scholarly journals Quantitative Impact of Thymic Clonal Deletion on the T Cell Repertoire

1997 ◽  
Vol 185 (3) ◽  
pp. 377-384 ◽  
Author(s):  
Joost P.M. van Meerwijk ◽  
Samuel Marguerat ◽  
Rosemary K. Lees ◽  
Ronald N. Germain ◽  
B.J. Fowlkes ◽  
...  
Keyword(s):  
Positive Selection ◽  
Negative Selection ◽  
De Novo ◽  
Thymic Epithelial Cells ◽  
Cell Repertoire ◽  
Clonal Deletion ◽  
Mhc Molecules ◽  
Specific Receptors ◽  
Bone Marrow Chimeras ◽  
Quantitative Impact

Interactions between major histocompatibility complex (MHC) molecules expressed on stromal cells and antigen-specific receptors on T cells shape the repertoire of mature T lymphocytes emerging from the thymus. Some thymocytes with appropriate receptors are stimulated to undergo differentiation to the fully mature state (positive selection), whereas others with strongly autoreactive receptors are triggered to undergo programmed cell death before completing this differentiation process (negative selection). The quantitative impact of negative selection on the potentially available repertoire is currently unknown. To address this issue, we have constructed radiation bone marrow chimeras in which MHC molecules are present on radioresistant thymic epithelial cells (to allow positive selection) but absent from radiosensitive hematopoietic elements responsible for negative selection. In such chimeras, the number of mature thymocytes was increased by twofold as compared with appropriate control chimeras. This increase in steady-state numbers of mature thymocytes was not related to proliferation, increased retention, or recirculation and was accompanied by a similar two- to threefold increase in the de novo rate of generation of mature cells. Taken together, our data indicate that half to two-thirds of the thymocytes able to undergo positive selection die before full maturation due to negative selection.

scholarly journals Clonal deletion induced by either radioresistant thymic host cells or lymphohemopoietic donor cells at different stages of class I-restricted T cell ontogeny.

1992 ◽  
Vol 175 (5) ◽  
pp. 1277-1283 ◽  
Author(s):  
D E Speiser ◽  
H Pircher ◽  
P S Ohashi ◽  
D Kyburz ◽  
H Hengartner ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Positive Selection ◽  
Negative Selection ◽  
Host Cells ◽  
Thymic Epithelial Cells ◽  
Clonal Deletion ◽  
Mhc Molecules ◽  
Donor Cells ◽  
Self Antigens

Major histocompatibility complex (MHC) products and self-antigens expressed in the thymus determine the repertoire of mature alpha/beta T cells. While positive selection of self-MHC-restricted T cells is directed by MHC molecules expressed by thymic epithelial cells, negative selection depends to a large extent on self-antigens presented by lymphohemopoietic cells. However, radioresistant components of the thymus also influence negative selection, but it remains controversial whether this is accomplished by clonal deletion, clonal anergy, or other mechanisms. In this study, T cell development in mice expressing a transgenic T cell receptor (TCR) specific for lymphocytic choriomeningitis virus (LCMV) plus H-2Db was analyzed in the presence or absence of the viral antigen. A novel approach to analyze the thymic tissue requirements for negative selection was possible by comparing thymocyte selection in H-2Db versus H-2Dbm13 mice, since the latter allowed positive selection but not LCMV-specific deletion of transgenic TCR-expressing thymocytes. In irradiation bone marrow chimeras expressing the restriction element for negative selection (H-2Db) on host tissue, we show that radioresistant recipient cells in the thymus deleted developing T cells at an early stage of differentiation. In contrast, chimeras expressing H-2Db on lymphohemopoietic donor cells showed clonal deletion at a later stage during ontogeny.

scholarly journals B7-CD28 co-stimulation modulates central tolerance via thymic clonal deletion and Treg generation through distinct mechanisms

