FoxP3+RORgammat+ T helper intermediates display suppressive function against autoimmune diabetes

T-helper cells flexibility: the possibility of reprogramming T cells fate

Various disciplines cooperate to find novel approaches to cure impaired body functions by repairing, replacing, or regenerating cells, tissues, or organs. The possibility that a stable differentiated cell can reprogram itself opens the door to new therapeutic strategies against a multitude of diseases caused by the loss or dysfunction of essential, irreparable, and specific cells. One approach to cell therapy is to induce reprogramming of adult cells into other functionally active cells. Understanding the factors that cause or contribute to T cell plasticity is not only of clinical importance but also expands the knowledge of the factors that induce cells to differentiate and improves the understanding of normal developmental biology. The present review focuses on the advances in the conversion of peripheral CD4+ T cells, the conditions of their reprogramming, and the methods proposed to control such cell differentiation.

The TH1 cell lineage-determining transcription factor T-bet suppresses TH2 gene expression by redistributing GATA3 away from TH2 genes

Lineage-determining transcription factors (LD-TFs) drive the differentiation of progenitor cells into a specific lineage. In CD4+ T cells, T-bet dictates differentiation of the TH1 lineage, whereas GATA3 drives differentiation of the alternative TH2 lineage. However, LD-TFs, including T-bet and GATA3, are frequently co-expressed but how this affects LD-TF function is not known. By expressing T-bet and GATA3 separately or together in mouse T cells, we show that T-bet sequesters GATA3 at its target sites, thereby removing GATA3 from TH2 genes. This redistribution of GATA3 is independent of GATA3 DNA binding activity and is instead mediated by the T-bet DNA binding domain, which interacts with the GATA3 DNA binding domain and changes GATA3's sequence binding preference. This mechanism allows T-bet to drive the TH1 gene expression program in the presence of GATA3. We propose that redistribution of one LD-TF by another may be a common mechanism that could explain how specific cell fate choices can be made even in the presence of other transcription factors driving alternative differentiation pathways.

Interferon-β acts directly on T cells to prolong allograft survival by enhancing regulatory T cell induction through Foxp3 acetylation

Type I interferons (IFNs) are pleiotropic cytokines with potent antiviral properties that also promote protective T cell and humoral immunity. Paradoxically, type I IFNs, including the widely expressed IFNβ, also have immunosuppressive properties, including promoting persistent viral infections and treating T-cell-driven, remitting-relapsing multiple sclerosis. Although associative evidence suggests that IFNβ mediates these immunosuppressive effects by impacting regulatory T (Treg) cells, mechanistic links remain elusive. Here, we found that IFNβ enhanced graft survival in a Treg-cell-dependent murine transplant model. Genetic conditional deletion models revealed that the extended allograft survival was Treg cell-mediated and required IFNβ signaling on T cells. Using an in silico computational model and analysis of human immune cells, we found that IFNβ directly promoted Treg cell induction via STAT1- and P300-dependent Foxp3 acetylation. These findings identify a mechanistic connection between the immunosuppressive effects of IFNβ and Treg cells, with therapeutic implications for transplantation, autoimmunity, and malignancy.

Growth hormone secretagogue receptor deficiency promotes lung cancer growth by affecting the Th17/Treg balance

Background

Cluster of differentiation 4 (CD4⁺) T cells plays a prominent role in eliminating cancer cells. The balance between T helper (Th)17 and regulatory T (Treg) cells is crucial for optimal immune response and protection against cancer. Growth hormone secretagogue receptor 1a (GHSR1a), a member of the G protein-coupled protein receptor superfamily, plays a critical role in immune cell function. The aim of our study is to investigate the role of GHSR1a in CD4⁺ T cell differentiation and lung cancer progression.

Methods

A subcutaneous lung cancer model was used to examine the role of GHSR1a in controlling tumor growth. Lewis lung carcinoma (LLC) cells were subcutaneously implanted into Ghsr1a^−/− mice and wild-type (WT) mice. The ratio of Th17 and Treg in the draining lymph node of Ghsr1a^−/− mice and WT tumor-bearing mice was detected by fluorescence-activated cell sorting (FACS). The effect of GHSR1a deficiency on Th17 and Treg cell differentiation was examined using an in vitro differentiation assay. The phosphorylation of mammalian target of rapamycin (mTOR), signal transducer, and activator of transcription (STAT)3 and STAT5 signaling was detected with Western blot.

Results

We found that the ablation of GHSR1a resulted in impaired anti-tumor immunity to control lung cancer growth in vivo. We also demonstrated that the deficiency of GHSR1a promoted a shift in the Th17/Treg balance toward enhanced Treg differentiation and inhibited Th17 differentiation both in vivo and in vitro, which suggests that GHSR1a regulates T cell lineage choices between Th17 and Treg cell commitment in the tumor microenvironment. Mechanistically, the deficiency of GHSR1a resulted in reduced phosphorylation in mTOR and STAT3, and increased phosphorylation in STAT5.

Conclusions

Our findings showed the important role of GHSR1a in CD4⁺ T cell differentiation in the context of the lung cancer microenvironment. This research provides a novel molecular target and insights into interventions for the prevention and treatment of lung cancer.

c-Rel employs multiple mechanisms to promote the thymic development and peripheral function of regulatory T cells in mice

The NF-κB transcription factor c-Rel is a critical regulator of Treg ontogeny, controlling multiple points of the stepwise developmental pathway. Here, we found that the thymic Treg defect in c-Rel-deficient (cRel^-/- ) mice is quantitative, not qualitative, based on analyses of TCR repertoire and TCR signaling strength. However, these parameters are altered in the thymic Treg-precursor population, which is also markedly diminished in cRel^-/- mice. Moreover, c-Rel governs the transcriptional programme of both thymic and peripheral Tregs, controlling a core of genes involved with immune signaling, and separately in the periphery, cell cycle progression. Last, the immune suppressive function of peripheral cRel^-/- tTregs is diminished in a lymphopenic model of T cell proliferation and is associated with decreased stability of Foxp3 expression. Collectively, we show that c-Rel is a transcriptional regulator that controls multiple aspects of Treg development, differentiation, and function via distinct mechanisms.

ApoB-Specific CD4+ T Cells in Mouse and Human Atherosclerosis

Atherosclerosis is a chronic inflammatory condition of the arterial wall that leads to the formation of vessel-occluding plaques within the subintimal space of middle-sized and larger arteries. While traditionally understood as a myeloid-driven lipid-storage disease, growing evidence suggests that the accumulation of low-density lipoprotein cholesterol (LDL-C) ignites an autoimmune response with CD4⁺ T-helper (T_H) cells that recognize self-peptides from Apolipoprotein B (ApoB), the core protein of LDL-C. These autoreactive CD4⁺ T cells home to the atherosclerotic plaque, clonally expand, instruct other cells in the plaque, and induce clinical plaque instability. Recent developments in detecting antigen-specific cells at the single cell level have demonstrated that ApoB-reactive CD4⁺ T cells exist in humans and mice. Their phenotypes and functions deviate from classical immunological concepts of distinct and terminally differentiated T_H immunity. Instead, ApoB-specific CD4⁺ T cells have a highly plastic phenotype, can acquire several, partially opposing and mixed transcriptional programs simultaneously, and transit from one T_H subset into another over time. In this review, we highlight adaptive immune mechanisms in atherosclerosis with a focus on CD4⁺ T cells, introduce novel technologies to detect ApoB-specific CD4⁺ T cells at the single cell level, and discuss the potential impact of ApoB-driven autoimmunity in atherosclerosis.

