The clinical role of IL-23p19 in patients with rheumatoid arthritis

A Pathogenic Th17/CD38+ Macrophage Feedback Loop Drives Inflammatory Arthritis through TNF-α

The pathobiology of rheumatoid inflammatory diseases, including rheumatoid arthritis (RA) and psoriatic arthritis, involves the interplay between innate and adaptive immune components and resident synoviocytes. Single-cell analyses of patient samples and relevant mouse models have characterized many cellular subsets in RA. However, the impact of interactions between cell types is not fully understood. In this study, we temporally profiled murine arthritic synovial isolates at the single-cell level to identify perturbations similar to those found in human RA. Notably, murine macrophage subtypes like those found in RA patients were expanded in arthritis and linked to promoting the function of Th17 cells in the joint. In vitro experiments identified a capacity for murine macrophages to maintain the functionality and expansion of Th17 cells. Reciprocally, murine Th17 cell-derived TNF-α induced CD38⁺ macrophages that enhanced Th17 functionality. Murine synovial CD38⁺ macrophages were expanded during arthritis, and their depletion or blockade via TNF-α neutralization alleviated disease while reducing IL-17A-producing cells. These findings identify a cellular feedback loop that promotes Th17 cell pathogenicity through TNF-α to drive inflammatory arthritis.

Elevated IL-38 inhibits IL-23R expression and IL-17A production in thyroid-associated ophthalmopathy

IL-23/IL-23R and PGE₂/EP2+EP4 have been recognized as crucial signals that promote Th17 differentiation in many autoimmune diseases, including thyroid-associated ophthalmopathy (TAO). However, the interactive role of IL-23R in IL-23/Th17 signaling and PGE₂/Th17 signaling has not been clarified in TAO. Furthermore, the role of IL-38, a novel anti-inflammatory cytokine, has not been explored in TAO. Thus, we aimed to investigate the roles of IL-23R and IL-38 in the pathogenesis of TAO. Activated peripheral blood mononuclear cells (PBMCs) were cultured with or without IL-23 and PGE₂. The results showed that IL-23R and IL-17A were upregulated to different degrees and reached the highest levels with both stimuli, indicating that IL-23 induced PBMCs to secrete PGE₂, which further boosted the proportion of IL-23R+CD4+T cells to promote IL-17A secretion. Pretreatment with antagonists aimed at EP2/EP4 receptors diminished PGE₂-induced upregulation of IL-23R and IL-17A. IL-38 in TAO patients was increased. Activated orbital fibroblasts (OFs) and PBMCs were pretreated with different concentrations of IL-38. IL-23R and IL-17A expression in circulating PBMCs and IL-6 and IL-8 in resident OFs were suppressed by IL-38 at relatively low concentrations. Our findings suggest that the feedback loop of IL-23/IL-23R/PGE₂/EP2+EP4/IL-23R/IL-17A plays a significant role in the pathogenesis of TAO and that IL-23R is one of the key targets. Increased IL-38 in TAO could not only inhibit the expression of IL-23R and IL-17A in PBMCs but also suppress inflammation in OFs. Therapies targeting IL-23R may be effective, and IL-38 could be a potential therapeutic approach for TAO.

Association analysis of interleukin-23 receptor SNPs and SAPHO syndrome in Chinese people

OBJECTIVE

SAPHO syndrome (synovitis, acne, pustulosis, hyperostosis, and osteitis) is an autoimmune disease of unknown etiology that seriously affects patients' daily lives. Family-based investigations support genetic contributions toward disease susceptibility. The present study evaluated whether the previously reported autoimmune disease-associated single nucleotide polymorphisms (SNPs) have any genetic overlap with SAPHO syndrome.

METHOD

Genomic DNA was obtained from 71 SAPHO patients and 104 healthy controls. The SNP genotypes of each patient were determined with polymerase chain reaction and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Genotype, allele, and haplotype frequencies were analyzed with SPSS software.

RESULTS

Three SNP sites (rs10889677 and rs2201841 of interleukin [IL]-23R, and rs2243248 of IL-4) showed significant correlation with the occurrence of SAPHO syndrome in additive and dominant genetic models, while rs7517847 of IL-23R showed substantial correlation with SAPHO in the dominant genetic model. The G allele of rs2243248 (IL-4) was a high risk factor for SAPHO (P = 2.41e-5, odds ratio [OR] =7.79, 95% CI: 2.59-23.3). The haplotype (A-G-C-G-T), comprising 5 SNPs of the IL-23R gene, had a significantly higher frequency in the SAPHO cohort than in the controls (P = .011, OR = 2.05, 95% CI: 1.12-3.60).

CONCLUSION

Variants rs10889677, rs2201841, and rs7517847 of IL-23R, and variant rs2243248 of IL-4, showed strong associations with SAPHO syndrome. Patients carrying the A-G-C-G-T haplotype of IL-23 are significantly more likely to develop SAPHO syndrome.

An emerging role of interleukin-23 in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune, chronic inflammatory disease and is characterized by destruction of the articular cartilage. A number of pro-inflammatory cytokines work sequentially and in concert with one another to induce the development of RA. IL-23, a member of IL-12 family, is composed of p19 and p40 subunits and it interacts with IL-23 receptor complex to trigger plethora of biochemical actions. A number of preclinical studies have shown the role of IL-23 in the development of RA in rodents. IL-23 receptor signaling is primarily linked to the activation of JAK-STAT, tyrosine kinase 2, NF-kB, and retinoic acid receptor-related orphan receptors. IL-23 produces its osteoclastogenic effects, mainly through IL-17 and Th17 cells suggesting the importance of IL-23/IL-17/Th17 in the joint inflammation and destruction in RA. Monoclonal antibodies targeted against IL-23, including tildrakizumab and guselkumab have been developed and evaluated in clinical trials. However, there are very limited clinical studies regarding the use of IL-23 modulators in RA patients. The present review discusses the different aspects of IL-23 including its structural features, signal transduction pathway, preclinical, and clinical role in RA.

IL-23 and Th17 Disease in Inflammatory Arthritis

IL-23, which is composed of p19 and p40 subunits, is a proinflammatory cytokine that contributes to the formation and maintenance of Th17 cells in inflammatory autoimmune diseases. IL-23 is a human osteoclastogenic cytokine and anti-IL-23 antibody attenuates paw volume and joint destruction in CIA rats. IL-23 levels in serum and synovial fluid are high in rheumatoid arthritis (RA) patients, and IL-23 may be a useful biomarker for the diagnosis of RA. In addition, IL-23 affects the pathogenesis of inflammation and bone destruction through interaction with other cytokines such as IL-17 and TNF-α. Furthermore, polymorphisms of IL23R are a risk factor for ankylosing spondylitis (AS) and psoriatic arthritis (PsA), which indicates that IL-23 is also involved in the pathogenesis of spondyloarthritis (SpA). Finally, IL-17 and IL-23 inhibitors reduce the clinical manifestations of SpA. Thus, the IL-23/Th17 pathway is a therapeutic target for the treatment of inflammatory arthritis.

