IL-2 and autoimmune disease

Performance of urinary biomarkers in differentiating dysfunctional voiding in women with overactive bladder syndrome: a prospective pilot study

PURPOSE

Dysfunctional voiding (DV) in women is a common disorder that causes bladder outlet obstruction (BOO) and may aggravate overactive bladder (OAB) symptoms. The diagnosis of DV relies on clinical alertness and videourodynamic study (VUDS). In this pilot study, we aimed to explore the diagnostic potential of urinary biomarkers in women with DV.

METHODS

Women who visited our institute for the management of OAB were enrolled in this prospective study. Urine samples were collected before treatment and urinary proteins were quantified using enzyme-linked immunosorbent assay (ELISA) kits. Patients with DV and patients with normal tracings were included in the study and control group, respectively. The patients with DV were further divided into two subgroups: those with and those without detrusor overactivity (DO). VUDS parameters and urinary protein levels were compared between each subgroup.

RESULTS

A total of 67 women were enrolled. There were 47 patients with VUDS-diagnosed DV and 20 patients in the control group. Urinary 8-OHdG level (32.65 vs. 15.59, p < 0.001) and urinary TNF-α level (1.43 vs. 0.83, p = 0.031) were significantly higher in the DV group, and urinary IL-2 level (0.29 vs. 0.83, p < 0.001) was significantly lower in the DV group. Among the DV patients, urinary PGE2 level was higher in the DO group (240.4 vs 149.6, p = 0.049).

CONCLUSIONS

In women with DV, urinary 8-OHdG level is elevated compared to women with normal VUDS. Urinary PGE2 level is elevated in patients with DV and DO. These finding suggests increased reactive-oxidative stress response and detrusor hyperactivity in DV patients. Urinary biomarkers can serve as potential non-invasive diagnostic tools in women with OAB.

The Blockade of Interleukin-2 During the Acute Phase of Trypanosoma cruzi Infection Reveals Its Dominant Regulatory Role

Trypanosoma cruzi infection causes Chagas’ disease in humans. The infection activates the innate and adaptative immunity in an orchestrated immune response to control parasite growth, guaranteeing host survival. Despite an effective immune response to the parasite in the acute phase, the infection progresses to a chronic stage. The parasite infects different tissues such as peripheral neurons, the brain, skeletal muscle, and heart muscle, among many others. It is evident now that tissue-specific immune responses may develop along with anti-parasite immunity. Therefore, mechanisms to regulate immunity and to ensure tissue-specific tolerance are operating during the infection. Studying those immunoregulatory mechanisms is fundamental to improve host protection or control inflammatory reactions that may lead to pathology. The role of IL-2 during T. cruzi infection is not established. IL-2 production by T cells is strongly down-modulated early in the disease by unknown mechanisms and remains low during the chronic phase of the disease. IL-2 activates NK cells, CD4, and CD8 T cells and may be necessary to immunity development. Also, the expansion and maintenance of regulatory T cells require IL-2. Thus, IL-2 may be a key cytokine involved in promoting or down-regulating immune responses, probably in a dose-dependent manner. This study blocked IL-2 during the acute T. cruzi infection by using a neutralizing monoclonal antibody. The results show that parasitemia and mortality rate was lower in animals treated with anti-IL-2. The percentages and total numbers of CD4⁺CD25⁺Foxp3⁺ T cells diminished within three weeks of infection. The numbers of splenic activated/memory CD4 and CD8 splenic T cells increased during the acute infection. T cells producing IFN-γ, TNF-α and IL-10 also augmented in anti-IL-2-treated infected mice. The IL-2 blockade also increased the numbers of inflammatory cells in the heart and skeletal muscles and the amount of IL-17 produced by heart T cells. These results suggest that IL-2 might be involved in the immune regulatory response during the acute T. cruzi infection, dampening T cell activation through the expansion/maintenance of regulatory T cells and regulating IL-17 production. Therefore, the IL-2 pathway is an attractive target for therapeutic purposes in acute and chronic phases of Chagas’ disease.

A novel multi-biomarker combination predicting relapse from long-term remission after discontinuation of biological drugs in rheumatoid arthritis

Biological disease modifying anti-rheumatic drugs (bDMARDs) show dramatic treatment efficacy in rheumatoid arthritis (RA). Long-term use of bDMARDs, however, has disadvantages such as high costs and infection risk. Therefore, a methodology is needed to predict any future RA relapse. Herein, we report a novel multi-biomarker combination which predicts relapse after bDMARDs-withdrawal in patients in remission. Forty patients with RA in remission for more than 12 months were enrolled. bDMARDs were withdrawn and they were followed monthly for the next 24 months. Fourteen patients (35%) of 40 in the cohort remained in remission at 24 months, whereas 26 (65%) relapsed at various time-points. Serum samples obtained longitudinally from patients in remission were assessed for the relapse-prediction biomarkers and index from 73 cytokines by the exploratory multivariate ROC analysis. The relapse-prediction index calculated from the 5 cytokines, IL-34, CCL1, IL-1β, IL-2 and IL-19, strongly discriminated between patients who relapsed and those who stayed in remission. These findings could contribute to clinical decision-making as to the timing of when to discontinue bDMARDs in RA treatment.

TLR-Mediated Cytokine Gene Expression in Chicken Peripheral Blood Mononuclear Cells as a Measure to Characterize Immunobiotics

Immunobiotics are probiotics that promote intestinal health by modulating immune responses. Immunobiotics are recognized by Toll-like receptors (TLRs) and activate cytokine gene expression. This study aimed to characterize cytokine gene expression in the chicken peripheral blood mononuclear cells (PBMC) stimulated with purified TLR ligands and live probiotics. PBMC were isolated from the whole blood. PBMC were stimulated with: lipopolysaccharide (LPS), CpG ODN, Pam3CSK4, Zymosan, galactooligosaccharides (GOS), Lactococcuslactis subsp. cremoris (L. lactis), and Saccharomyces cerevisiae at 42.5 °C and 5% CO₂ for 3 h, 6 h, and 9 h. After each time-point, PBMC were harvested for RNA isolation. Relative gene expression was analyzed with RT-qPCR for cytokine genes (IL-1β, IL-2, IL-3, IL-4, IL-6, IL-8, IL-10, IL-12p40, and IFN-ɣ) and reference genes (ACTB and G6PDH). Genes were clustered into pro-inflammatory genes, Th1/Th2 genes, and Th1-regulators. The gene expression differed between treatments in IL1-β, IL-6, IL-8, IL-10, and IL-12p40 (p < 0.001). The genes IL-1β, IL-6, and IL-8 had the highest fold change of mRNA expression at 3 h in response to TLR ligands. L. lactis up-regulated the pro-inflammatory genes at the 6 h time-point. L. lactis did not activate the anti-inflammatory IL-10 gene, but activated IL-12p40 at 6 h. Hereby, L. lactis was proven to exert immunostimulatory properties in PBMC.

