Skin-derived TSLP systemically expands regulatory T cells

Regulatory T cells (Tregs) are a subset of CD4+ T cells with suppressive function and are critical for limiting inappropriate activation of T cells. Hence, the expansion of Tregs is an attractive strategy for the treatment of autoimmune diseases. Here, we demonstrate that the skin possesses the remarkable capacity to systemically expand Treg numbers by producing thymic stromal lymphopoietin (TSLP) in response to vitamin D receptor stimulation. An ∼2-fold increase in the proportion and absolute number of Tregs was observed in mice treated topically but not systemically with the Vitamin D3 analog MC903. This expansion of Tregs was dependent on TSLP receptor signaling but not on VDR signaling in hematopoietic cells. However, TSLP receptor expression by Tregs was not required for their proliferation. Rather, skin-derived TSLP promoted Treg expansion through dendritic cells. Importantly, treatment of skin with MC903 significantly lowered the incidence of autoimmune diabetes in non-obese diabetic mice and attenuated disease score in experimental autoimmune encephalomyelitis. Together, these data demonstrate that the skin has the remarkable potential to control systemic immune responses and that Vitamin D-mediated stimulation of skin could serve as a novel strategy to therapeutically modulate the systemic immune system for the treatment of autoimmunity.

A TSLP-complement axis mediates neutrophil killing of methicillin-resistant Staphylococcus aureus

Community-acquired Staphylococcus aureus infections often present as serious skin infections in otherwise healthy individuals and have become a worldwide epidemic problem fueled by the emergence of strains with antibiotic resistance, such as methicillin-resistant S. aureus (MRSA). The cytokine thymic stromal lymphopoietin (TSLP) is highly expressed in the skin and in other barrier surfaces and plays a deleterious role by promoting T helper cell type 2 (TH2) responses during allergic diseases; however, its role in host defense against bacterial infections has not been well elucidated. We describe a previously unrecognized non-TH2 role for TSLP in enhancing neutrophil killing of MRSA during an in vivo skin infection. Specifically, we demonstrate that TSLP acts directly on both mouse and human neutrophils to augment control of MRSA. Additionally, we show that TSLP also enhances killing of Streptococcus pyogenes, another clinically important cause of human skin infections. Unexpectedly, TSLP mechanistically mediates its antibacterial effect by directly engaging the complement C5 system to modulate production of reactive oxygen species by neutrophils. Thus, TSLP increases MRSA killing in a neutrophil- and complement-dependent manner, revealing a key connection between TSLP and the innate complement system, with potentially important therapeutic implications for control of MRSA infection.

Molecular Models of STAT5A Tetramers Complexed to DNA Predict Relative Genome-Wide Frequencies of the Spacing between the Two Dimer Binding Motifs of the Tetramer Binding Sites

STAT proteins bind DNA as dimers and tetramers to control cellular development, differentiation, survival, and expansion. The tetramer binding sites are comprised of two dimer-binding sites repeated in tandem. The genome-wide distribution of the spacings between the dimer binding sites shows a distinctive, non-random pattern. Here, we report on estimating the feasibility of building possible molecular models of STAT5A tetramers bound to a DNA double helix with all possible spacings between the dimer binding sites. We found that the calculated feasibility estimates correlated well with the experimentally measured frequency of tetramer-binding sites. This suggests that the feasibility of forming the tetramer complex was a major factor in the evolution of this DNA sequence variation.

Cutting Edge: IL-4, IL-21, and IFN-γ Interact To Govern T-bet and CD11c Expression in TLR-Activated B Cells

T-bet and CD11c expression in B cells is linked with IgG2c isotype switching, virus-specific immune responses, and humoral autoimmunity. However, the activation requisites and regulatory cues governing T-bet and CD11c expression in B cells remain poorly defined. In this article, we reveal a relationship among TLR engagement, IL-4, IL-21, and IFN-γ that regulates T-bet expression in B cells. We find that IL-21 or IFN-γ directly promote T-bet expression in the context of TLR engagement. Further, IL-4 antagonizes T-bet induction. Finally, IL-21, but not IFN-γ, promotes CD11c expression independent of T-bet. Using influenza virus and Heligmosomoides polygyrus infections, we show that these interactions function in vivo to determine whether T-bet(+) and CD11c(+) B cells are formed. These findings suggest that T-bet(+) B cells seen in health and disease share the common initiating features of TLR-driven activation within this circumscribed cytokine milieu.