Critical Role of LTB4/BLT1 in IL-23-Induced Synovial Inflammation and Osteoclastogenesis via NF-κB

IL-23 activates the synthesis and production of leukotriene B₄ (LTB₄) in myeloid cells, which modulate inflammatory arthritis. In this study we investigated the role of LTB₄ and its receptor LTB₄R1 (BLT1) in synovial inflammation and osteoclast differentiation. Specifically, we used IL-23 in vivo gene transfer to induce arthritis in mice and showed that elevated serum LTB₄ and synovial expression of 5-lipoxygenase correlated with increased disease severity by histological evaluation and paw swelling compared with GFP gene transfer controls. To further investigate the effect of the LTB₄ pathway in bone loss, we performed osteoclast differentiation assays by stimulating with M-CSF and receptor activator of NF-κB ligand bone marrow cells derived from BLT1^+/+ and/or BLT1^-/- mice and used quantitative PCR for gene expression analysis in terminally differentiated osteoclasts. Deficiency in BLT1 resulted in the upregulation of osteoclast-related genes and an increase in the formation of giant, multinucleated TRAP⁺ cells capable of F-actin ring formation. Additionally, BLT1 deficiency showed an increase of phosphorylated NF-κB and phosphorylated IκB levels in osteoclasts. We also performed real-time calcium imaging to study the effect of BLT1 deficiency in receptor activator of NF-κ-B ligand-induced activation of intracellular calcium flux in vitro. Our data show that LTB₄ and its receptor BLT1 exacerbate synovial inflammation in vivo and bone resorption in vitro, suggesting that LTB₄ and BLT1 could be effectively targeted for the treatment of musculoskeletal diseases.

(p40)2-Fc reduces immune-inflammatory response through the activation of T cells in collagen induced arthritis mice

IL-12p40 homodimer, a natural antagonist of IL-12 and IL-23, performs an important role in the expression of proinflammatory cytokines that is essential for Th1 and Th17 immune responses. Here, we reveal the therapeutic and immunosuppressive effect of the IL-12p40 subunit ((p40)2-Fc) in an experimental autoimmune arthritis model. We hypothesized that (p40)2-Fc may reduce the inflammatory response and the activation of T cells. In this study, we intraperitoneally injected (p40)2-Fc into collagen induced arthritis (CIA) mice to identify whether (p40)2-Fc attenuates CIA severity. (p40)2-Fc reduced the development of CIA, joint inflammation and cartilage destruction. (p40)2-Fc also significantly decreased the concentration of serum immunoglobulin as well as the number of T cells and C II specific T cells. In addition, osteoclastogenesis in (p40)2-Fc treated mice was down-regulated compared to the mice treated with (p40)2-Fc control. We observed that (p40)2-Fc treatment alleviates arthritis in mice with CIA, reducing inflammation and osteoclast differentiation. These findings suggest that (p40)2-Fc can be a potential therapeutic approach for autoimmune arthritis.

Protective role of R381Q (rs11209026) polymorphism in IL-23R gene in immune-mediated diseases: A comprehensive review

Interleukin-23 (IL-23) is a regulator of cellular immune responses involved in controlling infection and autoimmune diseases. Strong evidence has shown that IL-23 plays a role in the maintenance of immune responses by influencing the proliferation and survival of IL-17-producing T-helper (TH)-17 cells. The critical role of the IL-23/TH17 axis in immune-mediated diseases has emerged from different studies. It has also been seen that polymorphisms in the IL-23 receptor (IL-23R) gene might influence IL-23 responses. Interestingly, a functional single nucleotide polymorphism (SNP) in the IL-23 receptor gene (IL-23R; rs11209026, 1142 G wild-type A reduced function, Arg381Gln, R381Q) seems to confer a measure of protection against development of inflammatory bowel disease (IBD; Crohn's disease, ulcerative colitis), ankylosing spondylitis, rheumatoid arthritis, psoriasis, thyroiditis, recurrent spontaneous abortion and asthma, suggesting that a perturbation in the IL-23 signaling pathway is likely to be relevant to the pathophysiology of these diseases. The aim of this review was to provide an evaluation of what is currently known about the protective role of R381Q variant in IL-23R gene in immune-based diseases.

IL-12p40 Homodimer Ameliorates Experimental Autoimmune Arthritis

IL-23 is the key cytokine that induces the expansion of Th17 cells. It is composed of p19 and p40 subunits of IL-12. The p40 subunit binds competitively to the receptor of IL-23 and blocks its activity. Our aim was to assess the preventive and therapeutic effect of the IL-12p40 homodimer (p40)2 subunit in autoimmune arthritis animal models. In the current study, using IL-1R antagonist-knockout mice and a collagen-induced arthritis model, we investigated the suppressive effect of (p40)2 on inflammatory arthritis. We demonstrated that the recombinant adenovirus-expressing mouse (p40)2 model prevented the development of arthritis when given before the onset of arthritis. It also decreased the arthritis index and joint erosions in the mouse model if transferred after arthritis was established. (p40)2 inhibited the production of inflammatory cytokines and Ag-specific T cell proliferation. It also induced CD4(+)CD25(+)Foxp3 regulatory T (Treg) cells in vitro and in vivo, whereas the generation of retinoic acid receptor-related organ receptor γt and Th17 cells was suppressed. The induction of Treg cells and the suppression of Th17 cells were mediated via activated STAT5 and suppressed STAT3. Our data suggest that (p40)2 suppressed inflammatory arthritis successfully. This could be a useful therapeutic approach in autoimmune arthritis to regulate the Th17/Treg balance and IL-23 signaling.

Effect of the blockade of the IL-23-Th17-IL-17A pathway on streptozotocin-induced diabetic retinopathy in rats

PURPOSE

T helper 17 (Th17) cells are believed to play a critical role in the chronic inflammatory and immune response in streptozotocin (STZ)-induced retinopathy. The purpose of our study was to investigate the effect of the IL-23-Th17-IL-17A pathway via the blood-retinal barrier on STZ-induced diabetic retinopathy in rats.

