most mature of T cells. If CD45 p180- thymocytes constitute the generative lineage and CD45 p180+ cells are commited to intrathymic death, then the CD45 p180- subset should have enhanced proliferative potential. By combining depletion methods with a limiting dilution assay for clonogenic potential, we found that 100% of the clonogenic precursors present in unfractionated thymus were CD45R+ CD45 p180- cells. This indicates that the CD45 p180+ majority of thymocytes has a very limited capability for proliferation consistent with a commitment to intrathymic death. The clonogenic potential of CD45 p180- thymocytes indicates a greater functional resemblance to PBL T cells than to CD45 p180+ thymocytes. In so far as clonogenic potential in vitro reflects generative potential in vivo, expression of high molecular weight CD45 isoforms appears to define the generative thymic lineage. Our working hypothesis proposes that expression of CD45 p180 implements the mechanism for eliminating thymocytes with self-reactive receptor specificities.

Antigens, Differentiation↗
PubMedDate not supplied

Apoptosis in the mammalian thymus during normal histogenesis and under various in vitro and in vivo experimental conditions.

Programmed cell death (PCD), also known as apoptosis, is a genetically controlled cellular response, manifested in morphologically distinct non-necrotic cellular destruction: cell shrinkage, cytoplasmic "boiling", condensation of chromatin, loss of nuclear membrane followed by DNA fragmentation and cell membrane blebbing, all of which initiate the formation of apoptotic bodies. During the early stages of PCD, cell membrane phospholipid asymmetry is altered, resulting in the dislocation of phosphatidylserine (PS) to the cell surface. During apoptosis, DNA is cut by endonucleases at DNA-linked sites between nucleosomes, producing a number of multimers of nucleosomal DNA units in the cell nuclei. The mechanism of apoptosis and the cellular signals involved in its induction have been studied during thymic prenatal ontogenesis and postnatal development, mainly in immature thymocytes and in the cells of the reticulo-epithelial (RE) network. In thymocytes or resting T lymphocytes, p53 tumor suppressor protein was identified to be a critical mediator of apoptosis in response to DNA damage. The cellular interaction of immature, cortical thymocytes (characterized by a double positive CD4+CD8+TCRlow immunophenotype) with thymic RE cells induces positive selection of T lymphocytes that recognize, but are not activated by self-MHC molecules (tolerance induction). Double positive CD4+CD8+CD3- thymocytes undergo Fas-mediated apoptosis, while CD4+CD8+CD3+ cells use the CD3 mediated pathway of PCD. Two step, apoptotic cell death is mainly restricted to the CD4+CD8+TCRdull thymocyte subpopulation. T-lymphocytes which do not undergo positive selection are killed by apoptosis in response to a number of intrinsic and extrinsic factors, such as chemical toxins, viral infections, X- and UV irradiation, mild hyperthermia, the actions of various hormones, extracellular survival factors, calcium ionophores (such as A23187), various chemotherapeutic drugs (adriamycin, actinomycin D, etc) and antibodies directed to the CD3-TCR (T cell receptor) complex. Immature thymocytes also undergo a second selective process, so-called negative selection, when thymic stromal cells eliminate autoreactive T lymphocytes. This process has been termed clonal deletion and also involves apoptosis. In addition to the two intrathymic T lymphocyte selection mechanisms, Immunocompetent, but autoreactive T lymphocytes which have already reached the periphery are also eliminated by apoptosis. All the divers stimuli of PCD are associated with an increase in the concentration of cytosolic calcium ions (Ca+2), which activate an endogenous endonuclease. This trigger for PCD results in rapid cleavage of DNA, a hallmark of apoptosis. Despite the diversity of the signals that can trigger apoptosis, the changes in cellular morphology characteristic of PCD are very similar. The uniformity of the morphological changes suggests the existence of a predetermined, final and common cell suicide pathway. Apoptosis requires energy in the form of ATP, indicating that PCD, as opposed to necrosis, is an energy dependent, active physiological and pathophysiological phenomenon.

Adolescent↗
PubMedDate not supplied

The role of apoptosis in normal ontogenesis and solid human neoplasms.

