Interleukin-23 promotes a distinct CD4 T cell activation state characterized by the production of interleukin-17

Investigation of the IL23R gene in a Spanish rheumatoid arthritis cohort

Recently, a genome-wide association study identified the interleukin-23 receptor gene (IL23R) as an inflammatory bowel disease (IBD) associated gene. Given the involvement of IL23R in T-cell regulation, we decided to test whether this gene is associated with rheumatoid arthritis (RA). Eight IL23R gene polymorphisms (rs1,004,819, rs7,517,847, rs10,489,629, rs11,209,026, rs1,343,151, rs10,889,677, rs11,209,032, and rs1,495,965) were selected among the 10 most associated SNPs from the IBD study. A total of 322 RA patients and 342 healthy controls were genotyped for the selected SNPs using a Taqman 5' allelic discrimination assay. We did not find statistically significant differences when we compared allele and genotype frequencies between RA patients and controls for none of the IL23R gene polymorphisms under study. We did not observe significant differences when RA patients were stratified according to their clinical and demographic features. We conclude that the IL23R gene does not seem to be associated with RA predisposition in a Spanish population.

Francisella tularensis induces IL-23 production in human monocytes

Francisella tularensis, the causative agent of tularemia, is phagocytosed by immune cells such as monocytes and macrophages. Instead of being destroyed in the phagolysosome, the bacterium escapes the phagosome and replicates within the host cytosol. Recent studies indicate that phagosomal escape may have a major impact on the nature of the inflammatory cytokine response to infection. To better understand the host cell response to Francisella infection, we exposed human peripheral blood monocytes to Francisella novicida and analyzed transcriptional changes using high-density oligonucleotide microarrays. Results showed a nearly 300-fold up-regulation of transcripts for the p19 subunit of IL-23, and a nearly 18-fold up-regulation for the p40 subunit of IL-12. IL-23 is formed by the heterodimerization of p19 and p40, and is an important cytokine of the innate immune response. Up-regulation of p19 and p40 was confirmed at the protein level by Western blotting and ELISA analyses, and was found to be largely dependent on PI3K and NF-kappaB activity. Studies using medium from infected monocytes with or without a p19 blocking Ab showed that the secreted IL-23 induced IFN-gamma production from NK cells, suggesting a potential biologically important role for IL-23 in host defense. Finally, infection of human monocytes by the highly virulent Francisella SCHU S4 strain likewise led to IL-23 production, suggesting that the IL-23 response may be relevant during tularemia.

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.

C57BL/6 mice genetically deficient in IL-12/IL-23 and IFN-gamma are susceptible to experimental autoimmune myasthenia gravis, suggesting a pathogenic role of non-Th1 cells

Immunization with Torpedo acetylcholine receptor (TAChR) induces experimental autoimmune myasthenia gravis (EAMG) in C57BL/6 (B6) mice. EAMG development needs IL-12, which drives differentiation of Th1 cells. The role of IFN-gamma, an important Th1 effector, is not clear and that of IL-17, a proinflammatory cytokine produced by Th17 cells, is unknown. In this study, we examined the effect of simultaneous absence of IL-12 and IFN-gamma on EAMG susceptibility, using null mutant B6 mice for the genes of both the IL-12/IL-23 p40 subunit and IFN-gamma (dKO mice). Wild-type (WT) B6 mice served as control for EAMG induction. All mice were immunized with TAChR in Freund's adjuvant. dKO mice developed weaker anti-TAChR CD4(+)T cells and Ab responses than WT mice. Yet, they developed EAMG symptoms, anti-mouse acetylcholine receptor (AChR) Ab, and CD4(+) T cell responses against mouse AChR sequences similar to those of WT mice. dKO and WT mice had similarly reduced AChR content in their muscles, and IgG and complement at the neuromuscular junction. Naive dKO mice had significantly fewer NK, NKT, and CD4(+)CD25(+)Foxp3(+) T regulatory (Treg) cells than naive WT mice. Treg cells from TAChR-immunized dKO mice had significantly less suppressive activity in vitro than Treg cells from TAChR-immunized WT mice. In contrast, TAChR-specific CD4(+) T cells from TAChR-immunized dKO and WT mice secreted comparable amounts of IL-17 after stimulation in vitro with TAChR. The susceptibility of dKO mice to EAMG may be due to reduced Treg function, in the presence of a normal function of pathogenic Th17 cells.

Syk- and CARD9-dependent coupling of innate immunity to the induction of T helper cells that produce interleukin 17

The C-type lectin dectin-1 binds to yeast and signals through the kinase Syk and the adaptor CARD9 to induce production of interleukin 10 (IL-10) and IL-2 in dendritic cells (DCs). However, whether this pathway promotes full DC activation remains unclear. Here we show that dectin-1-Syk-CARD9 signaling induced DC maturation and the secretion of proinflammatory cytokines, including IL-6, tumor necrosis factor and IL-23, but little IL-12. Dectin-1-activated DCs 'instructed' the differentiation of CD4+ IL-17-producing effector T cells (T(H)-17 cells) in vitro, and a dectin-1 agonist acted as an adjuvant promoting the differentiation of T(H)-17 and T helper type 1 cells in vivo. Infection with Candida albicans induced CARD9-dependent T(H)-17 responses to the organism. Our data indicate that signaling through Syk and CARD9 can couple innate to adaptive immunity independently of Toll-like receptor signals and that CARD9 is required for the development of T(H)-17 responses to some pathogens.

IL-17-mediated regulation of innate and acquired immune response against pulmonary Mycobacterium bovis bacille Calmette-Guerin infection

IL-17 is a cytokine that induces neutrophil-mediated inflammation, but its role in protective immunity against intracellular bacterial infection remains unclear. In the present study, we demonstrate that IL-17 is an important cytokine not only in the early neutrophil-mediated inflammatory response, but also in T cell-mediated IFN-gamma production and granuloma formation in response to pulmonary infection by Mycobacterium bovis bacille Calmette-Guérin (BCG). IL-17 expression in the BCG-infected lung was detected from the first day after infection and the expression depended on IL-23. Our observations indicated that gammadelta T cells are a primary source of IL-17. Lung-infiltrating T cells of IL-17-deficient mice produced less IFN-gamma in comparison to those from wild-type mice 4 wk after BCG infection. Impaired granuloma formation was also observed in the infected lungs of IL-17-deficient mice, which is consistent with the decreased delayed-type hypersensitivity response of the infected mice against mycobacterial Ag. These data suggest that IL-17 is an important cytokine in the induction of optimal Th1 response and protective immunity against mycobacterial infection.

Stat3 and Stat4 direct development of IL-17-secreting Th cells

IL-17-secreting CD4(+) T cells are critically involved in inflammatory immune responses. Development of these cells is promoted in vivo and in vitro by IL-23 or TGFbeta1 plus IL-6. Despite growing interest in this inflammatory Th subset, little is known about the transcription factors that are required for their development. We demonstrate that Stat3 is required for programming the TGFbeta1 plus IL-6 and IL-23-stimulated IL-17-secreting phenotype, as well as for RORgammat expression in TGFbeta1 plus IL-6-primed cells. Moreover, retroviral transduction of a constitutively active Stat3 into differentiating T cell cultures enhances IL-17 production from these cells. We further show that Stat4 is partially required for the development of IL-23-, but not TGFbeta1 plus IL-6-primed IL-17-secreting cells, and is absolutely required for IL-17 production in response to IL-23 plus IL-18. The requirements for Stat3 and Stat4 in the development of these IL-17-secreting subsets reveal additional mechanisms in Th cell fate decisions during the generation of proinflammatory cell types.

