PU.1 controls fibroblast polarization and tissue fibrosis

Fibroblasts are polymorphic cells with pleiotropic roles in organ morphogenesis, tissue homeostasis and immune responses. In fibrotic diseases, fibroblasts synthesize abundant amounts of extracellular matrix which lead to scaring and organ failure. In contrast, the hallmark feature of fibroblasts in arthritis is matrix degradation by the release of metalloproteinases and degrading enzymes, and subsequent tissue destruction. The mechanisms driving these functionally opposing pro-fibrotic and pro-inflammatory phenotypes of fibroblasts are enigmatic. We identified the transcription factor PU.1 as an essential orchestrator of the pro-fibrotic gene expression program. The interplay between transcriptional and post-transcriptional mechanisms which normally control PU.1 expression is perturbed in various fibrotic diseases, resulting in upregulation of PU.1, induction of fibrosis-associated gene sets, and a phenotypic switch in matrix-producing pro-fibrotic fibroblasts. In contrast, pharmacological and genetic inactivation of PU.1 disrupts the fibrotic network and enables re-programming of fibrotic fibroblasts into resting fibroblasts with regression of fibrosis in different organs.

STAT6 and Furin Are Successive Triggers for the Production of TGF-β by T Cells

Production of TGF-β by T cells is key to various aspects of immune homeostasis, with defects in this process causing or aggravating immune-mediated disorders. The molecular mechanisms that lead to TGF-β generation by T cells remain largely unknown. To address this issue, we take advantage of the fact that intestinal helminths stimulate Th2 cells besides triggering TGF-β generation by T lymphocytes and regulate immune-mediated disorders. We show that the Th2 cell-inducing transcription factor STAT6 is necessary and sufficient for the expression of TGF-β propeptide in T cells. STAT6 is also necessary for several helminth-triggered events in mice, such as TGF-β-dependent suppression of alloreactive inflammation in graft-versus-host disease. Besides STAT6, helminth-induced secretion of active TGF-β requires cleavage of propeptide by the endopeptidase furin. Thus, for the immune regulatory pathway necessary for TGF-β production by T cells, our results support a two-step model, composed of STAT6 and furin.

Effector T Helper Cell Subsets in Inflammatory Bowel Diseases

The gastrointestinal tract is a site of high immune challenge, as it must maintain a delicate balance between tolerating luminal contents and generating an immune response toward pathogens. CD4⁺ T cells are key in mediating the host protective and homeostatic responses. Yet, CD4⁺ T cells are also known to be the main drivers of inflammatory bowel disease (IBD) when this balance is perturbed. Many subsets of CD4⁺ T cells have been identified as players in perpetuating chronic intestinal inflammation. Over the last few decades, understanding of how each subset of Th cells plays a role has dramatically increased. Simultaneously, this has allowed development of therapeutic innovation targeting specific molecules rather than broad immunosuppressive agents. Here, we review the emerging evidence of how each subset functions in promoting and sustaining the chronic inflammation that characterizes IBD.

Defining IL-2 mediated regulation of Il9 activation using knock-in reporter mice

T cells are critical regulators of inflammatory disease and immunity. CD4+ T helper cells develop into various subsets that are specialized in secretion of particular cytokines and mediate restricted types of inflammation. One of these subsets, IL-9 secreting Th9 cells, have proven to be effective in clearing helminthic infections and in tumor immunotherapy. Inappropriate Th9 activity has also been associated with colitis and atopic inflammation. While IL-4 and TGF-β are primary cytokines required for Th9 differentiation, other stimuli, including an IL-2/STAT5 pathway, are necessary for acute activation. Recent studies have reported a reduction in IL-9, when differentiated Th9 cells are stimulated in the absence of exogenous IL-2. This implies that IL-2 plays an important role in modulating IL-9 expression in Th9 cells, in a paracrine manner. Using two distinct IL-9 reporter mice, one with a reporter knocked-in to the first Il9 exon and the other with a downstream IRES-reporter, we noted that exon 1 disruption results in reduced allele expression. Specifically, the allele is no longer responsive to IL-2. This is correlated with diminished STAT5 binding near the promoter, suggesting novel effects of the first exon on cytokine responsiveness of the allele. In ongoing studies we will more precisely map STAT5 binding across the promoter and the 5-prime end of the Il9 gene to define how gene regulation and cytokine responsiveness might be exploited to control IL-9-dependent immune responses.