Mammalian cells are capable of committing "active suicide" or apoptosis in response to specialized pathological mechanisms employing a phylogenetically developed intrinsic program of death, triggered by signal transduction through specific receptors. Changes in cellular structure such as: 1) condensation of the nuclear (chromatin) and cytoplasmic structures (especially the mitochondria); 2) blebbing of the cell membrane; 3) characteristic swelling of the endoplasmic reticulum; and 4) fragmentation of the cells in membrane bound apoptotic bodies, are the dramatic signs of total cell destruction. Apoptosis requires energy in the from of ATP, indicating that programmed cell death (PCD), as opposed to necrosis, is an energy dependent, active physiological and pathophysiological phenomenon. During this immunocytochemical study, we observed the presence of PCD in the prenatal thymus and various human neoplastically transformed tissues. During the intrauterine ontogenesis, in thymocytes or resting T lymphocytes, p53 tumor suppressor protein was identified to be a critical mediator of PCD in response to DNA damage. The cellular interaction of immature, cortical thymocytes (characterized by a double positive CD4+CD8+TCRlow immunophenotype-IP) with thymic RE cells induces positive selection of T lymphocytes that recognize, but are not activated, by self-MHC molecules (tolerance induction). Double positive CD4+CD8+CD3- thymocytes undergo FasL-mediated apoptosis, while CD4+CD8+CD3+ cells use the CD3 mediated pathway of PCD. Two step, apoptotic cell death is mainly restricted to the CD4+CD8+TCR dull thymocyte subpopulation. T-lymphocytes which do not undergo positive selection are killed by apoptosis in response to a number of intrinsic and extrinsic factors, such as chemical toxins, viral infections, X- and UV irradiation, mild hyperthermia, the actions of various hormones, extracellular survival factors, calcium ionophores (such as A23187), various chemotherapeutic drugs (adriamycin, actinomycin D, etc) and antibodies directed to the CD3-TCR (T cell receptor) complex. Immature thymocytes also undergo a second selective process, so-called negative selection, when thymic stromal cells eliminate autoreactive T lymphocytes. As a typical model of embryonal neoplasms, we observed 34 childhood PNET/MED tissues samples. A systematic observation for the presence of apoptosis related markers (especially FasR) and cells in PCD was carried out. A strong expression (intensity of staining: "A"--the highest possible; number of stained neoplastic cells: +++ to ++++, between 50% to 90%) of FasR was detected. We also observed 42 childhood glial tumors, divided as follows: 6 pilocytic ASTRs; 14 low grade ASTRs; 16 anaplastic ASTRs; and 6 GBMs. The GBMs represent an end-stage brain tumor IP dedifferentiation of glial origin. During the immunocytochemical screening of these 42 childhood ASTRs, we detected strong expression (intensity of staining: "A"--the highest possible; number of stained cells: ++ to ++++, between 20% to 90%) of FasR, employing 4 microns thick, formalin fixed, paraffin-wax embedded tissue slides. FasR expression was rated high, 70% to 90% on the tumor cells in pylocytic ASTRs, lowered to 50% to 60% on the neoplastic cells in low grade ASTRs, even lower between 30% to 40% in anaplastic ASTRs and significantly lower, between 20% to 35% on the neoplastically transformed cells of GBM tissues. The presence of apoptotic neoplastic cells was also regularly detected in other human adult neoplasms, such as thyroid, pancreatic, hepatocellular, gastric, colon, breast, ovarian, prostata, and renal cell carcinomas, as well as, in Hodgkin and non-Hodgkin lymphomas and some sarcomas. The expression of apoptosis related cell surface molecules on the surface of both neoplastically transformed cells and on tumor cell specific, cytotoxic T lymphocyte (CTL) surfaces (FasR-FasL system) raises a distinct possibility of active PCD induction in CTL by tumor cells. Juxtacrine interactions between CTL and neoplastically transformed cells, coupled with observations that tumor cells can modulate the intracellular, signaling domains of cell surface receptors to elicit responses quite often contrary to the expected, may even provide a way for CTL to enhance the proliferation and dedifferentiation of cancer cells. Adoptive cellular immunotherapies employing CTL raised against autologous neoplastically transformed cells in vitro should be employed in the control of minimal residual disease following surgical resection of the primary malignant growth.

Adult↗
PubMed2006

Foxp3+ CD25+ regulatory T cells specific for a neo-self-antigen develop at the double-positive thymic stage.

Thymus-derived regulatory T cells (Tregs) expressing CD4, CD25, and the transcription factor Foxp3 play major roles in preventing autoimmunity. The Treg population is enriched in T cells expressing high-avidity self-reactive T cell receptors, and thymic epithelial cells expressing self-antigens (Ag) have been implicated in their induction and/or selection. However, the thymic selection events leading to Treg lineage commitment remain unclear. We followed the thymic development of self-Ag-specific Tregs in double-transgenic mice coexpressing a neo-self-Ag, hemagglutinin (HA) under the control of a neural tissue-specific promoter, and a transgenic class II-restricted T cell antigen receptor specific for HA111-119. Our data show that the promiscuous expression of the HA transgene in thymic epithelial cells is involved in the selective induction and/or expansion of HA-specific Foxp3(+) Treg thymic precursors as early as the double-positive stage.