Airways therapy of obstructive sleep apnea dramatically improves aberrant levels of soluble cytokines involved in autoimmune disease

Obstructive Sleep Apnea (OSA) damages the health of 35% of adult Americans. Disordered sleep results in increased risk of several autoimmune disorders, but the molecular links to autoimmunity are poorly understood. Herein, we identified four cytokines associated with autoimmune disease, whose median serum levels were significantly different for OSA patients receiving airways therapy, from the levels in untreated OSA patients, APRIL (5.2-fold lower, p = 3.5 × 10^-11), CD30 (1.6-fold higher, p = 7.7 × 10^-5), IFN-Alpha-2 (2.9-fold higher, p = 9.6 × 10^-14) and IL-2 (1.9-fold higher, p = 0.0003). Cytokine levels in airways treated patients were similar to the levels in control subjects. t-SNE and UMAP analysis of these high dimensional patient cytokine data identified only two groups, suggesting a similar global response for all four cytokines to airways therapy. Our findings suggest the levels of these four cytokines may be altered by disordered sleep and perhaps by chronic hypoxia. Therapeutic options are discussed.

Chinese herbal medicine SS-1 inhibits T cell activation and abrogates TH responses in Sjögren's syndrome

BACKGROUND/PURPOSE

Sjögren's syndrome (SS) is an autoimmune disease and its conventional treatment has exhibited limited therapeutic efficacy. Traditional Chinese medicine has been demonstrated to ameliorate the sicca symptoms of SS by decreasing the level of T_H1 and T_H2 cytokines and increasing salivary flow rate. A newly designed traditional Chinese medicine, SS-1, showed improved efficacy in alleviating the dryness symptoms of SS patients in the National Taiwan SS cohort investigation. Here, we investigated the effect of SS-1 on T cell responses.

METHODS

SS-1 was authenticated and its major compounds were verified by high-performance liquid chromatography. We examined the effects of SS-1 on the activation and T_H1, T_H2, and T_H17 polarization of murine T cells. We also determined the level of T_H1, T_H2, and T_H17 cytokine RNA in peripheral blood mononuclear cells of SS patients before and after SS-1 treatment.

RESULTS

SS-1 treatment inhibits the activation and T_H1, T_H2, and IL-17A⁺IFNγ⁺ T_H polarization of murine T cells. SS-1 treatment also significantly reduces IFN-γ, IL-4, and IL-13 expression, and moderately reduces IL-17A expression in peripheral blood mononuclear cells of SS patients.

CONCLUSION

Our results suggest that SS-1 inhibits T cell activation and diminishes T_H1, T_H2, and IL-17⁺IFN-γ⁺ T_H responses in SS patients.

Modes of Communication between T Cells and Relevance for Immune Responses

T cells are essential mediators of the adaptive immune system, which constantly patrol the body in search for invading pathogens. During an infection, T cells that recognise the pathogen are recruited, expand and differentiate into subtypes tailored to the infection. In addition, they differentiate into subsets required for short and long-term control of the pathogen, i.e., effector or memory. T cells have a remarkable degree of plasticity and heterogeneity in their response, however, their overall response to a given infection is consistent and robust. Much research has focused on how individual T cells are activated and programmed. However, in order to achieve a critical level of population-wide reproducibility and robustness, neighbouring cells and surrounding tissues have to provide or amplify relevant signals to tune the overall response accordingly. The characteristics of the immune response-stochastic on the individual cell level, robust on the global level-necessitate coordinated responses on a system-wide level, which facilitates the control of pathogens, while maintaining self-tolerance. This global coordination can only be achieved by constant cellular communication between responding cells, and faults in this intercellular crosstalk can potentially lead to immunopathology or autoimmunity. In this review, we will discuss how T cells mount a global, collective response, by describing the modes of T cell-T cell (T-T) communication they use and highlighting their physiological relevance in programming and controlling the T cell response.

Rethinking Communication in the Immune System: The Quorum Sensing Concept

Quorum sensing was first described as the communication process bacteria employ to coordinate changes in gene expression and therefore, their collective behavior in response to population density. Emerging new evidence suggests that quorum sensing can also contribute to the regulation of immune cell responses. Quorum sensing might be achieved by the ability of immune cells to perceive the density of their own populations or those of other cells in their environment; responses to alterations in cell density might then be coordinated via changes in gene expression and protein signaling. Quorum sensing mechanisms can regulate T and B cell as well as macrophage function. We posit that perturbations in quorum sensing may undermine the balance between diverse immune cell populations and predispose the host to immune abnormalities.

Calcineurin-mediated IL-2 production by CD11chighMHCII+ myeloid cells is crucial for intestinal immune homeostasis

The intestinal immune system can respond to invading pathogens yet maintain immune tolerance to self-antigens and microbiota. Myeloid cells are central to these processes, but the signaling pathways that underlie tolerance versus inflammation are unclear. Here we show that mice lacking Calcineurin B in CD11c^highMHCII⁺ cells (Cnb1^CD11c mice) spontaneously develop intestinal inflammation and are susceptible to induced colitis. In these mice, colitis is associated with expansion of T helper type 1 (Th1) and Th17 cell populations and a decrease in the number of FoxP3⁺ regulatory T (Treg) cells, and the pathology is linked to the inability of intestinal Cnb1-deficient CD11c^highMHCII⁺ cells to express IL-2. Deleting IL-2 in CD11c^highMHCII⁺ cells induces spontaneous colitis resembling human inflammatory bowel disease. Our findings identify that the calcineurin–NFAT–IL-2 pathway in myeloid cells is a critical regulator of intestinal homeostasis by influencing the balance of inflammatory and regulatory responses in the mouse intestine.

Treg cells can maintain intestinal homeostasis and limit intestinal bowel disease. Here the authors use a mouse model of spontaneous colitis to show that calcineurin-NFAT-induced IL-2 production by dendritic cells regulates the balance between Treg and effector T cells in the gut lamina propria.

