Th memory for interleukin-17 expression is stable in vivo

TH17 cell: a double-edged sword in the development of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic nonspecific inflammatory disease of the gastrointestinal tract, and its pathogenesis has not been fully understood. Extensive dysregulation of the intestinal mucosal immune system is critical in the development and progression of IBD. T helper (Th) 17 cells have the characteristics of plasticity. They can transdifferentiate into subpopulations with different functions in response to different factors in the surrounding environment, thus taking on different roles in regulating the intestinal immune responses. In this review, we will focus on the plasticity of Th17 cells as well as the function of Th17 cells and their related cytokines in IBD. We will summarize their pathogenic and protective roles in IBD under different conditions, respectively, hoping to further deepen the understanding of the pathological mechanisms underlying IBD and provide insights for future treatment.

Batf stabilizes Th17 cell development via impaired Stat5 recruitment of Ets1-Runx1 complexes

Although the activator protein-1 (AP-1) factor Batf is required for Th17 cell development, its mechanisms of action to underpin the Th17 program are incompletely understood. Here, we find that Batf ensures Th17 cell identity in part by restricting alternative gene programs through its actions to restrain IL-2 expression and IL-2-induced Stat5 activation. This, in turn, limits Stat5-dependent recruitment of Ets1-Runx1 factors to Th1- and Treg-cell-specific gene loci. Thus, in addition to pioneering regulatory elements in Th17-specific loci, Batf acts indirectly to inhibit the assembly of a Stat5-Ets1-Runx1 complex that enhances the transcription of Th1- and Treg-cell-specific genes. These findings unveil an important role for Stat5-Ets1-Runx1 interactions in transcriptional networks that define alternate T cell fates and indicate that Batf plays an indispensable role in both inducing and maintaining the Th17 program through its actions to regulate the competing actions of Stat5-assembled enhanceosomes that promote Th1- and Treg-cell developmental programs.

Emergent dynamics of a three-node regulatory network explain phenotypic switching and heterogeneity: a case study of Th1/Th2/Th17 cell differentiation

Naïve helper (CD4+) T-cells can differentiate into distinct functional subsets including Th1, Th2, and Th17 phenotypes. Each of these phenotypes has a 'master regulator' - T-bet (Th1), GATA3 (Th2) and RORγT (Th17) - that inhibits the other two master regulators. Such mutual repression among them at a transcriptional level can enable multistability, giving rise to six experimentally observed phenotypes - Th1, Th2, Th17, hybrid Th/Th2, hybrid Th2/Th17 and hybrid Th1/Th17. However, the dynamics of switching among these phenotypes, particularly in the case of epigenetic influence, remains unclear. Here, through mathematical modeling, we investigated the coupled transcription-epigenetic dynamics in a three-node mutually repressing network to elucidate how epigenetic changes mediated by any 'master regulator' can influence the transition rates among different cellular phenotypes. We show that the degree of plasticity exhibited by one phenotype depends on relative strength and duration of mutual epigenetic repression mediated among the master regulators in a three-node network. Further, our model predictions can offer putative mechanisms underlying relatively higher plasticity of Th17 phenotype as observed in vitro and in vivo. Together, our modeling framework characterizes phenotypic plasticity and heterogeneity as an outcome of emergent dynamics of a three-node regulatory network, such as the one mediated by T-bet/GATA3/RORγT.

Altered T cell plasticity favours Th17 cells in early arthritis

OBJECTIVES

The predominance of differentiated Th17 cells has been implied as a key driver of autoimmune arthritis, including early RA. Because accumulating evidence suggests that Th cell differentiation is a plastic process, we investigated plasticity and underlying molecular mechanisms to address the shift towards the Th17 phenotype in early RA.

METHODS

A cohort of 61 patients with early, active, untreated RA and 45 age- and sex-matched healthy controls were studied. Viable in vitro- and in vivo-generated Th1, Th2 and Th17 cells were FACS-sorted and transdifferentiated under Th1-, Th2- or Th17-inducing conditions. The cytokine Th profile of the transdifferentiated cells was assessed by flow cytometry. Th cell-associated cytokine and transcription factor gene loci were analysed by chromatin immunoprecipitation assay and their expression by quantitative real-time PCR.

RESULTS

In vitro-generated Th cells showed substantial plasticity, which was similar between RA and healthy controls, whereas in vivo-derived Th1 and Th2 cells from RA patients demonstrated an enhanced plasticity towards IL-17-expressing phenotypes compared with healthy controls. Further, in vivo-generated Th17 cells from RA patients showed a resistance to transdifferentiate into Th1 or Th2 cells. The serum/glucocorticoid-regulated kinase 1-forkhead box protein O1-IL-23 receptor (SGK1-FOXO1-IL-23R) axis together with increased RORC expression was associated with the predominant Th17 phenotype in early RA.

CONCLUSIONS

Our data indicate that in vivo-originated Th subsets are prone to Th17 cell transdifferentiation in early RA, while Th17 cells are resistant to changes in their phenotype. Together, the data imply that an altered plasticity contributes to the Th17 shift in early RA.

High-Dimensional T Helper Cell Profiling Reveals a Broad Diversity of Stably Committed Effector States and Uncovers Interlineage Relationships

CD4⁺ T helper (Th) cells are fundamental players in immunity. Based on the expression of signature cytokines and transcription factors, several Th subsets have been defined. Th cells are thought to be far more heterogeneous and multifunctional than originally believed, but characterization of the full diversity has been hindered by technical limitations. Here, we employ mass cytometry to analyze the diversity of Th cell responses generated in vitro and in animal disease models, revealing a vast heterogeneity of effector states with distinct cytokine footprints. The diversities of cytokine responses established during primary antigen encounters in Th1- and Th2-cell-polarizing conditions are largely maintained after secondary challenge, regardless of the new inflammatory environment, highlighting many of the identified states as stable Th cell sublineages. We also find that Th17 cells tend to upregulate Th2-cell-associated cytokines upon challenge, indicating a closer developmental connection between Th17 and Th2 cells than previously anticipated.

TH17 cells require ongoing classic IL-6 receptor signaling to retain transcriptional and functional identity

Acting in concert with TGF-β, interleukin-6 (IL-6) signaling induces T helper 17 (T_H17) cell development by programming T_H17-related genes via signal transducers and activators of transcription 3 (STAT3). A role for IL-6 signaling beyond the inductive phase of T_H17 cell development has not been defined because IL-23 signaling downstream of T_H17 cell induction also activates STAT3 and is thought responsible for T_H17 cell maintenance. Here, we find that IL-6 signaling is required for both induction and maintenance of mouse T_H17 cells; IL-6Rα-deficient T_H17 cells rapidly lost their T_H17 phenotype and did not cause disease in two models of colitis. Cotransfer of wild-type T_H17 cells with IL-6Rα-deficient T_H17 cells induced colitis but was unable to rescue phenotype loss of the latter. High IL-6 expression in the colon promoted classic, or cis, rather than transreceptor signaling that was required for maintenance of T_H17 cells. Thus, ongoing classic IL-6 signaling underpins the T_H17 program and is required for T_H17 cell maintenance and function.