Animals↗
PubMed2003

Negative selection and autoimmunity.

The impaired elimination of self-reactive T cells is one factor that contributes to autoimmunity. Although the mechanism of thymic negative selection has been studied for decades, recent data demonstrate that the mechanisms underlying this fundamental process remain extremely controversial. Nonetheless, new models such as the Aire-deficient mice have demonstrated the importance of thymic negative selection in autoimmune disease progression in mice and humans.

Animals↗
PubMed2001

Specialisation of thymic epithelial cells for positive selection of CD4+8+ thymocytes.

Following their migration into the thymus, hemopoeitic stem cell precursors enter a complex developmental pathway involving proliferation, differentiation and alphabetaT-cell receptor (alphabetaTCR)-mediated selection procedures, in order to generate mature T-cell populations ready for export to the periphery. Thus, a critical stage during intrathymic T-cell development involves the generation of functionally mature CD4+8- and CD4-8+ cells from immature CD4+8- precursor thymocytes, a poorly understood process referred to as positive selection. While interactions between the alphabetaTCR and MHC-peptide complexes are known to be essential for the initiation of positive selection, additional unknown signals are also required. Using an in vitro reaggregate thymic organ culture system which allows comparison of the abilities of various cell types to induce maturation of CD4+8+ precursors, we provide evidence that both MHC-peptide complexes and specialised accessory molecules must be provided by thymic epithelium for efficient mediation of positive selection. Moreover, analysis of positive selection in the presence of thymic and non-thymic stromal cells expressing MHC class II molecules with the same limited peptide array suggests that this unique ability of thymic epithelium to mediate positive selection of CD4+8- cells is not solely due to presentation of a specialised peptide repertoire, but is dependent upon provision of specialised accessory interactions.

Animals↗
PubMed2006

Agonist ligands expressed by thymic epithelium enhance positive selection of regulatory T lymphocytes from precursors with a normally diverse TCR repertoire.

CD4+CD25+ regulatory T lymphocytes play a crucial role in inhibition of autoimmune pathology. In accordance with this physiological role, it is now well established that the repertoire of these lymphocytes is strongly enriched in autospecific cells. However, despite extensive investigation, the thymic mechanisms involved in development of regulatory T cells remain incompletely defined. To address the issue of selection of regulatory T cell precursors in mice with a naturally diverse TCR repertoire, we have analyzed development of superantigen-specific regulatory T cells in hemopoietic chimeras in which endogenous super-antigens are exclusively presented by thymic epithelial cells. Our results demonstrate that recognition of agonist ligands expressed by thymic epithelium does not lead to deletion but substantially enhances development of mature regulatory T cells. Interestingly, also development of a small subpopulation of CD25-expressing T cells lacking expression of the transcription factor Foxp3, thought to be autospecific, is enhanced by expression of the agonist ligand on thymic epithelium. Based on quantitative arguments, we propose that commitment to the regulatory T cell lineage is not dictated by the specificity of precursors, but that recognition of the agonist ligand expressed by thymic epithelium substantially enhances their positive selection.

Animals↗
PubMed2003

AIRE-1 (autoimmune regulator type 1) as a regulator of the thymic induction of negative selection.

The monogenic autoimmune syndrome, APS-1 (autoimmune polyglandular syndrome type 1), is characterized by the loss of self-tolerance to multiple organs. Although mutations in the AIRE (autoimmune regulator) gene are responsible for the APS-1, the function of AIRE is not known. AIRE may determine thymic induction of tolerance to self-antigens in multiple organs. To study the function of AIRE in induction of self-tolerance, an in vitro negative selection system was made using 10(6) DO11.10 TCR transgenic thymocytes, 10(5) antigen-presenting cells (APC), and the different constructs of ovalbumin (OVA). In this system, the addition of the immunodominant epitopes of OVA peptide, the antigenic ligand for the DO11.10, made the thymocytes apoptotic and negatively selected. Overexpression of the AIRE gene in APC using retroviral transduction did not cause more thymocytes to become apoptotic. However, the suppression of the expression of AIRE in APC using the dominant-negative gene made the recovery rates of the thymocytes higher than those with the expression of LacZ as a control, and consequently inducing loss of self-tolerance. From these studies, it might be possible to suggest that the AIRE gene might regulate thymic induction of the negative selection process. The target genes for transcriptional regulation by AIRE have been investigated to study the influence of AIRE expression on other proteins in antigen presentation. The expression level of B7.1 was higher in APC expressing the dominant-negative form of AIRE. The target gene regulated by AIRE in transcription will be screened using cDNA microarray.

