The oncogenic fusion protein-tyrosine kinase ZNF198/fibroblast growth factor receptor-1 has signaling function comparable with interleukin-6 cytokine receptors

The reciprocal t(8;13) chromosome translocation results in a fusion gene (FUS) in which the N-terminal half of the zinc finger protein ZNF198 is combined with the cytoplasmic domain of the fibroblast growth factor receptor-1 (FGFR1). Expression of FUS is suggested to provide growth-promoting activity to myeloid cells similar to the activity of hematopoietic cytokine receptors. This study determined the specificity of FUS to activate signal transduction pathways. Because no tumor cell line expressing FUS was available, the mode of FUS action was identified in cells transiently and stably transfected with an expression vector for FUS. FUS acted as a constitutively active protein-tyrosine kinase and mediated phosphorylation of STAT1, 3, and 5 but not STAT4 and 6. The same specificity but lower activity was determined for normal FGFR1. STAT activation by FUS, similar to that by interleukin-6-type cytokines, promoted STAT-specific induction of genes. The functionality of FUS, as well as the relative recruitment of STAT isoforms, was determined by the dimerizing function of the zinc finger domain. Replacement of the ZNF198 portion by the Bcr portion as present in the t(8;22) translocation shifted the signaling toward a more prominent STAT5 activation. This study documents that both gene partners forming the fusion oncogene define the activity and the signaling specificity of the protein-tyrosine kinase of FGFR1.

Differential contribution of IL-4 and STAT6 vs STAT4 to the development of lupus nephritis

Mechanisms that initiate lupus nephritis and cause progression to end-stage renal disease remain poorly understood. In this study, we show that lupus-prone New Zealand Mixed 2410 mice that develop a severe glomerulosclerosis and rapidly progressive renal disease overexpress IL-4 in vivo. In these mice, STAT6 deficiency or anti-IL-4 Ab treatment decreases type 2 cytokine responses and ameliorates kidney disease, particularly glomerulosclerosis, despite the presence of high levels of IgG anti-dsDNA Abs. STAT4 deficiency, however, decreases type 1 and increases type 2 cytokine responses, and accelerates nephritis, in the absence of high levels of IgG anti-dsDNA Abs. Thus, STAT6 and IL-4 may selectively contribute to the development of glomerulosclerosis, whereas STAT4 may play a role in autoantibody production.

Infection-triggered regulatory mechanisms override the role of STAT 4 in control of the immune response to influenza virus antigens

Accurate control of the balance of the T1 and T2 cells during antiviral immunity is essential for optimizing immune effector functions and for avoiding potentially severe immunopathology. We examined the in vivo role of the signal transducer and activator of transcription (STAT) 4 in regulating the T1/T2 balance during the response to live influenza virus and isolated viral proteins. We found that the differentiation of gamma interferon (IFN-gamma)-producing Th1 and Tc1 cells after inoculation of live virus occurred independently of STAT 4 expression. Influenza virus-specific T2 and Tc2 responses were well controlled in such STAT 4-deficient mice unless IFN-gamma was eliminated as well. In contrast, the STAT 4-dependent signaling pathway played a more essential role in regulating the T1/T2 balance after immunization with viral proteins and, in particular, inactivated nonreplicating virus. Pulmonary infection was cleared even in the absence of both functional STAT 4 genes and functional IFN-gamma genes because virus-neutralizing antibodies were still generated, consistent with a substantial redundancy in different antiviral effector pathways. Thus, replicating agents such as live influenza virus can elicit IFN-gamma and control T2 immunity independently of STAT 4, whereas the profile of immunity to isolated proteins is more reliant on an intact STAT 4 signaling pathway.

CD2 mediates activation of the IFN-gamma intronic STAT binding region in mucosal T cells

