Th1 cells regulate hematopoietic progenitor cell homeostasis by production of oncostatin M

Regulation of hematopoietic progenitor cell homeostasis is crucial for maintenance of innate immunity and the ability of the body to respond to injury and infection. In this report, we demonstrate that progenitor cell numbers and cycling status in vivo are dramatically increased in mice deficient in Stat6 and decreased in mice deficient in Stat4, targeted mutations which also alter T helper cell polarization. Experiments using mice that have T cell restricted transgenic expression of Stat4 or Stat6 or have been in vivo depleted of T cell subsets demonstrate that CD4(+) T cells regulate progenitor cell activity. Injection of the Th1 cytokine Oncostatin M but not other cytokines into Stat4-deficient mice recovers progenitor cell activity to wild-type levels. Thus, T helper cells actively regulate hematopoietic progenitor cell homeostasis.

Induction of the chemokine receptor CXCR3 on TCR-stimulated T cells: dependence on the release from persistent TCR-triggering and requirement for IFN-gamma stimulation

The chemokine receptor CXCR3 has been shown to play a key role in the recruitment of T cells to sites of inflammation such as allografts. Here, we investigated which signals and conditions areresponsible for CXCR3 induction. CXCR3 was induced on T cells that were stimulated with anti-CD3 plus anti-CD28 monoclonal antibodies and then recultured without any external stimuli. CXCR3 expression was inhibited when TCR stimulation was persistent in the reculture. CXCR3 induction also depended on the stimulation with IFN-gamma because CXCR3 expression was not induced in IFN-gamma-deficient T cells. The induction of another Th1 chemokine receptor CCR5 absolutely required IL-12 stimulation and STAT4 involvement. In contrast, CXCR3 was induced on STAT4-deficient T cells independently of IL-12 stimulation as long as IFN-gamma was produced as a result of potent TCR stimulation. These results show that CXCR3 induction on TCR-triggered T cells requires the release of these T cells from persistent TCR signaling and the stimulation with IFN-gamma and also indicate the differential regulatory mechanisms underlying the induction of two Th1 chemokine receptors.

T-bet is a STAT1-induced regulator of IL-12R expression in naïve CD4+ T cells

T helper type 1 (T(H)1) cell development involves interferon-gamma (IFN-gamma) signaling through signal transducer and activator of transcription 1 (STAT1) and interleukin-12 (IL-12) signaling through STAT4 activation. We examined here T-bet regulation and evaluated the actions of T-bet in STAT1- and STAT4-dependent T(H)1 development processes. We found that T-bet expression during T cell activation was strongly dependent on IFN-gamma signaling and STAT1 activation, but was independent of STAT4. Ectopic T-bet expression strongly increased IFN-gamma production in T(H)2 cells activated by PMA-ionomycin, but weakly increased IFN-gamma production in T(H)2 cells stimulated by IL-12 IL-18 or OVA peptide antigen-presenting cell stimulation. In contrast, IL-12 IL-18 induced IFN-gamma production remained STAT4-dependent despite ectopic T-bet expression. Ectopic T-bet expression selectively induced expression of IL-12Rbeta2, but not IL-18Ralpha, in wild-type and STAT1(-/-) T(H)2 cells, but did not extinguish expression of GATA-3 and T(H)2 cytokines. Finally, ectopic T-bet did not directly induce expression of endogenous T- bet independently of IFN-gamma or STAT1. Thus, T-bet is induced by IFN-gamma and STAT1 signaling during T cell activation. In addition, T-bet mediates STAT1-dependent processes of T(H)1 development, including the induction of IL-12Rbeta2.

