T Cells With Activated STAT4 Drive the High-Risk Rejection State to Renal Allograft Failure After Kidney Transplantation

In kidney transplantation, deteriorated progression of rejection is considered to be a leading course of postoperative mortality. However, the conventional histologic diagnosis is limited in reading the rejection status at the molecular level, thereby triggering mismatched pathogenesis with clinical phenotypes. Here, by applying uniform manifold approximation and projection and Leiden algorithms to 2,611 publicly available microarray datasets of renal transplantation, we uncovered six rejection states with corresponding signature genes and revealed a high-risk (HR) state that was essential in promoting allograft loss. By identifying cell populations from single-cell RNA sequencing data that were associated with the six rejection states, we identified a T-cell population to be the pathogenesis-triggering cells associated with the HR rejection state. Additionally, by constructing gene regulatory networks, we identified that activated STAT4, as a core transcription factor that was regulated by PTPN6 in T cells, was closely linked to poor allograft function and prognosis. Taken together, our study provides a novel strategy to help with the precise diagnosis of kidney allograft rejection progression, which is powerful in investigating the underlying molecular pathogenesis, and therefore, for further clinical intervention.

Sustained Post-Developmental T-Bet Expression Is Critical for the Maintenance of Type One Innate Lymphoid Cells In Vivo

Innate lymphoid cells (ILC) play a significant role in the intestinal immune response and T-bet+ CD127+ group 1 cells (ILC1) have been linked to the pathogenesis of human inflammatory bowel disease (IBD). However, the functional importance of ILC1 in the context of an intact adaptive immune response has been controversial. In this report we demonstrate that induced depletion of T-bet using a Rosa26-Cre-ERT2 model resulted in the loss of intestinal ILC1, pointing to a post-developmental requirement of T-bet expression for these cells. In contrast, neither colonic lamina propria (cLP) ILC2 nor cLP ILC3 abundance were altered upon induced deletion of T-bet. Mechanistically, we report that STAT1 or STAT4 are not required for intestinal ILC1 development and maintenance. Mice with induced deletion of T-bet and subsequent loss of ILC1 were protected from the induction of severe colitis in vivo. Hence, this study provides support for the clinical development of an IBD treatment based on ILC1 depletion via targeting T-bet or its downstream transcriptional targets.

Type I Interferon-Activated STAT4 Regulation of Follicular Helper T Cell-Dependent Cytokine and Immunoglobulin Production in Lupus

OBJECTIVE

To assess the role of STAT4 activation in driving pathogenic follicular helper T (Tfh) cell secretion of the cytokines interleukin-21 (IL-21) and interferon-γ (IFNγ) in murine and human lupus.

METHODS

The effect of STAT4-dependent Tfh cell signaling on cytokine production and autoreactive B cell maturation was assessed temporally during the course of lupus in a murine model, with further assessment of Tfh cell gene transcription performed using RNA-Seq technology. STAT4-dependent signaling and cytokine production were also determined in circulating Tfh-like cells in patients with systemic lupus erythematosus (SLE), as compared to cells from healthy control subjects, and correlations with disease activity were assessed in the Tfh-like cells from SLE patients.

RESULTS

IL-21- and IFNγ-coproducing Tfh cells expanded prior to the detection of potentially pathogenic IgG2c autoantibodies in lupus-prone mice. Tfh cells transcriptionally evolved during the course of disease with acquisition of a STAT4-dependent gene signature. Maintenance of Tfh cell cytokine synthesis was dependent upon STAT4 signaling, driven by type I IFNs. Circulating Tfh-like cells from patients with SLE also secreted IL-21 and IFNγ, with STAT4 phosphorylation enhanced by IFNβ, in association with the extent of clinical disease activity.

CONCLUSION

We identified a role for type I IFN signaling in driving STAT4 activation and production of IL-21 and IFNγ by Tfh cells in murine and human lupus. Enhanced STAT4 activation in Tfh cells may underlie pathogenic B cell responses in both murine and human lupus. These data indicate that STAT4 guides pathogenic cytokine and immunoglobulin production in SLE, demonstrating a potential therapeutic target to modulate autoimmunity.