The pathways leading to activation of mucosal lamina propria (LP) T cells differ from those of peripheral T cells. LP T cells exhibit enhanced IFN-gamma secretion when activated through the CD2 pathway. This study demonstrates CD2 signaling is followed by activation of STAT proteins in both peripheral blood mononuclear cells (PBMC) and lamina propria mononuclear cells (LPMC), although, distinct differences exist in regulation of IFN-gamma promoter gene expression. Both PBMC and LPMC exhibit enhanced secretion and transactivation of the -2.7 kb IFN-gamma promoter region following CD2 signaling, but the IFN-gamma STAT-binding region (within the first intron) serves as an orientation-independent enhancer of promoter activity only in LPMC. Mutation of the STAT site impairs enhancer activity. In LPMC, but not PBMC, CD2 mediates binding of STAT1 and STAT4 to the IFN-gamma intronic element. Unstimulated LMPC exhibit low levels of phosphotyrosine-STAT4 and STAT1 and phosphoserine-STAT1, which increase substantially following CD2 activation. In PBMC, CD2-mediated phosphorylation is primarily restricted to enhanced levels of phosphotyrosine-STAT1. Thus, these results indicate that both common as well as unique molecular mechanisms are involved in CD2 signaling and activation of the STAT pathway in LP T cells which are critical for regulation of IFN-gamma expression in the gut.

Ligation of OX40 (CD134) regulates graft-versus-host disease (GVHD) and graft rejection in allogeneic bone marrow transplant recipients

OX40 (CD134) is expressed on activated T cells; its ligand, OX40 ligand (OX40L) is expressed on dendritic cells, B cells, and activated endothelial cells. To determine how OX40-OX40L interaction affects graft-versus-host disease (GVHD), we used antagonistic anti-OX40L monoclonal antibody (mAb) or OX40(-/-) donor or OX40L(-/-) recipient mice. Similar degrees of GVHD reduction were observed with each approach. Despite the fact that OX40 is up-regulated on both CD4(+) and CD8(+) T cells isolated during GVHD, the major effects of OX40 ligation were on CD4(+) and not CD8(+) T-cell-mediated alloresponses as assessed in both GVHD and engraftment model systems. GVHD inhibition by blockade of the OX40/OX40L pathway did not require CD28 signaling. Some studies have indicated OX40 is essential for inducing T-helper type 2 (Th2) responses. However, in vivo blockade of OX40-OX40L interactions reduced GVHD mortality induced by either signal transducer and activator of transcription-6(-/-) (Stat-6(-/-)) (Th2-defective) or Stat-4(-/-) (Th1-defective) major histocompatibility complex (MHC)-disparate splenocytes, indicating that the GVHD-ameliorating effects did not require Stat-4 or Stat-6 signaling. Although OX40L has been reported to be expressed on activated T cells, no effects on GVHD were observed when OX40L(-/-) versus OX40L(+/+) T cells were infused in different models. These data provide insights as to the mechanisms responsible for OX40/OX40L regulation of GVHD.

IFN-gamma up-regulation of IL-12 beta 2 receptor is associated with experimental autoimmune uveitis susceptible B10.A mice, but not in EAU resistant BALB/c mice

IFN-gamma production is a hallmark of Th1 response, and IFN-gamma has multiple roles in Th1 development, depending on the experimental conditions. In this study, the correlation between IFN-gamma and interleukin 12 receptor beta2 (IL-12R beta 2) expression was investigated in experimental autoimmune uveitis (EAU) susceptible B10.A and resistant BALB/c mice. B10.A mice expressed high IL-12R beta 2 on T cells either in the disease target eyes or draining lymph node cells (LNC), and its expression correlated with the Th1-type response. In contrast, BALB/c mice only expressed minimal IL-12R beta 2 in draining LNC and had lower Th1-response. B10.A mice produced more IFN-gamma and generated a higher number of Th1 cells than that of BALB/c in the draining LNC. Furthermore, IL-12R beta 2 expression and STAT4 signaling were inhibited by anti-IFN-gamma mAb in the cultured draining LNC from B10.A mice, but enhanced by adding exogenous IFN-gamma in the cultured cells from BALB/c mice. The IL-12R beta 2 expression on Th1 cells from draining LNC was increased in the presence of IL-12 and IFN-gamma. In conclusion, IFN-gamma production correlated with IL-12R beta 2 expression on Th1-cells and IFN-gamma had a potential to regulate IL-12R beta 2 expression in vivo. This regulatory mechanism might be involved in EAU induction.