Maternal vitamin D deficiency during pregnancy affects expression of adipogenic-regulating genes peroxisome proliferator-activated receptor gamma (PPARγ) and vitamin D receptor (VDR) in lean male mice offspring

PURPOSE

Maternal vitamin D deficiency during pregnancy is a widespread issue that may have long-lasting consequences on offspring adiposity. We sought to determine how maternal vitamin D deficiency during the perinatal period would affect offspring adipose tissue development and gene expression.

METHODS

Female C57BL/6 J mice were fed either a vitamin D deficient (VDD) or control diet from 4 weeks before pregnancy (periconception) until 7 days postparturition. Male offspring were weighed and euthanized at 75 days of age (early adult period), at which point serum was collected for biochemical analyses, and perigonadal and subcutaneous white adipose tissue (PGAT and SQAT, respectively) were excised, weighed, then flash-frozen for later histology and analyses of adipogenic gene expression.

RESULTS

All adult male offspring were nonobese; there were no significant differences in body weight, adipose pad weight, or adipocyte size. However, VDD-exposed offspring had greater expression of the adipogenic-regulating genes peroxisome proliferator-activated receptor gamma (Pparg) and vitamin D receptor (Vdr).

CONCLUSIONS

This study suggests that exposure to vitamin D deficiency during the perinatal period can directly affect genes involved in the development of adipose tissue in nonobese offspring. These novel findings invite further investigation into the mechanisms by which maternal vitamin D status during pregnancy affects adipose development and metabolic health of offspring.

IL-12/IL-23p40 Is Highly Expressed in Secondary Lymphoid Organs and the CNS during All Stages of EAE, but Its Deletion Does Not Affect Disease Perpetuation

Background

Interleukin (IL)-12 and IL-23 are heterodimers that share the p40 subunit, and both cytokines are critical in the differentiation of T helper (Th)1 and Th17 cells, respectively. Th1 and Th17 effector cells have been implicated in the pathogenesis of experimental autoimmune encephalitis (EAE), an animal model of the human central nervous system (CNS) autoimmune demyelinating disorder multiple sclerosis (MS). However, ustekinumab, a monoclonal antibody (mAb) against p40 failed to show efficacy over placebo in a phase II clinical trial in patients with MS. The role of p40 in initial T cell priming and maintenance in secondary lymphoid tissues is not yet well understood.

Methods

Active EAE was induced in the B6.129-IL12b strain of p40eYFP reporter mice (yet40 mice), and Th1 and Th17 polarized cells were adoptively transferred into p40-deficient mice. Cellular subsets were phenotyped by multi-parameter flow cytometry, and p40 tissue expression was identified by confocal microscopy.

Results

We show that yet40 mice are susceptible to EAE, and that p40 is highly expressed in secondary lymphoid organs and the CNS during all stages of the disease. Interestingly, p40 expression in the recipient is not required for EAE induction after adoptive transfer of activated and differentiated encephalitogenic Th1 and Th17 cells into p40-deficient mice. Peripheral antagonism of T helper cell trophic factors critical for the differentiation and maintenance of Th1 and Th17 cells ameliorates EAE, indicating that p40 may play a critical role in the induction of CNS autoimmunity but not in its perpetuation.

Conclusion

Our data may explain why ustekinumab did not ameliorate paraclinical and clinical disease in patients with MS. In patients with already established disease, activated antigen-specific encephalitogenic CD4⁺ T cells are likely already differentiated, and are not dependent on p40 for maintenance. A clinical trial of longer duration with anti-p40 mAbs or other forms of pharmacological p40 antagonism, or sequential anti-p40 therapy following T cell depletion may show a benefit by affecting de novo generation of autoimmune T cells.

BCL6 controls Th9 cell development by repressing Il9 transcription

The transcriptional repressor B cell lymphoma 6 (BCL6) is required for the development of Th follicular cells, and it has been shown to suppress Th2 cell differentiation. We demonstrate that BCL6 is a key regulator of Th9 cell development. BCL6 expression is transiently downregulated in polarized Th9 cells, and forced expression of BCL6 in Th9 cells impairs Th9 cell differentiation. In contrast, BCL6 knockdown upregulated IL-9 production in Th9 cells. The function of BCL6 in Th9 cells is under the control of IL-2/JAK3/STAT5 signaling pathway. Using chromatin immunoprecipitation, we show that, in Th9 cells, BCL6 and STAT5 bind to adjacent motifs in the Il9 promoter. Furthermore, we found that STAT5 binding was associated with the abundance of a permissive histone mark at the Il9 promoter, whereas under conditions in which BCL6 binding was predominant, a repressive histone mark was prevalent. The effects of STAT5 and BCL6 on IL-9 transcription were further demonstrated using an IL-9 luciferase reporter assay in which BCL6 repressed STAT5-mediated Il9 transactivation. In experimental autoimmune encephalomyelitis, forced expression of BCL6 in myelin oligodendrocyte glycoprotein35-55-specific Th9 cells resulted in decreased IL-9 production and induction of IFN-γ, causing an exacerbation of the clinical disease. Our findings demonstrate a novel role of BCL6 in the regulation of Th9 cell development and their encephalitogenicity.

Interleukin-2 gene polymorphism in Turkish patients with Behçet's disease and its association with ocular involvement

Behçet's disease (BD) is a chronic immune-mediated systemic disease, characterized by oral and genital lesions and ocular inflammation. Several cytokine genes may play crucial roles in host susceptibility to BD, because the cytokine production capacity varies among individuals and depends on the cytokine gene polymorphisms. The association of the interleukin (IL)-2 gene polymorphisms with the susceptibility to BD was investigated in this study. DNA samples were obtained from a Turkish population of 97 patients with BD and 76 healthy control subjects. Polymorphisms of IL-2 gene at position -330 and +166 were determined using the polymerase chain reaction with sequence-specific primers. In the patients with BD, there was a significantly increased frequency of IL-2 -330 GT genotype. Interestingly, we demonstrated that the frequencies of IL-2 -330 GT and IL-2 + 166 GG genotypes were increased in BD patients with ocular involvement, whilst IL-2 -330 TT genotype was significantly decreased. Also, analysis of allele frequency demonstrated that the presence of G allele at position +166 of IL-2 seems to be a risk factor for ocular involvement. These results reveal that IL-2 -330 GT genotype may be a susceptibility factor for BD, whereas IL-2 -330 TT genotype seems to display a protective association with BD. Additionally, IL-2 gene polymorphisms might be associated with ocular involvement in BD.

