scholarly journals In Pursuit of Adult Progenitors of Thymic Epithelial Cells

2021 ◽  
Vol 12 ◽  
Author(s):  
Tatsuya Ishikawa ◽  
Nobuko Akiyama ◽  
Taishin Akiyama
Keyword(s):  
T Cells ◽  
Epithelial Cells ◽  
Adaptive Immune System ◽  
Thymic Epithelial Cells ◽  
Adaptive Immune ◽  
Peripheral T Cells ◽  
Robust Adaptive ◽  
Adult Thymus ◽  
Shed Light ◽  
Selection Of

Peripheral T cells capable of discriminating between self and non-self antigens are major components of a robust adaptive immune system. The development of self-tolerant T cells is orchestrated by thymic epithelial cells (TECs), which are localized in the thymic cortex (cortical TECs, cTECs) and medulla (medullary TECs, mTECs). cTECs and mTECs are essential for differentiation, proliferation, and positive and negative selection of thymocytes. Recent advances in single-cell RNA-sequencing technology have revealed a previously unknown degree of TEC heterogeneity, but we still lack a clear picture of the identity of TEC progenitors in the adult thymus. In this review, we describe both earlier and recent findings that shed light on features of these elusive adult progenitors in the context of tissue homeostasis, as well as recovery from stress-induced thymic atrophy.

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 The Role of Proteasomes in the Thymus

2021 ◽  
Vol 12 ◽  
Author(s):  
Melina Frantzeskakis ◽  
Yousuke Takahama ◽  
Izumi Ohigashi
Keyword(s):  
T Cells ◽  
Epithelial Cells ◽  
T Cell Development ◽  
Thymic Epithelial Cells ◽  
Ubiquitinated Proteins ◽  
Self Tolerance ◽  
Essential Components ◽  
Medullary Thymic Epithelial Cells ◽  
Selection Of

The thymus provides a microenvironment that supports the generation and selection of T cells. Cortical thymic epithelial cells (cTECs) and medullary thymic epithelial cells (mTECs) are essential components of the thymic microenvironment and present MHC-associated self-antigens to developing thymocytes for the generation of immunocompetent and self-tolerant T cells. Proteasomes are multicomponent protease complexes that degrade ubiquitinated proteins and produce peptides that are destined to be associated with MHC class I molecules. cTECs specifically express thymoproteasomes that are essential for optimal positive selection of CD8+ T cells, whereas mTECs, which contribute to the establishment of self-tolerance in T cells, express immunoproteasomes. Immunoproteasomes are also detectable in dendritic cells and developing thymocytes, additionally contributing to T cell development in the thymus. In this review, we summarize the functions of proteasomes expressed in the thymus, focusing on recent findings pertaining to the functions of the thymoproteasomes and the immunoproteasomes.

Promoter IV of the class II transactivator gene is essential for positive selection of CD4+ T cells

Blood ◽  
2003 ◽  
Vol 101 (9) ◽  
pp. 3550-3559 ◽  
Author(s):  
Jean-Marc Waldburger ◽  
Simona Rossi ◽  
Georg A. Hollander ◽  
Hans-Reimer Rodewald ◽  
Walter Reith ◽  
...  
Keyword(s):  
Bone Marrow ◽  
T Cells ◽  
T Cell ◽  
Epithelial Cells ◽  
Positive Selection ◽  
Negative Selection ◽  
Cd4 T Cell ◽  
Thymic Epithelial Cells ◽  
Mhcii Expression ◽  
Selection Of

Major histocompatibility complex class II (MHCII) expression is regulated by the transcriptional coactivator CIITA. Positive selection of CD4+ T cells is abrogated in mice lacking one of the promoters (pIV) of the Mhc2ta gene. This is entirely due to the absence of MHCII expression in thymic epithelia, as demonstrated by bone marrow transfer experiments between wild-type and pIV−/− mice. Medullary thymic epithelial cells (mTECs) are also MHCII− in pIV−/− mice. Bone marrow–derived, professional antigen-presenting cells (APCs) retain normal MHCII expression in pIV−/− mice, including those believed to mediate negative selection in the thymic medulla. Endogenous retroviruses thus retain their ability to sustain negative selection of the residual CD4+ thymocytes in pIV−/− mice. Interestingly, the passive acquisition of MHCII molecules by thymocytes is abrogated in pIV−/−mice. This identifies thymic epithelial cells as the source of this passive transfer. In peripheral lymphoid organs, the CD4+T-cell population of pIV−/− mice is quantitatively and qualitatively comparable to that of MHCII-deficient mice. It comprises a high proportion of CD1-restricted natural killer T cells, which results in a bias of the Vβ repertoire of the residual CD4+ T-cell population. We have also addressed the identity of the signal that sustains pIV expression in cortical epithelia. We found that the Jak/STAT pathways activated by the common γ chain (CD132) or common β chain (CDw131) cytokine receptors are not required for MHCII expression in thymic cortical epithelia.