BACH2 regulates CD8(+) T cell differentiation by controlling access of AP-1 factors to enhancers

T cell antigen receptor (TCR) signaling drives distinct responses depending on the differentiation state and context of CD8(+) T cells. We hypothesized that access of signal-dependent transcription factors (TFs) to enhancers is dynamically regulated to shape transcriptional responses to TCR signaling. We found that the TF BACH2 restrains terminal differentiation to enable generation of long-lived memory cells and protective immunity after viral infection. BACH2 was recruited to enhancers, where it limited expression of TCR-driven genes by attenuating the availability of activator protein-1 (AP-1) sites to Jun family signal-dependent TFs. In naive cells, this prevented TCR-driven induction of genes associated with terminal differentiation. Upon effector differentiation, reduced expression of BACH2 and its phosphorylation enabled unrestrained induction of TCR-driven effector programs.

T helper 1 immunity requires complement-driven NLRP3 inflammasome activity in CD4⁺ T cells

The NLRP3 inflammasome controls interleukin-1β maturation in antigen-presenting cells, but a direct role for NLRP3 in human adaptive immune cells has not been described. We found that the NLRP3 inflammasome assembles in human CD4(+) T cells and initiates caspase-1-dependent interleukin-1β secretion, thereby promoting interferon-γ production and T helper 1 (T(H)1) differentiation in an autocrine fashion. NLRP3 assembly requires intracellular C5 activation and stimulation of C5a receptor 1 (C5aR1), which is negatively regulated by surface-expressed C5aR2. Aberrant NLRP3 activity in T cells affects inflammatory responses in human autoinflammatory disease and in mouse models of inflammation and infection. Our results demonstrate that NLRP3 inflammasome activity is not confined to "innate immune cells" but is an integral component of normal adaptive T(H)1 responses.

TSLP acts on neutrophils to drive complement-mediated killing of methicillin-resistant Staphylococcus aureus

Community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections, often presenting as serious skin infections in otherwise healthy individuals, have become a world-wide epidemic problem and warrant attention for therapeutic intervention. Accordingly, defining the mechanisms that govern the activation and regulation of the immune response to MRSA is clinically important and could lead to the discovery of much needed rational targets for therapeutic manipulation. The cytokine thymic stromal lymphopoeitin (TSLP) is most well characterized as a major contributor to Th2-type responses in which it plays a deleterious role in the promotion of allergic responses. However, while TSLP is highly expressed at barrier surfaces, including the skin, its role in host-defense against bacterial infections has not been well elucidated. Unexpectedly, we found that TSLP can play a protective role in the skin by acting directly on mouse neutrophils to increase their killing of MRSA in both an in vitro killing assay and an in vivo skin infection model. Additionally, TSLP also directly acts on purified human blood neutrophils to reduce MRSA burden. Therefore, neutrophils represent previously unrecognized potent responders to TSLP. Surprisingly, we found that TSLP mediates these effects by directly engaging the complement C5 system to modulate reactive oxygen species production by neutrophils. Thus, TSLP increases MRSA killing in a neutrophil- and complement-dependent manner, revealing an unanticipated key connection between TSLP and the innate complement system. These data demonstrate an unrecognized beneficial role for TSLP in the skin, with potentially important clinical implications.

Autocrine NLPR3 inflammasome activity is critical to normal adaptive immunity via regulation of IFN-γ in CD4+ T cells