FOXP3+ regulatory T cells and age-related diseases

Regulatory T (Treg) cells are critical for the maintenance of immune homeostasis. Dysregulation of Treg cells has been implicated in the pathogenesis of autoimmunity and chronic inflammation, while aging is characterized by an accumulation of inflammatory markers in the peripheral blood, a phenomenon known as 'inflammaging'. The relationship between Treg cells and age-related diseases remains to be further studied. Increasing evidence revealed that Treg cells' dysfunction occurs in aged patients, suggesting that immune therapies targeting Treg cells may be a promising approach to treat diseases such as cancers and autoimmune diseases. Furthermore, drugs targeting Treg cells show encouraging results and contribute to CD8⁺ T-cell-mediated cytotoxic killing of tumor and infected cells. In general, a better understanding of Treg cell function may help us to develop new immune therapies against aging. In this review, we discuss potential therapeutic strategies to modify immune responses of relevance for aging to prevent and treat age-related diseases, as well as the challenges posed by the translation of novel immune therapies into clinical practice.

Heterogeneity of T Cells in Atherosclerosis Defined by Single-Cell RNA-Sequencing and Cytometry by Time of Flight

The infiltration and accumulation of pro- and anti-inflammatory leukocytes within the intimal layer of the arterial wall is a hallmark of developing and progressing atherosclerosis. While traditionally perceived as macrophage- and foam cell-dominated disease, it is now established that atherosclerosis is a partial autoimmune disease that involves the recognition of peptides from ApoB (apolipoprotein B), the core protein of LDL (low-density lipoprotein) cholesterol particles, by CD4⁺ T-helper cells and autoantibodies against LDL and ApoB. Autoimmunity in the atherosclerotic plaque has long been understood as a pathogenic T-helper type-1 driven response with proinflammatory cytokine secretion. Recent developments in high-parametric cell immunophenotyping by mass cytometry, single-cell RNA-sequencing, and in tools exploring antigen-specificity have established the existence of several unforeseen layers of T-cell diversity with mixed T_H1 and T regulatory cells transcriptional programs and unpredicted fates. These findings suggest that pathogenic ApoB-reactive T cells evolve from atheroprotective and immunosuppressive CD4⁺ T regulatory cells that lose their protective properties over time. Here, we discuss T-cell heterogeneity in atherosclerosis with a focus on plasticity, antigen-specificity, exhaustion, maturation, tissue residency, and its potential use in clinical prediction.

Transient Expression of IL-17A in Foxp3 Fate-Tracked Cells in Porphyromonas gingivalis-Mediated Oral Dysbiosis

In periodontitis Porphyromonas gingivalis contributes to the development of a dysbiotic oral microbiome. This altered ecosystem elicits a diverse innate and adaptive immune response that simultaneously involves Th1, Th17, and Treg cells. It has been shown that Th17 cells can alter their gene expression to produce interferon-gamma (IFN-γ). Forkhead box P3 (Foxp3) is considered the master regulator of Treg cells that produce inhibitory cytokines like IL-10. Differentiation pathways that lead to Th17 and Treg cells from naïve progenitors are considered antagonistic. However, it has been reported that Treg cells expressing IL-17A as well as IFN-γ producing Th17 cells have been observed in several inflammatory conditions. Each scenario appears plausible with T cell transdifferentiation resulting from persistent microbial challenge and consequent inflammation. We established that oral colonization with P. gingivalis drives an initial IL-17A dominated Th17 response in the oral mucosa that is dependent on intraepithelial Langerhans cells (LCs). We hypothesized that Treg cells contribute to this initial IL-17A response through transient expression of IL-17A and that persistent mucosal colonization with P. gingivalis drives Th17 cells toward an IFN-γ phenotype at later stages of infection. We utilized fate-tracking mice where IL-17A- or Foxp3-promoter activity drives the permanent expression of red fluorescent protein tdTomato to test our hypothesis. At day 28 of infection timeline, Th17 cells dominated in the oral mucosa, outnumbering Th1 cells by 3:1. By day 48 this dominance was inverted with Th1 cells outnumbering Th17 cells by nearly 2:1. Tracking tdTomato⁺ Th17 cells revealed only sporadic transdifferentiation to an IFN-γ-producing phenotype by day 48; the appearance of Th1 cells at day 48 was due to a late de novo Th1 response. tdTomato⁺ Foxp3⁺ T cells were 35% of the total live CD4⁺T cells in the oral mucosa and 3.9% of them developed a transient IL-17A-producing phenotype by day 28. Interestingly, by day 48 these IL-17A-producing Foxp3⁺ T cells had disappeared. Therefore, persistent oral P. gingivalis infection stimulates an initial IL-17A-biased response led by Th17 cells and a small but significant number of IL-17A-expressing Treg cells that changes into a late de novo Th1 response with only sporadic transdifferentiation of Th17 cells.

Co-expression of master transcription factors determines CD4+ T cell plasticity and functions in auto-inflammatory diseases

Master CD4⁺ T cell lineage determined transcription factors are found to be dysregulated in pathogenesis of autoimmune and inflammatory diseases. CD4⁺ T cells categorized into different lineages based on their functions, cell surface markers and master transcription factors those required for expression of lineage specific cytokines. T-bet, GATA3, RORγt and Foxp3 are major transcription regulators of Th1, Th2, Th17 and Treg cells respectively. Significant progress has been made in understanding expression of lineage specific master regulators that drives CD4⁺ T cell differentiation. It is known that each CD4⁺ T cell lineage express precise determined transcription factor and due to cross regulation between these factors the CD4⁺ T cells able to maintain thier specific phenotype. However, recent studies shows that the lineage specifying transcription factors frequently co-expressed. There is an emerging area of research revealing that the co-expression of lineage-specifying transcription factors alters the potential function and flexibility of subsets of CD4⁺ T cell, this in turn favors the autoimmune pathology. Here, we discuss similarities and differences between mutually co-expressed transcription factors in CD4⁺ T cell subsets and then recapitulates on cell type specific and dynamic balance between the lineage restricted transcription factors in determining plasticity of CD4⁺ T cell subsets. Furthermore, we discuss abnormal regulation of such transcription factors that establishes a pathogenic CD4⁺ T cell phenotype in autoimmune diseases and how this understanding will provide further insight into potential therapeutic development.

Roles of Porphyromonas gingivalis and its virulence factors in periodontitis

Periodontitis is an infection-driven inflammatory disease, which is characterized by gingival inflammation and bone loss. Periodontitis is associated with various systemic diseases, including cardiovascular, respiratory, musculoskeletal, and reproductive system related abnormalities. Recent theory attributes the pathogenesis of periodontitis to oral microbial dysbiosis, in which Porphyromonas gingivalis acts as a critical agent by disrupting host immune homeostasis. Lipopolysaccharide, proteases, fimbriae, and some other virulence factors are among the strategies exploited by P. gingivalis to promote the bacterial colonization and facilitate the outgrowth of the surrounding microbial community. Virulence factors promote the coaggregation of P. gingivalis with other bacteria and the formation of dental biofilm. These virulence factors also modulate a variety of host immune components and subvert the immune response to evade bacterial clearance or induce an inflammatory environment. In this chapter, our focus is to discuss the virulence factors of periodontal pathogens, especially P. gingivalis, and their roles in regulating immune responses during periodontitis progression.