T(H)-17 cells in the circle of immunity and autoimmunity

CD4(+) effector T cells have been categorized into two subsets: T helper type 1 (T(H)1) and T(H)2. Another subset of T cells that produce interleukin 17 (IL-17; 'T(H)-17 cells') has been identified that is highly proinflammatory and induces severe autoimmunity. Whereas IL-23 serves to expand previously differentiated T(H)-17 cell populations, IL-6 and transforming growth factor-beta (TGF-beta) induce the differentiation of T(H)-17 cells from naive precursors. These data suggest a dichotomy between CD4(+) regulatory T cells positive for the transcription factor Foxp3 and T(H)-17 cells: TGF-beta induces Foxp3 and generates induced regulatory T cells, whereas IL-6 inhibits TGF-beta-driven Foxp3 expression and together with TGF-beta induces T(H)-17 cells. Emerging data regarding T(H)-17 cells suggest a very important function for this T cell subset in immunity and disease.

Increased interleukin-17 production both in helper T cell subset Th17 and CD4-negative T cells in human immunodeficiency virus infection

Interleukin (IL)-17 is produced mainly by activated CD4(+) T cells, currently known as Th17. Human immunodeficiency virus (HIV) pathogenesis leads to CD4(+) T cell depletion. This is the first report of IL-17 in HIV infection. We assessed IL-17 expression in the CD4(+) T cells (Th17) of 40 asymptomatic HIV-infected treatment-naive patients compared with 40 HIV-seronegative volunteers. Peripheral blood mononuclear cells (PBMCs), with/without phorbol myristate acetate (PMA)/ionomycin stimulation, were stained with CD3, CD4, IL-17, and interferon (IFN)-gamma antibodies and analyzed by four-color flow cytometry. Both groups had comparable baseline data, except for age (mean+/-SD): 36 +/- 9 versus 30 +/- 9 yr (p= 0.001), CD4(+) T cell counts (median): 218 versus 623 cells/microL (p < 0.0001), CD8(+) T cell counts (median): 875.5 versus 382.5 cells/microL ((p) < 0.0001), and CD4(+)/CD8(+) cell ratios (median): 0.225 versus 1.45 (p< 0.0001). Without stimulation, the percentages of IL-17(+) CD3(+) CD4() and IL-17(+) CD3(+) CD4() cells among HIV-seropositive and -seronegative volunteers (median) were as follows: 0.68 versus 0.12% (p< 0.0001) and 0.92 versus 0.09% (p< 0.0001), respectively. With PMA/ionomycin stimulation, the percent IL-17 expression in CD4(+) cells (median) was 1.45 versus 0.65 (p< 0.0001) and in CD4() T cells it was 1.0 versus 0.12 (p< 0.0001). In conclusion, HIV infection is associated with a significant increase in IL-17 production in both CD4(+) and CD4() T cells in peripheral blood. IL-17 expression was further inducible by PMA/ionomycin stimulation in vitro only in CD4(+) T cells. The roles of IL-17 and Th17 in HIV viral replication and immunopathogenesis are under further investigation.

IL-6-gp130-STAT3 in T cells directs the development of IL-17+ Th with a minimum effect on that of Treg in the steady state

IL-17-producing Th (Th17) comprise a distinct lineage of pro-inflammatory Th that are major contributors to autoimmune diseases. Treatment with IL-6 and transforming growth factor beta (TGFbeta) induces naive CD4+ T cells to generate Th17, which also requires expression of the IL-6/TGFbeta target RORgammat. We reported that IL-6 transduces two signaling pathways via tyrosine redidues of the signal transducer gp130: one depends on signal transducers and activators of transcription (STAT)-3 activation and the other on Src homology region 2 domain-containing phosphatase 2 (SHP2)/Grb2 associated binder (Gab)/mitogen-activated protein kinase (MAPK) activation. Here, we showed that CD4+ T cells carrying a mutant gp130 that transduces the SHP2/Gab/MAPK pathway but not the STAT3-mediated one failed to develop into Th17, while CD4+ T cells whose mutant gp130 transduces the STAT3 signal only generated Th17, indicating that IL-6 acts directly on T cells through the tyrosine residues of gp130 required for STAT3 activation to promote the development of Th17. Moreover, we found that gp130-STAT3 pathway is essential for Th17 development and for the expression of RORgammat by using T cells specifically lacking gp130 and STAT3. Noteworthy is that the regulatory T cell (Treg) percentages and numbers were comparable between all mutant mice we tested in vivo, although we showed that IL-6-gp130-STAT3 pathway suppressed Treg development in vitro. Thus, we conclude that IL-6 acts directly to promote the development of Th17 by activating the T cell gp130-STAT3 pathway but has a minimum effect on Treg development at least in the steady state in vivo. Therefore, blockade of IL-6-gp130-STAT3 pathway in CD4+ T cells could be a good target for controlling unwanted Th17-mediated immune responses including autoimmune diseases.

IL-23 promotes CD4+ T cells to produce IL-17 in Vogt-Koyanagi-Harada disease

BACKGROUND

Vogt-Koyanagi-Harada (VKH) disease is a systemic refractory autoimmune disease. IL-23 has been thought to play a critical role in autoimmune disease through inducing the development of IL-17-producing CD4(+) T cells.

OBJECTIVE

To investigate the expression of IL-23 and IL-17 and the influence of IL-23 on IL-17 production in patients with VKH disease.

METHODS

Blood samples were taken from 25 patients with VKH disease and 16 healthy controls. Peripheral blood mononuclear cells (PBMCs) were subjected to analysis of IL-23p19 mRNA and IL-23 protein expression using RT-PCR and ELISA, respectively. The IL-17 levels in the supernatants of PBMCs and CD4(+) T cells cultured in the absence or presence of recombinant (r)IL-23, rIL-12, or anti-IFN-gamma were determined by ELISA.

RESULTS

The patients with VKH disease with active uveitis showed an elevated level of IL-23p19 mRNA in PBMCs, higher IL-23 in the serum and supernatants of PBMCs, and increased production of IL-17 by polyclonally stimulated PBMCs and CD4(+) T cells. Recombinant IL-23 significantly enhanced IL-17 production, whereas rIL-12 and IFN-gamma inhibited IL-17 production. More importantly, IL-17 production was significantly increased in patients with active uveitis in the presence of rIL-23. Both rIL-23 and rIL-12 enhanced IFN-gamma production.

CONCLUSION

The results suggest that IL-23-stimulated production of IL-17 by CD4(+) T cells may be responsible for the development of uveitis seen in patients with VKH disease.

CLINICAL IMPLICATIONS

This study provides a new insight into the mechanism involved in the development of VKH disease.

A phase 1, double-blind, placebo-controlled study evaluating single subcutaneous administrations of a human interleukin-12/23 monoclonal antibody in subjects with plaque psoriasis

OBJECTIVE

To evaluate safety, pharmacokinetics, pharmacodynamics, and clinical response of single subcutaneous (s.c.) administrations of a human monoclonal antibody against the p40 subunit of IL-12/23 (IL-12/23 mAb) in subjects with moderate-to-severe psoriasis.

METHODS

Twenty-one subjects were enrolled sequentially into 4 dose cohorts (0.27, 0.675, 1.35, and 2.7 mg/kg) and randomized to IL-12/23 mAb or placebo in a 4:1 ratio. Laboratory/clinical parameters and pharmacokinetics were evaluated through Week 24; mRNA cytokine expression was measured in psoriatic plaques at Week 1.

RESULTS

Mostly mild adverse events and no serious adverse events were reported. The pharmacokinetics (Cmax and AUC) of IL-12/23 mAb increased in an approximately dose-proportional manner. Of the 17 subjects who received IL-12/23 mAb, 13 achieved PASI 75 (compared with no placebo subjects). mRNA expression of IL-8, IL-18, and IFN-gamma in psoriatic plaques decreased in subjects with sustained Psoriasis Area and Severity Index (PASI) improvement.