T-Bet Controls Cellularity of Intestinal Group 3 Innate Lymphoid Cells

Innate lymphoid cells (ILC) play a significant immunological role at mucosal surfaces such as the intestine. T-bet-expressing group 1 innate lymphoid cells (ILC1) are believed to play a substantial role in inflammatory bowel disease (IBD). However, a role of T-bet-negative ILC3 in driving colitis has also been suggested in mouse models questioning T-bet as a critical factor for IBD. We report here that T-bet deficient mice had a greater cellularity of NKp46-negative ILC3 correlating with enhanced expression of RORγt and IL-7R, but independent of signaling through STAT1 or STAT4. We observed enhanced neutrophilia in the colonic lamina propria (cLP) of these animals, however, we did not detect a greater risk of T-bet-deficient mice to develop spontaneous colitis. Furthermore, by utilizing an in vivo fate-mapping approach, we identified a population of T-bet-positive precursors in NKp46-negative ILC3s. These data suggest that T-bet controls ILC3 cellularity, but does do not drive a pathogenic role of ILC3 in mice with a conventional specific pathogen-free microbiota.

Immune Suppression Mediated by STAT4 Deficiency Promotes Lymphatic Metastasis in HNSCC

Head and neck squamous cell carcinoma (HNSCC) is a prevalent form of cancer with 5-years survival rates around 57%, and metastasis is a leading cause of mortality. Host-derived immunological factors that affect HNSCC tumor development and metastasis are not completely understood. We investigated the role of host-derived signal transducer and activator of transcription 4 (STAT4) during experimental HNSCC using an aggressive and metastatic HNSCC cell line, LY2, which was orthotopically injected into the buccal sulcus of wild type (WT) and STAT4 deficient (Stat4-/-) BALB/c mice. Necropsies performed at terminal sacrifice revealed that Stat4-/- mice displayed comparable primary tumor growth to the WT mice. However, the rate and extent of lymph node and lung metastasis among Stat4-/- mice was significantly higher. Downstream analyses performed on primary tumors, draining lymph nodes, spleens and bone marrow revealed significant upregulation of lymphocytic immunosuppressive biomarkers as well as an accumulation of granulocytic MDSC subpopulations in draining lymph nodes of metastatic Stat4-/- mice. Further, we observed a significant decrease in TH1, TH17, and cytotoxic activity in tumor bearing Stat4-/- compared to WT mice. Our results demonstrate that STAT4 mediates resistance to HNSCC metastasis, and activation of STAT4 could potentially mitigate lymphatic metastasis in HNSCC patients.

Altered effector functions of NK cells in chronic hepatitis C are associated with IFNL3 polymorphism

Interferon α-mediated effector functions of NK cells may contribute to the control of HCV replication and the pathogenesis of liver disease. The single-nucleotide polymorphism rs12979860 near IFNL3 (previously known as IL28B) is important in response to IFN-α treatment and in spontaneous resolution of acute hepatitis C. The role of the IFNL3 polymorphism in NK cell function is unclear. Thus, we investigated the role of IFNL3 polymorphism in type I IFN-dependent regulation of NK cell functions in patients with cHC and healthy control subjects. We demonstrated a marked polarization of NK cells toward cytotoxicity in response to IFN-α stimulation in patients with hepatitis C. That TRAIL up-regulation was present, particularly in patients with the IFNL3-TT allele, was supported by a shift in the pSTAT-1:pSTAT-4 ratios toward pSTAT-1. In patients bearing the IFNL3-TT allele, NK cell effector function correlated with liver disease activity. In contrast, higher cytokine production of NK cells was observed in healthy individuals with the IFNL3-CC genotype, which may support spontaneous HCV clearance in acute infection. Overall, these findings show that the role of NK cells may differ in chronic infection vs. early antiviral defense and that the IFNL3 genotype differentially influences NK cell function.

Interleukin-12: Functional activities and implications for disease

Interleukin-12 (IL-12) was the first member of the IL-12 family of cytokines to be identified and has therefore become its eponym. It is a heterodimeric protein of two subunits (p35, p40) secreted by phagocytic cells in response to pathogens and mainly acts through STAT4 to induce IFN-γ production in T and NK cells. IFN-γ in turn mediates proinflammatory functions and activates T-bet. As IL-12 engages in TH1 development, it is believed to represent an important link between innate and adaptive immunity. Following its identification and the finding of its association to TH1 commitment, great hopes were placed in IL-12 to become a target for therapeutic applications in multiple settings of autoimmunity and cancer. Though, the discovery of the related members of the IL-12 family and several rather disappointing attempts to translate experimental results into clinical practice, have relativized these hopes. Nevertheless, IL-12 remains a cytokine of outstanding importance with lots of unresolved questions. In this review, we will first briefly depict the biochemistry of the cytokine, its receptor and the related signal transduction, before summarizing the regulation of IL-12 production and its biological functions. We will then describe the current knowledge about the implication of IL-12 in different murine disease models as well as in the corresponding human conditions and comment on possible consequences for future clinical applications.

