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 109 records · Page 6Linked to original sources
PubMed2006

Thymic selection threshold defined by compartmentalization of Ras/MAPK signalling.

A healthy individual can mount an immune response to exogenous pathogens while avoiding an autoimmune attack on normal tissues. The ability to distinguish between self and non-self is called 'immunological tolerance' and, for T lymphocytes, involves the generation of a diverse pool of functional T cells through positive selection and the removal of overtly self-reactive thymocytes by negative selection during T-cell ontogeny. To elucidate how thymocytes arrive at these cell fate decisions, here we have identified ligands that define an extremely narrow gap spanning the threshold that distinguishes positive from negative selection. We show that, at the selection threshold, a small increase in ligand affinity for the T-cell antigen receptor leads to a marked change in the activation and subcellular localization of Ras and mitogen-activated protein kinase (MAPK) signalling intermediates and the induction of negative selection. The ability to compartmentalize signalling molecules differentially in the cell endows the thymocyte with the ability to convert a small change in analogue input (affinity) into a digital output (positive versus negative selection) and provides the basis for establishing central tolerance.

Animals↗
PubMed2006

A conformational change senses the strength of T cell receptor-ligand interaction during thymic selection.

T cell antigen receptor (TCR) triggering determines the fate of immature thymocytes. The affinity of the TCR for its endogenous peptide/MHC ligands serves as a signal for positive or negative selection through mechanisms that are still little understood. We have used a conformation-specific antibody to demonstrate that recognition of TCR ligands that lead to negative selection induces a conformational change in the TCR in situ. In contrast, this conformational change is elicited in only a small percentage of immature thymocytes during positive selection. Using a TUNEL assay, we demonstrate that the conformational change in the TCR is strongly linked to activation of programmed cell death in conditions leading to negative selection. Furthermore, the few conformational change-positive thymocytes detected in conditions that preferably lead to positive selection are also TUNEL-positive. Thus, the conformational change in the TCR may underlie the discrimination of ligands leading to positive and negative selection.

Animals↗
PubMed1994

Thymic selection of CD8+ single positive cells with a class II major histocompatibility complex-restricted receptor.

We describe mice that express a transgenic T cell receptor alpha/beta (TCR-alpha/beta) specific for peptide 111-119 from influenza hemagglutinin presented by I-Ed class II major histocompatibility complex (MHC) molecules. The transgenic TCR is expressed on CD4+8- as well as CD4-8+ mature T cells even in mice that are deficient in rearrangement or do not express endogenous TCR-alpha genes. The CD4-8+ T cells require I-Ed class II MHC molecules for positive selection and can be activated to proliferate and to kill by I-Ed molecules presenting the relevant peptide. Full maturation of these cells, however, also requires the presence of class I MHC molecules. The results are compatible with the notion that T cell maturation requires multiple receptor-ligand interactions and establish an exception to the rule that class II-restricted TCRs are exclusively expressed by mature CD4+8- cells.

Animals↗
PubMed1996

Requirement for p56lck tyrosine kinase activation in T cell receptor-mediated thymic selection.

The nonreceptor protein tyrosine kinase p56lck (Lck) serves as a fundamental regulator of thymocyte development by delivering signals from the pre-T cell receptor (pre-TCR) that permit subsequent maturation. However, considerable evidence supports the view that Lck also participates in signal transduction from the mature TCR. We have tested this conjecture by expressing a dominant-negative form of Lck under the control of a promoter element (the distal lck promoter) that directs high expression in CD4+CD8+ thymocytes, mature thymocytes, and peripheral T cells, thereby avoiding, complications that result from the well-documented ability of dominant-negative Lck to block very early events in thymocyte maturation. Here we report that expression of the catalytically inactive Lck protein at twice normal concentrations inhibits thymocyte positive selection by as much as 80%, while leaving other aspects of cell maturation intact. This effect was studied in more detail in mice simultaneously bearing the male-specific H-Y alpha/beta TCR transgene and ovalbumin-specific DO10 alpha/beta TCR transgene, where even equimolar expression of the dominant-negative Lck protein substantially vitiated the positive selection process. Although deletion of H-Y alpha/beta thymocytes proceeded normally in male mice despite the presence of catalytically inactive Lck, modest inhibition of superantigen-mediated deletion was in some cases observed. These data further implicate Lck in the propagation of all TCR-derived signals, and indicate that even very modest deficiencies in the representation of functional Lck molecules could in humans, profoundly alter the character of the peripheral TCR repertoire.