LIMITATIONS

Interpretation of results is limited due to the small sample size in each dose cohort.

CONCLUSION

A single s.c. administration of IL-12/23 mAb was well tolerated and showed clinical response in subjects with moderate-to-severe psoriasis.

Distinct functional motifs within the IL-17 receptor regulate signal transduction and target gene expression

IL-17 is the founding member of a novel family of proinflammatory cytokines that defines a new class of CD4+ effector T cells, termed "Th17." Mounting evidence suggests that IL-17 and Th17 cells cause pathology in autoimmunity, but little is known about mechanisms of IL-17RA signaling. IL-17 through its receptor (IL-17RA) activates genes typical of innate immune cytokines, such as TNFalpha and IL-1beta, despite minimal sequence similarity in their respective receptors. A previous bioinformatics study predicted a subdomain in IL-17-family receptors with homology to a Toll/IL-1R (TIR) domain, termed the "SEFIR domain." However, the SEFIR domain lacks motifs critical for bona fide TIR domains, and its functionality was never verified. Here, we used a reconstitution system in IL-17RA-null fibroblasts to map functional domains within IL-17RA. We demonstrate that the SEFIR domain mediates IL-17RA signaling independently of classic TIR adaptors, such as MyD88 and TRIF. Moreover, we identified a previously undescribed"TIR-like loop" (TILL) required for activation of NF-kappaB, MAPK, and up-regulation of C/EBPbeta and C/EBPdelta. Mutagenesis of the TILL domain revealed a site analogous to the LPS(d) mutation in TLR4, which renders mice insensitive to LPS. However, a putative salt bridge typically found in TIR domains appears to be dispensable. We further identified a C-terminal domain required for activation of C/EBPbeta and induction of a subset IL-17 target genes. This structure-function analysis of a IL-17 superfamily receptor reveals important differences in IL-17RA compared with IL-1/TLR receptors.

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 interleukin-17 and interleukin-17-induced cytokines interleukin-6 and interleukin-8 in unstable coronary artery disease

BACKGROUND

Atherosclerosis is a chronic inflammatory disease and interleukins are considered to play a key role in the chronic vascular inflammatory response that is typical of atherosclerosis. The serum levels of several of these cytokines have been found to positively correlate with coronary arterial disease and its sequelae.

AIM

The aim of our study was to evaluate the levels of a comparatively new cytokine IL-17, in patients with stable and unstable coronary artery disease in order to assess whether unstable coronary artery disease patients had higher IL-17 levels.

MATERIALS AND METHODS

We analyzed the concentrations of IL-17, IL-6, IL-8 and IL-10 using enzyme-linked immunosorbent assay and heat-sensitive C-reactive protein using latex particle-enhanced immunoturbidimetry in 58 consecutive unselected patients divided into three groups: stable angina (n=14), unstable angina (n=24) and acute myocardial infarction (n=20). We further compared them with 20 healthy controls. These 58 patients were also angiographically studied and divided into two groups: simple lesion (n=22) and complex lesion (n=36), on the basis of the coronary plaque morphology.

RESULTS

Our results show increased concentrations of the proinflammatory cytokines IL-17, IL-6, IL-8 and heat-sensitive C-reactive protein, and decreased concentration of IL-10 in plasma of unstable angina and acute myocardial infarction patients. Plasma concentration of IL-17 was also positively correlated with plasma concentrations of IL-6 and heat-sensitive C-reactive protein. Our findings further showed that IL-17 values were higher in patients having angiographically visible complex types of lesions but no difference was observed between complex and simple lesion morphology patients.

CONCLUSION

In conclusion, these findings point towards a role of inflammation in the form of increased activity of IL-17, IL-6 and IL-8 in patients of unstable angina and acute myocardial infarction and thus suggest that IL-17-driven inflammation may play a role in the promotion of clinical instability in patients with coronary artery disease.

Interleukin-23 (IL-23)-IL-17 cytokine axis in murine Pneumocystis carinii infection

Host defense mechanisms against Pneumocystis carinii are not fully understood. Previous work in the murine model has shown that host defense against infection is critically dependent upon host CD4(+) T cells. The recently described Th17 immune response is predominantly a function of effector CD4(+) T cells stimulated by interleukin-23 (IL-23), but whether these cells are required for defense against P. carinii infection is unknown. We tested the hypothesis that P. carinii stimulates the early release of IL-23, leading to increases in IL-17 production and lung effector CD4(+) T-cell population that mediate clearance of infection. In vitro, stimulation of alveolar macrophages with P. carinii induced IL-23, and IL-23p19 mRNA was expressed in lungs of mice infected with this pathogen. To address the role of IL-23 in resistance to P. carinii, IL-23p19-/- and wild-type control C57BL/6 mice were infected and their fungal burdens and cytokine/chemokine responses were compared. IL-23p19-/- mice displayed transient but impaired clearance of infection, which was most apparent 2 weeks after inoculation. In confirmatory studies, the administration of either anti-IL-23p19 or anti-IL-17 neutralizing antibody to wild-type mice infected with P. carinii also caused increases in fungal burdens. IL-17 and the lymphocyte chemokines IP-10, MIG, MIP-1alpha, MIP-1beta, and RANTES were decreased in the lungs of infected IL-23p19-/- mice in comparison to their levels in the lungs of wild-type mice. In IL-23p19-/- mice infected with P. carinii, there were fewer effector CD4(+) T cells in the lung tissue. Collectively, these studies indicate that the IL-23-IL-17 axis participates in host defense against P. carinii.

The PD-1/PD-L pathway is up-regulated during IL-12-induced suppression of EAE mediated by IFN-gamma

Experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS), is mediated by autoantigen-specific T-helper1 (Th1) cells. IL-12, an inducer of Th1 cell development, exerts immunomodulatory effects in EAE. Programmed death-1 (PD-1) and PD-1 ligand (PD-L), new members of the B7 superfamily of costimulatory molecules, play a critical role in regulating EAE. Whether the interaction of IL-12 and the PD-1/PD-L pathway regulates EAE is unclear. We have previously shown that IL-12 suppresses EAE induced by MOG35-55 in C57BL/6 mice, but not in IFN-gamma-deficient mice, suggesting that IFN-gamma is required for the inhibitory effects of IL-12 on EAE. In the current study, PD-L1 expression is up-regulated following IL-12 treatment in wild-type mice, but not in IFN-(-deficient EAE mice. Similarly, IL-12 induces IFN-gamma and PD-L1 expression in cultured MOG-specific T cells from wild-type mice but not from IFN-gamma-deficient mice. Furthermore, PD-L1 expression increased specifically in CD11b+ antigen presenting cells (APCs) after IL-12 administration. These data suggest that one mechanism of IL-12 suppression of EAE is mediated by PD-1/PD-L signaling downstream of IFN-gamma induction in CD11b+ APCs. The regulation of PD-1/PD-L1 may have potential therapeutic effects for EAE and MS.

Borrelia burgdorferipotently activates bone marrow-derived conventional dendritic cells for production of IL-23 required for IL-17 release by T cells

Lyme borreliosis is characterized by cellular inflammatory responses at multiple body sites. Recently, an association of interleukin-17 (IL-17) and Lyme arthritis was suggested. In this context, it is of special interest that the heterodimeric cytokine IL-23 can act on T cells and initiate the up-regulation of effector cytokines such as IL-17. To determine the role of this specific cytokine cascade for the induction of subsequently induced proinflammatory events we developed an in vitro system to investigate the IL-23-inducing capacity of Borrelia burgdorferi and the potential of the spirochete for inducing the IL-23/IL-17 axis. We used cells derived from mice deficient for IL-23 or IL-12 only or deficient for both IL-12 and IL-23 to define precisely the function of these cytokines. Experiments with bone marrow-derived dendritic cells (BMDC) identified these cells as sources for IL-23 but not for IL-12 after B. burgdorferi exposure. Subsequent investigations with T cell-depleted splenocyte fractions revealed a tight IL-23/IL-17 axis in response to the spirochetes. Monoclonal antibodies that block IL-23 showed further that BMDC-derived IL-23 was required for production of IL-17 in this experimental model. These in vitro data describing a spirochete-induced release of IL-23 may help to define IL-17-dependent inflammatory responses in the disease.

