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Shichkin VP, Antica M. Key Factors for Thymic Function and Development. Front Immunol 2022; 13:926516. [PMID: 35844535 PMCID: PMC9280625 DOI: 10.3389/fimmu.2022.926516] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2022] [Accepted: 05/31/2022] [Indexed: 11/17/2022] Open
Abstract
The thymus is the organ responsible for T cell development and the formation of the adaptive immunity function. Its multicellular environment consists mainly of the different stromal cells and maturing T lymphocytes. Thymus-specific progenitors of epithelial, mesenchymal, and lymphoid cells with stem cell properties represent only minor populations. The thymic stromal structure predominantly determines the function of the thymus. The stromal components, mostly epithelial and mesenchymal cells, form this specialized area. They support the consistent developmental program of functionally distinct conventional T cell subpopulations. These include the MHC restricted single positive CD4+ CD8- and CD4- CD8+ cells, regulatory T lymphocytes (Foxp3+), innate natural killer T cells (iNKT), and γδT cells. Several physiological causes comprising stress and aging and medical treatments such as thymectomy and chemo/radiotherapy can harm the thymus function. The present review summarizes our knowledge of the development and function of the thymus with a focus on thymic epithelial cells as well as other stromal components and the signaling and transcriptional pathways underlying the thymic cell interaction. These critical thymus components are significant for T cell differentiation and restoring the thymic function after damage to reach the therapeutic benefits.
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In vitro and in vivo functions of T cells produced in complemented thymi of chimeric mice generated by blastocyst complementation. Sci Rep 2022; 12:3242. [PMID: 35217706 PMCID: PMC8881621 DOI: 10.1038/s41598-022-07159-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2021] [Accepted: 02/07/2022] [Indexed: 11/19/2022] Open
Abstract
Blastocyst complementation is an intriguing way of generating humanized animals for organ preparation in regenerative medicine and establishing novel models for drug development. Confirming that complemented organs and cells work normally in chimeric animals is critical to demonstrating the feasibility of blastocyst complementation. Here, we generated thymus-complemented chimeric mice, assessed the efficacy of anti-PD-L1 antibody in tumor-bearing chimeric mice, and then investigated T-cell function. Thymus-complemented chimeric mice were generated by injecting C57BL/6 (B6) embryonic stem cells into Foxn1nu/nu morulae or blastocysts. Flow cytometry data showed that the chimeric mouse thymic epithelial cells (TECs) were derived from the B6 cells. T cells appeared outside the thymi. Single-cell RNA-sequencing analysis revealed that the TEC gene-expression profile was comparable to that in B6 mice. Splenic T cells of chimeric mice responded very well to anti-CD3 stimulation in vitro; CD4+ and CD8+ T cells proliferated and produced IFNγ, IL-2, and granzyme B, as in B6 mice. Anti-PD-L1 antibody treatment inhibited MC38 tumor growth in chimeric mice. Moreover, in the chimeras, anti-PD-L1 antibody restored T-cell activation by significantly decreasing PD-1 expression on T cells and increasing IFNγ-producing T cells in the draining lymph nodes and tumors. T cells produced by complemented thymi thus functioned normally in vitro and in vivo. To successfully generate humanized animals by blastocyst complementation, both verification of the function and gene expression profiling of complemented organs/cells in interspecific chimeras will be important in the near future.
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Nam JH, Lee JH, Choi SY, Jung NC, Song JY, Seo HG, Lim DS. Functional Ambivalence of Dendritic Cells: Tolerogenicity and Immunogenicity. Int J Mol Sci 2021; 22:ijms22094430. [PMID: 33922658 PMCID: PMC8122871 DOI: 10.3390/ijms22094430] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Revised: 04/15/2021] [Accepted: 04/20/2021] [Indexed: 12/12/2022] Open
Abstract
Dendritic cells (DCs) are the most potent professional antigen-presenting cells (APCs) and inducers of T cell-mediated immunity. Although DCs play a central role in promoting adaptive immune responses against growing tumors, they also establish and maintain peripheral tolerance. DC activity depends on the method of induction and/or the presence of immunosuppressive agents. Tolerogenic dendritic cells (tDCs) induce immune tolerance by activating CD4+CD25+Foxp3+ regulatory T (Treg) cells and/or by producing cytokines that inhibit T cell activation. These findings suggest that tDCs may be an effective treatment for autoimmune diseases, inflammatory diseases, and infertility.
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Affiliation(s)
- Ji-Hee Nam
- Department of Biotechnology, CHA University, 335 Pangyo-ro, Bundang-gu, Seongnam, Gyeonggi-do 13488, Korea; (J.-H.N.); (S.-Y.C.)
| | - Jun-Ho Lee
- Pharos Vaccine Inc., 14 Galmachiro 288 bun-gil, Jungwon-gu, Seongnam, Gyeonggi-do 13201, Korea; (J.-H.L.); (N.-C.J.)
| | - So-Yeon Choi
- Department of Biotechnology, CHA University, 335 Pangyo-ro, Bundang-gu, Seongnam, Gyeonggi-do 13488, Korea; (J.-H.N.); (S.-Y.C.)
| | - Nam-Chul Jung
- Pharos Vaccine Inc., 14 Galmachiro 288 bun-gil, Jungwon-gu, Seongnam, Gyeonggi-do 13201, Korea; (J.-H.L.); (N.-C.J.)
| | - Jie-Young Song
- Department of Radiation Cancer Sciences, Korea Institute of Radiological and Medical Sciences, 75 Nowon-ro, Nowon-gu, Seoul 01812, Korea;
| | - Han-Geuk Seo
- Department of Food Science and Biotechnology of Animal Products, Sanghuh College of Life Sciences, Konkuk University, 120 Neungdong-ro, Gwangjin-gu, Seoul 05029, Korea;
| | - Dae-Seog Lim
- Department of Biotechnology, CHA University, 335 Pangyo-ro, Bundang-gu, Seongnam, Gyeonggi-do 13488, Korea; (J.-H.N.); (S.-Y.C.)
- Correspondence: ; Tel.: +82-10-2770-4777
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4
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Kasahara M. Role of immunoproteasomes and thymoproteasomes in health and disease. Pathol Int 2021; 71:371-382. [PMID: 33657242 DOI: 10.1111/pin.13088] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Accepted: 02/11/2021] [Indexed: 12/14/2022]
Abstract
The proteasome is a multisubunit protease that degrades intracellular proteins into small peptides. Besides playing a pivotal role in many cellular processes indispensable for survival, it is involved in the production of peptides presented by major histocompatibility complex class I molecules. In addition to the standard proteasome shared in all eukaryotes, jawed vertebrates have two specialized forms of proteasome known as immunoproteasomes and thymoproteasomes. The immunoproteasome, which contains cytokine-inducible catalytic subunits with distinct cleavage specificities, produces peptides presented by class I molecules more efficiently than the standard proteasome. The thymoproteasome, which contains a unique catalytic subunit β5t, is a tissue-specific proteasome expressed exclusively in cortical thymic epithelial cells. It plays a critical role in CD8+ cytotoxic T cell development via positive selection. This review provides a brief overview on the structure and function of these specialized forms of proteasome and their involvement in human disease.
