Browsing by Subject "Regulatory T cells"

Now showing 1 - 6 of 6
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    CD4 T cells in the protection and pathogenesis of persistent Salmonella infection
    (2010-10) Johanns, Tanner Michael
    CD4 T cells contribute a diverse and non-redundant role to host defense against infections by orchestrating the activation and quality of the innate and adaptive immune responses. The diversity of CD4 T cell function is accomplished by differentiating into a plethora of distinct effector and regulatory lineages that dictate the kinetics and extent of immune activation. However, due to the range and breadth of CD4 T cell function, the precise role and mechanism of these various effector and regulatory subsets in host immunity remains incompletely understood. As persistent infections represent a significant source of morbidity and mortality worldwide, and CD4 T cells play a critical role in protection against this class of pathogens, we sought to elucidate the relative contribution of effector and regulatory CD4 T cell subsets in the pathogenesis and protection of this class of pathogens. Using a murine model of persistent Salmonella infection, we demonstrate that CD4 T cells are required for protection during primary infection but dispensable for secondary immunity. Moreover, both host and pathogen factors limit the generation of a protective effector CD4 T cell response during primary disease including increased regulatory CD4 T cell suppressive function and Salmonella-associated virulence genes, respectively, that enables establishment and persistence of disease. Together, these findings provide novel insight into disease process of persistent Salmonella infection that will aid in the design of future therapeutic and prevention strategies.
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    Development Of Regulatory T Cells Capable Of Maintaining Immune Homeostasis
    (2020-09) Owen, David
    The adaptive immune response, comprised of both T cells and B cells, is essential to control infections and eliminate transformed cancer cells. The success of the adaptive immune system relies on the ability to discriminate self from non-self-antigens. The thymus is the site of selection for T cells, where self-reactive T cells are eliminated, generating a non-self focused T cell compartment. However, this selection process is leaky and potentially pathogenic cells do escape thymic, or central, tolerance. Thus, a population of suppressor cells termed regulatory T cells (Treg cells) co-evolved in order to keep these self-reactive escapees in check. Treg cells that develop in the thymus as part of central tolerance induction are a critical population of T cells that are required to maintain immune homeostasis and prevent autoimmunity. Without intervention, mice or humans that lack the ability to generate Treg cells die shortly after birth from widespread autoimmune-mediated tissue destruction. Further, neonatal thymectomy in mice causes the development of an autoimmune wasting phenotype. These observations highlight the importance of thymic Treg cell selection in immune homeostasis. Thymic Treg cell development occurs via a two-step process. Step one involves developing CD4+ thymocytes receiving strong T cell receptor (TCR) stimulation via engagement of thymic self-antigens, leading to upregulation of CD25, the high affinity subunit of the IL-2 receptor, or FOXP3, the lineage defining transcription factor of Treg cells, generating either CD25+ or FOXP3lo Treg cell progenitors (TregP). Step two is driven by encounters between TregP cell and intrathymic STAT5 activating cytokines, predominantly IL-2, leading to co-expression of CD25 and FOXP3. These CD25+FOXP3+ cells represent fully mature Treg cells that disseminate from the thymus to mediate immune tolerance. While the framework of this two-step development process is understood, many details of each step remain incompletely understood. This thesis addresses several aspects of thymic Treg cell development. First, we identify that T cells are the critical source of IL-2 required to drive Treg differentiation. Second, we provide evidence that CD25+ and FOXP3lo TregP arise via distinct selection programs and contribute functionally distinct TCRs to the mature Treg compartment. Third, using single-cell RNA-sequencing analysis of conventional and Treg lineage thymocytes we provide a more detailed analysis of transcriptional signatures and intermediates of thymic Treg development. Finally, we gathered preliminary data to better understand the heterogeneity and function of recirculating or resident thymic Treg cells. Developing a holistic understanding of Treg development is essential to discern the etiology of immune disorders and properly modulate Treg cells to treat autoimmune disease, infections and cancer.