Tolerising cellular therapies: what is their promise for autoimmune disease?

The current management of autoimmunity involves the administration of immunosuppressive drugs coupled to symptomatic and functional interventions such as anti-inflammatory therapies and hormone replacement. Given the chronic nature of autoimmunity, however, the ideal therapeutic strategy would be to reinduce self-tolerance before significant tissue damage has accrued. Defects in, or defective regulation of, key immune cells such as regulatory T cells have been documented in several types of human autoimmunity. Consequently, it has been suggested that the administration of ex vivo generated, tolerogenic immune cell populations could provide a tractable therapeutic strategy. Several potentially tolerogenic cellular therapies have been developed in recent years; concurrent advances in cell manufacturing technologies promise scalable, affordable interventions if safety and efficacy can be demonstrated. These therapies include mesenchymal stromal cells, tolerogenic dendritic cells and regulatory T cells. Each has advantages and disadvantages, particularly in terms of the requirement for a bespoke versus an ‘off-the-shelf’ treatment but also their suitability in particular clinical scenarios. In this review, we examine the current evidence for these three types of cellular therapy, in the context of a broader discussion around potential development pathway(s) and their likely future role. A brief overview of preclinical data is followed by a comprehensive discussion of human data.

A Mechanistic Computational Model Reveals That Plasticity of CD4+ T Cell Differentiation Is a Function of Cytokine Composition and Dosage

CD4⁺ T cells provide cell-mediated immunity in response to various antigens. During an immune response, naïve CD4⁺ T cells differentiate into specialized effector T helper (Th1, Th2, and Th17) cells and induced regulatory (iTreg) cells based on a cytokine milieu. In recent studies, complex phenotypes resembling more than one classical T cell lineage have been experimentally observed. Herein, we sought to characterize the capacity of T cell differentiation in response to the complex extracellular environment. We constructed a comprehensive mechanistic (logical) computational model of the signal transduction that regulates T cell differentiation. The model's dynamics were characterized and analyzed under 511 different environmental conditions. Under these conditions, the model predicted the classical as well as the novel complex (mixed) T cell phenotypes that can co-express transcription factors (TFs) related to multiple differentiated T cell lineages. Analyses of the model suggest that the lineage decision is regulated by both compositions and dosage of signals that constitute the extracellular environment. In this regard, we first characterized the specific patterns of extracellular environments that result in novel T cell phenotypes. Next, we predicted the inputs that can regulate the transition between the canonical and complex T cell phenotypes in a dose-dependent manner. Finally, we predicted the optimal levels of inputs that can simultaneously maximize the activity of multiple lineage-specifying TFs and that can drive a phenotype toward one of the co-expressed TFs. In conclusion, our study provides new insights into the plasticity of CD4⁺ T cell differentiation, and also acts as a tool to design testable hypotheses for the generation of complex T cell phenotypes by various input combinations and dosages.

Generation of RORγt+ Antigen-Specific T Regulatory 17 Cells from Foxp3+ Precursors in Autoimmunity

Th17 cells are potent mediators in autoimmune diseases, and RORγt is required for their development. Recent studies have shown that RORγt⁺ Treg cells in the gut regulate intestinal inflammation by inhibiting effector T cell function. In the current study, we report that RORγt⁺ Treg cells were also found in lymph nodes following immunization. Not only distinct from intestinal RORγt⁺ Treg cells in their transcriptomes, peripheral RORγt⁺ Treg cells were derived from Foxp3⁺ thymic Treg cells in an antigen-specific manner. Development of these RORγt⁺ Treg cells, coined T regulatory 17 (Tr17) cells, depended on IL-6/Stat3 signaling. Tr17 cells showed suppressive activity against antigen-specific effector T cells in vitro. In addition, Tr17 cells efficiently inhibited myelin-specific Th17-cell-mediated CNS auto-inflammation in a passive EAE model. Collectively, our study demonstrates that Tr17 cells are effector Treg cells that potentially restrict autoimmunity.

On the Role IL-4/IL-13 Heteroreceptor Plays in Regulation of Type 1 Diabetes

Type 1 diabetes (T1D) manifests when the insulin-producing pancreatic β cells are destroyed as a consequence of an inflammatory process initiated by lymphocytes of the immune system. The NOD mouse develops T1D spontaneously and serves as an animal model for human T1D. The IL-4Rα/IL-13Rα1 heteroreceptor (HR) serves both IL-4 and IL-13 cytokines, which are believed to function as anti-inflammatory cytokines in T1D. However, whether the HR provides a responsive element to environmental (i.e., physiologic) IL-4/IL-13 in the regulation of peripheral tolerance and the development of T1D has yet to be defined. In this study, NOD mice deficient for the HR have been generated by means of IL-13Rα1 gene disruption and used to determine whether such deficiency affects the development of T1D. Surprisingly, the findings indicate that NOD mice lacking the HR (13R^-/-) display resistance to T1D as the rise in blood glucose level and islet inflammation were significantly delayed in these HR-deficient relative to HR-sufficient (13R^+/+) mice. In fact, the frequency and spleen-to-pancreas dynamics of both Th1 and Th17 cells were affected in 13R^-/- mice. This is likely due to an increase in the frequency of mTGFβ⁺Foxp3^int regulatory T cells and the persistence of CD206⁺ macrophages in the pancreas as both types of cells confer resistance to T1D upon transfer to 13R^+/+ mice. These findings reveal new insights as to the role environmental IL-4/IL-13 and the HR play in peripheral tolerance and the development of T1D.

Intragastric administration of Lactobacillus casei BL23 induces regulatory FoxP3+RORγt+ T cells subset in mice

Many studies have highlighted the immunomodulatory properties of the probiotic strain Lactobacillus casei BL23. Recently, we demonstrated the ability of this strain to modulate the Th2-oriented immune response in a mouse model of cow’s milk allergy based on the induction of a Th17-biased immune response. The probiotic function of L. casei has been also linked to gut-microbiota modifications which could been potentially involved in the immune regulation; however, its precise mechanism of action remains poorly understood. In this regard, recent studies suggest that gut microbiota induces a specific subset of CD4+FoxP3+ Treg cells that also express RORγt+, the specific transcription factor of Th17 cells. This new type of regulatory T cells, called type 3 Treg, displays suppressive function during intestinal inflammation, participating in inflammation control. We thus explored the ability of L. casei BL23 to specifically induce type 3 Treg cells, both in vitro and in vivo. Our results showed that intragastric administration of L. casei BL23 to mice induces local and systemic FoxP3+ RORγt+ type 3 Treg cells that could then participate in the beneficial effects of L. casei BL23 in different intestinal-related disorders.

Human IL-6RhiTIGIT- CD4+CD127lowCD25+ T cells display potent in vitro suppressive capacity and a distinct Th17 profile

To date many clinical studies aim to increase the number and/or fitness of CD4⁺ CD127^lowCD25⁺ regulatory T cells (Tregs) in vivo to harness their regulatory potential in the context of treating autoimmune disease. Here, we sought to define the phenotype and function of Tregs expressing the highest levels of IL-6 receptor (IL-6R). We have identified a population of CD4⁺ CD127^lowCD25⁺ TIGIT⁻ T cells distinguished by their elevated IL-6R expression that lacked expression of HELIOS, showed higher CTLA-4 expression, and displayed increased suppressive capacity compared to IL-6R^hiTIGIT⁺ Tregs. IL-6R^hiTIGIT⁻ CD127^lowCD25⁺ T cells contained a majority of cells demethylated at FOXP3 and displayed a Th17 transcriptional signature, including RORC (RORγt) and the capacity of producing both pro- and anti-inflammatory cytokines, such as IL-17, IL-22 and IL-10. We propose that in vivo, in the presence of IL-6-associated inflammation, the suppressive function of CD4⁺ CD127^lowCD25⁺ FOXP3⁺ IL-6R^hiTIGIT⁻ T cells is temporarily disarmed allowing further activation of the effector functions and potential pathogenic tissue damage.

