T-bet is a critical determinant in the instability of the IL-17-secreting T-helper phenotype

Factors impacting the benefits and pathogenicity of Th17 cells in the tumor microenvironment

Tumor development is closely associated with a complex tumor microenvironment, which is composed of tumor cells, blood vessels, tumor stromal cells, infiltrating immune cells, and associated effector molecules. T helper type 17 (Th17) cells, which are a subset of CD4+ T cells and are renowned for their ability to combat bacterial and fungal infections and mediate inflammatory responses, exhibit context-dependent effector functions. Within the tumor microenvironment, different molecular signals regulate the proliferation, differentiation, metabolic reprogramming, and phenotypic conversion of Th17 cells. Consequently, Th17 cells exert dual effects on tumor progression and can promote or inhibit tumor growth. This review aimed to investigate the impact of various alterations in the tumor microenvironment on the antitumor and protumor effects of Th17 cells to provide valuable clues for the exploration of additional tumor immunotherapy strategies.

GATA3 induces the pathogenicity of Th17 cells via regulating GM-CSF expression

T-bet-expressing Th17 (T-bet+RORγt+) cells are associated with the induction of pathology during experimental autoimmune encephalomyelitis (EAE) and the encephalitic nature of these Th17 cells can be explained by their ability to produce GM-CSF. However, the upstream regulatory mechanisms that control Csf2 (gene encoding GM-CSF) expression are still unclear. In this study, we found that Th17 cells dynamically expressed GATA3, the master transcription factor for Th2 cell differentiation, during their differentiation both in vitro and in vivo. Early deletion of Gata3 in three complimentary conditional knockout models by Cre-ERT2, hCd2 Cre and Tbx21 Cre, respectively, limited the pathogenicity of Th17 cells during EAE, which was correlated with a defect in generating pathogenic T-bet-expressing Th17 cells. These results indicate that early GATA3-dependent gene regulation is critically required to generate a de novo encephalitogenic Th17 response. Furthermore, a late deletion of Gata3 via Cre-ERT2 in the adoptive transfer EAE model resulted in a cell intrinsic failure to induce EAE symptoms which was correlated with a substantial reduction in GM-CSF production without affecting the generation and/or maintenance of T-bet-expressing Th17 cells. RNA-Seq analysis of Gata3-sufficient and Gata3-deficient CNS-infiltrating CD4+ effector T cells from mixed congenic co-transfer recipient mice revealed an important, cell-intrinsic, function of GATA3 in regulating the expression of Egr2, Bhlhe40, and Csf2. Thus, our data highlights a novel role for GATA3 in promoting and maintaining the pathogenicity of T-bet-expressing Th17 cells in EAE, via putative regulation of Egr2, Bhlhe40, and GM-CSF expression.

Role of rare immune cells in common variable immunodeficiency

Common variable immunodeficiency disorder (CVID) is a heterogeneous disorder and the most common symptomatic antibody deficiency disease characterized with hypogammaglobulinemia and a broad range of clinical manifestations. Multiple genetic, epigenetic, and immunological defects are involved in the pathogenesis of CVID. These immunological defects include abnormalities in the number and/or function of B lymphocytes, T lymphocytes, and other rare immune cells. Although some immune cells have a relatively lower proportion among total immune subsets in the human body, they could have important roles in the pathogenesis of immunological disorders like CVID. To the best of our knowledge, this is the first review that described the role of rare immune cells in the pathogenesis and clinical presentations of CVID.

Chitosan hydrogel loaded with recombinant protein containing epitope C from HSP90 of Candida albicans induces protective immune responses against systemic candidiasis

We reported previously a recombinant protein (rP-HSP90C) containing epitope C from heat shock protein 90 of Candida albicans mediates protective immune responses against systemic candidiasis. However, it exhibits weak immunogenicity. Therefore, we evaluated the potential and mechanisms of thermosensitive chitosan hydrogel (CH-HG) as an adjuvant in rP-HSP90C vaccine. CH-HG synthesized by ionic cross-linking showed buffering capacity and control-released rP-HSP90C in vitro. In comparison to naked rP-HSP90C, CH-HG-loaded rP-HSP90C (CH-HG/rP-HSP90C) not only evoked a long-lasting rP-HSP90C-specific IgG, but also enhanced Th1, Th2, Th17 responses and the ratio of Th1/Th2 in vivo; Meanwhile, CH-HG/rP-HSP90C provoked a stronger CTL response than rP-HSP90C. Notably, CH-HG increased the protective immune responses against systemic candidiasis in rP-HSP90C-immunized mice since CH-HG/rP-HSP90C enhanced the survival rate of infected mice, and diminished the CFUs in kidneys compared to rP-HSP90C, which were similar to that of QuilA. Further in vitro investigation displayed CH-HG upgraded the expressions of costimulators, MHCs and cytokines in BMDCs compared to rP-HSP90C；CH-HG also promoted cellular uptake, endosomal escape and "cross-presentation" of rP-HSP90C. In addition, it recruited immune cells at the injection site. Our study demonstrated that CH-HG can be an efficient adjuvant in fungal vaccines.

Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis is associated with IRF7, BANK1 and TBX21 polymorphisms in two populations

BACKGROUND AND PURPOSE

Autoantibodies targeting the GluN1(NR1) subunit of the anti-N-methyl-D-aspartate receptor (NMDAR) cause encephalitis. Although it has been shown that anti-NMDAR encephalitis is associated with human leukocyte antigen (HLA) loci, susceptibility genes for the disease outside the HLA loci remain unidentified. In this study, we aimed to explore the association of anti-NMDAR encephalitis with non-HLA genes.

METHODS

Two Chinese anti-NMDAR encephalitis cohorts from Han populations were recruited for this study. The North Chinese case-control set consisted of 98 patients and 460 controls, while the South Chinese case-control set included 78 patients and 541 controls. All participants were genotyped for 28 single nucleotide polymorphisms that are associated with autoimmune disorders or infectious diseases.

RESULTS

In two independent case-control sets, we identified significant associations of anti-NMDAR encephalitis with IRF7 rs1131665 (odds ratio [OR] 3.34, 95% confidence interval [CI] 1.99-5.63; P < 0.000001, P^adjusted  = 0.00004), BANK1 rs4522865 (OR 1.44, 95% CI 1.15-1.82; P = 0.0017, P^adjusted  = 0.0149), and TBX21 rs17244587 (OR 2.03, 95% CI 1.35-3.05; P = 0.00051, P^adjusted  = 0.0066). Furthermore, analysis of the three polymorphisms with clinical features of the disease revealed that the IRF7 rs1131665 was associated with tumor status.

CONCLUSION

The present study has for the first time identified non-HLA susceptibility genes for anti-NMDAR encephalitis. The association of IRF7, BANK1 and TBX21 with anti-NMDAR encephalitis suggests that B-cell activation, Th1 responses, virus infection and the type I interferon signaling pathway are involved in the pathogenesis of the disease.