The NLRP3 inflammasome controls IL-1β maturation in antigen presenting cells but a direct role in human adaptive immune cells has not been described. Here we show that the NLRP3 inflammasome assembles in human CD4+ T cells and initiates caspase-1-dependent IL-1b secretion, thereby promoting IFN-γ production and Th1 differentiation in an autocrine fashion. Importantly, NLRP3 assembly requires intracellular C5 activation and stimulation of C5a receptor 1 (C5aR1), which drive reactive oxygen species (ROS) production. The alternative cell surface expressed C5a receptor 2 (C5aR2) negatively regulates this process. Dysregulation of NLRP3 activity in T cells affects inflammatory responses in autoimmune disease or infection. Firstly, CD4+ T cells from patients with cryopyrin-associated periodic syndromes (CAPS), who have constitutively-active NLRP3, exhibit overactive Th1 responses that are normalized by NLRP3 inhibitor treatment. Secondly, IFN-γ production is impaired in T cells from Nlpr3−/− or Il1a/Il1b−/− mice upon viral infection. Our results demonstrate that NLRP3 inflammasome activity is not confined to ‘innate immune cells’ but is an integral component of normal adaptive Th1 responses.

IL-21 Signaling in Immunity

IL-21 is a type I cytokine produced by T cells and natural killer T cells that has pleiotropic actions on a wide range of immune and non-immune cell types. Since its discovery in 2000, extensive studies on the biological actions of IL-21 have been performed in vitro and in vivo. Recent reports describing patients with primary immunodeficiency caused by mutations of IL21 or IL21R have further deepened our knowledge of the role of this cytokine in host defense. Elucidation of the molecular mechanisms that mediate IL-21's actions has provided the rationale for targeting IL-21 and IL-21 downstream mediators for therapeutic purposes. The use of next-generation sequencing technology has provided further insights into the complexity of IL-21 signaling and has identified transcription factors and co-factors involved in mediating the actions of this cytokine. In this review, we discuss recent advances in the biology and signaling of IL-21 and how this knowledge can be potentially translated into clinical settings.

Cutting Edge: Expression of IRF8 in Gastric Epithelial Cells Confers Protective Innate Immunity against Helicobacter pylori Infection

IFN regulatory factor 8 (IRF8) is expressed in many types of blood cells and plays critical roles in cellular differentiation and function. However, the role of IRF8 in nonhematopoietic systems remains poorly understood. In this study, we provide evidence that IRF8 is a transcriptional modulator of the gastric mucosa necessary for limiting Helicobacter pylori colonization. H. pylori infection significantly upregulated expression of IRF8, which, in turn, promoted IFN-γ expression by gastric epithelial cells. Mice deficient in IRF8 exhibited increased H. pylori colonization and aborted induction of mucosal IFN-γ. Genome-wide analyses of IFN-γ-treated gastric epithelial cells by chromatin immunoprecipitation sequencing and RNA sequencing led to the identification of IRF8 target genes, with many belonging to the IFN-regulated gene family that was observed previously in immune cells. Our results identify the IRF8-IFN-γ circuit as a novel gastric innate immune mechanism in the host defense against infection with H. pylori.

Mitochondrial Membrane Potential Identifies Cells with Enhanced Stemness for Cellular Therapy

Long-term survival and antitumor immunity of adoptively transferred CD8(+) T cells is dependent on their metabolic fitness, but approaches to isolate therapeutic T cells based on metabolic features are not well established. Here we utilized a lipophilic cationic dye tetramethylrhodamine methyl ester (TMRM) to identify and isolate metabolically robust T cells based on their mitochondrial membrane potential (ΔΨm). Comprehensive metabolomic and gene expression profiling demonstrated global features of improved metabolic fitness in low-ΔΨm-sorted CD8(+) T cells. Transfer of these low-ΔΨm T cells was associated with superior long-term in vivo persistence and an enhanced capacity to eradicate established tumors compared with high-ΔΨm cells. Use of ΔΨm-based sorting to enrich for cells with superior metabolic features was observed in CD8(+), CD4(+) T cell subsets, and long-term hematopoietic stem cells. This metabolism-based approach to cell selection may be broadly applicable to therapies involving the transfer of HSC or lymphocytes for the treatment of viral-associated illnesses and cancer.