Cell-intrinsic and -extrinsic control of Treg-cell homeostasis and function revealed by induced CD28 deletion

While the requirement for CD28 and its ligands for the generation and function of "natural" (n)Treg cells is well established, it has not been possible yet to investigate cell-intrinsic effects after interrupted CD28 expression. Here, we demonstrate a selective loss of Treg cells after disruption of the CD28 gene. The decline in Treg-cell number was accompanied by reduced homeostatic proliferation, probably due to lack of costimulation during self-antigen recognition, and by impaired Treg-cell function including downregulation of CTLA-4. The decline in Treg-cell number was unaffected by thymectomy or by the presence of CD28 expressing T cells within the same animal, indicating that impairment of peripheral homeostasis and function of nTreg cells by CD28 deletion is cell-intrinsic. In contrast, downregulation of CD25, the α chain of the IL-2R, did not occur in the presence of WT T cells, indicating that its expression does not depend on CD28 signals in cis.

RANKL-RANK interaction in immune regulatory systems

The interaction between the receptor activator of NF-κB ligand (RANKL) and its receptor RANK plays a critical role in the development and function of diverse tissues. This review summarizes the studies regarding the functions of RANKL signaling in immune regulatory systems. Previous in vitro and in vivo studies have indicated that the RANKL signal promotes the survival of dendritic cells (DCs), thereby activating the immune response. In addition, RANKL signaling to DCs in the body surface barriers controls self-tolerance and oral-tolerance through regulatory T cell functions. In addition to regulating DC functions, the RANKL and RANK interaction is critical for the development and organization of several lymphoid organs. The RANKL signal initiates the formation of clusters of lymphoid tissue inducer cells, which is crucial for lymph node organogenesis. Moreover, the RANKL-RANK interaction controls the differentiation of M cells, specialized epithelial cells in mucosal tissues, that take up and transcytose antigen particles to control the immune response to pathogens or commensal bacterium. The development of epithelial cells localized in the thymic medulla (mTECs) is also regulated by the RANKL-RANK signal. Given that the unique property of mTECs to express a wide variety of tissue-specific self-antigens is critical for the elimination of self-antigen reactive T cells in the thymus, the RANKL-RANK interaction contributes to the suppression of autoimmunity. Future studies on the roles of the RANKL-RANK system in immune regulatory functions would be informative for the development and application of inhibitors of RANKL signaling for disease treatment.

The molecular mechanisms of regulatory T cell immunosuppression

CD4⁺CD25⁺Foxp3⁺ T lymphocytes, known as regulatory T cells or T(regs), have been proposed to be a lineage of professional immune suppressive cells that exclusively counteract the effects of the immunoprotective "helper" and "cytotoxic" lineages of T lymphocytes. Here we discuss new concepts on the mechanisms and functions of T(regs). There are several key points we emphasize: 1. Tregs exert suppressive effects both directly on effector T cells and indirectly through antigen-presenting cells; 2. Regulation can occur through a novel mechanism of cytokine consumption to regulate as opposed to the usual mechanism of cytokine/chemokine production; 3. In cases where CD4⁺ effector T cells are directly inhibited by T(regs), it is chiefly through a mechanism of lymphokine withdrawal apoptosis leading to polyclonal deletion; and 4. Contrary to the current view, we discuss new evidence that T(regs), similar to other T-cells lineages, can promote protective immune responses in certain infectious contexts (Chen et al., 2011; Pandiyan et al., 2011). Although these points are at variance to varying degrees with the standard model of T(reg) behavior, we will recount developing findings that support these new concepts.

Sjögren's syndrome: studying the disease in mice

Sjögren's syndrome (SS), a systemic autoimmune disease, is characterized by inflammation of exocrine tissues accompanied by a significant loss of their secretory function. Clinical symptoms develop late and there are no diagnostic tests enabling early diagnosis of SS. Thus, particularly to study these covert stages, researchers turn to studying animal models where mice provide great freedom for genetic manipulation and testing the effect of experimental intervention. The present review summarizes current literature pertaining to both spontaneous and extrinsic-factor induced SS-like diseases in mouse models, discussing advantages and disadvantages related to the use of murine models in SS research.

Type I diabetes-associated tolerogenic properties of interleukin-2

Type 1 Diabetes (T1D) results from insulin-producing beta cells destruction by diabetogenic T lymphocytes in humans and nonobese diabetic (NOD) mice. The breakdown of tolerance has been associated with a defect in the number and the function of naturally occurring regulatory T cells (nTreg) that are the master player in peripheral tolerance. Gene knockout experiments in mouse models have shown a nonredundant activity of IL-2 related to its critical role in inducing nTreg and controlling peripheral T cell tolerance. Whereas strong evidence has suggested that IL-2 is critically required for nTreg-mediated T1D control, several fundamental questions remain to be addressed. In this paper, we highlight the recent findings and controversies regarding the tolerogenic properties of IL-2 mediated through nTreg. We further discuss a potential link between the immunomodulatory role of interleukin-2 and the pathogenesis of type 1 diabetes.

Why do T cells express the vitamin D receptor?

Vitamin D is an important regulator of immune function. T cells express the vitamin D receptor (VDR) and have been shown to be direct and indirect vitamin D targets. Why should T cells be responsive to vitamin D? The data suggest that expression of the VDR is required for the development of two cell types, NKT cells and CD8αα T cells, which inhibit autoimmunity. In addition, effector T cell cytokine production is regulated by vitamin D. Available evidence suggests that NKT and CD8αα T cells express the VDR as part of the selection process to protect against the generation of autoimmunity, particularly in the gut.

The power and the promise of restimulation-induced cell death in human immune diseases

Controlled expansion and contraction of lymphocytes both during and after an adaptive immune response are imperative to sustain a healthy immune system. Both extrinsic and intrinsic pathways of lymphocyte apoptosis are programmed to eliminate cells at the proper time to ensure immune homeostasis. Genetic disorders of apoptosis described in mice and humans have established Fas and Bim as critical pro-apoptotic molecules responsible for T-cell death in response to T-cell receptor restimulation and cytokine withdrawal, respectively. Emerging evidence prompts revision of this classic paradigm, especially for our understanding of restimulation-induced cell death (RICD) and its physiological purpose. Recent work indicates that RICD employs both Fas and Bim for T-cell deletion, dispelling the notion that these molecules are assigned to mutually exclusive apoptotic pathways. Furthermore, new mouse model data combined with our discovery of defective RICD in X-linked lymphoproliferative disease (XLP) patient T cells suggest that RICD is essential for precluding excess T-cell accumulation and associated immunopathology during the course of certain infections. Here, we review how these advances offer a refreshing new perspective on the phenomenon of T-cell apoptosis induced through antigen restimulation, including its relevance to immune homeostasis and potential for therapeutic interventions.

