Interleukin-7 Influences FOXP3+CD4+ Regulatory T Cells Peripheral Homeostasis

Mechanisms governing peripheral CD4+ FOXP3+ regulatory T cells (Treg) survival and homeostasis are multiple suggesting tight and complex regulation of regulatory T cells homeostasis. Some specific factors, such as TGF-β, interleukin-2 (IL-2) and B7 costimulatory molecules have been identified as essentials for maintenance of the peripheral Treg compartment. Conversely, Treg dependency upon classical T cell homeostatic factors such as IL-7 is still unclear. In this work, we formally investigated the role of IL-7 in Treg homeostasis in vivo in murine models. We demonstrated that IL-7 availability regulated the size of peripheral Treg cell pool and thus paralleled the impact of IL-7 on conventional T cell pool. Moreover, we showed that IL-7 administration increased Treg cell numbers by inducing thymic-independent Treg peripheral expansion. Importantly the impact of IL-7 on Treg expansion was detected whether conventional T cells were present or absent as IL-7 directly participates to the peripheral expansion of Treg after adoptive transfer into lymphopenic hosts. Our results definitively identify IL-7 as a central factor contributing to Treg peripheral homeostasis, thus reassembling Treg to other T cell subsets in respect of their need for IL-7 for their peripheral maintenance

Critical Role of TCF-1 in Repression of the IL-17 Gene

Overwhelming activation of IL-17, a gene involved in inflammation, leads to exaggerated Th17 responses associated with numerous autoimmune conditions, such as experimental autoimmune encephalomyelitis (EAE). Here we show that TCF-1 is a critical factor to repress IL-17 gene locus by chromatin modifications during T cell development. Deletion of TCF-1 resulted in increased IL-17 gene expression both in thymus and peripheral T cells, which led to enhanced Th17 differentiation. As a result, TCF-1-/- mice were susceptible to Th17-dependent EAE induction. Rag1-/- mice reconstituted with TCF-1-/- T cells were also susceptible to EAE, indicating TCF-1 is intrinsically required to repress IL-17. However, expression of wild-type TCF-1 or dominant negative TCF-1 did not interfere with Th17 differentiation in mature T cells. Furthermore, expression of TCF-1 in TCF-1-/- T cells could not restore Th17 differentiation to wild-type levels, indicating that TCF-1 cannot affect IL-17 production at the mature T cell stage. This is also supported by the normal up-regulation or activation in mature TCF-1-/- T cells of factors known to regulate Th17 differentiation, including RORγt and Stat3. We observed hyperacetylation together with trimethylation of Lys-4 at the IL-17 locus in TCF-1-/- thymocytes, two epigenetic modifications indicating an open active state of the gene. Such epigenetic modifications were preserved even when TCF-1-/- T cells migrated out of thymus. Therefore, TCF-1 mediates an active process to repress IL-17 gene expression via epigenetic modifications during T cell development. This TCF-1-mediated repression of IL-17 is critical for peripheral T cells to generate balanced immune responses

c-Rel Controls Multiple Discrete Steps in the Thymic Development of Foxp3+ CD4 Regulatory T Cells

The development of natural Foxp3+ CD4 regulatory T cells (nTregs) proceeds via two steps that involve the initial antigen dependent generation of CD25+GITRhiFoxp3−CD4+ nTreg precursors followed by the cytokine induction of Foxp3. Using mutant mouse models that lack c-Rel, the critical NF-κB transcription factor required for nTreg differentiation, we establish that c-Rel regulates both of these developmental steps. c-Rel controls the generation of nTreg precursors via a haplo-insufficient mechanism, indicating that this step is highly sensitive to c-Rel levels. However, maintenance of c-Rel in an inactive state in nTreg precursors demonstrates that it is not required for a constitutive function in these cells. While the subsequent IL-2 induction of Foxp3 in nTreg precursors requires c-Rel, this developmental transition does not coincide with the nuclear expression of c-Rel. Collectively, our results support a model of nTreg differentiation in which c-Rel generates a permissive state for foxp3 transcription during the development of nTreg precursors that influences the subsequent IL-2 dependent induction of Foxp3 without a need for c-Rel reactivation

Central CD4+ T cell tolerance: deletion versus regulatory T cell differentiation

The diversion of MHC class II-restricted thymocytes into the regulatory T (Treg) cell lineage, similarly to clonal deletion, is driven by intrathymic encounter of agonist self-antigens. Somewhat paradoxically, it thus seems that the expression of an autoreactive T cell receptor is a shared characteristic of T cells that are subject to clonal deletion and those that are diverted into the Treg cell lineage. Here, we discuss how thymocyte-intrinsic and -extrinsic determinants may specify the choice between these two fundamentally different T cell fates

Cell-Intrinsic NF-κB Activation Is Critical for the Development of Natural Regulatory T Cells in Mice

regulatory T (Treg) cells develop in the thymus and represent a mature T cell subpopulation critically involved in maintaining peripheral tolerance. The differentiation of Treg cells in the thymus requires T cell receptor (TCR)/CD28 stimulation along with cytokine-promoted Foxp3 induction. TCR-mediated nuclear factor kappa B (NF-κB) activation seems to be involved in differentiation of Treg cells because deletion of components of the NF-κB signaling pathway, as well as of NF-κB transcription factors, leads to markedly decreased Treg cell numbers in thymus and periphery. thymic Treg precursors and their further differentiation into mature Treg cells. Treg cell development could neither be completely rescued by the addition of exogenous Interleukin 2 (IL-2) nor by the presence of wild-type derived cells in adoptive transfer experiments. However, peripheral NF-κB activation appears to be required for IL-2 production by conventional T cells, thereby participating in Treg cell homeostasis. Moreover, pharmacological NF-κB inhibition via the IκB kinase β (IKKβ) inhibitor AS602868 led to markedly diminished thymic and peripheral Treg cell frequencies.Our results indicate that Treg cell-intrinsic NF-κB activation is essential for thymic Treg cell differentiation, and further suggest pharmacological NF-κB inhibition as a potential therapeutic approach for manipulating this process