Effect of synbiotics in the treatment of smokers and non-smokers with gingivitis: randomized controlled trial

BACKGROUND

To evaluate the efficacy of synbiotic tablets on the clinical and biochemical parameters of smokers and non-smokers with gingivitis.

METHODS

Eighty patients with gingivitis [40 smokers (+), 40 non-smokers (-)] were randomly assigned to test (T) or control (C) groups. Four groups were defined: T(+), T(-), C(+) and C(-). The subjects daily chewed a synbiotic or placebo tablet for 30 days. The gingival crevicular fluid levels of interleukin (IL)-6, IL-8 and IL-10 were determined as the primary outcome variables.

RESULTS

The clinical and biochemical parameters for all groups significantly reduced compared with the baseline (P < 0.05). While there were no significant differences between the groups for gingival index, the plaque index was significantly higher in both smoker groups than that in the T(-) group during the second month (P < 0.05). IL-8 levels in C(-) and IL-6 levels in both control groups were significantly higher than those in the T(+) group. The IL-10 levels in both control groups were significantly higher than those in the T(-) group during the second month (P < 0.05).

CONCLUSIONS

Adjunctive synbiotic tablets significantly reduce subclinical therapeutic outcomes for both smokers and non-smokers compared with placebo according to the biochemical parameters.

Increased plasticity of non-classic Th1 cells toward the Th17 phenotype

Objectives: To analyze occurrence and plasticity of two recently described distinct subtypes of Th1 cells named classic (CD161-/CCR6-) and non-classic (CD161+/CCR6+) Th1 cells in early rheumatoid arthritis (RA) patients and healthy controls (HCs).Methods: Frequencies of in vivo-generated Th1 cell populations were assessed after cytokine secretion assay for IFNγ/IL-17 and surface staining for CD161/CCR6. Viable Th1 cells (IFNγ+IL-17-) were sorted into classic Th1 (CD161-CCR6-) and non-classic Th1 (CD161+CCR6+) cells, trans-differentiated under different Th cell-inducing conditions, and assessed for plastic changes by analyzing the Th cell-associated cytokine and transcription factor profiles.Results: Ex vivo frequencies of classic (CD161-CCR6-) and non-classic (CD161+CCR6+) Th1 cells as well as related Th1 cell subpopulations CD161+CCR6- and CD161-/CCR6+ did not differ significantly between RA and HCs. However, trans-differentiation of ex vivo non-classic (CD161+CCR6+) and CD161-/CCR6+ Th1 cells resulted in a substantial shift toward Th17 and Th1/Th17 phenotypes, particularly under Th17-inducing conditions. In contrast, classic (CD161-/CCR6-) and CD161+CCR6- Th1 cells showed higher plasticity towards IL-4-producing cells, most of them shifting to a Th1/Th2 phenotype.Conclusion: Whereas non-classic (CD161+/CCR6+) and CD161-CCR6+ Th1 cells demonstrated an increased plasticity towards IL-17- phenotypes, classic Th1 and CD161+CCR6- Th1 cells showed more plasticity towards IL-4-producing phenotypes.

Biological and clinical significance of T helper 17 cell plasticity

Mature T helper (Th) effector cells originate following antigen recognition by naive T precursors. The maturation process is accompanied by the acquisition of specific effector functions that distinguish at least three different T helper subsets: Th1, Th2 and Th17. In general, maturation of somatic cells is accompanied by terminal differentiation. However, accumulating evidence shows that effector T cells retain a certain degree of plasticity. This is especially true for Th17 cells, which have been shown to converge towards other phenotypes in response to specific microenvironmental pressure. In this review we will discuss the experimental evidence that supports the hypothesis of Th17 plasticity, with particular emphasis on the generation of Th17-derived 'non-classic' Th1 cells, and the molecular networks that control it. Moreover, we will consider why Th17 plasticity is important for host protection, but also why it can have pathogenic functions during chronic inflammation. Regarding the last point, we will discuss a possible role for biological drugs in the control of Th17 plasticity and disease course.

Interleukin-10 (IL-10) Produced by Mutant Toxic Shock Syndrome Toxin 1 Vaccine-Induced Memory T Cells Downregulates IL-17 Production and Abrogates the Protective Effect against Staphylococcus aureus Infection

Development of long-term memory is crucial for vaccine-induced adaptive immunity against infectious diseases such as Staphylococcus aureus infection. Toxic shock syndrome toxin 1 (TSST-1), one of the superantigens produced by S. aureus, is a possible vaccine candidate against infectious diseases caused by this pathogen. We previously reported that vaccination with less toxic mutant TSST-1 (mTSST-1) induced T helper 17 (Th17) cells and elicited interleukin-17A (IL-17A)-mediated protection against S. aureus infection 1 week after vaccination. In the present study, we investigated the host immune response induced by mTSST-1 vaccination in the memory phase, 12 weeks after the final vaccination. The protective effect and IL-17A production after vaccination with mTSST-1 were eliminated because of IL-10 production. In the presence of IL-10-neutralizing monoclonal antibody (mAb), IL-17A production was restored in culture supernatants of CD4⁺ T cells and macrophages sorted from the spleens of vaccinated mice. Vaccinated mice treated with anti-IL-10 mAb were protected against systemic S. aureus infection in the memory phase. From these results, it was suggested that IL-10 produced in the memory phase suppresses the IL-17A-dependent vaccine effect through downregulation of IL-17A production.

Regulation of Fatty Acid Oxidation by Twist 1 in the Metabolic Adaptation of T Helper Lymphocytes to Chronic Inflammation

Objective

Inflamed tissue is characterized by low availability of oxygen and nutrients. Yet CD4+ T helper lymphocytes persist over time in such tissue and probably contribute to the chronicity of inflammation. This study was undertaken to analyze the metabolic adaptation of these cells to the inflamed environment.

Methods

Synovial and blood CD4+ T cells isolated ex vivo from patients with juvenile idiopathic arthritis (JIA) and murine CD4+ T cells were either stimulated once or stimulated repeatedly. Their dependency on particular metabolic pathways for survival was then analyzed using pharmacologic inhibitors. The role of the transcription factor Twist 1 was investigated by determining lactate production and oxygen consumption in Twist1‐sufficient and Twist1‐deficient murine T cells. The dependency of these murine cells on particular metabolic pathways was analyzed using pharmacologic inhibitors.

Results

Programmed death 1 (PD‐1)+ T helper cells in synovial fluid samples from patients with JIA survived via fatty acid oxidation (mean ± SEM survival of 3.4 ± 2.85% in the presence of etomoxir versus 60 ± 7.08% in the absence of etomoxir on day 4 of culture) (P < 0.0002; n = 6) and expressed the E‐box–binding transcription factor TWIST1 (2–14‐fold increased expression) (P = 0.0156 versus PD‐1− T helper cells; n = 6). Repeatedly restimulated murine T helper cells, which expressed Twist1 as well, needed Twist1 to survive via fatty acid oxidation. In addition, Twist1 protected the cells against reactive oxygen species.

Conclusion

Our findings indicate that TWIST1 is a master regulator of metabolic adaptation of T helper cells to chronic inflammation and a target for their selective therapeutic elimination.