Protein kinase C θ regulates the phenotype of murine CD4+ Th17 cells

Protein kinase C θ (PKCθ) is involved in signaling downstream of the T cell antigen receptor (TCR) and is important for shaping effector T cell functions and inflammatory disease development. Acquisition of Th1-like effector features by Th17 cells has been linked to increased pathogenic potential. However, the molecular mechanisms underlying Th17/Th1 phenotypic instability remain largely unknown. In the current study, we address the role of PKCθ in differentiation and function of Th17 cells by using genetic knock-out mice. Implementing in vitro (polarizing T cell cultures) and in vivo (experimental autoimmune encephalomyelitis model, EAE) techniques, we demonstrated that PKCθ-deficient CD4⁺ T cells show normal Th17 marker gene expression (interleukin 17A/F, RORγt), accompanied by enhanced production of the Th1-typical markers such as interferon gamma (IFN-γ) and transcription factor T-bet. Mechanistically, this phenotype was linked to aberrantly elevated Stat4 mRNA levels in PKCθ^−/− CD4⁺ T cells during the priming phase of Th17 differentiation. In contrast, transcription of the Stat4 gene was suppressed in Th17-primed wild-type cells. This change in cellular effector phenotype was reflected in vivo by prolonged neurological impairment of PKCθ-deficient mice during the course of EAE. Taken together, our data provide genetic evidence that PKCθ is critical for stabilizing Th17 cell phenotype by selective suppression of the STAT4/IFN-γ/T-bet axis at the onset of differentiation.

Further evidence of subphenotype association with systemic lupus erythematosus susceptibility loci: a European cases only study

Introduction

Systemic Lupus Erythematosus (SLE) shows a spectrum of clinical manifestations that complicate its diagnosis, treatment and research. This variability is likely related with environmental exposures and genetic factors among which known SLE susceptibility loci are prime candidates. The first published analyses seem to indicate that this is the case for some of them, but results are still inconclusive and we aimed to further explore this question.

Methods

European SLE patients, 1444, recruited at 17 centres from 10 countries were analyzed. Genotypes for 26 SLE associated SNPs were compared between patients with and without each of 11 clinical features: ten of the American College of Rheumatology (ACR) classification criteria (except ANAs) and age of disease onset. These analyses were adjusted for centre of recruitment, top ancestry informative markers, gender and time of follow-up. Overlap of samples with previous studies was excluded for assessing replication.

Results

There were three new associations: the SNPs in XKR6 and in FAM167A-BLK were associated with lupus nephritis (OR = 0.76 and 1.30, P_corr = 0.007 and 0.03, respectively) and the SNP of MECP2, which is in chromosome X, with earlier age of disease onset in men. The previously reported association of STAT4 with early age of disease onset was replicated. Some other results were suggestive of the presence of additional associations. Together, the association signals provided support to some previous findings and to the characterization of lupus nephritis, autoantibodies and age of disease onset as the clinical features more associated with SLE loci.

Conclusion

Some of the SLE loci shape the disease phenotype in addition to increase susceptibility to SLE. This influence is more prominent for some clinical features than for others. However, results are only partially consistent between studies and subphenotype specific GWAS are needed to unravel their genetic component.

T-bet(+) Treg cells undergo abortive Th1 cell differentiation due to impaired expression of IL-12 receptor β2

Foxp3⁺ regulatory T (Treg) cells limit inflammatory responses and maintain immune homeostasis. Although comprised of several phenotypically and functionally distinct subsets, the differentiation of specialized Treg cell populations within the periphery is poorly characterized. We demonstrate that the development of T-bet⁺ Treg cells that potently inhibit T helper 1 (Th1) cell responses was dependent on the transcription factor STAT1 and occurred directly in response to interferon-γ produced by effector T cells. Additionally, delayed induction of the IL-12Rβ2 receptor component after STAT1 activation helped ensure that Treg cells do not readily complete STAT4-dependent Th1 cell development and lose their ability to suppress effector T cell proliferation. Thus, we define a pathway of abortive Th1 cell development that results in the specialization of peripheral Treg cells and demonstrate that impaired expression of a single cytokine receptor helps maintain Treg cell-suppressive function in the context of inflammatory Th1 cell responses.