Animals↗
PubMed1990

Cell generation within human thymic subsets defined by selective expression of CD45 (T200) isoforms.

Although the thymus is the source of all mature peripheral T lymphocytes, the majority of thymocytes die intrathymically. Until recently, there has been no phenotypic marker to allow definition of the generative thymocyte lineage, thereby distinguishing those thymocytes committed to death from those which will eventually give rise to thymic emigrants. We believe that expression of the high-molecular-mass isoforms (p190, p205, and/or p220) of the leukocyte common antigen (CD45) distinguishes the thymic generative lineage from the vast majority of thymocytes expressing the low-molecular-mass isoform (p180) of CD45 and committed to die within the thymus. The thymocytes defined by their lack of CD45 p180, the low-molecular-mass isoform, comprise all thymocytes with clonogenic potential and include all major subsets defined by CD4 and CD8. We have proposed that a CD45 p180- lineage exists in the human thymus and that this lineage results in the production of mature thymocytes and thymic emigrants. The objective of the present study was to determine by DNA analysis whether the degree of cell cycling in subsets of human thymus, defined by selective expression of high-molecular-mass isoforms of CD45, was sufficient to account for the generation of thymic emigrants. Multicolor immunofluorescence analysis of surface markers and 7-amino actinomycin D as well as propidium iodide staining was used to measure the DNA content of thymic subsets. Negative depletion methods were used to isolate and characterize human thymocyte subsets defined by CD45 isoform, CD3, CD4, and CD8, and subsequently to determine the cell cycle status of the isolated subsets by flow-cytometric analysis of cellular DNA content. CD3-/lo thymocytes had a high number and CD1-/lo thymocytes a low number of cycling cells, consistent with murine data. CD45 p180- cells, as well as the CD4-(8-) and CD3-(4-)(8-) subsets, which express high molecular-weight CD45 isoforms, exhibited a significant number of cycling cells. Since CD45 p180- thymocytes exhibited a significant number of cycling cells, based on numerical arguments we conclude that this cycling thymocyte fraction is capable of generating the daily requirement of mature thymocytes and thymic emigrants.

Adolescent↗
PubMed1996

Peripheral tolerance of CD4 T cells following local activation in adolescent mice.

In addition to thymic T cell selection, post-thymic mechanisms of tolerance induction are required to eliminate autoreactive T cells with specificities for peripheral self antigens. While CD8+ T cells can recognize their target antigen on a wide variety of cell types, CD4+ T cells generally depend on the presence of specialized antigen-presenting cells. Because of this fundamental difference in antigen recognition peripheral tolerance of CD4+ T cells appears more difficult to achieve than of CD8+ T cells. Utilizing T cell receptor (TCR)-transgenic mice in which CD4+ T cells specific for a pancreatic beta cell neoantigen (the simian virus 40 T antigen) are constantly generated at low frequency, we have now established a mouse model of peripheral, tissue-specific CD4+ T cell tolerance. In these animals, tolerance is preceded by a phase of activation of the autoreactive T cells as characterized by up-regulation of CD69 and CD44, and down-regulation of the L-selectin lymph node homing receptor. T antigen-specific T cells bearing this phenotype can be detected in the local lymphoid environment of the pancreas but not in more remote locations like axillary or inguinal lymph nodes. The proportion of activated, autoreactive T cells is maximal at 2-3 weeks of age, after which these cells are gradually deleted from the peripheral lymphocyte pool. We further demonstrate that deletion of the autoreactive T cells does not occur in TCR-transgenic mice bred to the RAG-1-deficient background in which the transgenic T cells represent the only functional lymphocyte population.

Animals↗
PubMed1999

Negative selection of T cells occurs throughout thymic development.

Thymic positive and negative selections govern the development of a self-MHC-reactive, yet self-tolerant, T cell repertoire. Whether these processes occur independently or sequentially remains controversial. To investigate these issues, we have employed tetrameric peptide-MHC complexes to fluorescently label and monitor polyclonal populations of thymocytes that are specific for moth cytochrome c (MCC)/I-Ek. In TCR beta mice tetramer-positive thymocytes are detectable even in the most immature TCR-expressing cells. In the presence of MCC peptide, thymocytes that bind strongly to MCC/I-Ek tetramers are deleted earlier in development and more extensively than cells that bind weakly. This negative selection of the MCC/I-Ek-specific cells occurs continuously throughout development and before any evidence of positive selection. Thus, positive and negative selections are independent processes that need not occur sequentially.