Kinetics and STAT4- or STAT6-mediated regulation of genes involved in lymphocyte polarization to Th1 and Th2 cells

Many genes implicated in Th1 and Th2 differentiation have been identified in both human and mouse. However, the functional roles and hierarchy of these factors in the signaling pathways leading to either Th1 or Th2 responses are less clear. To explore at which stage of polarization the differences between Th1 and Th2 cells occur, we have studied the expression of 23 key genes implicated in the process during the first week of polarization from human precursor T helper cells using quantitative real-time reverse transcription-PCR. According to our results, 14 of the genes were clearly regulated differentially in Th1 and Th2 conditions in distinct time-dependent patterns, either during the first 2 days or after 1 week of polarization. Furthermore, 6 of these genes were identified to be targets of STAT4/6 regulation. Thus, for the first time we demonstrate expression kinetics of a number of key genes involved in Th1 and Th2 differentiation during the first week of polarization in both human and mouse. In addition, our study shows for the first time that the genes BCL-6 and TRADD are differentially regulated during the polarization of human Th1 and Th2 cells.

Resistance to acute babesiosis is associated with interleukin-12- and gamma interferon-mediated responses and requires macrophages and natural killer cells

We examined the role of the cytokines gamma interferon (IFN-gamma) and interleukin-12 (IL-12) in the model of acute babesiosis with the WA1 Babesia. Mice genetically deficient in IFN-gamma-mediated responses (IFNGR2KO mice) and IL-12-mediated responses (Stat4KO mice) were infected with the WA1 Babesia, and observations were made on the course of infection and cytokine responses. Levels of IFN-gamma and IL-12 in serum increased 24 h after parasite inoculation. The augmented susceptibility observed in IFNGR2KO and Stat-4KO mice suggests that the early IL-12- and IFN-gamma-mediated responses are involved in protection against acute babesiosis. Resistance appears to correlate with an increase in nitric oxide (NO) production. In order to assess the contribution of different cell subsets to resistance against the parasite, we also studied mice lacking B cells, CD4+ T cells, NK cells, and macrophages. Mice genetically deficient in B lymphocytes or CD4+ T lymphocytes were able to mount protective responses comparable to those of immunosufficient mice. In contrast, in vivo depletion of macrophages or NK cells resulted in elevated susceptibility to the infection. Our observations suggest that a crucial part of the response that protects from the pathogenic Babesia WA1 is mediated by macrophages and NK cells, probably through early production of IL-12 and IFN-gamma, and induction of macrophage-derived effector molecules like NO.

STAT4 signal pathways regulate inflammation and airway physiology changes in allergic airway inflammation locally via alteration of chemokines

Mice homozygous for the STAT4-null mutation were sensitized to cockroach Ag, challenged intratracheally 21 days later, and compared with STAT4-competent allergic mice. The STAT4(-/-) mice showed significant decreases in airway hyperreactivity (AHR) and peribronchial eosinophils compared with wild-type controls. In addition, pulmonary levels of chemokines were decreased in the STAT4(-/-) mice, including CC chemokine ligand (CCL)5, CCL6, CCL11, and CCL17. However, levels of Th2-type cytokines, such as IL-4 and IL-13, as well as serum IgE levels were similar in the two groups. Transfer of splenic lymphocytes from sensitized wild-type mice into sensitized STAT4(-/-) mice did not restore AHR in the mutant mice. Furthermore, chemokine production and peribronchial eosinophilia were not restored during the cellular transfer experiments. Thus, it appears that STAT4 expression contributes to a type 2 process such as allergen-induced chemokine production and AHR. In additional studies, competent allergic mice were treated with anti-IL-12 locally in the airways at the time of allergen rechallenge. These latter studies also demonstrated a decrease in AHR. Altogether, these data suggest that STAT4-mediated pathways play a role locally within the airway for the exacerbation of the allergen-induced responses.

Suppressive effect of a traditional Japanese medicine, Hachimi-jio-gan (Ba-Wei-Di-Huang-Wan), on the hyperresponsiveness to IL-18 in autoimmune MRL/MPJ-lpr/lpr mice

