T helper differentiation proceeds through Stat1-dependent, Stat4-dependent and Stat4-independent phases

Deciphering the developmental trajectory of tissue-resident Foxp3+ regulatory T cells

Foxp3+ TREG cells have been at the focus of intense investigation for their recognized roles in preventing autoimmunity, facilitating tissue recuperation following injury, and orchestrating a tolerance to innocuous non-self-antigens. To perform these critical tasks, TREG cells undergo deep epigenetic, transcriptional, and post-transcriptional changes that allow them to adapt to conditions found in tissues both at steady-state and during inflammation. The path leading TREG cells to express these tissue-specialized phenotypes begins during thymic development, and is further driven by epigenetic and transcriptional modifications following TCR engagement and polarizing signals in the periphery. However, this process is highly regulated and requires TREG cells to adopt strategies to avoid losing their regulatory program altogether. Here, we review the origins of tissue-resident TREG cells, from their thymic and peripheral development to the transcriptional regulators involved in their tissue residency program. In addition, we discuss the distinct signalling pathways that engage the inflammatory adaptation of tissue-resident TREG cells, and how they relate to their ability to recognize tissue and pathogen-derived danger signals.

STAT1-Dependent Recruitment of Ly6ChiCCR2+ Inflammatory Monocytes and M2 Macrophages in a Helminth Infection

Signal Transducer and Activator of Transcription (STAT) 1 signaling is critical for IFN-γ-mediated immune responses and resistance to protozoan and viral infections. However, its role in immunoregulation during helminth parasitic infections is not fully understood. Here, we used STAT1^-/- mice to investigate the role of this transcription factor during a helminth infection caused by the cestode Taenia crassiceps and show that STAT1 is a central molecule favoring susceptibility to this infection. STAT1^-/- mice displayed lower parasite burdens at 8 weeks post-infection compared to STAT1^+/+ mice. STAT1 mediated the recruitment of inflammatory monocytes and the development of alternatively activated macrophages (M2) at the site of infection. The absence of STAT1 prevented the recruitment of CD11b⁺Ly6C^hiLy6G^- monocytic cells and therefore their suppressive activity. This failure was associated with the defective expression of CCR2 on CD11b⁺Ly6C^hiLy6G^- cells. Importantly, CD11b⁺Ly6C^hiLy6G^- cells highly expressed PDL-1 and suppressed T-cell proliferation elicited by anti-CD3 stimulation. PDL-1⁺ cells were mostly absent in STAT1^-/- mice. Furthermore, only STAT1^+/+ mice developed M2 macrophages at 8 weeks post-infection, although macrophages from both T. crassiceps-infected STAT1^+/+ and STAT1^-/- mice responded to IL-4 in vitro, and both groups of mice were able to produce the Th2 cytokine IL-13. This suggests that CD11b⁺CCR2⁺Ly6C^hiLy6G^- cells give rise to M2 macrophages in this infection. In summary, a lack of STAT1 resulted in impaired recruitment of CD11b⁺CCR2⁺Ly6C^hiLy6G^- cells, failure to develop M2 macrophages, and increased resistance against T. crassiceps infection.

Targeting Canonical and Non-Canonical STAT Signaling Pathways in Renal Diseases

Signal transducer and activator of transcription (STAT) plays an essential role in the inflammatory reaction and immune response of numerous renal diseases. STATs can transmit the signals of cytokines, chemokines, and growth factors from the cell membrane to the nucleus. In the canonical STAT signaling pathways, upon binding with their cognate receptors, cytokines lead to a caspase of Janus kinases (JAKs) and STATs tyrosine phosphorylation and activation. Besides receptor-associated tyrosine kinases JAKs, receptors with intrinsic tyrosine kinase activities, G-protein coupled receptors, and non-receptor tyrosine kinases can also activate STATs through tyrosine phosphorylation or, alternatively, other post-translational modifications. Activated STATs translocate into the nucleus and mediate the transcription of specific genes, thus mediating the progression of various renal diseases. Non-canonical STAT pathways consist of preassembled receptor complexes, preformed STAT dimers, unphosphorylated STATs (U-STATs), and non-canonical functions including mitochondria modulation, microtubule regulation and heterochromatin stabilization. Most studies targeting STAT signaling pathways have focused on canonical pathways, but research extending into non-canonical STAT pathways would provide novel strategies for treating renal diseases. In this review, we will introduce both canonical and non-canonical STAT pathways and their roles in a variety of renal diseases.

Increased frequency of regulatory T cells in the peripheral blood of patients with endometrioid adenocarcinoma

The aim of the present study was to investigate the frequency of cluster of differentiation (CD)4⁺CD25⁺CD127^- regulatory T cells (Tregs) in the peripheral blood mononuclear cells (PBMCs) of patients with endometrioid adenocarcinoma (EA). A total of 82 female patients with EA were recruited. The PBMCs were flow cytometrically analyzed to determine the percentage of CD4⁺CD25⁺CD127^- Tregs within the CD4⁺ T cell population. The associations between the prevalence of Tregs in PBMCs and defined clinical prognostic parameters were evaluated. To study the immunoregulatory capacity of Tregs, the level of specific cytokines were detected by ELISA, and the proliferation of cells was analyzed by incorporation of ³H-thymidine. It was revealed that Treg/CD4⁺ ratio in the peripheral blood of patients with EA was 4.89±1.42%, significantly higher than Treg/CD4⁺ ratio in healthy women. No correlation was observed between Treg frequency and stage, grade of differentiation, menopausal status or age. CD4⁺CD25⁺CD127^- Tregs secreted large amounts of IL-10 but not IFN-γ. The level of IL-10 secreted by Tregs from patients with EA and healthy controls was not significantly different. In addition, there was no significant difference in the suppressive activity of Tregs in patients with EA compared with that of the healthy controls. These findings demonstrate that the increased frequency of immunosuppressive Tregs in patients with EA may be responsible for immune tolerance in endometrial cancer.