Animals↗
PubMed1997

Asynchronous coreceptor downregulation after positive thymic selection: prolonged maintenance of the double positive state in CD8 lineage differentiation due to sustained biosynthesis of the CD4 coreceptor.

In several experimental systems analyzing the generation of single positive (SP) thymocytes from double positive (DP) thymocytes, CD4 SP cells have been shown to appear before CD8 SP cells. This apparent temporal asymmetry in the maturation of CD4 SP and CD8 SP thymocytes could either be due to divergent molecular differentiation programs of the two T cell lineages, or merely to slower degradation kinetics of the CD4 protein. To study this question in unmanipulated in vivo differentiation, we developed a four-color flow cytometry protocol which identifies a recently activated TCRintCD69pos thymocyte population containing DP cells and early CD4 SP cells but no CD8 SP cells. We show that these TCRintCD69pos thymocytes represent a transitory stage in the mainstream alphabeta T cell lineage. The precursors of the CD8 SP cells are contained in this population as incompletely selected DP cells. Moreover, we show that expression of both coreceptors in the TCRintCD69pos population depends on transcriptional and translational activity, thus excluding differences in turnover rates of the CD4 and CD8 proteins as the cause of the asynchrony in differentiation of the CD4 and CD8 lineages.

Animals↗
PubMed1998

Modulation of thymic selection by expression of an immediate-early gene, early growth response 1 (Egr-1).

The potential involvement of early growth response (Egr)-1, a zinc-finger transcription factor belonging to the immediate-early genes, in positive/negative selection of thymocytes has been implicated by its expression in the population of CD4(+)CD8(+) double positive (DP) cells undergoing selection. To further investigate this possibility, transgenic mice overexpressing Egr-1 in thymocytes were bred with a transgenic mouse line expressing a T cell receptor (TCR) recognizing the H-Y male antigen in the context of H-2(b) class I major histocompatibility complex (MHC) molecules. In Egr-1/TCR H-Y double-transgenic mice, efficient positive selection of H-Y CD8(+) T cells occurred, even in mice on either a nonselecting H-2(d) background or a beta2-microglobulin (beta2m)-deficient background in which the expression of class I MHC heavy chains is extremely low; no positive selection was observed on a Kb-/-Db-/-beta2m-/- background where class I MHC expression is entirely absent. Similarly, when the Egr-1 transgene was introduced into a class II MHC-restricted TCR transgenic mouse line, Egr-1/TCR double-transgenic mice revealed increased numbers of CD4(+) T cells selected by class II MHC, as well as significant numbers of CD8(+) T cells selected by class I MHC (for which the transgenic TCR might have weak affinity). Thus, Egr-1 overexpression allows positive selection of thymocytes via TCR-MHC interactions of unusually low avidity, possibly by lowering the threshold of avidity required for positive selection. Supporting this possibility, increased numbers of alloreactive T cells were positively selected in Egr-1 transgenic mice, resulting in a strikingly enhanced response against allo-MHC. These results suggest that expression of Egr-1 and/or its target gene(s) may directly influence the thresholds required for thymocyte selection.

Animals↗
PubMed2002

Involvement of the TCR Cbeta FG loop in thymic selection and T cell function.

The asymmetric disposition of T cell receptor (TCR) Cbeta and Calpha ectodomains creates a cavity with a side-wall formed by the rigid Cbeta FG loop. To investigate the significance of this conserved structure, we generated loop deletion (betaDeltaFG) and betawt transgenic (tg) mice using the TCR beta subunit of the N15 CTL. N15betawt and N15betaDeltaFG H-2(b) animals have comparable numbers of thymocytes in S phase and manifest developmental progression through the CD4(-)CD8(-) double-negative (DN) compartment. N15betaDeltaFG facilitates transition from DN to CD4(+)8(+) double-positive (DP) thymocytes in recombinase activating gene (RAG)-2(-/-) mice, showing that pre-TCR function remains. N15betaDeltaFG animals possess approximately twofold more CD8(+) single-positive (SP) thymocytes and lymph node T cells, consistent with enhanced positive selection. As an altered Valpha repertoire observed in N15betaDeltaFG mice may confound the deletion's effect, we crossed N15alphabeta TCR tg RAG-2(-/-) with N15betaDeltaFG tg RAG-2(-/-) H-2(b) mice to generate N15alphabeta RAG-2(-/-) and N15alphabeta.betaDeltaFG RAG-2(-/-) littermates. N15alphabeta.betaDeltaFG RAG-2(-/-) mice show an 8-10-fold increase in DP thymocytes due to reduced negative selection, as evidenced by diminished constitutive and cognate peptide-induced apoptosis. Compared with N15alphabeta, N15alphabeta.betaDeltaFG T cells respond poorly to cognate antigens and weak agonists. Thus, the Cbeta FG loop facilitates negative selection of thymocytes and activation of T cells.