Programmed T cell differentiation: Implications for transplantation

While T cells play a critical role in protective immunity against infection, they are also responsible for graft rejection in the setting of transplantation. T cell differentiation is regulated by both intrinsic transcriptional pathways as well as extrinsic factors such as antigen encounter and the cytokine milieu. Herein, we review recent discoveries in the transcriptional regulation of T cell differentiation and their impact on the field of transplantation. Recent studies uncovering context-dependent differentiation programs that differ in the setting of infection or transplantation will also be discussed. Understanding the key transcriptional pathways that underlie T cell responses in transplantation has important clinical implications, including development of novel therapeutic agents to mitigate graft rejection.

The evolving role of T-bet in resistance to infection

The identification of T-bet as a key transcription factor associated with the development of IFNγ-producing CD4⁺ T cells predicted a crucial role for T-bet in cell-mediated immunity and in resistance to many intracellular infections. This idea was reinforced by initial reports showing that T-bet-deficient mice were more susceptible to pathogens that survived within the lysosomal system of macrophages. However, subsequent studies revealed IFNγ-dependent, T-bet-independent pathways of resistance to diverse classes of microorganisms that occupy other intracellular niches. Consequently, a more complex picture has emerged of how T-bet and the related transcription factor eomesodermin (EOMES) coordinate many facets of the immune response to bona fide pathogens as well as commensals. This article provides an overview of the discovery and evolutionary relationship between T-bet and EOMES and highlights the studies that have uncovered broader functions of T-bet in innate and adaptive immunity and in the development of the effector and memory T cell populations that mediate long-term resistance to infection.

Asthma phenotypes and T-bet protein expression in cells treated with Fluticasone Furoate/Vilanterol

Asthma is a complex disease with diverse clinical manifestations ranging from mild to severe. Despite existing guidelines for asthma recognition and treatment, still a proportion of patients stay uncontrolled. Combinational therapy which comprises inhaled corticosteroids (ICS) and a long acting B2 adrenreceptor agonist (LABA) has been suggested to control asthma. In this study T-bet expression was attested in CD4 T cells treated with Fluticasone Furoate (FF), Vilanterol (V) and FF/V combination in severe asthmatic patients compared to patients with moderate asthma and healthy controls using Immunocytochemistry (ICC). First, CD4 T cells were isolated from PBMCs of 12 patients and controls using CD4 T cell isolation kit. Subsequently, isolated CD4 T cells were cultured with FF, V and FF/V for 1 h. To accomplish ICC, cells were incubated with anti-T-bet antibody, and then stained with HRP-bound secondary antibody. T-bet expression was evaluated using light microscopy. Statistical analyses were performed using R 3.5.2 software and visualized by ggplot2 3.1.0 package. Significant increasing in T-bet expression was seen in CD4 T cells from patients with moderate asthma treated with FF and FF/V. Suggesting conclusion would be distinct mechanisms responsible for severe asthma and moderate asthma in the patients and the needs for novel therapies. Further molecular studies in different asthma phenotypes would be instructive for asthma treatment.

T Helper Cell Differentiation, Heterogeneity, and Plasticity

Naïve CD4 T cells, on activation, differentiate into distinct T helper (Th) subsets that produce lineage-specific cytokines. By producing unique sets of cytokines, effector Th subsets play critical roles in orchestrating immune responses to a variety of infections and are involved in the pathogenesis of many inflammatory diseases including autoimmunity, allergy, and asthma. The differentiation of Th cells relies on the strength of T-cell receptor (TCR) signaling and signals triggered by polarizing cytokines that activate and/or up-regulate particular transcription factors. Several lineage-specific master transcription factors dictate Th cell fates and functions. Although these master regulators cross-regulate each other, their expression can be dynamic. Sometimes, they are even coexpressed, resulting in massive Th-cell heterogeneity and plasticity. Similar regulation mediated by these master regulators is also found in innate lymphoid cells (ILCs) that are innate counterparts of Th cells.

Dynamic balance between master transcription factors determines the fates and functions of CD4 T cell and innate lymphoid cell subsets

Fang and Zhu discuss similarities and differences between CD4 T cell and ILC subsets and the master transcription factors that determine the heterogeneity and plasticity of these subsets.

CD4 T cells, including T regulatory cells (Treg cells) and effector T helper cells (Th cells), and recently identified innate lymphoid cells (ILCs) play important roles in host defense and inflammation. Both CD4 T cells and ILCs can be classified into distinct lineages based on their functions and the expression of lineage-specific genes, including those encoding effector cytokines, cell surface markers, and key transcription factors. It was first recognized that each lineage expresses a specific master transcription factor and the expression of these factors is mutually exclusive because of cross-regulation among these factors. However, recent studies indicate that the master regulators are often coexpressed. Furthermore, the expression of master regulators can be dynamic and quantitative. In this review, we will first discuss similarities and differences between the development and functions of CD4 T cell and ILC subsets and then summarize recent literature on quantitative, dynamic, and cell type–specific balance between the master transcription factors in determining heterogeneity and plasticity of these subsets.

STAT3 Activation Impairs the Stability of Th9 Cells

Th9 cells regulate multiple immune responses, including immunity to pathogens and tumors, allergic inflammation, and autoimmunity. Despite ongoing research into Th9 development and function, little is known about the stability of the Th9 phenotype. In this study, we demonstrate that IL-9 production is progressively lost in Th9 cultures during several rounds of differentiation. The loss of IL-9 is not due to an outgrowth of cells that do not secrete IL-9, as purified IL-9 secretors demonstrate the same loss of IL-9 in subsequent rounds of differentiation. The loss of IL-9 production correlates with increases in phospho-STAT3 levels within the cell, as well as the production of IL-10. STAT3-deficient Th9 cells have increased IL-9 production that is maintained for longer in culture than IL-9 in control cultures. IL-10 is responsible for STAT3 activation during the first round of differentiation, and it contributes to instability in subsequent rounds of culture. Taken together, our results indicate that environmental cues dictate the instability of the Th9 phenotype, and they suggest approaches to enhance Th9 activity in beneficial immune responses.

