Synergistic effects of IL-4 and IL-18 on IL-12-dependent IFN-gamma production by dendritic cells

Mouse splenic dendritic cells (DCs) produce IFN-gamma in response to IL-12. In the present study, we analyzed effects of Th1 and Th2 cytokines on IFN-gamma production by DCs. IL-18 produced by DCs and macrophages acts in an autocrine manner and augments IL-12-induced IFN-gamma production by DCs as also observed in T and NK cells. Surprisingly, IL-4, a Th2 cytokine, also acts synergistically with IL-12 on IFN-gamma production by DCs. In addition, IL-4 markedly enhances IFN-gamma production when DCs are stimulated through CD40 or MHC class II. These results indicate that both Th1 and Th2 cytokines act on DCs during T cell-DC interaction upon Ag presentation. p38 mitogen-activated protein kinase is constitutively activated in mature DCs and is required for IFN-gamma production by DCs. IL-18 but not IL-4 or IL-12 further activates the p38 mitogen-activated protein kinase activity, suggesting that IL-4 and IL-18 enhance IFN-gamma production through distinct intracellular signal transduction pathways in DCs.     

IL-12-independent IFN-gamma production by T cells in experimental Chagas' disease is mediated by IL-18.

IL-12p35-deficient (IL-12p35(-/-)) mice were highly susceptible to Trypanosoma cruzi infection and succumbed during acute infection, demonstrating the crucial importance of endogenous IL-12 in resistance to experimental Chagas' disease. Delayed immune responses were observed in mutant mice, although comparable IFN-gamma and TNF-alpha blood levels as in wild-type mice were detected 2 wk postinfection. In vivo and in vitro analysis demonstrated that T cells, but not NK cells, were recruited to infected organs. Analysis of mice double deficient in the recombinase-activating gene 2 (RAG2) and IL-12p35, as well as studies involving T cell depletion, identified CD4(+) T cells as the cellular source for IL-12-independent IFN-gamma production. IL-18 was induced in IL-12p35(-/-) mice and was responsible for IFN-gamma production, as demonstrated by in vivo IL-18 neutralization studies. In conclusion, evidence is presented for an IL-12-independent IFN-gamma production in experimental Chagas' disease that is T cell and IL-18 dependent.     

Ischemia/reperfusion-induced IFN-gamma up-regulation: involvement of IL-12 and IL-18

Tissue injury as a consequence of ischemia followed by reperfusion is characterized by early as well as late signs of inflammation. The latter, among others, involves IFN-gamma-dependent up-regulation of MHC class I and II Ag expression. Employing a murine model of renal ischemia, we show that renal IL-18 mRNA up-regulation coincides with caspase-1 activation at day 1 following ischemia. IFN-gamma and IL-12 mRNA are subsequently up-regulated at day 6 following ischemia. Combined, but not separate, in vivo neutralization of the IFN-gamma inducing cytokines IL-12 and IL-18 reduces IFN-gamma-dependent MHC class I and II up-regulation to a similar extent as IFN-gamma neutralization, suggesting the involvement of functional IL-12, IL-18, and IFN-gamma protein. These results reveal a novel relationship between tissue injury of nonmicrobial origin and the induction of IL-12 as well as IL-18. The collaboration observed between endogenous IL-12 and IL-18 in the induction of IFN-gamma after renal ischemia/reperfusion, resembles the immune response to bacterial infections.     

IL-12 induces monocyte IL-18 binding protein expression via IFN-gamma

IL-18 is a Th1 cytokine that synergizes with IL-12 and IL-2 in the stimulation of lymphocyte IFN-gamma production. IL-18 binding protein (IL-18BP) is a recently discovered inhibitor of IL-18 that is distinct from the IL-1 and IL-18 receptor families. In this report we show that IL-18BPa, the IL-18BP isoform with the highest affinity for IL-18, was strongly induced by IL-12 in human PBMC. Other Th1 cytokines, including IFN-gamma, IL-2, IL-15, and IL-18, were also capable of augmenting IL-18BPa expression. In contrast, IL-1alpha, IL-1beta, TNF-alpha, IFN-gamma-inducible protein-10, and Th2 cytokines such as IL-4 and IL-10 did not induce IL-18BPa. Although monocytes were found to be the primary source of IL-18BPa, the induction of IL-18BPa by IL-12 was mediated through IFN-gamma derived predominantly from NK cells. IL-18BPa production was observed in cancer patients receiving recombinant human IL-12 and correlated with the magnitude of IFN-gamma production. The IFN-gamma/IL-18BPa negative feedback loop identified in this study may be capable of broadly controlling immune activation by cytokines that synergize with IL-18 to induce IFN-gamma and probably plays a key role in the modulation of both innate and adaptive immunity.     