METHODS

The ratio of IL-17A(+)CD4(+) T cells in peripheral blood mononuclear cells of STZ-treated and wild-type rats was determined using flow cytometry. The IL-17A mRNA levels in the retinas were measured using real-time PCR. The protein expression of IL-17A in the peripheral blood and retinas was measured using an ELISA kit. The retinal structure in the wild-type and STZ-treated rats was examined using hematoxylin and eosin (H&E) staining. Additionally, the permeability of the blood-retinal barrier was quantified using the Evans blue technique.

RESULTS

The ratio of IL-17A(+)CD4(+) T cells in peripheral blood mononuclear cells was markedly increased in rats treated with STZ compared to the wild-type group. IL-17A protein levels in the peripheral blood and retinas were also significantly elevated in STZ-treated rats. However, when the anti-IL 23Rp19 antibody was injected into the vitreous cavity in the eyes of STZ-treated rats for a period of one week, retinal pigment epithelium cells became markedly tighter, and micrangium and endothelial cells were significantly reduced. The expression of IL-17A mRNA and protein in the retina also decreased significantly compared with the placebo-treated group.

CONCLUSIONS

This study provided further insight into the function of the IL-23-Th17-IL-17A pathway in STZ-induced diabetic retinopathy in rats. Local injection of the anti-IL-23Rp19 antibody may improve the structure of the blood-retinal barrier, thus offering the potential for treatment using intravitreal anti-IL-23Rp19 antibodies.

Interleukin-17 increases the expression of Toll-like receptor 3 via the STAT3 pathway in rheumatoid arthritis fibroblast-like synoviocytes

We examined the effect of interleukin-17 (IL-17) on the expression of Toll-like receptors (TLRs) in fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA) and osteoarthritis (OA). We investigated the region downstream of IL-17 for TLR expression. We also investigated the downstream signals responsible for the effect of IL-17 in TLR expression. Levels of IL-17 protein in the serum and synovial fluid of RA and OA patients were measured by ELISA. The IL-17 mRNA expression in peripheral blood mononuclear cells and synovial fluid mononuclear cells was measured by RT-PCR. RA and OA FLS were incubated with IL-17 and/or IL-23 for 24 hr. To block the signal transducer and activator of transcription 3 (STAT3) pathway, FLS were treated with S3I-201 before incubation with IL-17 and IL-23. Synovial tissue samples from RA and OA patients were stained with antibodies to IL-17, TLR2, TLR3, TLR4, STAT3 and phospho-STAT3. Levels of IL-17 protein were higher in the serum and synovial fluid from RA patients compared with those from OA patients. The IL-17 mRNA expression in synovial fluid monocytes was also higher in RA than in OA patients. Immunohistochemical staining showed greater expression of IL-17, TLR2, TLR3 and TLR4 in synovial samples from RA compared with OA patients. Interleukin-17 increased the expression of TLR2, TLR3 and TLR4 in RA FLS; IL-23 augmented the IL-17-induced expression of TLR2, TLR3 and TLR4 in RA FLS. Blocking STAT3 with S3I-201 reduced IL-17-induced TLR3 expression in RA FLS. Our results suggest that IL-17 is a major cytokine in pathogenesis on RA. The IL-17 influences the innate immune system by increasing the synovial expression of TLR2, TLR3 and TLR4. We may control TLR3 expression via the STAT3 pathway in RA FLS.

Pivotal roles of T-helper 17-related cytokines, IL-17, IL-22, and IL-23, in inflammatory diseases

T-helper 17 (Th17) cells are characterized by producing interleukin-17 (IL-17, also called IL-17A), IL-17F, IL-21, and IL-22 and potentially TNF- α and IL-6 upon certain stimulation. IL-23, which promotes Th17 cell development, as well as IL-17 and IL-22 produced by the Th17 cells plays essential roles in various inflammatory diseases, such as experimental autoimmune encephalomyelitis, rheumatoid arthritis, colitis, and Concanavalin A-induced hepatitis. In this review, we summarize the characteristics of the functional role of Th17 cells, with particular focus on the Th17 cell-related cytokines such as IL-17, IL-22, and IL-23, in mouse models and human inflammatory diseases.

IL-23/IL-17A axis correlates with the nitric oxide pathway in inflammatory bowel disease: immunomodulatory effect of retinoic acid

Inflammatory bowel diseases (IBDs) are chronic inflammatory diseases of the gastrointestinal tract, which are clinically present as 1 of the 2 disorders, Crohn's disease (CD) or ulcerative colitis (UC) (Rogler 2004). The immune dysregulation in the intestine plays a critical role in the pathogenesis of IBD, involving a wide range of molecules, including cytokines. The aim of this work was to study the involvement of T-helper 17 (Th17) subset in the bowel disease pathogenesis by the nitric oxide (NO) pathway in Algerian patients with IBD. We investigated the correlation between the proinflammatory cytokines [(interleukin (IL)-17, IL-23, and IL-6] and NO production in 2 groups of patients. We analyzed the expression of messenger RNAs (mRNAs) encoding Th17 cytokines, cytokine receptors, and NO synthase 2 (NOS2) in plasma of the patients. In the same way, the expression of p-signal transducer and activator of transcription 3 (STAT3) and NOS2 was measured by immunofluorescence and immunohistochemistry. We also studied NO modulation by proinflammatory cytokines (IL-17A, IL-6, tumor necrosis factor α, or IL-1β) in the presence or absence of all-trans retinoic acid (At RA) in peripheral blood mononuclear cells (PBMCs), monocytes, and in colonic mucosa cultures. Analysis of cytokines, cytokine receptors, and NOS2 transcripts revealed that the levels of mRNA transcripts of the indicated genes are elevated in all IBD groups. Our study shows a significant positive correlation between the NO and IL-17A, IL-23, and IL-6 levels in plasma of the patients with IBD. Interestingly, the correlation is significantly higher in patients with active CD. Our study shows that both p-STAT3 and inducible NOS expression was upregulated in PBMCs and colonic mucosa, especially in patients with active CD. At RA downregulates NO production in the presence of proinflammatory cytokines for the 2 groups of patients. Collectively, our study indicates that the IL-23/IL-17A axis plays a pivotal role in IBD pathogenesis through the NO pathway.