Mucosal-associated invariant T-cell activation and accumulation after in vivo infection depends on microbial riboflavin synthesis and co-stimulatory signals

Despite recent breakthroughs in identifying mucosal-associated invariant T (MAIT) cell antigens (Ags), the precise requirements for in vivo MAIT cell responses to infection remain unclear. Using major histocompatibility complex-related protein 1 (MR1) tetramers, the MAIT cell response was investigated in a model of bacterial lung infection employing riboflavin gene-competent and -deficient bacteria. MAIT cells were rapidly enriched in the lungs of C57BL/6 mice infected with Salmonella Typhimurium, comprising up to 50% of αβ-T cells after 1 week. MAIT cell accumulation was MR1-dependent, required Ag derived from the microbial riboflavin synthesis pathway, and did not occur in response to synthetic Ag, unless accompanied by a Toll-like receptor agonist or by co-infection with riboflavin pathway-deficient S. Typhimurium. The MAIT cell response was associated with their long-term accumulation in the lungs, draining lymph nodes and spleen. Lung MAIT cells from infected mice displayed an activated/memory phenotype, and most expressed the transcription factor retinoic acid-related orphan receptor γt. T-bet expression increased following infection. The majority produced interleukin-17 while smaller subsets produced interferon-γ or tumor necrosis factor, detected directly ex vivo. Thus the activation and expansion of MAIT cells coupled with their pro-inflammatory cytokine production occurred in response to Ags derived from microbial riboflavin synthesis and was augmented by co-stimulatory signals.

Targeted delivery of let-7b to reprogramme tumor-associated macrophages and tumor infiltrating dendritic cells for tumor rejection

Both tumor associated macrophages (TAMs) and tumor infiltrating dendritic cells (TIDCs) are important components in the tumor microenvironment that mediate tumor immunosuppression and promote cancer progression. Targeting these cells and altering their phenotypes may become a new strategy to recover their anti-tumor activities and thereby restore the local immune surveillance against tumor. In this study, we constructed a nucleic acid delivery system for the delivery of let-7b, a synthetic microRNA mimic. Our carrier has an affinity for the mannose receptors on TAMs/TIDCs and is responsive to the low-pH tumor microenvironment. The delivery of let-7b could reactivate TAMs/TIDCs by acting as a TLR-7 agonist and suppressing IL-10 production in vitro. In a breast cancer mouse model, let-7b delivered by this system efficiently reprogrammed the functions of TAMs/TIDCs, reversed the suppressive tumor microenvironment, and inhibited tumor growth. Taken together, this strategy, designed based upon TAMs/TIDCs-targeting delivery and the dual biological functions of let-7b (TLR-7 ligand and IL-10 inhibitor), may provide a new approach for cancer immunotherapy.

Immune Mechanisms in Arterial Hypertension

Traditionally, arterial hypertension and subsequent end-organ damage have been attributed to hemodynamic factors, but increasing evidence indicates that inflammation also contributes to the deleterious consequences of this disease. The immune system has evolved to prevent invasion of foreign organisms and to promote tissue healing after injury. However, this beneficial activity comes at a cost of collateral damage when the immune system overreacts to internal injury, such as prehypertension. Renal inflammation results in injury and impaired urinary sodium excretion, and vascular inflammation leads to endothelial dysfunction, increased vascular resistance, and arterial remodeling and stiffening. Notably, modulation of the immune response can reduce the severity of BP elevation and hypertensive end-organ damage in several animal models. Indeed, recent studies have improved our understanding of how the immune response affects the pathogenesis of arterial hypertension, but the remarkable advances in basic immunology made during the last few years still await translation to the field of hypertension. This review briefly summarizes recent advances in immunity and hypertension as well as hypertensive end-organ damage.

Elevated expression of T-bet in mycobacterial antigen-specific CD4(+) T cells from patients with tuberculosis

T-bet is a T-box transcriptional factor that controls the differentiation and effector functions of CD4 T cells. In this study, we studied the role of T-bet in regulating CD4(+) T cell immunity against tuberculosis (TB). T-bet expression in Mycobacterium tuberculosis antigen-specific CD4(+) T cells was significantly higher in patients with active TB than in individuals with latent TB infection (p<0.0001). Comparison of T-bet expression in TCM and TEM subsets showed that CD4(+)T-bet(+)M. tuberculosis antigen-specific CD4(+) T cells had significantly lower frequency of TCM (p=0.003) and higher frequency of TEM (p=0.003) than CD4(+)T-bet(-) cells. The expression of PD-1 in antigen-specific CD4(+) T cells was significantly higher in patients with TB than in individuals with latent TB infection (p=0.006). CD4(+)CD154(+)T-bet(+) T cells had significantly higher expression of PD-1 than CD4(+)CD154(+)T-bet(-) T cells (p=0.0028). It is concluded that T-bet expression might be associated with differentiation into effector memory cells and PD-1 expression in mycobacterial antigen-specific CD4(+) T cells.

IL17 Promotes Mammary Tumor Progression by Changing the Behavior of Tumor Cells and Eliciting Tumorigenic Neutrophils Recruitment

The aggressiveness of invasive ductal carcinoma (IDC) of the breast is associated with increased IL17 levels. Studying the role of IL17 in invasive breast tumor pathogenesis, we found that metastatic primary tumor-infiltrating T lymphocytes produced elevated levels of IL17, whereas IL17 neutralization inhibited tumor growth and prevented the migration of neutrophils and tumor cells to secondary disease sites. Tumorigenic neutrophils promote disease progression, producing CXCL1, MMP9, VEGF, and TNFα, and their depletion suppressed tumor growth. IL17A also induced IL6 and CCL20 production in metastatic tumor cells, favoring the recruitment and differentiation of Th17. In addition, IL17A changed the gene-expression profile and the behavior of nonmetastatic tumor cells, causing tumor growth in vivo, confirming the protumor role of IL17. Furthermore, high IL17 expression was associated with lower disease-free survival and worse prognosis in IDC patients. Thus, IL17 blockade represents an attractive approach for the control of invasive breast tumors.

Transcriptional regulatory networks for CD4 T cell differentiation

CD4(+) T cells play a central role in controlling the adaptive immune response by secreting cytokines to activate target cells. Naïve CD4(+) T cells differentiate into at least four subsets, Th1Th1 , Th2Th2 , Th17Th17 , and inducible regulatory T cellsregulatory T cells , each with unique functions for pathogen elimination. The differentiation of these subsets is induced in response to cytokine stimulation, which is translated into Stat activation, followed by induction of master regulator transcription factorstranscription factors . In addition to these factors, multiple other transcription factors, both subset specific and shared, are also involved in promoting subset differentiation. This review will focus on the network of transcription factors that control CD4(+) T cell differentiation.

Th17 differentiation and their pro-inflammation function

CD4(+) T helper cells are classical but constantly reinterpreted T-cell subset, playing critical roles in a diverse range of inflammatory responses or diseases. Depending on the cytokines they release and the immune responses they mediate, CD4(+) T cells are classically divided into two major cell populations: Th1 and Th2 cells. However, recent studies challenged this Th1/Th2 paradigm by discovering several T-helper cell subsets with specific differentiation program and functions, including Th17 cells, Treg cells, and Tfh cells. In this chapter, we summarize the current understanding and recent progresses on the Th17 lineage differentiation and its effector impacts on variety of inflammatory responses or disease pathogenesis.