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Masashi Watanabe ◽  
Ying Lu ◽  
Michael Breen ◽  
Richard J. Hodes
Keyword(s):  
Treg Cell ◽  
Specific Antigen ◽  
Cell Generation ◽  
Thymic Epithelial Cells ◽  
T Cell Repertoire ◽  
Cellular Mechanisms ◽  
Cell Repertoire ◽  
Clonal Deletion ◽  
Central Tolerance ◽  
Antigen Presenting

AbstractThe molecular and cellular mechanisms mediating thymic central tolerance and prevention of autoimmunity are not fully understood. Here we show that B7-CD28 co-stimulation and B7 expression by specific antigen-presenting cell (APC) types are required for clonal deletion and for regulatory T (Treg) cell generation from endogenous tissue-restricted antigen (TRA)-specific thymocytes. While B7-CD28 interaction is required for both clonal deletion and Treg induction, these two processes differ in their CD28 signaling requirements and in their dependence on B7-expressing dendritic cells, B cells, and thymic epithelial cells. Meanwhile, defective thymic clonal deletion due to altered B7-CD28 signaling results in the accumulation of mature, peripheral TRA-specific T cells capable of mediating destructive autoimmunity. Our findings thus reveal a function of B7-CD28 co-stimulation in shaping the T cell repertoire and limiting autoimmunity through both thymic clonal deletion and Treg cell generation.

scholarly journals Thymic negative selection is functional in NOD mice

2012 ◽  
Vol 209 (3) ◽  
pp. 623-637 ◽  
Author(s):  
Michael Mingueneau ◽  
Wenyu Jiang ◽  
Markus Feuerer ◽  
Diane Mathis ◽  
Christophe Benoist
Keyword(s):  
Genetic Variation ◽  
Negative Selection ◽  
Biochemical Analysis ◽  
Large Fraction ◽  
Nod Mice ◽  
Double Positive ◽  
Clonal Deletion ◽  
Nonobese Diabetic ◽  
Early Expression ◽  
Bone Marrow Chimeras

Based on analyses of multiple TCR transgenic (tg) models, the emergence of pathogenic T cells in diabetes-prone NOD mice has been ascribed to a failure to censure autoreactive clones in the thymus. In contrast, using isolated and preselected thymocytes, we show that nonobese diabetic (NOD) genetic variation impairs neither clonal deletion nor downstream transcriptional programs. However, we find that NOD genetic variation influences αβ/γδ-lineage decisions promoted by early expression of tg αβ-TCRs at the double-negative (DN) stage. In B6 and other genetic backgrounds, tg αβ-TCRs behave like γδ-TCRs and commit a large fraction of DNs toward the γδ-lineage, thereby decreasing the size of the double-positive (DP) pool, which is efficiently positively and negatively selected. In NOD DNs, αβ-TCR signalosomes instead behave like pre-TCRs, resulting in high numbers of DPs competing for limited selection niches, and poor positive and negative selection. Once niche effects are neutralized in mixed bone marrow chimeras, positive and negative selection are equally efficient on B6 and NOD backgrounds. Biochemical analysis revealed a selective defect in the activation of Erk1/2 downstream of NOD αβ-TCR signalosomes. Therefore, NOD genetic variation influences αβ/γδ-lineage decisions when the αβ-TCR heterodimer is prematurely expressed, but not the process of negative selection.

scholarly journals Selection bias in mutation accumulation

2021 ◽  
Author(s):  
Lindi M Wahl ◽  
Deepa Agashe
Keyword(s):  
Positive Selection ◽  
Negative Selection ◽  
De Novo ◽  
Mutation Accumulation ◽  
Microbial Populations ◽  
Single Individual ◽  
Deleterious Mutations ◽  
De Novo Mutations ◽  
Fitness Effects ◽  
Wide Range