Molecular mechanisms for gender differences in susceptibility to T cell-mediated autoimmune diabetes in nonobese diabetic mice

Nonobese diabetic (NOD) mice spontaneously develop diabetes with a strong female prevalence; however, the mechanisms for this gender difference in susceptibility to T cell-mediated autoimmune diabetes are poorly understood. This investigation was initiated to find mechanisms by which sex hormones might affect the development of autoimmune diabetes in NOD mice. We examined the expression of IFN-gamma, a characteristic Th1 cytokine, and IL-4, a characteristic Th2 cytokine, in islet infiltrates of female and male NOD mice at various ages. We found that the most significant difference in cytokine production between sexes was during the early stages of insulitis at 4 wk of age. IFN-gamma was significantly higher in young females, whereas IL-4 was higher in young males. CD4(+) T cells isolated from lymph nodes of female mice and activated with anti-CD3 and anti-CD28 Abs produced more IFN-gamma, but less IL-4, as compared with males. Treatment of CD4(+) T cells with estrogen significantly increased, whereas testosterone treatment decreased the IL-12-induced production of IFN-gamma. We then examined whether the change in IL-12-induced IFN-gamma production by treatment with sex hormones was due to the regulation of STAT4 activation. We found that estrogen treatment increased the phosphorylation of STAT4 in IL-12-stimulated T cells. We conclude that the increased susceptibility of female NOD mice to the development of autoimmune diabetes could be due to the enhancement of the Th1 immune response through the increase of IL-12-induced STAT4 activation by estrogen.

Promotion of hepatic ischemia/reperfusion injury by IL-12 is independent of STAT4

BACKGROUND

We have recently demonstrated a role for interleukin-12 (IL-12) in the induction and development of hepatic ischemia/reperfusion injury. IL-12 mediates its effects through the transcription factor, signal transducer and activator of transcription-4 (STAT4). Therefore, we investigated the response to hepatic ischemia/reperfusion in STAT4-deficient mice.

METHODS

Wild-type and STAT4-deficient mice were subjected to 90 min of partial hepatic ischemia followed by reperfusion. In some experiments, IL-12 was neutralized with antibody administered intravenously.

RESULTS

Wild-type mice demonstrated rapid activation of STAT4 in liver after ischemia/reperfusion, which mirrored hepatic protein expression of IL-12. Interestingly, STAT4-deficient mice were indistinguishable from wild-type mice in their response to hepatic ischemia reperfusion. No differences were observed in serum levels of tumor necrosis factor alpha (TNF-alpha), liver accumulation of neutrophils, or hepatocellular injury. However, blockade of endogenous IL-12 significantly reduced these parameters in STAT4-knockout mice.

CONCLUSIONS

These data demonstrate that IL-12 promotes hepatic inflammation in a manner that is independent of STAT4 and implicate a novel mechanism for the pro-inflammatory effects of IL-12.

Administration of two macrophage-derived interferon-gamma-inducing factors (IL-12 and IL-15) induces a lethal systemic inflammatory response in mice that is dependent on natural killer cells but does not require interferon-gamma

Activation of macrophages by microbes results in the rapid production of monokines (e.g., interleukin-12 (IL-12), IL-15, and IL-18), which induce production of interferon-gamma (IFN-gamma) by natural killer (NK) cells. We examined the effects of administering IL-15 in combination with IL-12 in a murine toxicity model to determine how these two cytokines might contribute to the inflammatory state that accompanies infectious processes. The daily, simultaneous administration of IL-15 (3 x 10(5)U) and IL-12 (1 microg) to normal mice resulted in shock and 100% mortality within 3-7 days, whereas minimal toxicity was observed following the administration of IL-15 or IL-12 alone. Mice treated with IL-15 plus IL-12 exhibited lesions of the gastrointestinal tract, elevated serum levels of acute phase reactants and pro-inflammatory cytokines, and NK cell apoptosis. Neutralization of IFN-gamma, TNF-alpha, and IL-1beta was not protective in cytokine-treated mice, however, toxicity and death could be completely abrogated by depletion of NK cells. Mice deficient in the STAT4 transcription factor also exhibited complete protection while mice deficient in IFN-gamma or its downstream mediator, STAT1, did not. These findings suggest that cytokine- stimulated NK cells are able to promote systemic inflammation via the induction of STAT4-responsive genes other than IFN-gamma or TNF-alpha.