Diverse roles for T-bet in the effector responses required for resistance to infection

The transcription factor T-bet has been most prominently linked to NK and T cell production of IFN-γ, a cytokine required for the control of a diverse array of intracellular pathogens. Indeed, in mice challenged with the parasite Toxoplasma gondii, NK and T cell responses are characterized by marked increases of T-bet expression. Unexpectedly, T-bet(-/-) mice infected with T. gondii develop a strong NK cell IFN-γ response that controls parasite replication at the challenge site, but display high parasite burdens at secondary sites colonized by T. gondii and succumb to infection. The loss of T-bet had a modest effect on T cell production of IFN-γ but did not impact on the generation of parasite-specific T cells. However, the absence of T-bet resulted in lower T cell expression of CD11a, Ly6C, KLRG-1, and CXCR3 and fewer parasite-specific T cells at secondary sites of infection, associated with a defect in parasite control at these sites. Together, these data highlight T-bet-independent pathways to IFN-γ production and reveal a novel role for this transcription factor in coordinating the T cell responses necessary to control this infection in peripheral tissues.

Faecalibacterium prausnitzii inhibits interleukin-17 to ameliorate colorectal colitis in rats

Background and Aims

It has been shown that Faecalibacterium prausnitzii (F. prausnitzii), one of the dominant intestinal bacterial flora, may protect colonic mucosa against the development of inflammation and subsequent inflammatory bowel disease (IBD), with the underlying mechanisms being unclear.

Methods

The impacts of F. prausnitzii and its metabolites on IL-23/Th17/IL-17 pathway markers were determined in human monocytes and a rat model of colitis induced by 2,4,6-trinitrobenzene sulfonic acid. F. prausnitzii and its culture medium (containing complete metabolites) were used to treat the rats in vivo, as well as rat splenocytes and human monocytes in vitro. Inflammatory cytokines were measured in colon tissue, plasma and cell culture medium.

Results

The culture supernatant of F. prausnitzii increased plasma anti-Th17 cytokines (IL-10 and IL-12)and suppressed IL-17 levels in both plasma and colonic mucosa, with ameliorated colonic colitis lesions. This inhibition of IL-17 release has also been observed in both rat splenocytes and human venous monocytes in vitro. The culture supernatant of F. prausnitzii also suppressed Th17 cell differentiation induced by cytokines (TGF-ß and IL-6) and bone marrow-derived dendritic cells (BMDCs) in vitro. The metabolites of F. prausnitzii in the culture supernatant exert a stronger anti-inflammatory effect than the bacterium itself. F. prausnitzii protected the colon mucosa against the development of IBD by its metabolites, suggesting a promising potential for the use of F. prausnitzii and its metabolic products in the treatment of IBD.

Role of cytokines and Toll-like receptors in the immunopathogenesis of Guillain-Barré syndrome

Guillain-Barré syndrome (GBS) is an autoimmune disease of the peripheral nervous system, mostly triggered by an aberrant immune response to an infectious pathogen. Although several infections have been implicated in the pathogenesis of GBS, not all such infected individuals develop this disease. Moreover, infection with a single agent might also lead to different subtypes of GBS emphasizing the role of host factors in the development of GBS. The host factors regulate a broad range of inflammatory processes that are involved in the pathogenesis of autoimmune diseases including GBS. Evidences suggest that systemically and locally released cytokines and their involvement in immune-mediated demyelination and axonal damage of peripheral nerves are important in the pathogenesis of GBS. Toll-like receptors (TLRs) link innate and adaptive immunity through transcription of several proinflammatory cytokines. TLR genes may increase susceptibility to microbial infections; an attenuated immune response towards antigen and downregulation of cytokines occurs due to mutation in the gene. Herein, we discuss the crucial role of host factors such as cytokines and TLRs that activate the immune response and are involved in the pathogenesis of the disease.

Th17 cells demonstrate stable cytokine production in a proallergic environment

Th17 cells are critical for the clearance of extracellular bacteria and fungi, but also contribute to the pathology of autoimmune diseases and allergic inflammation. After exposure to an appropriate cytokine environment, Th17 cells can acquire a Th1-like phenotype, but less is known about their ability to adopt Th2 and Th9 effector programs. To explore this in more detail, we used an IL-17F lineage tracer mouse strain that allows tracking of cells that formerly expressed IL-17F. In vitro-derived Th17 cells adopted signature cytokine and transcription factor expression when cultured under Th1-, Th2-, or Th9-polarizing conditions. In contrast, using two models of allergic airway disease, Th17 cells from the lungs of diseased mice did not adopt Th1, Th2, or Th9 effector programs, but remained stable IL-17 secretors. Although in vitro-derived Th17 cells expressed IL-4Rα, those induced in vivo during allergic airway disease did not, possibly rendering them unresponsive to IL-4-induced signals. However, in vitro-derived, Ag-specific Th17 cells transferred in vivo to OVA and aluminum hydroxide-sensitized mice also maintained IL-17 secretion and did not produce alternative cytokines upon subsequent OVA challenge. Thus, although Th17 cells can adopt new phenotypes in response to some inflammatory environments, our data suggest that in allergic inflammation, Th17 cells are comparatively stable and retain the potential to produce IL-17. This might reflect a cytokine environment that promotes Th17 stability, and allow a broader immune response at tissue barriers that are susceptible to allergic inflammation.

Computational modeling of heterogeneity and function of CD4+ T cells

The immune system is composed of many different cell types and hundreds of intersecting molecular pathways and signals. This large biological complexity requires coordination between distinct pro-inflammatory and regulatory cell subsets to respond to infection while maintaining tissue homeostasis. CD4+ T cells play a central role in orchestrating immune responses and in maintaining a balance between pro- and anti- inflammatory responses. This tight balance between regulatory and effector reactions depends on the ability of CD4+ T cells to modulate distinct pathways within large molecular networks, since dysregulated CD4+ T cell responses may result in chronic inflammatory and autoimmune diseases. The CD4+ T cell differentiation process comprises an intricate interplay between cytokines, their receptors, adaptor molecules, signaling cascades and transcription factors that help delineate cell fate and function. Computational modeling can help to describe, simulate, analyze, and predict some of the behaviors in this complicated differentiation network. This review provides a comprehensive overview of existing computational immunology methods as well as novel strategies used to model immune responses with a particular focus on CD4+ T cell differentiation.

The transcription factor Etv5 controls TH17 cell development and allergic airway inflammation

BACKGROUND

The differentiation of TH17 cells, which promote pulmonary inflammation, requires the cooperation of a network of transcription factors.

OBJECTIVES

We sought to define the role of Etv5, an Ets-family transcription factor, in TH17 cell development and function.