Mutation accumulation (MA) experiments, in which de novo mutations are sampled and subsequently characterized, are an essential tool in understanding the processes underlying evolution. In microbial populations, MA protocols typically involve a period of population growth between severe bottlenecks, such that a single individual can form a visible colony. While it has long been appreciated that the action of positive selection during this growth phase cannot be eliminated, it is typically assumed to be negligible. Here, we quantify the effect of both positive and negative selection in MA studies, demonstrating that selective effects can substantially bias the distribution of fitness effects (DFE) and mutation rates estimated from typical MA protocols in microbes. We then present a simple correction for this bias which applies to both beneficial and deleterious mutations, and can be used to correct the observed DFE in multiple environments. Finally, we use simulated MA experiments to illustrate the extent to which the MA-inferred DFE differs from the underlying true DFE, and demonstrate that the proposed correction accurately reconstructs the true DFE over a wide range of scenarios. These results highlight that positive selection during microbial MA experiments is in fact not negligible, but can be corrected to gain a more accurate understanding of fundamental evolutionary parameters.

In Vivo T-Lymphocyte Tolerance in the Absence of Thymic Clonal Deletion Mediated by Hematopoietic Cells

Blood ◽  
1999 ◽  
Vol 93 (11) ◽  
pp. 3856-3862 ◽  
Author(s):  
Joost P.M. van Meerwijk ◽  
H. Robson MacDonald
Keyword(s):  
T Cells ◽  
T Cell ◽  
Negative Selection ◽  
Apoptotic Cell ◽  
Hematopoietic Cells ◽  
Cell Receptor ◽  
Cell Repertoire ◽  
Clonal Deletion

Abstract 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.

scholarly journals Macroautophagy substrates are loaded onto MHC class II of medullary thymic epithelial cells for central tolerance

2013 ◽  
Vol 210 (2) ◽  
pp. 287-300 ◽  
Author(s):  
Martin Aichinger ◽  
Chunyan Wu ◽  
Jelena Nedjic ◽  
Ludger Klein
Keyword(s):  
Epithelial Cells ◽  
Mhc Class Ii ◽  
Negative Selection ◽  
Class Ii ◽  
Single Amino Acid ◽  
Thymic Epithelial Cells ◽  
Clonal Deletion ◽  
Central Tolerance ◽  
Metabolic Functions ◽  
Physiological Relevance

Macroautophagy serves cellular housekeeping and metabolic functions through delivery of cytoplasmic constituents for lysosomal degradation. In addition, it may mediate the unconventional presentation of intracellular antigens to CD4+ T cells; however, the physiological relevance of this endogenous MHC class II loading pathway remains poorly defined. Here, we characterize the role of macroautophagy in thymic epithelial cells (TECs) for negative selection. Direct presentation for clonal deletion of MHC class II–restricted thymocytes required macroautophagy for a mitochondrial version of a neo-antigen, but was autophagy-independent for a membrane-bound form. A model antigen specifically expressed in Aire+ medullary TECs (mTECs) induced efficient deletion via direct presentation when targeted to autophagosomes, whereas interference with autophagosomal routing of this antigen through exchange of a single amino acid or ablation of an essential autophagy gene abolished direct presentation for negative selection. Furthermore, when this autophagy substrate was expressed by mTECs in high amounts, endogenous presentation and indirect presentation by DCs operated in a redundant manner, whereas macroautophagy-dependent endogenous loading was essential for clonal deletion at limiting antigen doses. Our findings suggest that macroautophagy supports central CD4+ T cell tolerance through facilitating the direct presentation of endogenous self-antigens by mTECs.

scholarly journals Self-mediated positive selection of T cells sets an obstacle to the recognition of nonself

2021 ◽  
Vol 118 (37) ◽  
pp. e2100542118
Author(s):  
Balázs Koncz ◽  
Gergő M. Balogh ◽  
Benjamin T. Papp ◽  
Leó Asztalos ◽  
Lajos Kemény ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
Epithelial Cells ◽  
Positive Selection ◽  
Thymic Epithelial Cells ◽  
Immune Recognition ◽  
T Cell Repertoire ◽  
Cell Repertoire ◽  
Adaptive Immune ◽  
Selection Of