Synergism of NOD2 and NLRP3 activators promotes a unique transcriptional profile in murine dendritic cells

NLRs are cytoplasmic proteins that sense cellular stress and intracellular damage resulting from pathogen uptake. To date, the role of NLRs has been studied using combinations of NLR and TLR agonists, but the interplay between two different NLRs remains uncharacterized. In this study, we employed microarrays to investigate in DCs the regulation of gene transcription mediated by activation of NOD2 and NLRP3 pathways using MDP and MSU. MDP and MSU co-stimulation of murine BMDCs up-regulated the expression of genes encoding molecules for antigen presentation and co-stimulation (MHC class II, CD80, CD86), integrins (ITGB3, ITGAV), cytokines (IL-1α, IL-1β, IL-6, IL-2, IL-23p19, IL-12p40), and chemokines (CXCL1, CXCL2). Transcription of the cytokine genes induced by MDP and MSU partially depended on NOD2 but was independent of NLRP3. Finally, we showed that ERK1 and c-JUN activation increased upon MDP and MSU co-stimulation. As a whole, the results indicate that two different NLR activators synergize at the transcriptional level, leading to unique differential expression of genes involved in the innate immune response.

Estrogenic activity of coumestrol, DDT, and TCDD in human cervical cancer cells

Endogenous estrogens have dramatic and differential effects on classical endocrine organ and proliferation. Xenoestrogens are environmental estrogens that have endocrine impact, acting as both estrogen agonists and antagonists, but whose effects are not well characterized. In this investigation we sought to delineate effects of xenoestrogens. Using human cervical cancer cells (HeLa cells) as a model, the effects of representative xenoestrogens (Coumestrol-a phytoestrogen, tetrachlorodioxin (TCDD)-a herbicide and DDT-a pesticide) on proliferation, cell cycle, and apoptosis were examined. These xenoestrogens and estrogen inhibited the proliferation of Hela cells in a dose dependent manner from 20 to 120 nM suggesting, that 17-beta-estrtadiol and xenoestrogens induced cytotoxic effects. Coumestrol produced accumulation of HeLa cells in G2/M phase, and subsequently induced apoptosis. Similar effects were observed in estrogen treated cells. These changes were associated with suppressed bcl-2 protein and augmented Cyclins A and D proteins. DDT and TCDD exposure did not induce apoptosis. These preliminary data taken together, suggest that xenoestrogens have direct, compound-specific effects on HeLa cells. This study further enhances our understanding of environmental modulation of cervical cancer.

Analysis of multiple candidate genes in association with phenotypes of multiple sclerosis

Multiple sclerosis is a heterogeneous neurological disease with varying degrees of severity. The common hypothesis is that susceptibility to multiple sclerosis and its phenotype are caused by a combination of environmental and genetic factors. The genetic part exerts its effect through several genes, each having modest effects.

We evaluated whether disease severity could be predicted by a model based on clinical data and data from a DNA chip. The DNA chip was designed containing several single nucleotide polymorphisms in 44 genes, previously described to be associated with multiple sclerosis.

A total of 605 patients with multiple sclerosis were included in this analysis, using gender, onset type and age at onset as clinical covariates. We correlated 80 single nucleotide polymorphisms to the degree of disease severity using the following three outcome measures: linear Multiple Sclerosis Severity Score, dichotomous Multiple Sclerosis Severity Score (using a cut-off point of 2.5) and time to reach Expanded Disability Status Scale score 6.

Sixty-nine single nucleotide polymorphisms were included in the analysis. No individual single nucleotide polymorphism showed a significant association; however, a combination of single nucleotide polymorphisms significantly improved the prediction of disease severity in addition to the clinical variables. In all three models the Interleukin 2 gene was included, confirming a previously reported modest effect on disease severity. The highest power was obtained using the dichotomized Multiple Sclerosis Severity Score as outcome.

Several single nucleotide polymorphisms showed their added predictive value over the clinical data in the predictive models. These results support our hypothesis that disease severity is determined by clinical variables and genetic influences (through several genes with small effects) in concert.

Roles of the NF-kappaB pathway in lymphocyte development and function

This article focuses on the functions of NF-kappaB that vitally impact lymphocytes and thus adaptive immunity. NF-kappaB has long been known to be essential for many of the responses of mature lymphocytes to invading pathogens. In addition, NF-kappaB has important functions in shaping the immune system so it is able to generate adaptive responses to pathogens. In both contexts, NF-kappaB executes critical cell-autonomous functions within lymphocytes as well as within supportive cells, such as antigen-presenting cells or epithelial cells. It is these aspects of NF-kappaB's physiologic impact that we address in this article.

STIM1-independent T cell development and effector function in vivo

Store-operated Ca(2+) entry (SOCE) is believed to be of pivotal importance in T cell physiology. To test this hypothesis, we generated mice constitutively lacking the SOCE-regulating Ca(2+) sensor stromal interaction molecule 1 (STIM1). In vitro analyses showed that SOCE and Ag receptor complex-triggered Ca(2+) flux into STIM1-deficient T cells is virtually abolished. In vivo, STIM1-deficient mice developed a lymphoproliferative disease despite normal thymic T cell maturation and normal frequencies of CD4(+)Foxp3(+) regulatory T cells. Unexpectedly, STIM1-deficient bone marrow chimeric mice mounted humoral immune responses after vaccination and STIM1-deficient T cells were capable of inducing acute graft-versus-host disease following adoptive transfer into allogeneic hosts. These results demonstrate that STIM1-dependent SOCE is crucial for homeostatic T cell proliferation, but of much lesser importance for thymic T cell differentiation or T cell effector functions.