Synergy of IL-12 and IL-18 for IFN-gamma gene expression: IL-12-induced STAT4 contributes to IFN-gamma promoter activation by up-regulating the binding activity of IL-18-induced activator protein 1

IL-12 and IL-18 synergistically enhance IFN-gamma mRNA transcription by activating STAT4 and AP-1, respectively. However, it is still unknown how STAT4/AP-1 elicit IFN-gamma promoter activation. Using an IL-12/IL-18-responsive T cell clone, we investigated the mechanisms underlying synergistic enhancement of IFN-gamma mRNA expression induced by these two cytokines. Synergy was observed in a reporter gene assay using an IFN-gamma promoter fragment that binds AP-1, but not STAT4. An increase in c-Jun, a component of AP-1, in the nuclear compartment was elicited by stimulation with either IL-12 or IL-18, but accumulation of serine-phosphorylated c-Jun was induced only by IL-18 capable of activating c-Jun N-terminal kinase. The binding of AP-1 to the relevant promoter sequence depended on the presence of STAT4. STAT4 bound with c-Jun, and a phosphorylated c-Jun-STAT4 complex most efficiently interacted with the AP-1-relevant promoter sequence. Enhanced cobinding of STAT4 and c-Jun to the AP-1 sequence was also observed when activated lymph node T cells were exposed to IL-12 plus IL-18. These results show that STAT4 up-regulates AP-1-mediated IFN-gamma promoter activation without directly binding to the promoter sequence, providing a mechanistic explanation for IL-12/IL-18-induced synergistic enhancement of IFN-gamma gene expression.

IL-23: a cytokine that acts on memory T cells

The newly discovered cytokine interleukin (IL)-23 shares some in vivo functions with IL-12, including the activation of the transcription factor STAT4 (signal tranducer and activator of transcription-4). Indeed, the receptors for each appear to share one subunit, but also have at least one distinct subunit. Frucht discusses the similarities of IL-12 and IL-23 and the effects that distinguish one from the other. In contrast to IL-12, IL-23 appears to participate in the proliferative signal in memory T cells. More functions that distinguish IL-23 from IL-12 are likely to be uncovered as soon as the other component(s) of the IL-23 receptor are molecularly cloned and characterized.

Accumulation of transcripts in the mature human sperm nucleus: implication of the haploid genome in a functional role

The existence of sperm-specific transcripts has been suggested by a number of studies performed both in man and rodents but their origin and role are not yet elucidated. For evaluating the functional significance of these mRNAs, transcripts coding for proteins expressed during spermiogenesis or potentially implicated in the early steps of zygote development, have been searched in human testis and sperm cells by RT-PCR. Furthermore their localization in spermatozoa has been checked by in situ hybridization. Our results confirm the presence of basic nucleoproteins (Transition proteins 1 and 2, Protamines 1 and 2) spermatozoal transcripts which probably represent remnants of previous transcription. They also reveal the existence of sperm specific mRNAs coding for the transcription factor Stat 4, the cyclin B1 and for the testicular isozyme of the angiotensin converting enzyme ACE. On the contrary, mRNAs coding for the heat shock protein Hsp 70 have been found in testis but not in spermatozoa. The possible roles of these transcripts either during the fertilization process or in zygote are discussed.