STAT4 regulates antiviral gamma interferon responses and recurrent disease during herpes simplex virus 2 infection

STAT4 is an important transcription factor that contributes to the incidence and severity of different autoimmune diseases and is implicated in the antiviral immune responses in mice. In this study, we evaluated the role of STAT4 in human and murine herpes simplex virus 2 (HSV-2) infections. We show that STAT4 regulates antiviral gamma interferon (IFN-γ) responses and disease severity during chronic HSV-2 infections in humans and vaccine-induced IFN-γ-mediated protection against HSV-2 infection in mice. In a cohort of 228 HSV-2-infected individuals, representing both patients with recurrent disease and asymptomatic HSV-2 carriers, we found that genetic variations in the STAT4 gene were associated with asymptomatic HSV-2 infection, as well as with increased in vitro secretion of IFN-γ in response to the virus. Mice that lacked STAT4 had impaired HSV-2-specific IFN-γ production and delayed-type hypersensitivity responses following vaccination, which led to impaired viral clearance in the genital tract of vaccinated animals after a genital HSV-2 challenge. We conclude that STAT4 plays an important role in IFN-γ-mediated HSV-2-specific immunity, affecting the severity of genital HSV-2 infection.

The composition and signaling of the IL-35 receptor are unconventional

Interleukin 35 (IL-35) belongs to the IL-12 family of heterodimeric cytokines but has a distinct functional profile. IL-35 suppresses T cell proliferation and converts naive T cells into IL-35-producing induced regulatory T cells (iTr35 cells). Here we found that IL-35 signaled through a unique heterodimer of receptor chains IL-12Rβ2 and gp130 or homodimers of each chain. Conventional T cells were sensitive to IL-35-mediated suppression in the absence of one receptor chain but not both receptor chains, whereas signaling through both chains was required for IL-35 expression and conversion into iTr35 cells. Signaling through the IL-35 receptor required the transcription factors STAT1 and STAT4, which formed a unique heterodimer that bound to distinct sites in the promoters of the genes encoding the IL-12 subunits p35 and Ebi3. This unconventional mode of signaling, distinct from that of other members of the IL-12 family, may broaden the spectrum and specificity of IL-35-mediated suppression.

Early changes in interferon signaling define natural killer cell response and refractoriness to interferon-based therapy of hepatitis C patients

Natural killer (NK) cells exhibit a polarized phenotype with increased cytotoxicity and decreased interferon gamma (IFN-γ) production in chronic hepatitis C virus (HCV) infection. Here, we asked whether this is caused by type I interferon (IFN)-induced expression and phosphorylation levels of signal transducer and activator of transcription (STAT) molecules in NK cells and whether it affects the response and refractoriness of NK cells to IFN-α-based therapy of HCV. STAT1 levels in NK cells were significantly higher in patients with chronic HCV infection than in uninfected controls. STAT1 levels and induction of phosphorylated STAT1 (pSTAT1) increased further during IFN-α-based therapy with preferential STAT1 over STAT4 phosphorylation. Induction of pSTAT1 correlated with increased NK cytotoxicity (tumor necrosis factor-apoptosis-inducing ligand [TRAIL] expression and degranulation) and decreased IFN-γ production. NK cells from patients with a greater than 2 log(10) first-phase HCV RNA decline to IFN-α-based therapy (>99% IFN effectiveness) displayed strong pSTAT1 induction in vivo and were refractory to further stimulation in vitro. In contrast, NK cells from patients with a less than 2 log(10) first-phase HCV RNA decline exhibited lower pSTAT1 induction in vivo (P = 0.024), but retained greater IFN-α responsiveness in vitro (P = 0.024). NK cells of all patients became refractory to in vivo and in vitro stimulation by IFN-α during the second-phase virological response.

CONCLUSION

These data show that IFN-α-induced modulation of STAT1/4 phosphorylation underlies the polarization of NK cells toward increased cytotoxicity and decreased IFN-γ production in HCV infection, and that NK cell responsiveness and refractoriness correlate to the antiviral effectiveness of IFN-α-based therapy.

