Instruct: Given a scientific claim, retrieve documents that support or refute the claim.
Query: RANK-RANKL pathway signalling is linked to development of Aire-expressing medullary thymic epithelial cells.
Aire-expressing medullary thymic epithelial cells (mTECs) play a key role in preventing autoimmunity by expressing tissue-restricted antigens to help purge the emerging T cell receptor repertoire of self-reactive specificities. Here we demonstrate a novel role for a CD4+3− inducer cell population, previously linked to development of organized secondary lymphoid structures and maintenance of T cell memory in the functional regulation of Aire-mediated promiscuous gene expression in the thymus. CD4+3− cells are closely associated with mTECs in adult thymus, and in fetal thymus their appearance is temporally linked with the appearance of Aire+ mTECs. We show that RANKL signals from this cell promote the maturation of RANK-expressing CD80−Aire− mTEC progenitors into CD80+Aire+ mTECs, and that transplantation of RANK-deficient thymic stroma into immunodeficient hosts induces autoimmunity. Collectively, our data reveal cellular and molecular mechanisms leading to the generation of Aire+ mTECs and highlight a previously unrecognized role for CD4+3−RANKL+ inducer cells in intrathymic self-tolerance.
Expression of the intermediate filament protein keratin 17 (K17) is robustly upregulated in inflammatory skin diseases and in many tumors originating in stratified and pseudostratified epithelia. We report that autoimmune regulator (Aire), a transcriptional regulator, is inducibly expressed in human and mouse tumor keratinocytes in a K17-dependent manner and is required for timely onset of Gli2-induced skin tumorigenesis in mice. The induction of Aire mRNA in keratinocytes depends on a functional interaction between K17 and the heterogeneous nuclear ribonucleoprotein hnRNP K. Further, K17 colocalizes with Aire protein in the nucleus of tumor-prone keratinocytes, and each factor is bound to a specific promoter region featuring an NF-κB consensus sequence in a relevant subset of K17- and Aire-dependent proinflammatory genes. These findings provide radically new insight into keratin intermediate filament and Aire function, along with a molecular basis for the K17-dependent amplification of inflammatory and immune responses in diseased epithelia.
Immunosuppressive drugs and cytotoxic chemotherapy agents are designed to kill or suppress autoreactive, alloaggressive, or hyperinflammatory T cells, or disseminated malignancies. However, they also cause severe immunological side effects ranging from interrupted thymopoiesis and general immunodeficiency to, paradoxically, autoimmunity. Consistent with the cross-talk between thymocytes and stromal cells, we now show that these common therapeutic agents have major effects on murine thymic epithelial cells (TEC), crucially required to rebuild immunity posttreatment. We show that the immunosuppressant cyclosporine A, which has been linked to a thymus-dependent autoimmune syndrome in some patients, causes extensive loss of autoimmune regulator (Aire(+)) tolerance-inducing MHC class II(high) medullary TEC (mTEC(high)). Post-cyclosporine A, Aire expression was restored within 7 days. Full recovery of the mTEC(high) subset occurred within 10 days and was linked to a decrease in a relatively resistant MHC class II(low) mTEC subset (mTEC(low)), consistent with a previously described precursor-product relationship. Cyclophosphamide and dexamethasone caused more extensive ablation of thymocytes and stromal cells but again severely depleted tolerance-inducing mTEC(high). Together, these data show that Aire(+) mTECs are highly sensitive to damage and that mTEC regeneration follows a conserved pattern regardless of the treatment regimen used.
Expression of peripheral antigens in the thymus has been implicated in T cell tolerance and autoimmunity. Here we identified medullary thymic epithelial cells as being a unique cell type that expresses a diverse range of tissue-specific antigens. We found that this promiscuous gene expression was a cell-autonomous property of medullary epithelial cells and was maintained during the entire period of thymic T cell output. It may facilitate tolerance induction to self-antigens that would otherwise be temporally or spatially secluded from the immune system. However, the array of promiscuously expressed self-antigens appeared random rather than selected and was not confined to secluded self-antigens.