Endothelial interleukin-21 receptor up-regulation in peripheral artery disease

In most patients with symptomatic peripheral artery disease (PAD), severe stenosis in or occlusion of the major blood vessels that supply the legs make the amount of distal blood flow dependent on the capacity to induce angiogenesis and collateral vessel formation. Currently, there are no medications that improve perfusion to the ischemic limb, and thus directly treat the primary problem of PAD. A recent report from our group in a pre-clinical mouse PAD model showed that interleukin-21 receptor (IL-21R) is up-regulated in the endothelial cells from ischemic hindlimb muscle. We further showed that loss of IL-21R resulted in impaired perfusion recovery in this model. In our study, we sought to determine whether IL-21R is present in the endothelium from ischemic muscle of patients with PAD. Using human gastrocnemius muscle biopsies, we found increased levels of IL-21R in the skeletal muscle endothelial cells of patients with PAD compared to control individuals. Interestingly, PAD patients had approximately 1.7-fold higher levels of circulating IL-21. These data provide direct evidence that the IL-21R pathway is indeed up-regulated in patients with PAD. This pathway may serve as a therapeutic target for modulation.

Cutting Edge: IL-1 Receptor Signaling is Critical for the Development of Autoimmune Uveitis

IL-1β is a proinflammatory cytokine important for local and systemic immunity. However, aberrant production of this cytokine is implicated in pathogenic mechanisms of a number of inflammatory diseases, including Behçet's disease and age-related macular degeneration. In this study, we report the increased secretion of IL-1β in the retina by neutrophils, macrophages, and dendritic cells during ocular inflammation and show that loss of IL-1R signaling confers protection from experimental autoimmune uveitis. Moreover, the amelioration of experimental autoimmune uveitis in Il1r-deficient mice was associated with reduced infiltration of inflammatory cells into the retina and decreased numbers of uveitogenic Th17 cells that mediate uveitis. These findings indicate the possible utility of IL-1R-blocking agents for the treatment of ocular inflammatory diseases.

New insights into heterogeneity of peritoneal B-1a cells

Peritoneal B-1a cells are characterized by their expression of CD5 and enrichment for germline-encoded IgM B cell receptors. Early studies showing expression of a diverse array of VDJ sequences among purified B-1a cells provided a molecular basis for understanding the heterogeneity of the B-1a cell repertoire. Antigen-driven positive selection and the identification of B-1a specific progenitors suggest multiple origins of B-1a cells. The introduction of new markers such as PD-L2, CD25, CD73, and PC1 (plasma cell alloantigen 1, also known as ectonucleotide phosphodiesterase/pyrophosphatase 1) further helped to identify phenotypically and functionally distinct B-1a subsets. Among many B-1a subsets defined by these new markers, PC1 is unique in that it subdivides B-1a cells into PC1(hi) and PC1(lo) subpopulations with distinct functions, such as production of natural IgM and gut IgA, response to the pneumococcal antigen PPS-3, secretion of interleukin-10, and support for T helper 1 (TH 1) cell differentiation. RNA sequencing of these subsets revealed differential expression of genes involved in cellular movement and immune cell trafficking. We will discuss these new insights underlying the heterogeneous nature of the B-1a cell repertoire.

Comprehensive assembly of novel transcripts from unmapped human RNA-Seq data and their association with cancer

Crucial parts of the genome including genes encoding microRNAs and noncoding RNAs went unnoticed for years, and even now, despite extensive annotation and assembly of the human genome, RNA-sequencing continues to yield millions of unmappable and thus uncharacterized reads. Here, we examined > 300 billion reads from 536 normal donors and 1,873 patients encompassing 21 cancer types, identified ∼300 million such uncharacterized reads, and using a distinctive approach de novo assembled 2,550 novel human transcripts, which mainly represent long noncoding RNAs. Of these, 230 exhibited relatively specific expression or non-expression in certain cancer types, making them potential markers for those cancers, whereas 183 exhibited tissue specificity. Moreover, we used lentiviral-mediated expression of three selected transcripts that had higher expression in normal than in cancer patients and found that each inhibited the growth of HepG2 cells. Our analysis provides a comprehensive and unbiased resource of unmapped human transcripts and reveals their associations with specific cancers, providing potentially important new genes for therapeutic targeting.