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    The Role of Anergy in Peripheral Regulatory T cell Generation
    (2016-06) Kalekar, Lokesh
    The role that anergy, an acquired state of T cell functional unresponsiveness, plays in natural peripheral tolerance remains unclear. In this study, we demonstrate that anergy is selectively induced in fetal antigen-specific maternal CD4+ T cells during pregnancy. A naturally occurring subpopulation of anergic polyclonal CD4+ T cells, enriched in self antigen-specific T cell receptors, is also observed in healthy hosts. Neuropilin-1 expression in anergic conventional CD4+ T cells is associated with thymic regulatory T cell (Treg cell)-related gene hypomethylation, and this correlates with their capacity to differentiate into Foxp3+ Treg cells that suppress immunopathology. Thus, our data suggest that not only is anergy induction important in preventing autoimmunity, but it also generates the precursors for peripheral Treg cell differentiation
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    The role of the IL-2R beta-mediated cytokine signaling in natural regulatory T cell development.
    (2009-02) Yang, Jianying
    Nature regulatory T cells (Tregs) are a group of CD4+Foxp3+ T cells that develop in the thymus, and they are crucial in maintaining the peripheral tolerance. Although it has been shown that IL-2/IL-2R mediated cytokine signaling is essential for Treg homeostasis, it is still controversial whether IL-2/IL-2R is required for Treg development, or how IL-2R-mediated signaling events govern Treg development. To answer these questions, I examined Foxp3+ Treg populations from 2 - 4 weeks old IL-2Rbeta-/- mice, and my data showed that Tregs were largely absent even in young and disease-free IL-2Rbeta-/- mice, indicating that IL-2Rbeta is required for Treg development. To investigate how IL-2Rbeta mediated cytokine signaling governs Treg development, I examined Treg development in STAT5abDeltaN/DeltaN and CD4Cre x STAT5fl/fl mice. My data suggested that STAT5 activation is the major signaling event downstream of IL-2beta that promotes Treg development. This conclusion was further corroborated by the observation that a restored Treg population was present in STAT5bCA x IL2Rbeta-/- mice. Furthermore, reconstitution of IL-2Rbeta-/- bone marrow with an IL2Rbeta-STAT5 mutant construct that selectively activates STAT5 restored CD4+Foxp3+ Treg development and prevented T cell activation. These data collectively suggests that STAT5 activation downstream of IL-2Rbeta is both necessary and sufficient to drive CD4+Foxp3+ Treg development. To study how cytokine signals cooperate with TCR signals in shaping Treg development, or any other factors involved in this process, I compared Treg progenitor (CD4+CD25+CD8-Foxp3-) and mature Treg populations (CD4+CD8-Foxp3+) in the thymus from several mouse strains that have either reduced or enhanced TCR signaling or STAT5-dependent signaling, including STAT5bCA, IL-2Rgamma-/-, and CD28-/- mice. Our data suggest that TCR/CD28 signaling is crucial in generating Treg progenitor cells, while cytokine signaling is essential in converting Treg progenitor T cells into mature Tregs in the thymus. My further studies also indicate that Carma1 is a major effector molecule downstream of TCR/CD28 signaling pathways in governing Treg progenitor cell development; likewise, STAT5 is a crucial factor downstream of IL-2Rbeta that converts Treg progenitor cells into mature Tregs, possibly by enhancing DNA methylation in the Foxp3 locus.