The thymic transcription factor autoimmune regulator (Aire) prevents autoimmunity in part by promoting expression of tissue-specific self-antigens, which include many cancer antigens. For example, AIRE-deficient patients are predisposed to vitiligo, an autoimmune disease of melanocytes that is often triggered by efficacious immunotherapies against melanoma. Therefore, we hypothesized that Aire deficiency in mice may elevate immune responses to cancer and provide insights into how such responses might be triggered. In this study, we show that Aire deficiency decreases thymic expression of TRP-1 (TYRP1), which is a self-antigen in melanocytes and a cancer antigen in melanomas. Aire deficiency resulted in defective negative selection of TRP-1-specific T cells without affecting thymic numbers of regulatory T cells. Aire-deficient mice displayed elevated T-cell immune responses that were associated with suppression of melanoma outgrowth. Furthermore, transplantation of Aire-deficient thymic stroma was sufficient to confer more effective immune rejection of melanoma in an otherwise Aire wild-type host. Together, our work showed how Aire deficiency can enhance immune responses against melanoma and how manipulating TRP-1-specific T-cell negative selection may offer a logical strategy to enhance immune rejection of melanoma.
Autoimmune polyendocrinopathy syndrome type 1 is a recessive Mendelian disorder resulting from mutations in a novel gene, AIRE, and is characterized by a spectrum of organ-specific autoimmune diseases. It is not known what tolerance mechanisms are defective as a result of AIRE mutation. By tracing the fate of autoreactive CD4+ T cells with high affinity for a pancreatic antigen in transgenic mice with an Aire mutation, we show here that Aire deficiency causes almost complete failure to delete the organ-specific cells in the thymus. These results indicate that autoimmune polyendocrinopathy syndrome 1 is caused by failure of a specialized mechanism for deleting forbidden T cell clones, establishing a central role for this tolerance mechanism.
The expression of melanoma-associated antigens (MAA) being limited to normal melanocytes and melanomas, MAAs are ideal targets for immunotherapy and melanoma vaccines. As MAAs are derived from self, immune responses to these may be limited by thymic tolerance. The extent to which self-tolerance prevents efficient immune responses to MAAs remains unknown. The autoimmune regulator (AIRE) controls the expression of tissue-specific self-antigens in thymic epithelial cells (TECs). The level of antigens expressed in the TECs determines the fate of auto-reactive thymocytes. Deficiency in AIRE leads in both humans (APECED patients) and mice to enlarged autoreactive immune repertoires. Here we show increased IgG levels to melanoma cells in APECED patients correlating with autoimmune skin features. Similarly, the enlarged T cell repertoire in AIRE(-/-) mice enables them to mount anti-MAA and anti-melanoma responses as shown by increased anti-melanoma antibodies, and enhanced CD4(+) and MAA-specific CD8(+) T cell responses after melanoma challenge. We show that thymic expression of gp100 is under the control of AIRE, leading to increased gp100-specific CD8(+) T cell frequencies in AIRE(-/-) mice. TRP-2 (tyrosinase-related protein), on the other hand, is absent from TECs and consequently TRP-2 specific CD8(+) T cells were found in both AIRE(-/-) and AIRE(+/+) mice. This study emphasizes the importance of investigating thymic expression of self-antigens prior to their inclusion in vaccination and immunotherapy strategies.
The expression of self-antigen in the thymus is believed to be responsible for the deletion of autoreactive T lymphocytes, a critical process in the maintenance of unresponsiveness to self. The Autoimmune regulator (Aire) gene, which is defective in the disorder autoimmune polyglandular syndrome type 1, has been shown to promote the thymic expression of self-antigens. A clear link, however, between specific thymic self-antigens and a single autoimmune phenotype in this model has been lacking. We show that autoimmune eye disease in aire-deficient mice develops as a result of loss of thymic expression of a single eye antigen, interphotoreceptor retinoid-binding protein (IRBP). In addition, lack of IRBP expression solely in the thymus, even in the presence of aire expression, is sufficient to trigger spontaneous eye-specific autoimmunity. These results suggest that failure of thymic expression of selective single self-antigens can be sufficient to cause organ-specific autoimmune disease, even in otherwise self-tolerant individuals.