Selection of Foxp3+ regulatory T cells specific for self antigen expressed and presented by Aire+ medullary thymic epithelial cells

2007 ◽  
Vol 8 (4) ◽  
pp. 351-358 ◽  
Author(s):  
Katharina Aschenbrenner ◽  
Louise M D'Cruz ◽  
Elisabeth H Vollmann ◽  
Maria Hinterberger ◽  
Jan Emmerich ◽  
...  
Keyword(s):  
T Cells ◽  
Epithelial Cells ◽  
Regulatory T Cells ◽  
Thymic Epithelial Cells ◽  
Medullary Thymic Epithelial Cells ◽  
Self Antigen ◽  
Selection Of

PDGFRα-expressing mesenchyme regulates thymus growth and the availability of intrathymic niches

Blood ◽  
2006 ◽  
Vol 109 (3) ◽  
pp. 954-960 ◽  
Author(s):  
William E. Jenkinson ◽  
Simona W. Rossi ◽  
Sonia M. Parnell ◽  
Eric J. Jenkinson ◽  
Graham Anderson
Keyword(s):  
T Cells ◽  
T Cell ◽  
Epithelial Cells ◽  
Growth Factor Receptor ◽  
Thymic Epithelial Cells ◽  
Thymic Tissue ◽  
Mhc Molecules ◽  
Histocompatibility Complex ◽  
Medullary Epithelial Cells ◽  
Selection Of

Abstract The thymus provides a specialized site for the production of T cells capable of recognizing foreign antigens in the context of self–major histocompatibility complex (MHC) molecules. During development, the thymus arises from an epithelial rudiment containing bipotent progenitors that differentiate into distinct cortical and medullary epithelial cells to regulate the maturation and selection of self-tolerant CD4+ and CD8+ T cells. In addition to their differentiation, thymic epithelial cells undergo cellular expansion to ensure that sufficient intrathymic cellular niches are available to support the large number of immature thymocytes required to form a self-tolerant T-cell pool. Thus, intrathymic T-cell production is intimately linked to the formation and availability of niches within thymic microenvironments. Here, we show the increase in intrathymic niches caused by the proliferation of the epithelium in the developing thymus is temporally regulated, and correlates with the presence of a population of fetal thymic mesenchyme defined by platelet-derived growth factor receptor α (PDGFRα) expression. Depletion of PDGFRα+ mesenchyme from embryonic thymi prior to their transplantation to ectopic sites results in the formation of functional yet hypoplastic thymic tissue. In summary, we highlight a specialized role for PDGFRα+ fetal mesenchyme in the thymus by determining availability of thymic niches through the regulation of thymic epithelial proliferation.

scholarly journals T Cells Limit Accumulation of Aggregate Pathology Following Intrastriatal Injection of α-Synuclein Fibrils

2021 ◽  
pp. 1-19
Author(s):  
Sonia George ◽  
Trevor Tyson ◽  
Nolwen L. Rey ◽  
Rachael Sheridan ◽  
Wouter Peelaerts ◽  
...  
Keyword(s):  
T Cells ◽  
Immune System ◽  
B Cells ◽  
Substantia Nigra ◽  
Adaptive Immune System ◽  
Proteinase K ◽  
T And B Cells ◽  
Adaptive Immune ◽  
Immunocompromised Mice ◽  
The Impact