The ataxia telangiectasia mutated kinase pathway regulates IL-23 expression by human dendritic cells

Little is known of the regulation of IL-23 secretion in dendritic cells (DC) despite its importance for human Th17 responses. In this study, we show for first time, to our knowledge, that the ataxia telangiectasia mutated (ATM) pathway, involved in DNA damage sensing, acts as an IL-23 repressor. Inhibition of ATM with the highly selective antagonist KU55933 markedly increased IL-23 secretion in human monocyte-derived DC and freshly isolated myeloid DC. In contrast, inhibiting the closely related mammalian target of rapamycin had no effect on IL-23. Priming naive CD4(+) T cells with ATM-inhibited DC increased Th17 responses over and above those obtained with mature DC. Although ATM blockade increased the abundance of p19, p35, and p40 mRNA, IL-12p70 secretion was unaffected. To further examine a role for ATM in IL-23 regulation, we exposed DC to low doses of ionizing radiation. Exposure of DC to x-rays resulted in ATM phosphorylation and a corresponding depression of IL-23. Importantly, ATM inhibition with KU55933 prevented radiation-induced ATM phosphorylation and abrogated the capacity of x-rays to suppress IL-23. To explore how ATM repressed IL-23, we examined a role for endoplasmic reticulum stress responses by measuring generation of the spliced form of X-box protein-1, a key endoplasmic reticulum stress transcription factor. Inhibition of ATM increased the abundance of X-box protein-1 mRNA, and this was followed 3 h later by increased peak p19 transcription and IL-23 release. In summary, ATM activation or inhibition, respectively, inhibited or augmented IL-23 release. This novel role of the ATM pathway represents a new therapeutic target in autoimmunity and vaccine development.

Elevated levels of T helper 17 cells are associated with disease activity in patients with rheumatoid arthritis

Background

Interleukin-17 (IL-17)-producing T helper (Th) 17 cells are considered as a new subset of cells critical to the development of rheumatoid arthritis (RA). We aimed to investigate the distribution of Th1 and Th17 cells and their association with disease activity, and determine the Th17-related cytokine levels in the peripheral blood of RA patients.

Methods

Peripheral blood mononuclear cells from 55 RA and 20 osteoarthritis (OA) patients were stimulated with mitogen, and the distributions of CD4⁺Interferon (INF)⁺IL-17^- (Th1 cells) and CD4⁺INF-IL-17⁺ (Th17 cells) were examined by flow cytometry. Serum levels of IL-6, IL-17, IL-21, IL-23, and tumor necrosis factor (TNF)-α were measured by ELISA. Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) were recorded. The 28-joint disease activity score (DAS28) was also assessed.

Results

The median percentage of Th17 cells was higher in RA patients than in OA patients (P=0.04), and in active than in inactive RA (P=0.03), whereas that of Th1 cells was similar in both groups. Similarly, the levels of IL-17, IL-21, and IL-23 were detected in a significantly higher proportion of RA patients than OA patients and the frequencies of detectable IL-6, IL-17, and IL-21 were higher in active RA than in inactive RA group. The percentage of Th17 cells positively correlated with the DAS28, ESR, and CRP levels.

Conclusions

These observations suggest that Th17 cells and Th17-related cytokines play an important role in RA pathogenesis and that the level of Th17 cells in peripheral blood is associated with disease activity in RA.

Possible roles of IL-12-family cytokines in rheumatoid arthritis

The IL-12 family members, IL-12, IL-23, IL-27 and IL-35, are heterodimeric cytokines that share subunits and have important roles in autoimmunity. As well as their structural relationship the IL-12 family cytokines share some biological characteristics but have functional differences. These cytokines contribute to immune-mediated inflammation and our improved knowledge of their actions has led to alteration of the T(H)1-T(H)2 paradigm. In rheumatoid arthritis (RA), leukocyte migration, bone erosions and angiogenesis are modulated by an IL-23-IL-17 cascade, which can be negated in part by IL-12, IL-27 and IL-35 function. However, the IL-12 family members are a relatively new area of research and data have been generated mostly at the preclinical stage. Further studies in patients with RA are, therefore, required to determine whether these cytokines are valid targets for RA therapy.

TWEAK promotes the production of Interleukin-17 in rheumatoid arthritis

Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) is an inflammatory cytokine that modulates several biological responses by inducing chemokines and proinflammatory cytokines. We hypothesized that TWEAK could promote secretion of IL-17, an amplifier of inflammatory arthritis. To test this, we investigated the capacity of TWEAK to induce IL-17 production in T cells via the fibroblast growth factor-inducible gene 14 (Fn14, also known as TWEAK receptor) signal pathway in rheumatoid arthritis (RA). Fn14 and IL-17 were highly expressed in arthritic tissues of collagen-induced arthritis (CIA) mice. TWEAK induced production of IL-17 alone and synergistically with lipopolysaccharide. In naïve murine T cells, TWEAK promoted Th17 differentiation. The expression of Fn14 was predominant in Th17 cells. TWEAK and IL-17 concentrations were significantly higher in synovial fluid and serum in RA patients than OA patients. In addition, we identified CD4(+)IL-17(+)Fn14(+) cells in synovium from RA patients. TWEAK promoted IL-17 production synergistically with IL-23 or IL-21 and blockade of Fn14 with Fn14-Fc suppressed Th17 differentiation. Conversely, this treatment enhanced Treg differentiation. These results suggest that TWEAK induces IL-17 production and may be a therapeutic target in the treatment of RA.

Ustekinumab in psoriasis immunopathology with emphasis on the Th17-IL23 axis: a primer

Psoriasis is a chronic relapsing immunoinflammatory dermatosis that is commonly associated with systemic comorbidities. The pathogenic importance of interleukin (IL)-12 and IL-23 is beyond doubt, as well as the involvement of T helper cells (Th)1 and Th17 cells. There is upregulation of the p40 subunit shared by IL-12 and IL-23 and of the IL-23 p19 subunit, but not an increased expression of the IL-12 p35 subunit. This indicates that IL-23 appears more involved than IL-12 in the pathogenesis of psoriatic plaques. Ustekinumab is a fully human monoclonal antibody of the immunoglobulin (Ig) G1 class targeting the p40 subunit common to both IL-12 and IL-23, thus inhibiting both IL-12 and IL-23 receptor-mediated signalling. Ustekinumab is part of the recent biologic therapies active in psoriasis, autoimmune arthritides, and inflammatory bowel diseases.

Pleiotropic targets: the problem of shared signaling circuitry in rheumatoid arthritis disease progression and protection

The immune response is replete with feedback control at many levels. These protective circuits are even functional within the arthritic joint, tempering disease to varying extents. An optimal therapy would inhibit autoimmune processes while maintaining protective circuitry. However, many of the cells and proteins that serve as important mediators of disease progression also play an active role in these protective circuits. The hypothesis considered in this review is that the inadvertent inhibition of protective circuitry adversely affects efficacy. Conversely, if therapeutics can be designed, which avoid inhibiting known regulatory circuits, efficacy will be improved. Understanding where these processes share signaling molecules will be crucial to the development of the next generation of therapeutics. This review discusses three well-defined signal transduction cascades; IL-2, IFNγ and TNF-α, and demonstrate within two cell types, T cells and macrophages, how these cytokines may contribute both to protection and to disease progression.