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Affiliation(s)
- Masanori Kasahara
- Department of Pathology, Faculty of Medicine and Graduate School of Medicine, Hokkaido University, Hokkaido, Japan
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5
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Barraza F, Montero R, Wong-Benito V, Valenzuela H, Godoy-Guzmán C, Guzmán F, Köllner B, Wang T, Secombes CJ, Maisey K, Imarai M. Revisiting the Teleost Thymus: Current Knowledge and Future Perspectives. BIOLOGY 2020; 10:biology10010008. [PMID: 33375568 PMCID: PMC7824517 DOI: 10.3390/biology10010008] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Revised: 12/14/2020] [Accepted: 12/22/2020] [Indexed: 12/13/2022]
Abstract
Simple Summary The thymus is the immune organ producing T lymphocytes that are essential to create immunity after encountering pathogens or vaccination. This review summarizes the thymus localization and histological studies, cell composition, and function in teleost fishes. We also describe how seasonal changes, photoperiod, water temperature fluctuations, and hormones can affect thymus development in fish species. Overall, the information helps identify future studies needed to understand thymus function in fish species and the immune system’s evolutionary origins. Since fish are exposed to pathogens, especially under aquaculture conditions, knowledge about the fish thymus and T lymphocyte can also help improve fish farming protocols, considering intrinsic and environmental conditions that can contribute to achieving the best vaccine responsiveness for disease resistance. Abstract The thymus in vertebrates plays a critical role in producing functionally competent T-lymphocytes. Phylogenetically, the thymus emerges early during evolution in jawed cartilaginous fish, and it is usually a bilateral organ placed subcutaneously at the dorsal commissure of the operculum. In this review, we summarize the current understanding of the thymus localization, histology studies, cell composition, and function in teleost fishes. Furthermore, we consider environmental factors that affect thymus development, such as seasonal changes, photoperiod, water temperature fluctuations and hormones. Further analysis of the thymus cell distribution and function will help us understand how key stages for developing functional T cells occur in fish, and how thymus dynamics can be modulated by external factors like photoperiod. Overall, the information presented here helps identify the knowledge gaps and future steps needed for a better understanding of the immunobiology of fish thymus.
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Affiliation(s)
- Felipe Barraza
- Laboratory of Immunology, Center of Aquatic Biotechnology, Department of Biology, Faculty of Chemistry and Biology, University of Santiago of Chile, Av. Bernardo O’Higgins, Estación Central, Santiago 3363, Chile; (F.B.); (V.W.-B.); (H.V.)
| | - Ruth Montero
- Friedrich-Loeffler-Institute, Federal Research Institute for Animal Health, 17493 Greifswald, Insel Riems, Germany; (R.M.); (B.K.)
| | - Valentina Wong-Benito
- Laboratory of Immunology, Center of Aquatic Biotechnology, Department of Biology, Faculty of Chemistry and Biology, University of Santiago of Chile, Av. Bernardo O’Higgins, Estación Central, Santiago 3363, Chile; (F.B.); (V.W.-B.); (H.V.)
| | - Héctor Valenzuela
- Laboratory of Immunology, Center of Aquatic Biotechnology, Department of Biology, Faculty of Chemistry and Biology, University of Santiago of Chile, Av. Bernardo O’Higgins, Estación Central, Santiago 3363, Chile; (F.B.); (V.W.-B.); (H.V.)
| | - Carlos Godoy-Guzmán
- Center for Biomedical and Applied Research (CIBAP), School of Medicine, Faculty of Medical Sciences, Av. Bernardo O’Higgins, Estación Central, Santiago 3363, Chile;
| | - Fanny Guzmán
- Núcleo Biotecnología Curauma, Pontificia Universidad Católica de Valparaíso, Valparaíso 2373223, Chile;
| | - Bernd Köllner
- Friedrich-Loeffler-Institute, Federal Research Institute for Animal Health, 17493 Greifswald, Insel Riems, Germany; (R.M.); (B.K.)
| | - Tiehui Wang
- Scottish Fish Immunology Research Centre, School of Biological Sciences, University of Aberdeen, Aberdeen AB24 2TZ, UK; (T.W.); (C.J.S.)
| | - Christopher J. Secombes
- Scottish Fish Immunology Research Centre, School of Biological Sciences, University of Aberdeen, Aberdeen AB24 2TZ, UK; (T.W.); (C.J.S.)
| | - Kevin Maisey
- Laboratory of Comparative Immunology, Center of Aquatic Biotechnology, Department of Biology, Faculty of Chemistry and Biology, University of Santiago of Chile, Av. Bernardo O’Higgins, Estación Central, Santiago 3363, Chile;
| | - Mónica Imarai
- Laboratory of Immunology, Center of Aquatic Biotechnology, Department of Biology, Faculty of Chemistry and Biology, University of Santiago of Chile, Av. Bernardo O’Higgins, Estación Central, Santiago 3363, Chile; (F.B.); (V.W.-B.); (H.V.)
- Correspondence:
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Kondo K, Ohigashi I, Takahama Y. Thymus machinery for T-cell selection. Int Immunol 2020; 31:119-125. [PMID: 30476234 DOI: 10.1093/intimm/dxy081] [Citation(s) in RCA: 42] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2018] [Accepted: 11/20/2018] [Indexed: 01/01/2023] Open
Abstract
An immunocompetent and self-tolerant pool of naive T cells is formed in the thymus through the process of repertoire selection. T cells that are potentially capable of responding to foreign antigens are positively selected in the thymic cortex and are further selected in the thymic medulla to help prevent self-reactivity. The affinity between T-cell antigen receptors expressed by newly generated T cells and self-peptide-major histocompatibility complexes displayed in the thymic microenvironments plays a key role in determining the fate of developing T cells during thymic selection. Recent advances in our knowledge of the biology of thymic epithelial cells have revealed unique machinery that contributes to positive and negative selection in the thymus. In this article, we summarize recent findings on thymic T-cell selection, focusing on the machinery unique to thymic epithelial cells.
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Affiliation(s)
- Kenta Kondo
- Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA.,Division of Experimental Immunology, Institute of Advanced Medical Sciences, University of Tokushima, Kuramoto, Tokushima, Japan
| | - Izumi Ohigashi
- Division of Experimental Immunology, Institute of Advanced Medical Sciences, University of Tokushima, Kuramoto, Tokushima, Japan
| | - Yousuke Takahama
- Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA.,Division of Experimental Immunology, Institute of Advanced Medical Sciences, University of Tokushima, Kuramoto, Tokushima, Japan
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Insights into Thymus Development and Viral Thymic Infections. Viruses 2019; 11:v11090836. [PMID: 31505755 PMCID: PMC6784209 DOI: 10.3390/v11090836] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2019] [Revised: 09/03/2019] [Accepted: 09/06/2019] [Indexed: 12/16/2022] Open
Abstract
T-cell development in the thymus is a complex and highly regulated process, involving a wide variety of cells and molecules which orchestrate thymocyte maturation into either CD4+ or CD8+ single-positive (SP) T cells. Here, we briefly review the process regulating T-cell differentiation, which includes the latest advances in this field. In particular, we highlight how, starting from a pool of hematopoietic stem cells in the bone marrow, the sequential action of transcriptional factors and cytokines dictates the proliferation, restriction of lineage potential, T-cell antigen receptors (TCR) gene rearrangements, and selection events on the T-cell progenitors, ultimately leading to the generation of mature T cells. Moreover, this review discusses paradigmatic examples of viral infections affecting the thymus that, by inducing functional changes within this lymphoid gland, consequently influence the behavior of peripheral mature T-lymphocytes.
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8
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Kasahara M, Flajnik MF. Origin and evolution of the specialized forms of proteasomes involved in antigen presentation. Immunogenetics 2019; 71:251-261. [PMID: 30675634 DOI: 10.1007/s00251-019-01105-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Accepted: 01/09/2019] [Indexed: 01/10/2023]
Abstract
Proteasomes are a multi-subunit protease complex that produces peptides bound by major histocompatibility complex (MHC) class I molecules. Phylogenetic studies indicate that two specialized forms of proteasomes, immunoproteasomes and thymoproteasomes, and the proteasome activator PA28αβ emerged in a common ancestor of jawed vertebrates which acquired adaptive immunity based on the MHC, T cell receptors, and B cell receptors ~ 500 million years ago. Comparative genomics studies now provide strong evidence that the genes coding for the immunoproteasome subunits emerged by genome-wide duplication. On the other hand, the gene encoding the thymoproteasome subunit β5t emerged by tandem duplication from the gene coding for the β5 subunit. Strikingly, birds lack immunoproteasomes, thymoproteasomes, and the proteasome activator PA28αβ, raising an interesting question of whether they have evolved any compensatory mechanisms.
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Affiliation(s)
- Masanori Kasahara
- Department of Pathology, Faculty of Medicine and Graduate School of Medicine, Hokkaido University, Sapporo, 060-8638, Japan.
| | - Martin F Flajnik
- Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, MD, 21201, USA.
