IL-27 regulates IL-12 responsiveness of naive CD4+ T cells through Stat1-dependent and -independent mechanisms

IL-27, a novel anti-HIV cytokine, activates multiple interferon-inducible genes in macrophages

OBJECTIVE

IL-27 is a novel anti-HIV cytokine that inhibits HIV-1 replication in both CD4 T cells and monocyte-derived macrophages (MDM) as IFN-alpha does. To elucidate the mechanism of the antiviral activity, we compared the activity and the gene expression profile of IL-27-treated cells with that of IFN-alpha-treated cells.

METHODS

CD4 T cells and monocytes were isolated from peripheral blood mononuclear cells of healthy donors. CD4 T cells were stimulated with phytohemagglutinin, and MDM were induced from monocytes using macrophage-colony stimulating factor. HIV-1 replication was monitored by p24 antigen capture assay. The gene expression profiles were analysed using DNA microarray analysis. The increase in the expression of IFN-inducible genes (IFIG) was confirmed by the Quantigene plex assay.

RESULTS

Both cytokines preferentially inhibited HIV-1 replication in MDM compared with CD4 T cells. Quantitative real time polymerase chain reaction, enzyme-linked immunosorbent assay and neutralization assay using anti-IFN indicated that IFN-alpha, IFN-beta and IFN-gamma had no significant impact on IL-27-mediated HIV inhibition. DNA microarray analysis illustrated that IFN-alpha induced 33 and 18 IFIG in MDM and CD4 T cells, respectively. IL-27 induced 28 IFIG in MDM and five IFIG in CD4 T cells. The quantitative assay confirmed that IL-27 activated genes of RNA-dependent kinase, oligoadenylate synthetase, myxovirus protein, and apolipoprotein B messenger RNA-editing enzyme-catalytic polypeptide-like 3G.

CONCLUSION

IL-27 differentially regulates the gene expression between CD4 T cells and MDM. IL-27 significantly induces antiviral genes in MDM as does IFN-alpha, suggesting that IL-27 inhibits HIV replication in MDM via mechanism(s) similar to that of IFN-alpha.

IL27: its roles in the induction and inhibition of inflammation

IL27 is the newest member of the IL6/IL12 family. It consists of Epstein-Barr virus-induced gene 3 (EBI3) and p28 subunits and signals through the IL27 receptor complex formed by WSX-1 and gp130 subunits. IL27-IL27 receptor interaction was initially shown to induce an early signal for the induction of Th1 responses. Recently other studies indicate that IL27 inhibits inflammatory Th17 lineage development. Despite the overall effects observed, the role of individual IL27 subunits remains controversial and is largely unclear. EBI3, while predominately found with p28 to form IL27, has different expression kinetics than p28. P28 has also been shown to signal independently of EBI3. Moreover, EBI3 has other potential binding partners such as the p35 subunit of IL12 and theoretically may regulate the inflammatory response through yet undiscovered mechanisms. Understanding the inflammatory and anti-inflammatory roles of IL27 and its subunits are essential before the immunological regulatory therapies can be developed.

IL-27 inhibits the development of regulatory T cells via STAT3

Regulatory CD4+ T cells are important for the homeostasis of the immune system and their absence correlates with autoimmune disorders. Here, we investigate the capacity of IL-27, a cytokine with pro- and anti-inflammatory properties, to regulate the generation of transforming growth factor beta (TGFbeta)-inducible forkhead box P3 (Foxp3)-positive regulatory T (Treg) cells. Our results demonstrate that IL-27 inhibits the acquisition of the Treg phenotype at the level of Foxp3, CD25 and CTLA-4 (CD152) expression as well as the suppressive function. In contrast to TGFbeta-induced Treg cells, the cells generated after differentiation in the presence of TGFbeta and IL-27 maintained the ability for IL-2 and tumour necrosis factor alpha (TNFalpha) production. The inhibitory effect of IL-27 on Treg generation was at least partially signal transducer and activator of transcription 3 (STAT3) dependent as examined by targeted STAT3 protein inhibition using small interfering RNA (siRNA), while STAT1-dependent signals seemed to oppose the STAT3 signals. In turn, TGFbeta blocked IL-27-induced T(h)1 differentiation. Thus, IL-27 and TGFbeta mutually control their effects on CD4+ T-cell differentiation, whereby IL-27 favours inflammatory conditions through a STAT3-dependent inhibition of Treg generation.

Transformation of hematopoietic cells and activation of JAK2-V617F by IL-27R, a component of a heterodimeric type I cytokine receptor

From a patient with acute myeloid leukemia (AML), we have identified IL-27Ra (also known as TCCR and WSX1) as a gene whose expression can induce the transformation of hematopoietic cells. IL-27Ra (IL-27R) is a type I cytokine receptor that functions as the ligand binding component of the receptor for IL-27 and functions with the glycoprotein 130 (gp130) coreceptor to induce signal transduction in response to IL-27. We show that IL-27R is expressed on the cell surface of the leukemic cells of AML patients. 32D myeloid cells transformed by IL-27R contain elevated levels of activated forms of various signaling proteins, including JAK1, JAK2, STAT1, STAT3, STAT5, and ERK1/2. Inhibition of JAK family proteins induces cell cycle arrest and apoptosis in these cells, suggesting the transforming properties of IL-27R depend on the activity of JAK family members. IL-27R also transforms BaF3 cells to cytokine independence. Because BaF3 cells lack expression of gp130, this finding suggests that IL-27R-mediated transformation of hematopoietic cells is gp130-independent. Finally, we show that IL-27R can functionally replace a homodimeric type I cytokine receptor in the activation of JAK2-V617F, a critical JAK2 mutation in various myeloproliferative disorders (MPDs). Our data demonstrate that IL-27R possesses hematopoietic cell-transforming properties and suggest that, analogous to homodimeric type I cytokine receptors, single-chain components of heterodimeric receptors can also enhance the activation of JAK2-V617F. Therefore, such receptors may play unappreciated roles in MPDs.

Contribution of IL-12R mediated feedback loop to Th1 cell differentiation

T helper 1 (Th1) cell fate is induced by overlapping signaling pathways, whose kinetic principles and regulatory motifs are largely unknown. We identified a simple positive feedback loop in the STAT4 signaling pathway, whereby activation by IL-12 leads to the increased expression in IL-12 receptor. A computational analysis shows that this feedback loop synergizes with the one mediated by the IFN-gamma secreted by differentiating cells, when the induction of Th1 cell fate is weak. Positive feedback loops are often utilized to enhance phenotypic differentiation. This effect was confirmed by experiments showing that stochastic fluctuations in the expression of IL-12 receptor gene were amplified, leading to two discrete levels of expression in a cell population.

Interleukins 27 and 6 induce STAT3-mediated T cell production of interleukin 10

Interleukin 10 (IL-10) has a prominent function in regulating the balance between protective and pathological T cell responses. Consistent with that activity, many sources of this cytokine are found in vivo, including from myeloid cells and a variety of T cell subsets. However, although there are many pathways that regulate innate production of IL-10, the factors that govern its synthesis by the adaptive response are poorly understood. Here we report that IL-27 and IL-6 induced T helper type 1 and type 2 cells, as well as T helper cells that produce IL-17, to secrete IL-10. This effect was dependent on the transcription factors STAT1 and STAT3 for IL-27 and on STAT3 for IL-6. Our studies identify a previously unknown pathway that allows the immune system to temper inflammatory responses.