Interleukin-12 receptor/STAT4 signaling is required for the development of autoimmune myocarditis in mice by an interferon-gamma-independent pathway

BACKGROUND

Interleukin (IL)-12 exerts a potent proinflammatory effect by stimulating T-helper (Th) 1 responses. This effect is believed to be mediated primarily through the activation of STAT4 and subsequent production of interferon (IFN)-gamma. Methods and Results- We examined the role of IL-12 receptor (IL-12R) signaling in the development of murine experimental autoimmune myocarditis (EAM) induced by cardiac myosin immunization. Both IL-12Rbeta1-deficient mice and STAT4-deficient mice were resistant to the induction of myocarditis. Treatment with exogenous IL-12 exacerbated disease. We questioned whether IFN-gamma is required for the disease-promoting activity of IL-12. On the contrary, we found that IFN-gamma suppresses EAM. Lack of IFN-gamma due to either depletion with an antibody or a genetic deficiency exacerbated myocarditis. Spleens from IFN-gamma-deficient mice immunized with cardiac myosin showed increased cellularity; greater numbers of CD3+, CD4+, CD8+, and IL-2-producing cells; and heightened ability to produce cytokines on stimulation in vitro. Treatment of mice with recombinant IFN-gamma suppressed the development of myocarditis.

CONCLUSIONS

IL-12/IL-12R/STAT4 signaling promotes the development of EAM. In contrast, IFN-gamma plays a protective role. The disease-limiting effects of IFN-gamma might be explained by its ability to control the expansion of activated T lymphocytes.

A mandatory role for STAT4 in IL-12 induction of mouse T cell CCR5

IL-12 was recently shown to induce CCR5 on TCR-triggered mouse T cells. Considering that STAT4 is the most critical of IL-12 signaling molecules, this study investigated the role for STAT4 in the induction of CCR5 expression. IL-12R was induced by stimulation with anti-CD3 plus anti-CD28 mAb similarly on T cells from wild-type (WT) and STAT4-deficient (STAT4(-/-)) mice, but the levels of IL-12R induced on IFN-gamma-deficient (IFN-gamma(-/-)) T cells were lower compared with WT T cells. Exposure of TCR-triggered WT T cells to IL-12 induced CCR5 expression. In contrast, TCR-triggered STAT4(-/-) T cells failed to express CCR5 in response to IL-12. IL-12 stimulation induced detectable albeit reduced levels of CCR5 expression on IFN-gamma(-/-) T cells. Addition of rIFN-gamma to cultures of IFN-gamma(-/-) T cells, particularly to cultures during TCR triggering resulted in restoration of CCR5 expression. However, CCR5 expression was not induced in STAT4(-/-) T cells by supplementation of rIFN-gamma. These results indicate that for the induction of CCR5 on T cells, 1) STAT4 plays an indispensable role; 2) such a role is not substituted by simply supplementing rIFN-gamma; and 3) IFN-gamma amplifies CCR5 induction depending on the presence of STAT4.

Inability of IL-12 to down-regulate IgE synthesis due to defective production of IFN-gamma in atopic NC/Nga mice

NC/Nga mice raised in nonsterile circumstances spontaneously suffer from atopic dermatitis-like skin lesions with IgE hyperproduction. We investigated effects of rIL-12 on the IgE production in NC/Nga mice. rIL-12 administration was successful to suppress the increase of IgE levels in BALB/c mice immunized with OVA and aluminum hydroxide, but failed to abrogate that in NC/Nga mice. Both in vivo and in vitro IFN-gamma production induced by rIL-12 was less in NC/Nga mice than in BALB/c mice. Addition of rIFN-gamma to rIL-4 and LPS completely abrogated IgE production by B cells of BALB/c mice, but was insufficient to suppress it by B cells of NC/Nga mice. In splenic cells pretreated with Con A, STAT4 was phosphorylated at the tyrosine residue by addition of rIL-12, which was more weakly inducible in NC/Nga mice than in BALB/c mice. Finally, we examined the preventive ability of rIL-12 on the clinical aspects of atopic dermatitis in NC/Nga mice. rIL-12 administration resulted in exacerbation of development of the skin lesions and IgE production in NC/Nga mice raised in nonsterile circumstances. These results suggest that defective production of IFN-gamma by T cells less sensitive to IL-12 and low responsiveness of B cells to IFN-gamma may contribute to IgE hyperproduction in NC/Nga mice, and that IL-12 may have no ability to improve the clinical aspects of NC/Nga mice.