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9
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Spetz J, Presser AG, Sarosiek KA. T Cells and Regulated Cell Death: Kill or Be Killed. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2018; 342:27-71. [PMID: 30635093 DOI: 10.1016/bs.ircmb.2018.07.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Cell death plays two major complementary roles in T cell biology: mediating the removal of cells that are targeted by T cells and the removal of T cells themselves. T cells serve as major actors in the adaptive immune response and function by selectively killing cells which are infected or dysfunctional. This feature is highly involved during homeostatic maintenance, and is relied upon and modulated in the context of cancer immunotherapy. The vital recognition and elimination of both autoreactive T cells and cells which are unable to recognize threats is a highly selective and regulated process. Moreover, detection of potential threats will result in the activation and expansion of T cells, which on resolution of the immune response will need to be eliminated. The culling of these T cells can be executed via a multitude of cell death pathways which are used in context-specific manners. Failure of these processes may result in an accumulation of misdirected or dysfunctional T cells, leading to complications such as autoimmunity or cancer. This review will focus on the role of cell death regulation in the maintenance of T cell homeostasis, as well as T cell-mediated elimination of infected or dysfunctional cells, and will summarize and discuss the current knowledge of the cellular mechanisms which are implicated in these processes.
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Affiliation(s)
- Johan Spetz
- John B. Little Center for Radiation Sciences, Harvard T.H. Chan School of Public Health, Boston, MA, United States; Laboratory of Systems Pharmacology, Harvard Program in Therapeutic Science, Department of Systems Biology, Harvard Medical School, Boston, MA, United States
| | - Adam G Presser
- John B. Little Center for Radiation Sciences, Harvard T.H. Chan School of Public Health, Boston, MA, United States; Laboratory of Systems Pharmacology, Harvard Program in Therapeutic Science, Department of Systems Biology, Harvard Medical School, Boston, MA, United States
| | - Kristopher A Sarosiek
- John B. Little Center for Radiation Sciences, Harvard T.H. Chan School of Public Health, Boston, MA, United States; Laboratory of Systems Pharmacology, Harvard Program in Therapeutic Science, Department of Systems Biology, Harvard Medical School, Boston, MA, United States
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10
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Takaba H, Takayanagi H. The Mechanisms of T Cell Selection in the Thymus. Trends Immunol 2017; 38:805-816. [PMID: 28830733 DOI: 10.1016/j.it.2017.07.010] [Citation(s) in RCA: 162] [Impact Index Per Article: 23.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2017] [Revised: 07/25/2017] [Accepted: 07/25/2017] [Indexed: 12/17/2022]
Abstract
T cells undergo positive and negative selection in the thymic cortex and medulla, respectively. A promiscuous expression of a wide array of self-antigens in the thymus is essential for the negative selection of self-reactive T cells and the establishment of central tolerance. Aire was originally thought to be the exclusive factor regulating the expression of tissue-restricted antigens, but Fezf2 recently emerged as a critical transcription factor in this regulatory activity. Fezf2 is selectively expressed in thymic medullary epithelial cells, regulates a large number of tissue-restricted antigens and suppresses the onset of autoimmune responses. Here, we discuss novel findings on the transcriptional mechanisms of tissue restricted-antigen expression in the medullary thymic epithelial cells and its effects on T cell selection.
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Affiliation(s)
- Hiroyuki Takaba
- Department of Immunology, Graduate School of Medicine and Faculty of Medicine, University of Tokyo, Tokyo, Japan
| | - Hiroshi Takayanagi
- Department of Immunology, Graduate School of Medicine and Faculty of Medicine, University of Tokyo, Tokyo, Japan.
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11
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Gaczynska M, Osmulski PA. Targeting Protein-Protein Interactions in the Ubiquitin-Proteasome Pathway. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2017; 110:123-165. [PMID: 29412995 DOI: 10.1016/bs.apcsb.2017.09.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The ubiquitin-proteasome pathway (UPP) is a major venue for controlled intracellular protein degradation in Eukaryota. The machinery of several hundred proteins is involved in recognizing, tagging, transporting, and cleaving proteins, all in a highly regulated manner. Short-lived transcription factors, misfolded translation products, stress-damaged polypeptides, or worn-out long-lived proteins, all can be found among the substrates of UPP. Carefully choreographed protein-protein interactions (PPI) are involved in each step of the pathway. For many of the steps small-molecule inhibitors have been identified and often they directly or indirectly target PPI. The inhibitors may destabilize intracellular proteostasis and trigger apoptosis. So far this is the most explored option used as an anticancer strategy. Alternatively, substrate-specific polyubiquitination may be regulated for a precise intervention aimed at a particular metabolic pathway. This very attractive opportunity is moving close to clinical application. The best known drug target in UPP is the proteasome: the end point of the journey of a protein destined for degradation. The proteasome alone is a perfect object to study the mechanisms and roles of PPI on many levels. This giant protease is built from multisubunit modules and additionally utilizes a service from transient protein ligands, for example, delivering substrates. An elaborate set of PPI within the highest-order proteasome assembly is involved in substrate recognition and processing. Below we will outline PPI involved in the UPP and discuss the growing prospects for their utilization in pharmacological interventions.
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Affiliation(s)
- Maria Gaczynska
- Institute of Biotechnology, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States.
| | - Pawel A Osmulski
- Institute of Biotechnology, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States
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12
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Takada K, Kondo K, Takahama Y. Generation of Peptides That Promote Positive Selection in the Thymus. THE JOURNAL OF IMMUNOLOGY 2017; 198:2215-2222. [PMID: 28264997 DOI: 10.4049/jimmunol.1601862] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2016] [Accepted: 11/29/2016] [Indexed: 11/19/2022]
Abstract
To establish an immunocompetent TCR repertoire that is useful yet harmless to the body, a de novo thymocyte repertoire generated through the rearrangement of genes that encode TCR is shaped in the thymus through positive and negative selection. The affinity between TCRs and self-peptides associated with MHC molecules determines the fate of developing thymocytes. Low-affinity TCR engagement with self-peptide-MHC complexes mediates positive selection, a process that primarily occurs in the thymic cortex. Massive efforts exerted by many laboratories have led to the characterization of peptides that can induce positive selection. Moreover, it is now evident that protein degradation machineries unique to cortical thymic epithelial cells play a crucial role in the production of MHC-associated self-peptides for inducing positive selection. This review summarizes current knowledge on positive selection-inducing self-peptides and Ag processing machineries in cortical thymic epithelial cells. Recent studies on the role of positive selection in the functional tuning of T cells are also discussed.
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Affiliation(s)
- Kensuke Takada
- Division of Experimental Immunology, Institute of Advanced Medical Sciences, University of Tokushima, Tokushima 770-8503, Japan
| | - Kenta Kondo
- Division of Experimental Immunology, Institute of Advanced Medical Sciences, University of Tokushima, Tokushima 770-8503, Japan
| | - Yousuke Takahama
- Division of Experimental Immunology, Institute of Advanced Medical Sciences, University of Tokushima, Tokushima 770-8503, Japan
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13
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Ohigashi I, Ohte Y, Setoh K, Nakase H, Maekawa A, Kiyonari H, Hamazaki Y, Sekai M, Sudo T, Tabara Y, Sawai H, Omae Y, Yuliwulandari R, Tanaka Y, Mizokami M, Inoue H, Kasahara M, Minato N, Tokunaga K, Tanaka K, Matsuda F, Murata S, Takahama Y. A human PSMB11 variant affects thymoproteasome processing and CD8+ T cell production. JCI Insight 2017; 2:93664. [PMID: 28515360 DOI: 10.1172/jci.insight.93664] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Accepted: 04/11/2017] [Indexed: 11/17/2022] Open
Abstract
The Psmb11-encoded β5t subunit of the thymoproteasome, which is specifically expressed in cortical thymic epithelial cells (cTECs), is essential for the optimal positive selection of functionally competent CD8+ T cells in mice. Here, we report that a human genomic PSMB11 variation, which is detectable at an appreciable allele frequency in human populations, alters the β5t amino acid sequence that affects the processing of catalytically active β5t proteins. The introduction of this variation in the mouse genome revealed that the heterozygotes showed reduced β5t expression in cTECs and the homozygotes further exhibited reduction in the cellularity of CD8+ T cells. No severe health problems were noticed in many heterozygous and 5 homozygous human individuals. Long-term analysis of health status, particularly in the homozygotes, is expected to improve our understanding of the role of the thymoproteasome-dependent positive selection of CD8+ T cells in humans.