The IL-12 Cytokine and Receptor Family in Graft-vs.-Host Disease

Allogeneic hematopoietic cell transplantation (allo-HCT) is performed with curative intent for high- risk blood cancers and bone marrow failure syndromes; yet the development of acute and chronic graft-vs.-host disease (GVHD) remain preeminent causes of death and morbidity. The IL-12 family of cytokines is comprised of IL-12, IL-23, IL-27, IL-35, and IL-39. This family of cytokines is biologically distinct in that they are composed of functional heterodimers, which bind to cognate heterodimeric receptor chains expressed on T cells. Of these, IL-12 and IL-23 share a common β cytokine subunit, p40, as well as a receptor chain: IL-12Rβ1. IL-12 and IL-23 have been documented as proinflammatory mediators of GVHD, responsible for T helper 1 (Th1) differentiation and T helper 17 (Th17) stabilization, respectively. The role of IL-27 is less defined, seemingly immune suppressive via IL-10 secretion by Type 1 regulatory (Tr1) cells yet promoting inflammation through impairing CD4⁺ T regulatory (Treg) development and/or enhancing Th1 differentiation. More recently, IL-35 was described as a potent anti-inflammatory agent produced by regulatory B and T cells. The role of the newest member, IL-39, has been implicated in proinflammatory B cell responses but has not been explored in the context of allo-HCT. This review is directed at discussing the current literature relevant to each IL-12-family cytokine and cognate receptor engagement, as well as the consequential downstream signaling implications, during GVHD pathogenesis. Additionally, we will provide an overview of translational strategies targeting the IL-12 family cytokines, their receptors, and subsequent signal transduction to control GVHD.

Arterial Hypertension and Interleukins: Potential Therapeutic Target or Future Diagnostic Marker?

Hypertension as a multifactorial pathology is one of the most important cardiovascular risk factors, affecting up to 30-40% of the general population. Complex immune responses are involved in the inflammatory mechanism of hypertension, with evidence pointing to increased inflammatory mediators even in prehypertensive patients. Increased vascular permeability, thrombogenesis, and fibrosis, effects that are associated with sustained hypertension, could be attributed to chronic inflammation. Chronic inflammation triggers endothelial dysfunction via increased production of ROS through proinflammatory cytokines. Increased serum level of proinflammatory cytokines such as IL-1β, IL-6, IL-8, IL-17, IL-23, TGFβ, and TNFα in hypertensive patients has been associated with either increased blood pressure values and/or end-organ damage. Moreover, some cytokines (i.e., IL-6) seem to determine a hypertensive response to angiotensin II, regardless of blood pressure values. Understanding hypertension as an inflammatory-based pathology gives way to new therapeutic targets. As such, conventional cardiovascular drugs (statins, calcium channels blockers, and ACEIs/ARBs) have shown additional anti-inflammatory effects that could be linked to their blood pressure lowering properties. Moreover, anti-inflammatory drugs (mycophenolate mofetil) have been shown to decrease blood pressure in hypertensive patients or prevent its development in normotensive individuals. Further research is needed to evaluate whether drugs targeting hypertensive-linked proinflammatory cytokines, such as monoclonal antibodies, could become a new therapeutic option in treating arterial hypertension.

Pathogenicity of In Vivo Generated Intestinal Th17 Lymphocytes is IFNγ Dependent

BACKGROUND AND AIMS

T helper 17 [Th17] cells are crucially involved in the immunopathogenesis of inflammatory bowel diseases in humans. Nevertheless, pharmacological blockade of interleukin 17A [IL17A], the Th17 signature cytokine, yielded negative results in patients with Crohn's disease [CD], and attempts to elucidate the determinants of Th17 cells' pathogenicity in the gut have so far proved unsuccessful. Here, we aimed to identify and functionally validate the pathogenic determinants of intestinal IL-17-producing T cells.

METHODS

In vivo-generated murine intestinal IL-17-producing T cells were adoptively transferred into immunodeficient Rag1-/- recipients to test their pathogenicity. Human IL-17, IFNγ/IL-17, and IFNγ actively secreting T cell clones were generated from lamina propria lymphocytes of CD patients. The pathogenic activity of intestinal IL-17-producing T cells against the intestinal epithelium was evaluated.

RESULTS

IL-17-producing cells with variable colitogenic activity can be generated in vivo using different experimental colitis models. The pathogenicity of IL-17-secreting cells was directly dependent on their IFNγ secretion capacity, as demonstrated by the reduced colitogenic activity of IL-17-secreting cells isolated from IFNγ-/- mice. Moreover, IFNγ production is a distinguished attribute of CD-derived lamina propria Th17 cells. IFNγ secretion by CD-derived IL-17-producing intestinal clones is directly implicated in the epithelial barrier disruption through the modulation of tight junction proteins.

CONCLUSIONS

Intestinal Th17 cell pathogenicity is associated with IFNγ production, which directly affects intestinal permeability through the disruption of epithelial tight junctions.

A cellular and molecular view of T helper 17 cell plasticity in autoimmunity

Since the original identification of the T helper 17 (Th17) subset in 2005, it has become evident that these cells do not only contribute to host defence against pathogens, such as bacteria and fungi, but that they are also critically involved in the pathogenesis of many autoimmune diseases. In contrast to the classic Th1 and Th2 cells, which represent rather stably polarized subsets, Th17 cells display remarkable heterogeneity and plasticity. This has been attributed to the characteristics of the key transcription factor that guides Th17 differentiation, retinoic acid receptor-related orphan nuclear receptor gamma (RORγ). Unlike the 'master regulators' T-bet and GATA3 that orchestrate Th1 and Th2 differentiation, respectively, RORγ controls transcription at relatively few loci in Th17 cells. Moreover, its expression is not stabilized by positive feedback loops but rather influenced by environmental cues, allowing for substantial functional plasticity. Importantly, a subset of IL-17/IFNγ double-producing Th17 cells was identified in both human and mouse models. Evidence is accumulating that these IL-17/IFNγ double-producing cells are pathogenic drivers in autoimmune diseases, including rheumatoid arthritis, multiple sclerosis and inflammatory bowel disease. In addition, IL-17/IFNγ double-producing cells have been identified in disorders in which the role of autoimmunity remains unclear, such as sarcoidosis. The observed plasticity of Th17 cells towards the Th1 phenotype can be explained by extensive epigenetic priming of the IFNG locus in Th17 cells. In fact, Th17 cells display an IFNG chromatin landscape that is remarkably similar to that of Th1 cells. On the other hand, pathogenic capabilities of Th17 cells can be restrained by stimulating IL-10 production and transdifferentiation into IL-10 producing T regulatory type 1 (Tr1) cells. In this review, we discuss recent advances in our knowledge on the cellular and molecular mechanisms involved in Th17 differentiation, heterogeneity and plasticity. We focus on transcriptional regulation of the Th17 expression program, the epigenetic dynamics involved, and how genetic variants associated with autoimmunity may affect immune responses through distal gene regulatory elements. Finally, the implications of Th17 cell plasticity for the pathogenesis and treatment of human autoimmune diseases will be discussed.