A dominant function for interleukin 27 in generating interleukin 10-producing anti-inflammatory T cells

Regulatory T cells (T(reg) cells) expressing the transcription factor Foxp3 are key in maintaining the balance of immune homeostasis. However, distinct induced T regulatory type 1 (Tr1) cells that lack Foxp3 expression also regulate T cell function, mainly by producing the immunosuppressive cytokine interleukin 10 (IL-10). However, the factors required for the induction of IL-10-producing suppressive T cells are not fully understood. Here we demonstrate that dendritic cells modified by T(reg) cells induced the generation of IL-10-producing Tr1 cells. The differentiation of naive CD4+ T cells into IL-10-producing cells was mediated by IL-27 produced by the T(reg) cell-modified dendritic cells, and transforming growth factor-beta amplified the generation of induced IL-10+ Tr1 cells by IL-27. Thus, IL-27 and transforming growth factor-beta promote the generation of IL-10-producing Tr1 cells.

Production of IL-12, IL-23 and IL-27p28 by bone marrow-derived conventional dendritic cells rather than macrophages after LPS/TLR4-dependent induction by Salmonella Enteritidis

Induction of the interleukin-12 (IL-12) cytokine family comprising IL-12, IL-23, IL-27, and IL-12p40 by intracellular pathogens is required for orchestration of cell-mediated immune responses. Macrophages (MPhi) have been shown to be a source of IL-12 following TLR4-dependent activation by Salmonella (S.). In this study another antigen-presenting cell type, the conventional dendritic cell (cDC), was analyzed and its cytokine responses compared with those of MPhi. We generated bone marrow-derived conventional dendritic cells (BMDC) and macrophages (BMMPhi) by incubating murine bone marrow cells with supernatants containing granulocyte/macrophage colony-stimulating factor (GM-CSF) or macrophage colony-stimulating factor (M-CSF), respectively. Stimulation of BMDC and BMMPhi with S. enterica serovar Enteritidis (SE) or LPS resulted in the release of IL-12 and IL-23 by BMDC but not by BMMPhi. Furthermore, BMDC secreted approx. 20-fold more IL-12p40 and IL-27p28 than BMMPhi. However, BMDC and BMMPhi produced similar levels of IL-10. Using BMDC originating from wild-type (wt), TLR2(def) and TLR4(def) mice, we show that in BMDC the induction of IL-12, IL-23, and IL-27p28 by SE is dependent on TLR4, whereas low-level production of p40 is also mediated by pattern recognition receptors (PRR) other than TLR4. Interestingly, LPS- and SE-provoked responses of BMDC were remarkably similar indicating that LPS is the primary danger molecule of SE. Taken together, our results point to cDC rather than MPhi as the major producers of the IL-12 family members during in vitro infection with SE. The mechanisms of recognition of SE, however, appear to be the same for cDC and MPhi.

IL-27 suppresses Th2 cell development and Th2 cytokines production from polarized Th2 cells: a novel therapeutic way for Th2-mediated allergic inflammation

IL-27 up-regulates Th1 but down-regulates Th2 responses. However, its molecular mechanism and regulatory effects on polarized Th2 cells remain unclear. In this study, we have revealed that IL-27 inhibits Th2 cell development as well as Th2 cytokines production from already polarized Th2 cells by down-regulation of GATA-3 and up-regulation of T-bet expression simultaneously. In vivo daily IL-27 treatment for 1 wk after Leishmania major infection protects BALB/c mice from footpad swelling by diminishing parasite burden via reciprocal regulation of Th1 and Th2 responses. Furthermore, IL-27 stimulation causes marked reduction in the capacity of host mouse to mount a Th2 response against Strongyloides venezuelensis infection. Thus, IL-27-treated mice failed to develop intestinal mastocytosis after S. venezuelensis infection and exhibited a marked delay in parasite expulsion. Finally, intranasal administration of IL-27 inhibits OVA-induced airway hyperresponsiveness and inflammation in OVA-sensitized animals. Thus, IL-27 could provide us with a novel therapeutic way for treating Th2-associated diseases such as bronchial asthma.

IL-27 controls the development of inducible regulatory T cells and Th17 cells via differential effects on STAT1

IL-27 is an IL-12-related cytokine frequently present at sites of inflammation that can promote both anti- and pro-inflammatory immune responses. Here, we have analyzed the mechanisms how IL-27 may drive such divergent immune responses. While IL-27 suppressed the development of proinflammatory Th17 cells, a novel role for this cytokine in inhibiting the development of anti-inflammatory, inducible regulatory T cells (iTreg) was identified. In fact, IL-27 suppressed the development of adaptive, TGF-beta-induced Forkhead box transcription factor p3-positive (Foxp3(+)) Treg. Whereas the blockade of Th17 development was dependent on the transcription factor STAT1, the suppression of iTreg development was STAT1 independent, suggesting that IL-27 utilizes different signaling pathways to shape T cell-driven immune responses. Our data thus demonstrate that IL-27 controls the development of Th17 and iTreg cells via differential effects on STAT1.

Suppressive Effect of IL-27 on Encephalitogenic Th17 Cells and the Effector Phase of Experimental Autoimmune Encephalomyelitis

IL-27 has been shown to play a suppressive role in experimental autoimmune encephalomyelitis (EAE) as demonstrated by more severe disease in IL-27R-deficient (WSX-1(-/-)) mice. However, whether IL-27 influences the induction or effector phase of EAE is unknown. This is an important question as therapies for autoimmune diseases are generally started after autoreactive T cells have been primed. In this study, we demonstrate maximal gene expression of IL-27 subunits and its receptor in the CNS at the effector phases of relapsing-remitting EAE including disease peak and onset of relapse. We also show that activated astrocyte cultures secrete IL-27p28 protein which is augmented by the endogenous factor, IFN-gamma. To investigate functional significance of a correlation between gene expression and disease activity, we examined the effect of IL-27 at the effector phase of disease using adoptive transfer EAE. Exogenous IL-27 potently suppressed the ability of encephalitogenic lymph node and spleen cells to transfer EAE. IL-27 significantly inhibited both nonpolarized and IL-23-driven IL-17 production by myelin-reactive T cells thereby suppressing their encephalitogenicity in adoptive transfer EAE. Furthermore, we demonstrate a strong suppressive effect of IL-27 on active EAE in vivo when delivered by s.c. osmotic pump. IL-27-treated mice had reduced CNS inflammatory infiltration and, notably, a lower proportion of Th17 cells. Together, these data demonstrate the suppressive effect of IL-27 on primed, autoreactive T cells, particularly, cells of the Th17 lineage. IL-27 can potently suppress the effector phase of EAE in vivo and, thus, may have therapeutic potential in autoimmune diseases such as multiple sclerosis.

IFN-alpha regulates Toll-like receptor-mediated IL-27 gene expression in human macrophages

IL-27 is a novel member of the IL-12 cytokine family. IL-27 has pro- and anti-inflammatory properties, and it controls the responses of adaptive immunity. It promotes the differentiation of naïve Th cells and suppresses the effector functions of Th17 cells. Biologically active IL-27 is a heterodimer composed of EBV-induced gene 3 (EBI3) and p28 proteins. We report that TLR-dependent expression of IL-27 in human macrophages is mediated by IFN-alpha. Stimulation of macrophages with agonists for TLR3 {polyinosinic:polycytidylic acid [poly(I:C)]}, TLR4 (LPS), or TLR7/8 (R848) results in concurrent expression of EBI3 and p28. The p28 expression is inhibited with neutralizing anti-IFN-alpha antibodies. Unlike poly(I:C), LPS, and R848, TLR2 agonist (S)-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-N-palmitoyl-(R)-Cys-(S)-Ser(S)-Lys4-OH trihydrochloride does not stimulate macrophages to produce IFN-alpha, and therefore, it is not able to turn on the expression of p28. There is an IFN-stimulated response element (ISRE) in the p28 gene promoter. IFN-alpha enhances the expression of IFN regulatory factor 1 (IRF-1) in macrophages and induces binding of IRF-1 to the p28 ISRE site. The data provide a mechanistic basis for the IFN-alpha-mediated activation of IL-27. The data emphasize a role of IFN-alpha in immune responses, which rely on the recognition of pathogens by TLRs.