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Affiliation(s)
- Izumi Ohigashi
- Division of Experimental Immunology, Institute of Advanced Medical Sciences, University of Tokushima, Tokushima, Japan
| | - Yuki Ohte
- Laboratory of Protein Metabolism, Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo, Japan
| | - Kazuya Setoh
- Center for Genomic Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Hiroshi Nakase
- Division of Experimental Immunology, Institute of Advanced Medical Sciences, University of Tokushima, Tokushima, Japan
| | - Akiko Maekawa
- Division of Experimental Immunology, Institute of Advanced Medical Sciences, University of Tokushima, Tokushima, Japan
| | - Hiroshi Kiyonari
- Animal Resource Development Unit and Genetic Engineering Team, RIKEN Center for Life Science Technologies, Kobe, Japan
| | - Yoko Hamazaki
- Department of Immunology and Cell Biology, Graduate School of Medicine
| | - Miho Sekai
- Department of Immunology and Cell Biology, Graduate School of Medicine
| | - Tetsuo Sudo
- Department of Nanobio Drug Discovery, Graduate School of Pharmaceutical Science, Kyoto University, Kyoto, Japan
| | - Yasuharu Tabara
- Center for Genomic Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Hiromi Sawai
- Department of Human Genetics, Graduate School of Medicine, University of Tokyo, Tokyo, Japan
| | - Yosuke Omae
- Department of Human Genetics, Graduate School of Medicine, University of Tokyo, Tokyo, Japan
| | - Rika Yuliwulandari
- Department of Pharmacology, Faculty of Medicine, YARSI University, Jakarta Pusat, Indonesia
| | - Yasuhito Tanaka
- Department of Virology and Liver Unit, Nagoya City University Graduate School of Medical Sciences, Nagoya, Japan
| | - Masashi Mizokami
- Research Center for Hepatitis and Immunology, National Center for Global Health and Medicine, Ichikawa, Japan
| | - Hiroshi Inoue
- Division of Genetic Information, Institute for Genome Research, University of Tokushima, Tokushima, Japan
| | - Masanori Kasahara
- Department of Pathology, Graduate School of Medicine, Hokkaido University, Sapporo, Japan
| | - Nagahiro Minato
- Department of Immunology and Cell Biology, Graduate School of Medicine
| | - Katsushi Tokunaga
- Department of Human Genetics, Graduate School of Medicine, University of Tokyo, Tokyo, Japan
| | - Keiji Tanaka
- Laboratory of Protein Metabolism, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Fumihiko Matsuda
- Center for Genomic Medicine, Graduate School of Medicine, Kyoto University, Kyoto, Japan
| | - Shigeo Murata
- Laboratory of Protein Metabolism, Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo, Japan
| | - Yousuke Takahama
- Division of Experimental Immunology, Institute of Advanced Medical Sciences, University of Tokushima, Tokushima, Japan
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14
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Abstract
The ability of T cells to respond to a wide array of foreign antigens while avoiding reactivity to self is largely determined by cellular selection of developing T cells in the thymus. While a great deal is known about the cell types and molecules involved in T-cell selection in the thymus, our understanding of the spatial and temporal aspects of this process remain relatively poorly understood. Thymocytes are highly motile within the thymus and travel between specialized microenvironments at different phases of their development while interacting with distinct sets of self-peptides and peptide presenting cells. A knowledge of when, where, and how thymocytes encounter self-peptide MHC ligands at different stages of thymic development is key to understanding T-cell selection. In the past several years, our laboratory has investigated this topic using two-photon time-lapse microscopy to directly visualize thymocyte migration and signaling events, together with a living thymic slice preparation to provide a synchronized experimental model of T-cell selection in situ. Here, we discuss recent advances in our understanding of the temporal and spatial aspects of T-cell selection, highlighting our own work, and placing them in the context of work from other groups.
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Affiliation(s)
- Nadia Kurd
- Division of Immunology and Pathogenesis, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA, 94720, USA
| | - Ellen A Robey
- Division of Immunology and Pathogenesis, Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA, 94720, USA
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15
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Dalum AS, Griffiths DJ, Valen EC, Amthor KS, Austbø L, Koppang EO, Press CM, Kvellestad A. Morphological and functional development of the interbranchial lymphoid tissue (ILT) in Atlantic salmon (Salmo salar L). FISH & SHELLFISH IMMUNOLOGY 2016; 58:153-164. [PMID: 27633679 DOI: 10.1016/j.fsi.2016.09.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2016] [Revised: 08/27/2016] [Accepted: 09/11/2016] [Indexed: 06/06/2023]
Abstract
The interbranchial lymphoid tissue (ILT) of Atlantic salmon originates from an embryological location that in higher vertebrates gives rise to both primary and secondary lymphoid tissues. Still much is unknown about the morphological and functional development of the ILT. In the present work a standardized method of organ volume determination was established to study its development in relation to its containing gill and the thymus. Based on morphological findings and gene transcription data, the ILT shows no signs of primary lymphoid function. In contrast to the thymus, an ILT-complex first became discernible after the yolk-sac period. After its appearance, the ILT-complex constitutes 3-7% of the total volume of the gill (excluding the gill arch) with the newly described distal ILT constituting a major part, and in adult fish it is approximately 13 times larger than the thymus. Confined regions of T-cell proliferation are present within the ILT. Communication with systemic circulation through the distal ILT is also highly plausible thus offering both internal and external recruitment of immune cells in the growing ILT.
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Affiliation(s)
- Alf Seljenes Dalum
- Department of Basic Sciences and Aquatic Medicine, Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, Oslo, Norway.
| | - David James Griffiths
- Department of Basic Sciences and Aquatic Medicine, Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, Oslo, Norway
| | - Elin Christine Valen
- Department of Basic Sciences and Aquatic Medicine, Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, Oslo, Norway
| | | | - Lars Austbø
- Department of Basic Sciences and Aquatic Medicine, Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, Oslo, Norway
| | - Erling Olaf Koppang
- Department of Basic Sciences and Aquatic Medicine, Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, Oslo, Norway
| | - Charles McLean Press
- Department of Basic Sciences and Aquatic Medicine, Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, Oslo, Norway
| | - Agnar Kvellestad
- Department of Basic Sciences and Aquatic Medicine, Faculty of Veterinary Medicine and Biosciences, Norwegian University of Life Sciences, Oslo, Norway
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16
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β-catenin activation drives thymoma initiation and progression in mice. Oncotarget 2016; 6:13978-93. [PMID: 26101855 PMCID: PMC4546445 DOI: 10.18632/oncotarget.4368] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2015] [Accepted: 06/01/2015] [Indexed: 11/25/2022] Open
Abstract
Thymoma is the most commonly identified cancer in the anterior mediastinum. To date, the causal mechanism that drives thymoma progression is not clear. Here, we generated K5-ΔN64Ctnnb1/ERT2 transgenic mice, which express an N-terminal deletion mutant of β-catenin fused to a mutated ligand-binding domain of estrogen receptor (ERT2) under the control of the bovine cytokeratin 5 (K5) promoter. The transgenic mouse lines named Tg1 and Tg4 were characterized. Forced expression of ΔN64Ctnnb1/ERT2 in the Tg1 and Tg4 mice developed small thymoma lesions in response to tamoxifen treatment. In the absence of tamoxifen, the Tg1 mice exhibited leaky activation of β-catenin, which activated the TOP-Gal transgene and Wnt/β-catenin-targeted genes. As the Tg1 mice aged in the absence of tamoxifen, manifest thymomas were found at 10-12 months. Interestingly, we detected loss of AIRE and increase of p63 in the thymomas of Tg1 mice, similar to that observed in human thymomas. Moreover, the β5t protease subunit, which was reported as a differential marker for human type B3 thymoma, was expressed in the Tg1 thymomas. Thus, the Tg1 mice generated in this study accurately mimic the characteristics of human thymomas and may serve as a model for understanding thymoma pathogenesis.