Identification of a conserved multi-lineage Il9 enhancer

The immune system provides resistance to the myriad of pathogens in the environment, but can also respond inappropriately causing allergic inflammation and autoimmune disease. CD4+ T cells, which play a crucial role in adaptive immune system, can be divided into subsets based on their effector functions. T helper 9 (Th9) cells, derived by the IL-4/STAT6 and TGFβ signaling pathways, produce IL-9 as a hallmark cytokine. Through IL-9 production, Th9 cells protect against parasite infection but are also involved in allergic inflammation and autoimmune diseases. In this study, we demonstrate that a conserved noncoding sequence (CNS) located 25kb upstream of the Il9 transcription start site, termed Il9 CNS-25, is critical for regulating Il9 expression in Th cell subsets and IL-9 producing CD8+ T cells (Tc9). Th9 cells derived from Il9 CNS-25 mutant (Il9ΔCNS-25) mice produce significantly less IL-9. Il9 CNS-25 was bound by factors that promote Il9 gene expression including STATs, IRF4 and BATF, promoted chromatin modifications and transcription factor binding at the promoter, and mediated accessibility of the locus. Il9ΔCNS-25 mice showed attenuated airway inflammation compared to control mice. The Il9 CNS-25 region in mice is conserved with an IL9 CNS-18 region in the human genome. We deleted CNS-18 in primary human Th9 cells and observed diminished IL-9 production. Thus, we have demonstrated that the Il9 CNS-25/IL9 CNS-18 elements are respectively critical for Il9/IL9 gene expression in Th9 cells and other IL-9 producing T cell subsets.

Defining the mechanism of BATF specificity in Th cell lineages

IL-9 is a pleiotropic cytokine produced by Th9 cells and inappropriate expression is associated with immune disorders. The basic leucine zipper transcription factor (BATF) is expressed in multiple Th subsets and cooperates with other factors to regulate gene transcription. BATF-deficiency results in diminished IL-9 in Th9 cells and decreased IL-17 in Th17 cells. However, ectopic expression of BATF activates only the lineage-specific cytokine; IL-9 in Th9 cells and IL-17 in Th17 cells. The mechanism for this restricted activity is unclear. In this study, we demonstrate a lineage specific mechanism of how BATF activates Il9 in Th9 and Th17 cells. Using ChIP and chromatin accessibility assays we found that BATF binds to the Il9 gene locus at a greater level in Th9 cells compared to Th17 cells. This observation may be because the DNA in Th17 cells is in a heterochromatic state. Increasing the chromatin accessibility of Il9 gene locus in Th17 cells followed by BATF overexpression leads to increased IL-9 production. BATF forms a heterodimer with Jun family members to induce gene expression. The expression level of c-Jun and JunB in Th17 cells is lower compared to Th9 cells. In testing the role of these factors, we observed that the loss of c-Jun or JunB impairs IL-9 production in Th9 cells, indicating that Jun family members promote IL-9 production. Ectopic expression of BATF with either c-Jun or JunB significantly increases IL-9 production in Th17 cells, suggesting the low expression of Jun family members limits the ability of BATF to induce IL-9 in Th17 cells. Taken together, our results reveal a mechanism for how BATF achieves specificity of cytokine induction in Th subsets.

Differing effects of TGFβ family members in the generation of IL-9-secreting T cells

The development of Th subsets results from cellular and cytokine cues that are present in the inflammatory environment. The developing T cell is able to integrate multiple signals from the environment, and those signals sculpt the cytokine-producing capacity of the effector T cell. Even when cytokines activate similar intracellular signaling pathways, the T cell can discriminate the cytokine signal to generate distinct outcomes. IL-9-secreting Th9 cells regulate multiple immune responses, including immunity to pathogens and tumors, allergic inflammation, and autoimmunity. In combination with IL-4, both TGFβ and Activin A promote IL-9 production, yet it is not clear if both cytokines generate Th9 cells with identical phenotype and function. We observed that in contrast to TGFβ that efficiently represses Th2 cytokines in Th9 cultures, Activin A produced a multi-cytokine phenotype with secretion of IL-4, IL-5, IL-13, IL-10, in addition to IL-9. Ongoing experiments will define the function of these populations of cells in vivo. These observations suggest that although TGFβ and IL-4 were identified as cytokines that stimulate optimal IL-9 production, they might not be the cytokines that generate optimal function from Th9 cells in immunity and disease.