Interleukin-23: as a drug target for autoimmune inflammatory diseases

Interleukin-23 (IL-23) is a member of the IL-12 family of cytokines with pro-inflammatory properties. Its ability to potently enhance the expansion of T helper type 17 (Th17) cells indicates the responsibility for many of the inflammatory autoimmune responses. Emerging data demonstrate that IL-23 is a key participant in central regulation of the cellular mechanisms involved in inflammation. Both IL-23 and IL-17 form a new axis through Th17 cells, which has evolved in response to human diseases associated with immunoactivation and immunopathogeny, including bacterial or viral infections and chronic inflammation. Targeting of IL-23 or the IL-23 receptor or IL-23 axis is a potential therapeutic approach for autoimmune diseases including psoriasis, inflammatory bowel disease, rheumatoid arthritis and multiple sclerosis. The current review focuses on the immunobiology of IL-23 and summarizes the most recent findings on the role of IL-23 in the pre-clinical and ongoing clinical studies.

IL-23R rs11209026 polymorphism modulates IL-17A expression in patients with rheumatoid arthritis

The interleukin (IL)-17/IL-23 axis is an important pro-inflammatory pathway in rheumatoid arthritis (RA). IL-23 maintains CD4(+) T-helper 17 (Th(17)) cells, whereas IL-12 negates IL-17A production by promoting Th(1)-cell differentiation. We sought evidence for any effect of polymorphisms within the interleukin-23 receptor (IL-23R), IL-12 or IL-21 genes on serum cytokine concentrations in 81 patients with RA. Serum cytokines were measured using bead-based multiplex assays. Targeted cytokines were detected in up to 66% of samples. A subgroup of 48 patients had detectable serum IL-17A. Within this subgroup, patients, homozygous for the IL-23R rs11209026 major allele had significantly higher serum IL-17A concentrations compared with patients with the minor allele (394.51 ± 529.72 pg ml(-1) vs 176.11 ± 277.32 pg ml(-1); P = 0.017). There was no significant difference in any of the cytokine concentrations examined in patients positive for the minor allele vs homozygosity for the major allele of IL-12B rs3213337, IL-12Bpro rs17860508 and IL-21 rs6822844. Our results suggest the IL-23R Arg381Gln substitution may influence serum IL-17A concentrations. In patients with the 381Gln allele higher IL-23 concentrations may be needed to produce similar IL-17A concentrations to those in patients with the 381Arg allele. This suggests altered IL-23R function in patients with the minor allele and warrants further functional studies.

A cytokine-centric view of the pathogenesis and treatment of autoimmune arthritis

Cytokines are immune mediators that play an important role in the pathogenesis of rheumatoid arthritis (RA), an autoimmune disease that targets the synovial joints. The cytokine environment in the peripheral lymphoid tissues and the target organ (the joint) has a strong influence on the outcome of the initial events that trigger autoimmune inflammation. In susceptible individuals, these events drive inflammation and tissue damage in the joints. However, in resistant individuals, the inflammatory events are controlled effectively with minimal or no overt signs of arthritis. Animal models of human RA have permitted comprehensive investigations into the role of cytokines in the initiation, progression, and recovery phases of autoimmune arthritis. The discovery of interleukin-17 (IL-17) and its association with inflammation and autoimmune pathology has reshaped our viewpoint regarding the pathogenesis of arthritis, which previously was based on a simplistic T helper 1 (Th1)-Th2 paradigm. This review discusses the role of the newer cytokines, particularly those associated with the IL-17/IL-23 axis in arthritis. Also presented herein is the emerging information on IL-32, IL-33, and IL-35. Ongoing studies examining the role of the newer cytokines in the disease process would improve understanding of RA as well as the development of novel cytokine inhibitors that might be more efficacious than the currently available options.

Interleukin-23: a key cytokine in inflammatory diseases

Interleukin-23 (IL-23) is a pro-inflammatory cytokine composed of two subunits, p19 and p40. The p40 subunit is shared with IL-12. IL-23 and IL-12 have different receptors and different effects. Whereas IL-12 induces development of Th1 cells, which produce interferon-γ, IL-23 is involved in differentiation of Th17 cells in a pro-inflammatory context and especially in the presence of TGF-β and IL-6. Activated Th17 cells produce IL-17A, IL-17F, IL-6, IL-22, TNF-α, and GM-CSF. Inflammatory macrophages express IL-23R and are activated by IL-23 to produce IL-1, TNF-α, and IL-23 itself. These effects identify IL-23 as a central cytokine in autoimmunity and a highly promising treatment target for inflammatory diseases. IL-23 is found in the skin of patients with psoriasis, in the bowel wall of patients with chronic inflammatory bowel disease, and in synovial membrane of patients with rheumatoid arthritis. IL-23 is involved in osteoclastogenesis, independently from IL-17, via induction of RANKL expression. Debate continues to surround the role for IL-23 in the pathophysiology of inflammatory joint diseases (rheumatoid arthritis and spondyloarthritis). Ustekinumab, which inhibits IL-12 and IL-23 by blocking p40, has been found effective in cutaneous psoriasis and psoriatic arthritis, as well as in Crohn's disease. Treatments that specifically target IL-23 (antibodies to p19) are being developed.

Interleukin-23 as a potential therapeutic target for rheumatoid arthritis

Cytokine-mediated immunity plays a crucial role in the pathogenesis of various autoimmune diseases, including rheumatoid arthritis (RA). Increasing evidence has revealed the importance of IL-23, which closely resembles IL-12 structurally and immunologically, in linking innate and adaptive immunity. IL-23, a newly identified heterodimeric pro-inflammatory cytokine, is composed of a p40 subunit in common with IL-12 and a unique p19 subunit. Recent evidence suggests that IL-23, rather than IL-12, is the crucial factor in the pathogenesis of various immune-mediated disorders. In addition, recent studies have explored the role of IL-23 in patients with RA. An elevated expression of IL-23 has been demonstrated in the synovial fibroblasts and plasma of patients with RA. Moreover, an association between IL-23 and IL-23R polymorphisms with susceptibility to RA has been reported. Therefore, the targeting of IL-23 or the IL-23 receptor has been proposed as a potential therapeutic approach for RA. In this review we will discuss the biological features of IL-23, and summarize recent advances in our understanding of the role of IL-23 in the pathogenesis and treatment of RA.