Interleukin-2 activity can be fine tuned with engineered receptor signaling clamps

Interleukin-2 (IL-2) regulates lymphocyte function by signaling through heterodimerization of the IL-2Rβ and γc receptor subunits. IL-2 is of considerable therapeutic interest, but harnessing its actions in a controllable manner remains a challenge. Previously, we have engineered an IL-2 "superkine" with enhanced affinity for IL-2Rβ. Here, we describe next-generation IL-2 variants that function as "receptor signaling clamps." They retained high affinity for IL-2Rβ, inhibiting binding of endogenous IL-2, but their interaction with γc was weakened, attenuating IL-2Rβ-γc heterodimerization. These IL-2 analogs acted as partial agonists and differentially affected lymphocytes poised at distinct activation thresholds. Moreover, one variant, H9-RETR, antagonized IL-2 and IL-15 better than blocking antibodies against IL-2Rα or IL-2Rβ. Furthermore, this mutein prolonged survival in a model of graft-versus-host disease and blocked spontaneous proliferation of smoldering adult T cell leukemia (ATL) T cells. This receptor-clamping approach might be a general mechanism-based strategy for engineering cytokine partial agonists for therapeutic immunomodulation.

Complex interactions of transcription factors in mediating cytokine biology in T cells

T-helper (Th) cells play critical roles within the mammalian immune system, and the differentiation of naive CD4(+) T cells into distinct T-helper subsets is critical for normal immunoregulation and host defense. These carefully regulated differentiation processes are controlled by networks of cytokines, transcription factors, and epigenetic modifications, resulting in the generation of multiple CD4(+) T-cell subsets, including Th1, Th2, Th9, Th17, Treg, and Tfh cells. In this review, we discuss the roles of transcription factors in determining the specific type of differentiation and in particular the role of interleukin-2 (IL-2) in promoting or inhibiting Th differentiation. In addition to discussing master regulators and subset-specific transcription factors for distinct T-helper cell populations, we focus on signal transducer and activator of transcription (STAT) proteins and on the cooperative action of interferon regulatory factor 4 (IRF4) with activator protein 1 (AP-1) family proteins and STAT3 in the assembly of complexes that broadly influence T-cell differentiation.

Loss of interleukin-21 receptor activation in hypoxic endothelial cells impairs perfusion recovery after hindlimb ischemia

OBJECTIVE

Surgical hindlimb ischemia (HLI) in mice has become a valuable preclinical model to study peripheral arterial disease. We previously identified that the different phenotypic outcomes after HLI across inbred mouse strains is related to a region on the short arm of mouse chromosome 7. The gene coding the interleukin-21 receptor (IL-21R) lies at the peak of association in this region.

APPROACH AND RESULTS

With quantitative real-time polymerase chain reaction, we found that a mouse strain with a greater ability to upregulate IL-21R after HLI had better perfusion recovery than a strain with no upregulation after HLI. Immunofluorescent staining of ischemic hindlimb tissue showed IL-21R expression on endothelial cells (ECs) from C57BL/6 mice. An EC-enriched fraction isolated from ischemic hindlimb muscle showed higher Il-21R levels than an EC-enriched fraction from nonischemic limbs. In vitro, human umbilical vein ECs showed elevated IL-21R expression after hypoxia and serum starvation. Under these conditions, IL-21 treatment increased cell viability, decreased cell apoptosis, and augmented tube formation. In vivo, either knockout Il21r or blocking IL-21 signaling by treating with IL-21R-Fc (fusion protein that blocks IL-21 binding to its receptor) in C57BL/6 mice resulted in less perfusion recovery after HLI. Both in vitro and in vivo modulation of the IL-21/IL-21R axis under hypoxic conditions resulted in increased signal transducer and activator of transcription 3 phosphorylation and a subsequent increase in the B-cell lymphoma leukemia-2/BCL-2-associated X protein ratio.

CONCLUSION

Our data indicate that IL-21R upregulation and ligand activation in hypoxic ECs may help perfusion recovery by limiting/preventing apoptosis and favoring cell survival and angiogenesis through the signal transducer and activator of transcription 3 pathway.