Critical role for tumor necrosis factor alpha in controlling the number of lumenal pathogenic bacteria and immunopathology in infectious colitis

Infection of mice with the intestinal bacterial pathogen Citrobacter rodentium results in colonic mucosal hyperplasia and a local Th1 inflammatory response similar to that seen in mouse models of inflammatory bowel disease. In these latter models, and in patients with Crohn's disease, neutralization of tumor necrosis factor alpha (TNF-alpha) is of therapeutic benefit. Since there is no information on the role of TNF-alpha in either immunity to noninvasive bacterial pathogens or on the role of TNF-alpha in the immunopathology of infectious colitis, we investigated C. rodentium infection in TNFRp55(-/-) mice. In TNFRp55(-/-) mice, there were higher colonic bacterial burdens, but the organisms were cleared at the same rate as C57BL/6 mice, showing that TNF-alpha is not needed for protective antibacterial immunity. The most striking feature of infection in TNFRp55(-/-) mice, however, was the markedly enhanced pathology, with increased mucosal weight and thickness, increased T-cell infiltrate, and a markedly greater mucosal Th1 response. Interleukin-12 p40 transcripts were markedly elevated in C. rodentium-infected TNFRp55(-/-) mice, and this was associated with enhanced mucosal STAT4 phosphorylation. TNF-alpha is not obligatory for protective immunity to C. rodentium in mice; however, it appears to play some role in downregulating mucosal pathology and Th1 immune responses.

STAT4 is required for antibacterial defense but enhances mortality during polymicrobial sepsis

The signal transducer and activator of transcription factor 4 (STAT4) pathway mediates the intracellular effects of interleukin-12 (IL-12), leading to the production of gamma interferon, induction of a T helper type 1 response, and increased natural killer cell cytotoxicity. The purpose of this study was to determine the role of the STAT4 pathway during polymicrobial peritonitis in the cecal ligation and puncture (CLP) model. CLP was performed on STAT4-deficient (STAT4(-/-)) and wild-type control (BALB/c) mice. At 4 h after CLP, STAT4(-/-) mice had significantly higher bacterial counts in the peritoneal lavage fluid, liver, and blood. This difference persisted for 18 h in the peritoneal lavage fluid and blood. Neutrophil migration to the site of infection and into remote tissues was unaffected. Despite higher bacterial counts locally and systemically, STAT4(-/-) mice had a lower mortality rate than BALB/c controls. In contrast, blockade of IL-12 in BALB/c mice was detrimental to host survival. A blunted serum IL-12 response at 18 h after CLP was exhibited in STAT4(-/-) mice. These results suggest several critical roles for the STAT4 pathway in the resolution of polymicrobial infections. Additionally, the disparate effects observed with IL-12 blockade and STAT4 deficiency on host survival suggest that IL-12 may activate alternate pathways promoting survival.

Human microglial cells express a functional IL-12 receptor and produce IL-12 following IL-12 stimulation

Microglial cells (MC) are IL-12 producers in the central nervous system. Here, we found that IL-12 receptor subunits beta1 and beta2 were both constitutively expressed, and up-regulated by IFN-gamma, in human primary MC. IL-12p70, after binding to its receptor, is internalized into vesicles that qualify as early endosomes as indicated by intracellular colocalization with transferrin. IL-12 induced tyrosine phosphorylation and nuclear translocation of STAT4. IL-12 signaling in human MC also involved members of the NFkappaB family. IL-12p70 and, more effectively, the combination of IL-12p70 and IFN-gamma, induced IL-12p40 mRNA expression and bioactive IL-12p70 production. Human MC, thus, express a functional IL-12 receptor and produce bioactive IL-12 following IL-12 stimulation.