Contribution of the glycosyltransferase FucT-VII to allergic skin inflammation

The development of E and P selectin ligands on the surface of immune cells requires α1,3 fucosyltransferase FucT-VII, an enzyme encoded by the Fut7 gene. T cell activation and cytokine environments regulate glycosyltransferase expression, eventual glycan formation and cell migration. The T helper 2 (Th2) subset are mediators of allergic inflammation, but the requirement for FucT-VII-dependent migration in allergic inflammation is less clear. In this study we determined if Fut7 expression was required for allergic inflammation in the constitutively active STAT6VT model in which mice are predisposed to a spontaneous inflammatory phenotype similar to that of atopic dermatitis. STAT6VT mice were crossed with Fut7−/− animals and compared for the development of disease and inflammation. Decreased incidence of disease was observed in Fut7−/− STAT6VT mice, compared to STAT6VT mice. Interestingly, if disease did occur in Fut7−/− animals, the inflammation was not attenuated and in some cases was more severe. One factor that impacted disease development was related to offspring who inherited the STAT6VT allele from their maternal parent. The dams would have experienced inflammation throughout pregnancy and might have promoted a mechanism of migration independent of Fut7 gene expression. Together, these data indicate that Fut7 promotes, but is not strictly required for, allergic skin inflammation.

Identification of an Il9 gene locus regulatory element in mast cells and basophils

Interleukin 9 (IL-9) is a pleiotropic cytokine that plays a central role in immunological disorders. Extensive work has been done to describe the Il9 gene locus and its transcriptional regulation in Th9 and other T cell subsets. Some innate immune cells, such as mast cells and basophils, can also produce a substantial amount of IL-9 in an inflammatory milieu. However, very little is known about how the Il9 gene is regulated in these cells. In this study, we show for the first time that IL-33, and not IgE cross linking, induces IL-9 production in mast cells and basophils and that this is an IL-3 dependent effect. Using the CRISPR-Cas9-mediated deletion approach, we show that IL-9 production in mast cells and basophils is dependent on a conserved non-coding sequence -25 kb (CNS-25) upstream of the IL-9 promoter. Our results show that the CNS-25 region is important for mast cell and basophil IL-9 production in vitro and in vivo. ChIP assays show that the CNS-25 can bind multiple transcription factors at a higher magnitude than the Il9 promoter. Additionally, this region has high chromatin remodeling and p300, an acetyl transferase, binding in mast cells. We show that p300 is essential for IL-33 induced IL-9 production in mast cells and basophils. Taken together, our data define a mechanism for Il9 gene regulation orchestrated by IL-33 and IL-3 signaling in mast cells and basophils.

Platelet-Activating Factor-Induced Reduction in Contact Hypersensitivity Responses Is Mediated by Mast Cells via Cyclooxygenase-2-Dependent Mechanisms

Platelet-activating factor (PAF) stimulates numerous cell types via activation of the G protein-coupled PAF receptor (PAFR). PAFR activation not only induces acute proinflammatory responses, but it also induces delayed systemic immunosuppressive effects by modulating host immunity. Although enzymatic synthesis and degradation of PAF are tightly regulated, oxidative stressors, such as UVB, chemotherapy, and cigarette smoke, can generate PAF and PAF-like molecules in an unregulated fashion via the oxidation of membrane phospholipids. Recent studies have demonstrated the relevance of the mast cell (MC) PAFR in PAFR-induced systemic immunosuppression. The current study was designed to determine the exact mechanisms and mediators involved in MC PAFR-mediated systemic immunosuppression. By using a contact hypersensitivity model, the MC PAFR was not only found to be necessary, but also sufficient to mediate the immunosuppressive effects of systemic PAF. Furthermore, activation of the MC PAFR induces MC-derived histamine and PGE₂ release. Importantly, PAFR-mediated systemic immunosuppression was defective in mice that lacked MCs, or in MC-deficient mice transplanted with histidine decarboxylase- or cyclooxygenase-2-deficient MCs. Lastly, it was found that PGs could modulate MC migration to draining lymph nodes. These results support the hypothesis that MC PAFR activation promotes the immunosuppressive effects of PAF in part through histamine- and PGE₂-dependent mechanisms.