Adaptive immune recognition is mediated by the binding of peptide–human leukocyte antigen complexes by T cells. Positive selection of T cells in the thymus is a fundamental step in the generation of a responding T cell repertoire: only those T cells survive that recognize human peptides presented on the surface of cortical thymic epithelial cells. We propose that while this step is essential for optimal immune function, the process results in a defective T cell repertoire because it is mediated by self-peptides. To test our hypothesis, we focused on amino acid motifs of peptides in contact with T cell receptors. We found that motifs rarely or not found in the human proteome are unlikely to be recognized by the immune system just like the ones that are not expressed in cortical thymic epithelial cells or not presented on their surface. Peptides carrying such motifs were especially dissimilar to human proteins. Importantly, we present our main findings on two independent T cell activation datasets and directly demonstrate the absence of naïve T cells in the repertoire of healthy individuals. We also show that T cell cross-reactivity is unable to compensate for the absence of positively selected T cells. Additionally, we show that the proposed mechanism could influence the risk for different infectious diseases. In sum, our results suggest a side effect of T cell positive selection, which could explain the nonresponsiveness to many nonself peptides and could improve the understanding of adaptive immune recognition.

scholarly journals An essential role for gp39, the ligand for CD40, in thymic selection.

1995 ◽  
Vol 182 (5) ◽  
pp. 1377-1388 ◽  
Author(s):  
T M Foy ◽  
D M Page ◽  
T J Waldschmidt ◽  
A Schoneveld ◽  
J D Laman ◽  
...  
Keyword(s):  
T Cell ◽  
Negative Selection ◽  
Costimulatory Molecule ◽  
Immunohistochemical Analysis ◽  
Cell Receptor ◽  
Thymic Epithelial Cells ◽  
High Dose ◽  
Cell Repertoire ◽  
Endogenous Expression ◽  
Staphylococcus Enterotoxin B

The interactions between CD40 on B cells and its ligand gp39 on activated T helper cells are known to be essential for the development of thymus-dependent humoral immunity. However, CD40 is also functionally expressed on thymic epithelial cells and dendritic cells, suggesting that gp39-CD40 interactions may also play a role in thymic education, the process by which self-reactive cells are deleted from the T cell repertoire. Six systems of negative selection were studied for their reliance on gp39-CD40 interactions to mediate negative selection. In all cases, when the antigen/superantigen was endogenously expressed (in contrast to exogenously administered), negative selection was blocked by loss of gp39 function. Specifically, blockade of gp39-CD40 interactions prevented the deletion of thymocytes expressing V beta 3, V beta 11, and V beta 12, specificities normally deleted in BALB/c mice because of the endogenous expression of minor lymphocyte-stimulating determinants. Independent verification of a role of gp39 in negative selection was provided by studies in gp39-deficient mice where alterations in T cell receptor (TCR) V beta expression were also observed. Studies were also performed in the AND TCR transgenic (Tg) mice, which bear the V alpha 11, V beta 3 TCR and recognize both pigeon cytochrome c (PCC)/IEk and H-2As. Neonatal administration of anti-gp39 to AND TCR Tg mice that endogenously express H-2As or endogenously produce PCC prevented the deletion of TCR Tg T cells. In contrast, deletion mediated by high-dose PCC peptide antigen (administered exogenously) in AND TCR mice was unaltered by administration of anti-gp39. In addition, deletion by Staphylococcus enterotoxin B in conventional mice was also unaffected by anti-gp39 administration. gp39 expression was induced on thymocytes by mitogens or by antigen on TCR Tg thymocytes. Immunohistochemical analysis of B7-2 expression in the thymus indicated that, in the absence of gp39, B7-2 expression was substantially reduced. Taken together, these data suggest that gp39 may influence negative selection through the regulation of costimulatory molecule expression. Moreover, the data support the hypothesis that, for negative selection to some endogenously produced antigens, negative selection may be dependent on TCR engagement and costimulation.

scholarly journals Thymic selection and cell division.