STAT4 and STAT6 regulate systemic inflammation and protect against lethal endotoxemia

Members of the signal transducer and activator of transcription (STAT) family are transcription factors that mediate many of the effects of pro- and anti-inflammatory cytokines. The progressive systemic inflammatory response induced by endotoxin is mediated by overzealous cytokine production. Here we identify STAT4 and STAT6 as critical regulators of the systemic inflammatory response to endotoxin. Mice deficient for STAT4 or STAT6 were highly susceptible to lethal endotoxemia. In STAT4(-/-) mice, antibody blockade of IL-12 prevented mortality, suggesting that STAT4 confers protection, while another signaling pathway mediates the detrimental effects of IL-12. In STAT6(-/-) mice we observed dysregulated activation of the transcription factor NF-kappaB, resulting in augmented production of proinflammatory cytokines and chemokines. Furthermore, STAT6(-/-) mice displayed increased organ accumulation of leukocytes and significant hepatocellular injury. These findings demonstrate that STAT4 and STAT6 confer protection against endotoxin-induced death and that for STAT6 these protective effects occur through the regulation of NF-kappaB activation and subsequent production of proinflammatory cytokines and chemokines.

IL-12, STAT4-dependent up-regulation of CD4(+) T cell core 2 beta-1,6-n-acetylglucosaminyltransferase, an enzyme essential for biosynthesis of P-selectin ligands

TCR activation of naive T cells in the presence of IL-12 drives polarization toward a Th1 phenotype and synthesis of P- and E-selectin ligands. Fucosyltransferase VII (Fuc-T VII) and core 2 beta-1,6-N-acetylglucosaminyltransferase (C2GnT) are critical for biosynthesis of selectin ligands. P-selectin glycoprotein ligand-1 is the best characterized ligand for P-selectin and also binds E-selectin. The contributions of TCR and cytokine signaling pathways to up-regulate Fuc-T VII and C2GnT during biosynthesis of E- and P-selectin ligands, such as P-selectin glycoprotein ligand 1, are unknown. IL-12 signals via the STAT4 pathway. Here, naive DO11.10 TCR transgenic and STAT4(-/-) TCR transgenic CD4(+) T cells were stimulated with Ag and IL-12 (Th1 condition), IL-4 (Th2), or neutralizing anti-IL-4 mAb only (Th0). The levels of Fuc-T VII and C2GnT mRNA in these cells were compared with their adhesive interactions with P- and E-selectin in vitro under flow. The data show IL-12/STAT4 signaling is necessary for induction of C2GnT, but not Fuc-TVII mRNA, and that STAT4(-/-) Th1 cells do not traffic normally to sites of inflammation in vivo, do not interact with P-selectin, and exhibit a partial reduction of E-selectin interactions under shear stress in vitro. Ag-specific TCR activation in CD4(+) T cells was sufficient to trigger induction of Fuc-TVII, but not C2GnT, mRNA and expression of E-selectin, but not P-selectin, ligands. Thus, Fuc-T VII and C2GnT are regulated by different signals during Th cell differentiation, and both cytokine and TCR signals are necessary for the expression of E- and P-selectin ligands.

IFN-gamma production by antigen-presenting cells: mechanisms emerge

The suggestion that antigen-presenting cells (APCs) produce interferon gamma (IFN-gamma) is controversial because it conflicts with the initial paradigm in which the production of IFN-gamma was restricted to lymphoid cells. However, some answers to this skepticism have been provided by recent findings of high-level production and intracellular expression of IFN-gamma by interleukin-12 (IL-12)-stimulated macrophages and dendritic cells. New data are now emerging to explain the mechanism of production of IFN-gamma vby APCs. As in lymphoid cells, IL-12-induced IFN-gamma production in APCs requires signal transducer and activator of transcription 4 (STAT4), although the precise molecular events that govern the transcription of the gene encoding IFN-gamma are enigmatic still. Understanding these processes in lymphoid, and now nonlymphoid, cells remains an important challenge.