TRAF1/C5, eNOS, C1q, but not STAT4 and PTPN22 gene polymorphisms are associated with genetic susceptibility to systemic lupus erythematosus in Turkey

A significant source of variability in the literature on systemic lupus erythematosus (SLE) susceptibility genes has been the inability to replicate genetic findings across different racial or ethnic groups. We investigated whether a single nucleotide polymorphism (SNP) of the STAT4 (rs7574865), PTPN22 (rs2476601), TRAF1/C5 (rs10818488), and C1q (rs292001) genes as well as the 27-bp VNTR polymorphism on intron 4 of eNOS, previously associated with SLE in other populations, are also associated with SLE risk in Turkey. A group of 158 SLE patients and 155 healthy controls were included in this study. A genetic association of the TRAF1/C5, C1q, and eNOS gene polymorphism, but not of STAT4 and PTPN22, was found to confer a degree of risk for SLE. These data highlight the importance of comparative studies in different populations to confirm the previously detected genetic associations.

Signal transducer and activator of transcription and the risk of rheumatoid arthritis and thyroid autoimmune disorders

OBJECTIVES

The signal transducer and activator of transcription 4 (STAT4) gene localised on chromosome 2q32.2-q32.3 is known to be essential for mediating responses to interleukin 12 in lymphocytes and regulating the differentiation of T helper cells. The aim of this study was to investigate the role of the STAT4 gene in susceptibility to rheumatoid arthritis (RA) and autoimmune thyroid diseases (AITDs) in Tunisian case control studies.

METHODS

Genotyping of STAT4 rs7574865 single nucleotide polymorphism (SNP) was performed in 140 patients affected with RA, 159 patients affected with AITDs and 200 healthy controls using TaqMan® allelic discrimination assay. Data were analysed by χ2-test, genotype relative risk (GRR) and odds ratio (OR).

RESULTS

Our results revealed that frequencies of the T allele and the T/T genotype were significantly higher among RA patients compared to controls (p=0.008; p=0.003, respectively). However, no significant associations with the risk of autoimmune thyroid diseases were detected. Moreover, the stratification of RA patients subgroups revealed a significant association of both T allele and T/T genotype in patients presented erosion (p=0.003; p=0.004, respectively) as well as anti-cyclic peptides-negative RA (ACPA-) (p=0.002; p=0.0003, respectively). Furthermore, genotypic association was found according to the absence of rheumatoid factor antibody (RF) (p=0.0014). But, no significant differences in allele and genotype frequencies of STAT4 rs7574865 polymorphism were detected according to the presence of another autoimmune disease, nodules and in HLA-DRB1*04 and HLA-DRB1*0404 positive subgroups.

CONCLUSIONS

Our results support involvement of the STAT4 gene in the genetic susceptibility to RA but not to AITDs in the Tunisian population.

T-bet, a Th1 transcription factor regulates the expression of Tim-3

T-cell immunoglobulin, mucin domain-3 (Tim-3) is a membrane protein expressed at late stages of IFN-gamma secreting CD4(+) Th1 cell differentiation and constitutively on DC. Ligation of Tim-3 on Th1 cells terminates Th1 immune responses. In addition, Tim-3 plays a role in tolerance induction, although the mechanism by which this is accomplished has yet to be elucidated. While it is clear that Tim-3 plays an important role in the immune system, little is known regarding the molecular pathways that regulate Tim-3 expression. In the current study, we examine the role of Th1-associated transcription factors in regulating Tim-3 expression. Our experiments reveal that Tim-3 expression is regulated by the Th1-specific transcription factor T-bet. This introduces a novel paradigm into the generation of a Th1 response, whereby a transcription factor responsible for effector Th1 cell differentiation also increases the expression of a specific counter-regulatory molecule to ensure appropriate termination of pro-inflammatory Th1 immune responses.

Oral tolerization with cardiac myosin peptide (614-629) ameliorates experimental autoimmune myocarditis: role of STAT 6 genes in BALB/CJ mice

INTRODUCTION

Experimental autoimmune myocarditis (EAM) is mediated by myocardial infiltration by myosin-specific T cells secreting inflammatory cytokines.

MATERIALS AND METHODS

To clarify the role of cytokines in EAM, we compared STAT 6-deficient ((-/-)) with STAT 4(-/-) and wild-type (BALB/CJ) mice following immunization with cardiac myosin peptide (614-629).

RESULTS

Wild-type mice developed severe disease with a small increase in severity in STAT 6(-/-) mice, while STAT 4(-/-) mice were resistant to EAM. STAT 6(-/-) mice had increased splenocyte proliferation and INF-gamma production versus wild type, while STAT 4(-/-) mice had decreased proliferation and INF-gamma. Following oral administration of myosin (614-629), tolerization was induced in wild-type mice evidenced by amelioration of myocarditis and up-regulation of IL-4. Adoptive transfer of splenocytes from orally tolerized mice resulted in inhibition of disease in STAT 6(-/-) mice.