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

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

Association of STAT4 and PTPN22 polymorphisms and their interactions with type-1 autoimmune hepatitis susceptibility in Chinese Han children

AIMS

To investigate the impact of signal transducer and activator of transcription 4 (STAT4) and the protein tyrosine phosphatase N22 (PTPN22) gene single nucleotide polymorphisms (SNPs), gene-gene interactions and haplotype on type-1 Autoimmune Hepatitis (AIH) risk.

RESULTS

Logistic regression analysis showed that type 1 AIH was significantly higher in carriers of T allele of rs7574865 than those with GG genotype (P- value less than 0.001), higher in carriers of C allele of rs7582694 than those with GG genotype (P- value < 0.001), and lower in carriers of T allele of rs2476601 than those with CC genotype (P- value < 0.001). GMDR model indicated a significant two-locus model (p = 0.0100) involving rs7582694 and rs2476601. Participants with GC or CC of rs7582694 and CC of rs2476601 genotype have the highest type 1 AIH risk (P- value < 0.001), after covariates adjustment. Haplotype containing the rs7582694-C and rs7574865-T alleles were associated with a statistically increased type 1 AIH risk (P < 0.001).

MATERIALS AND METHODS

Logistic regression was performed to investigate association between SNPs within STAT4 and PTPN22 gene and susceptibility to type 1 AIH. Generalized multifactor dimensionality reduction (GMDR) was used to screen the best interaction combinations among the 4 SNPs.

CONCLUSIONS

We conclude that rs7574865 and rs7582694 in STAT4 gene minor alleles, interaction between rs7582694 and rs2476601, and haplotype containing the rs7582694-C and rs7574865-T alleles are associated with increased type 1 AIH risk, but rs2476601 in PTPN22 gene minor allele is associated with decreased type 1 AIH risk.

Increasing JAK/STAT Signaling Function of Infant CD4+ T Cells during the First Year of Life

Most infant deaths occur in the first year of life. Yet, our knowledge of immune development during this period is scarce and derived from cord blood (CB) only. To more effectively combat pediatric diseases, a deeper understanding of the kinetics and the factors that regulate the maturation of immune functions in early life is needed. Increased disease susceptibility of infants is generally attributed to T helper 2-biased immune responses. The differentiation of CD4⁺ T cells along a specific T helper cell lineage is dependent on the pathogen type, and on costimulatory and cytokine signals provided by antigen-presenting cells. Cytokines also regulate many other aspects of the host immune response. Therefore, toward the goal of increasing our knowledge of early immune development, we defined the temporal development of the Janus kinase (JAK)/signal transducers and activators of transcription (STAT) signaling function of CD4⁺ T cells using cross-sectional blood samples from healthy infants ages 0 (birth) to 14 months. We specifically focused on cytokines important in T cell differentiation (IFN-γ, IL-12, and IL-4) or in T cell survival and expansion (IL-2 and IL-7) in infant CD4⁺ T cells. Independent of the cytokine tested, JAK/STAT signaling in infant compared to adult CD4⁺ T cells was impaired at birth, but increased during the first year, with the most pronounced changes occurring in the first 6 months. The relative change in JAK/STAT signaling of infant CD4⁺ T cells with age was distinct for each cytokine tested. Thus, while about 60% of CB CD4⁺ T cells could efficiently activate STAT6 in response to IL-4, less than 5% of CB CD4⁺ T cells were able to activate the JAK/STAT pathway in response to IFN-γ, IL-12 or IL-2. By 4-6 months of age, the activation of the cytokine-specific STAT molecules was comparable to adults in response to IL-4 and IFN-γ, while IL-2- and IL-12-induced STAT activation remained below adult levels even at 1 year. These results suggest that common developmental and cytokine-specific factors regulate the maturation of the JAK/STAT signaling function in CD4⁺ T cells during the first year of life.

Transcriptional and epigenetic regulation of T-helper lineage specification

Combined with TCR stimuli, extracellular cytokine signals initiate the differentiation of naive CD4(+) T cells into specialized effector T-helper (Th) and regulatory T (Treg) cell subsets. The lineage specification and commitment process occurs through the combinatorial action of multiple transcription factors (TFs) and epigenetic mechanisms that drive lineage-specific gene expression programs. In this article, we review recent studies on the transcriptional and epigenetic regulation of distinct Th cell lineages. Moreover, we review current study linking immune disease-associated single-nucleotide polymorphisms with distal regulatory elements and their potential role in the disease etiology.