After interleukin-12p40, are interleukin-23 and interleukin-17 the next therapeutic targets for inflammatory bowel disease?

Inflammatory bowel disease (IBD), typified by Crohn's disease and ulcerative colitis, is a common disorder characterized by recurrent and serious inflammation of the gastrointestinal tract. Recent immunologic advances have established that T cells and inflammatory cytokines play a pivotal role in the gastrointestinal inflammation of IBD. However, many cytokines not only elicit inflammation but also protect host against microbial invasion. Hence, suppression of these dual-purpose cytokines often exposes the patients to significant risk of infection. Recent research on Interleukin (IL)-23, IL-17, and IL-17 producing T cells has become the vanguard of further understanding the contribution of cytokines to autoimmune and inflammatory diseases. IL-23 is a newly discovered member of the IL-12-related cytokine family, and is primarily involved in the differentiation of pathogenic T cells characterized by their production of IL-17. IL-17 is a potent inflammatory mediator implicated in a number of autoimmune diseases. The discovery of this IL-23/IL-17-mediated inflammatory axis is having a profound impact on the elucidation of T cell-mediated pathogenesis as well as development of novel therapeutic targets. In this review, we discuss the current literature and present our recent studies on the role of IL-23 and IL-17 in the pathogenesis of IBD. Controlling the expression/production of IL-23 and IL-17 is an approach that would allow the development of a novel treatment strategy with more anti-inflammatory efficacy and potentially with less suppressive effects on host defenses.

Association of gamma interferon and interleukin-17 production in intestinal CD4+ T cells with protection against rotavirus shedding in mice intranasally immunized with VP6 and the adjuvant LT(R192G)

Mucosal immunization of mice with chimeric, Escherichia coli-expressed VP6, the protein that comprises the intermediate capsid layer of the rotavirus particle, together with attenuated E. coli heat-labile toxin LT(R192G) as an adjuvant, reduces fecal shedding of rotavirus antigen by >95% after murine rotavirus challenge, and the only lymphocytes required for protection are CD4+ T cells. Because these cells produce cytokines with antiviral properties, the cytokines whose expression is upregulated in intestinal memory CD4+ T cells immediately after rotavirus challenge of VP6/LT(R192G)-immunized mice may be directly or indirectly responsible for the rapid suppression of rotavirus shedding. This study was designed to identify which cytokines are significantly upregulated in intestinal effector sites and secondary lymphoid tissues of intranasally immunized BALB/c mice after challenge with murine rotavirus strain EDIM. Initially, this was done by using microarray analysis to quantify mRNAs for 96 murine common cytokines. With this procedure, the synthesis of mRNAs for gamma interferon (IFN-gamma) and interleukin-17 (IL-17) was found to be temporarily upregulated in intestinal lymphoid cells of VP6/LT(R192G)-immunized mice at 12 h after rotavirus challenge. These cytokines were also produced in CD4+ T cells obtained from intestinal sites specific to VP6/LT(R192G)-immunized mice after in vitro exposure to VP6 as determined by intracellular cytokine staining and secretion of cytokines. Although genetically modified mice that lack receptors for either IFN-gamma or IL-17 remained protected after immunization, these results provide suggestive evidence that these cytokines may play direct or indirect roles in protection against rotavirus after mucosal immunization of mice with VP6/LT(R192G).

The straw that stirs the drink: insight into the pathogenesis of inflammatory bowel disease revealed through the study of microflora-induced inflammation in genetically modified mice

Abnormal response to enteric microflora is a critical factor driving bowel inflammation in patients with inflammatory bowel disease (IBD). Mice with genetically engineered mutations have played a central role in both formulating this hypothesis and elucidating the mechanism that normally protect the host from excessive inflammation within the bowel. One emerging theme is the importance of regulation within the innate immune system in protecting from microflora-driven pathology. In this review, I describe how genetically engineered mice have played a crucial role in shaping our conceptual understanding of pathways that regulate the development of chronic bowel inflammation, and furthermore, explore data derived from the study of genetically engineered mice that implicates the fundamental importance of regulation within the innate immune system in the control of this process.

The role of T helper 17 (Th17) and regulatory T cells (Treg) in human organ transplantation and autoimmune disease

Uncommitted (naive) murine CD4+ T helper cells (Thp) can be induced to differentiate towards T helper 1 (Th1), Th2, Th17 and regulatory (Treg) phenotypes according to the local cytokine milieu. This can be demonstrated most readily both in vitro and in vivo in murine CD4+ T cells. The presence of interleukin (IL)-12 [signalling through signal transduction and activator of transcription (STAT)-4] skews towards Th1, IL-4 (signalling through STAT-6) towards Th2, transforming growth factor (TGF)-beta towards Treg and IL-6 and TGF-beta towards Th17. The committed cells are characterized by expression of specific transcription factors, T-bet for Th1, GATA-3 for Th2, forkhead box P3 (FoxP3) for Tregs and RORgammat for Th17 cells. Recently, it has been demonstrated that the skewing of murine Thp towards Th17 and Treg is mutually exclusive. Although human Thp can also be skewed towards Th1 and Th2 phenotypes there is as yet no direct evidence for the existence of discrete Th17 cells in humans nor of mutually antagonistic development of Th17 cells and Tregs. There is considerable evidence, however, both in humans and in mice for the importance of interferon (IFN)-gamma and IL-17 in the development and progression of inflammatory and autoimmune diseases (AD). Unexpectedly, some models of autoimmunity thought traditionally to be solely Th1-dependent have been demonstrated subsequently to have a non-redundant requirement for Th17 cells, notably experimental allergic encephalomyelitis and collagen-induced arthritis. In contrast, Tregs have anti-inflammatory properties and can cause quiescence of autoimmune diseases and prolongation of transplant function. As a result, it can be proposed that skewing of responses towards Th17 or Th1 and away from Treg may be responsible for the development and/or progression of AD or acute transplant rejection in humans. Blocking critical cytokines in vivo, notably IL-6, may result in a shift from a Th17 towards a regulatory phenotype and induce quiescence of AD or prevent transplant rejection. In this paper we review Th17/IL-17 and Treg biology and expand on this hypothesis.

IL-18, but not IL-12, is required for optimal cytokine production by influenza virus-specific CD8+ T cells

The potent innate cytokines IL-12 and IL-18 are considered to be important antigen-independent mediators of IFN-gamma production by NK cells and T lymphocytes. The present analysis addresses the physiological role of IL-12 and IL-18 in the generation of virus-specific CD8+ T cells. Both wt C57BL/6J (B6) mice and mice with disrupted IL-12p40 (IL-12p40(-/-)) or IL-18 (IL-18(-/-)) genes were infected with an influenza A virus and the characteristics of the resultant epitope-specific CD8+ T cell responses were compared. While IL-12 appeared to have no notable effect on either virus growth or on CD8+ T cell response profiles, the absence of IL-18 was associated with delayed virus clearance from the lung and, despite normal numbers, a significantly reduced production of IFN-gamma, TNF-alpha, and IL-2 by epitope-specific CD8+ T cells. While this cytokine phenotype was broadly maintained in IL-12p40/IL-18 double-knockout mice, no evidence was seen for any additive effect. Together, our results suggest that IL-18, but not IL-12, induces optimal, antigen-specific production of key cytokines by CD8+ T cells for the efficient clearance of influenza virus from the lungs of infected mice.