Production of IL-12 and IL-18 in human dendritic cells upon infection by Listeria monocytogenes

Dendritic cells (DCs) are major antigen-presenting cells of the immune system, which need to be activated in order to initiate an immune response. Here, we describe the immunostimulatory effects on human monocyte-derived DCs observed upon infection with Listeria monocytogenes or after treatment with listerial lipoteichoic acid (LTA) and lipopolysaccharide (LPS), respectively. All stimuli caused upregulation of costimulatory molecules, induced T-cell proliferative responses and secretion of cytokines in vitro. Infection of DCs with L. monocytogenes induced release of interleukin (IL)-12 and IL-18. In contrast treatment with purified listerial LTA yielded high levels of IL-18 release, but only minimal IL-12 production. Treatment of DCs with LPS conversely induced significant amounts of IL-12 production, but no IL-18. The release of both stimulating cytokines IL-12 and IL-18 upon infection with entire bacteria suggests that attenuated strains of L. monocytogenes may be a valuable tool for subunit vaccine delivery.     

IL-12 induces SDS-stable class II alphabeta dimers in murine dendritic cells

We assessed the effect of rIL-12 on the expression of class II molecules and on the ratio between SDS-stable and unstable alphabeta dimers in dendritic cells. We found that in vitro exposure of the cells to IL-12 increased their surface expression of mature class II molecules, despite a marked decline in class II biosynthesis. This effect was accompanied by a striking increase in the overall proportion of SDS-stable heterodimers.     

The production of IFN-gamma by IL-12/IL-18-activated macrophages requires STAT4 signaling and is inhibited by IL-4

Macrophages release IFN-gamma on combined stimulation with IL-12 and IL-18, but the signaling requirements of this process and its regulation by other cytokines are unknown. Here, we demonstrate that STAT4 is indispensable for IL-12/IL-18-induced production of IFN-gamma by mouse peritoneal macrophages. Type 2 NO synthase (NOS2), which we previously found to be a prerequisite for IL-12-induced IFN-gamma production in NK cells, was not required for IFN-gamma production by these macrophages. IL-12 alone already induced the expression of IFN-gamma mRNA, but nuclear translocation of STAT4, the release of IFN-gamma protein, and the subsequent production of NO was strictly dependent on the simultaneous presence of IL-18. NF-kappa B, which mediates IL-18 effects in T cells, was only weakly activated by IL-12 and/or IL-18 in macrophages. Known inhibitors of macrophage functions (e.g., IL-4 and TGF-beta) also suppressed macrophage IFN-gamma production and the subsequent production of NOS2-derived NO. The inhibitory effect of IL-4 was paralleled by nuclear translocation of STAT6, which in EMSAs was able to bind to the same DNA oligonucleotide as STAT4. These results further define the production of IFN-gamma by macrophages and point to a diversity in the signals required for IFN-gamma production by various cell types.     

Expression and release of IL-18 binding protein in response to IFN-gamma.

IL-18 and IL-18 binding protein (IL-18BP) are two newly described opponents in the cytokine network. Local concentrations of these two players may determine biological functions of IL-18 in the context of inflammation, infection, and cancer. As IL-18 appears to be involved in the pathogenesis of Crohn's disease and may modulate tumor growth, we investigated the IL-18/IL-18BPa system in the human colon carcinoma/epithelial cell line DLD-1. In this study, we report that IFN-gamma induces expression and release of IL-18BPa from DLD-1 cells. mRNA induction and secretion of IL-18BPa immunoreactivity were associated with an activity that significantly impaired release of IFN-gamma by IL-12/IL-18-stimulated PBMC. Inducibility of IL-18BPa by IFN-gamma was also observed in LoVo, Caco-2, and HCT116 human colon carcinoma cell lines and in the human keratinocyte cell line HaCaT. Induction of IL-18BPa in colon carcinoma/epithelial cell lines was suppressed by coincubation with sodium butyrate. IFN-gamma-mediated IL-18BPa and its suppression by sodium butyrate were confirmed in organ cultures of intestinal colonic biopsy specimens. In contrast, sodium butyrate did not modulate expression of IL-18. The present data suggest that IFN-gamma may limit biological functions of IL-18 at sites of colonic immune activation by inducing IL-18BPa production. Down-regulation of IL-18BPa by sodium butyrate suggests that reinforcement of local IL-18 activity may contribute to actions of this short-chain fatty acid in the colonic microenvironment.     