STAT4 is critical for immunity but not for antileishmanial activity of antimonials in experimental visceral leishmaniasis

We and others have previously shown that IL-12 is indispensable for immunity and is required for the optimal antiparasitic activity of antimonials in experimental visceral leishmaniasis caused by Leishmania donovani. Here we investigated the role of STAT4 in immunity against L. donovani using STAT4 knockout mice and also determined the effect of STAT4 deficiency in response to antimonial therapy. Upon infection with L. donovani, stat4⁻/⁻ BALB/c and C57BL/6 mice showed enhanced susceptibility to Leishmania during late time points of infection which was associated with a marked reduction in Th1 responses and hepatic immunopathology. Interestingly, these defects in Th1 responses in stat4⁻/⁻ did not impair the antimonial chemotherapy as both stat4⁻/⁻ and WT mice showed comparable levels of parasite clearance from the liver and spleen. These findings highlight the role of STAT4 in immunity to L. donovani infection and also provide evidence that STAT4 is dispensable for antimonial-based chemotherapy.

Genetic markers associated with progression in early mycosis fungoides

BACKGROUND

Mycosis fungoides (MF) is a rare, but potentially devastating malignancy. It classically presents with cutaneous patches and plaques and can progress to tumours on the skin with lymph node, blood and visceral involvement. While most patients with MF have a relatively benign disease course, a subset of patients will develop progressive disease that is often fatal.

OBJECTIVE

The aim of this study was to identify genetic markers in early MF limited to the skin (stages IA-IIA) that distinguish those patients who will have progressive disease from those who will not, so that early appropriate treatment may be instituted.

METHODS

The study includes 18 patients who were diagnosed with early stage MF at the time of biopsy and had follow-up to determine which patients developed progressive disease. RNA was extracted from skin biopsy specimens and analysed for expression of CD3, FOXP3, IFNγ, Interleukin (IL)-4, IL-13, KIR3DL2, MICB, PLS3 and STAT4 by quantitative real-time polymerase chain reaction.

RESULTS/CONCLUSIONS

Reduced expression of FOXP3 and STAT4 and increased expression of IL-4 relative to CD3 expression levels were significantly associated with MF progression. Further studies will be needed to fully assess the usefulness of these genetic markers to predict disease progression and guide treatment options in patients diagnosed with early MF.

Association of STAT4 polymorphisms with susceptibility to type-1 autoimmune hepatitis in the Japanese population

Background/Aims

Recent studies demonstrated an association of STAT4 polymorphisms with autoimmune diseases including systemic lupus erythematosus and rheumatoid arthritis, indicating multiple autoimmune diseases share common susceptibility genes. We therefore investigated the influence of STAT4 polymorphisms on the susceptibility and phenotype of type-1 autoimmune hepatitis in a Japanese National Hospital Organization (NHO) AIH multicenter cohort study.

Methodology/Principal Findings

Genomic DNA from 460 individuals of Japanese origin including 230 patients with type-1 autoimmune hepatitis and 230 healthy controls was analyzed for two single nucleotide polymorphisms in the STAT4 gene (rs7574865, rs7582694). The STAT4 rs7574865T allele conferred risk for type-1 autoimmune hepatitis (OR = 1.61, 95% CI = 1.23–2.11; P = 0.001), and patients without accompanying autoimmune diseases exhibited an association with the rs7574865T allele (OR = 1.50, 95%CI = 1.13–1.99; P = 0.005). Detailed genotype-phenotype analysis of type-1 autoimmune hepatitis patients with (n = 44) or without liver cirrhosis (n = 186) demonstrated that rs7574865 was not associated with the development of liver cirrhosis and phenotype (biochemical data and the presence of auto-antibodies).

Conclusions/Significance

This is the first study to show a positive association between a STAT4 polymorphism and type-1 autoimmune hepatitis, suggesting that autoimmune hepatitis shares a gene commonly associated with risk for other autoimmune diseases.

STATs shape the active enhancer landscape of T cell populations

Signaling pathways are intimately involved in cellular differentiation, allowing cells to respond to their environment by regulating gene expression. Although enhancers are recognized as key elements that regulate selective gene expression, the interplay between signaling pathways and actively used enhancer elements is not clear. Here, we use CD4(+) T cells as a model of differentiation, mapping the activity of cell-type-specific enhancer elements in T helper 1 (Th1) and Th2 cells. Our data establish that STAT proteins have a major impact on the activation of lineage-specific enhancers and the suppression of enhancers associated with alternative cell fates. Transcriptome analysis further supports a functional role for enhancers regulated by STATs. Importantly, expression of lineage-defining master regulators in STAT-deficient cells fails to fully recover the chromatin signature of STAT-dependent enhancers. Thus, these findings point to a critical role of STATs as environmental sensors in dynamically molding the specialized enhancer architecture of differentiating cells.

The CXCL12/CXCR4 axis is involved in the maintenance of Th2 bias at the maternal/fetal interface in early human pregnancy

The regulatory mechanism of Th2 bias at the maternal/fetal interface remains unclear. In this study, we characterized cytokine production in decidual stromal cells (DSCs), decidual immune cells (DICs) and embryo-derived trophoblast cells, and investigated the regulation of CXCL12/CXCR4 interaction on Th2 bias at the maternal/fetal interface in early human pregnancy. We found differential production of Th1-type and Th2-type cytokines by trophoblasts, DSCs and DICs. The secretion of these cytokines varied in different cell cocultures, conduced to Th2 bias. Flow cytometry showed that coculture of trophoblasts with DSCs and DICs significantly increased IL-4 and IL-10 production in trophoblasts, and IL-10 production in DSCs. However, the coculture of trophoblasts with DSCs and DICs significantly increased interferon (IFN)-γ expression in DSCs, and tumor-necrosis factor (TNF)-α expression in DICs. No change was seen in Th1-type cytokine production in trophoblasts, and in Th2-type cytokine production in DICs in all cocultures. Furthermore, pre-treatment with anti-CXCR4 neutralizing antibody upregulated the production of the Th1-type cytokines IFN-γ and TNF-α, and downregulated the production of the Th2-type cytokines IL-4 and IL-10, in trophoblasts, DSCs, DICs or their cocultures. Interestingly, rhCXCL12 inhibited production of the Th1-type cytokine TNF-α and enhanced the expression of the Th2-type cytokines such as IL-4 and IL-10 in DICs; this effect was abrogated by anti-CXCR4 antibody. Our present study has elucidated the individual contributions of component cells to the shaping of Th2 bias, and uncovered a complicated cross-talk via the CXCL12/CXCR4 signal at the maternal/fetal interface in early human pregnancy.