Thymic epithelial cells (TEC) form the structural and functional microenvironment necessary for the establishment and quality control of the T cell repertoire. In addition, they provide an ectopic source of numerous tissue-restricted antigens (TRA), a feature called promiscuous gene expression (pGE). How the regulation of pGE is related to the cell biology of TEC subset(s), e.g. their turnover and developmental interrelationship is still poorly understood. The observation that pGE is foremost a property of phenotypically and functionally mature medullary TEC (mTEC) implies that the full implementation of pGE is contingent on mTEC differentiation. Here, we show that the emergence of TEC subsets and pGE is tightly correlated during ontogeny and we provide evidence that mature CD80pos mTEC develop from an immature CD80neg subset. This differentiation step proceeds continuously in the postnatal thymus. While mature mTEC turnover in 2 to 3 weeks, immature mTEC encompass a smaller cycling and a larger non-cycling pool. The latter might serve as a reservoir of committed precursors, which sustain this renewal process. Our data document that mTEC represent a highly dynamic cell population, and they imply that the availability and display of TRA in the thymus undergoes a perpetual temporal and spatial reorganization.
Interleukin 7 (IL-7) stimulates the proliferation of B cell progenitors, thymocytes, and mature T cells through an interaction with a high affinity receptor (IL-7R) belonging to the hematopoietin receptor superfamily. We have further addressed the role of IL-7 and its receptor during B and T cell development by generating mice genetically deficient in IL-7R. Mutant mice display a profound reduction in thymic and peripheral lymphoid cellularity. Analyses of lymphoid progenitor populations in IL-7R-deficient mice define precisely those developmental stages affected by the mutation and reveal a critical role for IL-7R during early lymphoid development. Significantly, these studies indicate that the phase of thymocyte expansion occurring before the onset of T cell receptor gene rearrangement is critically dependent upon, and mediated by the high affinity receptor for IL-7.
Expression of the receptor-type tyrosine phosphatase LAR was studied in cells of the murine hemopoietic system. The gene is expressed in all cells of the T cell lineage but not in cells of any other hemopoietic lineage and the level of expression in T cells is developmentally regulated. The CD4(-)8(-)44(+) early thymic immigrants and mature (CD4(+)8(-)/CD4(-)8(+)) thymocytes and T cells express low levels, whereas immature (CD4(-)8(-)44(-) and CD4(+)8(+)) thymocytes express high levels of LAR. Among bone marrow cells only uncommitted c-kit(+)B220(+)CD19(-) precursors, but not B cell lineage committed c-kit(+)B220(+)CD19(+) precursors, express low levels of LAR. In contrast to the c-kit(+)B220(+)CD19(+) pre-BI cells from normal mice, counterparts of pre-BI cells from PAX-5-deficient mice express LAR, indicating that PAX-5-mediated commitment to the B cell lineage results in suppression of LAR. During differentiation of PAX-5-deficient pre-BI cell line into non-T cell lineages, expression of LAR is switched off, but it is up-regulated during differentiation into thymocytes. Thus, within the hemopoietic system, LAR appears to be a T cell lineage-specific receptor-type phosphatase. However, surprisingly, truncation of its phosphatase domains has no obvious effect on T cell development, repertoire selection or function.
Recent elucidation of the role of central tolerance in preventing organ-specific autoimmunity has changed our concepts of self/nonself discrimination. This paradigmatic shift is largely attributable to the discovery of promiscuous expression of tissue-restricted self-antigens (TRAs) by medullary thymic epithelial cells (mTECs). TRA expression in mTECs mirrors virtually all tissues of the body, irrespective of developmental or spatio-temporal expression patterns. This review summarizes current knowledge on the cellular and molecular regulation of TRA expression in mTECs, outlines relevant mechanisms of antigen presentation and modes of tolerance induction, and discusses implications for the pathogenesis of autoimmune diseases and other biological processes such as fertility, pregnancy, puberty, and tumor defense.
Epidermal growth factor receptor (EGFR) is known to be critically involved in tissue development and homeostasis as well as in the pathogenesis of cancer. Here we showed that Foxp3(+) regulatory T (Treg) cells express EGFR under inflammatory conditions. Stimulation with the EGF-like growth factor Amphiregulin (AREG) markedly enhanced Treg cell function in vitro, and in a colitis and tumor vaccination model we showed that AREG was critical for efficient Treg cell function in vivo. In addition, mast cell-derived AREG fully restored optimal Treg cell function. These findings reveal EGFR as a component in the regulation of local immune responses and establish a link between mast cells and Treg cells. Targeting of this immune regulatory mechanism may contribute to the therapeutic successes of EGFR-targeting treatments in cancer patients.