Mechanism for initiation of food allergy: Dependence on skin barrier mutations and environmental allergen costimulation

BACKGROUND

Mechanisms for the development of food allergy in neonates are unknown but clearly linked in patient populations to a genetic predisposition to skin barrier defects. Whether skin barrier defects contribute functionally to development of food allergy is unknown.

OBJECTIVE

The purpose of the study was to determine whether skin barrier mutations, which are primarily heterozygous in patient populations, contribute to the development of food allergy.

METHODS

Mice heterozygous for the filaggrin (Flg)^ft and Tmem79^ma mutations were skin sensitized with environmental and food allergens. After sensitization, mice received oral challenge with food allergen, and then inflammation, inflammatory mediators, and anaphylaxis were measured.

RESULTS

We define development of inflammation, inflammatory mediators, and food allergen-induced anaphylaxis in neonatal mice with skin barrier mutations after brief concurrent cutaneous exposure to food and environmental allergens. Moreover, neonates of allergic mothers have increased responses to suboptimal sensitization with food allergens. Importantly, responses to food allergens by these neonatal mice were dependent on genetic defects in skin barrier function and on exposure to environmental allergens. ST2 blockade during skin sensitization inhibited the development of anaphylaxis, antigen-specific IgE, and inflammatory mediators. Neonatal anaphylactic responses and antigen-specific IgE were also inhibited by oral pre-exposure to food allergen, but interestingly, this was blunted by concurrent pre-exposure of the skin to environmental allergen.

CONCLUSION

These studies uncover mechanisms for food allergy sensitization and anaphylaxis in neonatal mice that are consistent with features of human early-life exposures and genetics in patients with clinical food allergy and demonstrate that changes in barrier function drive development of anaphylaxis to food allergen.

Rapid molecular assays to study human centromere genomics

The centromere is the structural unit responsible for the faithful segregation of chromosomes. Although regulation of centromeric function by epigenetic factors has been well-studied, the contributions of the underlying DNA sequences have been much less well defined, and existing methodologies for studying centromere genomics in biology are laborious. We have identified specific markers in the centromere of 23 of the 24 human chromosomes that allow for rapid PCR assays capable of capturing the genomic landscape of human centromeres at a given time. Use of this genetic strategy can also delineate which specific centromere arrays in each chromosome drive the recruitment of epigenetic modulators. We further show that, surprisingly, loss and rearrangement of DNA in centromere 21 is associated with trisomy 21. This new approach can thus be used to rapidly take a snapshot of the genetics and epigenetics of each specific human centromere in nondisjunction disorders and other biological settings.

STAT4 Regulates the CD8+ Regulatory T Cell/T Follicular Helper Cell Axis and Promotes Atherogenesis in Insulin-Resistant Ldlr-/- Mice

The metabolic syndrome and diabetic conditions support atherosclerosis, but the exact mechanisms for accelerated atherogenesis remain unclear. Although the proinflammatory role of STAT4 in atherosclerosis and diet-induced insulin resistance (IR) was recently established, the impact of STAT4 on atherogenesis in conditions of IR is not known. In this study, we generated Stat4^-/-Ldlr^-/- mice that were fed a diabetogenic diet with added cholesterol (DDC). DDC-fed Stat4^-/-Ldlr^-/- mice demonstrated improved glucose tolerance, insulin sensitivity, and a 36% reduction in atherosclerosis compared with Ldlr^-/- controls. Interestingly, we detected a reduction in T follicular helper (Tfh) cells and plasma B cells but a sharp elevation in CD8⁺ regulatory T cells (Tregs) in spleens and aortas of Stat4^-/-Ldlr^-/- mice compared with Ldlr^-/- mice. Similarly, STAT4 deficiency supported CD8⁺ Treg differentiation in vitro. STAT4-deficient CD8⁺ Tregs suppressed Tfh cell and germinal center B cell development upon immunization with keyhole limpet hemocyanin, indicating an important role for STAT4 in CD8⁺ Treg functions in vivo. Furthermore, adoptive transfer of Stat4^-/-Ldlr^-/- CD8⁺ Tregs versus Ldlr^-/- CD8⁺ Tregs resulted in a significant reduction in plaque burden and suppression of Tfh cell and germinal center B cells in DDC-fed Ldlr^-/- recipients. STAT4 expression in macrophages (MΦs) also affected the Tfh/CD8⁺ Treg axis, because conditioned media from Stat4^-/-Ldlr^-/- MΦs supported CD8⁺ Treg differentiation, but not Tfh cell differentiation, in a TGF-β-dependent manner. These findings suggest a novel mechanism by which STAT4 supports atherosclerosis in IR Ldlr^-/- mice via STAT4-dependent MΦs, as well as cell-intrinsic suppression of CD8⁺ Treg generation and functions and maintenance of Tfh cell generation and the accompanying humoral immune response.