METHODS

TH17 development was examined in primary mouse T cells wherein Etv5 expression was altered by retroviral transduction, small interfering RNA targeting a specific gene, and mice with a conditional deletion of Etv5 in T cells. The direct function of Etv5 on the Il17 locus was tested with chromatin immunoprecipitation and reporter assays. The house dust mite-induced allergic inflammation model was used to test the requirement for Etv5-dependent TH17 functions in vivo.

RESULTS

We identify Etv5 as a signal transducer and activator of transcription 3-induced positive regulator of TH17 development. Etv5 controls TH17 differentiation by directly promoting Il17a and Il17f expression. Etv5 recruits histone-modifying enzymes to the Il17a-Il17f locus, resulting in increased active histone marks and decreased repressive histone marks. In a model of allergic airway inflammation, mice with Etv5-deficient T cells have reduced airway inflammation and IL-17A/F production in the lung and bronchoalveolar lavage fluid compared with wild-type mice, without changes in TH2 cytokine production.

CONCLUSIONS

These data define signal transducer and activator of transcription 3-dependent feed-forward control of TH17 cytokine production and a novel role for Etv5 in promoting T cell-dependent airway inflammation.

Effect of iodine excess on Th1, Th2, Th17, and Treg cell subpopulations in the thyroid of NOD.H-2h4 mice

Iodine is an indispensable micronutrient for thyroid hormone synthesis and metabolism. Iodine excess may trigger and exacerbate autoimmune thyroiditis (AIT). The pathogenetic mechanism of iodine excess-induced AIT is partly regarded as T helper type 1 (Th1) cell and/or T helper type 17 (Th17) cell dominant autoimmune disease. It is still unknown whether other cluster of differentiation 4+ T (CD4+T) cell subpopulations are involved. Therefore, we studied the profile of all the CD4+T cell subpopulations of the thyroid in iodine excess-induced nonobese diabetic-H2h4 (NOD.H-2h4) mice to explore the potential immunologic mechanism of iodine excess-induced AIT. A total of 40 healthy 8-week-old NOD.H-2h4 mice were randomly allocated into the normal group (NG, n=20) and the test group (TG, n=20), which were fed with double-distilled water and 0.05% sodium iodine (NaI) for 8 weeks, respectively. Compared to the NG, in the TG, the incidence of AIT was significantly higher, the expressions of interleukin-17 (IL-17), interleukin-23 (IL-23), interleukin-6 (IL-6), and transforming growth factor-β (TGF-β) remarkably increased by immunohistochemistry, which were further verified by reverse transcription polymerase chain reaction (RT-PCR), while the protein and mRNA expressions of interleukin-4 (IL-4) and interferon-γ (INF-γ) decreased markedly. In the AIT mice, the expressions of retinoic acid-related orphan receptor gamma t (RORγt), retinoic acid-related orphan receptor alpha (RORα), and signal transducer and activator of transcription 3 (STAT3) were much higher, the expression of forkhead/winged helix transcription factor p3 (Foxp3) significantly lower by western blot, and the proportion of Th17 cells by flow cytometry method (FCM) much larger compared to those of the NG group. In conclusion, Th17 cells may promote an inflammatory reaction in the development of iodine-excess-induced AIT, which is negatively regulated by Th1, T helper type 2 (Th2), and regulatory T (Treg) cells.

The role of protein modifications of T-bet in cytokine production and differentiation of T helper cells

T-Bet (T-box protein expressed in T cells, also called as TBX21) was originally cloned as a key transcription factor involved in the commitment of T helper (Th) cells to the Th1 lineage. T-Bet directly activates IFN-γ gene transcription and enhances development of Th1 cells. T-Bet simultaneously modulates IL-2 and Th2 cytokines in an IFN-γ-independent manner, resulting in an attenuation of Th2 cell development. Numerous studies have demonstrated that T-bet plays multiple roles in many subtypes of immune cells, including B cell, dendritic cells, natural killer (NK) cells, NK T cells, and innate lymphoid cells. Therefore, T-bet is crucial for the development and coordination of both innate and adaptive immune responses. To fulfill these multiple roles, T-bet undergoes several posttranslational protein modifications, such as phosphorylation at tyrosine, serine, and threonine residues, and ubiquitination at lysine residues, which affect lineage commitment during Th cell differentiation. This review presents a current overview of the progress made in understanding the roles of various types of T-bet protein modifications in the regulation of cytokine production during Th cell differentiation.

Th17 Cells in Immunopathogenesis and treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by the sequestration of various leukocyte subpopulations within both the developing pannus and synovial space. The chronic nature of this disease results in inflammation of multiple joints, with subsequent destruction of the joint cartilage and erosion of bone. Identification of T helper (Th)17 cells led to breaking the dichotomy of the Th1/Th2 axis in immunopathogenesis of autoimmune diseases such as RA, and its experimental model, collagen-induced arthritis (CIA). Th17 cells produce cytokines, including interleukin (IL)-17, IL-6, IL-21, IL-22 and tumor necrosis factor (TNF)-α, with pro-inflammatory effects, which appear to have a role in immunopathogenesis of RA. Regarding the wide ranging production of pro-inflammatory cytokines and chemokines by Th17 cells, it is expected that Th17 cell could be a potent pathogenic factor in disease immunopathophysiology. Thus the identification of effector mechanisms used by Th17 cells in induction of disease lesions may open new prospects for designing a new therapeutic strategy for treatment of RA.

T-bet regulates immunity to Francisella tularensis live vaccine strain infection, particularly in lungs

Upregulation of the transcription factor T-bet is correlated with the strength of protection against secondary challenge with the live vaccine strain (LVS) of Francisella tularensis. Thus, to determine if this mediator had direct consequences in immunity to LVS, we examined its role in infection. Despite substantial in vivo gamma interferon (IFN-γ) levels, T-bet-knockout (KO) mice infected intradermally (i.d.) or intranasally (i.n.) with LVS succumbed to infection with doses 2 log units less than those required for their wild-type (WT) counterparts, and exhibited significantly increased bacterial burdens in the lung and spleen. Lungs of LVS-infected T-bet-KO mice contained fewer lymphocytes and more neutrophils and interleukin-17 than WT mice. LVS-vaccinated T-bet-KO mice survived lethal LVS intraperitoneal secondary challenge but not high doses of LVS i.n. challenge, independently of the route of vaccination. Immune T lymphocytes from the spleens of i.d. LVS-vaccinated WT or KO mice controlled intracellular bacterial replication in an in vitro coculture system, but cultures with T-bet-KO splenocyte supernatants contained less IFN-γ and increased amounts of tumor necrosis factor alpha. In contrast, immune T-bet-KO lung lymphocytes were greatly impaired in controlling intramacrophage growth of LVS; this functional defect is the likely mechanism underpinning the lack of respiratory protection. Taken together, T-bet is important in host resistance to primary LVS infection and i.n. secondary challenge. Thus, T-bet represents a true, useful correlate for immunity to LVS.