TCR-independent functions of Th17 cells mediated by the synergistic actions of cytokines of the IL-12 and IL-1 families

The development of Th17 cells is accompanied by the acquisition of responsiveness to both IL-12 and IL-23, cytokines with established roles in the development and/or function of Th1 and Th17 cells, respectively. IL-12 signaling promotes antigen-dependent Th1 differentiation but, in combination with IL-18, allows the antigen-independent perpetuation of Th1 responses. On the other hand, while IL-23 is dispensable for initial commitment to the Th17 lineage, it promotes the pathogenic function of the Th17 cells. In this study, we have examined the overlap between Th1 and Th17 cells in their responsiveness to common pro-inflammatory cytokines and how this affects the antigen-independent cytokine responses of Th17 cells. We found that in addition to the IL-1 receptor, developing Th17 cells also up-regulate the IL-18 receptor. Consequently, in the presence of IL-1β or IL-18, and in the absence of TCR activation, Th17 cells produce Th17 lineage cytokines in a STAT3-dependent manner when stimulated with IL-23, and IFN© via a STAT4-dependent mechanism when stimulated with IL-12. Thus, building on previous findings of antigen-induced plasticity of Th17 cells, our results indicate that this potential of Th17 cells extends to their cytokine-dependent antigen-independent responses. Collectively, our data suggest a model whereby signaling via either IL-1β or IL-18 allows for bystander responses of Th17 cells to pathogens or pathogen products that differentially activate innate cell production of IL-12 or IL-23.

Mesenchymal stem cells and their immunosuppressive role in transplantation tolerance

Since they were first described, mesenchymal stem cells (MSCs) have been shown to have important effector mechanisms and the potential for use in cell therapy. A great deal of research has been focused on unveiling how MSCs contribute to anti-inflammatory responses, including describing several cell populations involved and identifying soluble and other effector molecules. In this review, we discuss some of the contemporary evidence for use of MSCs in the field of immune tolerance, with a special emphasis on transplantation. Although considerable effort has been devoted to understanding the biological function of MSCs, additional resources are required to clarify the mechanisms of their induction of immune tolerance, which will undoubtedly lead to improved clinical outcomes for MSC-based therapies.

Cellular and Molecular Dynamics of Th17 Differentiation and its Developmental Plasticity in the Intestinal Immune Response

After emerging from the thymus, naive CD4 T cells circulate through secondary lymphoid tissues, including gut-associated lymphoid tissue of the intestine. The activation of naïve CD4 T cells by antigen-presenting cells offering cognate antigen initiate differentiation programs that lead to the development of highly specialized T helper (Th) cell lineages. Although initially believed that developmental programing of effector T cells such as T helper 1 (Th1) or T helper 2 (Th2) resulted in irreversible commitment to a fixed fate, subsequent studies have demonstrated greater flexibility, or plasticity, in effector T cell stability than originally conceived. This is particularly so for the Th17 subset, differentiation of which is a highly dynamic process with overlapping developmental axes with inducible regulatory T (iTreg), T helper 22 (Th22), and Th1 cells. Accordingly, intermediary stages of Th17 cells are found in various tissues, which co-express lineage-specific transcription factor(s) or cytokine(s) of developmentally related CD4 T cell subsets. A highly specialized tissue like that of the intestine, which harbors the largest immune compartment of the body, adds several layers of complexity to the intricate process of Th differentiation. Due to constant exposure to millions of commensal microbes and periodic exposure to pathogens, the intestinal mucosa maintains a delicate balance between regulatory and effector T cells. It is becoming increasingly clear that equilibrium between tolerogenic and inflammatory axes is maintained in the intestine by shuttling the flexible genetic programming of a developing CD4 T cell along the developmental axis of iTreg, Th17, Th22, and Th1 subsets. Currently, Th17 plasticity remains an unresolved concern in the field of clinical research as targeting Th17 cells to cure immune-mediated disease might also target its related subsets. In this review, we discuss the expanding sphere of Th17 plasticity through its shared developmental axes with related cellular subsets such as Th22, Th1, and iTreg in the context of intestinal inflammation and also examine the molecular and epigenetic features of Th17 cells that mediate these overlapping developmental programs.

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.

Adoptively transferred donor IL-17-producing CD4+ T cells augment, but IL-17 alleviates, acute graft-versus-host disease

The role of IL-17 and IL-17-producing CD4⁺ T cells in acute graft-versus-host disease (GVHD) has been controversial in recent mouse and human studies. We carried out studies in a murine acute GVHD model of fully major histocompatibility complex-mismatched myeloablative bone marrow transplantation. We showed that donor wild-type CD4⁺ T cells exacerbated acute GVHD compared with IL-17^-/- CD4⁺ T cells, while IL-17 reduced the severity of acute GVHD. The augmentation of acute GVHD by transferred donor IL-17-producing CD4⁺ T cells was associated with increased Th1 responses, while IL-17 decreased the percentages of Th1 cells in the GVHD target organs. Furthermore, IL-17 reduced the infiltration of macrophages into the GVHD tissues. In vitro study showed that IL-17 could downregulate Th1 responses, possibly through inhibiting IL-12 production by donor macrophages. Depletion of macrophages in vivo diminished the protective effect of IL-17. Our results demonstrated the differential roles of adoptively transferred donor IL-17-producing CD4⁺ T cells and IL-17 in the same acute GVHD model.

RORγt antagonist suppresses M3 muscarinic acetylcholine receptor-induced Sjögren's syndrome-like sialadenitis

We showed recently that M3 muscarinic acetylcholine receptor (M3R)-reactive CD3⁺ T cells play a pathogenic role in the development of murine autoimmune sialadenitis (MIS), which mimics Sjögren's syndrome (SS). The aim of this study was to determine the effectiveness and mechanism of action of retinoic acid-related orphan receptor-gamma t (RORγt) antagonist (A213) in MIS. Splenocytes from M3R knockout (M3R^-/- ) mice immunized with murine M3R peptide mixture were inoculated into recombination-activating gene 1 knockout (Rag-1^-/- ) mice (M3R^-/- →Rag-1^-/- ) with MIS. Immunized M3R^-/- mice (pretransfer treatment) and M3R^-/- →Rag-1^-/- mice (post-transfer treatment) were treated with A213 every 3 days. Salivary volume, severity of sialadenitis and cytokine production from M3R peptide-stimulated splenocytes and lymph node cells were examined. Effects of A213 on cytokine production were analysed by enzyme-linked immunosorbent assay (ELISA) and on T helper type 1 (Th1), Th17 and Th2 differentiation from CD4⁺ T cells by flow cytometry. Pretransfer A213 treatment maintained salivary volume, improved MIS and reduced interferon (IFN)-γ and interleukin (IL)-17 production significantly compared with phosphate-buffered saline (PBS) (P < 0·05). These suppressive effects involved CD4⁺ T cells rather than CD11c⁺ cells. Post-transfer treatment with A213 increased salivary volume (P < 0·05), suppressed MIS (P < 0·005) and reduced IFN-γ and IL-17 production (P < 0·05). In vitro, A213 suppressed IFN-γ and IL-17 production from M3R-stimulated splenocytes and CD4⁺ T cells of immunized M3R^-/- mice (P < 0·05). In contrast with M3R specific responses, A213 suppressed only IL-17 production from Th17 differentiated CD4⁺ T cells without any effect on Th1 and Th2 differentiation in vitro. Our findings suggested that RORγt antagonism is potentially suitable treatment strategy for SS-like sialadenitis through suppression of IL-17 and IFN-γ production by M3R-specific T cells.