Novel approach for interleukin-23 up-regulation in human dendritic cells and the impact on T helper type 17 generation

Interleukin-23 (IL-23) is important for T helper type 17 (Th17) responses and strategies to regulate IL-23 in human dendritic cells (DC) are limited. This study describes a novel means to control IL-23 secretion by conditioning DC with a phosphatidyl inositol 3-kinase inhibitor Wortmannin (WM). Treatment of monocyte-derived DC with WM increased Toll-like receptor (TLR) -dependent IL-23 secretion 10-fold and IL-12p70 twofold, but IL-27 was unaffected. The effect of WM was restricted to TLR3/4 pathways, did not occur through TLR2, TLR7/8 or Dectin-1, and was characterized by increased p19, p35 and p40 transcription. These responses were not solely dependent on phosphatidyl inositol 3-kinase as the alternative inhibitor LY294002 did not modulate IL-23 production. The normal patterns of activation of mitogen-activated protein kinase pathways were unaffected by WM-conditioning but IL-23 secretion required p38, ERK and JNK pathways. Importantly, this effect was manifest in populations of blood DC. Conditioning freshly isolated myeloid DC with WM before TLR3 or TLR4 triggering resulted in high levels of IL-23 secretion and an absence of IL-12p70. These WM-conditioned myeloid DC were highly effective at priming Th17 responses from naive CD4(+) T cells. Our findings provide a novel means to generate IL-23-rich environments and Th17 responses and suggest as yet unidentified regulatory factors, identification of which will provide new approaches to control IL-23-dependent immunity in infectious disease, autoimmunity and malignancy.

Posttranscriptional regulation of IL-23 expression by IFN-gamma through tristetraprolin

IL-23 plays an essential role in maintenance of IL-17-producing Th17 cells that are involved in the pathogenesis of several autoimmune diseases. Regulation of Th17 cells is tightly controlled by multiple factors such as IL-27 and IFN-γ. However, the detailed mechanisms responsible for IFN-γ-mediated Th17 cell inhibition are still largely unknown. In this study, we demonstrate that IFN-γ differentially regulates IL-12 and IL-23 production in both dendritic cells and macrophages. IFN-γ suppresses IL-23 expression by selectively targeting p19 mRNA stability through its 3'-untranslated region (3'UTR). Furthermore, IFN-γ enhances LPS-induced tristetraprolin (TTP) mRNA expression and protein production. Overexpression of TTP suppresses IL-23 p19 mRNA expression and p19 3'UTR-dependent luciferase activity. Additionally, deletion of TTP completely abolishes IFN-γ-mediated p19 mRNA degradation. We further demonstrate that IFN-γ suppresses LPS-induced p38 phosphorylation, and blockade of p38 MAPK signaling pathway with SB203580 inhibits IFN-γ- and LPS-induced p19 mRNA expression, whereas overexpression of p38 increases p19 mRNA expression via reducing TTP binding to the p19 3'UTR. Finally, inhibition of p38 phosphorylation by IFN-γ leads to TTP dephosphorylation that could result in stronger binding of the TTP to the adenosine/uridine-rich elements in the p19 3'UTR and p19 mRNA degradation. In summary, our results reveal a direct link among TTP, IFN-γ, and IL-23, indicating that IFN-γ-mediated Th17 cell suppression might act through TTP by increasing p19 mRNA degradation and therefore IL-23 inhibition.

New interleukin-23 pathway inhibitors in dermatology: ustekinumab, briakinumab, and secukinumab

Interleukin (IL)-23 is an important regulator of T helper-17 lymphocytes, which influence the cutaneous immune system by production of IL-17 and several other proinflammatory cytokines. This pathway has been recently linked to the pathogenesis of psoriasis and numerous other skin diseases. A newly developed biologic drug, ustekinumab (CNTO-1275), which targets the p40 subunit of IL-12 and IL-23, was approved by the US FDA and the European Medicines Agency in 2009 for the treatment of moderate to severe psoriasis. Administered as subcutaneous injections of 45 mg at weeks 0 and 4, and then every 12 weeks, ustekinumab produces a 75% improvement in the Psoriasis Area and Severity Index (PASI) in 66.4-75.7% of patients and a Dermatology Life Quality Index (DLQI) score of 0 or 1 in 55-56% of patients after 12 weeks of therapy. A recent clinical trial also indicates the possible efficacy of ustekinumab in psoriatic arthritis. The proportion of patients who had at least one adverse event through 12 weeks in clinical studies was 51.6-57.6% in the ustekinumab group and 50.4% in the placebo group. Serious adverse events were observed in 1.4-1.6% of patients treated with ustekinumab and in 1.4% of patients receiving placebo. Injection-site reactions occurred in 1-2% of patients and 5% of patients developed anti-ustekinumab antibodies. Further studies are needed to evaluate the long-term efficacy and safety of ustekinumab. Another biologic drug that targets the same molecules, briakinumab (ABT-874), has recently had its approval application withdrawn in the US and Europe to conduct further analysis and clinical trials. The company plans resubmission at a later date. Other IL-23 pathway inhibitors in the pipeline include anti-p19 monoclonal antibody and apilimod (STA-5326), which interfere with IL-23 activity, as well as secukinumab (AIN-457), LY-2439821, and AMG-827, which exhibit their activity at other targets of the IL-23 pathway.

Th17 cells, not IL-17+ γδ T cells, drive arthritic bone destruction in mice and humans

The mechanism whereby IL-17 drives rheumatoid arthritis remains incompletely understood. We demonstrate that anti-IL-17 therapy in collagen-induced arthritis ameliorates bone damage by reducing the number of osteoclasts in joints. We found equal numbers of CD4(+) Th17 and IL-17 producing γδ T cells in the joints of arthritic mice, and in vitro, both populations similarly induced osteoclastogenesis. However, individual depletion and adoptive transfer studies revealed that in vivo, Th17 cells dominated with regard to bone destruction. Unlike γδ T cells, Th17 cells were found in apposition to tartrate-resistant acid phosphatase positive osteoclasts in subchondral areas of inflamed joints, a pattern reproduced in patient biopsies. This localization was caused by Ag-specific retention, because OVA-primed Th17 cells showed a γδ T cell-like diffuse distribution. Because IL-23, as produced by osteoclasts, enhanced T cell-mediated osteoclastogenesis, we propose that Ag-specific juxtaposition is key to foster the molecular cross talk of Th17 cells and osteoclasts, thus driving arthritic bone destruction.