An essential role for the IL-2 receptor in Treg cell function

Regulatory T cells (Treg cells), which have abundant expression of the interleukin 2 receptor (IL-2R), are reliant on IL-2 produced by activated T cells. This feature indicates a key role for a simple network based on the consumption of IL-2 by Treg cells in their suppressor function. However, congenital deficiency in IL-2R results in reduced expression of the Treg cell lineage–specification factor Foxp3, which has confounded experimental efforts to understand the role of IL-2R expression and signaling in the suppressor function of Treg cells. Using genetic gain- and loss-of-function approaches, we found that capture of IL-2 was dispensable for the control of CD4+ T cells but was important for limiting the activation of CD8+ T cells, and that IL-2R-dependent activation of the transcription factor STAT5 had an essential role in the suppressor function of Treg cells separable from signaling via the T cell antigen receptor

Genetic determinants of risk in pulmonary arterial hypertension: international genome-wide association studies and meta-analysis

Background Rare genetic variants cause pulmonary arterial hypertension, but the contribution of common genetic variation to disease risk and natural history is poorly characterised. We tested for genome-wide association for pulmonary arterial hypertension in large international cohorts and assessed the contribution of associated regions to outcomes. Methods We did two separate genome-wide association studies (GWAS) and a meta-analysis of pulmonary arterial hypertension. These GWAS used data from four international case-control studies across 11744 individuals with European ancestry (including 2085 patients). One GWAS used genotypes from 5895 whole-genome sequences and the other GWAS used genotyping array data from an additional 5849 individuals. Cross-validation of loci reaching genome-wide significance was sought by meta-analysis. Conditional analysis corrected for the most significant variants at each locus was used to resolve signals for multiple associations. We functionally annotated associated variants and tested associations with duration of survival. All-cause mortality was the primary endpoint in survival analyses. Findings A locus near SOX17 (rs10103692, odds ratio 1·80 [95% CI 1·55–2·08], p=5·13×10– ¹⁵) and a second locus in HLA-DPA1 and HLA-DPB1 (collectively referred to as HLA-DPA1/DPB1 here; rs2856830, 1·56 [1·42–1·71], p=7·65×10– ²⁰) within the class II MHC region were associated with pulmonary arterial hypertension. The SOX17 locus had two independent signals associated with pulmonary arterial hypertension (rs13266183, 1·36 [1·25–1·48], p=1·69×10– ¹²; and rs10103692). Functional and epigenomic data indicate that the risk variants near SOX17 alter gene regulation via an enhancer active in endothelial cells. Pulmonary arterial hypertension risk variants determined haplotype-specific enhancer activity, and CRISPR-mediated inhibition of the enhancer reduced SOX17 expression. The HLA-DPA1/DPB1 rs2856830 genotype was strongly associated with survival. Median survival from diagnosis in patients with pulmonary arterial hypertension with the C/C homozygous genotype was double (13·50 years [95% CI 12·07 to >13·50]) that of those with the T/T genotype (6·97 years [6·02–8·05]), despite similar baseline disease severity. Interpretation This is the first study to report that common genetic variation at loci in an enhancer near SOX17 and in HLA-DPA1/DPB1 is associated with pulmonary arterial hypertension. Impairment of SOX17 function might be more common in pulmonary arterial hypertension than suggested by rare mutations in SOX17. Further studies are needed to confirm the association between HLA typing or rs2856830 genotyping and survival, and to determine whether HLA typing or rs2856830 genotyping improves risk stratification in clinical practice or trials. Funding UK NIHR, BHF, UK MRC, Dinosaur Trust, NIH/NHLBI, ERS, EMBO, Wellcome Trust, EU, AHA, ACClinPharm, Netherlands CVRI, Dutch Heart Foundation, Dutch Federation of UMC, Netherlands OHRD and RNAS, German DFG, German BMBF, APH Paris, INSERM, Université Paris-Sud, and French ANR

T cell receptor induced intracellular redistribution of type I protein kinase A

The productive activation of CD4(+) T lymphocytes, leading to proliferation and cytokine secretion, requires precise temporal regulation of intracellular cyclic AMP concentrations. The major effector molecule activated by cyclic AMP in mammalian cells is the cyclic AMP-dependent protein kinase A (PKA). The type I PKA isozyme mediates the inhibitory effects of cyclic AMP on T-cell activation. Using laser scanning confocal microscopy, we demonstrated that the regulation of PKA type I activity involves spatial redistribution of PKA type I molecules following T-cell receptor (TCR) stimulation. In resting T cells, PKA type I was located in membrane proximal regions and distributed equally across the cell. Shortly after antigen engagement, T cells and antigen-presenting cells formed an area of intense contact, known as the immunological synapse. TCR concentrated at the synapse, whereas PKA type I molecules redistributed to the opposite cell pole within 10 min after T-cell stimulation. Type I PKA redistribution was solely dependent on TCR signalling, because we observed the same temporal and spatial distribution after antibody-mediated cross-linking of the TCR-associated CD3 complex. Segregation of TCR and PKA type I molecules was maintained for at least 20 min. Thirty minutes after stimulation, PKA type I partially colocalized with the TCR. After 60 min, PKA type I distribution again approached the resting state. Considering that initial TCR signals lead to increases in intracellular cyclic AMP, PKA type I molecules may be targeted towards localized cyclic AMP accumulations or transported away from these areas, depending on the requirements of the cellular response