Biphasic regulation of Il2 transcription in CD4+ T cells: roles for TNF-alpha receptor signaling and chromatin structure

We describe a novel biphasic regulation of Il2 transcription in naive CD4(+) T cells. Few ( approximately 5%) CD4(+) T cells transcribe Il2 within 6 h of anti-TCR-beta plus anti-CD28 stimulation (early phase). Most naive CD4(+) T cells do not initiate Il2 transcription until after an additional approximately 12 h of T cell stimulation (late phase). In comparison, essentially all previously activated (Pre-Ac) CD4(+) T cells that transcribe Il2 do so with an early-phase response. Late-phase Il2 expression mostly requires c-Rel, CD28, and TNFR signaling. In contrast, early-phase transcription is only partly c-Rel and CD28 dependent and TNFR independent. There was also increased stable DNA accessibility at the Il2 locus and elevated c-Rel expression in resting Pre-Ac CD4(+) cells. Upon T cell activation, a faster and greater increase in DNA accessibility as well as c-Rel nuclear expression were observed in Pre-Ac CD4(+) cells relative to naive CD4(+) T cells. In addition, both acetylated histone H3 and total H3 decreased at the Il2 locus upon rechallenge of Pre-Ac CD4(+) T cells, whereas increased acetylated histone H3 with no change in total H3 was observed following activation of naive CD4(+) T cells. We propose a model in which nucleosome disassembly facilitates rapid initiation of Il2 transcription in CD4(+) T cells, and suggest that a threshold level of c-Rel must be reached for Il2 promoter activity in both naive and Pre-Ac CD4(+) T cells. This is provided, at least partially, by TNFR signaling during priming, but not during recall.

Interleukin 2: from immunostimulation to immunoregulation and back again

Interleukin 2 (IL-2) was one of the first cytokines to be discovered. However, the complex role of IL-2 and its receptor in the regulation of immune responses is only now emerging. This review explores the various signals triggered by IL-2 and discusses their translation into biological function. A model is outlined that accommodates the seemingly contradictory functions of IL-2, and explains how one cytokine can be an essential T-cell growth and differentiation factor and yet also be indispensable to maintain peripheral tolerance.

Advances in type I diabetes associated tolerance mechanisms

Type 1 diabetes (T1D) is an autoimmune disease resulting from the destruction of insulin-producing pancreatic beta cells by autoreactive T cells. The polygenic trait for T1D risk implicates many genes that have an impact on fundamental immunological processes such as central and peripheral tolerance. Several pieces of evidence have suggested that many of the genetic loci that are directly linked to type 1 diabetes susceptibility modulate the generation and/or the activation of autoreactive T-lymphocytes. We and others have proposed a critical role for medullary thymic epithelial cells (mTEC) forming the Hassall's corpuscles in T-cell tolerance. Indeed, mTEC have been found to express promiscuous self-antigens, used directly or through thymic dendritic cells to drive either negative selection of insulin-reacting precursors or their differentiation into naturally occurring regulatory Foxp3+ CD4+ CD25+ T cells. In the periphery, naturally occurring Foxp3+ CD4+ CD25+regulatory T (Treg) cells represent the master cells in dominant peripheral T-cell tolerance. The development and function of Treg cells are ultimately linked to IL-2 and Foxp3 expression. This review addresses recent literature and emerging concepts of central and peripheral T-cell tolerance with regards to T1D.

Bcl-xL is associated with the anti-apoptotic effect of IL-15 on the survival of CD56(dim) natural killer cells

Human NK cells can be distinguished into CD56(bright) and CD56(dim) subsets based on cell surface CD56 density. It has been shown that IL-2 and IL-15 have opposing effects on life and death of CD8(+) T cells. However, the roles of IL-2 and IL-15 in regulating these two NK cell subsets remain elusive. In this study, we comparatively analyzed the effects of IL-2 and IL-15 on two NK cell subsets. IL-15 improved the proliferation and activation of CD56(dim) NK cells in long-term cord blood mononuclear cell culture, but IL-2 only maintained the survival of CD56(bright) NK cells. The percentage of CD56(+)Annexin V(+) NK cells cultured with IL-15 was lower than that with IL-2; moreover, most of Annexin V(+) NK cells were primarily in the CD56(dim) NK cells. IL-15 cultured NK cells expressed higher level of Bcl-xL than IL-2 cultured cells. Furthermore, IL-15 more strongly upregulated CD25 expression and better maintained the expression of IL-15Ralpha than IL-2. These results suggest that CD56(dim) NK cells undergo apoptosis when cultured with IL-2, but IL-15 inhibits their apoptosis and Bcl-xL is associated with the anti-apoptotic effect of IL-15. So IL-15 played a crucial role in sustaining long-lasting functions of CD56(dim) NK cells.

Characterization of mouse CD4 T cell subsets defined by expression of KLRG1

The mouse killer cell lectin-like receptor G1 (KLRG1) is an inhibitory receptor known to be expressed on a subset of NK cells and antigen-experienced CD8 T cells. Here, we have characterized expression of KLRG1 on CD4+ T cells from normal mice. While a polyclonal TCR repertoire suggests thymic origin of KLRG1+ CD4+ cells, KLRG1 expression was found to be restricted to peripheral CD4+ T cells. Based on phenotypic analyses, a minority of KLRG1+ CD4+ cells are effector/memory cells with a proliferative history. The majority of KLRG1+ CD4+ cells are, however, bona fide Treg cells that depend on IL-2 and/or CD28 and express both FoxP3 and high levels of intracellular CD152. KLRG1-expressing Treg are contained within the CD38+ subset but are only partially overlapping with the CD25+ CD4+ Treg subset. In functional assays, KLRG1+ CD4+ cells were anergic to TCR stimulation with respect to proliferation, and sorted KLRG1+ CD25+ CD4+ cells were equal or superior to KLRG1+ CD25- CD4+ cells, which were more potent than KLRG1- CD25+ CD4+ cells in suppressing responder cell proliferation. Together, our results demonstrate that KLRG1 expression defines novel and distinctive subsets of senescent effector/memory and potent regulatory CD4+ T cells.

The control of CD4+CD25+Foxp3+ regulatory T cell survival

CD4⁺CD25⁺Foxp3⁺ regulatory T (T_reg) cells are believed to play an important role in suppressing autoimmunity and maintaining peripheral tolerance. How their survival is regulated in the periphery is less clear. Here we show that T_reg cells express receptors for gamma chain cytokines and are dependent on an exogenous supply of these cytokines to overcome cytokine withdrawal apoptosis in vitro. This result was validated in vivo by the accumulation of T_reg cells in Bim^-/- and Bcl-2 tg mice which have arrested cytokine deprivation apoptosis. We also found that CD25 and Foxp3 expression were down-regulated in the absence of these cytokines. CD25⁺ cells from Scurfy mice do not depend on cytokines for survival demonstrating that Foxp3 increases their dependence on cytokines by suppressing cytokine production in T_reg cells. Our study reveals that the survival of T_reg cells is strictly dependent on cytokines and cytokine producing cells because they do not produce cytokines. Our study thus, demonstrates that different gamma chain cytokines regulate T_reg homeostasis in the periphery by differentially regulating survival and proliferation. These findings may shed light on ways to manipulate T_reg cells that could be utilized for their therapeutic applications.