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17
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Ohigashi I, Kozai M, Takahama Y. Development and developmental potential of cortical thymic epithelial cells. Immunol Rev 2016; 271:10-22. [DOI: 10.1111/imr.12404] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Izumi Ohigashi
- Division of Experimental Immunology; Institute for Genome Research; University of Tokushima; Tokushima Japan
| | - Mina Kozai
- Division of Experimental Immunology; Institute for Genome Research; University of Tokushima; Tokushima Japan
| | - Yousuke Takahama
- Division of Experimental Immunology; Institute for Genome Research; University of Tokushima; Tokushima Japan
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18
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Guo D, Ye Y, Qi J, Xu L, Zhang L, Tan X, Tan Z, Yu X, Zhang Y, Ma Y, Li Y. MicroRNA-195a-5p inhibits mouse medullary thymic epithelial cells proliferation by directly targeting Smad7. Acta Biochim Biophys Sin (Shanghai) 2016; 48:290-7. [PMID: 26837421 DOI: 10.1093/abbs/gmv136] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Accepted: 11/02/2015] [Indexed: 01/17/2023] Open
Abstract
MiR-195 has been implicated in inhibiting cell proliferation in different types of tumors. Whether it contributes to the process of thymic epithelial cells (TECs) proliferation remains unclear. In this study, we found that miR-195a-5p was highly up-regulated in the TECs isolated from the aging mice. Further experiments showed that miR-195a-5p mimic transfection inhibited the proliferation of mouse medullary thymic epithelial cell line 1 (MTEC1), whereas the transfection of miR-195a-5p inhibitor in MTEC1 had the opposite effect. In addition, miR-195a-5p had no obvious effect on MTEC1 apoptosis. Furthermore, Smad7, a negative regulator of transforming growth factor β pathway, was confirmed as a direct target of miR-195a-5p by luciferase assays. Taken together, our results indicate that miR-195a-5p inhibits MTEC1 proliferation, at least in part, via down-regulation of Smad7.
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Affiliation(s)
- Dongguang Guo
- College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China
| | - Yaqiong Ye
- College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China
| | - Junjie Qi
- College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China
| | - Lifeng Xu
- College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China
| | - Lihua Zhang
- College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China
| | - Xiaotong Tan
- College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China
| | - Zhigang Tan
- College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China
| | - Xiaofang Yu
- College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China
| | - Yuan Zhang
- College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China
| | - Yongjiang Ma
- College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China
| | - Yugu Li
- College of Veterinary Medicine, South China Agricultural University, Guangzhou 510642, China
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19
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Bredenkamp N, Jin X, Liu D, O'Neill KE, Manley NR, Blackburn CC. Construction of a functional thymic microenvironment from pluripotent stem cells for the induction of central tolerance. Regen Med 2016; 10:317-29. [PMID: 25933240 DOI: 10.2217/rme.15.8] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The thymus is required for generation of a self-tolerant, self-restricted T-cell repertoire. The capacity to manipulate or replace thymus function therapeutically would be beneficial in a variety of clinical settings, including for improving recovery following bone marrow transplantation, restoring immune system function in the elderly and promoting tolerance to transplanted organs or cells. An attractive strategy would be transplantation of thymus organoids generated from cells produced in vitro, for instance from pluripotent stem cells. Here, we review recent progress toward this goal, focusing on advances in directing differentiation of pluripotent stem cells to thymic epithelial cells, a key cell type of the thymic stroma, and related direct reprogramming strategies.
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Affiliation(s)
- Nicholas Bredenkamp
- MRC Centre for Regenerative Medicine, Institute for Stem Cell Research, School of Biological Sciences, The University of Edinburgh, SCRM Building, 5 Little France Drive, Edinburgh, EH16 4UU, UK
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20
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Takada K, Van Laethem F, Xing Y, Akane K, Suzuki H, Murata S, Tanaka K, Jameson SC, Singer A, Takahama Y. TCR affinity for thymoproteasome-dependent positively selecting peptides conditions antigen responsiveness in CD8(+) T cells. Nat Immunol 2015; 16:1069-76. [PMID: 26301566 DOI: 10.1038/ni.3237] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Accepted: 07/01/2015] [Indexed: 12/12/2022]
Abstract
In the thymus, low-affinity T cell antigen receptor (TCR) engagement facilitates positive selection of a useful T cell repertoire. Here we report that TCR responsiveness of mature CD8(+) T cells is fine tuned by their affinity for positively selecting peptides in the thymus and that optimal TCR responsiveness requires positive selection on major histocompatibility complex class I-associated peptides produced by the thymoproteasome, which is specifically expressed in the thymic cortical epithelium. Thymoproteasome-independent positive selection of monoclonal CD8(+) T cells results in aberrant TCR responsiveness, homeostatic maintenance and immune responses to infection. These results demonstrate a novel aspect of positive selection, in which TCR affinity for positively selecting peptides produced by thymic epithelium determines the subsequent antigen responsiveness of mature CD8(+) T cells in the periphery.
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Affiliation(s)
- Kensuke Takada
- Division of Experimental Immunology, Institute for Genome Research, University of Tokushima, Tokushima, Japan
| | - Francois Van Laethem
- Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Yan Xing
- Center for Immunology, Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, Minnesota, USA
| | - Kazuyuki Akane
- Department of Immunology, Graduate School of Medicine, Nagoya University, Nagoya, Japan
| | - Haruhiko Suzuki
- Department of Immunology, Graduate School of Medicine, Nagoya University, Nagoya, Japan
| | - Shigeo Murata
- Graduate School of Pharmaceutical Sciences, University of Tokyo, Tokyo, Japan
| | - Keiji Tanaka
- Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Stephen C Jameson
- Center for Immunology, Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, Minnesota, USA
| | - Alfred Singer
- Experimental Immunology Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Yousuke Takahama
- Division of Experimental Immunology, Institute for Genome Research, University of Tokushima, Tokushima, Japan
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21
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Hu Z, Lancaster JN, Ehrlich LIR. The Contribution of Chemokines and Migration to the Induction of Central Tolerance in the Thymus. Front Immunol 2015; 6:398. [PMID: 26300884 PMCID: PMC4528182 DOI: 10.3389/fimmu.2015.00398] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2015] [Accepted: 07/20/2015] [Indexed: 02/01/2023] Open
Abstract
As T cells develop, they migrate throughout the thymus where they undergo essential bi-directional signaling with stromal cells in distinct thymic microenvironments. Immature thymocyte progenitors are located in the thymic cortex. Following T cell receptor expression and positive selection, thymocytes undergo a dramatic transition: they become rapidly motile and relocate to the thymic medulla. Antigen-presenting cells (APCs) within the cortex and medulla display peptides derived from a wide array of self-proteins, which promote thymocyte self-tolerance. If a thymocyte is auto-reactive against such antigens, it undergoes either negative selection, via apoptosis, or differentiation into the regulatory T cell lineage. This induction of central tolerance is critical for prevention of autoimmunity. Chemokines and adhesion molecules play an essential role in tolerance induction, as they promote migration of developing thymocytes through the different thymic microenvironments and enhance interactions with APCs displaying self-antigens. Herein, we review the contribution of chemokines and other regulators of thymocyte localization and motility to T cell development, with a focus on their contribution to the induction of central tolerance.
