Project description:With the exception of the T-helper 2 (Th2) subset, cytokine driven pathways provide a robust mechanistic explanation for the observed outcomes of CD4+ T-cell differentiation. Using a quantitative model of activation, we studied the integration of TCR-signal-strength with cytokine signalling during Th2 differentiation. Upon the initial activation of Th-naïve cells, TCR signalling was found to set early expression levels for the master regulators of differentiation Tbet and GATA3, independent of the presence of polarizing cytokines. Subsequently cytokine stimuli modulated transcription factor (TF) expression levels to tune the outcome of differentiation. Here, weak TCR signalling was sufficient to drive the early upregulation of GATA3 and induce Th2 differentiation, in an IL-4 independent manner. Th1 differentiation was however shown to require additional cytokine signalling input, either in the form of autocrine IFNγ or exogenous IL-12. Using mathematical modelling we demonstrate that T-helper differentiation occurs along a continuum of states. Set by the relative co-expression of regulatory TFs, where effector cytokine production is controlled in a probabilistic manner determined by the relative levels GATA3 and Tbet expressed. Together, our data indicate TCR signalling inputs drive an early bifurcation in the T-helper differentiation pathway. Together, the integration of TCR signal strength with cytokine inputs act as a mechanism for the detection of immuno-evasive parasitic infections, whilst providing an additional checkpoint to prevent aberrant Th1 associated immunopathology.
Project description:Transcriptional regulation of cell fate decisions in the immune system endows cells with specialized function; an iterative process that adapts to the changing landscape of infections. As coordinators of the immune system, T helper cells of the CD4+ lineage possess the ability to differentiate into an array of functional cell states in order to guide the response towards antibody production via the formation of T follicular helper (Tfh) cells or inflammation by the generation of T effector (Teff) cells. Tfh–Teff cell fate choice is mediated by the BCL6–Blimp-1 counter-antagonistic gene regulatory module, polarizing Tfh and Teff cells, respectively. A key question is how T helper cells establish and negotiate BCL6–Blimp-1 counter antagonism to control the output of Tfh and Teff cells. We show that the T cell receptor (TCR)-signal induced transcription factor, IRF4, is necessary for the generation of both BCL6-expressing Tfh cells and Blimp-1-expressing Teff cells. Importantly, we show that increasing TCR signal strength augments the amounts of IRF4 expressed as well as Teff cell fate trajectories that occur at the expense of Tfh cells. Using an orthogonal genetic system, based on a tet-inducible allele of Irf4, we demonstrate that increasing IRF4 expression during priming redirected Tfh cell fate choices towards those of Teff. Importantly, promotion of Teff cell fate trajectories by increased IRF4 expression occurred independently of IL-2 signals. At the molecular level, we link greater IRF4 abundance with its recruitment to low affinity DNA binding sites embedded within regulatory elements affiliated with the Teff gene program, including Blimp-1. Together, these results demonstrate that the Irf4 locus functions as the “reader” of TCR signal strength, in turn, the concentration dependent activity of the IRF4 transcription factor “writes” T helper cell fate choice.
Project description:The development of CD4+ T cells and CD8+ T cells in the thymus is critical to adaptive immunity and is widely studied as a model of lineage commitment. Recognition of self-MHCI or MHCII by the T cell antigen receptor (TCR) determines the CD8+ T cell or CD4+ T cell lineage choice, respectively, but how distinct TCR signals drive transcriptional programs of lineage commitment remains largely unknown. Here we applied CITE-seq to measure RNA and surface proteins in thymocytes from wild-type and T cell lineage-restricted mice to generate a comprehensive timeline of cell state for each T cell lineage. These analyses identified a sequential process whereby all thymocytes initiate CD4+ T cell lineage differentiation during an initial wave of TCR signaling, followed by a second TCR signaling wave that coincides with CD8+ T cell lineage specification. CITE-seq and pharmaceutical inhibition experiments implicated a TCR-calcineurin-NFAT-GATA3 axis in driving the CD4+ T cell fate. Our data provide a resource for understanding cell fate decisions and implicate multiple redundant mechanisms in guiding lineage choice.