Interleukin-12 increases interleukin 8 production and release by human polymorphonuclear neutrophils

Interleukin (IL) 12 is a heterodimeric cytokine mainly produced by phagocytes-important target cells for IL-12 in particular with a chemotactic effect-and antigen-presenting cells in response to various microorganisms. Because IL-8 is a strong chemokine for polymorphonuclear neutrophils (PMNs), we investigated the effect of IL-12 on PMN IL-8 production. IL-12 alone had no significant effect, but with lipopolysaccharide (LPS) it was additive at both protein and mRNA levels. Actinomycin D at the beginning of culture inhibited IL-8 mRNA induction, whereas late addition affected IL-8 transcript stability, suggesting gene transcription involvement. Results with parthenolide and tyrphostin AG490 suggest that nuclear factor-kappaB and signal transducer and activator of transcription 4 play a role. The IL-12 additive effect was restricted to IL-8 release, with no action on cell-associated IL-8. IL-12 additive effects occurred after 18 h of culture, with no marked up-regulation of IL-12 receptor expression, and were blocked by actinomycin D added after 16 h of culture. Tumor necrosis factor (TNF) alpha and interferon (IFN) gamma had intermediate roles; their specific inhibition reduced IL-12's effect. IL-12's chemotactic mechanism seemed mediated by overproduction and release of IL-8 by human PMNs in the presence of LPS, an effect involving TNF-alpha and IFN-gamma secretion. These results point to a new role for IL-12 in inflammation, through an autocrine amplification loop.

Detection of intracellular phosphorylated STAT-4 by flow cytometry

The convergence of innate and adaptive immunity is critical for host defense, allowing for early protection and the generation of specific responses. STAT-4 is at that point of convergence, unifying the IFNalpha and IL-12 pathways. Activation of STAT-4 is crucial to T cell polarization, B cell and NK cell activation, and the control of intracellular pathogens. However, techniques to detect phosphorylated STAT-4 are cumbersome and require many cells. We have developed a flow cytometric detection technique to investigate IL-12 signaling in human peripheral blood mononuclear cells. Using different polyclonal antibodies that recognize either total STAT-4 protein or tyrosine-phosphorylated STAT-4, we can easily detect IL-12 and IFNalpha signaling in PHA/IL-2 blasts derived from peripheral blood lymphocytes. This technique not only allows us to evaluate IL-12 signaling, but it is also less time consuming and labor intensive than alternative methods. Using this flow cytometry-based method, we should be able to detect patients with defects in IL-12 receptor signal transduction, who typically present with disseminated nontuberculous mycobacterial infections.

Effect of targeted disruption of STAT4 and STAT6 on the induction of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is mediated by myelin-specific CD4(+) T cells secreting Th1 cytokines, while recovery from disease is associated with expression of Th2 cytokines. Investigations into the role of individual cytokines in disease induction have yielded contradictory results. Here we used animals with targeted deletion of the STAT4 or STAT6 genes to determine the role of these signaling molecules in EAE. The STAT4 pathway controls the differentiation of cells into a Th1 phenotype, while the STAT6 pathway controls the differentiation of cells into a Th2 phenotype. We found that mice deficient in STAT4 are resistant to the induction of EAE, with minimal inflammatory infiltrates in the central nervous system. In contrast, STAT6-deficient mice, which have a predominantly Th1 phenotype, experience a more severe clinical course of EAE as compared with wild-type or STAT4 knockout mice. In addition, adoptive transfer studies confirm the regulatory functions of a Th2 environment in vivo. These novel data indicate that STAT4 and STAT6 genes play a critical role in regulating the autoimmune response in EAE.

Single dose intranasal administration of retinal autoantigen generates a rapid accumulation and cell activation in draining lymph node and spleen: implications for tolerance therapy

BACKGROUND/AIMS

A single intranasal delivery of retinal autoantigen suppresses effectively experimental autoimmune uveoretinitis (EAU). To further unravel underlying mechanisms the authors wished to determine, firstly, the kinetics of antigen delivery and, secondly, the early cellular responses involved in the initial stages of nasal mucosal tolerance induction.