CONCLUSION

These results demonstrate that oral tolerization ameliorates EAM in BALB/CJ mice and indicate a down-regulatory role for STAT 6 genes.

Cytokines, signaling pathways, and effector molecules required for the control of Leishmania (Viannia) braziliensis in mice

Cutaneous leishmaniasis is caused by protozoan parasites of the genus Leishmania. The mechanisms of pathogen control have been established primarily in the mouse model of Leishmania major infection, but they might not hold true for other Leishmania species associated with cutaneous disease. Here, we analyzed the role of cytokines, signaling components, and effector molecules in the control of New World cutaneous leishmaniasis due to L. braziliensis. Unlike L. major, L. braziliensis caused small, nonulcerative, and self-healing skin swelling in C57BL/6 mice, as well as BALB/c mice. In contrast to the results obtained for L. mexicana, mice deficient for interleukin-12 or its key signaling molecule, signal transducer and activator of transcription 4, rapidly succumbed to severe visceral leishmaniasis. Infection of tumor necrosis factor knockout mice with L. braziliensis led to progressive, nonhealing skin lesions with erosions and hemorrhagic ulcerations, but in contrast to the results with L. major, only 20 to 30% of the mice developed fatal visceral disease. As seen with L. major, mice with a deleted inducible nitric oxide synthase gene (iNOS(-/-)) were unable to contain L. braziliensis in the skin, whereas the control of the parasite in the spleen remained unimpaired. Unlike what happens in L. major infections, NADPH oxidase had no impact on the course of disease in L. braziliensis-infected mice. These results not only define essential components of a protective immune response to L. braziliensis but also illustrate that the requirements for the control of cutaneous leishmaniasis vary between different parasite species.

Targeting of the Transcription Factor STAT4 by Antisense Phosphorothioate Oligonucleotides Suppresses Collagen-Induced Arthritis

The transcription factor STAT4 mediates signals of various proinflammatory cytokines, such as IL-12, IL-15, and IL-23, that initiate and stabilize Th1 cytokine production. Although Th1 cytokine production has been suggested to play a major pathogenic role in rheumatoid arthritis, the role of STAT4 in this disease is poorly understood. In this study, we demonstrate a key functional role of STAT4 in murine collagen-induced arthritis (CIA). In initial studies we found that STAT4 expression is strongly induced in CD4(+) T cells and to a lesser extent in CD11b(+) APCs during CIA. To analyze the role of STAT4 for arthritis manifestation, we next investigated the outcome of interfering with STAT4 gene expression in CIA by using STAT4-deficient mice. Interestingly, STAT4-deficient mice developed significantly less severe arthritis than wild-type control mice and the T cells from such mice produced less IL-6, TNF, and IL-17. In addition, the targeting of STAT4 expression by a specific antisense phosphorothioate oligonucleotide directed at the translation start site suppressed STAT4 levels and signs of CIA even when applied during the onset of disease manifestation. These data suggest a key regulatory role of STAT4 in the pathogenesis and manifestation of murine collagen-induced arthritis. Furthermore, the targeting of STAT4 emerges as a novel approach to therapy for chronic arthritis.

Recovery from spinal cord injury in tumor necrosis factor-alpha, signal transducers and activators of transcription 4 and signal transducers and activators of transcription 6 null mice

Tumor necrosis factor-alpha is a central cytokine involved in the regulation of the innate immune response. Signal transducers and activators of transcription 4 and signal transducers and activators of transcription 6 are second messengers mediating the Th1 and Th2-specific immune responses, respectively. We studied the outcome of spinal cord injury with respect to the locomotion and axonal regeneration in tumor necrosis factor-alpha, signal transducers and activators of transcription 4 and signal transducers and activators of transcription 6 knockout mice. Locomotor behavior after injury differed between mouse strains, but not between wild-type and the knockout genotypes of the same strain. Regeneration of descending tracts, assessed by fluorogold/fluororuby retrograde double-labeling, however, appeared hampered by Th2 deficiency.