Expression of interleukin-27 by human trophoblast cells

Cytokines produced at the fetal-maternal interface play a key role in regulating maternal tolerance to the fetus and successful pregnancy. Previously, we showed that EBV-induced gene 3 (EBI3), an interleukin (IL)-12 p40 homologue, was expressed at very high levels by syncytiotrophoblasts and extravillous trophoblasts throughout human pregnancy. EBI3 was recently shown to associate with a novel ligand, p28, to form a new heterodimeric cytokine with important immunoregulatory functions, IL-27. In this study, we investigated whether EBI3 expression by trophoblast cells is associated with that of p28 to form IL-27. We found that genes encoding IL-27 (EBI3 and p28) and its receptor (IL-27R and gp130) were expressed in the placenta at various stages of pregnancy. Co-immunoprecipitation experiments performed from placental lysates, and ELISA of culture supernatants from placental explants, showed that IL-27 heterodimer was produced and released from placental cells. In situ studies of placentae of first, second and third trimester of pregnancy, and of choriocarcinomas, demonstrated that syncytiotrophoblast cells co-expressed EBI3 and p28. Similarly, extravillous trophoblast cells invading the decidua were found to co-express both subunits of IL-27. These data suggest that IL-27 may be part of the cytokine network regulating local immune responses and angiogenesis during human pregnancy.

IL-17 family cytokines and the expanding diversity of effector T cell lineages

Since its conception two decades ago, the Th1-Th2 paradigm has provided a framework for understanding T cell biology and the interplay of innate and adaptive immunity. Naive T cells differentiate into effector T cells with enhanced functional potential for orchestrating pathogen clearance largely under the guidance of cytokines produced by cells of the innate immune system that have been activated by recognition of those pathogens. This secondary education of post-thymic T cells provides a mechanism for appropriately matching adaptive immunity to frontline cues of the innate immune system. Owing in part to the rapid identification of novel cytokines of the IL-17 and IL-12 families using database searches, the factors that specify differentiation of a new effector T cell lineage-Th17-have now been identified, providing a new arm of adaptive immunity and presenting a unifying model that can explain many heretofore confusing aspects of immune regulation, immune pathogenesis, and host defense.

Discovery and biology of IL-23 and IL-27: related but functionally distinct regulators of inflammation

Long-term resistance to many infections depends on the innate ability of the immune system to coordinate the development of antigen-specific adaptive responses. Deficiencies in these events can result in increased susceptibility to pathogens, whereas an inability to regulate an appropriate response can lead to devastating pathological conditions. For over a decade, interleukin (IL)-12 has been recognized as the canonical cytokine that links innate and adaptive immunity, and with the discovery of IL-23 and IL-27 as cytokines related to IL-12, there has been a concerted effort to understand the relationship between these factors. The results emerging from these studies have provided fundamental new insights into the developmental pathways that promote the differentiation and function of CD4(+) T helper cells and offer a dramatically altered perspective on the cause and prevention of autoimmune disease. In this review, we aim to highlight the discoveries that have led to our current understanding of the biology of IL-23 and IL-27 in the context of their role in resistance to infection, immune-mediated inflammation, and cancer.

IL-27 Synthesis Induced by TLR Ligation Critically Depends on IFN Regulatory Factor 3

IL-27 is a heterodimeric cytokine composed of EBV-induced gene 3 and p28. Produced by dendritic cells (DCs) in response to TLR ligands, IL-27 recently emerged as a key regulator of inflammatory responses. In this study, we first demonstrate that Toll/IL-1R-containing adaptor inducing IFN-beta and its associated IFN regulatory factor (IRF) 3 transcription factor are critically involved in IL-27p28 expression in mouse DCs stimulated by TLR ligands. We then show that IL-27 serum levels are dramatically reduced in IRF3(-/-) upon LPS injection, indicating a critical role for IRF3 in TLR4-mediated IL-27 production in vivo. We identified an IRF3-binding site within the IL-27p28 promoter region which is required for IL-27p28 gene activation in reporter gene assays. In human DCs, IL-27p28 mRNA was preferentially induced by Toll/IL-1R-containing adaptor inducing IFN-beta-coupled TLR ligands and following CMV infection. Furthermore, chromatin immunoprecipitation studies demonstrate that IRF3 is recruited to the endogenous p28 promoter in TLR4-stimulated human DCs. We conclude that IRF3 activation is a master switch for IL-27 synthesis.

Regulation of defense responses against protozoan infection by interleukin-27 and related cytokines

Cytokine-mediated immunity is crucial in the defense against pathogens. Recently, IL-23 and IL-27 were identified, which along with IL-12 belong to the IL-12 cytokine family. IL-27 is pivotal for the induction of helper T cell (Th) 1 responses while IL-23 is important for the proliferation of memory type Th1 cells. Recent studies revealed that IL-27 also has an anti-inflammatory property. In some protozoan infection, various proinflammatory cytokines were over produced causing lethal inflammatory responses in IL-27 receptor-deficient mice. The anti-inflammatory effect of IL-27 depends, at least partly, on inhibition of the development of Th17 cells, a newly identified Th population that is induced by IL-23 and is characterized by the production of the inflammatogenic cytokine, IL-17. IL-27 thus has a double identity as an initiator and as an attenuator of immune responses and inflammation. With the discoveries of the new IL-12-related cytokines and Th17 cells, Th development is facing a new paradigm.

Role of Stat4-mediated signal transduction events in the generation of aggressor CD4+ T cells in herpetic stromal keratitis pathogenesis

Ocular infection with herpes simplex virus (HSV) causes a vision-impairing inflammatory reaction called herpetic stromal keratitis. In murine models, herpetic stromal keratitis lesions appear to be immunopathologic, mediated by CD4(+) T cells of Th1 phenotype. To provide insight about cytokine networks and signaling events involved in the development of aggressor CD4(+) T cells, ocular HSV infection was followed in mice deficient in Stat4 (Stat4(-/-) mice), the signal transducer for the cytokine interleukin-12 (IL-12). After ocular HSV infection of Stat4(-/-) and control BALB/c mice, clinical, histologic, and immunologic analyses were carried out. Further, to evaluate the involvement of Stat4 in the development of this aggressor population, naive CD4(+) T cells from Stat4(-/-) and BALB/c mice were adoptively transferred to C.B-17 SCID mice 1 day after corneal infection. Although Stat4(-/-) mice demonstrated increased susceptibility to lethal encephalitis and facial lesions, interestingly, these mice had less severe stromal keratitis in comparison to control animals. Adoptive transfer of naive CD4(+) T cells from Stat4(-/-) mice failed to produce disease in infected SCID recipients. The data imply a significant role of Stat4-mediated signaling events in the generation of an aggressor CD4(+) T cell population in stromal keratitis pathogenesis.