Superior protective and therapeutic effects of IL-12 and IL-18 gene-transduced dendritic neuroblastoma fusion cells on liver metastasis of murine neuroblastoma

Fusion vaccine of dendritic cells (DCs) and tumor cells has the advantage of inducing an immune response against multiple tumor Ags, including unknown tumor Ags. Using the liver metastasis model of C1300 neuroblastoma cells, we assessed the protective and therapeutic effects of fusion cells transduced with the IL-12 gene and/or the IL-18 gene. Improving the fusion method by combining polyethylene glycol and electroporation increased loading efficiency. In the A/J mice vaccinated with fusion cells modified with the LacZ gene (fusion/LacZ), IFN-gamma production and CTL activity increased significantly compared with that of DCs/LacZ, C1300/LacZ, or a mixture of the two (mixture/LacZ). With the transduction of IL-12 and IL-18 genes into the fusion cells (fusion/IL-12/IL-18), the level of IFN-gamma increased more than five times that of other fusion groups. In addition, NK cell activity and CTL activity increased significantly compared with that of mixture/LacZ, fusion/LacZ, DC/LacZ, or C1300/LacZ. In the protective and therapeutic studies of fusion cell vaccine, mice vaccinated with fusion/LacZ, fusion/IL-12, fusion/IL-18, or fusion/IL-12/IL-18 showed a significant decrease in liver metastasis and a significant increase in survival compared with mice given a mixture/LacZ, DCs/LacZ, or C1300/LacZ. In particular, the mice receiving fusion/IL-12/IL-18 vaccine showed a complete protective effect and the highest therapeutic effects. The present study investigates the improved loading efficiency of fusion cells and suggests that the introduction of IL-12 and IL-18 genes can induce extremely strong protective and therapeutic effects on liver metastasis of neuroblastoma.     

Dual role of the IL-12/IFN-gamma axis in the development of autoimmune myocarditis: induction by IL-12 and protection by IFN-gamma.

IL-12 and IFN-gamma positively regulate each other and type 1 inflammatory responses, which are believed to cause tissue damage in autoimmune diseases. We investigated the role of the IL-12/IFN-gamma (Th1) axis in the development of autoimmune myocarditis. IL-12p40-deficient mice on a susceptible background resisted myocarditis. In the absence of IL-12, autospecific CD4(+) T cells proliferated poorly and showed increased Th2 cytokine responses. However, IFN-gamma-deficient mice developed fatal autoimmune disease, and blockade of IL-4R signaling did not confer susceptibility to myocarditis in IL-12p40-deficient mice, demonstrating that IL-12 triggers autoimmunity by a mechanism independent of the effector cytokines IFN-gamma and IL-4. In conclusion, our results suggest that the IL-12/IFN-gamma axis is a double-edged sword for the development of autoimmune myocarditis. Although IL-12 mediates disease by induction/expansion of Th1-type cells, IFN-gamma production from these cells limits disease progression.     

IL-23 and IL-12 have overlapping,but distinct,effects on murine dendritic cells

IL-23 is a recently discovered heterodimeric cytokine that shares biological properties with proinflammatory cytokines. The biologically active heterodimer consists of p19 and the p40 subunit of IL-12. IL-23 has been shown to possess biological activities on T cells that are similar as well distinct from those of IL-12. We have constructed single-chain IL-23 and IL-12 fusion proteins (IL-23-Ig and IL-12-Ig) and have compared the two recombinant proteins for effects on murine dendritic cells (DC). Here we show that the IL-23-Ig can bind a significant proportion of splenic DC of both the CD8alpha(-) and CD8alpha(+) subtypes. Furthermore, IL-23and IL-12-Ig exert biological activities on DC that are only in part overlapping. While both proteins induce IL-12 production from DC, only IL-23-Ig can act directly on CD8alpha(+) DC to promote immunogenic presentation of an otherwise tolerogenic tumor peptide. In addition, the in vitro effects of IL-23-Ig did not appear to require IL-12Rbeta2 or to be mediated by the production of IL-12. These data may establish IL-23 as a novel cytokine with major effects on APC.     