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Affiliation(s)
- Zicheng Hu
- Ehrlich Laboratory, Department of Molecular Biosciences, Institute for Cellular and Molecular Biology, The University of Texas at Austin , Austin, TX , USA
| | - Jessica Naomi Lancaster
- Ehrlich Laboratory, Department of Molecular Biosciences, Institute for Cellular and Molecular Biology, The University of Texas at Austin , Austin, TX , USA
| | - Lauren I R Ehrlich
- Ehrlich Laboratory, Department of Molecular Biosciences, Institute for Cellular and Molecular Biology, The University of Texas at Austin , Austin, TX , USA
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22
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Yamano T, Nedjic J, Hinterberger M, Steinert M, Koser S, Pinto S, Gerdes N, Lutgens E, Ishimaru N, Busslinger M, Brors B, Kyewski B, Klein L. Thymic B Cells Are Licensed to Present Self Antigens for Central T Cell Tolerance Induction. Immunity 2015; 42:1048-61. [PMID: 26070482 DOI: 10.1016/j.immuni.2015.05.013] [Citation(s) in RCA: 172] [Impact Index Per Article: 19.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2014] [Revised: 03/20/2015] [Accepted: 04/13/2015] [Indexed: 12/22/2022]
Abstract
Thymic antigen-presenting cells (APCs) such as dendritic cells and medullary thymic epithelial cells (mTECs) use distinct strategies of self-antigen expression and presentation to mediate central tolerance. The thymus also harbors B cells; whether they also display unique tolerogenic features and how they genealogically relate to peripheral B cells is unclear. Here, we found that Aire is expressed in thymic but not peripheral B cells. Aire expression in thymic B cells coincided with major histocompatibility class II (MHCII) and CD80 upregulation and immunoglobulin class-switching. These features were recapitulated upon immigration of naive peripheral B cells into the thymus, whereby this intrathymic licensing required CD40 signaling in the context of cognate interactions with autoreactive CD4(+) thymocytes. Moreover, a licensing-dependent neo-antigen selectively upregulated in immigrating B cells mediated negative selection through direct presentation. Thus, autoreactivity within the nascent T cell repertoire fuels a feed forward loop that endows thymic B cells with tolerogenic features.
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Affiliation(s)
- Tomoyoshi Yamano
- Institute for Immunology, Ludwig-Maximilians-University Munich, Goethestrasse 31, 80336 Munich, Germany
| | - Jelena Nedjic
- Institute for Immunology, Ludwig-Maximilians-University Munich, Goethestrasse 31, 80336 Munich, Germany
| | - Maria Hinterberger
- Institute for Immunology, Ludwig-Maximilians-University Munich, Goethestrasse 31, 80336 Munich, Germany
| | - Madlen Steinert
- Institute for Immunology, Ludwig-Maximilians-University Munich, Goethestrasse 31, 80336 Munich, Germany
| | - Sandra Koser
- Division of Theoretical Bioinformatics, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany
| | - Sheena Pinto
- Division of Developmental Immunology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany
| | - Norbert Gerdes
- Institute for Cardiovascular Prevention, Ludwig-Maximilians-University Munich, Pettenkoferstrasse 9, 80336 Munich, Germany
| | - Esther Lutgens
- Institute for Cardiovascular Prevention, Ludwig-Maximilians-University Munich, Pettenkoferstrasse 9, 80336 Munich, Germany; Department of Medical Biochemistry, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 Amsterdam, the Netherlands
| | - Naozumi Ishimaru
- Department of Oral Molecular Pathology, Institute of Health Biosciences, The University of Tokushima Graduate School, 3-18-15 Kuramoto, Tokushima 770-8504, Japan
| | - Meinrad Busslinger
- Research Institute of Molecular Pathology, Vienna Biocenter, Dr. Bohr-Gasse 7, 1030 Vienna, Austria
| | - Benedikt Brors
- Division of Theoretical Bioinformatics, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany
| | - Bruno Kyewski
- Division of Developmental Immunology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany
| | - Ludger Klein
- Institute for Immunology, Ludwig-Maximilians-University Munich, Goethestrasse 31, 80336 Munich, Germany.
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23
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Takada K, Takahama Y. Positive-Selection-Inducing Self-Peptides Displayed by Cortical Thymic Epithelial Cells. Adv Immunol 2015; 125:87-110. [DOI: 10.1016/bs.ai.2014.09.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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24
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Gaczynska M, Osmulski PA. Harnessing proteasome dynamics and allostery in drug design. Antioxid Redox Signal 2014; 21:2286-301. [PMID: 24410482 PMCID: PMC4241894 DOI: 10.1089/ars.2013.5816] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/30/2013] [Accepted: 01/12/2014] [Indexed: 12/14/2022]
Abstract
SIGNIFICANCE The proteasome is the essential protease that is responsible for regulated cleavage of the bulk of intracellular proteins. Its central role in cellular physiology has been exploited in therapies against aggressive cancers where proteasome-specific competitive inhibitors that block proteasome active centers are very effectively used. However, drugs regulating this essential protease are likely to have broader clinical usefulness. The non-catalytic sites of the proteasome emerge as an attractive alternative target in search of highly specific and diverse proteasome regulators. RECENT ADVANCES Crystallographic models of the proteasome leave the false impression of fixed structures with minimal molecular dynamics lacking long-distance allosteric signaling. However, accumulating biochemical and structural observations strongly support the notion that the proteasome is regulated by precise allosteric interactions arising from protein dynamics, encouraging the active search for allosteric regulators. Here, we discuss properties of several promising compounds that affect substrate gating and processing in antechambers, and interactions of the catalytic core with regulatory proteins. CRITICAL ISSUES Given the structural complexity of proteasome assemblies, it is a painstaking process to better understand their allosteric regulation and molecular dynamics. Here, we discuss the challenges and achievements in this field. We place special emphasis on the role of atomic force microscopy imaging in probing the allostery and dynamics of the proteasome, and in dissecting the mechanisms involving small-molecule allosteric regulators. FUTURE DIRECTIONS New small-molecule allosteric regulators may become a next generation of drugs targeting the proteasome, which is critical to the development of new therapies in cancers and other diseases.
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Affiliation(s)
- Maria Gaczynska
- Department of Molecular Medicine, Institute of Biotechnology, University of Texas Health Science Center at San Antonio , San Antonio, Texas
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25
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The amazing ubiquitin-proteasome system: structural components and implication in aging. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2014; 314:171-237. [PMID: 25619718 DOI: 10.1016/bs.ircmb.2014.09.002] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Proteome quality control (PQC) is critical for the maintenance of cellular functionality and it is assured by the curating activity of the proteostasis network (PN). PN is constituted of several complex protein machines that under conditions of proteome instability aim to, firstly identify, and then, either rescue or degrade nonnative polypeptides. Central to the PN functionality is the ubiquitin-proteasome system (UPS) which is composed from the ubiquitin-conjugating enzymes and the proteasome; the latter is a sophisticated multi-subunit molecular machine that functions in a bimodal way as it degrades both short-lived ubiquitinated normal proteins and nonfunctional polypeptides. UPS is also involved in PQC of the nucleus, the endoplasmic reticulum and the mitochondria and it also interacts with the other main cellular degradation axis, namely the autophagy-lysosome system. UPS functionality is optimum in the young organism but it is gradually compromised during aging resulting in increasing proteotoxic stress; these effects correlate not only with aging but also with most age-related diseases. Herein, we present a synopsis of the UPS components and of their functional alterations during cellular senescence or in vivo aging. We propose that mild UPS activation in the young organism will, likely, promote antiaging effects and/or suppress age-related diseases.
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26
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Biological significance of FoxN1 gain-of-function mutations during T and B lymphopoiesis in juvenile mice. Cell Death Dis 2014; 5:e1457. [PMID: 25299782 PMCID: PMC4237256 DOI: 10.1038/cddis.2014.432] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2014] [Revised: 08/31/2014] [Accepted: 09/05/2014] [Indexed: 12/12/2022]
Abstract
FoxN1 is cell-autonomously expressed in skin and thymic epithelial cells (TECs), essential for their development. Inborn mutation of FoxN1 results in hair follicle and TEC development failure, whereas insufficient postnatal FoxN1 expression induces thymic atrophy, resulting in declined T lymphopoiesis. Although upregulating FoxN1 expression in the aged FoxN1-declined thymus rejuvenates T lymphopoiesis, whether its over- and ectopic-expression in early life is beneficial for T lymphopoiesis is unknown. Using our newly generated Rosa26-STOPflox–FoxN1 mice, in which over- and ectopic-expression of FoxN1 can be induced by various promoter-driven Cre-mediated deletions of the roadblock STOPflox in early life, we found that K14Cre-mediated inborn FoxN1 overexpression induced neonatal lethality, exhibited abnormal permeability in the skin and abnormal nursing. Ubiquitous deletion of the STOPflox mediated by progressive uCreERT leakage in juvenile mice affected thymus and bone marrow normality, resulting in an increased ratio of medullary/cortical TECs, along with declined T and B lymphopoiesis. Although the K5CreERT-mediated FoxN1 overexpression mice had a normal lifespan, induction of K5CreERT activation in juveniles adversely influenced total thymoycte development and produced ichthyosis-like skin. Therefore, FoxN1 has temporal and tissue-specific activity. Over- and ectopic-expression of FoxN1 in early life adversely influence immature TEC, T and B cell, and skin epithelial development.
