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Abstract
About two decades ago, cloning of the autoimmune regulator (AIRE) gene materialized one of the most important actors on the scene of self-tolerance. Thymic transcription of genes encoding tissue-specific antigens (ts-ags) is activated by AIRE protein and embodies the essence of thymic self-representation. Pathogenic AIRE variants cause the autoimmune polyglandular syndrome type 1, which is a rare and complex disease that is gaining attention in research on autoimmunity. The animal models of disease, although not identically reproducing the human picture, supply fundamental information on mechanisms and extent of AIRE action: thanks to its multidomain structure, AIRE localizes to chromatin enclosing the target genes, binds to histones, and offers an anchorage to multimolecular complexes involved in initiation and post-initiation events of gene transcription. In addition, AIRE enhances mRNA diversity by favoring alternative mRNA splicing. Once synthesized, ts-ags are presented to, and cause deletion of the self-reactive thymocyte clones. However, AIRE function is not restricted to the activation of gene transcription. AIRE would control presentation and transfer of self-antigens for thymic cellular interplay: such mechanism is aimed at increasing the likelihood of engagement of the thymocytes that carry the corresponding T-cell receptors. Another fundamental role of AIRE in promoting self-tolerance is related to the development of thymocyte anergy, as thymic self-representation shapes at the same time the repertoire of regulatory T cells. Finally, AIRE seems to replicate its action in the secondary lymphoid organs, albeit the cell lineage detaining such property has not been fully characterized. Delineation of AIRE functions adds interesting data to the knowledge of the mechanisms of self-tolerance and introduces exciting perspectives of therapeutic interventions against the related diseases.
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Affiliation(s)
- Roberto Perniola
- Department of Pediatrics, Neonatal Intensive Care, Vito Fazzi Regional Hospital, Lecce, Italy
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2
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Cohn M. A Commentary on a Workshop ‘To Reveal the Foundational Concepts of Immune Regulation
’ (i.e. Tolerance). Scand J Immunol 2017; 85:312-320. [DOI: 10.1111/sji.12536] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2017] [Accepted: 02/01/2017] [Indexed: 01/06/2023]
Affiliation(s)
- M. Cohn
- Conceptual Immunology Group; The Salk Institute; La Jolla CA USA
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4
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Abstract
Some ideas because of their intuitive appeal never die by neglect and survive because they are not amenable to experimental disproof. They can only be evaluated by weighing them against competing ideas and by invoking a credibility factor when used to explain observation. Most scientists would recommend ignoring such ideas, yet there is much to be learned by engaging their proponents in debate. The immune system viewed as an idiotype network, and its tweaking by the new school of "contextualists" is an example of such an idea. As chance would have it, the supporters of this idea gathered in a meeting, thereby permitting a cumulative analysis of this conceptualization. The goal of this essay is to compare the views of each of the speakers in light of a competing theory with the hope that a better understanding of immune responsiveness will emerge.
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Affiliation(s)
- Melvin Cohn
- Conceptual Immunology Group, The Salk Institute, 10010 N. Torrey Pines Rd., La Jolla, CA, 92037-1099, USA,
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Cohn M. What would Treg-cell biology look like when viewed from a rationalized perspective? Eur J Immunol 2015; 45:3002-9. [PMID: 26256556 DOI: 10.1002/eji.201545799] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2015] [Revised: 06/25/2015] [Accepted: 08/04/2015] [Indexed: 11/09/2022]
Abstract
The argument that Treg cells play a role in determining the Self (S)-Nonself (NS) discrimination (i.e. tolerance) is challenged based on two theoretical constructs, the two stage-two signal model for the S-NS discrimination and the Tritope model of TCR function. The conclusions are then tested by reinterpreting a published probing set of data purporting to show that Treg cells regulate tolerance. It is concluded that the major role of suppression is to operate as a feedback mechanism modulating the magnitude of the effector response; it is not a determinant of the S-NS discrimination (i.e. tolerance).