Changes in the Th1:Th2 cytokine bias in pregnancy and the effects of the anti-inflammatory cyclopentenone prostaglandin 15-deoxy-Δ(12,14)-prostaglandin J2

Pregnancy is a complex immunological state in which a bias towards T helper 2 (Th2) protects the fetus. Evidence suggests that proinflammatory cytokines increase the risk of poor neonatal outcome, independently of the direct effect of preterm labour. The anti-inflammatory prostaglandin 15-deoxy-Δ^12,14-Prostaglandin J₂ (15dPGJ₂) inhibits nuclear factor Kappa B (NF-κB) in amniocytes and myocytes in vitro and is a ligand for the chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) receptor. Here we examine the Th1:Th2 cytokine bias in pregnancy and whether 15dPGJ₂ could be used to inhibit the production of the proinflammatory cytokines through inhibition of NF-κB while simultaneously promoting Th2 interleukin 4 (IL-4) synthesis via CRTH2 in T helper cells. Peripheral blood mononuclear cells (PBMCs) from women at 28 weeks, term pre-labour, term labour as well as non-pregnant female controls were cultured with 15dPGJ₂ or vehicle control and stimulated with phorbol myristyl acetate (PMA)/ionomycin. The percentage of CD4⁺ cells producing interferon gamma (IFN-γ) and tumor necrosis factor alpha (TNF-α) in response to PMA/ionomycin was significantly reduced in pregnancy. 15dPGJ₂ reduced IFN-γ and TNF-α production in stimulated T helper cells, but did not alter IL-4 production in CRTH2^+ve cells. 15dPGJ₂ also reduced phospho-p65 in stimulated PBMCs. In summary, 15dPGJ₂ suppresses the Th1 response of PBMCs during pregnancy and active labour whilst maintaining the Th2 response suggesting a therapeutic benefit in reducing neonatal morbidity in inflammation-induced PTL.

Inhibitory effects of the JAK inhibitor CP690,550 on human CD4(+) T lymphocyte cytokine production

Background

The new JAK3 inhibitor, CP690,550, has shown efficacy in the treatment of rheumatoid arthritis. The present study was undertaken to assess the effects of CP690,550 on cytokine production and cellular signaling in human CD4⁺ T cells.

Results

CD4⁺ T cells produced IL-2, IL-4, IL-17, IL-22 and IFN-γ in following stimulation with a CD3 antibody. At the optimal concentration, CP690,550 almost completely inhibited the production of IL-4, IL-17, IL-22 and IFN-γ from these activated CD4⁺ T cells, but only had marginal effects on IL-2 production. Moreover CP690,550 inhibited anti-CD3-induced phosphorylation of STAT1, STAT3, STAT4, STAT5, and STAT6, but not the TCR-associated phosphorylation of ZAP-70.

Conclusions

Therefore, CP690,550-mediated modification of the JAK/STAT pathway may be a new immunosuppressive strategy in the treatment of autoimmune diseases.

Regulation of the Ifng locus in the context of T-lineage specification and plasticity

Study of the development of distinct CD4(+) T-cell subsets from naive precursors continues to provide excellent opportunities for dissection of mechanisms that control lineage-specific gene expression or repression. Whereas it had been thought that the induction of transcription networks that control T-lineage commitment were highly stable, reinforced by epigenetic processes that confer heritability of functional phenotypes by the progeny of mature T cells, recent findings support a more dynamic view of T-lineage commitment. Here, we highlight advances in the mapping and functional characterization of cis elements in the Ifng locus that have provided new insights into the control of the chromatin structure and transcriptional activity of this signature T-helper 1 cell gene. We also examine epigenetic features of the Ifng locus that have evolved to enable its reprogramming for expression by other T-cell subsets, particularly T-helper 17 cells, and contrast features of the Ifng locus with those of the Il17a-Il17f locus, which appears less promiscuous.

Phenotypical and functional specialization of FOXP3+ regulatory T cells

Forkhead box P3 (FOXP3)(+) regulatory T (T(Reg)) cells prevent autoimmune disease, maintain immune homeostasis and modulate immune responses during infection. To accomplish these tasks, T(Reg) cell activity is precisely controlled, and this requires T(Reg) cells to alter their migratory, functional and homeostatic properties in response to specific cues in the immune environment. We review progress in understanding the diversity of T(Reg) cells, T(Reg) cell function in different anatomical and inflammatory settings, and the influence of the immune environment on T(Reg) cell activity. We also consider how these factors affect immune-mediated disease in the contexts of infection, autoimmunity, cancer and transplantation.