Targeting IL-17 and Th17 cells in rheumatoid arthritis

Identification of interleukin-17 (IL-17) as a powerful proinflammatory cytokine and the recent recognition of a T-helper cell subset that secretes it have focused attention on the role of IL-17 and Th17 cells in rheumatoid arthritis (RA) and other immune-mediated diseases. While understanding of its role in RA is still evolving, evidence from both animal models and human systems provides a compelling rationale for therapeutic targeting of IL-17 in RA. Both direct and indirect approaches to accomplish this are feasible. Mechanistic studies in the context of clinical trials will be required to understand why some strategies may be preferable from the perspectives of efficacy and safety.

[Role of Th17 cells in rheumatoid arthritis]

Th17 cells are the newly described subset of the CD4(+) T lymphocytes. Activated Th17 cells are characterized by their ability to produce IL-17A and other pro-inflammatory cytokines. IL-17A regulates immune function through its cell-surface receptor expressed on epithelial-and endothelial cells, fibroblasts and leukocytes by promoting neutrophil recruitment and releasing further pro-inflammatory mediators. Failures of the susceptible balance of the immunoregulation may lead to unchecked immune response and autoimmune diseases. The central role of Th17 cells and cytokines produced by Th17 cells were confirmed in a wide variety of human autoimmune diseases, including rheumatoid arthritis. Recently Th17 cells and its cytokines come into the focus of immunological research as potential therapeutic targets.

IL-23 in the pathogenesis of rheumatoid arthritis

Interleukin-23 (IL-23) is a heterodimeric cytokine belonging to the IL-6/IL-12 family that plays a key role in several of autoimmune and inflammatory disorders. This family contains the 34 type I cytokine receptor chains and 27 ligands, which share structural and functional similarities, but on the other hand they display distinct roles in shaping Th cells responses. IL-12 family cytokines have not only proinflammatory effects but they also promote inflammatory responses. IL-23 is composed of the p40 subunit in common with IL-12, and with a unique p19 subunit. IL-23 binding to an IL-23 receptor expressed on dendritic cells, macrophages and monocytes triggers the activation of Jak2 and Tyk2, which in turn phosphorylates STAT1, STAT3, STAT4 and STAT5 as well as induce formation of STAT3-STAT4 heterodimers. IL-23 is one of the essential factors required for the survival and/or expansion of Th17 cells, which produce IL-17, IL-17F, IL-6 and TNF-alpha. Th17 cells stimulated by the IL-23 promote osteoclastogenesis through production of IL-17, which induce receptor activator of NF-kappa B ligand on mesenchymal cells. The IL-23-IL-17 axis includes Th17 cells and plays a key role in the development of autoimmune arthritis.

Translational mini-review series on Th17 cells: function and regulation of human T helper 17 cells in health and disease

T helper (Th) cell have a central role in modulating immune responses. While Th1 and Th2 cells have long been known to regulate cellular and humoral immunity, Th17 cells have been identified only recently as a Th lineage that regulates inflammation via production of distinct cytokines such as interleukin (IL)-17. There is growing evidence that Th17 cells are pathological in many human diseases, leading to intense interest in defining their origins, functions and developing strategies to block their pathological effects. The cytokines that regulate Th17 differentiation have been the focus of much debate, due primarily to inconsistent findings from studies in humans. Evidence from human disease suggests that their in vivo development is driven by specialized antigen-presenting cells. Knowledge of how Th17 cells interact with other immune cells is limited, but recent data suggest that Th17 cells may not be subject to strict cellular regulation by T regulatory cells. Notably, Th17 cells and T regulatory cells appear to share common developmental pathways and both cell types retain significant plasticity. Herein, we will discuss the molecular and cellular regulation of Th17 cells with an emphasis on studies in humans.

Monocyte derived interleukin (IL)-23 is an important determinant of synovial IL-17A expression in rheumatoid arthritis

OBJECTIVE

To demonstrate gene expression of interleukin (IL)-17A, IL-23, and IL-12 and to determine the proximity of IL-17A and IL-23 producing cells in rheumatoid synovial tissue.

METHODS

Total RNA was isolated from 25 synovial membranes obtained from 20 patients with rheumatoid arthritis (RA). Quantitative real-time polymerase chain reaction was used to measure IL-17A, IL-12p35, IL-23p19, p40, and GAPDH expression. Immunohistochemistry was utilized to determine cell type and proximity of IL-17A, IL-12, and IL-23 in rheumatoid synovium.

RESULTS

IL-17A was present in 13/25 synovia. IL-12p35 was present in all samples while IL-23p19 was present in 23/25. p40 was present in 23/25 samples. Of the 2 p40- samples both were IL-23p19 and IL-12p35 positive. Mean expression of IL-23p19 was significantly higher in the IL-17A+ versus IL-17A- synovia (0.10 +/- 0.02 ng vs 0.05 +/- 0.01 ng; p < 0.05). There was no difference in IL-12p35 expression between IL-17A+ and IL-17A- synovia (0.5 +/- 0.21 ng vs 0.38 +/- 0.24 ng; p = 0.2). All IL-17A+ cells were in the vicinity of IL-23+ cells. IL-12+ cells were both close to and removed from IL-17A+ cells. Only a proportion of CD3+T cells appeared to produce IL-17A.

CONCLUSION

IL-17A gene expression occurs in only a subset of rheumatoid synovial membranes. IL-23 gene expression is higher in IL-17A+ versus IL-17A- membranes. In keeping with this, IL-17A+ and IL-23+ cells colocalize in synovial membranes. IL-17 is not an absolute requirement in RA but may be important in amplifying the inflammatory response. Anti-IL23 therapies may have a role in those patients with IL-17A expression.

The role of T helper type 17 cells in inflammatory arthritis

While T cells have been implicated in the pathogenesis of inflammatory arthritis for more than three decades, the focus on the T helper type 17 (Th17) subset of CD4 T cells and their secreted cytokines, such as interleukin (IL)-17, is much more recent. Proinflammatory actions of IL-17 were first identified in the 1990s, but the delineation of a distinct Th17 subset in late 2005 has sparked great interest in the role of these cells in a broad range of immune-mediated diseases. This review summarizes current understanding of the role of Th17 cells and their products in both animal models of inflammatory arthritis and human immune-driven arthritides.