This article was reviewed by: Avinash Bhandoola, Fred Ramsdell (nominated by Juan Carlos Zuniga-Pflucker) and Anne Cooke.

Digital NFATc2 activation per cell transforms graded T cell receptor activation into an all-or-none IL-2 expression

The expression of interleukin-2 (IL-2) is a key event in T helper (Th) lymphocyte activation, controlling both, the expansion and differentiation of effector Th cells as well as the activation of regulatory T cells. We demonstrate that the strength of TCR stimulation is translated into the frequency of memory Th cells expressing IL-2 but not into the amount of IL-2 per cell. This molecular switch decision for IL-2 expression per cell is located downstream of the cytosolic Ca²⁺ level. Here we show that in a single activated Th cell, NFATc2 activation is digital but NF-κB activation is graded after graded T cell receptor (TCR) signaling. Subsequently, NFATc2 translocates into the nucleus in an all-or-none fashion per cell, transforming the strength of TCR-stimulation into the number of nuclei positive for NFATc2 and IL-2 transcription. Thus, the described NFATc2 switch regulates the number of Th cells actively participating in an immune response.

IL-2 signals through Sgk1 and inhibits proliferation and apoptosis in kidney cancer cells

The interleukin-2 is a cytokine that is essential for lymphocytic survival and function. Ectopic expression of the IL-2 receptor in epithelial tissues has been reported previously, although the functional significance of this expression is still being investigated. We provided novel structural and functional information on the expression of the IL-2 receptor in kidney cancer cells and in other normal and neoplastic human epithelial tissues. In A-498 kidney cancer cells, we showed that IL-2 binding to its own receptor triggers a signal transduction pathway leading to the inhibition of proliferation and apoptosis. We found that the inhibition of proliferation is associated with Erk1/2 dephosphorylation, whereas the survival signals appear to be mediated by Sgk1 activation. This investigation focuses on the IL-2 induced regulation of Sgk1 and describes a role of the IL-2 receptor and Sgk1 in the regulation of epithelial tumor cell death and survival.

Differential role of IL-2R signaling for CD8+ T cell responses in acute and chronic viral infections

IL-2 is a cytokine with multiple and even divergent functions; it has been described as a key cytokine for in vitro T cell proliferation but is also essential for down-regulating T cell responses by inducing activation-induced cell death as well as regulatory T cells. The in vivo analysis of IL-2 function in regulating specific T cell responses has been hampered by the fact that mice deficient in IL-2 or its receptors develop lymphoproliferative diseases and/or autoimmunity. Here we generated chimeric mice harboring both IL-2R-competent and IL-2R-deficient T cells and assessed CD8+ T cell induction, function and maintenance after acute or persistent viral infections. Induction and maintenance of CD8+ T cells were relatively independent of IL-2R signaling during acute/resolved viral infection. In marked contrast, IL-2 was crucial for secondary expansion of memory CD8+ T cells and for the maintenance of virus-specific CD8+ T cells during persistent viral infections. Thus, depending on the chronicity of antigen exposure, IL-2R signaling is either essential or largely dispensable for induction and maintenance of virus-specific CD8+ T cell responses.

Tracing the action of IL-2 in tolerance to islet-specific antigen

Genetic variants of interleukin 2 (IL-2) and its receptor are associated with murine and human susceptibility to Type 1 diabetes, yet the role of IL-2 in controlling pancreatic islet-reactive T cells is unknown. Here, we develop a model where IL-2 deficiency precipitates a breakdown of self-tolerance and progression to diabetes, and its action upon diabetogenic islet-specific CD4 T cells can be tracked. We find that IL-2 is not required for Aire-dependent thymic clonal deletion of high-avidity diabetogenic clones, but is essential for thymic formation of islet-specific Foxp3-expressing CD4 T cells. The absence of IL-2 results in the expansion of low-avidity Foxp3(-) islet-reactive CD4 T cells. The mechanism by which IL-2 prevents diabetes is therefore through the establishment of a repertoire of islet-reactive Foxp3(+) T cells within the thymus, and limitation of the peripheral activation of low-avidity islet-reactive T cells that normally escape thymic negative selection.

Potential use of IL-2/anti-IL-2 antibody immune complexes for the treatment of cancer and autoimmune disease

Initially discovered as a potent T cell proliferation factor, IL-2 was soon used for cancer immunotherapy, especially for metastatic melanoma and renal cell carcinoma; however, the severe side effects of IL-2 therapy, plus the negative role of IL-2 in maintaining of CD4+ CD25+ T regulatory cells (Tregs), has somewhat dampened enthusiasm for using IL-2 in immunotherapy. This opinion article discusses the possibility of combining IL-2 with certain anti-IL-2 antibodies for reducing the dose of IL-2 needed and preferentially stimulating effector T cells, but not Tregs, an approach that might provide an improved strategy for anticancer immunotherapy. Alternatively, complexes of IL-2 with other anti-IL-2 antibodies can selectively stimulate Tregs and could, therefore, be useful for treating autoimmune diseases.

Manipulation of Regulatory T‐Cell Number and Function with CD28‐Specific Monoclonal Antibodies

Suppressor or "regulatory" CD4 T cells play a key role in the control of autoimmunity and overshooting immune responses to foreign antigens, but can also obstruct effective anticancer therapies. The homeostasis and activation of these regulatory T cells (Treg cells) is tightly connected to that of effector CD4 T cells via the costimulatory receptor CD28 and the cytokine IL-2: Both subsets require costimulation to be activated by antigen, and Treg cells additionally depend on IL-2 produced by effector CD4 T cells in a costimulation-dependent fashion. Depending on the therapeutic aim, blockade, or stimulation of CD28 with monoclonal antibodies (mAb) can therefore profoundly affect the size and activity of the Treg compartment. In this chapter, experiments performed in rodents with distinct types of CD28-specific mAb, and the recent failure to translate CD28-driven Treg activation into humans, are discussed.