Murine plasmacytoid dendritic cells produce IFN-gamma upon IL-4 stimulation

IL-4 plays a key role in inducing IL-4 production in CD4+ T cells, functioning as an important determinant for Th2 cell differentiation. We show here that IL-4 induces IFN-gamma production in B220+ plasmacytoid dendritic cells (PDCs). By searching for cell populations that produce IFN-gamma upon IL-4 stimulation, we found that PDCs were a major IFN-gamma-producing cell upon IL-4 stimulation in wild-type and Rag-2-/- splenocytes. Isolated PDCs, but not CD11b+ DCs or CD8+ DCs, produced IFN-gamma upon IL-4 stimulation. In vivo, the depletion of PDCs by anti-Ly6G/C Ab prevented IFN-gamma production induced by IL-4 administration. We also found that IL-4 induced IFN-gamma production, but not IL-12 or IFN-alpha production, in PDCs and also strongly enhanced CpG oligodeoxynucleotide-induced IFN-gamma production, but not CpG oligodeoxynucleotide-induced IL-12 or IFN-alpha production. However, IL-4 did not induce IFN-gamma production in Stat6-/- PDCs. Moreover, IL-4 induced Stat4 expression in PDCs through a Stat6-dependent mechanism, and only the Stat4-expressing PDCs produced IFN-gamma. Furthermore, IL-4 did not induce IFN-gamma production in Stat4-/- PDCs. These results indicate that PDCs preferentially produce IFN-gamma upon IL-4 stimulation by Stat6- and Stat4-dependent mechanisms.     

Distinct modulatory effects of LPS and CpG on IL-18-dependent IFN-gamma synthesis

Innate cellular production of IFN-gamma is suppressed after repeated exposure to LPS, whereas CpG-containing DNA potentiates IFN-gamma production. We compared the modulatory effects of LPS and CpG on specific cellular and cytokine responses necessary for NK-cell dependent IFN-gamma synthesis. C3H/HeN mice pretreated with LPS for 2 days generated 5-fold less circulating IL-12 p70 and IFN-gamma in response to subsequent LPS challenge than did challenged control mice. In contrast, CpG-pretreated mice produced 10-fold more circulating IFN-gamma without similar changes in IL-12 p70 levels, but with 10-fold increases in serum IL-18 relative to LPS-challenged control or endotoxin-tolerant mice. The role of IL-18 in CpG-induced immune potentiation was studied in splenocyte cultures from control, LPS-conditioned, or CpG-conditioned mice. These cultures produced similar amounts of IFN-gamma in response to rIL-12 and rIL-18. However, only CpG-conditioned cells produced IFN-gamma when cultured with LPS or CpG, and production was ablated in the presence of anti-IL-18R Ab. Anti-IL-18R Ab also reduced in vivo IFN-gamma production by >2-fold in CpG-pretreated mice. Finally, combined pretreatment of mice with LPS and CpG suppressed the production of circulating IFN-gamma, IL-12 p70, and IL-18 after subsequent LPS challenge. We conclude that CpG potentiates innate IFN-gamma production from NK cells by increasing IL-18 availability, but that the suppressive effects of LPS on innate cellular immunity dominate during combined LPS and CpG pretreatment. Multiple Toll-like receptor engagement in vivo during infection can result in functional polarization of innate immunity dominated by a specific Toll-like receptor response.     

Differential production of IL-12, IFN-alpha, and IFN-gamma by mouse dendritic cell subsets

Dendritic cells (DC) not only stimulate T cells effectively but are also producers of cytokines that have important immune regulatory functions. In this study we have extended information on the functional differences between DC subpopulations to include differences in the production of the major immune-directing cytokines IL-12, IFN-alpha, and IFN-gamma. Splenic CD4(-)8(+) DC were identified as the major IL-12 producers in response to microbiological or T cell stimuli when compared with splenic CD4(-)8(-) or CD4(+)8(-) DC; however, all three subsets of DC showed similar IL-12 regulation and responded with increased IL-12 p70 production if IL-4 was present during stimulation. High level CD8 expression also correlated with extent of IL-12 production for DC isolated from thymus and lymph nodes. By using gene knockout mice we ruled out any role for CD8alpha itself, or of priming by T cells, on the superior IL-12-producing capacity of the CD8(+) DC. Additionally, CD8(+) DC were identified as the major producers of IFN-alpha compared with the two CD8(-) DC subsets, a finding that suggests similarity to the human plasmacytoid DC lineage. In contrast, the CD4(-)8(-) DC produced much more IFN-gamma than the CD4(-)8(+) or the CD4(+)8(-) DC under all conditions tested.     