Oral administration of Hachimi-jio-gan (HMG, Ba-Wei-Di-Huang-Wan), a traditional Japanese herbal medicine, for several weeks, ameliorates some autoimmune symptoms of MRL/lpr mice. In the short time treatment for 9 days, hyperresponsiveness of mesenteric lymph node (MLN) cells to interleukin (IL)-18 manifested by the proliferation or the production of interferon (IFN)-gamma was significantly suppressed. Additionally, the treatment with HMG suppressed the expressions of IL-18Ralpha and IL-18Rbeta mRNA in CD45R(-) T cells, and also the expression of IL-18Ralpha mRNA in unpurified whole cells. Although the short treatment with HMG had no effect on the mRNA expressions of IL-10, IL-12 and IL-18, or the phosphorelated signal transducer and activator transcription (STAT)4 protein level in CD45R(-) MLN cells, the IL-4 mRNA expression or the phosphorelated STAT6 protein level were up-regulated by HMG, and the IL-4 mRNA up-regulation was clearer in whole cells than CD45R(-) cells. Furthermore, the treatment with HMG promoted the mRNA expression of invariant Valpha14 TCR that is uniquely expressed on NKT cells. Valpha14 NKT cells can produce large amount of IL-4 and play a crucial role in controlling the development of MRL/lpr mouse autoimmune disease. Therefore, these results suggested that HMG reduced the hyperresponsiveness of MRL/lpr mouse MLN cells to IL-18 through the reduction of IL-18Rs caused by Valpha14 NKT cell-produced IL-4, and consequently HMG suppressed the development of MRL/lpr autoimmune diseases.

GATA-3 suppresses Th1 development by downregulation of Stat4 and not through effects on IL-12Rbeta2 chain or T-bet

To further understand the interaction among GATA-3, Stat4, and T-bet in helper T cell development, we first showed that retroviral expression of GATA-3 in developing Th1 cells suppresses Th1 development through downregulation of Stat4 rather through downregulation of the IL-12Rbeta2 chain. Correspondingly, Stat4 levels are greatly suppressed during physiological Th2 development. Then, using cells doubly infected with GFP- and YFP-expressing retroviruses, we showed that retroviral GATA-3 expression in developing Th1 cells does not block Th1 development in cells coexpressing Stat4 but does so in cells coexpressing T-bet. Finally, we showed that retroviral Stat4 expression could facilitate Th2-->Th1 conversion in cells bearing an IL-12Rbeta2 transgene, even in cells lacking T-bet. These findings reassert that Stat4 signaling is a central element of Th1/Th2 development.

Stat signals release activated naive Th cells from an anergic checkpoint

Activation of naive Th lymphocytes by the TCR and the costimulatory molecule, CD28, is believed to provide competent signals for differentiation to effector cells. Such activated cells proliferated and expressed IL-2, but arrested in an immature state maintained by CTLA-4. Although unresponsive to restimulation by TCR/CD28 alone, restimulation with TCR/CD28 and either Stat4- or Stat6-mediated cytokine signals rescued cells to proliferate and differentiate to the appropriately matched canonical Th subsets. Addition of IL-4 at defined periods revealed that naive T cells were receptive to IL-4-mediated differentiation for up to 3 days after their initial priming. A Stat-dependent anergic checkpoint between clonal expansion and effector cell differentiation may defer the cytokine profile to be instructed at the site of infection, thus preventing the unregulated development of potentially damaging effector cells.

CD4+ T cells mediate abscess formation in intra-abdominal sepsis by an IL-17-dependent mechanism

Abscess formation associated with intra-abdominal sepsis causes severe morbidity and can be fatal. Previous studies have implicated T cells in the pathogenesis of abscess formation, and we have recently shown that CD4(+) T cells activated in vitro by zwitterionic capsular polysaccharides from abscess-inducing bacteria such as Staphylococcus aureus and Bacteroides fragilis initiate this host response when transferred to naive rats. In this study, we show that mice deficient in alphabetaTCR-bearing T cells or CD4(+) T cells fail to develop abscesses following challenge with B. fragilis or abscess-inducing zwitterionic polysaccharides, compared with CD8(-/-) or wild-type animals. Transfer of CD4(+) T cells from wild-type mice to alphabetaTCR(-/-) animals reconstituted this ability. The induction of abscesses required T cell costimulation via the CD28-B7 pathway, and T cell transfer experiments with STAT4(-/-) and STAT6(-/-) mice demonstrated that this host response is dependent on STAT4 signaling. Significantly higher levels of IL-17, a proinflammatory cytokine produced almost exclusively by activated CD4(+) T cells, were associated with abscess formation in Th2-impaired (STAT6(-/-)) mice, while STAT4(-/-) mice had significantly lower levels of this cytokine than control animals. The formation of abscesses was preceded by an increase in the number of activated CD4(+) T cells in the peritoneal cavity 24 h following bacterial challenge. Confocal laser-scanning microscopy analysis revealed that CD4(+) T cells comprise the abscess wall in these animals and produce IL-17 at this site. Administration of a neutralizing Ab specific for IL-17 prevented abscess formation following bacterial challenge in mice. These data delineate the specific T cell response necessary for the development of intra-abdominal abscesses and underscore the role of IL-17 in this disease process.