Th17 and regulatory T (Treg) cells play opposite roles in autoimmune diseases. However, the mechanisms underlying their proper migration to inflammatory tissues are unclear. In this study, we report that these two T cell subsets both express CCR6. CCR6 expression in Th17 cells is regulated by TGF-beta and requires two nuclear receptors, RORalpha and RORgamma. Th17 cells also express the CCR6 ligand CCL20, which is induced synergistically by TGF-beta and IL-6, which requires STAT3, RORgamma and IL-21. Th17 cells, by producing CCL20, promote migration of Th17 and Treg cells in vitro in a CCR6-dependent manner. Lack of CCR6 in Th17 cells reduces the severity of experimental autoimmune encephalomyelitis and Th17 and Treg recruitment into inflammatory tissues. Similarly, CCR6 on Treg cells is also important for their recruitment into inflammatory tissues. Our data indicate an important role of CCR6 in Treg and Th17 cell migration.
During ageing thymic function declines and is unable to meet the demand for peripheral T helper (Th) cell replenishment. Therefore, population maintenance of naive Th cells must be at least partly peripherally based. Such peripheral postthymic expansion of recent thymic emigrants (RTEs) during ageing consequently should lead to loss or dilution of T cell receptor excision circles (TRECs) from a subset of naive T cells. We have identified two subsets of naive Th cells in human adult peripheral blood characterized by a striking unequal content of TRECs, indicating different peripheral proliferative histories. TRECs are highly enriched in peripheral naive CD45RA+ Th cells coexpressing CD31 compared with peripheral naive CD45RA+ Th cells lacking CD31 expression, in which TRECs can hardly be detected. Furthermore we show that CD31−CD45RA+ Th cells account for increasing percentages of the naive peripheral Th cell pool during ageing but retain phenotypic and functional features of naive Th cells. As CD31 is lost upon T cell receptor (TCR) engagement in vitro, we hypothesize that TCR triggering is a prerequisite for homeostatically driven peripheral postthymic expansion of human naive RTEs. We describe here the identification of peripherally expanded naive Th cells in human adult blood characterized by the loss of CD31 expression and a highly reduced TREC content.
Thymic-derived natural T regulatory cells (Tregs) are characterized by functional and phenotypic heterogeneity. Recently, a small fraction of peripheral Tregs has been shown to express Klrg1, but it remains unclear as to what extent Klrg1 defines a unique Treg subset. In this study, we show that Klrg1(+) Tregs represent a terminally differentiated Treg subset derived from Klrg1(-) Tregs. This subset is a recent Ag-responsive and highly activated short-lived Treg population that expresses enhanced levels of Treg suppressive molecules and that preferentially resides within mucosal tissues. The development of Klrg1(+) Tregs also requires extensive IL-2R signaling. This activity represents a distinct function for IL-2, independent from its contribution to Treg homeostasis and competitive fitness. These and other properties are analogous to terminally differentiated short-lived CD8(+) T effector cells. Our findings suggest that an important pathway driving Ag-activated conventional T lymphocytes also operates for Tregs.
Previous reports have suggested that the protooncogene c-myb participates in T cell development in the thymus and mature T cell proliferation. We have generated two T cell-specific c-myb knockout mouse models, myb/LckCre and myb/CD4Cre. We have demonstrated that c-myb is required for the development of thymocytes at the DN3 stage, for survival and proliferation of double-positive thymocytes, for differentiation of single-positive CD4 and CD8 T cells, and for the proliferative responses of mature T cells. In addition, our data show that c-myb is directly involved in the formation of double-positive CD4+CD8+CD25+, CD4+CD25+, and CD8+CD25+ T cells, developmental processes that may imply a role for c-myb in autoimmune dysfunction.
Cells acquire their ultimate identities by activating combinations of transcription factors that initiate and sustain expression of the appropriate cell type-specific genes. T cell development depends on the progression of progenitor cells through three major phases, each of which is associated with distinct transcription factor ensembles that control the recruitment of these cells to the thymus, their proliferation, lineage commitment and responsiveness to T cell receptor signals, all before the allocation of cells to particular effector programmes. All three phases are essential for proper T cell development, as are the mechanisms that determine the boundaries between each phase. Cells that fail to shut off one set of regulators before the next gene network phase is activated are predisposed to leukaemic transformation.