A new mechanism for inhalational priming: IL-4 bypasses innate immune signals

Signaling via innate immune mechanisms is considered pivotal for T cell-mediated responses to inhaled Ags. Furthermore, Th2 cells specific for one inhaled Ag can facilitate priming of naive T cells to unrelated new inhaled Ags, a process we call "Th2 collateral priming". Interestingly, our previous studies showed that collateral priming is independent of signals via the innate immune system but depends on IL-4 secretion by CD4(+) T cells. We thus hypothesized that IL-4 can bypass the need for signals via the innate immune system, considered essential for pulmonary priming. Indeed, we were able to show that IL-4 bypasses the requirement for TLR4- and MyD88-mediated signaling for responses to new allergens. Furthermore, we characterized the mechanisms by which IL-4 primes for new inhaled allergens: "IL-4-dependent pulmonary priming" relies on IL-4 receptor expression on hematopoietic cells and structural cells. Transfer experiments indicate that within the hematopoietic compartment both T cells and dendritic cells need to express the IL-4 receptor. Finally, we were able to show that IL-4 induces recruitment and maturation of myeloid dendritic cells in vivo and increases T cell recruitment to the draining lymph nodes. Our findings bring new mechanistic knowledge to the phenomenon of polysensitization and primary sensitization in asthma.

Interferon-lambda1 (interleukin-29) preferentially down-regulates interleukin-13 over other T helper type 2 cytokine responses in vitro

Interferon (IFN)-lambda1 [interleukin (IL)-29] is a member of the interferon lambda family (also known as type III interferons), whose members are distantly related to both the type I interferons and members of the IL-10 family. While IFN-lambda1 has significant antiviral activity, it is also becoming apparent that it has important immunoregulatory properties, especially with regard to the T helper type 2 (Th2) response. Previously, we have shown that IFN-lambda1 is capable of down-regulating IL-13 production in an IFN-gamma-independent manner and that this is mediated in part via monocyte-derived dendritic cells. Here, we have extended our knowledge of IFN-lambda1 regulation of the human in vitro Th2 response by examining the regulation of three major Th2 cytokines, IL-4, IL-5 and IL-13, by IFN-lambda1. Our results reveal that IFN-lambda1 preferentially inhibits IL-13 production, compared with IL-4 or IL-5. Levels of IL-13 mRNA, the amount of secreted IL-13 protein and numbers of IL-13-positive CD3(+) CD4(+) cells were all significantly diminished by IFN-lambda1. IFN-lambda1 significantly decreased some aspects of IL-4 and IL-5 production, but its effects were not as consistent as those seen on IL-13. IFN-lambda1 was also effective at decreasing IL-13 secretion under conditions designed to support the generation of Th2 cells. Irrespective of whether Concanavalin-A or T-cell-stimulatory microbeads were used, IFN-lambda1 markedly diminished IL-13 secretion in cultures where IL-4 had been added. Thus, IFN-lambda1 appears to be an inhibitor of human Th2 responses whose action is primarily directed towards IL-13 but which may also affect Th2 responses generally and does not invoke a complementary elevation of IFN-gamma secretion.

New insights into the roles of Stat5a/b and Stat3 in T cell development and differentiation

T cell development and differentiation is carefully orchestrated by a series of cytokines. The importance of STAT family proteins in mediating signals by these cytokines is well-known, but new information on the role of STATs in novel aspects of T cell function and T cell subsets continues to accumulate. Recent studies have placed Stat5a/b and Stat3 center stage in T cell development and differentiation. Stat5a/b are indispensable in T regulatory (Treg) cell development and maintenance, and negatively regulate T helper 17 (Th17) cell differentiation. Conversely, Stat3 is essential for Th17 differentiation and inhibits Treg cells. The balance of Treg and Th17 cells is thought to be critical in maintaining immune tolerance, while preserving effective host defense. Therefore, Stat5a/b and Stat3 are emerging to be key players in T cell differentiation and homeostasis.

Exosomes as a tumor immune escape mechanism: possible therapeutic implications

Advances in cancer therapy have been substantial in terms of molecular understanding of disease mechanisms, however these advances have not translated into increased survival in the majority of cancer types. One unsolved problem in current cancer therapeutics is the substantial immune suppression seen in patients. Conventionally, investigations in this area have focused on antigen-nonspecific immune suppressive molecules such as cytokines and T cell apoptosis inducing molecules such as Fas ligand. More recently, studies have demonstrated nanovesicle particles termed exosomes are involved not only in stimulation but also inhibition of immunity in physiological conditions. Interestingly, exosomes secreted by cancer cells have been demonstrated to express tumor antigens, as well as immune suppressive molecules such as PD-1L and FasL. Concentrations of exosomes from plasma of cancer patients have been associated with spontaneous T cell apoptosis, which is associated in some situations with shortened survival. In this paper we place the "exosome-immune suppression" concept in perspective of other tumor immune evasion mechanisms. We conclude by discussing a novel therapeutic approach to cancer immune suppression by extracorporeal removal of exosomes using hollow fiber filtration technology

Pre-assembly of STAT4 with the human IFN-alpha/beta receptor-2 subunit is mediated by the STAT4 N-domain