Microenvironment-dependent requirement of STAT4 for the induction of P-selectin ligands and effector cytokines on CD4+ T cells in healthy and parasite-infected mice

T effector cells require selectin ligands to migrate into inflamed regions. In vitro, IL-12 promotes induction of these ligands as well as differentiation of CD4+ T cells into IFN-gamma-producing Th1 but not Th2 cells. STAT4 is strongly involved in these processes. However, the presence of selectin ligands on various T effector cell subsets in vivo points to more complex regulatory pathways. To clarify the role of the IL-12/STAT4 signaling pathway, we analyzed the impact of STAT4 deficiency on the expression of P-selectin ligands (P-lig) on CD4+ T cells in vitro and in vivo, including conditions of infection. In vitro, we found significant expression of P-lig upon activation not only in the presence, but also in the absence, of IL-12, which was independent of STAT4. TGF-beta, an alternative inducer of selectin ligands in human T cells, was not effective in murine CD4+ T cells, suggesting a role of additional signaling pathways. In vivo, a significant impact of STAT4 for the generation of P-lig+CD4+ T cells was observed for cells from peripheral lymph nodes, but not for those from spleen or lung. However, upon infection with the Th2-inducing parasite Nippostrongylus brasiliensis, P-lig expression became dependent on STAT4 signaling. Interestingly, also the frequency of IL-4-producing cells was greatly diminished in absence of STAT4. These data reveal a hitherto unknown contribution of STAT4 to the generation of Th2 cells in parasite infection and suggest that signals inducing inflammation-seeking properties in vivo vary depending on environmental conditions, such as type of organ and infection.

The STAT4 and STAT6 Pathways in Pancreatitis-Associated Lung Injury

BACKGROUND

The STAT pathways are integral to the inflammatory response and these proteins provide a direct link between the cytokine receptors and cytokine-induced gene transcription. We examined the roles of STAT4 and STAT6 in lung injury after caerulein-induced severe acute pancreatitis. We hypothesized that a modified organ expression of cytokines and chemokines that occurs in transgenic mice may affect the systemic response to severe acute pancreatitis.

METHODS

Acute pancreatitis [13-hourly intraperitoneal injections of caerulein (50 microg/kg body weight, 0.2 mL) or the same volume of saline] was induced in wild-type (BALB/c) and transgenic (STAT4 or STAT6) mice of the same background, 7 to 8 weeks old. The pancreatic and lung tissues were collected at 1, 6, 12, and 24 h after the completion of caerulein administration. Tissue leukocyte sequestration was assessed by myeloperoxidase (MPO) activity. Standard histological staining hematoxylin and eosin was performed and blindly scored by a pathologist for evidence of lung injury (pulmonary edema, accumulations of neutrophils and mononuclear cells, thickness of alveolar-capillary membrane, perivascular infiltrate, and hemorrhage).

RESULTS

Caerulein-treated wild-type mice exhibited increased lung injury score at 1 through 12 h, as compared to saline controls. As compared to wild-type, STAT6-deficient mice had increased lung injury from 1 to 6 h, with full recovery by 12 h. An opposite pattern was observed in STAT4-deficient mice with mild injury seen at 1 and 6 h, and maximal injury at 12 h. MPO activity was significantly increased at 6 h in caerulein-treated wild-type mice compared to saline-treated controls. Caerulein-treated STAT6 and STAT4 mice had markedly increased MPO activity as compared with their saline controls during the first 6 h. Both caerulein-treated STAT4- and STAT6-deficient mice had significantly increased MPO activity in comparison with wild-type mice with pancreatitis at 6 h.

CONCLUSION

We found the maximal lung injury after caerulein-induced pancreatitis occurred at different time-points in STAT4 and STAT6-deficient mice. These temporal differences may suggest alternative roles in the systemic inflammatory response associated with pancreatitis.

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.

Dendritic-cell maturation alters intracellular signaling networks, enabling differential effects of IFN-alpha/beta on antigen cross-presentation

The broad and often contrasting effects of type I interferons (IFNs) in innate and adaptive immunity are belied by the signaling via a single receptor, IFN-alpha receptor (IFNAR). Here, we show that IFN-alpha/beta induces opposing effects on the immunologic outcome of antigen cross-presentation depending on dendritic cell (DC) maturation status. Despite equivalent IFNAR expression, immature conventional DCs (cDCs) activate STAT1 in response to IFN-alpha/beta, whereas exposure of mature DCs to IFN-alpha/beta results in signaling via STAT4. Microarray analysis revealed numerous transcriptional changes resulting from the altered signaling. Importantly, STAT1 signaling resulted in significant inhibition of CD40L-induced IL-12 production, accounting for the inhibition of CD8+ T-cell activation. These data provide evidence for a molecular switch in signaling pathways concomitant with DC maturation that offers a novel mechanism by which DCs modulate the integration of signals from the surrounding environment.