CD4(+)CD25(+) regulatory T cells (T regs) play a major role in the maintenance of self-tolerance and immune suppression, although the mechanisms controlling T reg development and suppressor function remain incompletely understood. Herein, we provide evidence that Kruppel-like factor 10 (KLF10/TIEG1) constitutes an important regulator of T regulatory cell suppressor function and CD4(+)CD25(-) T cell activation through distinct mechanisms involving transforming growth factor (TGF)-beta1 and Foxp3. KLF10 overexpressing CD4(+)CD25(-) T cells induced both TGF-beta1 and Foxp3 expression, an effect associated with reduced T-Bet (Th1 marker) and Gata3 (Th2 marker) mRNA expression. Consistently, KLF10(-/-) CD4(+)CD25(-) T cells have enhanced differentiation along both Th1 and Th2 pathways and elaborate higher levels of Th1 and Th2 cytokines. Furthermore, KLF10(-/-) CD4(+)CD25(-) T cell effectors cannot be appropriately suppressed by wild-type T regs. Surprisingly, KLF10(-/-) T reg cells have reduced suppressor function, independent of Foxp3 expression, with decreased expression and elaboration of TGF-beta1, an effect completely rescued by exogenous treatment with TGF-beta1. Mechanistic studies demonstrate that in response to TGF-beta1, KLF10 can transactivate both TGF-beta1 and Foxp3 promoters, implicating KLF10 in a positive feedback loop that may promote cell-intrinsic control of T cell activation. Finally, KLF10(-/-) CD4(+)CD25(-) T cells promoted atherosclerosis by approximately 2-fold in ApoE(-/-)/scid/scid mice with increased leukocyte accumulation and peripheral pro-inflammatory cytokines. Thus, KLF10 is a critical regulator in the transcriptional network controlling TGF-beta1 in both CD4(+)CD25(-) T cells and T regs and plays an important role in regulating atherosclerotic lesion formation in mice.
The PI3K-Akt-mTORC1 axis contributes to the activation, survival, and proliferation of CD4(+) T cells upon stimulation through TCR and CD28. Here, we demonstrate that the suppression of this axis by deletion of p85α or PI3K/mTORC1 inhibitors as well as T cell-specific deletion of raptor, an essential component of mTORC1, impairs Th17 differentiation in vitro and in vivo in a S6K1/2-dependent fashion. Inhibition of PI3K-Akt-mTORC1-S6K1 axis impairs the downregulation of Gfi1, a negative regulator of Th17 differentiation. Furthermore, we demonstrate that S6K2, a nuclear counterpart of S6K1, is induced by the PI3K-Akt-mTORC1 axis, binds RORγ, and carries RORγ to the nucleus. These results point toward a pivotal role of PI3K-Akt-mTORC1-S6K1/2 axis in Th17 differentiation.
In a cell-type- and stimulus-dependent fashion, the early response gene immediate early gene X-1 (IEX-1) is involved in growth control and modulation of apoptosis. The present study demonstrates that, in the two acute promyelocytic leukemia (APL) cell lines NB4 and KG1, exhibiting distinct responsiveness to retinoic acids (RAs), IEX-1 expression is rapidly (30–60 min) induced by all-trans- or cis-RA and independently of other signal transduction mediators, such as TNFα, NF-κB or MAP kinases. In NB4 cells (expressing PML–RARα), this increase is transient and completely reversible, along with a cell cycle arrest, ongoing differentiation and lower sensitivity to anti-cancer-drug-induced apoptosis. In contrast, the RA-induced IEX-1 expression in KG1 cells (expressing PLZF–RARα) persists over days, along with continued cell cycle progression and increased apoptotic sensitivity. Furthermore, two functional RA-response elements in the IEX-1 promoter were identified by gel shift and luciferase reporter gene assays. IEX-1 might be a rather unique transcriptional target of the two X–RARα fusion receptors exhibiting distinct responsiveness to RAs. Following a different time course of direct transcriptional induction by PML–RARα and PLZF–RARα in NB4 and KG1 cells, respectively, IEX-1 expression may be involved in the modified actions of these receptors and the distinct phenotypes of APL cells.