CD4(+) T cells regulate adaptive responses to pathogens by secreting unique subsets of cytokines that mediate inflammatory processes. The innate cytokines IL-12 and IFN-alpha/beta regulate type I responses and promote acute IFN-gamma secretion through the activation of the STAT4 transcription factor. Although IL-12-induced STAT4 activation is a conserved pathway across species, IFN-alpha/beta-dependent STAT4 phosphorylation does not occur as efficiently in mice as it does in human T cells. In order to understand this species-specific pathway for IFN-alpha/beta-dependent STAT4 activation, we have examined the molecular basis of STAT4 recruitment by the human IFNAR. In this report, we demonstrate that the N-domain of STAT4 interacts with the cytoplasmic domain of the human, but not the murine IFNAR2 subunit. This interaction mapped to a membrane-proximal segment of the hIFNAR2 spanning amino acids 299-333. Deletion of this region within the hIFNAR2 completely abolishes IFN-alpha/beta-dependent STAT4 tyrosine phosphorylation when expressed in human IFNAR2-deficient fibroblasts. Thus, the human IFNAR2 cytoplasmic domain serves to link STAT4 to the IFNAR as a pre-assembled complex that facilitates cytokine-driven STAT4 activation.

Favored T helper 1 response in a mouse model of hepatosteatosis is associated with enhanced T cell-mediated hepatitis

Steatohepatitis enhances the severity of liver injury caused by acute inflammation. The purpose of this study was to test the hypothesis that fatty liver due to chronic choline-deficient diet exacerbates concanavalin A (ConA)-induced liver hepatitis, which is predominantly facilitated by T cells. Male C57BL/6 mice were fed either control choline-sufficient diet (CSD) or choline-deficient diet (CDD) for 6 weeks before ConA administration. Mice were sacrificed 3, 9, and 24 hours after ConA injection. Liver injury measured by aspartate aminotransferase (AST), alanine aminotransferase (ALT), pathology, and terminal deoxynucleotidyl transferase-mediated nick-end labeling (TUNEL) staining was minimal in mice fed either diet before ConA exposure. However, ConA-induced liver injury was significantly greater in CDD-fed mice compared with control-fed mice. Liver cytokines were assessed by quantitative real-time polymerase chain reaction (PCR). The expression of T helper (Th) 1 cytokines tumor necrosis factor alpha (TNF-alpha), interleukin 12 (IL-12), and interferon gamma (IFN-gamma) were dramatically elevated after ConA in CDD-fed mice compared with control-fed mice. CDD also enhanced ConA-induced STAT4 activation, but not STAT6. Notably, regulators of T-cell differentiation were strongly shifted toward a predominant Th1 profile. T-bet, regulator of the Th1 response, was up-regulated in CDD-fed mice, whereas Th2 regulator GATA-3 was significantly suppressed in CDD-fed mice after ConA. Moreover, the expression of suppressor of cytokine signaling (SOCS)-1, SOCS-3, and repressor of GATA-3 (ROG) favored a predominant Th1 cytokine response in CDD-fed mice. In conclusion, these data support the hypothesis that hepatosteatosis caused by CDD is associated with more severe ConA-induced hepatitis due to a predominant shift toward Th1 response.

Quantitative PCR on 5 genes reliably identifies CTCL patients with 5% to 99% circulating tumor cells with 90% accuracy

We previously identified a small number of genes using cDNA arrays that accurately diagnosed patients with Sézary Syndrome (SS), the erythrodermic and leukemic form of cutaneous T-cell lymphoma (CTCL). We now report the development of a quantitative real-time polymerase chain reaction (qRT-PCR) assay that uses expression values for just 5 of those genes: STAT4, GATA-3, PLS3, CD1D, and TRAIL. qRT-PCR data from peripheral blood mononuclear cells (PBMCs) accurately classified 88% of 17 patients with high blood tumor burden and 100% of 12 healthy controls in the training set using Fisher linear discriminant analysis (FLDA). The same 5 genes were then assayed on 56 new samples from 49 SS patients with blood tumor burdens of 5% to 99% and 69 samples from 65 new healthy controls. The average accuracy over 1000 resamplings was 90% using FLDA and 88% using support vector machine (SVM). We also tested the classifier on 14 samples from patients with CTCL with no detectable peripheral involvement and 3 patients with atopic dermatitis with severe erythroderma. The accuracy was 100% in identifying these samples as non-SS patients. These results are the first to demonstrate that gene expression profiling by quantitative PCR on a selected number of critical genes can be employed to molecularly diagnosis SS.

Issues in T-helper 1 development--resolved and unresolved

T-helper 1 cell (Th1) development participates in immunity to many pathogens in part by providing a source of interferon (IFN)-gamma that contributes numerous protective effects. The process of Th1 development involves signals provided by antigen-presenting cells and cytokines produced in response to pathogens, with IFN-gamma itself, interleukin (IL)-12, and IL-18 each promoting the process in some way. Despite the rapid progress into mechanisms of Th1 development in recent years, there are still a number of important unresolved issues in this area. The precise sequence of effector and cellular mechanisms represents a relatively recent avenue of research but is still the subject of current debate, as is the basis of mechanisms that may stabilize a Th1 response. Another unresolved issue is the role of type I IFNs in substituting for IL-12-mediated activation of signal transducer and activator of transcription 4 (Stat4) and induction of IFN-gamma in either murine or human T cells. It is now clear that Th1 cells acquire the property of being capable of nonantigen-dependent activation through the coordinate signaling of IL-12 and IL-18, but the precise order of intracellular signaling events and the uniqueness of this pathway's reliance on the p38 mitogen-activated protein kinase (MAPK) pathway are still issues in need of resolution. Finally, the process of verifying the effects of Stat4 mutations on functional responses has led to the recognition of an unexpected action of the STAT N-domain that may apply generally to other STAT proteins as well. None of these areas is static or resolved fully, and they likely will remain topics of rapid progress.