Stat4 and Stat6 signaling in hepatic ischemia/reperfusion injury in mice: HO-1 dependence of Stat4 disruption-mediated cytoprotection

Ischemia/reperfusion (I/R) injury remains an important problem in clinical organ transplantation. There is growing evidence that T lymphocytes, and activated CD4+ T cells in particular, play a key role in hepatic I/R injury. This study analyzes the role of signal transducer and activator of transcription 4 (Stat4) and Stat6 signaling in liver I/R injury. Using a partial lobar warm ischemia model, groups of wild-type (WT), T cell-deficient, Stat4-/Stat6-deficient knockout (KO) mice were assessed for the extent/severity of I/R injury. Ninety minutes of warm ischemia followed by 6 hours of reperfusion induced a fulminant liver failure in WT and Stat6 KO mice, as assessed by hepatocellular damage (serum alanine aminotransferase [sALT] levels), neutrophil accumulation (myeloperoxidase [MPO] activity) and histology (Suzuki scores). In contrast, T cell deficiency (nu/nu mice) or disruption of Stat4 signaling (Stat4 KO mice) reduced I/R insult. Unlike adoptive transfer of WT or Stat6-deficient T cells, infusion of Stat4-deficient T cells failed to restore hepatic I/R injury and prevented tumor necrosis factor alpha (TNF-alpha) production in nu/nu mice. Diminished TNF-alpha/Th1-type cytokine messenger RNA (mRNA)/protein elaborations patterns, along with overexpression of heme oxygenase-1 (HO-1)-accompanied hepatic cytoprotection in Stat4 KO recipients. In contrast, HO-1 depression restored hepatic injury in otherwise I/R resistant Stat4 KOs. In conclusion, Stat4 signaling is required for, whereas Stat4 disruption protects against, warm hepatic I/R injury in mice. The cytoprotection rendered by Stat4 disruption remains HO-1-dependent.

A reinterpretation of the dimerization interface of the N-terminal domains of STATs

The crystal structures of the N-terminal domain (N-domain) and the core region of the STAT family of transcription factors have been determined previously. STATs can form cooperative higher order structures (tetramers or higher oligomers) while bound to DNA. The crystal packing in the STAT4 N-domain crystal structure, determined at 1.5 A resolution, suggests two alternate organizations of the N-domain dimer. We now present the results of site directed mutagenesis of residues predicted to be involved at each dimer interface. Our results indicate that the dimer interface suggested earlier as being physiologically relevant is, in fact, unlikely to be so. Given the alternative model for the N-domain dimer, the ability of the N-domain to mediate interactions of two STAT dimers on DNA remains unchanged.

Relative importance of STAT4 in murine tuberculosis

This study was designed to determine the roles of STAT proteins in defence against mycobacterial infection. Airborne infection of STAT4 knockout (KO) mice with a Mycobacterium tuberculosis strain induced large granulomas with massive neutrophil infiltration over time, while that in STAT6 KO mice did not. The STAT4 KO mice succumbed to mycobacterial infection by the 80th day after infection. Compared with the levels in wild-type (WT) and STAT6 KO mice, pulmonary inducible nitric oxide synthase, interferon-alpha, -beta and -gamma mRNA levels were significantly lower in STAT4 KO mice, but expression of interleukin-2, -6, -12 and -18 mRNAs was slightly higher up to the fifth week after aerial infection. Therefore, STAT4, but not STAT6, appears to be a critical transcription factor in mycobacterial regulation.