Peroxisome proliferator-activated receptor-gamma agonists suppress the production of IL-12 family cytokines by activated glia

The IL-12 family of cytokines, which include IL-12, IL-23, and IL-27, play critical roles in the differentiation of Th1 cells and are believed to contribute to the development of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Relatively little is known concerning the expression of IL-12 family cytokines by cells of the CNS, the affected tissue in MS. Previously, we and others demonstrated that peroxisome proliferator-activated receptor (PPAR)-gamma agonists suppress the development of EAE, alter T cell proliferation and phenotype, and suppress the activation of APCs. The present studies demonstrated that PPAR-gamma agonists, including the naturally occurring 15-deoxy-Delta(12,14)-PGJ(2) and the synthetic thiazoladinedione rosiglitazone, inhibited the induction of IL-12p40, IL-12p70 (p35/p40), IL-23 (p19/p40), and IL-27p28 proteins by LPS-stimulated primary microglia. In primary astrocytes, LPS induced the production of IL-12p40, IL-23, and IL-27p28 proteins. However, IL-12p70 production was not detected in these cells. The 15-deoxy-Delta(12,14)-PGJ(2) potently suppressed IL-12p40, IL-23, and IL-27p28 production by primary astrocytes, whereas rosiglitazone suppressed IL-23 and IL-27p28, but not IL-12p40 in these cells. These novel observations suggest that PPAR-gamma agonists modulate the development of EAE, at least in part, by inhibiting the production of IL-12 family cytokines by CNS glia. In addition, we demonstrate that PPAR-gamma agonists inhibit TLR2, MyD88, and CD14 expression in glia, suggesting a possible mechanism by which these agonists modulate IL-12 family cytokine expression. Collectively, these studies suggest that PPAR-gamma agonists may be beneficial in the treatment of MS.

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.

Polarized type-1 dendritic cells (DC1) producing high levels of IL-12 family members rescue patient TH1-type antimelanoma CD4+ T cell responses in vitro

Deficiencies in TH1-type immunity in patients with cancer may facilitate tumor progression and limit the effectiveness of current immunotherapy approaches. We hypothesized that Type-1 polarized dendritic cells (DC1) might be able to recondition patient antitumor CD4+ T cell responses toward the TH1-type in vitro. Although DC1 have been previously demonstrated to prime TH1 responses from naive CD4+ T cells, their impact on antigen-experienced TH responses remains unknown. We confirmed our own earlier observations that patient CD4+ T cell reactivity against melanoma-associated antigens (MAA) was weaker and less Type-1-polarized than their corresponding antiviral responses. Stimulation of patient CD4 T cells with peptide-pulsed DC1 (producing multiple IL-12 family member cytokines, including IL-12p70, IL-23, and IL-27) promoted robust TH1-type, epitope-specific T cell responses. Addition of exogenous IL-12 family member cytokines alone, or in combination, to nonpolarized DC was insufficient to equate to the benefits associated with DC1-based stimulation; however, IL-27 and IL-12p70 blockade neutralized the ability of DC1 cells to enhance TH1-type antitumor immunity in vitro. Notably, DC1-based stimulation seemed capable of "revitalizing" defective TH1-type responses within the CD45RO+ subset of antigen-experienced CD4+ T cells in melanoma patients. In addition to promoting elevated levels of IFN-gamma from responder CD4+ T cells, DC1-based stimulation also led to increased levels of IL-12Rbeta2 and t-bet expression by TH cells. These results suggest that preexisting CD4+ T cell immunity to cancer is not relegated to Type-1 insufficiency and may be corrected via the application of DC1-based vaccination protocols.

The biology and therapeutic potential of interleukin 27

Interleukin (IL-) 27 is a helical cytokine of the greater IL-6/IL-12 family with a broad range of pro- and anti-inflammatory properties. It can skew T helper cell development, suppress T cell proliferation, stimulate cytotoxic T cell activity, induce isotype switching in B cells, and has diverse effects on innate immune cells. In vivo, its most important role appears to be that of immune regulation, as mice with defects in IL-27 or its receptor display enhanced immune responses in a range of infectious and noninfectious situations. In this review, we discuss the body of knowledge on IL-27 and its potential therapeutic utility.

The interleukin-12 family: new players in transplantation immunity?

Since several years ago, interleukin (IL)-12 is known to be responsible for the differentiation of naive CD4+ T cells into type 1 helper T cells producing interferon-gamma. Recently, two other cytokines of the IL-12 family, IL-23 and IL-27, were shown to play key roles in experimental autoimmune disorders mediated by Th17 cells, a novel pro-inflammatory CD4+ T-cell subset secreting IL-17. As our knowledge of IL-12 family members is rapidly growing and changing, it will be important to specify their involvement in the induction and regulation of allograft rejection in animal models as well as in clinical settings. Herein, we review key features of cytokines belonging to the IL-12 family and discuss their potential relevance to transplantation immunity.

New members of the interleukin-12 family of cytokines: IL-23 and IL-27 modulate autoimmune diabetes

Multiple low doses of streptozotocin (5 x 40 mg/kg) given to susceptible male C57BL6 mice induced delayed and sustained hyperglycemia accompanied by body weight loss, mononuclear cell infiltration in the islet, and apoptosis of beta cells. Shorter regimes (4 x 40 mg/kg) did not have such effect. Administration of IL-23 at a dose of 400 ng/mL for 10 consecutive days concomitantly with this subdiabetogenic regimen of STZ, however, induced significant hyperglycemia, weight loss, and mononuclear cellular infiltration. The same regimen of IL-27 induced milder effect on glycemia and no weight loss inspite of a massive peri-islet and intra-islet infiltration of mononuclear cells. The molecular mechanisms underlying the actions of these cytokines on diabetogenesis is under study.

IL-28A is a key regulator of T-cell-mediated liver injury via the T-box transcription factor T-bet

BACKGROUND & AIMS

T-cell-mediated fulminant hepatitis is a potentially life-threatening event for which the underlying pathogenic mechanisms are not fully understood. Here, we demonstrate a key regulatory role of IL-28A in T-cell-mediated hepatitis.

METHODS

We cloned the murine IL-28A gene by reverse-transcription polymerase chain reaction, assessed the effects of recombinant IL-28A, and generated IL-28A-transgenic mice.

RESULTS

IL-28A induced TH1 cytokine production by CD4+ T lymphocytes in a T-bet-dependent manner and was up-regulated in a murine model of T-cell-mediated hepatitis upon Con A administration. In vivo, CD4+ T cells from newly created IL-28A-transgenic animals revealed an increased proliferation and proinflammatory TH1 cytokine production, as compared with wild-type mice. In addition, IL-28A-transgenic mice showed markedly augmented Con A-induced hepatitis with up-regulated interferon-gamma cytokine production, as compared with wild-type mice. Transgenic mice exhibited an up-regulation of the interferon-gamma-T-bet signaling pathway in Con A hepatitis, and augmented hepatitis in these mice was suppressed by crossing them with T-bet-deficient mice. In addition, in vivo blockade of interferon-gamma but not IL-4 suppressed augmented liver inflammation in transgenic mice, suggesting that IL-28A induces the T-bet signaling pathway in T-cell-induced hepatitis. Finally, IL-28A-specific antisense phosphorothioate oligonucleotides suppressed liver pathology in Con A-treated wild-type mice, as compared with the case of control oligonucleotides.

CONCLUSIONS

IL-28A emerges as a key regulatory cytokine with pathogenic function in T-cell-mediated liver injury. Thus, targeting of IL-28A represents a potential novel approach for therapy of Th1-mediated inflammatory diseases such as T-cell-mediated hepatitis.