Specifically differentiated T cell subset promotes tumor immunity over fatal immunity

Ramadan et al. demonstrate that triggering the ST2–IL-33 pathway in IL-9–secreting T cells decreases the severity of graft-versus-host disease through AREG upregulation while maintaining graft versus leukemia activity by preserving the central memory phenotype of CD8, increasing CD8α and cytolytic molecule expression.

Allogeneic immune cells, particularly T cells in donor grafts, recognize and eliminate leukemic cells via graft-versus-leukemia (GVL) reactivity, and transfer of these cells is often used for high-risk hematological malignancies, including acute myeloid leukemia. Unfortunately, these cells also attack host normal tissues through the often fatal graft-versus-host disease (GVHD). Full separation of GVL activity from GVHD has yet to be achieved. Here, we show that, in mice and humans, a population of interleukin-9 (IL-9)–producing T cells activated via the ST2–IL-33 pathway (T9_IL-33 cells) increases GVL while decreasing GVHD through two opposing mechanisms: protection from fatal immunity by amphiregulin expression and augmentation of antileukemic activity compared with T9, T1, and unmanipulated T cells through CD8α expression. Thus, adoptive transfer of allogeneic T9_IL-33 cells offers an attractive approach for separating GVL activity from GVHD.

Bcl6 promotes follicular helper T-cell differentiation and PD-1 expression in a Blimp1-independent manner in mice

The transcription factors Bcl6 and Blimp1 have opposing roles in the development of the follicular helper T (T_FH ) cells: Bcl6 promotes and Blimp1 inhibits T_FH -cell differentiation. Similarly, Bcl6 activates, while Blimp1 represses, expression of the T_FH -cell marker PD-1. However, Bcl6 and Blimp1 repress each other's expression, complicating the interpretation of the regulatory network. Here we sought to clarify the extent to which Bcl6 and Blimp1 independently control T_FH -cell differentiation by generating mice with T-cell specific deletion of both Bcl6 and Blimp1 (double conditional KO [dcKO] mice). Our data indicate that Blimp1 does not control T_FH -cell differentiation independently of Bcl6. However, a population of T follicular regulatory (T_FR ) cells developed independently of Bcl6 in dcKO mice. We have also analyzed regulation of IL-10 and PD-1, two genes controlled by both Bcl6 and Blimp1, and observed that Bcl6 regulates both genes independently of Blimp1. We found that Bcl6 positively regulates PD-1 expression by inhibiting the ability of T-bet/Tbx21 to repress Pdcd1 transcription. Our data provide a novel mechanism for positive control of gene expression by Bcl6, and illuminate how Bcl6 and Blimp1 control T_FH -cell differentiation.