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IL-6R is highly expressed in certain Treg subsets.

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IL-6R^hiTIGIT⁻ CD127^lowCD25⁺ T cells contain a subset of antigen-experienced Tregs with potent suppression capacity.

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IL-6R^hiTIGIT⁻ Tregs display a Th17 transcriptional profile ex vivo, and the capacity to migrate to the gut.

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IL-2 treatment in humans elicits the trafficking and expansion of Tregs in circulation.

The Role of the Histone Methyltransferase Enhancer of Zeste Homolog 2 (EZH2) in the Pathobiological Mechanisms Underlying Inflammatory Bowel Disease (IBD)

Regulatory T (Treg) cells expressing the transcription factor FOXP3 play a pivotal role in maintaining immunologic self-tolerance. We and others have shown previously that EZH2 is recruited to the FOXP3 promoter and its targets in Treg cells. To further address the role for EZH2 in Treg cellular function, we have now generated mice that lack EZH2 specifically in Treg cells (EZH2Δ/ΔFOXP3+). We find that EZH2 deficiency in FOXP3+ T cells results in lethal multiorgan autoimmunity. We further demonstrate that EZH2Δ/ΔFOXP3+ T cells lack a regulatory phenotype in vitro and secrete proinflammatory cytokines. Of special interest, EZH2Δ/ΔFOXP3+ mice develop spontaneous inflammatory bowel disease. Guided by these results, we assessed the FOXP3 and EZH2 gene networks by RNA sequencing in isolated intestinal CD4+ T cells from patients with Crohn's disease. Gene network analysis demonstrates that these CD4+ T cells display a Th1/Th17-like phenotype with an enrichment of gene targets shared by FOXP3 and EZH2. Combined, these results suggest that the inflammatory milieu found in Crohn's disease could lead to or result from deregulation of FOXP3/EZH2-enforced T cell gene networks contributing to the underlying intestinal inflammation.

The Functional Stability of FOXP3 and RORγt in Treg and Th17 and Their Therapeutic Applications

The balance of CD4⁺CD25⁺FOXP3⁺ regulatory T cells (Tregs) and effector T cells plays a key role in maintaining immune homeostasis, while the imbalance of them is related to many inflammatory diseases in both human and mice. Here we discuss about the plasticity of Tregs and Th17 cells, and the related human diseases resulted from the imbalance of them. Further, we will focus on the mechanisms regulating the plasticity between Tregs and Th17 cells and the potential therapeutic strategies by targeting regulators of the expression and activity of FOXP3 and RORγt or regulators of Treg/Th17 balance in autoimmune diseases, allergy, infection, and cancer.

The relevance of immune responses to partial bladder outlet obstruction and reversal

AIMS

Partial bladder outlet obstruction (PBOO) causes tissue inflammation, a significant increase in markers of systemic oxidative stress, and proliferation of circulating myeloid-derived suppressor cells. Here, we investigated the regulatory mechanisms underlying inflammation and helper T cell involvement in PBOO.

METHODS

Surgical PBOO was performed in four groups of rats: control (C), obstruction at 2 (O2) and 4 (O4) weeks, and 4 weeks after the relief of PBOO (R4) (n = 6 each). The urinary levels of prostaglandin E metabolite (PGEM), expression of inflammatory cytokines (IL-6 and IL-17) in the bladder, numbers of peripheral blood regulatory T cells (Treg cells), and levels of TGF-β1 were assessed via immunohistochemistry, flow cytometry, or ELISA.

RESULTS

The levels of urinary PGEM, bladder IL-17, and TGF-β1 and the numbers of peripheral Treg cells (Foxp3) were all significantly increased at 2 and 4 weeks after PBOO. PGEM, IL-17, and Treg cells (Foxp3) were decreased after the relief of PBOO, while the levels of TGF-β1 continued to increase.

CONCLUSIONS

Transient PBOO triggers an acute, reversible increase in inflammatory cytokines and Treg cells. The distinct dynamics of individual inflammatory markers support their potential use as markers for monitoring bladder inflammation.

Antigen-Specific Immune Modulation Targets mTORC1 Function To Drive Chemokine Receptor-Mediated T Cell Tolerance

To contain autoimmunity, pathogenic T cells must be eliminated or diverted from reaching the target organ. Recently, we defined a novel form of T cell tolerance whereby treatment with Ag downregulates expression of the chemokine receptor CXCR3 and prevents diabetogenic Th1 cells from reaching the pancreas, leading to suppression of type 1 diabetes (T1D). This report defines the signaling events underlying Ag-induced chemokine receptor-mediated tolerance. Specifically, we show that the mammalian target of rapamycin complex 1 (mTORC1) is a major target for induction of CXCR3 downregulation and crippling of Th1 cells. Indeed, Ag administration induces upregulation of programmed death-ligand 1 on dendritic cells in a T cell-dependent manner. In return, programmed death-ligand 1 interacts with the constitutively expressed programmed death-1 on the target T cells and stimulates docking of Src homology 2 domain-containing tyrosine phosphatase 2 phosphatase to the cytoplasmic tail of programmed death-1. Active Src homology 2 domain-containing tyrosine phosphatase 2 impairs the signaling function of the PI3K/protein kinase B (AKT) pathway, leading to functional defect of mTORC1, downregulation of CXCR3 expression, and suppression of T1D. Thus, mTORC1 component of the metabolic pathway serves as a target for chemokine receptor-mediated T cell tolerance and suppression of T1D.

Protein kinase CK2 governs the molecular decision between encephalitogenic TH17 cell and Treg cell development

T helper 17 (TH17) cells represent a discrete TH cell subset instrumental in the immune response to extracellular bacteria and fungi. However, TH17 cells are considered to be detrimentally involved in autoimmune diseases like multiple sclerosis (MS). In contrast to TH17 cells, regulatory T (Treg) cells were shown to be pivotal in the maintenance of peripheral tolerance. Thus, the balance between Treg cells and TH17 cells determines the severity of a TH17 cell-driven disease and therefore is a promising target for treating autoimmune diseases. However, the molecular mechanisms controlling this balance are still unclear. Here, we report that pharmacological inhibition as well as genetic ablation of the protein kinase CK2 (CK2) ameliorates experimental autoimmune encephalomyelitis (EAE) severity and relapse incidence. Furthermore, CK2 inhibition or genetic ablation prevents TH17 cell development and promotes the generation of Treg cells. Molecularly, inhibition of CK2 leads to reduced STAT3 phosphorylation and strongly attenuated expression of the IL-23 receptor, IL-17, and GM-CSF. Thus, these results identify CK2 as a nodal point in TH17 cell development and suggest this kinase as a potential therapeutic target to treat TH17 cell-driven autoimmune responses.