Mapping of quantitative trait loci determining NK cell-mediated resistance to MHC class I-deficient bone marrow grafts in perforin-deficient mice

NK cells reject allogeneic and MHC class I-deficient bone marrow (BM) grafts in vivo. The mechanisms used by NK cells to mediate this rejection are not yet thoroughly characterized. Although perforin plays a major role, perforin-independent mechanisms are involved as well. C57BL/6 mice deficient in perforin (B6 perforin knockout (PKO)) reject class I-deficient TAP-1 KO BM cells as efficiently as normal B6 mice. In contrast, perforin-deficient 129S6/SvEvTac mice (129 PKO) cannot mediate this rejection while normal 129 mice efficiently reject. This suggests that in 129, but not in B6, mice, perforin is crucial for NK cell-mediated rejection of MHC class I-deficient BM grafts. To identify loci linked to BM rejection in perforin-deficient mice, we generated backcross 1 progeny by crossing (129 x B6)F(1) PKO mice to 129 PKO mice. In transplantation experiments, >350 backcross 1 progeny were analyzed and displayed a great variation in ability to reject TAP-1 KO BM grafts. PCR-based microsatellite mapping identified four quantitative trait loci (QTL) on chromosomes 2, 4, and 8, with the QTL on chromosome 8 showing the highest significance, as well as a fifth epistatic QTL on chromosome 3. This study describes the first important step toward identifying BM graft resistance gene(s).

IL-27 Induces Th1 Differentiation via p38 MAPK/T-bet- and Intercellular Adhesion Molecule-1/LFA-1/ERK1/2-Dependent Pathways

IL-27, a novel member of the IL-6/IL-12 family, activates both STAT1 and STAT3 through its receptor, which consists of WSX-1 and gp130 subunits, resulting in positive and negative regulations of immune responses. We recently demonstrated that IL-27 induces Th1 differentiation through ICAM-1/LFA-1 interaction in a STAT1-dependent, but T-bet-independent mechanism. In this study, we further investigated the molecular mechanisms by focusing on p38 MAPK and ERK1/2. IL-27-induced Th1 differentiation was partially inhibited by lack of T-bet expression or by blocking ICAM-1/LFA-1 interaction with anti-ICAM-1 and/or anti-LFA-1, and further inhibited by both. Similarly, the p38 MAPK inhibitor, SB203580, or the inhibitor of ERK1/2 phosphorylation, PD98059, partially suppressed IL-27-induced Th1 differentiation and the combined treatment completely suppressed it. p38 MAPK was then revealed to be located upstream of T-bet, and SB203580, but not PD98059, inhibited T-bet-dependent Th1 differentiation. In contrast, ERK1/2 was shown to be located downstream of ICAM-1/LFA-1, and PD98059, but not SB203580, inhibited ICAM-1/LFA-1-dependent Th1 differentiation. Furthermore, it was demonstrated that STAT1 is important for IL-27-induced activation of ERK1/2, but not p38 MAPK, and that IL-27 directly induces mRNA expression of growth arrest and DNA damage-inducible 45gamma, which is known to mediate activation of p38 MAPK. Finally, IL-12Rbeta2 expression was shown to be up-regulated by IL-27 in both T-bet- and ICAM-1/LFA-1-dependent mechanisms. Taken together, these results suggest that IL-27 induces Th1 differentiation via two distinct pathways, p38 MAPK/T-bet- and ICAM-1/LFA-1/ERK1/2-dependent pathways. This is in contrast to IL-12, which induces it via only p38 MAPK/T-bet-dependent pathway.

Noninfectious papilloma virus-like particles inhibit HIV-1 replication: implications for immune control of HIV-1 infection by IL-27

Human papilloma virus (HPV)-like particles (VLPs) have been used as a vaccine to prevent HPV infection. Recent studies demonstrate that VLPs bind to dendritic cells and induce the expression of antiviral cytokines such as interferon-alpha (IFN-alpha), interleukin-10 (IL-10) and IFN-gamma. In the present study, we evaluated the effect of VLPs on HIV-1 replication in peripheral blood mononuclear cells (PBMCs), CD4+ T cells, and macrophages. Here, we show that VLPs suppress the replication of both X4 and R5 HIV-1 without affecting the expression of CD4, CXCR4, and CCR5. Soluble factor(s) released by PBMCs and macrophages on VLPs treatment inhibited HIV-1 replication. To determine the inhibitory factors, DNA microarray analysis was performed using VLP-treated PBMCs and macrophages. VLPs induced the genes associated with IFN induction, immune responses, and antiviral responses, among with the recently described cytokine IL-27. Subsequently, IL-27 was found to be a potent inhibitor of HIV-1 replication in PBMCs, CD4+ T cells, and macrophages. Taken together, our studies identify a novel role of IL-27 in restricting HIV-1 replication and suggest that further examination of the inhibitory property of IL-27 may pave the way for a novel therapy for HIV-1 infection.

NF-{kappa}B is required for STAT-4 expression during dendritic cell maturation

The transcription factor STAT-4 plays a pivotal role in the IL-12-mediated development of naive CD4+ T cells into the Th1 phenotype. Initially thought to be restricted to the lymphoid lineage, STAT-4 was subsequently shown to be expressed in the myeloid compartment, mainly in activated monocytes, macrophages, and dendritic cells (DC). Here, we have studied STAT-4 in human monocyte-derived DC, and we demonstrated that its expression can be induced by multiple stimuli, such as the ligands for TLR-4, TLR-2, and TLR-3, different pathogens, CD40 ligand, and the proinflammatory cytokines TNF-alpha and IL-1beta. It is interesting that we found that STAT-4 is tyrosine-phosphorylated in response to type I IFN but not IL-12 in human mature DC. Cloning and functional analysis of the STAT-4 promoter showed that a NF-kappaB binding site, localized at -969/-959 bp upstream of the transcriptional start site, is involved in the regulation of this gene in primary human DC. EMSAs using a probe containing this NF-kappaB binding sequence and chromatin immunoprecipitation indicated that p65/p50 and p50/p50 dimers were the main NF-kappaB/Rel proteins involved in STAT-4 gene expression in maturing DC. The mutation of this kappaB site or the overexpression of the repressor IkappaBalpha exerted an inhibitory effect on a STAT-4 promoter-driven reporter as well as on STAT-4 expression. Altogether, these results indicate that STAT-4 can be finely tuned along with DC maturation through NF-kappaB activation and that its induction may be involved in preparing the DC to be receptive to the cytokine environment present in lymphoid organs.

IFN-gamma-inducing transcription factor, T-bet is upregulated by estrogen in murine splenocytes: role of IL-27 but not IL-12

Estrogen is believed to be involved in regulation of the differentiation, survival, or function of diverse immune cells as well as in many autoimmune and inflammatory diseases. However, the mechanisms behind the immunomodulatory effects of estrogen are poorly understood. Previously, we have shown that natural estrogen can upregulate IFN-gamma and IFN-gamma-mediated-inflammatory events (iNOS, nitric oxide, COX-2). Since IFN-gamma is regulated by T-bet, in this study, we investigated whether estrogen induces T-bet expression in primary murine splenocytes. We found that in vivo estrogen treatment primes splenocytes for early upregulation of T-bet upon activation by T cell stimulants, Concanavalin-A (Con-A) or anti-CD3 antibodies. The expression of T-bet protein was not altered by IL-12 while IFN-gamma had partial effects on T-bet in splenocytes from estrogen-treated mice. Notably, T-bet expression increased in Con-A-activated splenocytes from estrogen-treated mice in the presence of IL-27. Together, our studies show that in vivo estrogen exposure primes lymphocytes towards Th1 type development by promoting/upregulating T-bet expression, which is upregulated in part by IFN-gamma and IL-27. Given that T-bet is a potent inducer of IFN-gamma, these studies may lead to new lines of investigation in relation to many female-predominant autoimmune diseases and inflammatory disorders.