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Affiliation(s)
- Melvin Cohn
- Conceptual Immunology Group, The Salk Institute, La Jolla, CA, USA
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6
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Autoimmunity: Rationalizing possible pathways from initiation to disease. J Theor Biol 2015; 375:40-51. [DOI: 10.1016/j.jtbi.2014.05.030] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2014] [Revised: 05/12/2014] [Accepted: 05/20/2014] [Indexed: 12/23/2022]
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Kisand K, Peterson P, Laan M. Lymphopenia-induced proliferation in aire-deficient mice helps to explain their autoimmunity and differences from human patients. Front Immunol 2014; 5:51. [PMID: 24592265 PMCID: PMC3923166 DOI: 10.3389/fimmu.2014.00051] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2013] [Accepted: 01/29/2014] [Indexed: 12/23/2022] Open
Abstract
Studies on autoimmune polyendocrinopathy candidiasis ectodermal dystrophy (APECED) and its mouse model – both caused by mutant AIRE – have greatly advanced the understanding of thymic processes that generate a self-tolerant T-cell repertoire. Much is now known about the molecular mechanisms by which AIRE induces tissue-specific antigen expression in thymic epithelium, and how this leads to negative selection of auto-reactive thymocytes. However, we still do not understand the processes that lead to the activation of any infrequent naïve auto-reactive T-cells exported by AIRE-deficient thymi. Also, the striking phenotypic differences between APECED and its mouse models have puzzled researchers for years. The aim of this review is to suggest explanations for some of these unanswered questions, based on a fresh view of published experiments. We review evidence that auto-reactive T-cells can be activated by the prolonged neonatal lymphopenia that naturally develops in young Aire-deficient mice due to delayed export of mature thymocytes. Lymphopenia-induced proliferation (LIP) helps to fill the empty space; by favoring auto-reactive T-cells, it also leads to lymphocyte infiltration in the same tissues as in day 3 thymectomized animals. The LIP becomes uncontrolled when loss of Aire is combined with defects in genes responsible for anergy induction and Treg responsiveness, or in signaling from the T-cell receptor and homeostatic cytokines. In APECED patients, LIP is much less likely to be involved in activation of naïve auto-reactive T-cells, as humans are born with a more mature immune system than in neonatal mice. We suggest that human AIRE-deficiency presents with different phenotypes because of additional precipitating factors that compound the defective negative selection of potentially autoaggressive tissue-specific thymocytes.
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Affiliation(s)
- Kai Kisand
- Molecular Pathology, Institute of Biomedicine and Translational Medicine, University of Tartu , Tartu , Estonia
| | - Pärt Peterson
- Molecular Pathology, Institute of Biomedicine and Translational Medicine, University of Tartu , Tartu , Estonia
| | - Martti Laan
- Molecular Pathology, Institute of Biomedicine and Translational Medicine, University of Tartu , Tartu , Estonia
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Alves NL, Takahama Y, Ohigashi I, Ribeiro AR, Baik S, Anderson G, Jenkinson WE. Serial progression of cortical and medullary thymic epithelial microenvironments. Eur J Immunol 2014; 44:16-22. [PMID: 24214487 PMCID: PMC4253091 DOI: 10.1002/eji.201344110] [Citation(s) in RCA: 75] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2013] [Revised: 11/11/2013] [Accepted: 11/05/2013] [Indexed: 01/07/2023]
Abstract
Thymic epithelial cells (TECs) provide key instructive signals for T-cell differentiation. Thymic cortical (cTECs) and medullary (mTECs) epithelial cells constitute two functionally distinct microenvironments for T-cell development, which derive from a common bipotent TEC progenitor. While seminal studies have partially elucidated events downstream of bipotent TECs in relation to the emergence of mTECs and their progenitors, the control and timing of the emergence of the cTEC lineage, particularly in relation to that of mTEC progenitors, has remained elusive. In this review, we describe distinct models that explain cTEC/mTEC lineage divergence from common bipotent progenitors. In particular, we summarize recent studies in mice providing evidence that mTECs, including the auto-immune regulator(+) subset, derive from progenitors initially endowed with phenotypic properties typically associated with the cTEC lineage. These observations support a novel "serial progression" model of TEC development, in which progenitors serially acquire cTEC lineage markers, prior to their commitment to the mTEC differentiation pathway. Gaining a better understanding of the phenotypic properties of early stages in TEC progenitor development should help in determining the mechanisms regulating cTEC/mTEC lineage development, and in strategies aimed at thymus reconstitution involving TEC therapy.