Effect of aging on sputum inflammation and asthma control

BACKGROUND

Aged asthmatic patients experience increased morbidity and mortality. Knowledge of the aging effect on airway inflammation and asthma control is limited.

OBJECTIVE

We sought to compare airway inflammation and its relationship to asthma control in aged versus younger patients and determine whether differences are asthma specific or caused by "inflamm-aging."

METHODS

We performed a prospective study of aged (>60 years) and younger (21-40 years) inner-city patients with asthma. After a run-in period to control for inhaled corticosteroid use, induced sputum was collected. Age-matched nonasthmatic control subjects were included to measure age-related inflammatory changes.

RESULTS

Aged (mean age, 67.9 ± 5.1 years; n = 35) compared with younger (mean age, 30.8 ± 5.9 years; n = 37) asthmatic patients had significantly worse asthma control and lower FEV₁. Aged asthmatic patients had higher sputum neutrophil (30.5 × 10⁴/mL and 23.1%) and eosinophil (7.0 × 10⁴/mL and 3.8%) numbers and percentages compared with younger patients (neutrophils, 13.0 × 10⁴/mL [P < .01] and 6.9% [P < .01]; eosinophils, 2.0 × 10⁴/mL [P < .01] and 1.2% [P < .01]). Aged asthmatic patients had higher sputum IL-6 (P < .01) and IL-8 (P = .01) levels. No significant inflammatory differences between aged and younger control subjects were observed. In aged asthmatic patients increased sputum IL-6 and macrophage inflammatory protein 3α/CCL20 levels were significantly associated with decreased asthma control and increased sputum neutrophil numbers and IL-1β, IL-6, and macrophage inflammatory protein 3α/CCL20 levels were associated with hospitalization.

CONCLUSIONS

The inflammatory patterns of aged versus younger asthmatic patients are associated with increased sputum neutrophil and eosinophil values and cytokine levels related to neutrophil recruitment. Differences in airway inflammation can contribute to diminished asthma control in the aged. Further understanding of asthma pathophysiology in aged patients is needed to improve management of this vulnerable population.

Treatment with NAD(+) inhibited experimental autoimmune encephalomyelitis by activating AMPK/SIRT1 signaling pathway and modulating Th1/Th17 immune responses in mice

Nicotinamide adenine dinucleotide (NAD(+)) plays vital roles in mitochondrial functions, cellular energy metabolism and calcium homeostasis. In this study, we investigated the effect of NAD(+) administration for the treatment of experimental autoimmune encephalomyelitis (EAE) in C57BL/6 mice. EAE, a classical animal model of multiple sclerosis (MS), was induced by subcutaneous injection of myelin oligodendrocyteglycoprotein (MOG). The mice were treated with 250mg/kg (body weight) NAD(+) in PBS administered intraperitoneally once daily. We observed that NAD(+) treatment could lessen the severity of EAE. Additionally, NAD(+) treatment attenuated pathological injuries of EAE mice. We also found that the AMP-activated protein kinase (AMPK)/silent mating-type information regulation 2 homolog 1(SIRT1) pathway was activated in the NAD(+)-treated mice and NAD(+) treatment suppressed pro-inflammatory T cell responses. Our findings demonstrated that NAD(+) could be an effective and promising agent to treat multiple sclerosis and its effects on other autoimmune diseases should be explored.

Protective role of Th17 cells in pulmonary infection

Th17 cells are characterized as preferential producer of interleukins including IL-17A, IL-17F, IL-21 and IL-22. Corresponding receptors of these cytokines are expressed on number of cell types found in the mucosa, including epithelial cells and fibroblasts which constitute the prime targets of the Th17-associated cytokines. Binding of IL-17 family members to their corresponding receptors lead to modulation of antimicrobial functions of target cells including alveolar epithelial cells. Stimulated alveolar epithelial cells produce antimicrobial peptides and are involved in granulepoesis, neutrophil recruitment and tissue repair. Mucosal immunity mediated by Th17 cells is protective against numerous pulmonary pathogens including extracellular bacterial and fungal pathogens. This review focuses on the protective role of Th17 cells during pulmonary infection, highlighting subset differentiation, effector cytokines production, followed by study of the binding of these cytokines to their corresponding receptors, the subsequent signaling pathway they engender and their effector role in host defense.

Translational opportunities for targeting the Th17 axis in acute graft-vs.-host disease

Allogeneic stem cell transplantation (allo-SCT) is a curative therapy for different life-threatening malignant and non-malignant hematologic disorders. Acute graft-vs.-host disease (aGVHD) and particularly gastrointestinal aGVHD remains a major source of morbidity and mortality following allo-SCT, which limits the use of this treatment in a broader spectrum of patients. Better understanding of aGVHD pathophysiology is indispensable to identify new therapeutic targets for aGVHD prevention and therapy. Growing amount of data suggest a role for T helper (Th)17 cells in aGVHD pathophysiology. In this review, we will discuss the current knowledge in this area in animal models and in humans. We will then describe new potential treatments for aGVHD along the Th17 axis.

IL-22-Expressing Murine Lymphocytes Display Plasticity and Pathogenicity in Reporter Mice

IL-22 has multiple activities ranging from tissue repair to inflammation. To characterize the pathogenicity and plasticity of cells that produce IL-22, a novel reporter mouse strain was generated. Homeostatic IL-22 reporter expression was observed in intestinal lymphoid cells identified as CD4 T cells and ILC3 cells. In a model of inflammatory bowel disease, CD4 T cells strongly expressed the IL-22 reporter in mesenteric lymph node. To examine plasticity of IL-22(+) T cells, they were purified after generation in vitro or in vivo from inflamed colon, and then cultured under Th1, Th2, or Th17 conditions. In vitro-generated IL-22(+) CD4 T cells showed relatively durable IL-22 expression under Th1 or Th2 conditions, whereas in vivo-generated cells rapidly lost IL-22 expression under these conditions. In vitro-generated cells could not be diverted to express Th1 or Th2 cytokines despite the expression of "master regulators." In vivo-generated cells could be diverted, at very low frequency, to express Th1 or Th2 cytokines. Both in vitro- and in vivo-generated cells could be induced in vitro to express high levels of IL-17A and IL-17F, assigning them to a "Th17 biased" class. However, IL-27 potently downregulated IL-22 expression. To examine IL-22(+) T cell pathogenicity, in vitro-generated cells were transferred into Rag1(-/-) mice, retaining the modest reporter expression and inducing moderate colitis. In contrast, IL-22 expressers from colitic mice, transferred into secondary hosts, lost reporter expression, acquired high T-bet and modest IFNγ and IL-17 expression, and induced severe colitis. These findings are consistent with a model of strong polarization under optimal in vitro conditions, but a plastic state of T cells in vivo.