TL1A synergizes with IL-12 and IL-18 to enhance IFN-gamma production in human T cells and NK cells

TL1A, a recently described TNF-like cytokine that interacts with DR3, costimulates T cells and augments anti-CD3 plus anti-CD28 IFN-gamma production. In the current study we show that TL1A or an agonistic anti-DR3 mAb synergize with IL-12/IL-18 to augment IFN-gamma production in human peripheral blood T cells and NK cells. TL1A also enhanced IFN-gamma production by IL-12/IL-18 stimulated CD56(+) T cells. When expressed as fold change, the synergistic effect of TL1A on cytokine-induced IFN-gamma production was more pronounced on CD4(+) and CD8(+) T cells than on CD56(+) T cells or NK cells. Intracellular cytokine staining showed that TL1A significantly enhanced both the percentage and the mean fluorescence intensity of IFN-gamma-producing T cells in response to IL-12/IL-18. The combination of IL-12 and IL-18 markedly up-regulated DR3 expression in NK cells, whereas it had minimal effect in T cells. Our data suggest that TL1A/DR3 pathway plays an important role in the augmentation of cytokine-induced IFN-gamma production in T cells and that DR3 expression is differentially regulated by IL-12/IL-18 in T cells and NK cells.     

IL-12 and IL-18 are increased and stimulate IFN-gamma production in sarcoid lungs

Sarcoidosis is a systemic chronic granulomatous disease of unknown cause. Recent investigations revealed that the cytokine profile in inflamed lesions of sarcoidosis is Th1 dominant. To obtain better immunopathologic understanding of sarcoidosis, we examined the expression of IL-12 and IL-18 and their roles in IFN-gamma production in pulmonary sarcoidosis. Sarcoid cases had significantly elevated levels of IL-12 (p40 and p70) and IL-18 in bronchoalveolar lavage (BAL) fluids compared with healthy subjects. IL-12 p70 and IL-18 were immunohistochemically expressed in the epithelioid cells and giant cells of sarcoid granulomas. Significant induction of IFN-gamma, IL-12 p70, and IL-18 was observed from sarcoid BAL fluid cells with LPS stimulation, whereas LPS tended to induce only IL-12 p70 in BAL fluid cells from healthy subjects. Sarcoid cases had significantly greater IFN-gamma induction with LPS stimulation than healthy subjects did. IL-18 mRNA expression was observed in freshly isolated sarcoid BAL fluid cells as well as in LPS-stimulated sarcoid BAL fluid cells, but IFN-gamma and IL-12 mRNA expression was observed only in LPS-stimulated BAL fluid cells. Treatment with anti-IL-12- and anti-IL-18-neutralizing Abs significantly inhibited IFN-gamma production from LPS-stimulated BAL fluid cells of sarcoid cases. Coadministration of rIL-12 or rIL-18 induced greater IFN-gamma production in sarcoid BAL fluid cells than in normal BAL fluid cells. We concluded that bioactive IL-12 and IL-18 were produced in sarcoid BAL fluid cells and synergistically induced IFN-gamma production, indicating important cytokines in the Th1 response of sarcoidosis.     

Identification of IFN-gamma-producing cells in IL-12/IL-18-treated mice

Both IL-12 and IL-18 have been characterized as effective IFN-gamma-inducing cytokines. Concomitant treatment with IL-12 and IL-18 has been shown to synergistically induce IFN-gamma and may be an effective therapy for treating cancer, allergy, and infectious diseases. To understand the mechanisms underlying the strong induction of IFN-gamma by IL-12/IL-18 in mice, we focused our studies on the IFN-gamma-producing cells in various lymphoid organs and tissues and utilized the intracellular cytokine staining method to detect such cells in situ. After combined treatment with IL-12 and IL-18, IFN-gamma-positive cells in C57BL/6 mice were detected in the liver (12.18%), spleen (0.68%), bone marrow (1.80%), and peritoneum (2.12%), but not in the thymus or lymph nodes (<0.05 and <0.08%, respectively). A two-color staining method revealed that the majority of IFN-gamma-producing cells in the liver were NK1.1(+) cells, while those in the spleen were mostly CD3(+) cells, and to a lesser degree NK1.1(+) cells. Both CD4(+) and CD8(+) cells in the liver and in the spleen produced IFN-gamma. The CD19(+) B cell population was not definitely shown to produce IFN-gamma in our induction experiments. NKT cells, which are a subpopulation of NK1. 1(+) CD3(+) cells, were diminished in the liver and did not seem to contribute to IFN-gamma production arising from IL-12/IL-18 treatment. Further in vitro experiments confirmed the responsiveness of hepatic mononuclear cells to IL-12/IL-18 stimulation. This study is the first to show the IFN-gamma-producing mechanisms of IL-12/IL-18 treatment at the phenotypic level.