The NF-κB transcription factor RelA is required for the tolerogenic function of Foxp3(+) regulatory T cells

The properties of CD4(+) regulatory T cell (Treg) subsets are dictated by distinct patterns of gene expression determined by FOXP3 and different combinations of various transcription factors. Here we show the NF-κB transcription factor RelA is constitutively active in naïve and effector Tregs. The conditional inactivation of Rela in murine FOXP3(+) cells induces a rapid onset, multi-focal autoimmune disease that depends on RelA being expressed in conventional T cells. In addition to promoting Treg lineage stability, RelA determines the size of the effector Treg population, a function influenced by the presence or absence of RelA in conventional T cells. These findings showing that RelA controls Treg stability and promotes the competitive fitness of effector Tregs highlight the importance of RelA activity in peripheral Treg induced tolerance.

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.

Foxp3(+) T cells expressing RORγt represent a stable regulatory T-cell effector lineage with enhanced suppressive capacity during intestinal inflammation

Foxp3 (forkhead box P3 transcription factor)-expressing regulatory T cells (Tregs) are essential for immunological tolerance, best illustrated by uncontrolled effector T-cell responses and autoimmunity upon loss of Foxp3 expression. Tregs can adopt specific effector phenotypes upon activation, reflecting the diversity of functional demands in the different tissues of the body. Here, we report that Foxp3(+)CD4(+) T cells coexpressing retinoic acid-related orphan receptor-γt (RORγt), the master transcription factor for T helper type 17 (Th17) cells, represent a stable effector Treg lineage. Transcriptomic and epigenetic profiling revealed that Foxp3(+)RORγt(+) T cells display signatures of both Tregs and Th17 cells, although the degree of similarity was higher to Foxp3(+)RORγt(-) Tregs than to Foxp3(-)RORγt(+) T cells. Importantly, Foxp3(+)RORγt(+) T cells were significantly demethylated at Treg-specific epigenetic signature genes such as Foxp3, Ctla-4, Gitr, Eos, and Helios, suggesting that these cells have a stable regulatory rather than inflammatory function. Indeed, adoptive transfer of Foxp3(+)RORγt(+) T cells in the T-cell transfer colitis model confirmed their Treg function and lineage stability in vivo, and revealed an enhanced suppressive capacity as compared with Foxp3(+)RORγt(-) Tregs. Thus, our data suggest that RORγt expression in Tregs contributes to an optimal suppressive capacity during gut-specific immune responses, rendering Foxp3(+)RORγt(+) T cells as an important effector Treg subset in the intestinal system.

Th17 Cells in Type 1 Diabetes: Role in the Pathogenesis and Regulation by Gut Microbiome

Type 1 diabetes (T1D) is an autoimmune disease which is characterized by progressive destruction of insulin producing pancreatic islet β cells. The risk of developing T1D is determined by both genetic and environmental factors. A growing body of evidence supports an important role of T helper type 17 (Th17) cells along with impaired T regulatory (Treg) cells in the development of T1D in animal models and humans. Alteration of gut microbiota has been implicated to be responsible for the imbalance between Th17 and Treg cells. However, there is controversy concerning a pathogenic versus protective role of Th17 cells in murine models of diabetes in the context of influence of gut microbiota. In this review we will summarize current knowledge about Th17 cells and gut microbiota involved in T1D and propose Th17 targeted therapy in children with islet autoimmunity to prevent progression to overt diabetes.

A molecular marker of disease activity in autoimmune liver diseases with histopathological correlation; FoXp3/RORγt ratio

Autoimmune liver diseases (AILDs) encompass a group of diseases with variable clinicopathological manifestations. Th17 and Treg cells have roles in the pathogenesis of AILDs with a balance shifted towards a relative increase in activity of the Th17 cells. In this study, the balance between the transcription factors of Treg and Th17 cells (FoXp3 and RORγt) was sought as a molecular marker of disease activity and to highlight the pathogenesis. The peripheral blood samples of 46 treatment-naive patients were collected and RNA was extracted. Real time PCR was performed and the ratio of gene expression was calculated. Histopathology of 18 patients was obtained and the activity score of these biopsies were also corroborated with their respective molecular (FoXp3/RORγt) (FRGT=FoXp3-ROR Gamma T) ratio. The FRGT ratio in healthy individuals was close to 1 and in disease the ratio changed significantly. This ratio (FRGT) was not significantly different in different varieties of AILD or in adult or paediatric form of the disease. However, the ratio remained consistently below 1 (mean 0.3) in acute disease and high (mean 224.7) in chronic or asymptomatic form of the disease (p < 0.001). The histopathological activity score also significantly correlated with the ratio. This signified the relative excess of Th17 (RORγt) in active disease as compared to Treg (FoXp3) and the reverse in chronic form. This ratio can be an important peripheral molecular marker to assess the disease activity without the necessity of performing a liver biopsy.

FOXP3(+) Treg Cells and Gender Bias in Autoimmune Diseases

CD4⁺CD25⁺ regulatory T (Treg) cells play a pivotal role in the maintenance of immune homeostasis, where the X-linked master transcription factor forkhead box P3 (FOXP3) determines Treg cell development and function. Genetic deficiency of foxp3 induces dysfunction of Treg cells and immuno-dysregulation, polyendocrinopathy, enteropathy, and X-linked syndrome in humans. Functionally deficient Treg cells or the development of exTreg cells positively correlate with autoimmune diseases, such as systemic lupus erythematosus (SLE), multiple sclerosis (MS), and ankylosing spondylitis (AS). In general, females are more susceptible to SLE and MS but less susceptible to AS, where the expression of FOXP3 and its protein complex are perturbed by multiple factors, including hormonal fluctuations, inflammatory cytokines, and danger signals. Therefore, it is critical to explore the potential molecular mechanisms involved and these differences linked to gender. Here, we review recent findings on the regulation of FOXP3 activity in Treg cells and also discuss gender difference in the determination of Treg cell function in autoimmune diseases.

The Special Relationship in the Development and Function of T Helper 17 and Regulatory T Cells

T helper 17 (Th17) cells play an essential role in the clearance of extracellular pathogenic bacteria and fungi. However, this subset is critically involved in the pathology of many autoimmune diseases, e.g., psoriasis, multiple sclerosis, allergy, rheumatoid arthritis, and inflammatory bowel diseases in humans. Therefore, Th17 responses need to be tightly regulated in vivo to mediate effective host defenses against pathogens without causing excessive host tissue damage. Foxp3(+) regulatory T (Treg) cells play an important role in maintaining peripheral tolerance to self-antigens and in counteracting the inflammatory activity of effector T helper cell subsets. Although Th17 and Treg cells represent two CD4(+) T cell subsets with opposing principal functions, these cell types are functionally connected. In this review, we will first give an overview on the biology of Th17 cells and describe their development and in vivo function, followed by an account on the special developmental relationship between Th17 and Treg cells. We will describe the identification of Treg/Th17 intermediates and consider their lineage stability and function in vivo. Finally, we will discuss how Treg cells may regulate the Th17 cell response in the context of infection and inflammation, and elude on findings demonstrating that Treg cells can also have a prominent function in promoting the differentiation of Th17 cells.