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Affiliation(s)
- Nuno L Alves
- Infection and Immunity Unit, Institute for Molecular and Cellular Biology, University of PortoPorto, Portugal
| | - Yousuke Takahama
- Division of Experimental Immunology, Institute for Genome Research, University of TokushimaTokushima, Japan
| | - Izumi Ohigashi
- Division of Experimental Immunology, Institute for Genome Research, University of TokushimaTokushima, Japan
| | - Ana R Ribeiro
- Infection and Immunity Unit, Institute for Molecular and Cellular Biology, University of PortoPorto, Portugal
| | - Song Baik
- Medical Research Council Centre for Immune Regulation, Institute for Biomedical Research, Medical School, University of BirminghamBirmingham, UK
| | - Graham Anderson
- Medical Research Council Centre for Immune Regulation, Institute for Biomedical Research, Medical School, University of BirminghamBirmingham, UK
| | - William E Jenkinson
- Medical Research Council Centre for Immune Regulation, Institute for Biomedical Research, Medical School, University of BirminghamBirmingham, UK
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What is so special about thinking; after all, we all do it! Exp Mol Pathol 2012; 93:354-64. [DOI: 10.1016/j.yexmp.2012.08.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2012] [Accepted: 08/17/2012] [Indexed: 12/24/2022]
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Perniola R. Expression of the autoimmune regulator gene and its relevance to the mechanisms of central and peripheral tolerance. Clin Dev Immunol 2012; 2012:207403. [PMID: 23125865 PMCID: PMC3485510 DOI: 10.1155/2012/207403] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2012] [Revised: 08/26/2012] [Accepted: 09/11/2012] [Indexed: 01/12/2023]
Abstract
The autoimmune polyendocrine syndrome type 1 (APS-1) is a monogenic disease due to pathogenic variants occurring in the autoimmune regulator (AIRE) gene. Its related protein, AIRE, activates the transcription of genes encoding for tissue-specific antigens (TsAgs) in a subset of medullary thymic epithelial cells: the presentation of TsAgs to the maturating thymocytes induces the apoptosis of the autoreactive clones and constitutes the main form of central tolerance. Dysregulation of thymic AIRE expression in genetically transmitted and acquired diseases other than APS-1 may contribute to further forms of autoimmunity. As AIRE and its murine homolog are also expressed in the secondary lymphoid organs, the extent and relevance of AIRE participation in the mechanisms of peripheral tolerance need to be thoroughly defined.
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Affiliation(s)
- Roberto Perniola
- Neonatal Intensive Care, Department of Pediatrics, V. Fazzi Regional Hospital, Piazza F. Muratore, 73100 Lecce, Italy.
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Cohn M. Musings About Regulation by T-Suppressors: A Response to the Commentary by Kristofor Ellestad on ‘Meanderings into the Regulation of Effector Class by the Immune System: Derivation of the Trauma Model’. Scand J Immunol 2012; 76:92-8. [DOI: 10.1111/j.1365-3083.2012.02723.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Cohn M. Meanderings into the Regulation of Effector Class by the Immune System: Derivation of the Trauma Model. Scand J Immunol 2012; 76:77-88. [DOI: 10.1111/j.1365-3083.2012.02721.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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Cohn M. Ten experiments that would make a difference in understanding immune mechanisms. Cell Mol Life Sci 2012; 69:405-12. [PMID: 22042272 PMCID: PMC11115027 DOI: 10.1007/s00018-011-0869-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2011] [Revised: 09/28/2011] [Accepted: 10/18/2011] [Indexed: 11/26/2022]
Abstract
Jacques Monod used to say, "Never trust an experiment that is not supported by a good theory." Theory or conceptualization permits us to put order or structure into a vast amount of data in a way that increases understanding. Validly competing theories are most useful when they make testably disprovable predictions. Illustrating the theory-experiment interaction is the goal of this exercise. Stated bleakly, the answers derived from the theory-based experiments described here would impact dramatically on how we understand immune behavior.
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Affiliation(s)
- Melvin Cohn
- Conceptual Immunology Group, The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, San Diego, CA 92037, USA.
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Kuerten S, Lehmann PV. The Immune Pathogenesis of Experimental Autoimmune Encephalomyelitis: Lessons Learned for Multiple Sclerosis? J Interferon Cytokine Res 2011; 31:907-16. [DOI: 10.1089/jir.2011.0072] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Affiliation(s)
- Stefanie Kuerten
- Department of Anatomy I, University Hospitals of Cologne, Cologne, Germany
| | - Paul V. Lehmann
- Department of Pathology, Case Western Reserve University, Cleveland, Ohio
- Cellular Technology Limited, Shaker Heights, Cleveland, Ohio
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Cohn M. The evolutionary context for a self-nonself discrimination. Cell Mol Life Sci 2010; 67:2851-62. [PMID: 20585970 PMCID: PMC2956437 DOI: 10.1007/s00018-010-0438-z] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2010] [Accepted: 06/10/2010] [Indexed: 10/19/2022]
Abstract
This essay was written to illustrate how one might think about the immune system. The formulation of valid theories is the basic component of how-to-think because the reduction of large and complex data sets by the use of logic into a succinct model with predictability and explanatory power, is the only way that we have to arrive at "understanding". Whether it is to achieve effective manipulation of the system or for pure pleasure, "understanding" is a universally agreed upon goal. It is in the nature of science that theories are there to be disproven. An experimentally disproven theory is a successful one. As they fail experimental test one by one, we end up with a default theory, that is, one that has yet to fail. Here, using the self-nonself discrimination as an example, how-to-think as I see it, will be illustrated.
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Affiliation(s)
- Melvin Cohn
- Conceptual Immunology Group, The Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA, 92037, USA.
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