Amino Acid Sequence↗
PubMed2003

Negative selection imparts peptide specificity to the mature T cell repertoire.

The T cell alphabeta receptor (TCR) recognizes foreign peptide antigens bound to proteins encoded in the MHC. The MHC portion of this complex contributes much to the footprint of the TCR on the ligand, yet T cells are usually very specific for individual foreign peptides. Here, we show that the development of peptide-specific T cells is not intrinsic to thymocytes that undergo thymic-positive selection but is an outcome of eliminating, through negative selection, thymocytes bearing TCRs with extensive peptide cross-reactivity. Hence, thymic-negative selection imposes peptide specificity on the mature T cell repertoire.

Amino Acid Sequence↗
PubMed1995

Essential role for ZAP-70 in both positive and negative selection of thymocytes.

During thymic development, T cells that can recognize foreign antigen in association with self major histocompatibility complex (MHC) are selected for survival (positive selection) and autoreactive T cells are eliminated (negative selection). Both of these selective events are mediated by interaction between the T-cell receptor (TCR) and the peptide-MHC complex. But the signalling pathways that lead to cell survival or to cell death are still unclear. ZAP-70 is a protein tyrosine kinase (PTK) that is associated with the TCR signalling subunits (CD3 and zeta) and is expressed in T cells and natural killer cells. It has been shown that ZAP-70 plays a crucial role in T-cell activation and development. Here we show that mice lacking ZAP-70 had neither CD4 nor CD8 single-positive T cells, but human ZAP-70 reconstituted both CD4 and CD8 single-positive populations. Moreover, ZAP-70-/- thymocytes were not deleted by peptide antigens. Natural killer cell function was intact in the absence of ZAP-70. These data suggest that ZAP-70 is a central signalling molecule during thymic selection for CD4 and CD8 lineage.

Animals↗
PubMed1993

Reduction of leaky lymphocyte clones producing immunoglobulins and thymic lymphocytic leukemia by selective inbreeding of SCID (severe combined immunodeficiency) mice.

Selective inbreeding of C.B17-scid/scid mouse pairs showing undetectable IgG and IgM has been carried out in order to reduce the mortality of mice by early occurrence of thymic lymphocytic leukemia and abnormal lymphocyte clones producing immunoglobulins, both of which inhibit the successful heterotransplantation of normal and neoplastic human tissues. Although the majority of C.B17-scid/scid mice showed undetectable (< 1 microgram/ml) or low level (< or = 25 micrograms/ml) of serum IgG and IgM, some produced abnormally high concentrations of IgG and IgM (> 25 micrograms/ml). The incidence of such mice showing higher levels of IgG was very high at F1 and F2 generation (10/55, 18.2%), but significantly low after the F3 generation (18/446, 4.0%, p << 0.001). Although leukemia incidence was very high at F4 to F5 generations (8/40, 20.0%), death from leukemia was not observed early in life (4-6 months after birth) at F7 to F10 generations (0/36, 0%, p < 0.01) and was very low during the age of 6-10 months after the F8 generation (11/66, 16.7% at F4 and F5 vs 4/93, 4.3% at F8-10), p < 0.01). Scid mice improved by the selective inbreeding will provide an invaluable experimental system for the heterotransplantation of normal and neoplastic human tissues.

Animals↗
PubMed1999

In vivo T-lymphocyte tolerance in the absence of thymic clonal deletion mediated by hematopoietic cells.

Thymic negative selection renders the developing T-cell repertoire tolerant to self-major histocompatability complex (MHC)/peptide ligands. The major mechanism of induction of self-tolerance is thought to be thymic clonal deletion, ie, the induction of apoptotic cell death in thymocytes expressing a self-reactive T-cell receptor. Consistent with this hypothesis, in mice deficient in thymic clonal deletion mediated by cells of hematopoietic origin, a twofold to threefold increased generation of mature thymocytes has been observed. Here we describe the analysis of the specificity of T lymphocytes developing in the absence of clonal deletion mediated by hematopoietic cells. In vitro, targets expressing syngeneic MHC were readily lysed by activated CD8(+) T cells from deletion-deficient mice. However, proliferative responses of T cells from these mice on activation with syngeneic antigen presenting cells were rather poor. In vivo, deletion-deficient T cells were incapable of induction of lethal graft-versus-host disease in syngeneic hosts. These data indicate that in the absence of thymic deletion mediated by hematopoietic cells functional T-cell tolerance can be induced by nonhematopoietic cells in the thymus. Moreover, our results emphasize the redundancy in thymic negative selection mechanisms.

Animals↗