Regulatory T-cell Response to Enterotoxigenic Bacteroides fragilis Colonization Triggers IL17-Dependent Colon Carcinogenesis

Many epithelial cancers are associated with chronic inflammation. However, the features of inflammation that are procarcinogenic are not fully understood. Regulatory T cells (Treg) typically restrain overt inflammatory responses and maintain intestinal immune homeostasis. Their immune-suppressive activity can inhibit inflammation-associated cancers. Paradoxically, we show that colonic Tregs initiate IL17-mediated carcinogenesis in multiple intestinal neoplasia mice colonized with the human symbiote enterotoxigenic Bacteroides fragilis (ETBF). Depletion of Tregs in ETBF-colonized C57BL/6 FOXP3(DTR) mice enhanced colitis but diminished tumorigenesis associated with shifting of mucosal cytokine profile from IL17 to IFNγ; inhibition of ETBF-induced colon tumorigenesis was dependent on reduced IL17 inflammation and was independent of IFNγ. Treg enhancement of IL17 production is cell-extrinsic. IL2 blockade restored Th17 responses and tumor formation in Treg-depleted animals. Our findings demonstrate that Tregs limit the availability of IL2 in the local microenvironment, allowing the Th17 development necessary to promote ETBF-triggered neoplasia, and thus unveil a new mechanism whereby Treg responses to intestinal bacterial infection can promote tumorigenesis.

SIGNIFICANCE

Tregs promote an oncogenic immune response to a common human symbiote associated with inflammatory bowel disease and colorectal cancer. Our data define mechanisms by which mucosal Tregs, despite suppressing excessive inflammation, promote the earliest stages of immune procarcinogenesis via enhancement of IL17 production at the expense of IFNγ production.

Transcriptional regulatory networks for CD4 T cell differentiation

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

ENISI SDE: A New Web-Based Tool for Modeling Stochastic Processes

Modeling and simulations approaches have been widely used in computational biology, mathematics, bioinformatics and engineering to represent complex existing knowledge and to effectively generate novel hypotheses. While deterministic modeling strategies are widely used in computational biology, stochastic modeling techniques are not as popular due to a lack of user-friendly tools. This paper presents ENISI SDE, a novel web-based modeling tool with stochastic differential equations. ENISI SDE provides user-friendly web user interfaces to facilitate adoption by immunologists and computational biologists. This work provides three major contributions: (1) discussion of SDE as a generic approach for stochastic modeling in computational biology; (2) development of ENISI SDE, a web-based user-friendly SDE modeling tool that highly resembles regular ODE-based modeling; (3) applying ENISI SDE modeling tool through a use case for studying stochastic sources of cell heterogeneity in the context of CD4+ T cell differentiation. The CD4+ T cell differential ODE model has been published [8] and can be downloaded from biomodels.net. The case study reproduces a biological phenomenon that is not captured by the previously published ODE model and shows the effectiveness of SDE as a stochastic modeling approach in biology in general and immunology in particular and the power of ENISI SDE.

T-cell selection and intestinal homeostasis

Although intestinal bacteria live deep within the body, they are topographically on the exterior surface and thus outside the host. According to the classic notion that the immune system targets non-self rather than self, these intestinal bacteria should be considered foreign and therefore attacked and eliminated. While this appears to be true for some commensal bacterial species, recent data suggest that the immune system actively becomes tolerant to many bacterial organisms. The induction or activation of regulatory T (Treg) cells that inhibit, rather than promote, inflammatory responses to commensal bacteria appears to be a central component of mucosal tolerance. Loss of this mechanism can lead to inappropriate immune reactivity toward commensal organisms, perhaps contributing to mucosal inflammation characteristic of disorders such as inflammatory bowel disease.

Antigen-specific therapy against type 1 diabetes: mechanisms and perspectives

Type 1 diabetes (T1D) is an immune-mediated disease that occurs when the insulin-producing β‑cells of the pancreatic islets are destroyed by an inflammatory process perpetuated by cells of the immune system. The logical approach to suppress T1D is to inactivate or eliminate the lymphocytes responsible for inducing inflammation and targeting the β‑cells. Antigen-specific approaches have been devised and were able to target inflammatory lymphocytes and induce apoptosis or block trafficking to pancreatic islets. Lack of costimulation, expansion of Tregs and bystander suppression are likely mechanisms by which antigen-specific treatments modulate pathogenic T cells. This strategy, however, while prevents the onset of T1D, could not overcome overt T1D, perhaps because of collateral damage to the islet vascular network. Recent developments indicate that donor endothelial stem cell precursors can repair the islets' vascular niche and assist antigen-specific therapy against overt T1D.

Reducing CD73 expression by IL1β-Programmed Th17 cells improves immunotherapeutic control of tumors

T cells of the T helper (Th)17 subset offer promise in adoptive T-cell therapy for cancer. However, current protocols for ex vivo programming of Th17 cells, which include TGFβ exposure, increase the expression of CD39 and CD73, two cell surface ATP ectonucleotidases that reduce T-cell effector functions and promote immunosuppression. Here, we report that ATP-mediated suppression of IFNγ production by Th17 cells can be overcome by genetic ablation of CD73 or by using IL1β instead of TGFβ to program Th17 cells ex vivo. Th17 cells cultured in IL1β were also highly polyfunctional, expressing high levels of effector molecules and exhibiting superior short-term control of melanoma in mice, despite reduced stem cell-like properties. TGFβ addition at low doses that did not upregulate CD73 expression but induced stemness properties drastically improved the antitumor effects of IL1β-cultured Th17 cells. Effector properties of IL1β-dependent Th17 cells were likely related to their high glycolytic capacity, since ex vivo programming in pyruvate impaired glycolysis and antitumor effects. Overall, we show that including TGFβ in ex vivo cultures used to program Th17 cells blunts their immunotherapeutic potential and demonstrate how this potential can be more fully realized for adoptive T-cell therapy.

Th17 cells in cancer: the ultimate identity crisis

T helper 17 (Th17) cells play a complex and controversial role in tumor immunity and have been found to exhibit a fluctuating identity within the context of cancer. The recent, expanding literature on these cells attests to their puzzling nature, either promoting or suppressing tumor growth depending on the malignancy and course of therapeutic intervention investigated. This review addresses several newly appreciated factors that may help delineate Th17 cells' immunological properties in the context of cancer. Several reports suggest that inflammatory signals induced in the tumor milieu regulate the functional fate and antitumor activity of Th17 cells. Recent findings also point to significant alterations in Th17 cells due to their interplay with regulatory T lymphocytes and cytotoxic CD8(+) T cells within the tumor microenvironment. Finally, an appreciation for the stem cell-like properties of Th17 cells that augment their persistence and activity emerges from recent reports. The impact of these factors on Th17 cells' antitumor efficacy and how these factors may be exploited to improve cancer therapies will be discussed.

The multifaceted role of Th17 lymphocytes and their associated cytokines in cancer

While the role of T helper 17 lymphocytes (Th17) in the pathogenesis of autoimmune diseases and in infectious immunity has been relatively well defined, the impact of these cells and their associated cytokines on cancer development is still under debate. Although multiple reports have indicated that Th17 can promote anticancer immunity, others have argued that these cells may exhibit tumor-promoting properties. This dichotomy in the function of Th17 lymphocytes in cancer may be related to the versatile nature of these cells, being capable of differentiating into either proinflammatory Th1 or suppressive FoxP3-expressing Treg cells or hybrid T cell subsets depending on the underlying environmental conditions. In the current review, we examine the role of Th17 lymphocytes and Th17-associated cytokines in cancer and discuss how factors that control their final lineage commitment decision may influence the balance between their tumor-promoting versus tumor-suppressing properties.