Th17 response and its regulation in inflammatory upper airway diseases

Allergic rhinitis (AR) and chronic rhinosinusitis (CRS) are two widely prevalent inflammatory diseases in the upper airways. T cell immunity has been suggested to play an important pathogenic role in many chronic inflammatory diseases including inflammatory upper airway diseases. Inappropriate CD4(+) T cell responses, especially the dysregulation of the Th1/Th2 balance leading to excessive Th1 or Th2 cell activation, have been associated with allergic rhinitis and chronic rhinosinusitis. Nevertheless, recent studies suggest that IL-17A and IL-17A-producing Th17 cell subset, a distinct pro-inflammatory CD4(+) T cell lineage, may also play an important role in the pathophysiology of inflammatory upper airway diseases. Th17 cells may promote both eosinophilic and neutrophilic inflammation in AR and CRS. In addition, a few, but accumulating evidence shows that the Th17 responses can be tightly regulated by endogenous and exogenous substances in the context of AR and CRS. This review discusses recent advances in our understanding of the expression and function of the Th17 response and its regulation in inflammatory upper airway diseases, and the perspective for future investigation and clinical utility.

IL-7/IL-7 Receptor Signaling Differentially Affects Effector CD4+ T Cell Subsets Involved in Experimental Autoimmune Encephalomyelitis

IL-17-producing CD4(+) T (Th17) cells, along with IFN-γ-expressing Th1 cells, represent two major pathogenic T cell subsets in experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis (MS). The cytokines and transcription factors involved in the development and effector functions of Th1 and Th17 cells have been largely characterized. Among them, IL-23 is essential for the generation of stable and encephalitogenic Th17 cells and for the development of EAE. The IL-7/IL-7R signaling axis participates in cell survival, and perturbation of this pathway has been associated with enhanced susceptibility to MS. A link between IL-23-driven pathogenic T cells and IL-7/IL-7R signaling has previously been proposed, but has not been formally addressed. In the current study, we showed that Th17 cells from mice with EAE express high levels of IL-7Rα compared with Th1 cells. Using mice that constitutively express IL-7Rα on T cells, we determined that sustained IL-7R expression in IL-23R-deficient mice could not drive pathogenic T cells and the development of EAE. IL-7 inhibited the differentiation of Th17 cells, but promoted IFN-γ and GM-CSF secretion in vitro. In vivo IL-7/anti-IL-7 mAb complexes selectively expanded and enhanced the proliferation of CXCR3-expressing Th1 cells, but did not impact Th17 cells and EAE development in wild-type and IL-23R-deficient mice. Importantly, high IL-7 expression was detected in the CNS during EAE and could drive the plasticity of Th17 cells to IFN-γ-producing T cells. Together, these data address the contribution of IL-23/IL-23R and IL-7/IL-7R signaling in Th17 and Th1 cell dynamics during CNS autoimmunity.

Polyfunctional, Pathogenic CD161+ Th17 Lineage Cells Are Resistant to Regulatory T Cell-Mediated Suppression in the Context of Autoimmunity

In autoimmune diseases such as rheumatoid arthritis (RA), regulatory T cells (Tregs) fail to constrain autoimmune inflammation; however, the reasons for this are unclear. We investigated T cell regulation in the RA joint. Tregs from RA synovial fluid suppressed autologous responder T cells; however, when compared with Tregs from healthy control peripheral blood, they were significantly less suppressive. Despite their reduced suppressive activity, Tregs in the RA joint were highly proliferative and expressed FOXP3, CD39, and CTLA-4, which are markers of functional Tregs. This suggested that the reduced suppression is due to resistance of RA synovial fluid responder T cells to Treg inhibition. CD161(+) Th17 lineage cells were significantly enriched in the RA joint; we therefore investigated their relative susceptibility to Treg-mediated suppression. Peripheral blood CD161(+) Th cells from healthy controls were significantly more resistant to Treg-mediated suppression, when compared with CD161(-) Th cells, and this was mediated through a STAT3-dependant mechanism. Furthermore, depletion of CD161(+) Th cells from the responder T cell population in RA synovial fluid restored Treg-mediated suppression. In addition, CD161(+) Th cells exhibited pathogenic features, including polyfunctional proinflammatory cytokine production, an ability to activate synovial fibroblasts, and to survive and persist in the inflamed and hypoxic joint. Because CD161(+) Th cells are known to be enriched at sites of autoinflammation, our finding that they are highly proinflammatory and resistant to Treg-mediated suppression suggests an important pathogenic role in RA and other autoimmune diseases.

The IL-23-IL-17 axis in inflammatory arthritis

The discovery that the IL-23-IL-17 immune pathway is involved in many models of autoimmune disease has changed the concept of the role of T-helper cell subsets in the development of autoimmunity. In addition to TH17 cells, IL-17 is also produced by other T cell subsets and innate immune cells; which of these IL-17-producing cells have a role in tissue inflammation, and the timing, location and nature of their role(s), is incompletely understood. The current view is that innate and adaptive immune cells expressing the IL-23 receptor become pathogenic after exposure to IL-23, but further investigation into the role of IL-23 and IL-17 at different stages in the development and progression of chronic (destructive) inflammatory diseases is needed. Rheumatoid arthritis (RA) and spondyloarthritis (SpA) are the two most common forms of chronic immune-mediated inflammatory arthritis, and the IL-23-IL-17 axis is thought to have a critical role in both. This Review discusses the basic mechanisms of these cytokines in RA and SpA on the basis of findings from disease-specific animal models as well as human ex vivo studies. Promising therapeutic applications to modulate this immune pathway are in development or have already been approved. Blockade of IL-17 and/or TH17-cell activity in combination with anti-TNF therapy might be a successful approach to achieving stable remission or even prevention of chronic immune-mediated inflammatory diseases.

Stimulation with Concanavalin-A Induces IL-17 Production by Canine Peripheral T Cells

The characteristics of canine IL-17-producing cells are incompletely understood. Expression of mRNA encoding orthologs of IL-17 and the IL-17 receptor has been documented in tissues from dogs with arthritis, inflammatory bowel disease, and lymphoma; however, no associations have been found between IL-17 gene expression and disease phenotype in these conditions. Robust assessment of the role of IL-17-producing cells in dogs will require measuring the frequency of these cells in health and disease in balance with other lymphocyte subsets. The aim of this study was to confirm that the T-cell IL-17 response in dogs is evolutionarily conserved. Canine peripheral blood mononuclear cells were stimulated with Concanavalin A with or without polarizing cytokines. We used a canine specific IL-17 ELISA and flow cytometry to identify IL-17-producing T cells. Accumulation of intracellular IL-17 was observed in stimulated CD4 and CD8 T cells. The addition of pro-inflammatory cytokines appeared to enhance polarization of canine CD4 T cells to the Th17 phenotype. Conversely, the addition of IL-2 in the presence of TGF-β resulted in expansion of Treg cells. We conclude that canine IL-17-producing cells behave similarly to those from humans and mice when stimulated with mitogens and polarized with pro-inflammatory or immune regulatory cytokines.