Local delivery of T-bet shRNA reduces inflammation in collagen II-induced arthritis via downregulation of IFN-γ and IL-17

Th1 and Th17 cells are involved in the pathogenesis of rheumatoid arthritis (RA). T-bet, a Th1-specific transcription factor, appears to drive the maturation of Th1 and IFN-γ secretion. In the present study, we established the T-bet shRNA recombinant plasmid (p-T-shRNA) and explored its possible anti-inflammatory effect in a collagen-induced arthritis (CIA) model by local injection of plasmid vectors. For the initiation of CIA, DBA/1J mice were immunized with type II collagen (CII) in Freund's adjuvant and the CII-immunized mice were treated with p-T-shRNA. Levels of T-bet, IFN-γ, IL-17 and RORγt mRNA in splenocytes and synovial joints were measured by quantitative real-time PCR and T-bet expression in joint tissue was detected by immunohistochemistry staining. The intracellular IFN-γ and IL-17 were analyzed by flow cytometry (FCM). The results demonstrated that therapeutic administration on the local joints with p-T-shRNA significantly suppressed IFN-γ and IL-17 gene expression and improved the pathogenesis of arthritis in CIA mice, while administration of a plasmid expressing T-bet (pIRES-T-bet) accelerated the disease onset. Our study suggests that T-bet may be developed as a potential target for arthritis therapy.

Th17 cells in immunity and autoimmunity

Th17 and IL-17 play important roles in the clearance of extracellular bacterial and fungal infections. However, strong evidence also implicates the Th17 lineage in several autoimmune disorders including multiple sclerosis, psoriasis, rheumatoid arthritis, inflammatory bowel disease, systemic lupus erythematosus, and asthma. The Th17 subset has also been connected with type I diabetes, although whether it plays a role in the pathogenicity of or protection from the disease remains a controversial issue. In this review we have provided a comprehensive overview of Th17 pathogenicity and function, including novel evidence for a protective role of Th17 cells in conjunction with the microbiota gut flora in T1D onset and progression.

Dendritic Cell-Induced Th1 and Th17 Cell Differentiation for Cancer Therapy

The success of cellular immunotherapies against cancer requires the generation of activated CD4⁺ and CD8⁺ T-cells. The type of T-cell response generated (e.g., Th1 or Th2) will determine the efficacy of the therapy, and it is generally assumed that a type-1 response is needed for optimal cancer treatment. IL-17 producing T-cells (Th17/Tc17) play an important role in autoimmune diseases, but their function in cancer is more controversial. While some studies have shown a pro-cancerous role for IL-17, other studies have shown an anti-tumor function. The induction of polarized T-cell responses can be regulated by dendritic cells (DCs). DCs are key regulators of the immune system with the ability to affect both innate and adaptive immune responses. These properties have led many researchers to study the use of ex vivo manipulated DCs for the treatment of various diseases, such as cancer and autoimmune diseases. While Th1/Tc1 cells are traditionally used for their potent anti-tumor responses, mounting evidence suggests Th17/Tc17 cells should be utilized by themselves or for the induction of optimal Th1 responses. It is therefore important to understand the factors involved in the induction of both type-1 and type-17 T-cell responses by DCs.

Genome-wide regulatory analysis reveals that T-bet controls Th17 lineage differentiation through direct suppression of IRF4

The complex relationship between Th1 and Th17 cells is incompletely understood. The transcription factor T-bet is best known as the master regulator of Th1 lineage commitment. However, attention is now focused on the repression of alternate T cell subsets mediated by T-bet, particularly the Th17 lineage. It has recently been suggested that pathogenic Th17 cells express T-bet and are dependent on IL-23. However, T-bet has previously been shown to be a negative regulator of Th17 cells. We have taken an unbiased approach to determine the functional impact of T-bet on Th17 lineage commitment. Genome-wide analysis of functional T-bet binding sites provides an improved understanding of the transcriptional regulation mediated by T-bet, and suggests novel mechanisms by which T-bet regulates Th cell differentiation. Specifically, we show that T-bet negatively regulates Th17 lineage commitment via direct repression of the transcription factor IFN regulatory factor-4 (IRF4). An in vivo analysis of the pathogenicity of T-bet-deficient T cells demonstrated that mucosal Th17 responses were augmented in the absence of T-bet, and we have demonstrated that the roles of T-bet in enforcing Th1 responses and suppressing Th17 responses are separable. The interplay of the two key transcription factors T-bet and IRF4 during the determination of T cell fate choice significantly advances our understanding of the mechanisms underlying the development of pathogenic T cells.

T-bet: a bridge between innate and adaptive immunity

Originally described over a decade ago as a T cell transcription factor regulating T helper 1 cell lineage commitment, T-bet is now recognized as having an important role in many cells of the adaptive and innate immune system. T-bet has a fundamental role in coordinating type 1 immune responses by controlling a network of genetic programmes that regulate the development of certain immune cells and the effector functions of others. Many of these transcriptional networks are conserved across innate and adaptive immune cells and these shared mechanisms highlight the biological functions that are regulated by T-bet.

Interleukin 18: friend or foe in cancer

In the last few years, the field of tumor immunology has significantly expanded and its boundaries, never particularly clear, have become less distinct. Although the immune system plays an important role in controlling tumor growth, it has also become clear that tumor growth can be promoted by inflammatory immune responses. A good example that exemplifies the ambiguous role of the immune system in cancer progression is represented by interleukin 18 (IL-18) that was first identified as an interferon-γ-inducing factor (IGIF) involved in T helper type-1 (Th1) immune response. The expression and secretion of IL-18 have been observed in various cell types from immune cells to circulating cancer cells. In this review we highlighted the multiple roles played by IL-18 in immune regulation, cancer progression and angiogenesis and the clinical potential that may result from such understanding.

The transcription factor Twist1 limits T helper 17 and T follicular helper cell development by repressing the gene encoding the interleukin-6 receptor α chain

Cytokine responsiveness is a critical component of the ability of cells to respond to the extracellular milieu. Transcription factor-mediated regulation of cytokine receptor expression is a common mode of altering responses to the external environment. We identify the transcription factor Twist1 as a component of a STAT3-induced feedback loop that controls IL-6 signals by directly repressing Il6ra. Human and mouse T cells lacking Twist1 have an increased ability to differentiate into Th17 cells. Mice with a T cell-specific deletion of Twist1 demonstrate increased Th17 and T follicular helper cell development, early onset experimental autoimmune encephalomyelitis, and increased antigen-specific antibody responses. Thus, Twist1 has a critical role in limiting both cell-mediated and humoral immunity.