Two-Sided Roles of IL-27: Induction of Th1 Differentiation on Naive CD4+T Cells versus Suppression of Proinflammatory Cytokine Production Including IL-23-Induced IL-17 on Activated CD4+T Cells Partially Through STAT3-Dependent Mechanism

Recent lines of evidence have demonstrated that IL-27, a newly identified IL-12-related cytokine, has two apparently conflicting roles in immune responses: one as an initiator of Th1 responses and the other as an attenuator of inflammatory cytokine production. Although the IL-27-mediated Th1 initiation mechanism has been elucidated, little is known about the molecular basis for the suppression of cytokine production. In the present study, we demonstrated that IL-27 suppressed the production of various proinflammatory cytokines by fully activated CD4+ T cells while it had no effect on the cytokine production by CD4+ T cells at early phases of activation. IL-27 also suppressed IL-17 production by activated CD4+ T cells, thereby counteracting IL-23, another IL-12-related cytokine with proinflammatory effects. In fully activated CD4+ T cells, STAT3 was preferentially activated by IL-27 stimulation, whereas both STAT1 and 3 were activated by IL-27 in early activated CD4+ T cells. Lack of STAT3 in fully activated cells impaired the suppressive effects of IL-27. These data indicated that the preferential activation of STAT3 in fully activated CD4+ T cells plays an important role in the cytokine suppression by IL-27/WSX-1.

IFN-alpha-conditioned dendritic cells are highly efficient in inducing cross-priming CD8(+) T cells against exogenous viral antigens

Dendritic cells (DC) generated after a short-term exposure of monocytes to IFN-alpha and GM-CSF (IFN-DC) are highly effective in inducing cross-priming of CD8(+ )T cells against viral antigens. We have investigated the mechanisms responsible for the special attitude of these DC and compared their activity with that of reference DC. Antigen uptake and endosomal processing capabilities were similar for IFN-DC and IL-4-derived DC. Both DC types efficiently cross-presented soluble HCV NS3 protein to the specific CD8(+) T cell clone, even though IFN-DC were superior in cross-presenting low amounts of viral antigens. Moreover, when DC were pulsed with inactivated HIV-1 and injected into hu-PBL-SCID mice, the generation of virus-specific CD8(+ )T cells was markedly higher in animals immunized with IFN-DC than in mice immunized with CD40L-matured IL-4-DC. Of interest, in experiments with purified CD8(+ )T cells, IFN-DC were superior with respect to CD40L-matured IL-4-DC in inducing in vitro cross-priming of HIV-specific CD8(+ )T cells. This property correlated with enhanced potential to express the specific subunits of the IL-23 and IL-27 cytokines. These results suggest that IFN-DC are directly licensed for an efficient CD8(+) T cell priming by mechanisms likely involving enhanced antigen presentation and special attitude to produce IL-12 family cytokines.

Interleukin 27 negatively regulates the development of interleukin 17-producing T helper cells during chronic inflammation of the central nervous system

Studies have focused on the events that influence the development of interleukin 17 (IL-17)-producing T helper cells (T(H)-17 cells) associated with autoimmunity, such as experimental autoimmune encephalitis, but relatively little is known about the cytokines that antagonize T(H)-17 cell effector responses. Here we show that IL-27 receptor-deficient mice chronically infected with Toxoplasma gondii developed severe neuroinflammation that was CD4+ T cell dependent and was associated with a prominent IL-17 response. In vitro, treatment of naive primary T cells with IL-27 suppressed the development T(H)-17 cells induced by IL-6 and transforming growth factor-beta, which was dependent on the intracellular signaling molecule STAT1 but was independent of inhibition of IL-6 signaling mediated by the suppressor protein SOCS3. Thus IL-27, a potent inhibitor of T(H)-17 cell development, may be a useful target for treating inflammatory diseases mediated by these cells.

Interleukin 27 limits autoimmune encephalomyelitis by suppressing the development of interleukin 17-producing T cells

Interleukin 27 (IL-27) was first characterized as a proinflammatory cytokine with T helper type 1-inducing activity. However, subsequent work has demonstrated that mice deficient in IL-27 receptor (IL-27R alpha) show exacerbated inflammatory responses to a variety of challenges, suggesting that IL-27 has important immunoregulatory functions in vivo. Here we demonstrate that IL-27R alpha-deficient mice were hypersusceptible to experimental autoimmune encephalomyelitis and generated more IL-17-producing T helper cells. IL-27 acted directly on effector T cells to suppress the development of IL-17-producing T helper cells mediated by IL-6 and transforming growth factor-beta. This suppressive activity was dependent on the transcription factor STAT1 and was independent of interferon-gamma. Finally, IL-27 suppressed IL-6-mediated T cell proliferation. These data provide a mechanistic explanation for the IL-27-mediated immune suppression noted in several in vivo models of inflammation.

Interleukin-23 and interleukin-27 exert quite different antitumor and vaccine effects on poorly immunogenic melanoma

Recent studies revealed that two novel interleukin (IL)-12-related cytokines, IL-23 and IL-27, have potent antitumor activities. However, the antitumor effects were mainly evaluated in relatively highly immunogenic tumors and have not been fully evaluated against nonimmunogenic or poorly immunogenic tumors. In this study, we investigated the antitumor efficacies of IL-23 and IL-27 on poorly immunogenic B16F10 melanoma and found that the antitumor responses mediated by IL-23 and IL-27 were clearly different. In syngeneic mice, mouse single-chain (sc) IL-23-transfected B16F10 (B16/IL-23) tumors exhibited almost the same growth curve as B16F10 parental tumor about until day 20 after tumor injection and then showed growth inhibition or even regression. In contrast, scIL-27-transfected B16F10 (B16/IL-27) tumors exhibited significant retardation of tumor growth from the early stage. In vivo depletion assay revealed that the antitumor effect of B16/IL-23 was mainly mediated by CD8+ T cells and IFN-gamma whereas that of B16/IL-27 mainly involved natural killer cells and was independent of IFN-gamma. We also found that antitumor effects of B16/IL-23 and B16/IL-27 were synergistically enhanced by treatment with IL-18 and IL-12, respectively. Furthermore, B16/IL-23-vaccinated mice developed protective immunity against parental B16F10 tumors but B16/IL-27-vaccinated mice did not. When combined with prior in vivo depletion of CD25+ T cells, 80% of B16/IL-23-vaccinated mice completely rejected subsequent tumor challenge. Finally, we showed that the systemic administration of neither IL-23 nor IL-27 induced such intense toxicity as IL-12. Our data support that IL-23 and IL-27 might play a role in future cytokine-based immunotherapy against poorly immunogenic tumors.

Th17: an effector CD4 T cell lineage with regulatory T cell ties

The naive CD4 T cell is a multipotential precursor with defined antigen recognition specificity but substantial plasticity for development down distinct effector or regulatory lineages, contingent upon signals from cells of the innate immune system. The range of identified effector CD4 T cell lineages has recently expanded with description of an IL-17-producing subset, called Th17, which develops via cytokine signals distinct from, and antagonized by, products of the Th1 and Th2 lineages. Remarkably, Th17 development depends on the pleiotropic cytokine TGF-beta, which is also linked to regulatory T cell development and function, providing a unique mechanism for matching CD4 T cell effector and regulatory lineage specification. Here, we review Th17 lineage development, emphasizing similarities and differences with established effector and regulatory T cell developmental programs that have important implications for immune regulation, immune pathogenesis, and host defense.