Differential requirements for JAK2 and TYK2 in T cell proliferation and IFN-gamma production induced by IL-12 alone or together with IL-18

IL-12 activates TYK2 and Janus kinase (JAK)-2 to induce the phosphorylation of various signal transducers and activators of transcription (STAT) proteins. However, little is known regarding how these JAK exhibit the distinct biological effects of IL-12. Using two JAK inhibitors, tyrphostin A1 (A1) for TYK2 and tyrphostin B42 (B42) for JAK2, we investigated the involvement of JAK2 and TYK2 in IL-12-induced T cell proliferation and IFN-gamma production. B42, but not A1, inhibited T cell proliferation along with down-regulation of IL-12-induced c-Myc expression and STAT5 phosphorylation. In contrast, A1 but not B42 inhibited STAT4/STAT3 phosphorylation and IFN-gamma production. IL-18, but not IL-12, induced activator protein-1 (AP-1) responsible for high levels of IFN-gamma promoter activation. However, this IL-18 effect depended on the interaction of AP-1 with STAT4. A1 prevented AP-1 binding by inhibiting STAT4 involvement and down-regulated synergistic IFN-gamma promoter activation. These results indicate that JAK2 activation is required for IL-12-mediated T cell growth, whereas the TYK2-STAT4 signaling pathway is critical for IFN-gamma expression that is mediated by IL-12 alone and enhanced synergistically by combination with IL-18.

Multiple sclerosis: Cytokine receptors on oligodendrocytes predict innate regulation

Multiple sclerosis (MS) is an immune-mediated demyelinating condition in which numerous soluble mediators have been implicated. We have extended the repertoire of cytokines studied in MS tissue by examining interleukin (IL-4), IL-6, IL-10, IL-12, IL-18, interferon (IFNgamma), and their receptors and have compared patterns with those seen in normal subjects and other neurological diseases (OND). Expression was evaluated by immunocytochemistry and Western blots. Remarkably, oligodendrocytes expressed all the cytokine receptors examined, particularly Th2-type, constitutively in normal subjects and upregulated in disease. Microglial cells also expressed cytokine receptors at similar levels. Cytokine expression was invariably a feature of microglial cells, except for IL-10, which was exclusively astrocytic. Oligodendrocytes did not display cytokines, except for low levels of IL-18. Although no pattern was specific for MS, most molecules were upregulated in MS and OND. Downstream JAK/STAT molecules were correspondingly upregulated. Cytokine receptors on oligodendrocytes (and microglia), and their corresponding ligands on microglia (and astrocytes), may implicate paracrine/autocrine regulation and may bespeak innate immunity in the central nervous system.

Activated STAT4 and a functional role for IL-12 in human Peyer's patches

T cells in the Peyer's patches (PP) of the human ileum are exposed to a myriad of dietary and bacterial Ags from the gut lumen. Recall proliferative responses to common dietary Ags are readily demonstrable by PP T cells from healthy individuals, and the cytokine response is dominated by IFN-gamma. Consistent with Th1 skewing, PP cells spontaneously secrete IL-12p70, and IL-12p40 protein can be visualized underneath the PP dome epithelium. In this study, we have analyzed IL-12 signaling in PP and investigated whether IL-12 plays a functional role. CD3+ T lymphocytes isolated from PP and adjacent ileal mucosa spontaneously secrete IFN-gamma with negligible IL-4 or IL-5. RNA transcripts for IL-12Rbeta2, the signaling component of the IL-12R, are present in purified CD4+ and CD8+ T PP lymphocytes. Active STAT4, a transcription factor essential for IL-12-mediated Th1 differentiation, is readily detectable in biopsies from PP and ileal mucosa and STAT4-DNA binding activity is demonstrable by EMSA. Nuclear proteins from CD3+ T PP lymphocytes contain STAT4 and T-bet, a transcription factor selectively expressed in Th1 cells. Stimulation of freshly isolated PP cells with staphylococcal enterotoxin B dramatically enhanced the production of IFN-gamma, an effect which was largely inhibited by neutralizing anti-IL-12 Ab. These data show that IL-12 in human PP is likely to be responsible for the Th1-dominated cytokine response of the human mucosal immune system.

Negative regulation of interleukin-12 signaling by suppressor of cytokine signaling-1

Suppressor of cytokine signaling-1 (SOCS-1) is an inhibitory protein that regulates responses to cytokines. Previously, we have shown SOCS-1 to be a key inhibitor of interferon gamma (IFNgamma). Recent data suggest that SOCS-1 may regulate other cytokines in vivo, in addition to IFNgamma. Uncontrolled responses to interleukin-12 (IL-12), an inflammatory cytokine, could contribute to increased IFNgamma production and the development of inflammatory disease in SOCS-1(-/-) mice. Here, we assess responses of SOCS-1-deficient cells to IL-12. Both IL-12-induced T cell proliferation and NK cytotoxic activity are enhanced in SOCS-1-deficient cells, relative to controls. To examine the contribution of continued IL-12 signaling to the SOCS-1(-/-) disease, we generated mice lacking both SOCS-1 and signal transducer and activator of transcription 4 (STAT4), an essential component of the IL-12 signaling pathway. SOCS-1(-/-) STAT4(-/-) mice have improved survival relative to SOCS-1(-/-) mice, but die between 1 and 2 months of age. We conclude that, in addition to IFNgamma, SOCS-1 regulates responses to IL-12.