1995 ◽  
Vol 182 (4) ◽  
pp. 961-971 ◽  
Author(s):  
B Ernst ◽  
C D Surh ◽  
J Sprent
Keyword(s):  
Cell Division ◽  
T Cell ◽  
Positive Selection ◽  
High Rate ◽  
Thymic Epithelial Cells ◽  
Thymic Selection ◽  
Double Positive ◽  
Cell Repertoire ◽  
Single Positive ◽  
Blast Cells

Cell division during thymic selection was studied with a system in which purified populations of T cell antigen receptor (TCR)- CD4+8+ (double-positive [DP]) cells and fetal thymic epithelial cells (TEC) were reaggregated in tissue culture. In this system, immature DP cells differentiate into mature single-positive (SP) CD4+8- and CD4-8+ TCRhi cells within 3-4 d, indicative of positive selection. By adding the DNA precursor, bromodeoxyuridine, to the cultures and staining cells for bromodeoxyuridine incorporation, T cell division in reaggregation cultures was found to be high on day 1, low on day 2, and high on days 4-5. Cell separation studies established that cell division on day 1 was restricted to DP blast cells. In the absence of blast cells, small DP cells failed to proliferate and differentiated into SP cells without cell division, thus indicating that proliferation is not an essential component of positive selection. This applied to SP cells generated within the first 2-3 d. Surprisingly, the SP cells generated later in culture showed a high rate of cell division; the proliferating SP cells were TCRhi and included both CD4+8- and CD4-8+ cells. Turnover of TCRhi SP cells was also prominent in the normal neonatal thymus and in TEC reaggregation cultures prepared with adult lymph node T cells. We speculate that division of mature SP cells in the perinatal thymic microenvironment is driven by stimulatory cytokines released from TEC. Such proliferation could be a device to expand the mature T cell repertoire before export to the periphery.

scholarly journals Developmental regulation of thymocyte susceptibility to deletion by "self"-peptide.

1992 ◽  
Vol 176 (1) ◽  
pp. 213-223 ◽  
Author(s):  
L M Spain ◽  
L J Berg
Keyword(s):  
Cytochrome C ◽  
Organ Culture ◽  
Positive Selection ◽  
Negative Selection ◽  
Developmental Timing ◽  
Organ Cultures ◽  
Peptide Antigen ◽  
C Peptide ◽  
Mhc Molecules

The specificity of the T cell receptor (TCR) repertoire for foreign peptide bound to self-major histocompatibility complex (MHC) molecules is determined in large part by positive and negative selection processes in the thymus, yet the mechanisms of these selection events remain unknown. Using in vitro organ culture of thymi isolated from mice transgenic for a TCR-alpha/beta specific for cytochrome c peptide bound to I-Ek, we analyzed the developmental timing of negative selection (deletion). On the basis of the experiments described below, we conclude that all CD4+8+ thymocytes, and only CD4+8+ thymocytes, are susceptible to negative selection mediated by the cytochrome c peptide antigen. First, we found that deletion of thymocytes resulting from addition of the cytochrome c peptide to the thymic organ cultures can occur at the earliest stage of TCR, CD4, and CD8 coexpression. Second, we found that CD4+8+ thymocytes isolated from positively selecting or nonselecting MHC haplotypes were equally efficiently deleted in vitro, suggesting that positive selection is not a prerequisite for deletion. Third, we examined the effects of TCR/ligand avidity on the developmental timing of deletion by varying the concentration of cytochrome c peptide added to the organ cultures. We detected deletion only at the CD4+8+ stage: intermediate concentrations of peptide that resulted in partial deletion of CD4+8+ cells did not eliminate the appearance of mature CD4+8- cells. Finally, we found that CD4+8- thymocytes were resistant to deletion as well as activation by peptide antigen added to the intact organ cultures. Nevertheless, the CD4+8- thymocytes isolated from the peptide-treated organ cultures responded vigorously to peptide presented by spleen cells in vitro. Thus, the T cells were tolerant of (but not anergized by) self-antigen encountered in thymic organ culture. Together, these results indicate that thymocytes susceptible to negative selection are not developmentally distinct from those susceptible to positive selection, and further, that the thymic microenvironment plays a role in regulating the outcome of TCR/ligand interactions.

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