Thymic stromal lymphopoietin and interleukin-4 mediate the pathogenesis of halothane-induced liver injury in mice

Liver eosinophilia has been associated with incidences of drug-induced liver injury (DILI) for more than 50 years, although its role in this disease has remained largely unknown. In this regard, it was recently shown that eosinophils played a pathogenic role in a mouse model of halothane-induced liver injury (HILI). However, the signaling events that drove hepatic expression of eosinophil-associated chemokines, eotaxins, eosinophil infiltration, and subsequent HILI were unclear. We now provide evidence implicating hepatic epithelial-derived cytokine thymic stromal lymphopoietin (TSLP) and type 2 immunity, in particular, interleukin-4 (IL-4) production, in mediating hepatic eosinophilia and injury during HILI. TSLP was constitutively expressed by mouse hepatocytes and increased during HILI. Moreover, the severity of HILI was reduced in mice deficient in either the TSLP receptor (TSLPR) or IL-4 and was accompanied by decreases in serum levels of eotaxins and hepatic eosinophilia. Similarly, concanavalin A-induced liver injury, where type 2 cytokines and eosinophils play a significant role in its pathogenesis, was also reduced in TSLPR-deficient mice. Studies in vitro revealed that mouse and human hepatocytes produce TSLP and eotaxins in response to treatment with combinations of IL-4 and proinflammatory cytokines IL-1β and tumor necrosis factor alpha.

CONCLUSION

This report provides the first evidence implicating roles for hepatic TSLP signaling, type 2 immunity, and eosinophilia in mediating liver injury caused by a drug.

Potential role of myeloid cell/eosinophil-derived IL-17 in LPS-induced endotoxin shock

IL-17RA is a shared receptor subunit for several cytokines of the IL-17 family, including IL-17A, IL-17C, IL-17E (also called IL-25) and IL-17F. It has been shown that mice deficient in IL-17RA are more susceptible to sepsis than wild-type mice, suggesting that IL-17RA is important for host defense against sepsis. However, it is unclear which ligands for IL-17RA, such as IL-17A, IL-17C, IL-17E/IL-25 and/or IL-17F, are involved in the pathogenesis of sepsis. Therefore, we examined IL-17A, IL-17E/IL-25 and IL-17F for possible involvement in LPS-induced endotoxin shock. IL-17A-deficient mice, but not IL-25- or IL-17F-deficient mice, were resistant to LPS-induced endotoxin shock, as compared with wild-type mice. Nevertheless, studies using IL-6-deficient, IL-21Rα-deficient and Rag-2-deficient mice, revealed that neither IL-6 and IL-21, both of which are important for Th17 cell differentiation, nor Th17 cells were essential for the development of LPS-induced endotoxin shock, suggesting that IL-17A-producing cells other than Th17 cells were important in the setting. In this connection, IL-17A was produced by macrophages, DCs and eosinophils after LPS injection. Taken together, these findings indicate that IL-17A, but not IL-17F or IL-25, is crucial for LPS-induced endotoxin shock. In addition, macrophages, DCs and eosinophils, but not Th17 cells or γδ T cells, may be sources of IL-17A during LPS-induced endotoxin shock.

Autoimmunity: regulatory B cells--IL-35 and IL-21 regulate the regulators

IL-21 regulates the activity and number of IL-10-producing regulatory B cells (B10 cells) that modulate immune responses and limit diverse autoimmune diseases. A new study demonstrates that IL-35 has a similar function. Identifying regulatory circuits that control B10-cell function in vivo might open the door to future treatments for autoimmune diseases.

Interleukin-21: a double-edged sword with therapeutic potential

Interleukin-21 is a cytokine with broad pleiotropic actions that affect the differentiation and function of lymphoid and myeloid cells. Since its discovery in 2000, a tremendous amount has been learned about its biological actions and the molecular mechanisms controlling IL-21-mediated cellular responses. IL-21 regulates both innate and adaptive immune responses, and it not only has key roles in antitumour and antiviral responses but also exerts major effects on inflammatory responses that promote the development of autoimmune diseases and inflammatory disorders. Numerous studies have shown that enhancing or inhibiting the action of IL-21 has therapeutic effects in animal models of a wide range of diseases, and various clinical trials are underway. The current challenge is to understand how to specifically modulate the actions of IL-21 in the context of each specific immune response or pathological situation. In this Review, we provide an overview of the basic biology of IL-21 and discuss how this information has been - and can be - exploited therapeutically.