TLR sense microbial infections, and control activation of immune responses. Dendritic cells, macrophages, and B lymphocytes express TLR and the TLR-signaling adaptor protein MyD88. The impact of TLR-activated B cells on T cell-mediated inflammation is unknown. In this study, we have used mice carrying B cell-restricted deficiencies in MyD88 or in distinct TLR to examine the impact of TLR-activated B cells on a T cell-mediated autoimmune disease, experimental autoimmune encephalomyelitis (EAE). We demonstrate that TLR-signaling in B cells suppresses inflammatory T cell responses (both Th1 and Th17), and stimulates recovery from EAE. Only certain TLR are required on B cells for resolution of EAE, and these are dispensable for disease initiation, indicating that a category of TLR agonists preferentially triggers a suppressive function in B cells and thereby limits autoimmune disease. The TLR agonists controlling the regulatory function of B cells are provided by components of Mycobacterium tuberculosis present in the adjuvant. Thus, MyD88 signaling in B cells antagonizes MyD88 signaling in other cells, which drives differentiation of Th17 cells and is required for induction of EAE. Altogether, our data indicate that B cells link recognition of microbial products via TLR to suppression of a T cell-mediated autoimmune disease.
The molecular basis for the distinctive cytokine expression of CD4+ T helper 1 (Th1) and T helper 2 (Th2) subsets remains elusive. Here, we report that the proto-oncogene c-maf, a basic region/leucine zipper transcription factor, controls tissue-specific expression of IL-4. c-Maf is expressed in Th2 but not Th1 clones and is induced during normal precursor cell differentiation along a Th2 but not Th1 lineage. c-Maf binds to a c-Maf response element (MARE) in the proximal IL-4 promoter adjacent to a site footprinted by extracts from Th2 but not Th1 clones. Ectopic expression of c-Maf transactivates the IL-4 promoter in Th1 cells, B cells, and nonlymphoid cells, a function that maps to the MARE and Th2-specific footprint. Furthermore, c-Maf acts in synergy with the nuclear factor of activated T cells (NF-ATp) to initiate endogeneous IL-4 production by B cells. Manipulation of c-Maf may alter Th subset ratios in human disease.
Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is the only described systemic autoimmune disease with established monogenic background, and the first autoimmune disorder localized outside the major histocompatibility complex (MHC) region. The primary biochemical defect in APECED is unknown. We have isolated a novel gene, AIRE, encoding for a putative nuclear protein featuring two PHD-type zinc-finger motifs, suggesting its involvement in transcriptional regulation. Five mutations in AIRE are reported in individuals with this disorder. This is the first report of a single-gene defect causing a systemic human autoimmune disease, providing a tool for exploring the molecular basis of autoimmunity.
Activated T cells secrete multiple osteoclastogenic cytokines which play a major role in the bone destruction associated with rheumatoid arthritis. While the role of T cells in osteoclastogenesis has received much attention recently, the effect of T cells on osteoblast formation and activity is poorly defined. In this study, we investigated the hypothesis that in chronic inflammation activated T cells contribute to enhanced bone turnover by promoting osteoblastic differentiation. We show that T cells produce soluble factors that induce alkaline phosphatase activity in bone marrow stromal cells and elevated expression of mRNA for Runx2 and osteocalcin. This data indicate that T cell derived factors have the capacity to stimulate the differentiation of bone marrow stromal cells into the osteoblast phenotype. RANKL mRNA was undetectable under any conditions in highly purified bone marrow stromal cells. In contrast, RANKL was constitutively expressed in primary osteoblasts and only moderately up-regulated by activated T cell conditioned medium. Interestingly, both bone marrow stromal cells and osteoblasts expressed mRNA for RANK, which was strongly up-regulated in both cell types by activated T cell conditioned medium. Although, mRNA for the RANKL decoy receptor, osteoprotegerin, was also up-regulated by activated T cell conditioned medium, it's inhibitory effects may be mitigated by a simultaneous rise in the osteoprotegerin competitor TNF-related apoptosis-inducing ligand. Based on our data we propose that during chronic inflammation, T cells regulate bone loss by a dual mechanism involving both direct stimulation of osteoclastogenesis, by production of osteoclastogenic cytokines, and indirectly by induction of osteoblast differentiation and up-regulation of bone turnover via coupling.