1,25 Dihydroxyvitamin-D3 modulates JAK-STAT pathway in IL-12/IFNgamma axis leading to Th1 response in experimental allergic encephalomyelitis

Experimental allergic encephalomyelitis (EAE) is a Th1 cell-mediated autoimmune disease model of multiple sclerosis (MS). Vitamin D deficiency is commonly observed in MS patients and vitamin D supplements reduce the clinical symptoms of EAE and MS. Earlier studies have shown that in vivo treatment with vitamin D analogs ameliorates EAE in association with the inhibition of IL-12 production and Th1 differentiation. The mechanisms in the regulation of Th1 response by vitamin D in EAE/MS are, however, not known. We show that in vivo treatment of C57BL/6 and SJL/J mice (i.p.) with 100 ng of 1,25 dihydroxyvitamin D3, on every other day from Day 0-30, ameliorates EAE in association with the inhibition of IL-12 production and neural antigen-specific Th1 response. In vitro treatment with 1,25(OH)2D3 inhibited IFNgamma-induced tyrosine phosphorylation of STAT1, without affecting JAK2, in EOC-20 microglial cells. Treatment of activated T cells with 1,25(OH)2D3 also inhibited the IL-12-induced tyrosine phosphorylation of JAK2, TYK2, STAT3, and STAT4 in association with a decrease in T cell proliferation in vitro. These findings highlight the fact that vitamin D modulates JAK-STAT signaling pathway in IL-12/IFNgamma axis leading to Th1 differentiation and further suggest its use in the treatment of MS and other Th1 cell-mediated autoimmune diseases.

Antiangiogenic and antitumor activities of IL-27

IL-27 is a novel IL-6/IL-12 family cytokine playing an important role in the early regulation of Th1 responses. We have recently demonstrated that IL-27 has potent antitumor activity, which is mainly mediated through CD8(+) T cells, against highly immunogenic murine colon carcinoma. In this study, we further evaluated the antitumor and antiangiogenic activities of IL-27, using poorly immunogenic murine melanoma B16F10 tumors, which were engineered to overexpress single-chain IL-27 (B16F10 + IL-27). B16F10 + IL-27 cells exerted antitumor activity against not only s.c. tumor but also experimental pulmonary metastasis. Similar antitumor and antimetastatic activities of IL-27 were also observed in IFN-gamma knockout mice. In NOD-SCID mice, these activities were decreased, but were still fairly well-retained, suggesting that different mechanisms other than the immune response are also involved in the exertion of these activities. Immunohistochemical analyses with Abs against vascular endothelial growth factor and CD31 revealed that B16F10 + IL-27 cells markedly suppressed tumor-induced neovascularization in lung metastases. Moreover, B16F10 + IL-27 cells clearly inhibited angiogenesis by dorsal air sac method, and IL-27 exhibited dose-dependent inhibition of angiogenesis on chick embryo chorioallantoic membrane. IL-27 was revealed to directly act on HUVECs and induce production of the antiangiogenic chemokines, IFN-gamma-inducible protein (IP-10) and monokine induced by IFN-gamma. Finally, augmented mRNA expression of IP-10 and monokine induced by IFN-gamma was detected at the s.c. B16F10 + IL-27 tumor site, and antitumor activity of IL-27 was partially inhibited by the administration of anti-IP-10. These results suggest that IL-27 possesses potent antiangiogenic activity, which plays an important role in its antitumor and antimetastatic activities.

IL-23: changing the verdict on IL-12 function in inflammation and autoimmunity

IL-12 and IL-23 are molecules mainly produced by activated accessory and antigen-presenting cells. The tools for studying the biology of IL-12 in man and laboratory rodents have greatly advanced our appreciation of the central role of this molecule in cell-mediated immunity and inflammation. In particular, IL-12 is thought to be the prime-regulator of TH1 development. Targeting what was thought to be IL-12 function in vivo, resulted in drastic amelioration of inflammation and autoimmunity firmly linking TH1 polarisation to autoimmune development. Upon discovery of IL-23 and the fact that the large subunit of IL-23 is shared by IL-12, the research community only begins to grasp that the features attributed to IL-12 and TH1 development in inflammation are, in fact, dependent on IL-23 and not on IL-12. Hence, the perception of IL-12 biology is, to a large extent, based on a mistaken identity. In this review, the authors provide an overview of their current understanding of IL-12 and IL-23 biology in inflammation and autoimmunity, and how this viewpoint has been readjusted over the past 15 years.

Differential Effects of IL-27 on Human B Cell Subsets

IL-27 is a novel heterodimeric cytokine of the IL-12 family that plays an important role in the regulation of T cell responses. Its role on human B cells has not been previously studied. In this study, we show that both chains of the IL-27 receptor complex, IL-27R and gp130, are constitutively expressed at the surface of naive and memory human tonsillar B cells, and are induced on germinal center B cells following CD40 stimulation. In naive B cells, IL-27 induced strong STAT1 and STAT3 phosphorylation, whereas it induced moderate STAT1 and low STAT3 activation in memory B cells. IL-27 induced T-bet expression in naive and memory B cells stimulated by CD40 or surface Ig engagement, but induced significant IL-12Rbeta2 surface expression in anti-Ig-stimulated naive B cells only. In anti-Ig-stimulated naive or memory B cells, IL-27 also induced CD54, CD86, and CD95 surface expression. In addition, IL-27 increased proliferation of anti-Ig-activated naive B cells and of anti-CD40-activated naive and germinal center B cells, but not of CD40-activated memory B cells. These data indicate that the B cell response to IL-27 is modulated during B cell differentiation and varies depending on the mode of B cell activation.

IL-27 suppresses CD28-mediated [correction of medicated] IL-2 production through suppressor of cytokine signaling 3

IL-27 is a novel IL-6/IL-12 family cytokine that not only plays a role in the early regulation of Th1 differentiation, but also exerts an inhibitory effect on immune responses, including the suppression of proinflammatory cytokine production. However, the molecular mechanism by which IL-27 exerts the inhibitory effect remains unclear. In this study we demonstrate that IL-27 inhibits CD28-mediated IL-2 production and that suppressor of cytokine signaling 3 (SOCS3) plays a critical role in the inhibitory effect. Although IL-27 enhanced IFN-gamma production from naive CD4+ T cells stimulated with plate-coated anti-CD3 and anti-CD28 in the presence of IL-12, IL-27 simultaneously inhibited CD28-mediated IL-2 production. Correlated with the inhibition, IL-27 was shown to augment SOCS3 expression. Analyses using various mice lacking a signaling molecule revealed that the inhibition of IL-2 production was dependent on STAT1, but not on STAT3, STAT4, and T-bet, and was highly correlated with the induction of SOCS3 expression. Similar inhibition of CD28-mediated IL-2 production and augmentation of SOCS3 expression by IL-27 were observed in a T cell hybridoma cell line, 2B4. Forced expression of antisense SOCS3 or dominant negative SOCS3 in the T cell line blocked the IL-27-inudced inhibition of CD28-mediated IL-2 production. Furthermore, pretreatment with IL-27 inhibited IL-2-mediated cell proliferation and STAT5 activation, although IL-27 hardly affected the induction level of CD25 expression. These results suggest that IL-27 inhibits CD28-mediated IL-2 production and also IL-2 responses, and that SOCS3, whose expression is induced by IL-27, plays a critical role in the inhibitory effect in a negative feedback mechanism.

Expanding the effector CD4 T-cell repertoire: the Th17 lineage

The Th1/Th2 paradigm has provided the framework for understanding CD4 T-cell biology and the interplay between innate and adaptive immunity for almost two decades. Recent studies have defined a previously unknown arm of the CD4 T-cell effector response--the Th17 lineage--that promises to change our understanding of immune regulation, immune pathogenesis and host defense. The factors that specify differentiation of IL-17-producing effector T-cells from naïve T-cell precursors are being rapidly discovered and are providing insights into mechanisms by which signals from cells of the innate immune system guide alternative pathways of Th1, Th2 or Th17 development.