Arthritis induced with cartilage-specific antibodiesis IL-4-dependent

It is widely believed that IL-4 exerts its influence by profiling the immune response during priming and expansion of immune cells, and thereby modulates the outcome of chronic inflammation. In the present investigation, collagen antibody-induced arthritis (CAIA) was used to delineate the role of IL-4 in a T cell-independent inflammatory phase. Mice predisposed to Th2 cytokines (BALB/c and STAT4-deficient mice) developed a more severe arthritis than mice biased towards Th1 cytokines (C57BL/6 and STAT6-deficient mice). Reduced incidence of CAIA was observed in IL-4-deficient mice compared to control littermates. Infiltrating cells in the paws of IL-4-sufficient mice had increased osteoclast activity and tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta secretion. Massive infiltration of granulocytes and joint and cartilage damage were present in arthritic paws. Depletion of IL-4 suppressed CAIA, which was abrogated by IFN-gamma neutralization. IL-1R- and IL-1RTNFR-deficient mice were completely resistant to CAIA. Thus, IL-4 promotes an antibody-mediated and TNF-alpha/IL-1beta-dependent inflammation in vivo.

Activated T cells express the OX40 ligand: requirements for induction and costimulatory function

OX40/OX40 ligand (OX40L) interactions have been shown to exert potent costimulatory effects on T-cell activation. OX40 expression is transiently up-regulated on T cells following T-cell receptor engagement, while OX40L is expressed on antigen-presenting cells following activation. Although expression of the OX40L by T cells has been reported, the requirements for induction of OX40L on T cells have not been studied in detail. Here, we demonstrate that the OX40L can be induced on murine CD4(+) and CD8(+) T cells after 6 days of culture under T helper type 1 (Th1) conditions, but not under Th2 conditions. Induction of OX40L expression required a high concentration of interleukin-12 (IL-12), was not seen in the presence of interferon-gamma, and was dependent on signal transducer and activator of transcription type 4 (STAT4). Notably, induction of OX40L on T cells was only seen at very low concentrations of antigen or anti-CD3. T-cell-expressed OX40L was fully capable of delivering a potent costimulatory signal that enhanced the proliferation of CD4(+) T cells as well as promoted their differentiation to Th2 cells. OX40L expression could also be induced on CD4(+) T cells in vivo following immunization with low-dose antigen and an IL-12 inducer. OX40/OX40L interactions between antigen-specific T cells may occur in T-cell zones in lymph node and spleen when OX40L expression has diminished on APC. Costimulation by T-cell-expressed OX40L may result in deviation of a Th1 response to a Th2 response under conditions where T cells are exposed to low concentrations of foreign or autoantigens in the presence of high concentrations of IL-12.

Stat4-null non-obese diabetic mice: protection from diabetes and experimental allergic encephalomyelitis, but with concomitant epitope spread

There is much interest in therapeutic manipulation of cytokine responses in autoimmunity, yet studies in mouse models have sometimes produced conflicting findings as to the role of particular mediators in disease. Examples include the contradictory findings regarding susceptibility to experimental allergic encephalomyelitis (EAE) or diabetes in knockout mice for various individual Th1 or Th2 cytokines or their receptors. An alternative approach to the analysis of Th1 and Th2 mechanisms in these diseases is to investigate strains carrying a null mutation for molecules involved in cytokine receptor signal transduction, signal transducer and activator of transcription (Stat4) and Stat6. Stat4 is pivotal in Th1 polarization, being activated when IL-12 binds the IL-12R and leading to the production of IFNgamma. We here report disease susceptibility in non-obese diabetic mice carrying a Stat4-null mutation. Knockout mice were almost completely protected from diabetes, only rarely showing pancreatic peri-islet infiltrates. Furthermore, there was near complete protection from the induction of EAE by either of the two encephalitogenic myelin epitopes. Despite this protection, Stat4-null mice showed clear epitope spread compared with controls during myelin oligodendrocyte glycoprotein-induced EAE as judged by T cell proliferation, although this was not associated with a strong Th1 response to the initial or spread epitope and, furthermore, there was no evidence of a switch to Th2 cytokines.