Unique gene expression program of human germinal center T helper cells

Gene expression profiling was used to compare the gene expression patterns of human germinal center (GC) T helper (Th) cells with other CD4+ T-cell subsets (naive, central, and effector memory T cells). GC-Th cells, specifically localized in germinal centers to help B cells, are distantly related to central and effector memory T cells in global gene expression profiles. GC-Th cells displayed substantial differences in mRNA for adhesion molecules, chemoattractant receptors, and cytokines compared with other populations. Distinct expression of transcriptional factors by GC-Th cells is consistent with the hypothesis that they may be different from other T cells in cell lineage. Interestingly, CXCL13, a critical chemokine for B-cell entry to lymphoid follicles, is one of the most highly up-regulated genes in GC-Th cells. GC-Th cells (but not other T cells) produce and secrete large amounts of functional CXCL13 upon T-cell receptor activation, a process that is dependent on costimulation, requires translation and transcription, and is dramatically enhanced by activation in the presence of GC-B cells. This study revealed for the first time the unique gene expression program of GC-Th cells.

Genetic approaches to assessing evidence for a T helper type 1 cytokine defect in adult asthma

Recent evidence suggests that deficiency in the Th1 cytokine pathway may underlie the susceptibility to allergic asthma. This study examined whether (1) single-nucleotide polymorphisms exist in the promoter region of the two interleukin (IL)-12 subunit genes in patients with asthma; (2) messenger RNA and protein expressions of signal transducers and activators of transcription, IL-12, IFN-gamma, and their receptors are altered in asthma; and (3) linkage to genes in the Th1 pathway is present in families with asthma in Iceland. The promoter regions of the IL-12 subunit genes were sequenced in 94 patients with asthma and 94 control subjects without asthma. Linkage was examined in 169 families that included over 570 patients with asthma and 950 of their unaffected relatives. The results demonstrate no evidence of linkage to microsatellite markers in close association with genes within the Th1 pathway, and no polymorphism was detected in the promoter regions of the two IL-12 subunit genes in the cohort with asthma patients. Moreover, we found no differences in the messenger RNA or protein expression signals of genes in the IL-12 pathway between the patients and control subjects. We conclude that decrease in Th1 type cytokine response is unlikely to present a primary event in asthma.

IFN-alpha enhances CD40 ligand-mediated activation of immature monocyte-derived dendritic cells

Type I IFN are immune modulatory cytokines that are secreted during early stages of infection. Type I IFN bridge the innate and the adaptive immune system in humans and mice. We compared the capacity of type I and II IFN to induce the functional maturation of monocyte-derived dendritic cells (MoDC). Extending our earlier observation that type I IFN promote DC maturation, we report that these cytokines also enhance DC differentiation by augmenting CD40 ligand (CD40L)-induced cytokine secretion by MoDC. Type I IFN alone were poor inducers of MoDC maturation as compared with other stimuli. They up-regulated the expression of HLA-DR, CD80, CD86, partially CCR7 but not CD83, partially reduced antigen-uptake function, increased the levels of IL-12p35 mRNA, and prolonged surface expression of peptide-MHC class I complexes for presentation to cytotoxic T lymphocytes, but did not induce migration towards CCL21 chemokine. However, type I IFN were potent co-factors for CD40L-mediated function. Here, they enhanced CD40L-mediated IL-6, IL-10 and IL-12p70 secretion. Furthermore, when combined with IL-1beta and/or IL-4, IFN-alpha2a type I IFN increased CD40L-mediated IL-12p70 production by 2- to 3-fold, and biased the IL-12 p40/p70 ratio towards the IFN-gamma inducing p70 heterodimer, this correlating with higher levels of IFN-gamma secretion by allogeneic T cell subsets and NK cells. Our results suggest that the rapid expression of CD40L, IFN and IL-1beta at sites of infection and inflammation can act in concert on immature DC, thereby linking innate and adaptive immune responses. In this way, type I IFN play a dual role as DC maturation factors and enhancers of CD40L-mediated DC activation.

Regulation of signal transducer and activator of transcription and suppressor of cytokine-signaling gene expression in the brain of mice with astrocyte-targeted production of interleukin-12 or experimental autoimmune encephalomyelitis

Interleukin (IL)-12 and interferon (IFN)-gamma are implicated in the pathogenesis of immune disorders of the central nervous system (CNS). To define the basis for the actions of these cytokines in the CNS, we examined the temporal and spatial regulation of key signal transducers and activators of transcription (STATs) and suppressors of cytokine signaling (SOCS) in the brain of transgenic mice with astrocyte production of IL-12 or in mice with experimental autoimmune encephalomyelitis (EAE). In healthy mice, with the exception of STAT4 and STAT6, the expression of a number of STAT and SOCS genes was detectable. However, in symptomatic transgenic mice and in EAE significant up-regulation of STAT1, STAT2, STAT3, STAT4, IRF9, and SOCS1 and SOCS3 RNA transcripts was observed. Although the increased expression of STAT1 RNA was widely distributed and included neurons, astrocytes, and microglia, STAT4 and STAT3 and SOCS1 and SOCS3 RNA was primarily restricted to the infiltrating mononuclear cell population. The level and location of the STAT1, STAT3, and STAT4 proteins overlapped with their corresponding RNA and additionally showed nuclear localization indicative of activation of these molecules. Thus, in both the glial fibrillary acidic protein-IL-12 mice and in EAE the CNS expression of key STAT and SOCS genes that regulate IL-12 (STAT4) and IFN-gamma (STAT1, SOCS1, and SOCS3) receptor signaling is highly regulated and compartmentalized. We conclude the interaction between these positive and negative signaling circuits and their distinct cellular locations likely play a defining role in coordinating the actions of IL-12 and IFN-gamma during the pathogenesis of type 1 immune responses in the CNS.