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    Thymic interferons and protein O-GlcNAcylation in regulatory T cells: two tales of T cell tolerance
    (2021-03) Salgado Barrero, Oscar
    Immune tolerance mechanisms prevent the development of immune responses directed to the host. This is especially important for the adaptive immune system, whose potent and long-lasting responses would be extremely deleterious to the host if misguided. This work explores two aspects of immune tolerance: the role of protein O-GlcNAcylation in regulatory T (Treg) cells and the importance of interferons during T cell tolerance development in the thymus. In chapter 2 of this document, we show that the posttranslational modification by O- linked N-Acetylglucosamine (O-GlcNAc) stabilizes FOXP3 and activates STAT5, thus integrating these critical signaling pathways. O-GlcNAc-deficient Treg cells develop normally but display modestly reduced FOXP3 expression, strongly impaired lineage stability and effector function, and ultimately fatal autoimmunity in mice. Moreover, deficiency in protein O-GlcNAcylation attenuates IL-2/STAT5 signaling, while overexpression of a constitutively active form of STAT5 partially ameliorates Treg cell dysfunction and systemic inflammation in O-GlcNAc deficient mice. These data demonstrate that protein O-GlcNAcylation is essential for lineage stability and effector function in Treg cells. In chapter 3, we characterized the expression of interferons in the thymus. We found that developing thymocytes displayed a type I IFN signature that was mainly dependent on IFN-β. Using Ifnb tdtomato and luciferase reporter mouse strains, we found expression in a small population of medullary thymic epithelial cells (mTEC), which was AIRE dependent and peaked at 2-3 weeks of age. To study the cellular response to thymic interferon, we used an Mx1gfp reporter mouse strain and report that numerous thymic cell populations respond constitutively to IFN in vivo. The response in some cell populations was not abrogated unless both IFNAR and IFNLR, or STAT1 were deficient, suggesting that both type I and type III IFNs are at play. Indeed, single cell RNA sequencing analysis revealed dramatic transcriptional changes in all thymic APCs in IFNAR/ IFNLR deficient mice. These results show that steady state type I and type III IFN signaling drives a gene-expression program in thymic APCs that shapes the thymic microenvironment.
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    Tumor-Necrosis Factor Receptor Superfamily Costimulation Drives Thymic Regulatory T Cell Development
    (2014-07) Mahmud, Shawn
    Thymic-derived CD4+Foxp3+ regulatory T cells (Tregs) are critical for preventing autoimmune disease. Previous work has demonstrated that Tregs develop by an IL-2R/STAT5-dependent mechanism, and that the T cell antigen receptors (TCRs) collectively expressed by thymic-derived Tregs react with self-antigen with high-affinity. In this regard, Tregs are similar to autoreactive T cells undergoing negative selection. Relatively little is known about how the selection bias in the Treg TCR repertoire is imposed and how the decision to become a Treg as opposed to undergoing apoptosis is made. This thesis demonstrates that progenitors of thymic Tregs, which are CD25+ and Foxp3-, highly upregulate three family members of the TNF receptor superfamily (TNFRSF): GITR, OX40, and TNFR2. The expression level of these receptors directly mirrors perceived TCR signal strength by developing Tregs. Stimulating Treg progenitors with the ligands for these receptors enhances the expression of the IL-2 receptor alpha chain, CD25, resulting in increased sensitivity to IL-2, and ultimately increasing the likelihood of maturation into the Foxp3+ thymic Treg lineage. Loss of TNFRSF expression in Treg progenitors blocks Treg development in vivo. Finally, we demonstrate that TNFRSF costimulation directly shapes the Treg TCR repertoire. A second line of investigation aims to uncover the developmental and functional potential of a second, more recently described population of Treg progenitors which are CD25- and Foxp3lo. We find that despite lacking CD25, these cells do efficiently respond to IL-2, and that one potential explanation for this finding is that CD25-Foxp3lo Treg progenitors express higher levels of CD122 (the IL-2 receptor beta chain that mediates signaling upon ligand binding). CD25-Foxp3lo Treg progenitors are phenotypically `older' and have resided in the thymus longer than CD25+Foxp3- Treg progenitors, and this may also explain their ability to enter the Treg lineage given their elevated levels of CD122. Finally, we demonstrate that both populations of Treg progenitors are responsive to TNFRSF costimulation and that ligation of GITR in these cells shapes the resultant Treg TCR repertoire. Further pending studies involving TCR sequencing and in vivo competition experiments will fully elucidate the significance of this alternative population of Treg progenitors.