Ivana M. Djuretic

Runx3 and T-box proteins cooperate to establish the transcriptional program of effector CTLs

Activation of naive CD8+ T cells with antigen induces their differentiation into effector cytolytic T lymphocytes (CTLs). CTLs lyse infected or aberrant target cells by exocytosis of lytic granules containing the pore-forming protein perforin and a family of proteases termed granzymes. We show that effector CTL differentiation occurs in two sequential phases in vitro, characterized by early induction of T-bet and late induction of Eomesodermin (Eomes), T-box transcription factors that regulate the early and late phases of interferon (IFN) γ expression, respectively. In addition, we demonstrate a critical role for the transcription factor Runx3 in CTL differentiation. Runx3 regulates Eomes expression as well as expression of three cardinal markers of the effector CTL program: IFN-γ, perforin, and granzyme B. Our data point to the existence of an elaborate transcriptional network in which Runx3 initially induces and then cooperates with T-box transcription factors to regulate gene transcription in differentiating CTLs.

Pro-inflammatory human Th17 cells selectively express P-glycoprotein and are refractory to glucocorticoids

Inflammatory T helper 17 cells in humans are distinguished by selective expression of MDR1 and are enriched in the gut of patients with Crohn’s disease.

Deletion of a conserved Il4 silencer impairs T helper type 1-mediated immunity.

Helper T cell differentiation involves silencing as well as activation of gene expression. We have identified a conserved silencer of the gene encoding interleukin 4 (Il4) marked by DNase I hypersensitivity (HS IV) and permissive chromatin structure in all helper T cells. Deletion of HS IV increased Il4 and Il13 transcription by naive T cells and led to T helper type 2 skewing in vitro. HS IV controlled Il4 silencing during T helper type 1 differentiation, as HS IV–deficient T helper type 1 cells that expressed interferon-γ also produced abundant interleukin 4 in vitro and in vivo. Despite mounting a vigorous interferon-γ response, HS IV–deficient mice were more susceptible to Leishmania major infection than were wild-type littermate control mice, showing a critical function for Il4 silencing in T helper type 1–mediated immunity.

Cytokine signals through PI-3 kinase pathway modulate Th17 cytokine production by CCR6+ human memory T cells

PI-3K–mediated repression of FOXO1 and KLF2 promotes proinflammatory cytokine expression by lineage-committed human CCR6+ Th17/Th22 memory cells.

Halofuginone-induced amino acid starvation regulates Stat3-dependent Th17 effector function and reduces established autoimmune inflammation.

The IL-23 pathway is genetically linked to autoimmune disease in humans and is required for pathogenic Th17 cell function in mice. However, because IL-23R–expressing mature Th17 cells are rare and poorly defined in mice at steady-state, little is known about IL-23 signaling. In this study, we show that the endogenous CCR6+ memory T cell compartment present in peripheral lymphoid organs of unmanipulated mice expresses Il23r ex vivo, displays marked proinflammatory responses to IL-23 stimulation in vitro, and is capable of transferring experimental autoimmune encephalomyelitis. The prolyl-tRNA synthetase inhibitor halofuginone blocks IL-23–induced Stat3 phosphorylation and IL-23–dependent proinflammatory cytokine expression in endogenous CCR6+ Th17 cells via activation of the amino acid starvation response (AAR) pathway. In vivo, halofuginone shows therapeutic efficacy in experimental autoimmune encephalomyelitis, reducing both established disease progression and local Th17 cell effector function within the CNS. Mechanistically, AAR activation impairs Stat3 responses downstream of multiple cytokine receptors via selective, posttranscriptional suppression of Stat3 protein levels. Thus, our study reveals latent pathogenic functions of endogenous Th17 cells that are regulated by both IL-23 and AAR pathways and identifies a novel regulatory pathway targeting Stat3 that may underlie selective immune regulation by the AAR.