Modulation of autoimmune diseases by interleukin (IL)-17 producing regulatory T helper (Th17) cells

Following the discovery of interleukin (IL)-17 producing T helper (Th17) cells as a distinct lineage of CD4+ T helper cells it became clear that these cells play an important role in the host defense against extracellular fungal and bacterial pathogens and participate in the pathogenesis of multiple inflammatory and autoimmune disorders. Depending on the microenvironment, Th17 cells can alter their differentiation programme ultimately giving rise to either protective or pro-inflammatory pathogenic cells. We found that besides the conventional in vitro protocol for Th17 differentiation by transforming growth factor-beta (TGF-β) plus IL-6 cytokines, a combination of IL-23 plus IL-6 can also induce Th17 cells. The Th17 cells induced by IL-23 plus IL-6 (termed as effector Th17, Teff17 cells) are pathogenic upon adoptive transfer into non-obese diabetic (NOD) mice contributing to the development of type 1 diabetes (T1D) while cells induced by TGF-β plus IL-6 (termed as regulatory T cells, Treg17 cells) are non pathogenic and regulatory, and suppressed the pathogenic T cells in T1D. These cells differentially expressed a number of cytokines where Teff17 cells exhibited an increase in granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-22 whereas Treg17 cells demonstrated increased expression of IL-21 and immunosuppressive cytokine IL-10. Differentiation of Th17 cells is controlled by a transcription factor, RORγT although these cells also express variable levels of T-bet and FoxP3 transcription factors. This points to a dual functional role of Th17 subsets in autoimmune diseases particularly T1D. We suggest that similar to conventional regulatory T cells (Treg), induction of regulatory Treg17 cells could play an important role in modulating and preventing certain autoimmune diseases.

IL-17 gene ablation does not impact Treg-mediated suppression of graft-versus-host disease after bone marrow transplantation

Regulatory T cell (Treg) immunotherapy is a promising strategy for the treatment of graft rejection responses and autoimmune disorders. Our and other laboratories have shown that the transfer of highly purified CD4(+)CD25(+)Foxp3(+) natural Treg can prevent lethal graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation across both major and minor histocompatibility barriers. However, recent evidence suggests that the Treg suppressive phenotype can become unstable, a phenomenon that can culminate in Treg conversion into IL-17-producing cells. We hypothesized that the intense proinflammatory signals released during an ongoing alloreaction might redirect a fraction of the transferred Treg to the Th17 cell fate, thereby losing immunosuppressive potential. We therefore sought to evaluate the impact of Il17 gene ablation on Treg stability and immunosuppressive capacity in a major MHC mismatch model. We show that although Il17 gene ablation results in a mildly enhanced Treg immunosuppressive ability in vitro, such improvement is not observed when IL-17-deficient Treg are used for GVHD suppression in vivo. Similarly, when we selectively blocked IL-1 signaling in Treg, that was shown to be necessary for Th17 conversion, we did not detect any improvement on Treg-mediated GVHD suppressive ability in vivo. Furthermore, upon ex vivo reisolation of transferred wild-type Treg, we detected little or no Treg-mediated IL-17 production upon GVHD induction. Our results indicate that blocking Th17 conversion does not affect the GVHD suppressive ability of highly purified natural Treg in vivo, suggesting that IL-17 targeting is not a valuable strategy to improve Treg immunotherapy after hematopoietic cell transplantation.

Reduced effectiveness of CD4+Foxp3+ regulatory T cells in CD28-deficient NOD.H-2h4 mice leads to increased severity of spontaneous autoimmune thyroiditis

NOD.H-2h4 mice given NaI in their drinking water develop iodine-accelerated spontaneous autoimmune thyroiditis (ISAT) with chronic inflammation of the thyroid by T and B cells and production of anti-mouse thyroglobulin (MTg) autoantibody. CD28(-/-) NOD.H-2h4 mice, which have reduced numbers of CD4(+)Foxp3(+) regulatory T cells (Tregs), were developed to examine the role of Tregs in ISAT development. CD28(-/-) NOD.H2-h4 mice develop more severe ISAT than do wild-type (WT) mice, with collagen deposition (fibrosis) and low serum T4. CD28(-/-) mice have increased expression of proinflammatory cytokines IFN-γ and IL-6, consistent with increased mononuclear cell infiltration and tissue destruction in thyroids. Importantly, transferring purified CD4(+)Foxp3(+) Tregs from WT mice reduces ISAT severity in CD28(-/-) mice without increasing the total number of Tregs, suggesting that endogenous Tregs in CD28(-/-) mice are functionally ineffective. Endogenous CD28(-/-) Tregs have reduced surface expression of CD27, TNFR2 p75, and glucocorticoid-induced TNFR-related protein compared with transferred CD28(+/+) Tregs. Although anti-MTg autoantibody levels generally correlate with ISAT severity scores in WT mice, CD28(-/-) mice have lower anti-MTg autoantibody responses than do WT mice. The percentages of follicular B cells are decreased and those of marginal zone B cells are increased in spleens of CD28(-/-) mice, and they have fewer thyroid-infiltrating B cells than do WT mice. This suggests that CD28 deficiency has direct and indirect effects on the B cell compartment. B cell-deficient (B(-/-)) NOD.H-2h4 mice are resistant to ISAT, but CD28(-/-)B(-/-) mice develop ISAT comparable to WT mice and have reduced numbers of Tregs compared with WT B(-/-) mice.

Culture promotes transfer of thyroid epithelial cell hyperplasia and proliferation by reducing regulatory T cell numbers

IFN-γ(-/-) NOD.H-2h4 mice develop a spontaneous autoimmune thyroid disease, thyroid epithelial cell hyperplasia and proliferation (TEC H/P) when given NaI in their water for 7+ mo. TEC H/P can be transferred to IFN-γ(-/-) SCID mice by splenocytes from mice with severe (4-5+) disease, and transfer of TEC H/P is improved when splenocytes are cultured prior to transfer. Older (9+ mo) IFN-γ(-/-) NOD.H-2h4 mice have elevated numbers of FoxP3(+) T reg cells, up to 2-fold greater than younger (2 mo) mice. During culture, the number of T reg decreases and this allows the improved transfer of TEC H/P. Co-culture with IL-2 prior to transfer prevents the decrease of T reg and improves their in vitro suppressive ability resulting in reduced TEC H/P in recipient mice. Therefore, culturing splenocytes improves transfer of TEC H/P by reducing the number of T reg and IL-2 inhibits transfer by preserving T reg number and function.

Recovery from overt type 1 diabetes ensues when immune tolerance and β-cell formation are coupled with regeneration of endothelial cells in the pancreatic islets

Immune modulation of pancreatic inflammation induces recovery from type 1 diabetes (T1D), but remission was not durable, perhaps because of an inability to sustain the formation and function of new pancreatic β-cells. We have previously shown that Ig-GAD2, carrying GAD 206-220 peptide, induced in hyperglycemic mice immune modulation that was able to control pancreatic inflammation, stimulate β-cell regeneration, and prevent T1D progression. Herein, we show that the same Ig-GAD2 regimen given to mice with overt T1D was unable to reverse the course of disease despite eradication of Th1 and Th17 cells from the pancreas. However, the regimen was able to sustain recovery from T1D when Ig-GAD2 was accompanied with transfer of bone marrow (BM) cells from healthy donors. Interestingly, alongside immune modulation, there was concomitant formation of new β-cells and endothelial cells (ECs) in the pancreas. The new β-cells were of host origin while the donor BM cells gave rise to the ECs. Moreover, transfer of purified BM endothelial progenitors instead of whole BM cells sustained both β-cell and EC formation and reversal of diabetes. Thus, overcoming T1D requires both immune modulation and repair of the islet vascular niche to preserve newly formed β-cells.