The HMG-CoA reductase inhibitor, atorvastatin, promotes a Th2 bias and reverses paralysis in central nervous system autoimmune disease

Statins, 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, which are approved for cholesterol reduction, may also be beneficial in the treatment of inflammatory diseases. Atorvastatin (Lipitor) was tested in chronic and relapsing experimental autoimmune encephalomyelitis, a CD4(+) Th1-mediated central nervous system (CNS) demyelinating disease model of multiple sclerosis. Here we show that oral atorvastatin prevented or reversed chronic and relapsing paralysis. Atorvastatin induced STAT6 phosphorylation and secretion of Th2 cytokines (interleukin (IL)-4, IL-5 and IL-10) and transforming growth factor (TGF)-beta. Conversely, STAT4 phosphorylation was inhibited and secretion of Th1 cytokines (IL-2, IL-12, interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha) was suppressed. Atorvastatin promoted differentiation of Th0 cells into Th2 cells. In adoptive transfer, these Th2 cells protected recipient mice from EAE induction. Atorvastatin reduced CNS infiltration and major histocompatibility complex (MHC) class II expression. Treatment of microglia inhibited IFN-gamma-inducible transcription at multiple MHC class II transactivator (CIITA) promoters and suppressed class II upregulation. Atorvastatin suppressed IFN-gamma-inducible expression of CD40, CD80 and CD86 co-stimulatory molecules. l-Mevalonate, the product of HMG-CoA reductase, reversed atorvastatin's effects on antigen-presenting cells (APC) and T cells. Atorvastatin treatment of either APC or T cells suppressed antigen-specific T-cell activation. Thus, atorvastatin has pleiotropic immunomodulatory effects involving both APC and T-cell compartments. Statins may be beneficial for multiple sclerosis and other Th1-mediated autoimmune diseases.

A regulatory role for suppressor of cytokine signaling-1 in T(h) polarization in vivo

Suppressor of cytokine signaling (SOCS)-1 is an inhibitory molecule for JAK, and its deficiency in mice leads to lymphocyte-dependent multi-organ disease and perinatal death. Crossing of SOCS-1(-/-) mice on an IFN-gamma(-/-), STAT1(-/-) and STAT6(-/-) background revealed that the fatal disease of SOCS-1(-/-) mice is also dependent on IFN-gamma/STAT1 and IL-4/STAT6 signaling pathways. Since IFN-gamma and IL-4 are representative T(h)1 and T(h)2 cytokines respectively, here we investigated the role of SOCS-1 in T(h) differentiation. Freshly isolated SOCS-1(-/-) CD4(+) T cells stimulated with anti-CD3 rapidly produced larger amounts of IFN-gamma and IL-4 than control cells, suggesting that these mutant T cells had already differentiated into T(h)1 and T(h)2 cells in vivo. In addition, SOCS-1(+/-) CD4(+) T cells cultured in vitro produced significantly larger amounts of IFN-gamma and IL-4 than SOCS-1(+/+) cells. Similarly, SOCS-1(+/-) CD4(+) T cells produced more IFN-gamma and IL-4 than SOCS-1(+/+) cells after infection with Listeria monocytogenes and Nippostrongyrus braziliensis respectively. Since IL-12-induced STAT4 and IL-4-induced STAT6 activation is sustained in SOCS-1(-/-) T cells, the enhanced T(h) functions in SOCS-1(-/-) and SOCS-1(+/-) mice appear to be due to the enhanced effects of these cytokines. These results suggest that SOCS-1 plays a regulatory role in both T(h)1 and T(h)2 polarizations.