Amino Acid Sequence↗
PubMed1989

The nature of the immune response (Ir) gene defect for pigeon cytochrome c in [B10.A(4R) x B10.PL]F1 mice. A comparison between thymic selection and antigen presentation.

[B10.A(4R) x B10.PL]F1 mice are low responders to pigeon cytochrome c, while [B10.A(2R) x B10.PL]F1 and B10.A mice are high responders. The in vivo site at which the different allomorphs of the E alpha Ia molecule exert their Ir gene effect on the immune response to pigeon cytochrome c was examined by creating two different sets of radiation-induced bone marrow chimeras. [B10.A(4R) x B10.PL]F1(b.m.)----B10.A(irr.) chimeras, which possess antigen-presenting cells (APC) of the low responder, but whose T cells are educated in a high responder environment, were found to be low responders to pigeon cytochrome c. In contrast, B10.A(b.m.)----[B10.A(4R) x B10.PL]F1(irr.) chimeras, which possess APC of the high responder type, but whose T cells are educated in a low responder environment, responded to pigeon cytochrome c. Addition of B10.A APC to the first type of chimera, both prior to antigen priming and at the time of the secondary challenge in vitro, converted 50% of the animals to responders. Furthermore, [B10.A(4R) x B10.PL]F1 mice responded to pigeon cytochrome c if they were primed with a 10-fold greater antigen dose and restimulated in vitro in the presence of B10.A APC. These results suggest that the primary site of the Ir gene defect in this system is at the level of antigen presentation and not in the T cell repertoire.

Animals↗
PubMed1995

Thymic selection events mediated by the pre-TCR do not depend upon a limiting ligand.

Thymocyte differentiation requires the production of a functional TCR, the culmination of a carefully orchestrated series of events in which TCR beta chain gene rearrangement precedes that of TCR alpha genes. The product of a successful rearrangement of the TCR beta locus associates with an invariant protein in immature thymocytes to form the 'pre-TCR' complex, which is required for allelic exclusion at the TCR beta locus, the expression of CD4 and CD8 co-receptors, and the clonal expansion of immature thymocytes. The pivotal role for the beta chain protein during early thymocyte development led us to investigate the relative differentiation efficiency within the same thymus of cells which do and cells which do not possess productive TCR gene rearrangements. Using mixed radiation bone marrow chimeras to establish an in vivo competition between TCR beta transgenic (Tg) and non-Tg bone marrow cells, we show that the prior productive rearrangement of a TCR beta chain gene only subtly enhances the efficiency of intrathymic differentiation. Further, we have compared the relative differentiation efficiency of TCR alpha beta and TCR beta Tg cells within the mixed chimera system by altering the proportion of TCR Tg bone marrow cells in the reconstituting inoculum. As expected, Tg cells carrying both alpha and beta chains of a selectable TCR are developmentally hindered compared with their non-Tg counterparts by the lack of ample numbers of intrathymic positively selecting ligands or niches. In contrast, parallel experiments using TCR beta Tg bone marrow cells demonstrate that the early selection events mediated by the pre-TCR do not similarly depend upon a ligand present in limiting quantities.

Animals↗
PubMed1993

Thymic selection of cytotoxic T cells independent of CD8 alpha-Lck association.