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27
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Kisselev AF, Groettrup M. Subunit specific inhibitors of proteasomes and their potential for immunomodulation. Curr Opin Chem Biol 2014; 23:16-22. [PMID: 25217863 DOI: 10.1016/j.cbpa.2014.08.012] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2014] [Revised: 08/15/2014] [Accepted: 08/22/2014] [Indexed: 11/20/2022]
Abstract
Specialized variants of the constitutive 20S proteasome in the immune system like the immunoproteasomes and the thymoproteasome contain active site-bearing subunits which differ in their cleavage priorities and substrate binding pockets. The immunoproteasome plays a crucial role in antigen processing and for the differentiation of pro-inflammatory T helper cells which are involved in the pathogenesis of autoimmunity. Selective inhibitors of the immunoproteasome and constitutive proteasome have recently been generated which interfere with the development and progression of autoimmune diseases. Here we describe these inhibitors and their therapeutic potential as predicted from preclinical models.
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Affiliation(s)
- Alexei F Kisselev
- Department of Pharmacology & Toxicology, Norris Cotton Cancer Center, Geisel School of Medicine at Dartmouth, One Medical Center Drive, Lebanon, NH 03756, USA.
| | - Marcus Groettrup
- Division of Immunology, Department of Biology, University of Konstanz, D-78457 Konstanz, Germany; Biotechnology Institute Thurgau (BITg) at the University of Konstanz, CH-8280 Kreuzlingen, Switzerland.
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28
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Xing Y, Hogquist KA. Isolation, identification, and purification of murine thymic epithelial cells. J Vis Exp 2014:e51780. [PMID: 25145384 DOI: 10.3791/51780] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The thymus is a vital organ for T lymphocyte development. Of thymic stromal cells, thymic epithelial cells (TECs) are particularly crucial at multiple stages of T cell development: T cell commitment, positive selection and negative selection. However, the function of TECs in the thymus remains incompletely understood. In the article, we provide a method to isolate TEC subsets from fresh mouse thymus using a combination of mechanical disruption and enzymatic digestion. The method allows thymic stromal cells and thymocytes to be efficiently released from cell-cell and cell-extracellular matrix connections and to form a single-cell suspension. Using the isolated cells, multiparameter flow cytometry can be applied to identification and characterization of TECs and dendritic cells. Because TECs are a rare cell population in the thymus, we also describe an effective way to enrich and purify TECs by depleting thymocytes, the most abundant cell type in the thymus. Following the enrichment, cell sorting time can be decreased so that loss of cell viability can be minimized during purification of TECs. Purified cells are suitable for various downstream analyses like Real Time-PCR, Western blot and gene expression profiling. The protocol will promote research of TEC function and as well as the development of in vitro T cell reconstitution.
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Affiliation(s)
- Yan Xing
- Department of Laboratory Medicine & Pathology, Center for Immunology, University of Minnesota;
| | - Kristin A Hogquist
- Department of Laboratory Medicine & Pathology, Center for Immunology, University of Minnesota
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29
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Uechi H, Hamazaki J, Murata S. Characterization of the testis-specific proteasome subunit α4s in mammals. J Biol Chem 2014; 289:12365-74. [PMID: 24668818 DOI: 10.1074/jbc.m114.558866] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The 26 S proteasome is responsible for regulated proteolysis in eukaryotic cells. It is composed of one 20 S core particle (CP) flanked by one or two 19 S regulatory particles. The CP is composed of seven different α-type subunits (α1-α7) and seven different β-type subunits, three of which are catalytic. Vertebrates encode four additional catalytic β subunits that are expressed predominantly in immune tissues and produce distinct subtypes of CPs particularly well suited for the acquired immune system. In contrast, the diversity of α subunits remains poorly understood. Recently, another α subunit, referred to as α4s, was reported. However, little is known about α4s. Here we provide a detailed characterization of α4s and the α4s-containing CP. α4s is exclusively expressed in germ cells that enter the meiotic prophase and is incorporated into the CP in place of α4. A comparison of structural models revealed that the differences in the primary sequences between α4 and α4s are located on the outer surface of the CP, suggesting that α4s interacts with specific molecules via these unique regions. α4s-containing CPs account for the majority of the CPs in mouse sperm. The catalytic β subunits in the α4s-containing CP are β1, β2, and β5, and immunosubunits are not included in the α4s-containing CP. α4s-containing CPs have a set of peptidase activities almost identical to those of α4-containing CPs. Our results provide a basis for understanding the role of α4s and male germ cell-specific proteasomes in mammals.
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Affiliation(s)
- Hiroyuki Uechi
- From the Laboratory of Protein Metabolism, Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
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Micale N, Scarbaci K, Troiano V, Ettari R, Grasso S, Zappalà M. Peptide-Based Proteasome Inhibitors in Anticancer Drug Design. Med Res Rev 2014; 34:1001-69. [DOI: 10.1002/med.21312] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Nicola Micale
- Dipartimento di Scienze del Farmaco e dei Prodotti per la Salute; Università degli Studi di Messina; Viale Annunziata 98168 Messina Italy
| | - Kety Scarbaci
- Dipartimento di Scienze del Farmaco e dei Prodotti per la Salute; Università degli Studi di Messina; Viale Annunziata 98168 Messina Italy
| | - Valeria Troiano
- Dipartimento di Scienze del Farmaco e dei Prodotti per la Salute; Università degli Studi di Messina; Viale Annunziata 98168 Messina Italy
| | - Roberta Ettari
- Dipartimento di Scienze Farmaceutiche; Università degli Studi di Milano; Via Mangiagalli 25 20133 Milano Italy
| | - Silvana Grasso
- Dipartimento di Scienze del Farmaco e dei Prodotti per la Salute; Università degli Studi di Messina; Viale Annunziata 98168 Messina Italy
| | - Maria Zappalà
- Dipartimento di Scienze del Farmaco e dei Prodotti per la Salute; Università degli Studi di Messina; Viale Annunziata 98168 Messina Italy
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Thymic epithelial cell development and its dysfunction in human diseases. BIOMED RESEARCH INTERNATIONAL 2014; 2014:206929. [PMID: 24672784 PMCID: PMC3929497 DOI: 10.1155/2014/206929] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/16/2013] [Accepted: 11/28/2013] [Indexed: 12/01/2022]
Abstract
Thymic epithelial cells (TECs) are the key components in thymic microenvironment for T cells development. TECs, composed of cortical and medullary TECs, are derived from a common bipotent progenitor and undergo a stepwise development controlled by multiple levels of signals to be functionally mature for supporting thymocyte development. Tumor necrosis factor receptor (TNFR) family members including the receptor activator for NFκB (RANK), CD40, and lymphotoxin β receptor (LTβR) cooperatively control the thymic medullary microenvironment and self-tolerance establishment. In addition, fibroblast growth factors (FGFs), Wnt, and Notch signals are essential for establishment of functional thymic microenvironment. Transcription factors Foxn1 and autoimmune regulator (Aire) are powerful modulators of TEC development, differentiation, and self-tolerance. Dysfunction in thymic microenvironment including defects of TEC and thymocyte development would cause physiological disorders such as tumor, infectious diseases, and autoimmune diseases. In the present review, we will summarize our current understanding on TEC development and the underlying molecular signals pathways and the involvement of thymus dysfunction in human diseases.