Opposing roles of STAT4 and Dnmt3a in Th1 gene regulation

The STAT transcription factor STAT4 is a critical regulator of Th1 differentiation and inflammatory disease. Yet, how STAT4 regulates gene expression is still unclear. In this report, we define a STAT4-dependent sequence of events including histone H3 lysine 4 methylation, Jmjd3 association with STAT4 target loci, and a Jmjd3-dependent decrease in histone H3 lysine 27 trimethylation and DNA methyltransferase (Dnmt) 3a association with STAT4 target loci. Dnmt3a has an obligate role in repressing Th1 gene expression, and in Th1 cultures deficient in both STAT4 and Dnmt3a, there is recovery in the expression of a subset of Th1 genes that is sufficient to increase IFN-γ production. Moreover, although STAT4-deficient mice are protected from the development of experimental autoimmune encephalomyelitis, mice deficient in STAT4 and conditionally deficient in Dnmt3a in T cells develop paralysis. Th1 genes that are derepressed in the absence of Dnmt3a have greater induction after the ectopic expression of the Th1-associated transcription factors T-bet and Hlx1. Together, these data demonstrate that STAT4 and Dnmt3a play opposing roles in regulating Th1 gene expression, and that one mechanism for STAT4-dependent gene programming is in establishing a derepressed genetic state susceptible to transactivation by additional fate-determining transcription factors.

CD161 expression characterizes a subpopulation of human regulatory T cells that produces IL-17 in a STAT3-dependent manner

Treg cells are critical for the prevention of autoimmune diseases and are thus prime candidates for cell-based clinical therapy. However, human Treg cells are “plastic”, and are able to produce IL-17 under inflammatory conditions. Here, we identify and characterize the human Treg subpopulation that can be induced to produce IL-17 and identify its mechanisms. We confirm that a subpopulation of human Treg cells produces IL-17 in vitro when activated in the presence of IL-1β, but not IL-6. “IL-17 potential” is restricted to population III (CD4⁺CD25^hiCD127^loCD45RA⁻) Treg cells expressing the natural killer cell marker CD161. We show that these cells are functionally as suppressive and have similar phenotypic/molecular characteristics to other subpopulations of Treg cells and retain their suppressive function following IL-17 induction. Importantly, we find that IL-17 production is STAT3 dependent, with Treg cells from patients with STAT3 mutations unable to make IL-17. Finally, we show that CD161⁺ population III Treg cells accumulate in inflamed joints of patients with inflammatory arthritis and are the predominant IL-17-producing Treg-cell population at these sites. As IL-17 production from this Treg-cell subpopulation is not accompanied by a loss of regulatory function, in the context of cell therapy, exclusion of these cells from the cell product may not be necessary.

Altered T-bet dominance in IFN-γ-decoupled CD4+ T cells with attenuated cytokine storm and preserved memory in influenza

Cytokine storm has been postulated as one of the major causes of mortality in patients with severe respiratory viral infections such as influenza. With the help of an influenza Ag- specific mouse experimental system, we report that CD4(+) T cells contribute effector cytokines leading to lung inflammation in acute influenza. Although virus can no longer be detected from tissues 14 d postinfection, virus-derived Ag continues to drive a CD4(+) T cell response after viral clearance. Ag-specific CD4(+) T cells proliferate and evolve into memory CD4(+) T cells efficiently, but the production of effector cytokines is seriously hampered during this phase. This decoupling of proliferation and effector cytokine production doesn't appear in conjunction with increased suppression by regulatory T cells or decreased induction of transcription factors. Rather, GATA-3 and ROR-γt levels are elevated when compared with cells that have effector cytokine production. T-bet dominance over GATA-3 and ROR-γt decreases with the disarmament of effector cytokine production. Importantly, upon reinfection, these decoupled cells produce elevated levels of IFN-γ and were effective in virus eradication. These results provide a mechanism through altered T-bet dominance to dampen the cytokine storm without impeding the generation of memory T cells in influenza virus infection.

Regulatory T cells vs Th17: differentiation of Th17 versus Treg, are the mutually exclusive?

Naive CD4(+) cells differentiate into T helper (Th1, Th2, Th9, Th17) and regulatory T (Treg) cells to execute their immunologic function. Whereas TGF-β suppresses Th1 and Th2 cell differentiation, this cytokine promotes Th9, Th17 and Foxp3(+) regulatory T cells depending upon the presence of other cytokines. IL-6 promotes Th17, but suppresses regulatory T cell differentiation. Moreover, natural but not TGF-β-induced regulatory T cells convert into Th17 cells in the inflammatory milieu. Here an update of T cell differentiation and conversion, as well as underlying mechanisms are given.

NK cells inhibit T-bet-deficient, autoreactive Th17 cells

The differentiation and maintenance of Th17 cells require a unique cytokine milieu and activation of lineage-specific transcription factors. This process appears to be antagonized by the transcription factor T-bet, which controls the differentiation of Th1 cells. Considering that T-bet-deficient (T-bet(-/-) ) mice are largely devoid of natural killer (NK) cells due to a defect in the terminal maturation of these cells, and because NK cells can influence the differentiation of T helper cells, we investigated whether the absence of NK cells in T-bet-deficient mice contributes to the augmentation of autoreactive Th17 cell responses. We show that the loss of T-bet renders the transcription factors Rorc and STAT3 highly responsive to activation by stimuli provided by NK cells. Furthermore, reconstitution of T-bet(-/-) mice with wild-type NK cells inhibited the development of autoreactive Th17 cells through NK cell-derived production of IFN-γ. These results identify NK cells as critical regulators in the development of autoreactive Th17 cells and Th17-mediated pathology.

Plasticity within the αβ⁺CD4⁺ T-cell lineage: when, how and what for?

Following thymic output, αβ⁺CD4⁺ T cells become activated in the periphery when they encounter peptide-major histocompatibility complex. A combination of cytokine and co-stimulatory signals instructs the differentiation of T cells into various lineages and subsequent expansion and contraction during an appropriate and protective immune response. Our understanding of the events leading to T-cell lineage commitment has been dominated by a single fate model describing the commitment of T cells to one of several helper (T(H)), follicular helper (T(FH)) or regulatory (T(REG)) phenotypes. Although a single lineage-committed and dedicated T cell may best execute a single function, the view of a single fate for T cells has recently been challenged. A relatively new paradigm in αβ⁺CD4⁺ T-cell biology indicates that T cells are much more flexible than previously appreciated, with the ability to change between helper phenotypes, between helper and follicular helper, or, most extremely, between helper and regulatory functions. In this review, we comprehensively summarize the recent literature identifying when T(H) or T(REG) cell plasticity occurs, provide potential mechanisms of plasticity and ask if T-cell plasticity is beneficial or detrimental to immunity.