IL-17A expression in HIV-specific CD8 T cells is regulated by IL-4/IL-13 following HIV-1 prime-boost immunization

Although Th1 and Th2 cytokines can inhibit interleukin (IL)-17-secreting T cells, how these cells are regulated under different infectious conditions is still debated. Our previous studies have shown that vaccination of IL-4 and IL-13 gene knockout (KO) mice can induce high-avidity HIV K(d)Gag197-205-specific CD8 T cells with better protective efficacy. In this study, when IL-13, IL-4, STAT6 KO, and wild-type BALB/c mice were prime-boost immunized with an HIV poxviral modality, elevated numbers of IL-17A(+) splenic K(d)Gag197-205-specific CD8 T cells were observed in all the KO mice compared with the wt BALB/c control. Similarly, when wt BALB/c mice were immunized with IL-13Rα2-adjuvanted HIV vaccines (that transiently inhibited IL-13 activity and induced high-avidity CD8 T cells with enhanced protective efficacy), elevated IL-17A(+) K(d)Gag197-205-specific CD8 T cells were detected both in the lung and the spleen. However, at the transcriptional level, elevated TGF-β, IL-6, ROR-γt, and IL-17A mRNA copy numbers were mainly detected in IL-4 KO, but not the IL-13 KO mice. These data suggested that TGF-β, IL-6, ROR-γt, but not IL-23a, played a role in IL-17A regulation in K(d)Gag197-205-specific CD8 T cells. Collectively, our findings suggest that IL-4 and IL-13 differentially regulate the expression of IL-17A in K(d)Gag197-205-specific CD8 T cells at the transcriptional and translational level, respectively, implicating IL-17A as an indirect modulator of CD8 T cell avidity and protective immunity.

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.

Differentiation, regulation and function of Th9 cells

Naïve CD4(+) T cells are activated and differentiate to distinct lineages of T helper (Th) cells, which are involved in physiological and pathological processes by obtaining the potential to produce different lineage-specific cytokines that mediate adaptive immunity. In the past decade, our knowledge of Th cells has been significantly expanded with the findings of new lineages. Interleukin (IL)-9 producing T cells are recently identified. In consideration of the ability to preferentially secret IL-9, these cells are termed Th9 cells. Given the multiple function of IL-9, Th9 cells participate in the lesion of many diseases, such as allergic inflammation, tumor, and parasitosis. In this chapter, we will focus on the cytokines, co-stimulatory factors, and transcriptional signaling pathways, which regulate Th9 cells development as well as stability, plasticity, and the multiple roles of Th9 cells in vivo.

Development of a unique epigenetic signature during in vivo Th17 differentiation

Activated naive CD4⁺ T cells are highly plastic cells that can differentiate into various T helper (Th) cell fates characterized by the expression of effector cytokines like IFN-γ (Th1), IL-4 (Th2) or IL-17A (Th17). Although previous studies have demonstrated that epigenetic mechanisms including DNA demethylation can stabilize effector cytokine expression, a comprehensive analysis of the changes in the DNA methylation pattern during differentiation of naive T cells into Th cell subsets is lacking. Hence, we here performed a genome-wide methylome analysis of ex vivo isolated naive CD4⁺ T cells, Th1 and Th17 cells. We could demonstrate that naive CD4⁺ T cells share more demethylated regions with Th17 cells when compared to Th1 cells, and that overall Th17 cells display the highest number of demethylated regions, findings which are in line with the previously reported plasticity of Th17 cells. We could identify seven regions located in Il17a, Zfp362, Ccr6, Acsbg1, Dpp4, Rora and Dclk1 showing pronounced demethylation selectively in ex vivo isolated Th17 cells when compared to other ex vivo isolated Th cell subsets and in vitro generated Th17 cells, suggesting that this unique epigenetic signature allows identifying and functionally characterizing in vivo generated Th17 cells.

Role of circulating lymphocytes in patients with sepsis

Sepsis is a systemic inflammatory response syndrome due to infection. The incidence rate is estimated to be up to 19 million cases worldwide per year and the number of cases is rising. Infection triggers a complex and prolonged host response, in which both the innate and adaptive immune response are involved. The disturbance of immune system cells plays a key role in the induction of abnormal levels of immunoregulatory molecules. Furthermore, the involvement of effector immune system cells also impairs the host response to the infective agents and tissue damage. Recently, postmortem studies of patients who died of sepsis have provided important insights into why septic patients die and showed an extensive depletion of CD4 and CD8 lymphocytes and they found that circulating blood cells showed similar findings. Thus, the knowledge of the characterization of circulating lymphocyte abnormalities is relevant for the understanding of the sepsis pathophysiology. In addition, monitoring the immune response in sepsis, including circulating lymphocyte subsets count, appears to be potential biomarker for predicting the clinical outcome of the patient. This paper analyzes the lymphocyte involvement and dysfunction found in patients with sepsis and new opportunities to prevent sepsis and guide therapeutic intervention have been revealed.

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.

The dichotomous pattern of IL-12r and IL-23R expression elucidates the role of IL-12 and IL-23 in inflammation

IL-12 and IL-23 cytokines respectively drive Th1 and Th17 type responses. Yet, little is known regarding the biology of these receptors. As the IL-12 and IL-23 receptors share a common subunit, it has been assumed that these receptors are co-expressed. Surprisingly, we find that the expression of each of these receptors is restricted to specific cell types, in both mouse and human. Indeed, although IL-12Rβ2 is expressed by NK cells and a subset of γδ T cells, the expression of IL-23R is restricted to specific T cell subsets, a small number of B cells and innate lymphoid cells. By exploiting an IL-12- and IL-23-dependent mouse model of innate inflammation, we demonstrate an intricate interplay between IL-12Rβ2 NK cells and IL-23R innate lymphoid cells with respectively dominant roles in the regulation of systemic versus local inflammatory responses. Together, these findings support an unforeseen lineage-specific dichotomy in the in vivo role of both the IL-12 and IL-23 pathways in pathological inflammatory states, which may allow more accurate dissection of the roles of these receptors in chronic inflammatory diseases in humans.

Detection of choroid- and retina-antigen reactive CD8(+) and CD4(+) T lymphocytes in the vitreous fluid of patients with birdshot chorioretinopathy

Birdshot chorioretinopathy (BSCR), a progressive form of non-infectious uveitis, is the strongest HLA-associated disease described to date, with >95% of the patients displaying HLA-A29. Since indirect evidence indicates the involvement of T cells in the etiopathology of the disease, we now isolated, cultured and analyzed the vitreous fluid-infiltrating T cells from two BSCR patients with respect to their phenotype, cytokine profile, clonal distribution and antigen specificity. Phenotypic analyses revealed the predominant presence of both CD4(+) and CD8(+) T cells in vitreous fluid. Further analyses on short term expanded and cloned T cells suggested that eye-infiltrating T cells generally displayed a Th1 like cytokine profile with secretion of high levels of IFN-γ and TNF-α. In one patient an oligoclonal CD4(+) and CD8(+) T cell infiltration, with a moderate to strongly skewed TCR Vβ usage was suggestive for an antigen driven infiltration/expansion. Indeed, a number of intraocular CD4(+) and CD8(+) T cells responded to crude retinal and choroidal lysates. These results, which demonstrate for the first time the existence of eye-antigen-specific T cells in the vitreous fluid of BSCR patients, substantiate the current view on the role of eye-antigen specific T cells in the etiopathology of BSCR.