A Stat6/Pten Axis Links Regulatory T Cells with Adipose Tissue Function

Obesity and type 2 diabetes are associated with metabolic defects and adipose tissue inflammation. Foxp3+ regulatory T cells (Tregs) control tissue homeostasis by counteracting local inflammation. However, if and how T cells interlink environmental influences with adipocyte function remains unknown. Here, we report that enhancing sympathetic tone by cold exposure, beta3-adrenergic receptor (ADRB3) stimulation or a short-term high-calorie diet enhances Treg induction in vitro and in vivo. CD4+ T cell proteomes revealed higher expression of Foxp3 regulatory networks in response to cold or ADRB3 stimulation in vivo reflecting Treg induction. Specifically, Ragulator-interacting protein C17orf59, which limits mTORC1 activity, was upregulated in CD4+ T cells by either ADRB3 stimulation or cold exposure, suggesting contribution to Treg induction. By loss- and gain-of-function studies, including Treg depletion and transfers in vivo, we demonstrated that a T cell-specific Stat6/Pten axis links cold exposure or ADRB3 stimulation with Foxp3+ Treg induction and adipose tissue function. Our findings offer a new mechanistic model in which tissue-specific Tregs maintain adipose tissue function.

IRF4 Modulates CD8+ T Cell Sensitivity to IL-2 Family Cytokines

IFN regulatory factor 4 (IRF4) is a key transcription factor that promotes effector CD8⁺ T cell differentiation and expansion. The roles of IRF4 in regulating the CD8⁺ T cell response to cytokines have not been explored. In this article, we show that IL-2 and IL-15 signaling and STAT5 activation regulate IRF4 expression in CD8⁺ T cells. Gene-expression profile analysis has also revealed that IRF4 is required for expression of the receptors of IL-2 family cytokines CD122 and CD127. We found that IRF4 binds directly to CD122 and CD127 gene loci, indicating that it may directly promote CD122 and CD127 gene transcription. As a consequence, IRF4-deficient CD8⁺ T cells show diminished sensitivity to IL-2, IL-15, and IL-7 treatment in vitro. Furthermore, we found that IRF4-deficient CD8⁺ T cells had lower expression of CD122 and CD127 in vivo during influenza virus infection. These data suggest that IRF4 regulates the sensitivity of CD8⁺ T cells to IL-2 family cytokines, which correlates with the diminished effector and memory CD8⁺ T cell responses in IRF4-deficient CD8⁺ T cells.

Poly-ADP ribose polymerase-14 limits severity of allergic skin disease

Poly-ADP ribose polymerase-14 (PARP14 or ARTD8) was initially identified as a transcriptional co-activator for signal transducer and activator of transcription 6 (Stat6), where the presence of interleukin-4 (IL-4) and activated Stat6 induces the enzymatic activity of PARP14 that promotes T helper type 2 differentiation and allergic airway disease. To further our understanding of PARP14 in allergic disease, we studied the function of PARP14 in allergic inflammation of skin using mice that express constitutively active Stat6 in T cells (Stat6VT) and develop spontaneous inflammation of the skin. We mated Stat6VT mice to Parp14^-/- mice and observed that approximately 75% of the Stat6VT × Parp14^-/- mice develop severe atopic dermatitis (AD)-like lesions, compared with about 50% of Stat6VT mice, and have increased morbidity compared with Stat6VT mice. Despite this, gene expression in the skin and the cellular infiltrates was only modestly altered by the absence of PARP14. In contrast, we saw significant changes in systemic T-cell cytokine production. Moreover, adoptive transfer experiments demonstrated that decreases in IL-4 production reflected a cell intrinsic role for PARP14 in Th2 cytokine control. Hence, our data suggest that although PARP14 has similar effects on T-cell cytokine production in several allergic disease models, the outcome of those effects is distinct, depending on the target organ of disease.

Resolution of inflammation by interleukin-9-producing type 2 innate lymphoid cells

Inflammatory diseases such as arthritis are chronic conditions that fail to resolve spontaneously. While the cytokine and cellular pathways triggering arthritis are well defined, those responsible for the resolution of inflammation are incompletely characterized. Here we identified interleukin (IL)-9-producing type 2 innate lymphoid cells (ILC2s) as the mediators of a molecular and cellular pathway that orchestrates the resolution of chronic inflammation. In mice, the absence of IL-9 impaired ILC2 proliferation and activation of regulatory T (T_reg) cells, and resulted in chronic arthritis with excessive cartilage destruction and bone loss. In contrast, treatment with IL-9 promoted ILC2-dependent T_reg activation and effectively induced resolution of inflammation and protection of bone. Patients with rheumatoid arthritis in remission exhibited high numbers of IL-9⁺ ILC2s in joints and the circulation. Hence, fostering IL-9-mediated ILC2 activation may offer a novel therapeutic approach inducing resolution of inflammation rather than suppression of inflammatory responses.