Complement and Toll-like receptors: Key regulators of adaptive immune responses

The innate immune system provides sophisticated defense mechanisms to protect complex macroorganisms from the attack of microorganisms. Among those, the complement system and Toll-like receptors are of paramount importance to discriminate between infectious non-self and non-infectious self and to provide critical danger signals instructing adaptive immune responses. Here, we will discuss recent advances in our understanding of the mechanisms underlying complement and TLR-mediated regulation of adaptive immunity. We will focus on the regulation of T cell immunity and discuss recent findings on the cross-talk between complement receptor and TLR signaling pathways. Such cross-talk is likely to affect the outcome of infections with intracellular pathogens, as well as the initiation and maintenance of aberrant immune responses leading to autoimmunity and atopy.

IL-12 up-regulates T-bet independently of IFN-gamma in human CD4+ T cells

T-bet is an important Th1 driving transcription factor regulated by IFN-gamma/STAT1 pathway. T-bet turns on IFN-gamma transcription in CD4+ T cells and T-bet-deficient cells fail to differentiate to Th1 direction. Previous reports have characterized function of T-bet mainly in murine cells and very little is known about its functions in human cells. Here, we studied T-bet expression kinetics in parallel with GATA3 during Th1/Th2 polarization. We demonstrate that in addition to CD3/CD28 activation, cytokines IL-12 and IFN-alpha in the presence of neutralizing anti-IFN-gamma enhanced T-bet mRNA and protein expression in human CD4+ cells. T-bet is known to be a potent inducer of IFN-gamma. Even though IFN-gamma and IL-12 stimulation induced similar levels of T-bet protein in human CD4+ cells, IFN-gamma-treated cells produced considerably less IFN-gamma than cells treated with IL-12. Therefore, high T-bet protein expression does not necessarily correlate with IFN-gamma production. In addition, we show that the immunosuppressive cytokine TGF-beta inhibits T-bet and GATA3 protein expression only if it is present prior to primary T cell activation and is maintained in the cultures during the early polarization of Th1/Th2 cells. In conclusion, we report new insights into the cytokine regulation of T-bet in human CD4+ T cells.

IL-27 Limits IL-2 Production during Th1 Differentiation

Although the ability of IL-27 to promote T cell responses is well documented, the anti-inflammatory properties of this cytokine remain poorly understood. The current work demonstrates that during infection with Toxoplasma gondii, IL-27R-deficient mice generate aberrant IL-2 responses that are associated with the development of a lethal inflammatory disease. Because in vivo depletion of IL-2 prolongs the survival of infected IL-27R-/- mice, these data suggest that IL-27 curbs the development of immunopathology by limiting parasite-induced IL-2 production. Consistent with this hypothesis, IL-27R-/- CD4+ T cells produce more IL-2 than wild-type counterparts during in vitro differentiation, and when rIL-27 is introduced, it can suppress the expression of IL-2 mRNA and protein by the latter group. Additionally, these studies reveal that, like IL-27, IL-12 can inhibit IL-2 production, and although each employs distinct mechanisms, they can synergize to enhance the effect. In contrast, this property is not shared by closely related cytokines IL-6 and IL-23. Thus, while traditionally viewed as proinflammatory agents, the present findings establish that IL-27 and IL-12 cooperate to limit the availability of IL-2, a potent T cell growth and survival factor. Moreover, because the current studies demonstrate that both can induce expression of suppressor of cytokine signaling 3, a protein that tempers cytokine receptor signaling, they also suggest that IL-27 and IL-12 share additionally inhibitory properties.

Augmentation of effector CD8+ T cell generation with enhanced granzyme B expression by IL-27

IL-27 is a novel IL-12 family member that plays a role in the early regulation of Th1 initiation. We have recently demonstrated that IL-27 has a potent antitumor activity, which is mainly mediated through CD8+ T cells, and also has an adjuvant activity to induce epitope-specific CTL in vivo. In this study, we further investigated the in vitro effect of IL-27 on CD8+ T cells of mouse spleen cells. In a manner similar to CD4+ T cells, IL-27 activated STAT1, -2, -3, -4, and -5, and augmented the expression of T-bet, IL-12Rbeta2, and granzyme B, and slightly that of perforin in naive CD8+ T cells stimulated with anti-CD3. IL-27 induced synergistic IFN-gamma production with IL-12 and proliferation of naive CD8+ T cells. Moreover, IL-27 enhanced proliferation of CD4+ T cell-depleted spleen cells stimulated by allogeneic spleen cells and augmented the generation of CTL. In STAT1-deficient naive CD8+ T cells, IL-27-induced proliferation was not reduced, but synergistic IFN-gamma production with IL-12 was diminished with decreased expression of T-bet, IL-12Rbeta2, granzyme B, and perforin. In T-bet-deficient naive CD8+ T cells, IL-27-induced proliferation was hardly reduced, but synergistic IFN-gamma production with IL-12 was diminished with decreased expression of IL-12Rbeta2, granzyme B, and perforin. However, IL-27 still augmented the generation of CTL from T-bet-deficient CD4+ T cell-depleted spleen cells stimulated by allogeneic spleen cells with increased granzyme B expression. These results suggest that IL-27 directly acts on naive CD8+ T cells in T-bet-dependent and -independent manners and augments generation of CTL with enhanced granzyme B expression.

Pulmonary interleukin-23 gene delivery increases local T-cell immunity and controls growth of Mycobacterium tuberculosis in the lungs

Interleukin-23 (IL-23) is a heterodimeric cytokine that shares IL-12 p40 but contains a unique p19 subunit similar to IL-12 p35. Previous studies indicate a greater importance for intact IL-12/23 p40 expression than IL-12 p35 for immunity against Mycobacterium tuberculosis, suggesting a role for IL-23 in host defense. The effects of IL-23 on the outcome of pulmonary infection with M. tuberculosis have not been described. Here, we show that local delivery of replication-defective adenovirus vectors encoding IL-23 (AdIL-23) greatly stimulated expression of both gamma interferon (IFN-gamma) and IL-17 in lung tissues of otherwise normal mice. When given 72 h prior to infection with M. tuberculosis, AdIL-23 significantly reduced the bacterial burden at 14, 21, and 28 days. Markedly lower levels of lung inflammation were observed at 28 days than in control mice pretreated with control adenovirus (AdNull) or vehicle controls. AdIL-23 pretreatment resulted in increased numbers of CD4(+) CD25(+) activated T cells in lungs and draining lymph nodes compared to control groups and more CD4(+) T cells bearing surface memory markers in lung lymph nodes. IL-23 gene delivery also significantly enhanced host anti-mycobacterial T-cell responses, as shown by elevated levels of IFN-gamma and IL-17 secreted in vitro following restimulation with M. tuberculosis purified protein derivative. Overall, our data show that transient IL-23 gene delivery in the lung is well tolerated, and they provide the initial demonstration that this factor controls mycobacterial growth while augmenting early pulmonary T-cell immunity.

Proteome profiling of interleukin-12 treated human T helper cells

Selective activation of T helper subsets 1 (Th1) and 2 (Th2) plays a crucial role in different pathological conditions. Th1 cell response is involved in pathogenesis of autoimmune diseases, such as type II diabetes and multiple sclerosis, and Th2 cell response in pathogenesis of allergy and asthma. Cytokine interleukin-12 (IL-12) is one of the key factors in the differentiation of naïve CD4(+) T cells into Th1 cells. In this study we used 2-DE and MS to find and identify IL-12 regulated proteins in human CD4(+) T cells. In total, 42 protein spots were found to be differentially expressed following IL-12 stimulation, of which 22 were up- and 20 down-regulated. Among the upregulated proteins there are a multifunctional cytokine macrophage migration inhibitory factor and a known IL-12 target gene Programmed cell death 4. Downregulated proteins include p21-activated kinase 2 and its upstream GTPase Cdc42. Compared to previous reports our analysis provides a new view on the IL-12 induced changes on CD4(+) T cells underscoring the importance of creating and combining the data generated at various levels to build a comprehensive view of a given biological process of the cell.