T-bet regulates the fate of Th1 and Th17 lymphocytes in autoimmunity

IL-17-producing T cells (Th17) have recently been implicated in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), an animal model for the human disease multiple sclerosis. However, little is known about the transcription factors that regulate these cells. Although it is clear that the transcription factor T-bet plays an essential role in the differentiation of IFN-gamma-producing CD4(+) Th1 lymphocytes, the potential role of T-bet in the differentiation of Th17 cells is not completely understood. In this study, therapeutic administration of a small interfering RNA specific for T-bet significantly improved the clinical course of established EAE. The improved clinical course was associated with suppression of newly differentiated T cells that express IL-17 in the CNS as well as suppression of myelin basic protein-specific Th1 autoreactive T cells. Moreover, T-bet was found to directly regulate transcription of the IL-23R, and, in doing so, influenced the fate of Th17 cells, which depend on optimal IL-23 production for survival. We now show for the first time that suppression of T-bet ameliorates EAE by limiting the differentiation of autoreactive Th1 cells, as well as inhibiting pathogenic Th17 cells via regulation of IL-23R.

Association of polymorphisms in IL-12/IFN-gamma pathway genes with susceptibility to pulmonary tuberculosis in Indonesia

Upon infection with mycobacteria the IL-12/IFN-gamma axis plays an essential role in the activation of cell-mediated immunity required for the elimination of pathogens. Mutations in genes of the IL-12/IFN-gamma axis are known to cause extreme susceptibility to infection with environmental mycobacteria, and subtle variations in these genes may influence susceptibility to more virulent mycobacteria. We analyzed the distribution of polymorphisms in four essential genes from the IL-12/IFN-gamma axis, IL12B, IL12RB1, IFNG and IFNGR1, in 382 pulmonary tuberculosis patients and 437 healthy controls from an endemic region in Jakarta, Indonesia. The IL12RB1 gene was sequenced in a subset of individuals. Nine known single nucleotide polymorphisms (SNPs) and two new silent variations, 135G>A and 1056C>T, were detected in IL12RB1. Six functional SNPs (-2C>T, 467G>A, 641A>G, 1312C>T, 1573G>A, 1781G>A) in IL12RB1, an IL12B promoter insertion/deletion polymorphism and CA repeats in IFNG and IFNGR1 were analyzed in the cohort. The IFNGR1 allele CA(12) (p=0.004) and genotype CA(12)/CA(12) (p=0.01; OR 0.5) were associated with protection from pulmonary tuberculosis. Interestingly, IL12B promoter heterozygosity was associated with protection from tuberculosis in BCG-vaccinated individuals (p=0.03; OR=0.6). This new finding supports the role that IL-23-of which IL12B encodes a subunit--plays in generation of memory T cells.

IL-23 is critical in the induction but not in the effector phase of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE), a T cell-mediated inflammatory disease of the CNS, is a rodent model of human multiple sclerosis. IL-23 is one of the critical cytokines in EAE development and is currently believed to be involved in the maintenance of encephalitogenic responses during the tissue damage effector phase of the disease. In this study, we show that encephalitogenic T cells from myelin oligodendrocyte glycopeptide (MOG)-immunized wild-type (WT) mice caused indistinguishable disease when adoptively transferred to WT or IL-23-deficient (p19 knockout (KO)) recipient mice, demonstrating that once encephalitogenic cells have been generated, EAE can develop in the complete absence of IL-23. Furthermore, IL-12/23 double-deficient (p35/p19 double KO) recipient mice developed EAE that was indistinguishable from WT recipients, indicating that IL-12 did not compensate for IL-23 deficiency during the effector phase of EAE. In contrast, MOG-specific T cells from p19KO mice induced EAE with delayed onset and much lower severity when transferred to WT recipient mice as compared with the EAE that was induced by cells from WT controls. MOG-specific T cells from p19KO mice were highly deficient in the production of IFN-gamma, IL-17A, and TNF, indicating that IL-23 plays a critical role in development of encephalitogenic T cells and facilitates the development of T cells toward both Th1 and Th17 pathways.

Identification of an interleukin 17F/17A heterodimer in activated human CD4+ T cells

IL-17F and IL-17A are members of the IL-17 pro-inflammatory cytokine family. IL-17A has been implicated in the pathogenesis of autoimmune diseases. IL-17F is a disulfide-linked dimer that contains a cysteine-knot motif. We hypothesized that IL-17F and IL-17A could form a heterodimer due to their sequence homology and overlapping pattern of expression. We evaluated the structure of recombinant IL-17F and IL-17A proteins, as well as that of natural IL-17F and IL-17A derived from activated human CD4+ T cells, by enzyme-linked immunosorbent assay, immunoprecipitation followed by Western blotting, and mass spectrometry. We find that both IL-17F and IL-17A can form both homodimeric and heterodimeric proteins when expressed in a recombinant system, and that all forms of the recombinant proteins have in vitro functional activity. Furthermore, we find that in addition to the homodimers of IL-17F and IL-17A, activated human CD4+ T cells also produce the IL-17F/IL-17A heterodimer. These data suggest that the IL-17F/IL-17A heterodimer may contribute to the T cell-mediated immune responses.

IL-23 and IL-17 in the establishment of protective pulmonary CD4+ T cell responses after vaccination and during Mycobacterium tuberculosis challenge

Interferon-gamma is key in limiting Mycobacterium tuberculosis infection. Here we show that vaccination triggered an accelerated interferon-gamma response by CD4(+) T cells in the lung during subsequent M. tuberculosis infection. Interleukin 23 (IL-23) was essential for the accelerated response, for early cessation of bacterial growth and for establishment of an IL-17-producing CD4(+) T cell population in the lung. The recall response of the IL-17-producing CD4(+) T cell population occurred concurrently with expression of the chemokines CXCL9, CXCL10 and CXCL11. Depletion of IL-17 during challenge reduced the chemokine expression and accumulation of CD4(+) T cells producing interferon-gamma in the lung. We propose that vaccination induces IL-17-producing CD4(+) T cells that populate the lung and, after challenge, trigger the production of chemokines that recruit CD4(+) T cells producing interferon-gamma, which ultimately restrict bacterial growth.

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.

Interleukin-2 signaling via STAT5 constrains T helper 17 cell generation

Recent work has identified a new subset of effector T cells that produces interleukin (IL)-17 known as T helper 17 (Th17) cells, which is involved in the pathophysiology of inflammatory diseases and is thought to be developmentally related to regulatory T (Treg) cells. Because of its importance for Treg cells, we examined the role of IL-2 in Th17 generation and demonstrate that a previously unrecognized aspect of IL-2 function is to constrain IL-17 production. Genetic deletion or antibody blockade of IL-2 promoted differentiation of the Th17 cell subset. Whereas STAT3 appeared to be a key positive regulator of RORgammat and IL-17 expression, absence of IL-2 or disruption of its signaling by deletion of the transcription factor STAT5 resulted in enhanced Th17 cell development. We conclude that in addition to the promotion of activation-induced cell death of lymphocytes and the generation of Treg cells, inhibition of Th17 polarization appears to be an important function of IL-2.