IRAK4 kinase activity is required for Th17 differentiation and Th17-mediated disease

Both IL-23- and IL-1-mediated signaling pathways play important roles in Th17 cell differentiation, cytokine production, and autoimmune diseases. The IL-1R-associated kinase 4 (IRAK4) is critical for IL-1/TLR signaling. We show here that inactivation of IRAK4 kinase in mice (IRAK4 KI) results in significant resistance to experimental autoimmune encephalomyelitis due to a reduction in infiltrating inflammatory cells into the CNS and reduced Ag-specific CD4(+) T cell-mediated IL-17 production. Adoptive transfer of myelin oligodendrocyte glycoprotein 35-55-specific IRAK4 KI Th17 cells failed to induce experimental autoimmune encephalomyelitis in either wild-type or IRAK4 KI recipient mice, indicating the lack of autoantigen-specific Th17 cell activities in the absence of IRAK4 kinase activity. Furthermore, the absence of IRAK4 kinase activity blocked induction of IL-23R expression, STAT3 activation by IL-23, and Th17 cytokine expression in differentiated Th17 cells. Importantly, blockade of IL-1 signaling by IL-1RA inhibited Th17 differentiation and IL-23-induced cytokine expression in differentiated Th17 cells. The results of these studies demonstrate that IL-1-mediated IRAK4 kinase activity in T cells is essential for induction of IL-23R expression, Th17 differentiation, and autoimmune disease.

Infliximab treatment reduces the serum levels of interleukin-23 in patients with rheumatoid arthritis

In this study, we investigated the effect of the antitumor necrosis factor alpha (anti-TNF-alpha) antibody, infliximab, combined with methotrexate (MTX) and MTX alone on the serum levels of interleukin (IL)-23 and IL-17 in rheumatoid arthritis (RA) patients. Infliximab combined with MTX was administered to 26 patients with RA (infliximab group), and MTX alone was given to 20 patients with RA (MTX group). We evaluated clinical and laboratory parameters, including the Disease Activity Scores of 28 joints (DAS28) and serum levels of IL-23 and IL-17 at baseline and at 14 and 30 weeks after the initial treatment with these drugs. Single regression analysis was performed between the levels of serum IL-23 and other clinical and laboratory parameters at baseline before the initial treatment with infliximab or MTX. A significant reduction of DAS28 scores was observed in both the infliximab and the MTX group at 14 and 30 weeks after the initial treatment. A significant decrease in serum levels of IL-23 was observed in the infliximab group but not in the MTX group at 14 and 30 weeks after the initial treatment. Serum IL-17 levels did not show a significant change during the follow-up period. At baseline, before the initial treatment with infliximab or MTX, serum IL-23 levels showed a significant correlation with DAS28 and the number of swollen joints. This study indicated that the reduction of serum IL-23 levels in RA patients was a novel action of infliximab.

Human rheumatoid arthritis tissue production of IL-17A drives matrix and cartilage degradation: synergy with tumour necrosis factor-alpha, Oncostatin M and response to biologic therapies

INTRODUCTION

The aim of this study was to examine IL-17A in patients, following anti-TNF-alpha therapy and the effect of IL-17A on matrix turnover and cartilage degradation.

METHODS

IL-17A expression was examined by ELISA and immunohistology in the rheumatoid arthritis (RA) joints. RA whole synovial tissue explant (RA ST), primary synovial fibroblasts (RASFC), human cartilage and chondrocyte cultures were stimulated with IL-17A +/- TNF-alpha and Oncostatin M (OSM). Matrix metalloproteinase (MMP) and tissue inhibitor (TIMP-1) were assessed by ELISA and zymography. Cartilage proteoglycan release was assessed histologically by Safranin-O staining. Clinical parameters, IL-17A, MMP/TIMP were assessed in patients pre/post biologic therapy.

RESULTS

IL-17A levels were higher in RA vs osteoarthritis (OA)/normal joints (P < 0.05). IL-17A up-regulated MMP-1, -2, -9, and -13 in RA ST, RASFC, cartilage and chondrocyte cultures (P < 0.05). In combination with TNF-alpha and OSM, IL-17A shifted the MMP:TIMP-1 ratio in favor of matrix degradation (all P < 0.05). Cartilage proteoglycan depletion in response to IL-17A was mild; however, in combination with TNF-alpha or OSM showed almost complete proteoglycan depletion. Serum IL-17A was detected in 28% of patients commencing biologic therapy. IL-17A negative patients demonstrated reductions post therapy in serum MMP1/TIMP4, MMP3/TIMP1 and MMP3/TIMP4 ratios and an increase in CS846 (all P < 0.05). No significant changes were observed in IL-17A positive patients.

CONCLUSIONS

IL-17A is produced locally in the inflamed RA joint. IL-17A promotes matrix turnover and cartilage destruction, especially in the presence of other cytokines, mimicking the joint environment. IL-17A levels are modulated in vivo, following anti-TNF therapy, and may reflect changes in matrix turnover.

Th17 cells in human disease

SUMMARY

Our understanding of the role of T cells in human disease is undergoing revision as a result of the discovery of T-helper 17 (Th17) cells, a unique CD4(+) T-cell subset characterized by production of interleukin-17 (IL-17). IL-17 is a highly inflammatory cytokine with robust effects on stromal cells in many tissues. Recent data in humans and mice suggest that Th17 cells play an important role in the pathogenesis of a diverse group of immune-mediated diseases, including psoriasis, rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, and asthma. Initial reports also propose a role for Th17 cells in tumorigenesis and transplant rejection. Important differences, as well as many similarities, are emerging when the biology of Th17 cells in the mouse is compared with corresponding phenomena in humans. As our understanding of human Th17 biology grows, the mechanisms underlying many diseases are becoming more apparent, resulting in a new appreciation for both previously known and more recently discovered cytokines, chemokines, and feedback mechanisms. Given the strong association between excessive Th17 activity and human disease, new therapeutic approaches targeting Th17 cells are highly promising, but the potential safety of such treatments may be limited by the role of these cells in normal host defenses against infection.

Th17 cells in human disease

SUMMARY

Our understanding of the role of T cells in human disease is undergoing revision as a result of the discovery of T-helper 17 (Th17) cells, a unique CD4(+) T-cell subset characterized by production of interleukin-17 (IL-17). IL-17 is a highly inflammatory cytokine with robust effects on stromal cells in many tissues. Recent data in humans and mice suggest that Th17 cells play an important role in the pathogenesis of a diverse group of immune-mediated diseases, including psoriasis, rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, and asthma. Initial reports also propose a role for Th17 cells in tumorigenesis and transplant rejection. Important differences, as well as many similarities, are emerging when the biology of Th17 cells in the mouse is compared with corresponding phenomena in humans. As our understanding of human Th17 biology grows, the mechanisms underlying many diseases are becoming more apparent, resulting in a new appreciation for both previously known and more recently discovered cytokines, chemokines, and feedback mechanisms. Given the strong association between excessive Th17 activity and human disease, new therapeutic approaches targeting Th17 cells are highly promising, but the potential safety of such treatments may be limited by the role of these cells in normal host defenses against infection.