Immunomodulatory role of endogenous interleukin-18 in gamma interferon-mediated resolution of replicative Legionella pneumophila lung infection

The in vivo role of endogenous interleukin-18 (IL-18) in modulating gamma interferon (IFN-gamma)-mediated resolution of replicative Legionella pneumophila lung infection was assessed using a murine model of Legionnaires' disease. Intratracheal inoculation of A/J mice with virulent bacteria (10(6) L. pneumophila organisms per mouse) resulted in induction of IL-18 protein in bronchoalveolar lavage fluid (BALF) and intrapulmonary expression of IL-18 mRNA. Real-time quantitative RT-PCR analysis of infected lung tissue demonstrated that induction of IL-18 in BALF preceded induction of IL-12 and IFN-gamma mRNAs in the lung. Blocking intrapulmonary IL-18 activity by administration of a monoclonal antibody (MAb) to the IL-18 receptor (anti-IL-18R MAb) prior to L. pneumophila infection inhibited induction of intrapulmonary IFN-gamma production but did not significantly alter resolution of replicative L. pneumophila lung infection. In contrast, blocking endogenous IL-12 activity by administration of anti-IL-12 MAb) alone or in combination with anti-IL-18R MAb inhibited induction of intrapulmonary IFN-gamma and resulted in enhanced intrapulmonary growth of the bacteria within 5 days postinfection. Taken together, these results demonstrate that IL-18 plays a key role in modulating induction of IFN-gamma in the lung in response to L. pneumophila and that together with IL-12, IL-18 regulates intrapulmonary growth of the bacteria.

T helper type 2 cell differentiation occurs in the presence of interleukin 12 receptor beta2 chain expression and signaling

The differentiation of CD4(+) T cells into T helper type 1 (Th1) cells is driven by interleukin (IL)-12 through the IL-12 receptor beta2 (IL-12Rbeta2) chain, whereas differentiation into Th2 cells is driven by IL-4, which downregulates IL-12Rbeta2 chain. We reexamined such differentiation using IL-12Rbeta2 chain transgenic mice. We found that CD4(+) T cells from such mice were able to differentiate into Th2 cells when primed with IL-4 or IL-4 plus IL-12. In the latter case, the presence of IL-4 suppressed interferon (IFN)-gamma production 10-100-fold compared with cells cultured in IL-12 alone. Finally, in studies of the ability of IL-12 to convert Th2 cells bearing a competent IL-12R to the Th1 cells, we showed that: (a) T cells bearing the IL-12Rbeta2 chain transgene and primed under Th2 conditions could not be converted to Th1 cells by repeated restimulation under Th1 conditions; and (b) established Th2 clones transfected with the IL-12Rbeta2 chain construct continued to produce IL-4 when cultured with IL-12. These studies show that IL-4-driven Th2 differentiation can occur in the presence of persistent IL-12 signaling and that IL-4 inhibits IFN-gamma production under these circumstances. They also show that established Th2 cells cannot be converted to Th1 cells via IL-12 signaling.

Vitamin D and autoimmunity: is vitamin D status an environmental factor affecting autoimmune disease prevalence?

The environment in which the encounter of antigen with the immune system occurs determines whether tolerance, infectious immunity, or autoimmunity results. Geographical areas with low supplies of vitamin D (for example Scandinavia) correlate with regions with high incidences of multiple sclerosis, arthritis, and diabetes. The active form of vitamin D has been shown to suppress the development of autoimmunity in experimental animal models. Furthermore, vitamin D deficiency increases the severity of at least experimental autoimmune encephalomyelitis (mouse multiple sclerosis). Targets for vitamin D in the immune system have been identified, and the mechanisms of vitamin D-mediated immunoregulation are beginning to be understood. This review discusses the possibility that vitamin D status is an environmental factor, which by shaping the immune system affects the prevalence rate for autoimmune diseases such as multiple sclerosis, arthritis, and juvenile diabetes.

Th1/Th2 balance in infection

Cytokines produced by T helper (Th) cells are of critical importance for the outcome of many infectious diseases. Producing the "right" set of cytokines in response to an infectious agent can be a matter of life or death. The Th1/Th2 dichotomy, although an oversimplification has proven useful in the analysis of immune responses to infections. In some infectious diseases, most notably leishmaniasis or infections with gastrointestinal helminths, one Th subset is indispensable for clearing the infection, whereas the opposite Th subset is detrimental. More frequently, both Th1 and Th2 responses are required at different time points to effectively eradicate an infectious agent. The granuloma responses to either Mycobacterium tuberculosis or Schistosoma mansoni provide illustrative examples and are discussed in this review. There is accumulating evidence for frequent coexpression of Th1 and Th2 cytokines during the in vivo immune response to infections. The mechanisms by which infectious agents modulate Th1/Th2 phenotype development are summarized here. Finally, we review here the current evidence for cytokine imbalances induced by infections as pathogenic or protective factors in autoimmunity and allergy.