P2 purinergic receptor modulation of cytokine production

Cytokines serve important functions in controlling host immunity. Cells involved in the synthesis of these polypeptide mediators have evolved highly regulated processes to ensure that production is carefully balanced. In inflammatory and immune disorders, however, mis-regulation of the production and/or activity of cytokines is recognized as a major contributor to the disease process, and therapeutics that target individual cytokines are providing very effective treatment options in the clinic. Leukocytes are the principle producers of a number of key cytokines, and these cells also express numerous members of the purinergic P2 receptor family. Studies in several cellular systems have provided evidence that P2 receptor modulation can affect cytokine production, and mechanistic features of this regulation have emerged. This review highlights three separate examples corresponding to (1) P2Y₆ receptor mediated impact on interleukin (IL)-8 production, (2) P2Y₁₁ receptor-mediated affects on IL-12/23 output, and (3) P2X₇ receptor mediated IL-1β posttranslational processing. These examples demonstrate important roles of purinergic receptors in the modulation of cytokine production. Extension of these cellular observations to in vivo situations may lead to new therapeutic strategies for treating cytokine-mediated diseases.

Phenotypic differences between Th1 and Th17 cells and negative regulation of Th1 cell differentiation by IL-17

Recent evidence from several groups indicates that IL-17-producing Th17 cells, rather than, as once was thought, IFN-gamma-producing Th1 cells, can represent the key effector cells in the induction/development of several autoimmune and allergic disorders. Although Th17 cells exhibit certain phenotypic and developmental differences from Th1 cells, the extent of the differences between these two T cell subsets is still not fully understood. We found that the expression profile of cell surface molecules on Th17 cells has more similarities to that of Th1 cells than Th2 cells. However, although certain Th1-lineage markers [i.e., IL-18 receptor alpha, CXCR3, and T cell Ig domain, mucin-like domain-3 (TIM-3)], but not Th2-lineage markers (i.e., T1/ST2, TIM-1, and TIM-2), were expressed on Th17 cells, the intensity of expression was different between Th17 and Th1 cells. Moreover, the expression of CTLA-1, ICOS, programmed death ligand 1, CD153, Fas, and TNF-related activation-induced cytokine was greater on Th17 cells than on Th1 cells. We found that IL-23 or IL-17 can suppress Th1 cell differentiation in the presence of exogenous IL-12 in vitro. We also confirmed that IL-12 or IFN-gamma can negatively regulate Th17 cell differentiation. However, these cytokines could not modulate such effects on T cell differentiation in the absence of APC.

Interleukin-17 as a molecular target in immune-mediated arthritis: immunoregulatory properties of genetically modified murine dendritic cells that secrete interleukin-4

OBJECTIVE

Our previous studies have shown that murine dendritic cells (DCs) genetically modified to express interleukin-4 (IL-4) reduce the incidence and severity of murine collagen-induced arthritis. The present studies were performed to assess the immunoregulatory mechanisms underlying this response, by assessing the effects of IL-4 DCs on cytokine production by subsets of T helper cells.

METHODS

Male DBA mice ages 6-8 weeks old were immunized with type II collagen. Splenic T cells obtained during the initiation phase and the end stage of arthritis were cultured with IL-4 DCs or untransduced DCs in the presence of collagen rechallenge. Interferon-gamma (IFNgamma) and IL-17 responses were measured. Antibodies to IL-4, IL-12, and IL-23, and recombinant IL-4, IL-12, and IL-23 were used to further study the regulation of T cell cytokine production by IL-4 DCs.

RESULTS

Splenic T cells obtained during the initiation phase of arthritis produced less IL-17 when cultured in the presence of IL-4 DCs, despite their production of increased quantities of other proinflammatory cytokines (IFNgamma and tumor necrosis factor). T cell IL-17 production after collagen rechallenge was not inhibited by a lack of IL-23, since IL-4-mediated suppression of IL-17 was not reconstituted by IL-23, an otherwise potent inducer of IL-17 production by T cells. Although IL-4 DCs can produce increased quantities of IL-12 and IFNgamma, suppression of IL-17 production by IL-4 DCs was independent of both. While IL-17 production by T cells obtained during the initiation phase of arthritis was regulated by IL-4 DCs, IL-17 production by T cells obtained during end-stage arthritis was not altered.

CONCLUSION

Our data suggest that IL-4 DCs exert a therapeutic effect on collagen-induced arthritis by targeting IL-17. IL-17 suppression by IL-4 DCs is robust and is not reversed by IL-23. Timing might be important in IL-17-targeted therapy, since IL-17 production by T cells obtained during end-stage arthritis did not respond to suppression by IL-4 DCs.

A human interleukin-12/23 monoclonal antibody for the treatment of psoriasis

BACKGROUND

Skin-infiltrating lymphocytes expressing type 1 cytokines have been linked to the pathophysiology of psoriasis. We evaluated the safety and efficacy of a human interleukin-12/23 monoclonal antibody in treating psoriasis.

METHODS

In this double-blind, placebo-controlled trial, 320 patients with moderate-to-severe plaque psoriasis underwent randomization to treatment with the interleukin-12/23 monoclonal antibody (one 45-mg dose, one 90-mg dose, four weekly 45-mg doses, or four weekly 90-mg doses) or placebo; 64 patients were randomly assigned to each group. Patients assigned to the interleukin-12/23 monoclonal antibody received one additional dose at week 16 if needed. Patients assigned to placebo crossed over to receive one 90-mg dose of interleukin-12/23 monoclonal antibody at week 20.

RESULTS

There was at least 75% improvement in the psoriasis area-and-severity index at week 12 (the primary end point) in 52% of patients who received 45 mg of the interleukin-12/23 monoclonal antibody, in 59% of those who received 90 mg, in 67% of those who received four weekly 45-mg doses, and in 81% of those who received four weekly 90-mg doses, as compared with 2% of those who received placebo (P<0.001 for each comparison), and there was at least 90% improvement in 23%, 30%, 44%, and 52%, respectively, of patients who received the monoclonal antibody as compared with 2% of patients who received placebo (P<0.001 for each comparison). Adverse events occurred in 79% of patients treated with the interleukin-12/23 monoclonal antibody as compared with 72% of patients in the placebo group (P=0.19). Serious adverse events occurred in 4% of patients who received the monoclonal antibody and in 1% of those who received placebo (P=0.69).

CONCLUSIONS

This study demonstrates the therapeutic efficacy of an interleukin-12/23 monoclonal antibody in psoriasis and provides further evidence of a role of the interleukin-12/23 p40 cytokines in the pathophysiology of psoriasis. Larger studies are needed to determine whether serious adverse events might limit the clinical usefulness of this new therapeutic target. (ClinicalTrials.gov number, NCT00320216 [ClinicalTrials.gov].).

IL-23 mediates inflammatory responses to mucoid Pseudomonas aeruginosa lung infection in mice

Patients with cystic fibrosis (CF) develop chronic Pseudomonas aeruginosa lung infection with mucoid strains of P. aeruginosa; these infections cause significant morbidity. The immunological response in these infections is characterized by an influx of neutrophils to the lung and subsequent lung damage over time; however, the underlying mediators to this response are not well understood. We recently reported that IL-23 and IL-17 were elevated in the sputum of patients with CF who were actively infected with P. aeruginosa; however, the importance of IL-23 and IL-17 in mediating this inflammation was unclear. To understand the role that IL-23 plays in initiating airway inflammation in response to P. aeruginosa, IL-23p19(-/-) (IL-23 deficient) and wild-type (WT) mice were challenged with agarose beads containing a clinical, mucoid isolate of P. aeruginosa. Levels of proinflammatory cytokines, chemokines, bacterial dissemination, and inflammatory infiltrates were measured. IL-23-deficient mice had significantly lower induction of IL-17, keratinocyte-derived chemokine (KC), and IL-6, decreased bronchoalveolar lavage (BAL) neutrophils, metalloproteinase-9 (MMP-9), and reduced airway inflammation than WT mice. Despite the reduced level of inflammation in IL-23p19(-/-) mice, there were no differences in the induction of TNF and interferon-gamma or in bacterial dissemination between the two groups. This study demonstrates that IL-23 plays a critical role in generating airway inflammation observed in mucoid P. aeruginosa infection and suggests that IL-23 could be a potential target for immunotherapy to treat airway inflammation in CF.