Paracrine IL-2 Is Required for Optimal Type 2 Effector Cytokine Production

IL-2 is a pleiotropic cytokine that promotes the differentiation of Th cell subsets, including Th1, Th2, and Th9 cells, but it impairs the development of Th17 and T follicular helper cells. Although IL-2 is produced by all polarized Th subsets to some level, how it impacts cytokine production when effector T cells are restimulated is unknown. We show in this article that Golgi transport inhibitors (GTIs) blocked IL-9 production. Mechanistically, GTIs blocked secretion of IL-2 that normally feeds back in a paracrine manner to promote STAT5 activation and IL-9 production. IL-2 feedback had no effect on Th1- or Th17-signature cytokine production, but it promoted Th2- and Th9-associated cytokine expression. These data suggest that the use of GTIs results in an underestimation of the presence of type 2 cytokine-secreting cells and highlight IL-2 as a critical component in optimal cytokine production by Th2 and Th9 cells in vitro and in vivo.

STAT4 regulates CD8+Treg/Tfh cell axis and promotes atherogenesis in insulin-resistant Ldlr−/− mice

The metabolic syndrome support atherosclerosis, but the exact mechanisms for accelerated atherogenesis remain unclear. While the pro-inflammatory role of signal transducer and activator of transcription 4 (STAT4) in atherosclerosis and diet-induced insulin resistance (IR) was recently established, an impact of STAT4 on atherogenesis in conditions of IR is not known. To study the role of STAT4 in IR-accelerated atherosclerosis we generated Stat4−/−Ldlr−/− mice that were fed a diabetogenic diet with added cholesterol (DDC). DDC fed Stat4−/− Ldlr−/−mice demonstrated improved glucose tolerance, insulin sensitivity, and a 36% reduction in atherosclerosis compared with Ldlr−/−controls. Interestingly, we detected a reduction in T follicular helper (Tfh) and plasma B cells, but a sharp elevation in CD8+ Tregs in spleens and aortas of Stat4−/−Ldlr−/−versus Ldlr−/−mice. Similarly, STAT4 deficiency supported CD8+ Treg differentiation in vitro. Additionally, Stat4-deficient CD8+Tregs suppressed Tfh and germinal center B cell development upon immunization with KLH indicating an important role for STAT4 in CD8+ Treg functions in vivo. Effects of STAT4 deficiency were not only restricted to T cells, but had a significant impact on macrophage phenotype. Stat4−/−Ldlr−/− macrophages displayed decreased IFNγ and MHC-II expression. Conditioned media from Stat4−/−Ldlr−/−MFs supported CD8+ Treg but not Tfh cell differentiation in TGFβ-dependent manner, suggesting a role for MF-specific STAT4 in Th cell differentiation. These new findings suggest a novel mechanism by which STAT4 supports atherosclerosis in obese, IR Ldlr−/− mice via increases in MF activation, and modulation of the Tfh/ CD8+ Treg axis systemically and within the aorta.

Distinct Roles of Brd2 and Brd4 in Potentiating the Transcriptional Program for Th17 Cell Differentiation

The BET proteins are major transcriptional regulators and have emerged as new drug targets, but their functional distinction has remained elusive. In this study, we report that the BET family members Brd2 and Brd4 exert distinct genomic functions at genes whose transcription they co-regulate during mouse T helper 17 (Th17) cell differentiation. Brd2 is associated with the chromatin insulator CTCF and the cohesin complex to support cis-regulatory enhancer assembly for gene transcriptional activation. In this context, Brd2 binds the transcription factor Stat3 in an acetylation-sensitive manner and facilitates Stat3 recruitment to active enhancers occupied with transcription factors Irf4 and Batf. In parallel, Brd4 temporally controls RNA polymerase II (Pol II) processivity during transcription elongation through cyclin T1 and Cdk9 recruitment and Pol II Ser2 phosphorylation. Collectively, our study uncovers both separate and interdependent Brd2 and Brd4 functions in potentiating the genetic program required for Th17 cell development and adaptive immunity.