Interleukin 27 limits autoimmune encephalomyelitis by suppressing the development of interleukin 17-producing T cells

Interleukin 27 (IL-27) was first characterized as a proinflammatory cytokine with T helper type 1-inducing activity. However, subsequent work has demonstrated that mice deficient in IL-27 receptor (IL-27R alpha) show exacerbated inflammatory responses to a variety of challenges, suggesting that IL-27 has important immunoregulatory functions in vivo. Here we demonstrate that IL-27R alpha-deficient mice were hypersusceptible to experimental autoimmune encephalomyelitis and generated more IL-17-producing T helper cells. IL-27 acted directly on effector T cells to suppress the development of IL-17-producing T helper cells mediated by IL-6 and transforming growth factor-beta. This suppressive activity was dependent on the transcription factor STAT1 and was independent of interferon-gamma. Finally, IL-27 suppressed IL-6-mediated T cell proliferation. These data provide a mechanistic explanation for the IL-27-mediated immune suppression noted in several in vivo models of inflammation.

CCL19-IgG prevents allograft rejection by impairment of immune cell trafficking

An adaptive immune response is initiated in the T cell area of secondary lymphoid organs, where antigen-presenting dendritic cells may induce proliferation and differentiation in co-localized T cells after T cell receptor engagement. The chemokines CCL19 and CCL21 and their receptor CCR7 are essential in establishing dendritic cell and T cell recruitment and co-localization within this unique microenvironment. It is shown that systemic application of a fusion protein that consists of CCL19 fused to the Fc part of human IgG1 induces effects similar to the phenotype of CCR7-/- animals, like disturbed accumulation of T cells and dendritic cells in secondary lymphoid organs. CCL19-IgG further inhibited their co-localization, which resulted in a marked inhibition of antigen-specific T cell proliferation. The immunosuppressive potency of CCL19-IgG was tested in vivo using murine models for TH1-mediated immune responses (delayed-type hypersensitivity) and for transplantation of different solid organs. In allogeneic kidney transplantation as well as heterotopic allogeneic heart transplantation in different strain combinations, allograft rejection was reduced and organ survival was significantly prolonged by treatment with CCL19-IgG compared with controls. This shows that in contrast to only limited prolongation of graft survival in CCR7 knockout models, the therapeutic application of a CCR7 ligand in a wild-type environment provides a benefit in terms of immunosuppression.

BCL11B participates in the activation of IL2 gene expression in CD4+ T lymphocytes

BCL11A and BCL11B are transcriptional regulators important for lymphopoiesis and previously associated with hematopoietic malignancies. Ablation of the mouse Bcl11b locus results in failure to generate double-positive thymocytes, implicating a critical role of Bcl11b in T-cell development. However, BCL11B is also expressed in CD4+ T lymphocytes, both in resting and activated states. Here we show both in transformed and primary CD4+ T cells that BCL11B participates in the control of the interleukin-2 (IL2) gene expression following activation through T-cell receptor (TCR). BCL11B augments expression from the IL2 promoter through direct binding to the US1 site. In addition, BCL11B associates with the p300 coactivator in CD4+ T cells activated through TCR, which may account for its transcriptional activation function. These results provide the first evidence that BCL11B, originally described as a transcriptional repressor, activates transcription of a target gene in the context of T-cell activation.

FOXP3: of mice and men

The immune system has evolved mechanisms to recognize and eliminate threats, as well as to protect against self-destruction. Tolerance to self-antigens is generated through two fundamental mechanisms: (a) elimination of self-reactive cells in the thymus during selection and (b) generation of a variety of peripheral regulatory cells to control self-reactive cells that escape the thymus. It is becoming increasing apparent that a population of thymically derived CD4+ regulatory T cells, exemplified by the expression of the IL-2Ralpha chain, is essential for the maintenance of peripheral tolerance. Recent work has shown that the forkhead family transcription factor Foxp3 is critically important for the development and function of the regulatory T cells. Lack of Foxp3 leads to development of fatal autoimmune lymphoproliferative disease; furthermore, ectopic Foxp3 expression can phenotypically convert effector T cells to regulatory T cells. This review focuses on Foxp3 expression and function and highlights differences between humans and mice regarding Foxp3 regulation.

Reduced expression of interleukin-2 decreases the frequency of alopecia areata onset in C3H/HeJ mice

Alopecia areata (AA) is an autoimmune hair loss disease, that can be transferred between C3H/HeJ mice by skin grafting. We explored whether AA susceptibility is influenced by the availability of interleukin (IL)-2, a cytokine with leukocyte activating and regulatory properties. Mice heterozygous for a targeted deletion of IL-2 from the histocompatible C3.129P2(B6)-Il2(tm1Hor) substrain, that produce reduced levels of IL-2, were examined for AA development after grafting skin from AA-affected C3H/HeJ mice. After grafting, nine of 19 (47%) heterozygous IL-2+/-versus 16 of 18 (88%) IL-2+/+ wild-type littermates developed AA. Although dense follicular leukocyte infiltrates were apparent in AA affected wild-type mice, AA-developing IL-2+/- littermates had a reduced leukocyte infiltration, and AA-resistant IL-2+/- mice had no inflammation. Lymph node cell analysis revealed a reduction in leukocyte activation markers in AA-developing IL-2+/- mice. IL-2+/- mice presented with low level expression of cytokines (IL-4, IL-10, interferon-gamma, transforming growth factor-beta), upregulation of tumor necrosis factor receptors, and increased leukocyte apoptosis susceptibility independent of AA expression. In the skin, CD4+ cells and monocytes were reduced; activation markers were not upregulated and very few CD44v3+ or CD44v10+ leukocytes were recovered. Taken together, our data suggest that AA resistance of IL-2+/- mice is because of the failure of activated leukocyte recruitment, thus pointing toward an involvement of IL-2 in AA pathogenesis.

IL-2 production in developing Th1 cells is regulated by heterodimerization of RelA and T-bet and requires T-bet serine residue 508

Interleukin (IL)-2 is the predominant cytokine that is produced by naive Th cells in a primary response. It is required for proliferation and differentiation of Th precursor cells into effector cells. Initial high-level IL-2 production is followed by its decline, and the concomitant induction of cytokines that are typical of the differentiated state. Although the factors that are responsible for the early induction of IL-2 are well defined, the mechanisms that are responsible for its down-regulation in later stages of Th development have not been studied as much. Previous work from our laboratory revealed a repressor function for the T-box transcription factor, T-bet, in IL-2 gene transcription. Here, we report that T-bet(S508) is required for the optimal repression of IL-2 production in developing Th1 cells. Phosphorylation of T-bet(S508) by casein kinase I and glycogen synthase kinase-3 kinases accompanies T-bet's interaction with the RelA nuclear factor-kappaB transcription factor. Heterodimerization of T-bet and RelA interferes with the binding of RelA to the IL-2 promoter, and hence, transcriptional activation of the IL-2 gene by RelA.