Project description:TCR signal strength controls thymic differentiation of discrete proinflammatory γδT cell subsetsistinct TCR signal strength requirements in the thymus
Project description:IL-2 inducible tyrosine kinase (Itk) is a Tec family non-receptor tyrosine kinase that is known to regulate T cell receptor signal strength (TcR) and T cell development and differentiation. TcR signal strength and antigen affinity are parameters known to regulate the development of CD8+ T cell memory. However, the intersection between TcR signal strength and antigen affinity on CD8+ memory T cell development remains unclear. Therefore, we compared the transcriptomes of WT and Itk-/- OT-1/Rag-/- CD8+ T cells at day 0 and day 7 following infection with Listeria monocytogenes expressing the SIINFEKL (N4) or SIITFEKL (T4) OVA peptide variant (different affinities for TcR) by RNA sequencing.
Project description:Variable strengths of signaling via the T cell antigen receptor (TCR) can produce divergent outcomes, but the mechanism of this remains obscure. The abundance of the transcription factor IRF4 increases with TCR signal strength, but how this would induce distinct types of responses is unclear. We compared the expression of genes in the TH2 subset of helper T cells to enhancer occupancy by the BATF–IRF4 transcription factor complex at varying strengths of TCR stimulation. Genes dependent on BATF–IRF4 clustered into groups with distinct TCR sensitivities. Enhancers exhibited a spectrum of occupancy by the BATF–IRF4 ternary complex that correlated with the sensitivity of gene expression to TCR signal strength. DNA sequences immediately flanking the previously defined AICE motif controlled the affinity of BATF–IRF4 for direct binding to DNA. Analysis by the chromatin immunoprecipitation–exonuclease (ChIP-exo) method allowed the identification of a previously unknown high-affinity AICE2 motif at a human single-nucleotide polymorphism (SNP) of the gene encoding the immunomodulatory receptor CTLA-4 that was associated with resistance to autoimmunity. Thus, the affinity of different enhancers for the BATF–IRF4 complex might underlie divergent signaling outcomes in response to various strengths of TCR signaling
Project description:Affinity and dose of T cell receptor (TCR) interaction with antigens govern the magnitude of CD4+ T cell responses, but questions remain regarding the quantitative translation of TCR engagement into downstream signals. We find that while the response of CD4+ T cells to antigenic stimulation is bimodal, activated cells exhibit analog responses proportional to signal strength. Gene expression output reflects TCR signal strength, providing a signature of T cell activation. Expression changes rely on a pre-established enhancer landscape and quantitative acetylation at AP-1 binding sites. Finally, we show that graded expression of activation genes depends on ERK pathway activation, suggesting that an ERK-AP-1 axis translates TCR signal strength into proportional activation of enhancers and genes essential for T cell function.
Project description:Affinity and dose of T cell receptor (TCR) interaction with antigens govern the magnitude of CD4+ T cell responses, but questions remain regarding the quantitative translation of TCR engagement into downstream signals. We find that while the response of CD4+ T cells to antigenic stimulation is bimodal, activated cells exhibit analog responses proportional to signal strength. Gene expression output reflects TCR signal strength, providing a signature of T cell activation. Expression changes rely on a pre-established enhancer landscape and quantitative acetylation at AP-1 binding sites. Finally, we show that graded expression of activation genes depends on ERK pathway activation, suggesting that an ERK-AP-1 axis translates TCR signal strength into proportional activation of enhancers and genes essential for T cell function. CD4+ T cells from transgenic AND mice were sequenced under the conditions indicated. Replicates are included for each type of data (RNA-Seq, ChIP-Seq), and are numbered accordingly. The No Peptide condition serves as the untreated control for the peptide-treated samples, and inputs are provided for ChIP-Sequencing samples.