An interferon-gamma-producing Th1 subset is the major source of IL-17 in experimental autoimmune encephalitis

ThIL-17 (IL-17+/IFN-gamma-) cell lines are significantly more encephalitogenic than Th1 (IL-17-/IFN-gamma+) cell lines in adoptive transfer EAE models. In actively induced EAE short ex vivo peptide stimulation identifies an IL-17+/IFN-gamma+ population of CD4+ CNS-infiltrating MOG35-55-specific T cells, which outnumber IL-17+/IFN-gamma- cells by approximately 3:1 as disease develops. A decrease in numbers of IL-17+/IFN-gamma+ cells following in vitro culture is accompanied by an increase in IL-17-/IFN-gamma+ cell numbers. Together these ex vivo and in vitro observations imply that the Th1 lineage is more encephalitogenic than is suggested by adoptive transfer of Th1 (IL-17-/IFN-gamma+) cell lines which have been terminally differentiated in vitro.

Kinetics and Organ Distribution of IL-17-Producing CD4 Cells in Proteolipid Protein 139–151 Peptide-Induced Experimental Autoimmune Encephalomyelitis of SJL Mice

In experimental autoimmune encephalomyelitis (EAE), the production of proinflammatory cytokines by neuroantigen-specific T cells is thought to initiate and maintain the inflammatory autoimmune pathology. Because gene knockout strategies have shown that IFN-gamma and TNF are not essential for EAE development, there is increasing interest in establishing the role of other proinflammatory cytokines, primarily IL-17 in EAE. We used an IL-17 ELISPOT assay to track the neuroantigen-specific IL-17-producing T cells at single-cell resolution in various organs of SJL mice undergoing PLP 139-151-induced EAE. Overall, the migration patterns and population kinetics of the PLP 139-151-specific IL-17-producing CD4 cells were reminiscent of the IFN-gamma-producing cells, with the exception of IL-17 producers far outnumbering the IFN-gamma and IL-2 producers in the inflamed CNS. The selective enrichment of IL-17-producing CD4 cells in the CNS is suggestive of the pathogenic role of an independent (non-Th1) IL-17-producing proinflammatory effector T cell class in EAE.

Development of an anti-IL-17A auto-vaccine that prevents experimental auto-immune encephalomyelitis

IL-17 has been associated with multiple inflammatory disorders such as rheumatoid arthritis, asthma and multiple sclerosis. As these diseases require long-term treatment we turned to an auto-vaccine strategy for IL-17 neutralization in vivo. Mouse IL-17A was covalently linked to ovalbumin and used to immunize C57BL/6 mice. This vaccine induced the production of antibodies that blocked IL-17A bioactivity in vitro but did not react with the other IL-17 isoforms, including IL-17F. As the half-life of the Ab titers after the last immunogen administration was approximately 4 months, the vaccine provides for long lasting and selective inhibition of IL-17A activity in vivo. A monoclonal Ab (mAb) derived from these mice showed the same specificity for IL-17A. To test the ability of the vaccine to confer protection against an IL-17-dependent disorder, SJL mice were vaccinated with IL-17-OVA and encephalomyelitis (EAE) was induced by proteolipid protein (PLP) peptide 139-151. Vaccinated mice were completely protected against the disease. The above-mentioned anti-IL-17A mAb also prevented EAE development. The absence of clinical symptoms contrasted with unaltered PLP-induced cytokine production in vitro and unmodified anti-PLP IgG titers and isotypes. These results suggest that an anti-IL-17A auto-vaccine offers new perspectives for therapy of autoimmune diseases.

Diversity of regulatory T cells to control arthritis

During follow-up of the suppressive functions of CD4+ T helper (Th) 2 cells in recent years, the suppressive capacities of newly recognised CD4+ Th cells with more widespread suppressive potential have been extensively investigated. These Th cells, collectively termed regulatory T cells, are characterised by the secretion of specific cytokines, such as interleukin (IL)-10 (Tr1 Th cells), transforming growth factor (TGF)beta (Th3 cells) or the constitutive expression of CD25 (naturally occurring T regulatory cells, nTregs). The balance of these regulatory T cells with pro-inflammatory effector T cells, such as Th1 (interferon (IFN)gamma secreting), Th17 (IL-17 secreting) and CD25- Th cells, has been shown to be of pivotal importance for the development and persistence of autoimmune diseases. The high potential of regulatory T cells (in particular nTregs), to efficiently suppress several arthritic responses both in humans and in animal models of arthritis, make them therapeutic targets of interest in arthritic conditions such as rheumatoid arthritis.

Neutralization of IL-17 by active vaccination inhibits IL-23-dependent autoimmune myocarditis

The most common reason for heart failure in young adults is dilated cardiomyopathy often resulting from myocarditis. Clinical studies and animal models provide evidence that an autoimmune response against heart myosin is the underlying reason for the disease. IL-12 has been suggested to play a key role in development of experimental autoimmune myocarditis (EAM), as IL-12p40 and IL-12Rbeta1 knockouts are protected from disease. In this study, we have compared IL-12p40-/- mice, IL-12p35-/- mice and mice treated with a neutralizing IL-23 antibody in EAM and found that in fact IL-23, not IL-12, is responsible for inflammatory heart disease. However, these cytokines appear to have redundant activity for priming and expansion of autoreactive CD4 T cells, as specific T cell proliferation was only defective in the absence of both cytokines. IL-23 has been suggested to promote a pathogenic IL-17-producing T cell population. We targeted IL-17 by capitalizing on an active vaccination approach that effectively breaks B cell tolerance. Neutralization of IL-17 reduced myocarditis and heart autoantibody responses, suggesting that IL-17 is the critical effector cytokine responsible for EAM. Thus, targeting of IL-23 and IL-17 by passive and active vaccination strategies holds promise as a therapeutic approach to treat patients at risk for development of dilated cardiomyopathy.

New cytokine targets in inflammatory rheumatic diseases

With the advent of biological therapies, considerable advances have been achieved in the treatment of inflammatory arthritis. These have arisen primarily from studies elucidating mechanisms of pathophysiology and are best exemplified in the wide use of tumour necrosis factor (TNF) blockade in several rheumatic diseases. The identification of additional pro-inflammatory factors in rheumatic diseases and an understanding of their effector function, now offers major possibilities for the generation of novel therapeutics. To address unmet clinical need, such interventions will ideally fulfil several of the following criteria: (1) control of inflammation, (2) modulation of underlying immune dysfunction - promoting the re-establishment of immune tolerance, (3) protection of targeted tissues such as bone and cartilage - this should encompass promoting healing of previously damaged tissues, (4) preservation of host immune capability - to avoid profound immune suppression and (5) amelioration of co-morbidity associated with underlying inflammatory arthritis. This short review will consider those novel cytokine activities that represent optimal utility as therapeutic targets. Since we wish to reflect the current predominant research effort, we will focus primarily on rheumatoid arthritis (RA) based studies.

Coadministration of plasmid DNA constructs encoding an encephalitogenic determinant and IL-10 elicits regulatory T cell-mediated protective immunity in the central nervous system

We have previously shown that Ag-specific IL-10-producing regulatory T cells (Tr1) participate in the regulation of experimental autoimmune encephalomyelitis and that their specificity undergoes determinant spread in a reciprocal manner to effector T cell specificity. The current study shows that coadministration of plasmid DNA vaccines encoding IL-10 together with a plasmid encoding a myelin basic protein (MBP) encephalitogenic determinant during an ongoing disease rapidly amplifies this Tr1-mediated response, in a disease-specific manner. Thus, coadministration of both plasmids, but not the plasmid DNA encoding MBP alone, rapidly suppresses an ongoing disease. Tolerance included elevation in Ag-specific T cells producing IL-10 and an increase in apoptosis of cells around high endothelial venules in the CNS after successful therapy. Tolerance could be transferred by MBP-specific primary T cells isolated from protected donors and reversed by neutralizing Abs to IL-10 but not to IL-4. Due to the nature of determinant spread in this model, we could bring about evidence implying that rapid and effective induction of Tr1-induced active tolerance is dependent on redirecting the Tr1 response to the epitope to which the effector function dominates the response at a given time. The consequences of these findings to multiple sclerosis, and possibly other inflammatory autoimmune diseases are discussed.