Background: α-Synuclein (α-syn) is the predominant protein in Lewy-body inclusions, which are pathological hallmarks of α- synucleinopathies, such as Parkinson’s disease (PD) and multiple system atrophy (MSA). Other hallmarks include activation of microglia, elevation of pro-inflammatory cytokines, as well as the activation of T and B cells. These immune changes point towards a dysregulation of both the innate and the adaptive immune system. T cells have been shown to recognize epitopes derived from α-syn and altered populations of T cells have been found in PD and MSA patients, providing evidence that these cells can be key to the pathogenesis of the disease. Objective To study the role of the adaptive immune system with respect to α-syn pathology. Methods: We injected human α-syn preformed fibrils (PFFs) into the striatum of immunocompromised mice (NSG) and assessed accumulation of phosphorylated α-syn pathology, proteinase K-resistant α-syn pathology and microgliosis in the striatum, substantia nigra and frontal cortex. We also assessed the impact of adoptive transfer of naïve T and B cells into PFF-injected immunocompromised mice. Results: Compared to wildtype mice, NSG mice had an 8-fold increase in phosphorylated α-syn pathology in the substantia nigra. Reconstituting the T cell population decreased the accumulation of phosphorylated α-syn pathology and resulted in persistent microgliosis in the striatum when compared to non-transplanted mice. Conclusion: Our work provides evidence that T cells play a role in the pathogenesis of experimental α-synucleinopathy.

scholarly journals Functionally specialized human CD4+ T-cell subsets express physicochemically distinct TCRs

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Sofya A Kasatskaya ◽  
Kristin Ladell ◽  
Evgeniy S Egorov ◽  
Kelly L Miners ◽  
Alexey N Davydov ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
T Cell Receptors ◽  
Adaptive Immune System ◽  
T Cell Subsets ◽  
Effector Memory ◽  
Intrinsic Properties ◽  
Antigen Specificity ◽  
Adaptive Immune ◽  
Transition Pathways

The organizational integrity of the adaptive immune system is determined by functionally discrete subsets of CD4+ T cells, but it has remained unclear to what extent lineage choice is influenced by clonotypically expressed T-cell receptors (TCRs). To address this issue, we used a high-throughput approach to profile the αβ TCR repertoires of human naive and effector/memory CD4+ T-cell subsets, irrespective of antigen specificity. Highly conserved physicochemical and recombinatorial features were encoded on a subset-specific basis in the effector/memory compartment. Clonal tracking further identified forbidden and permitted transition pathways, mapping effector/memory subsets related by interconversion or ontogeny. Public sequences were largely confined to particular effector/memory subsets, including regulatory T cells (Tregs), which also displayed hardwired repertoire features in the naive compartment. Accordingly, these cumulative repertoire portraits establish a link between clonotype fate decisions in the complex world of CD4+ T cells and the intrinsic properties of somatically rearranged TCRs.

scholarly journals Regulation of T cell expansion by antigen presentation dynamics

2019 ◽  
Vol 116 (13) ◽  
pp. 5914-5919 ◽  
Author(s):  
Andreas Mayer ◽  
Yaojun Zhang ◽  
Alan S. Perelson ◽  
Ned S. Wingreen
Keyword(s):  
T Cells ◽  
T Cell ◽  
Cell Expansion ◽  
Essential Feature ◽  
Adaptive Immune Response ◽  
Adaptive Immune System ◽  
Effective Response ◽  
Effector Cells ◽  
Adaptive Immune ◽  
T Cell Expansion

An essential feature of the adaptive immune system is the proliferation of antigen-specific lymphocytes during an immune reaction to form a large pool of effector cells. This proliferation must be regulated to ensure an effective response to infection while avoiding immunopathology. Recent experiments in mice have demonstrated that the expansion of a specific clone of T cells in response to cognate antigen obeys a striking inverse power law with respect to the initial number of T cells. Here, we show that such a relationship arises naturally from a model in which T cell expansion is limited by decaying levels of presented antigen. The same model also accounts for the observed dependence of T cell expansion on affinity for antigen and on the kinetics of antigen administration. Extending the model to address expansion of multiple T cell clones competing for antigen, we find that higher-affinity clones can suppress the proliferation of lower-affinity clones, thereby promoting the specificity of the response. Using the model to derive optimal vaccination protocols, we find that exponentially increasing antigen doses can achieve a nearly optimized response. We thus conclude that the dynamics of presented antigen is a key regulator of both the size and specificity of the adaptive immune response.

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