Transcription factor interplay in T helper cell differentiation

The differentiation of CD4 helper T cells into specialized effector lineages has provided a powerful model for understanding immune cell differentiation. Distinct lineages have been defined by differential expression of signature cytokines and the lineage-specifying transcription factors necessary and sufficient for their production. The traditional paradigm of differentiation towards Th1 and Th2 subtypes driven by T-bet and GATA3, respectively, has been extended to incorporate additional T cell lineages and transcriptional regulators. Technological advances have expanded our view of these lineage-specifying transcription factors to the whole genome and revealed unexpected interplay between them. From these data, it is becoming clear that lineage specification is more complex and plastic than previous models might have suggested. Here, we present an overview of the different forms of transcription factor interplay that have been identified and how T cell phenotypes arise as a product of this interplay within complex regulatory networks. We also suggest experimental strategies that will provide further insight into the mechanisms that underlie T cell lineage specification and plasticity.

Antigen-specific therapeutic approaches in Type 1 diabetes

Development of strategies capable of specifically curbing pathogenic autoimmune responses in a disease- and organ-specific manner without impairing foreign or tumor antigen-specific immune responses represents a long sought-after goal in autoimmune disease research. Unfortunately, our current understanding of the intricate details of the different autoimmune diseases that affect mankind, including type 1 diabetes, is rudimentary. As a result, progress in the development of the so-called "antigen-specific" therapies for autoimmunity has been slow and fraught with limitations that interfere with bench-to-bedside translation. Absent or incomplete understanding of mechanisms of action and lack of adequate immunological biomarkers, for example, preclude the rational design of effective drug development programs. Here, we provide an overview of antigen-specific approaches that have been tested in preclinical models of T1D and, in some cases, human subjects. The evidence suggests that effective translation of these approaches through clinical trials and into patients will continue to meet with failure unless detailed mechanisms of action at the level of the organism are defined.

An alternative role for Foxp3 as an effector T cell regulator controlled through CD40

The BDC2.5 T cell clone is highly diabetogenic, but the transgenic mouse generated from that clone is surprisingly slow in diabetes development. Although defining pathogenic effector T cells in autoimmunity has been inconsistent, CD4(+) cells expressing the CD40 receptor (Th40 cells) are highly diabetogenic in NOD mice, and NOD.BDC2.5.TCR.Tg mice possess large numbers of these cells. Given the importance of CD40 for pathogenic T cell development, BDC2.5.CD40(-/-) mice were created. Regulatory T cells, CD4(+)CD25(hi)Foxp3(+), develop normally, but pathogenic effector cells are severely reduced in number. Th40 cells from diabetic BDC2.5 mice rapidly induce diabetes in NOD.scid recipients, but Th40 cells from prediabetic mice transfer diabetes very slowly. Demonstrating an important paradigm shift, effector Th40 cells from prediabetic mice are Foxp3(+). As mice age, moving to type 1 diabetes development, Th40 cells lose Foxp3. When Th40 cells that are Foxp3(+) are transferred to NOD.scid recipients, disease is delayed. Th40 cells that are Foxp3(-) rapidly transfer disease. Th40 cells from BDC2.5.CD40(-/-) mice do not transfer disease nor do they lose Foxp3 expression. Mechanistically, Foxp3(+) cells produce IL-17 but do not produce IFN-γ, whereas Foxp3(-) Th40 cells produce IFN-γ and IL-2. This poses a new consideration for the function of Foxp3, as directly impacting effector T cell function.

Antigen-specific effector CD4 T lymphocytes school lamina propria dendritic cells to transfer innate tolerance

Dendritic cells (DCs) have been shown to play a major role in oral tolerance, and this function has been associated with their ability to produce anti-inflammatory cytokines and to induce suppressive regulatory T cells. In this study, we demonstrate that upon oral administration of Ag, lamina propia (LP) DCs engage specific T cells and acquire a novel mechanism by which they transfer tolerance against diverse T cell specificities. Indeed, when Ig-myelin oligodendrocyte glycoprotein (MOG) carrying the MOG(35-55) epitope was orally administered into either T cell-sufficient or -deficient mice, only the T cell-sufficient hosts yielded CD8α(+) and CD8α(-) LP DCs that were able to transfer tolerance to a variety of MHC class II-restricted effector T cells. Surprisingly, these LP DCs upregulated programmed cell death ligand 1 during the initial interaction with MOG-specific T cells and used this inhibitory molecule to suppress activation of T cells regardless of Ag specificity. Furthermore, oral Ig-MOG was able to overcome experimental autoimmune encephalomyelitis induced with CNS homogenate, indicating that the DCs are able to modulate disease involving diverse T cell specificities. This previously unrecognized attribute potentiates DCs against autoimmunity.

Systems modeling of molecular mechanisms controlling cytokine-driven CD4+ T cell differentiation and phenotype plasticity

Differentiation of CD4+ T cells into effector or regulatory phenotypes is tightly controlled by the cytokine milieu, complex intracellular signaling networks and numerous transcriptional regulators. We combined experimental approaches and computational modeling to investigate the mechanisms controlling differentiation and plasticity of CD4+ T cells in the gut of mice. Our computational model encompasses the major intracellular pathways involved in CD4+ T cell differentiation into T helper 1 (Th1), Th2, Th17 and induced regulatory T cells (iTreg). Our modeling efforts predicted a critical role for peroxisome proliferator-activated receptor gamma (PPARγ) in modulating plasticity between Th17 and iTreg cells. PPARγ regulates differentiation, activation and cytokine production, thereby controlling the induction of effector and regulatory responses, and is a promising therapeutic target for dysregulated immune responses and inflammation. Our modeling efforts predict that following PPARγ activation, Th17 cells undergo phenotype switch and become iTreg cells. This prediction was validated by results of adoptive transfer studies showing an increase of colonic iTreg and a decrease of Th17 cells in the gut mucosa of mice with colitis following pharmacological activation of PPARγ. Deletion of PPARγ in CD4+ T cells impaired mucosal iTreg and enhanced colitogenic Th17 responses in mice with CD4+ T cell-induced colitis. Thus, for the first time we provide novel molecular evidence in vivo demonstrating that PPARγ in addition to regulating CD4+ T cell differentiation also plays a major role controlling Th17 and iTreg plasticity in the gut mucosa.

CD4+ T cells can differentiate into different phenotypes depending on the cytokine milieu. Due to the complexity of this process, we have constructed a computational and mathematical model with sixty ordinary differential equations representing a CD4+ T cell differentiating into either Th1, Th2, Th17 or iTreg cells. The model includes cytokines, nuclear receptors and transcription factors that define fate and function of CD4+ T cells. Computational simulations illustrate how a proinflammatory Th17 cell can undergo reprogramming into an anti-inflammatory iTreg phenotype following PPARγ activation. This modeling-derived hypothesis has been validated with in vitro and in vivo experiments. Experimental data support the modeling-derived prediction and demonstrate that the loss of PPARγ enhances a proinflammatory response characterized by Th17 in colitis-induced mice. Moreover, pharmacological activation of PPARγ in vivo can affect the Th17/iTreg balance by upregulating FOXP3 and downregulating IL-17A and RORγt. In summary, we demonstrate that computational simulations using our CD4+ T cell model provide novel unforeseen hypotheses related to the molecular mechanisms controlling differentiation and function of CD4+ T cells. In vivo findings validated the modeling prediction that PPARγ modulates differentiation and plasticity of CD4+ T cells in mice.