The CD8 alpha cytoplasmic domain associates with p56lck, a nonreceptor protein-tyrosine kinase. The biological relevance of CD8 alpha-Lck association in T cell development was tested with transgenic mice generated to express a CD8 alpha molecule with two amino acid substitutions in its cytoplasmic domain, which abolishes the association of CD8 alpha with Lck. The CD8 alpha mutant was analyzed in a CD8-/- background and in the context of the transgenic 2C T cell receptor. The development and function of CD8+ T cells in these mice were apparently normal. Thus, CD8 alpha-Lck association is not necessary for positive selection, negative selection, or CD8-dependent cytotoxic function.

Animals↗
PubMed2001

Assays of thymic selection. Fetal thymus organ culture and in vitro thymocyte dulling assay.

The in vitro methods of FTOC and DP dulling assay have been useful for defining the structural ligand requirements for positive selection of thymocytes. Both techniques, but especially the latter, have restrictions on their interpretation, which are outlined in the notes. The ability to study a cellular process in vitro has been, and will continue to be, of critical importance for immunologists. However, one should always be careful to confirm a hypothesis using in vivo techniques, whenever possible.

Animals↗
PubMed2001

Ordered and coordinated rearrangement of the TCR alpha locus: role of secondary rearrangement in thymic selection.

The Ag receptor of the T lymphocyte is composed of an alphabeta heterodimer. Both alpha- and beta-chains are products of the somatic rearrangement of V(D)J segments encoded on the respective loci. During T cell development, beta-chain rearrangement precedes alpha-chain rearrangement. The mechanism of allelic exclusion ensures the expression of a single beta-chain in each T cell, whereas a large number of T cells express two functional alpha-chains. Here we demonstrate evidence that TCR alpha rearrangement is initiated by rearranging a 3' Valpha segment and a 5' Jalpha segment on both chromosomes. Rearrangement then proceeds by using upstream Valpha and downstream Jalpha segments until it is terminated by successful positive selection. This ordered and coordinated rearrangement allows a single thymocyte to sequentially express multiple TCRs with different specificities to optimize the efficiency of positive selection. Thus, the lack of allelic exclusion and TCR alpha secondary rearrangement play a key role in the formation of a functional T cell repertoire.

Alleles↗
PubMed1999

Immune-associated nucleotide-1 (IAN-1) is a thymic selection marker and defines a novel gene family conserved in plants.

Positive selection of thymocytes is a complex and crucial event in T cell development that is characterized by cell death rescue, commitment toward the helper or cytotoxic lineage, and functional maturation of thymocytes bearing an appropriate TCR. To search for novel genes involved in this process, we compared gene expression patterns in positively selected thymocytes and their immediate progenitors in mice using the differential display technique. This approach lead to the identification of a novel gene, mIAN-1 (murine immune-associated nucleotide-1), that is switched on upon positive selection and predominantly expressed in the lymphoid system. We show that mIAN-1 encodes a 42-kDa protein sharing sequence homology with the pathogen-induced plant protein aig1 and that it defines a novel family of at least three putative GTP-binding proteins. Analysis of protein expression at various stages of thymocyte development links mIAN-1 to CD3-mediated selection events, suggesting that it represents a key player of thymocyte development and that it participates to peripheral specific immune responses. The evolutionary conservation of the IAN family provides a unique example of a plant pathogen response gene conserved in animals.

Amino Acid Sequence↗
PubMed1992

Involvement of the same region of the T cell antigen receptor in thymic selection and foreign peptide recognition.

The Ag receptor (TCR) on T lymphocytes has been shown to be specific for foreign antigenic peptides bound to MHC-encoded molecules. During T cell differentiation in the thymus this same TCR mediates the recognition of MHC molecules in the absence of foreign Ag, a process termed positive selection. To analyze the structural relationship between MHC-restricted Ag recognition and positive selection, we characterized two different transgenic lines of mice bearing TCR specific for pigeon cytochrome c and the Ek class II MHC molecule. The two TCR expressed in these animals differed by only one amino acid in the V-J junction of the alpha-chain. In vitro, we find that this TCR difference alters Ag fine specificity. Analysis of transgenic animals demonstrates that this change in the putative third complementarity determining region of the TCR also alters the specificity of positive selection in the thymus. These results suggest that the diversity of a TCR region that can be shown to affect the specificity of foreign Ag recognition may be influenced by selection in the thymus. The findings presented here are discussed in relation to the possible role of self-peptides in positive selection.

Amino Acid Sequence↗