Differential stimulation of IgE production, STAT activation and cytokine and CD86 expression by 2,4-dinitrochlorobenzene and trimellitic anhydride

It has been reported that dermal exposure to trimellitic anhydride (TMA, 50%), a respiratory allergen, induced greater production of serum IgE and expression of Th2 cytokines than 2,4-dinitrochlorobenzene (DNCB, 1%), a potent contact sensitizer, in female BALB/C mice. To determine if there is any strain difference, four strains (B6C3F1, C57BL/6, BDF1 and BALB/C) of female mice were employed in this study to compare the differential effects of these chemicals on the hypersensitivity responses. Serum IgE levels were increased in TMA-treated B6C3F1, C57BL/6 and BDF1 mice when compared with the DNCB treatment and vehicle controls; in contrast, no difference was observed between TMA- and DNCB-treated BALB/C mice, although both chemicals induced greater IgE production than vehicle controls. In vitro expression of interleukin 4 (IL-4) and IL-13 mRNA by overnight concanavalin A (ConA)-stimulated draining lymph node cells was enhanced following in vivo treatment with TMA but not with DNCB in the B6C3F1, C57BL/6 and BDF1 mice. In contrast, TMA and DNCB induced similar levels of IL-4 and IL-13 mRNA in the BALB/C mice. The IL-4 protein levels in the supernatants of overnight ConA-treated draining lymph node cells were also increased in TMA-treated B6C3F1 and C57BL/6 mice when compared with the DNCB treatment and vehicle controls. Further mechanistic evaluation in the B6C3F1 mice indicated that the activation of STAT6 but not STAT4 by ConA plus IL-2-treated draining lymph node cells was increased in TMA- but not DNCB-treated mice when compared with the vehicle controls. Furthermore, surface expression of B7.2 (CD86) by B cells was increased in both TMA- and DNCB-treated B6C3F1 mice when compared with the vehicles; however, greater B7.2 expression was observed in TMA-treated compared with DNCB-treated. Overall, these results demonstrate that a similar pattern of IgE and cytokine production was observed in these strains of mice except for BALB/C. Furthermore, differential activation of STAT6 and expression of CD86 following exposure to TMA and DNCB may contribute to the differential production of IgE and cytokines.

CpG DNA induced IL-12 p40 gene activation is independent of STAT1 activation or production of interferon consensus sequence binding protein

The host immune system responds to CpG motifs in bacterial DNA by rapidly producing proinflammatory cytokines. The host response to CpG DNA resembles, in many ways, the response to bacterial lipopolysaccharide (LPS). While both agents can induce a powerful inflammatory response, CpG DNA promotes Th1 and suppresses Th2 immunity. The regulation of macrophage IL-12 p40 secretion in response to stimulation with LPS and interferon-gamma (IFN-gamma) is dependent on the action of a nuclear transacting factor, interferon consensus sequence binding protein (ICSBP), a STAT1-dependent gene product. We found that CpG DNA induced IL-12 p40 secretion by macrophages from mice with either disrupted STAT1 or ICSBP genes. Additionally, CpG DNA did not induce translocation of transcription factors that bind to the gamma-activated sequence in the ICSBP gene nor did CpG DNA induce ICSBP transcription. CpG DNA, which activates macrophages by the TLR9 pathway, is a strong inducer of IL-12 p40, yet does so independently of IFN-gamma, STAT1 or ICSBP. Thus, CpG DNA-induced IL-12 p40 secretion is mediated by one or more signaling elements distinct from those induced by either LPS or IFN-gamma.

Control of New World cutaneous leishmaniasis is IL-12 independent but STAT4 dependent

Leishmania mexicana, a New World protozoan parasite, induces small, chronic, but non-progressive lesions in C57BL/6 (B6) mice. In this study we investigated the role of IL-12, and subsequent Th1 factors, in controlling cutaneous L. mexicana infection. IL-12 treatment failed to promote disease resolution, suggesting that the inability of mice to heal is not related to a deficiency of endogenous IL-12 production. Surprisingly, L. mexicana-induced cutaneous lesions in wild-type and IL-12p40-deficient mice were indistinguishable, with similar parasite burdens, immune responses, and lesion histopathology. In contrast, iNOS, IFN-gamma, and STAT4-deficient mice developed progressive disease and uncontrolled parasite growth. These results differ dramatically from L. major infection, in which IL-12p40-deficient mice are highly susceptible, with very rapid lesion growth, very large parasite burdens, and the development of a strong Th2 response. These data uncover the existence of an alternate IFN-gamma and iNOS pathway for control of Leishmania lesions, which is IL-12 independent, but which unexpectedly requires STAT4.