Interleukin-23 restores immunity to Mycobacterium tuberculosis infection in IL-12p40-deficient mice and is not required for the development of IL-17-secreting T cell responses

Host control of Mycobacterium tuberculosis is dependent on the activation of CD4+ T cells secreting IFN-gamma and their recruitment to the site of infection. The development of more efficient vaccines against tuberculosis requires detailed understanding of the induction and maintenance of T cell immunity. Cytokines important for the development of cell-mediated immunity include IL-12 and IL-23, which share the p40 subunit and the IL-12Rbeta1 signaling chain. To explore the differential effect of IL-12 and IL-23 during M. tuberculosis infection, we used plasmids expressing IL-23 (p2AIL-23) or IL-12 (p2AIL-12) alone in dendritic cells or macrophages from IL-12p40(-/-) mice. In the absence of the IL-12/IL-23 axis, immunization with a DNA vaccine expressing the M. tuberculosis Ag85B induced a limited Ag-specific T cell response and no control of M. tuberculosis infection. Co-delivery of p2AIL-23 or p2AIL-12 with DNA85B induced strong proliferative and IFN-gamma-secreting T cell responses equivalent to those observed in wild-type mice immunized with DNA85B. This response resulted in partial protection against aerosol M. tuberculosis; however, the protective effect was less than in wild-type mice owing to the requirement for IL-12 or IL-23 for the optimal expansion of IFN-gamma-secreting T cells. Interestingly, bacillus Calmette-Guérin immune T cells generated in the absence of IL-12 or IL-23 were deficient in IFN-gamma production, but exhibited a robust IL-17 secretion associated with a degree of protection against pulmonary infection. Therefore, exogenous IL-23 can complement IL-12 deficiency for the initial expansion of Ag-specific T cells and is not essential for the development of potentially protective IL-17-secreting T cells.

The role of CD4 T cells in the pathogenesis of multiple sclerosis

T lymphocytes play a central role in the pathogenesis of multiple sclerosis (MS) (Zhang et al., 1992). Both CD4+ and CD8+ T cells have been demonstrated in MS lesions, with CD4+ T cells predominating in acute lesions and CD8+ T cells being observed more frequently in chronic lesions (Raine, 1994). Additionally, T cells are found in all four of the described histopathologic subtypes of MS (Lucchinetti et al., 2000). Activated myelin-reactive CD4+ T cells are present in the blood and cerebrospinal fluid (CSF) of MS patients; in contrast, only nonactivated myelin-reactive T cells are present in the blood of controls (Zhang et al., 1994). The success of several T-cell-targeted therapies in MS reinforces the importance of the role of the T cell in MS pathogenesis. Here, we outline basic concepts in CD4+ T-cell immunology and summarize the current understanding of the role of CD4+ T cells in the pathogenesis of MS.

Effects of IL-23 and IL-27 on osteoblasts and osteoclasts: inhibitory effects on osteoclast differentiation

Interleukin (IL)-23 and IL-27 are IL-6/IL-12 family members that play a role in the regulation of T helper 1 cell differentiation. Cytokines are known to be involved in the bone remodeling process, although the effects of IL-23 and IL-27 have not been clarified. In this study, we examined the possible roles of these cytokines on osteoblast phenotypes and osteoclastogenesis. We found that IL-27 induced signal transducers and activators of transcription 3 activation in osteoblasts. However, neither IL-23 nor IL-27 showed any significant effects on alkaline phosphatase activity, receptor activator of nuclear factor kappaB ligand (RANKL) expression, mRNA expression such as alkaline phosphatase type I procollagen, or the proliferation of osteoblasts. Osteoclastogenesis from bone marrow cells induced by soluble RANKL was partially inhibited by IL-23 and IL-27 with reduced multinucleated cell numbers, but these interleukins did not affect the proliferation of osteoclast progenitor cells. These results indicate that IL-23 and IL-27 could partly modify cell fusion or the survival of multinucleated osteoclasts. On the other hand, partially purified T cells, which are activated by 2 microg/ml anti-CD3 antibody, completely inhibited osteoclastogenesis by M-CSF/RANKL. On using T cells activated with 0.2 microg/ml anti-CD3 antibody, in which osteoclastogenesis was partially inhibited, the interleukins had additive effects for inhibiting osteoclastogenesis. Although the consequences of phosphorylated signals in osteoblasts have not been identified, IL-23 and IL-27, partly and indirectly through activated T cells, inhibited osteoclastogenesis, indicating that these interleukins may protect against bone destructive autoimmune disorders.

Th17 cell induction and immune regulatory effects

The T help 1 (Th1) and Th2 cell classification have 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, which 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. In this review, we will focus on recent studies that have identified new subsets of Th cells, new insights regarding the induced generation and differentiation mechanisms of Th17 cells and immune regulatory effects.

TGF-beta: a mobile purveyor of immune privilege

Functionally barricaded immune responses or sites of immune privilege are no longer considered dependent on specific anatomical considerations, but rather, they can develop in any location where immunoregulatory cells congregate and express or release products capable of deviating the host response to foreign antigens. Among the pivotal molecules involved in orchestrating these ectopic sites of immune suppression is transforming growth factor-beta (TGF-beta), a secreted and cell-associated polypeptide with a multiplicity of actions in innate and adaptive immunity. While beneficial in initiating and controlling immune responses and maintaining immune homeostasis, immunosuppressive pathways mediated by TGF-beta may obscure immune surveillance mechanisms, resulting in failure to recognize or respond adequately to self, foreign, or tumor-associated antigens. CD4+CD25+Foxp3+ regulatory T cells represent a dominant purveyor of TGF-beta-mediated suppression and are found in infiltrating tumors and other sites of immune privilege, where they influence CD8+ T cells; CD4+ T-helper (Th)1, Th2, and Th17 cells; natural killer cells; and cells of myeloid lineage to choreograph and/or muck up host defense. Defining the cellular sources, mechanisms of action, and networking that distinguish the dynamic establishment of localized immune privilege is vital for developing strategic approaches to diminish or to embellish these tolerogenic events for therapeutic benefit.

A critical role of LFA-1 in the development of Th17 cells and induction of experimental autoimmune encephalomyelytis

The alphaLbeta2 integrin adhesion molecule LFA-1 is believed to be involved in the migration of autoreactive T cells to the central nervous system across the endothelial blood-brain barrier in experimental autoimmune encephalomyelitis (EAE). Here, we demonstrate that the incidence and clinical scores of EAE in LFA-1-/- mice induced by the immunization with the myelin oligodendrocyte glycoprotein (MOG)-peptide antigen were significantly lower than those in wild type mice. Further studies demonstrated that lymphocytes recruitment to the draining lymph nodes (dLN) after the immunization with the MOG-peptide was severely suppressed in LFA-1-/- mice. Moreover, generation of the MOG-specific IL-17-producing helper T (Th17) cells in the dLN was impaired in LFA-1-/- mice. These results suggest that LFA-1 may play an important role for the generation of MOG-specific Th17 cells in the dLN as well as the immigration of MOG-specific naïve CD4+ T cells to the dLN.