Interleukin-18 binding protein therapy is protective in adriamycin nephropathy

Adriamycin nephropathy (AN) is an experimental model of focal segmental glomerulosclerosis (FSGS) in which macrophages are considered to play a pathogenic role. We hypothesize that interleukin-18 (IL-18), largely derived from macrophages, is a key contributor to kidney injury in AN and a potential therapeutic target. In this study, BALB/c mice received adriamycin (9.6 mg/kg) via tail vein injection and subsequently were treated with either neutralizing IL-18 binding protein (IL-18BP; 250 μg) or normal saline (control). At 5 wk, IL-18 was upregulated in AN, and IL-18BP therapy afforded significant protection against the development of AN, resulting in less proteinuria (P < 0.01), kidney dysfunction (P < 0.01), glomerulosclerosis (P < 0.001), and interstitial accumulation of macrophages and T cells (P < 0.001). Gene expression of IL-18 downstream inflammatory molecules, including inducible nitric oxide synthase (P < 0.001), TNF-α (P < 0.001), and IFN-γ (P < 0.01); IL-17 (P < 0.001) and the chemokines CCL2 (P < 0.01) and CCL5 (P < 0.005), was reduced. We demonstrate that IL-18 plays a significant role in the pathogenesis of AN. The protective effect of IL-18BP therapy illustrates the importance of immune mediators in chronic proteinuric kidney disease and highlights the potential of IL-18BP therapy.

Nuclear orphan receptor NR2F6 directly antagonizes NFAT and RORγt binding to the Il17a promoter

Interleukin-17A (IL-17A) is the signature cytokine produced by Th17 CD4(+) T cells and has been tightly linked to autoimmune pathogenesis. In particular, the transcription factors NFAT and RORγt are known to activate Il17a transcription, although the detailed mechanism of action remains incompletely understood. Here, we show that the nuclear orphan receptor NR2F6 can attenuate the capacity of NFAT to bind to critical regions of the Il17a gene promoter. In addition, because NR2F6 binds to defined hormone response elements (HREs) within the Il17a locus, it interferes with the ability of RORγt to access the DNA. Consistently, NFAT and RORγt binding within the Il17a locus were enhanced in Nr2f6-deficient CD4(+) Th17 cells but decreased in Nr2f6-overexpressing transgenic CD4(+) Th17 cells. Taken together, our findings uncover an example of antagonistic regulation of Il17a transcription through the direct reciprocal actions of NR2F6 versus NFAT and RORγt.

Inflammatory bowel disease and pregnancy: overlapping pathways

Several studies have reported on the association between inflammatory bowel disease (IBD) and adverse pregnancy outcomes, such as preterm birth. The exact mechanisms of action are unclear; however, several pathways and processes are involved in both IBD and pregnancy that may help explain this. In this review, we discuss the immune system's T helper cells and human leukocyte antigens, inflammation, its function, and the role of Toll-like receptors (TLRs), NOD-like receptors (NLRs), and prostaglandins in the inflammatory response. For each of these topics, we consider their involvement in IBD and pregnancy, and we speculate as to how they can lead to preterm birth. Finally, we review briefly corticosteroids, biologic therapies, and immunosuppressants for the treatment of IBD, as well as their safety in use during pregnancy, with special focus on preterm birth.

Twist1 regulates Ifng expression in Th1 cells by interfering with Runx3 function

A transcription factor network that includes STAT4, T-bet, and Runx3 promotes the differentiation of Th1 cells and inflammatory immune responses. How additional transcription factors regulate the function of Th1 cells has not been defined. In this study we show that the negative regulatory factor Twist1 decreases expression of T-bet, Runx3, and IL-12Rβ2 as it inhibits IFN-γ production. Ectopic expression of Runx3, but not T-bet or IL-12Rβ2, compensates for the effects of Twist1 on IFN-γ production, and Twist1 regulation of Ifng depends on complex formation with Runx3. Twist1 decreases Runx3 and T-bet binding at the Ifng locus, and it decreases chromatin looping within the Ifng locus. These data define an IL-12/STAT4-induced negative regulatory loop that impacts multiple components of the Th1 transcriptional network and provide further insight into regulation of Th1 differentiation.

Th17 cells induce a distinct graft rejection response that does not require IL-17A

IL-17A-producing helper T (Th17) cells have been implicated in the pathogenesis of autoimmune disease, inflammatory bowel disease and graft rejection, however the mechanisms by which they cause tissue damage remain ill-defined. We examined what damage Th17 cell lines could inflict on allogeneic skin grafts in the absence of other adaptive lymphocytes. CD4(+) Th17 cell lines were generated from two TCR transgenic mouse strains, A1(M).RAG1(-/-) and Marilyn, each monospecific for the male antigen Dby. After prolonged in vitro culture in polarizing conditions, Th17 lines produced high levels of IL-17A with inherently variable levels of interferon gamma (IFNγ) and these cells were able to maintain IL-17A expression following adoptive transfer into lymphopenic mice. When transferred into lymphopenic recipients of male skin grafts, Th17 lines elicited a damaging reaction within the graft associated with pathological findings of epidermal hyperplasia and neutrophil infiltration. Th17 cells could be found in the grafted skins and spleens of recipients and maintained their polarized phenotype both in vivo and after ex vivo restimulation. Antibody-mediated neutralization of IL-17A or IFNγ did not interfere with Th17-induced pathology, nor did it prevent neutrophil infiltration. In conclusion, tissue damage by Th17 cells does not require IL-17A.

Regulation of proinflammatory Th17 responses during Trypanosoma cruzi infection by IL-12 family cytokines

Previously, we reported that the transcription factor T-bet (Tbx21) regulates Th17 responses to Trypanosoma cruzi infection in an IFN-γ-independent manner. In an effort to further understand this regulation, we examined the development and plasticity of Th17 cells during T. cruzi infection. Th17 cells recovered from infected Tbx21(-/-) mice were amenable to the inhibitory effects of T-bet, as ectopic expression of T-bet reduced IL-17 expression. We subsequently addressed the role of IL-12 family cytokines IL-12 and IL-27 and report that IL-12p35(-/-) mice infected with T. cruzi exhibited a significant increase in Th17 cells and Th17-associated inflammation. Ex vivo culture of these cells with IL-12 led to a dramatic reduction in IL-17 production and concomitant increase in IFN-γ. Importantly, the ability of IL-12 to suppress IL-17 was independent of IFN-γ. Surprisingly, and contrary to results reported for other pathogens, IL-27 had no inhibitory effect on Th17 development, as Ebi-3(-/-) mice failed to show any increase in their T. cruzi-specific Th17 response. Furthermore, IL-27 could not compensate or synergize with IL-12 to suppress IL-17 production ex vivo. Thus, we have established that IL-12, not IL-27, is critical for regulating Th17 responses to T. cruzi.