During activation, T cells express receptors for receiving positive and negative costimulatory signals. Here we identify the B and T lymphocyte attenuator (BTLA), an immunoglobulin domain-containing glycoprotein with two immunoreceptor tyrosine-based inhibitory motifs. BTLA is not expressed by naive T cells, but it is induced during activation and remains expressed on T helper type 1 (T(H)1) but not T(H)2 cells. Crosslinking BTLA with antigen receptors induces its tyrosine phosphorylation and association with the Src homology domain 2 (SH2)-containing protein tyrosine phosphatases SHP-1 and SHP-2, and attenuates production of interleukin 2 (IL-2). BTLA-deficient T cells show increased proliferation, and BTLA-deficient mice have increased specific antibody responses and enhanced sensitivity to experimental autoimmune encephalomyelitis. B7x, a peripheral homolog of B7, is a ligand of BTLA. Thus, BTLA is a third inhibitory receptor on T lymphocytes with similarities to cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) and programmed death 1 (PD-1).

T helper type 1 (T(H)1) cell development involves interferon-gamma (IFN-gamma) signaling through signal transducer and activator of transcription 1 (STAT1) and interleukin-12 (IL-12) signaling through STAT4 activation. We examined here T-bet regulation and evaluated the actions of T-bet in STAT1- and STAT4-dependent T(H)1 development processes. We found that T-bet expression during T cell activation was strongly dependent on IFN-gamma signaling and STAT1 activation, but was independent of STAT4. Ectopic T-bet expression strongly increased IFN-gamma production in T(H)2 cells activated by PMA-ionomycin, but weakly increased IFN-gamma production in T(H)2 cells stimulated by IL-12 IL-18 or OVA peptide antigen-presenting cell stimulation. In contrast, IL-12 IL-18 induced IFN-gamma production remained STAT4-dependent despite ectopic T-bet expression. Ectopic T-bet expression selectively induced expression of IL-12Rbeta2, but not IL-18Ralpha, in wild-type and STAT1(-/-) T(H)2 cells, but did not extinguish expression of GATA-3 and T(H)2 cytokines. Finally, ectopic T-bet did not directly induce expression of endogenous T- bet independently of IFN-gamma or STAT1. Thus, T-bet is induced by IFN-gamma and STAT1 signaling during T cell activation. In addition, T-bet mediates STAT1-dependent processes of T(H)1 development, including the induction of IL-12Rbeta2.

T regulatory cells that express the transcription factor Foxp3 (Foxp3+ Treg) promote tissue homeostasis in several settings. We now report that symbiotic members of the human gut microbiota induce a distinct Treg population in the mouse colon, which constrains immuno-inflammatory responses. This induction, which we find to map to a broad, but specific, array of individual bacterial species, requires the transcription factor Rorγ, paradoxically in that Rorγ is thought to antagonize FoxP3 and promote T helper 17 (Th17) cell differentiation. Rorγ's transcriptional footprint differs in colonic Tregs and Th17 cells, controlling important effector molecules. Rorγ, and the Tregs that express it, contribute substantially to regulating colonic Th1/Th17 inflammation. Thus, the marked context-specificity of Rorγ results in very different outcomes even in closely related cell-types.

The recognition of polarized T cell subsets defined by cytokine production was followed by a search to define the factors controlling this phenomenon. Suitable in vitro systems allowed the development of cytokine "recipes" that induced rapid polarization of naïve T cells into Th1 or Th2 populations. The next phase of work over the past several years has begun to define the intracellular processes set into motion during Th1/Th2 development, particularly by the strongly polarizing cytokines IL-12 and IL-4. Although somewhat incomplete, what has emerged is a richly detailed tapestry of signaling and transcription, controlling an important T cell developmental switch. In addition several new mediators of control have emerged, including IL-18, the intriguing Th2-selective T1/ST2 product, and heterogeneity in dendritic cells capable of directing cytokine-independent Th development.

We identified three RORγt-specific inhibitors that suppress T helper 17 (Th17) cell responses including Th17 cell-mediated autoimmune disease. We systemically characterized RORγt binding in the presence and absence of drug with corresponding whole-genome transcriptome sequencing. RORγt acts both as a direct activator of Th17 cell signature genes and as a direct repressor of signature genes from other T-cell lineages, with the strongest transcriptional effects on cis-regulatory sites containing the RORα binding motif. RORγt is central in a densely interconnected regulatory network that shapes the balance of T-cell differentiation. The three inhibitors identified here modulated the RORγt-dependent transcriptional network to varying extents and through distinct mechanisms. Whereas one inhibitor displaced RORγt from its target-loci, the two more potent inhibitors affected transcription predominantly without removing DNA-binding. Our work illustrates the power of a system-scale analysis of transcriptional regulation to characterize potential therapeutic compounds that inhibit pathogenic Th17 cells and suppress autoimmunity.

Interleukin-12 (IL-12) and IL-18 induce synergistic transcription of interferon gamma (IFN-gamma) that is T cell receptor (TCR)-independent, not inhibited by cyclosporin A and requires new protein synthesis. To characterize this pathway, we screened for genes that are induced in IL-12- and IL-18-treated T helper type 1 cells. GADD45 beta, which activates mitogen-activated protein kinase (MAPK)-extracellular signal-regulated kinase kinase 4 (MEKK4), was induced by IL-18 and augmented by IL-12. GADD45 beta expression in naïve CD4+ T cells activated p38 MAPK and selectively increased cytokine-induced, but not TCR-induced, IFN-gamma production. Kinase-inactive MEKK4 and inhibition of the p38 MAPK pathway both selectively inhibit cytokine-induced, but not TCR-induced, IFN-gamma production. Thus, the synergy between IL-12 and IL-18 may involve GADD45 beta induction, which can maintain the MEKK4 and p38 MAPK activation that is necessary for cytokine-induced, but not TCR-induced, IFN-gamma production.

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IL‐17 and IL‐22 are typical cytokines produced by the Th17 T cell subset, but it is unclear if Th17 cytokines can be produced by other cell types. We demonstrate that IL‐10‐deficient and IL‐10R‐deficient macrophages stimulated with lipopolysaccharide produce high levels of IL‐17 and IL‐22. Addition of exogenous IL‐10 to IL‐10‐deficient macrophages abolished IL‐17 production. When IL‐10‐deficient and IL‐10R‐deficient splenocytes were cultured under Th17 polarizing conditions, the population of IL‐17‐producing cells was increased and the cultures produced significantly higher levels of IL‐17 and IL‐22. The addition of recombinant IL‐10 to IL‐10‐deficient splenocytes significantly decreased the percentage of IL‐17‐producing CD4+ T cells. Finally, the mRNA for the Th17 transcription factor retinoic acid‐related orphan receptor (ROR)γt was significantly elevated in IL‐10‐deficient spleen cells and macrophages. These data demonstrate that Th17 cytokines and RORγt are also expressed in macrophages and that IL‐10 negatively regulates the expression of Th17 cytokines and RORγt by both macrophages and T cells.