METHODS

Flow cytometry, cell proliferation assays, and microscopy were used to track antigen following a single, intranasal dose of Alexa-488 labelled retinal antigen.

RESULTS

A rapid accumulation of antigen within both superficial cervical lymph nodes (SCLN) and spleen was observed after 30 minutes. Significant proliferative responses to IRBP were elicited by 48 hours indicating that systemic priming of naive T cells to retinal antigen had occurred. Cell activation was further confirmed by immunoprecipitation studies, which demonstrated phosphorylation of STAT4 but not STAT6 in both lymph nodes and spleen. However, at 24 hours, STAT4 heterodimerisation with STAT 3 was only observed in spleen.

CONCLUSIONS

The results provide novel evidence that following a single intranasal application rapid transfer of antigen occurs. Resulting T cell proliferation develops consequent to differential cell signalling in SCLN and spleen. Further understanding of these underlying cellular mechanisms, in particular as is inferred by the results the contribution of local versus systemic tolerance induction, may assist in strategies to clinically apply mucosal tolerance therapy successfully.

An absolute requirement for STAT4 and a role for IFN-gamma as an amplifying factor in IL-12 induction of the functional IL-18 receptor complex

IL-12 and IL-18 are both proinflammatory cytokines that contribute to promoting Th1 development and IFN-gamma expression. However, neither IL-12R nor IL-18R is expressed as a functional complex on most resting T cells. This study investigated the molecular mechanisms underlying the induction of an IL-18R complex in T cells. Resting T cells expressed IL-18Ralpha chains but did not exhibit IL-18 binding sites as detected by incubation with rIL-18 followed by anti-IL-18 Ab, suggesting a lack of IL-18Rbeta expression in resting T cells. Although they also failed to express IL-12R, stimulation with anti-CD3 plus anti-CD28 generated IL-12R. Exposure of these cells to IL-12 led not only to up-regulation of IL-18Ralpha expression but also to induction of IL-18R binding sites on both CD4(+) and CD8(+) T cells concomitant with IL-18Rbeta mRNA expression. The IL-18 binding site represented a functional IL-18R complex capable of exhibiting IL-18 responsiveness. IL-12 induction of an IL-18R complex and IL-18Rbeta mRNA expression was not observed in STAT4-deficient (STAT4(-/-)) T cells and was substantially decreased in IFN-gamma(-/-) T cells. However, the failure of STAT4(-/-) T cells to induce an IL-18R complex was not corrected by IFN-gamma. These results indicate that STAT4 and IFN-gamma play an indispensable role and a role as an amplifying factor, respectively, in IL-12 induction of the functional IL-18R complex.

Role of interleukin-12 and stat-4 in the regulation of airway inflammation and hyperreactivity in respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is a respiratory pathogen that can cause significant morbidity in infants and young children. Interestingly, the majority of children who acquire a RSV infection do not exhibit severe symptoms. Development of a Th1 response has been associated with resolution of symptoms in viral infections and may explain mild RSV illness. The current study investigated the cytokine response observed in mild disease in C57BL/6 mice that had low airway resistance and mucus production with little pulmonary inflammation. RSV infection in these mice was accompanied by a fourfold increase in interleukin-12(IL-12). Treatment of RSV-infected mice with anti-IL-12 resulted in an increase in airway hyperreactivity, mucus production, and airway inflammation (eosinophilia). Since IL-12 activation is dependent on Stat-4-mediated intracellular signal transduction, similar experiments were performed in Stat-4 deficient mice and demonstrated similar results to those obtained from anti-IL-12 treated mice. Again, there was an increase in airway hyperreactivity and mucus production, and goblet cell hypertrophy. These studies support the importance of IL-12 in the immune response to RSV infection resulting in resolution of disease and protection from inappropriate inflammatory responses.