Tumor-induced perturbations of cytokines and immune cell networks

Until recently, the intrinsically high level of cross-talk between immune cells, the complexity of immune cell development, and the pleiotropic nature of cytokine signaling have hampered progress in understanding the mechanisms of immunosuppression by which tumor cells circumvent native and adaptive immune responses. One technology that has helped to shed light on this complex signaling network is the cytokine antibody array, which facilitates simultaneous screening of dozens to hundreds of secreted signal proteins in complex biological samples. The combined applications of traditional methods of molecular and cell biology with the high-content, high-throughput screening capabilities of cytokine antibody arrays and other multiplexed immunoassays have revealed a complex mechanism that involves multiple cytokine signals contributed not just by tumor cells but by stromal cells and a wide spectrum of immune cell types. This review will summarize the interactions among cancerous and immune cell types, as well as the key cytokine signals that are required for tumors to survive immunoediting in a dormant state or to grow and spread by escaping it. Additionally, it will present examples of how probing secreted cell-cell signal networks in the tumor microenvironment (TME) with cytokine screens have contributed to our current understanding of these processes and discuss the implications of this understanding to antitumor therapies.

Th17-cell plasticity in Helicobacter hepaticus-induced intestinal inflammation

Bacterial-induced intestinal inflammation is crucially dependent on interleukin (IL)-23 and is associated with CD4(+) T helper type 1 (Th1) and Th17 responses. However, the relative contributions of these subsets during the induction and resolution of colitis in T-cell-sufficient hosts remain unknown. We report that Helicobacter hepaticus-induced typhlocolitis in specific pathogen-free IL-10(-/-) mice is associated with elevated frequencies and numbers of large intestinal interferon (IFN)-γ(+) and IFN-γ(+)IL-17A(+) CD4(+) T cells. By assessing histone modifications and transcript levels in IFN-γ(+), IFN-γ(+)IL-17A(+), and IL-17A(+) CD4(+) T cells isolated from the inflamed intestine, we show that Th17 cells are predisposed to upregulate the Th1 program and that they express IL-23R but not IL-12R. Using IL-17A fate-reporter mice, we further demonstrate that H. hepaticus infection gives rise to Th17 cells that extinguish IL-17A secretion and turn on IFN-γ within 10 days post bacterial inoculation. Together, our results suggest that bacterial-induced Th17 cells arising in disease-susceptible hosts contribute to intestinal pathology by switching phenotype, transitioning via an IFN-γ(+)IL-17A(+) stage, to become IFN-γ(+) ex-Th17 cells.

Highly polarized Th17 cells induce EAE via a T-bet independent mechanism

In the MOG35-55 induced EAE model, autoreactive Th17 cells that accumulate in the central nervous system acquire Th1 characteristics via a T-bet dependent mechanism. It remains to be determined whether Th17 plasticity and encephalitogenicity are causally related to each other. Here, we show that IL-23 polarized T-bet(-/-) Th17 cells are unimpaired in either activation or proliferation, and induce higher quantities of the chemokines RANTES and CXCL2 than WT Th17 cells. Unlike their WT counterparts, T-bet(-/-) Th17 cells retain an IL-17(hi) IFN-γ(neg-lo) cytokine profile following adoptive transfer into syngeneic hosts. This population of highly polarized Th17 effectors is capable of mediating EAE, albeit with a milder clinical course. It has previously been reported that the signature Th1 and Th17 effector cytokines, IFN-γ and IL-17, are dispensable for the development of autoimmune demyelinating disease. The current study demonstrates that the "master regulator" transcription factor, T-bet, is also not universally required for encephalitogenicity. Our results contribute to a growing body of data showing heterogeneity of myelin-reactive T cells and the independent mechanisms they employ to inflict damage to central nervous system tissues, complicating the search for therapeutic targets relevant across the spectrum of individuals with multiple sclerosis.

Epigenetic control of cytokine gene expression: regulation of the TNF/LT locus and T helper cell differentiation

Epigenetics encompasses transient and heritable modifications to DNA and nucleosomes in the native chromatin context. For example, enzymatic addition of chemical moieties to the N-terminal "tails" of histones, particularly acetylation and methylation of lysine residues in the histone tails of H3 and H4, plays a key role in regulation of gene transcription. The modified histones, which are physically associated with gene regulatory regions that typically occur within conserved noncoding sequences, play a functional role in active, poised, or repressed gene transcription. The "histone code" defined by these modifications, along with the chromatin-binding acetylases, deacetylases, methylases, demethylases, and other enzymes that direct modifications resulting in specific patterns of histone modification, shows considerable evolutionary conservation from yeast to humans. Direct modifications at the DNA level, such as cytosine methylation at CpG motifs that represses promoter activity, are another highly conserved epigenetic mechanism of gene regulation. Furthermore, epigenetic modifications at the nucleosome or DNA level can also be coupled with higher-order intra- or interchromosomal interactions that influence the location of regulatory elements and that can place them in an environment of specific nucleoprotein complexes associated with transcription. In the mammalian immune system, epigenetic gene regulation is a crucial mechanism for a range of physiological processes, including the innate host immune response to pathogens and T cell differentiation driven by specific patterns of cytokine gene expression. Here, we will review current findings regarding epigenetic regulation of cytokine genes important in innate and/or adaptive immune responses, with a special focus upon the tumor necrosis factor/lymphotoxin locus and cytokine-driven CD4+ T cell differentiation into the Th1, Th2, and Th17 lineages.

Th9 cells: differentiation and disease

CD4(+) T-helper cells regulate immunity and inflammation through the acquisition of potential to secrete specific cytokines. The acquisition of cytokine-secreting potential, in a process termed T-helper cell differentiation, is a response to multiple environmental signals including the cytokine milieu. The most recently defined subset of T-helper cells are termed Th9 and are identified by the potent production of interleukin-9 (IL-9). Given the pleiotropic functions of IL-9, Th9 cells might be involved in pathogen immunity and immune-mediated disease. In this review, I focus on recent developments in understanding the signals that promote Th9 differentiation, the transcription factors that regulate IL-9 expression, and finally the potential roles for Th9 cells in immunity in vivo.

The Th17 family: flexibility follows function

Discovery of the T-helper 17 (Th17) subset heralded a major shift in T-cell biology and immune regulation. In addition to defining a new arm of the adaptive immune response, studies of the Th17 pathway have led to a greater appreciation of the developmental flexibility, or plasticity, that is a feature of T-cell developmental programs. Since the initial finding that differentiation of Th17 cells is promoted by transforming growth factor-β (TGFβ), it became clear that Th17 cell development overlapped that of induced regulatory T (iTreg) cells. Subsequent findings established that Th17 cells are also unusually flexible in their late developmental programming, demonstrating substantial overlap with conventional Th1 cells through mechanisms that are just beginning to be understood but would appear to have important implications for immunoregulation at homeostasis and in immune-mediated diseases. Herein we examine the developmental and functional features of Th17 cells in relation to iTreg cells, Th1 cells, and Th22 cells, as a basis for understanding the contributions of this pathway to host defense, immune homeostasis, and immune-mediated disease.