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Abstract
The proteasome is a sophisticated, 2.5-MDa, multisubunit complex that contains a catalytic core particle (CP) and two terminal regulatory particles (RPs); the RPs associate with the termini of the central CP at opposite orientations. The CP consists of four axially stacked heptameric rings (two outer α-rings and two inner β-rings), which are made up of seven structurally related, but not identical, α and β subunits. The CP contains catalytic threonine residues (in β1, β2, and β5 with caspase-like, trypsin-like, and chymotrypsin-like activities, respectively) on the surface of the chamber formed by two abutting β-rings. The RP recognizes polyubiquitylated substrate proteins and unfolds and translocates these proteins to the interior of the CP for degradation. The RP comprises 19 different subunits, which are thought to form two subcomplexes called the lid and the base. One longstanding question is how the complex structure of the proteasome is organized with high fidelity. Recently, we proposed a novel assembly mechanism that is assisted by multiple proteasome-dedicated chaperones. In addition, we discovered two immuno-type proteasomes, the immunoproteasome and the thymoproteasome, whose catalytic subunits are replaced by homologous counterparts. These two isoforms perform specialized functions that help discriminate self from non-self in cell-mediated immunity (i.e., they function as enzymes that process intracellular antigens for cytotoxic T lymphocyte responses and thymic positive selection). Moreover, emerging evidence suggests that the proteasome is crucially involved in the pathophysiology of various intractable diseases that are increasing in today's aging society.
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Garfin PM, Min D, Bryson JL, Serwold T, Edris B, Blackburn CC, Richie ER, Weinberg KI, Manley NR, Sage J, Viatour P. Inactivation of the RB family prevents thymus involution and promotes thymic function by direct control of Foxn1 expression. ACTA ACUST UNITED AC 2013; 210:1087-97. [PMID: 23669396 PMCID: PMC3674705 DOI: 10.1084/jem.20121716] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
RB family genes control T cell production and promote thymic involution through reducing Foxn1 expression in thymic epithelial cells. Thymic involution during aging is a major cause of decreased production of T cells and reduced immunity. Here we show that inactivation of Rb family genes in young mice prevents thymic involution and results in an enlarged thymus competent for increased production of naive T cells. This phenotype originates from the expansion of functional thymic epithelial cells (TECs). In RB family mutant TECs, increased activity of E2F transcription factors drives increased expression of Foxn1, a central regulator of the thymic epithelium. Increased Foxn1 expression is required for the thymic expansion observed in Rb family mutant mice. Thus, the RB family promotes thymic involution and controls T cell production via a bone marrow–independent mechanism, identifying a novel pathway to target to increase thymic function in patients.
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Affiliation(s)
- Phillip M Garfin
- Department of Pediatrics, Stanford University, Stanford, CA 94305, USA
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Tomaru U, Kasahara M. Thymoproteasome: Role in Thymic Selection and Clinical Significance as a Diagnostic Marker for Thymic Epithelial Tumors. Arch Immunol Ther Exp (Warsz) 2013; 61:357-65. [DOI: 10.1007/s00005-013-0234-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2012] [Accepted: 04/26/2013] [Indexed: 11/24/2022]
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Yamada H, Shibata K, Sakuraba K, Fujimura K, Yoshikai Y. Positive selection of self-antigen-specific CD8+ T cells by hematopoietic cells. Eur J Immunol 2013; 43:2033-42. [PMID: 23636825 DOI: 10.1002/eji.201242957] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2012] [Revised: 04/03/2013] [Accepted: 04/26/2013] [Indexed: 11/05/2022]
Abstract
In contrast to thymic epithelial cells, which induce the positive selection of conventional CD8(+) T cells, hematopoietic cells (HCs) select innate CD8(+) T cells whose Ag specificity is not fully understood. Here we show that CD8(+) T cells expressing an H-Y Ag-specific Tg TCR were able to develop in mice in which only HCs expressed MHC class I, when HCs also expressed the H-Y Ag. These HC-selected self-specific CD8(+) T cells resemble innate CD8(+) T cells in WT mice in terms of the expression of memory markers and effector functions, but are phenotypically distinct from the thymus-independent CD8(+) T-cell population. The peripheral maintenance of H-Y-specific CD8(+) T cells required presentation of the self-Ag and IL-15 on HCs. HC-selected CD8(+) T cells in mice lacking the Tg TCR also showed these features. Furthermore, by using MHC class I tetramers with a male Ag peptide, we found that self-Ag-specific CD8(+) T cells in TCR non-Tg mice could develop via HC-induced positive selection, supporting results obtained from H-Y TCR Tg mice. These findings indicate the presence of self-specific CD8(+) T cells that are positively selected by HCs in the peripheral T-cell repertoire.
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Affiliation(s)
- Hisakata Yamada
- Division of Host Defense, Medical Institute of Bioregulation, Kyushu University, Fukuoka, Japan.
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Sun L, Luo H, Li H, Zhao Y. Thymic epithelial cell development and differentiation: cellular and molecular regulation. Protein Cell 2013; 4:342-55. [PMID: 23589020 DOI: 10.1007/s13238-013-3014-0] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2013] [Accepted: 03/11/2013] [Indexed: 11/26/2022] Open
Abstract
Thymic epithelial cells (TECs) are one of the most important components in thymic microenvironment supporting thymocyte development and maturation. TECs, composed of cortical and medullary TECs, are derived from a common bipotent progenitor, mediating thymocyte positive and negative selections. Multiple levels of signals including intracellular signaling networks and cell-cell interaction are required for TEC development and differentiation. Transcription factors Foxn1 and autoimmune regulator (Aire) are powerful regulators promoting TEC development and differentiation. Crosstalks with thymocytes and other stromal cells for extrinsic signals like RANKL, CD40L, lymphotoxin, fibroblast growth factor (FGF) and Wnt are also definitely required to establish a functional thymic microenvironment. In this review, we will summarize our current understanding about TEC development and differentiation, and its underlying multiple signal pathways.
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Affiliation(s)
- Lina Sun
- State Key Laboratory of Biomembrane and Membrane Biotechnology, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China
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Abstract
The thymic cortex provides a microenvironment that supports the generation and T cell antigen receptor (TCR)-mediated selection of CD4(+)CD8(+)TCRαβ(+) thymocytes. Cortical thymic epithelial cells (cTECs) are the essential component that forms the architecture of the thymic cortex and induces the generation as well as the selection of newly generated T cells. Here we summarize current knowledge on the development, function, and heterogeneity of cTECs, focusing on the expression and function of β5t, a cTEC-specific subunit of the thymoproteasome.
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Lo WL, Allen PM. Self-awareness: how self-peptide/MHC complexes are essential in the development of T cells. Mol Immunol 2012. [PMID: 23196128 DOI: 10.1016/j.molimm.2012.10.028] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The processing and presentation of self-proteins is essential to develop an effective immune system, with almost all T cells only ever encountering self-peptide/MHC ligands. How positive selection in the thymus occurs with a weak interaction between the TCR and self-pMHC remains unresolved. The recent identification of a naturally occurring positive selecting self-peptide, gp250, for the MCC/I-E(k) specific T cell, AND, has provided some key insights. Despite the weak 3D affinity of the positive selecting AND TCR:gp250/I-E(k) interaction, it induces a sustained Ca(2+) flux and Erk signaling. Transcriptional profiling revealed the unique expression of a voltage-gated sodium channel (VGSC) in DP thymocytes. Blocking of this channel with tetrodotoxin inhibited positive selection of AND and polyclonal CD4T cells in vitro. VGSC sh-RNA knockdown inhibited the selection of CD4, but not CD8T cells. Thus, the expression of a VGSC at the DP stage increases the sensitivity of signaling induced by positively selecting ligands, thereby, providing a mechanism by which a weak TCR:self-peptide interaction can result in a sustained developmental signal. One enigma regarding positive selection is that AND TCR recognizes gp250 self-peptide with a high degree of specificity, akin to what is seen with foreign antigen. The self-peptide repertoire is significantly smaller than the T cell repertoire, therefore, each self-peptide has to select many unrelated T cells. Other studies have shown that a single peptide/MHC can select a large number of T cells. To reconcile this dichotomy, we propose a model in which positive selection is not simply a live or die process, but that the strength of the interaction between a TCR and the positive selecting ligand is deterministic for the functional activity of the peripheral T cells.
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Affiliation(s)
- Wan-Lin Lo
- Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO 63110, USA
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