Human interleukin-17: A T cell-derived proinflammatory cytokine produced by the rheumatoid synovium

Gene expression induced by interleukin-17 in fibroblast-like synoviocytes of patients with rheumatoid arthritis: upregulation of hyaluronan-binding protein TSG-6

Interleukin-17 (IL-17) has been characterized as a proinflammatory cytokine produced by CD4+ CD45RO+ memory T cells. Overproduction of IL-17 was detected in the synovium of patients with rheumatoid arthritis (RA) compared with patients with osteoarthritis. This study examines differentially expressed genes after the stimulation of fibroblast-like synoviocytes of RA patients by IL-17. Among these genes we identified the following: tumor necrosis factor-stimulated gene-6 (TSG-6), IL-6, IL-8, GRO-beta, and bone morphogenetic protein-6 with an expression 3.6-10.6-fold that in the unstimulated control. IL-17 augmented the expression of TSG-6, a hyaluronan-binding protein, in a time- and dose-dependent manner. IL-17 showed additive effects with IL-1beta and tumour necrosis factor-alpha on the expression of TSG-6, IL-6 and IL-8. The mitogen-activated protein kinase p38 seems to be necessary for the regulation of TSG-6 expression by IL-17, as shown by inhibition with SB203580. Our results support the hypothesis that IL-17 is important in the pathogenesis of RA, contributing to an unbalanced production of cytokines as well as participating in connective tissue remodeling.

IL-17 expression in human herpetic stromal keratitis: modulatory effects on chemokine production by corneal fibroblasts

Herpetic stromal keratitis (HSK) is an immunopathologic disease triggered by infection of the cornea with HSV. Key events in HSK involve the interaction between cornea-infiltrating inflammatory cells and resident cells. This interaction, in which macrophages, producing IL-1 and TNF-alpha, and IFN-gamma-producing Th1 cells play a crucial role, results in the local secretion of immune-modulatory factors and a major influx of neutrophils causing corneal lesions and blindness. The Th1-derived cytokine IL-17 has been shown to play an important role in several inflammatory diseases characterized by a massive infiltration of neutrophils into inflamed tissue. Here we show that IL-17 is expressed in corneas from patients with HSK and that the IL-17R is constitutively expressed by human corneal fibroblasts (HCF). IL-17 exhibited a strong synergistic effect with TNF-alpha on the induction of IL-6 and IL-8 secretion by cultured HCF. Secreted IL-8 in these cultures had a strong chemotactic effect on neutrophils. IL-17 also enhanced TNF-alpha- and IFN-gamma-induced secretion of macrophage-inflammatory proteins 1alpha and 3alpha, while inhibiting the induced secretion of RANTES. Furthermore, considerable levels of IFN-gamma-inducible protein 10 and matrix metalloproteinase 1 were measured in stimulated HCF cultures, while the constitutive secretion of monocyte chemotactic protein 1 remained unaffected. The data presented suggest that IL-17 may play an important role in the induction and/or perpetuation of the immunopathologic processes in human HSK by modulating the secretion of proinflammatory and neutrophil chemotactic factors by corneal resident fibroblasts.

Isolation and characterization of chicken interleukin-17 cDNA

Interleukin-17 (IL-17) is a proinflammatory cytokine produced by activated T cells. A 917-bp cDNA encoding the IL-17 gene was isolated from our EST cDNA library prepared from intestinal intraepithelial lymphocytes (IELs) of Eimeria-infected chickens. It contained a 507-bp open reading frame (ORF) predicted to encode a protein of 169 amino acids (aa) with a molecular mass of 18.9 kDa, a 27-residue NH(2)-terminal signal peptide, a single potential N-linked glycosylation site, and 6 cysteine residues conserved with mammalian IL-17. Chicken IL-17 (chIL-17) shared 37%-46% amino acid sequence identity to the previously described mammalian homologs and also was homologous to the ORF 13 of Herpesvirus saimiri (HVS 13). By Northern blot analysis, IL-17 transcripts were identified in a reticuloendotheliosis virus (REV)-transformed chicken lymphoblast cell line (CU205) and conconavalin A (ConA)-stimulated splenic lymphocytes but not other chicken cell lines or normal tissues. Conditioned medium from COS-7 cells transfected with ChIL-17 cDNA induced IL-6 production by chicken embryonic fibroblasts, suggesting a functional role for the cytokine in avian immunity.

Transgenic overexpression of human IL-17E results in eosinophilia, B-lymphocyte hyperplasia, and altered antibody production

We have identified and cloned a novel human cytokine with homology to cytokines of the interleukin-17 (IL-17) family, which we have termed human IL-17E (hIL-17E). With the identification of several IL-17 family members, it is critical to understand the in vivo function of these molecules. We have generated transgenic mice overexpressing hIL-17E using an apolipoprotein E (ApoE) hepatic promoter. These mice displayed changes in the peripheral blood, particularly, a 3-fold increase in total leukocytes consisting of increases in eosinophils, lymphocytes, and neutrophils. Splenomegaly and lymphoadenopathy were predominant and included marked eosinophil infiltrates and lymphoid hyperplasia. CCR3(+) eosinophils increased in the blood and lymph nodes of the transgenic mice by 50- and 300-fold, respectively. Eosinophils also increased 8- to 18-fold in the bone marrow and spleen, respectively. In the bone marrow, most of the eosinophils had an immature appearance. CD19(+) B cells increased 2- to 5-fold in the peripheral blood, 2-fold in the spleen, and 10-fold in the lymph nodes of transgenic mice, whereas CD4(+) T lymphocytes increased 2-fold in both blood and spleen. High serum levels of the cytokines IL-2, IL-4, IL-5, granulocyte colony-stimulating factor, eotaxin, and interferon gamma were observed. Consistent with B-lymphocyte increases, serum immunoglobulin (Ig) M, IgG, and IgE were significantly elevated. Antigenic challenge of the transgenic mice with keyhole limpet hemocyanin (KLH) resulted in a decrease in anti-KLH IgG accompanied by increases of anti-KLH IgA and IgE. In situ hybridization of transgenic tissues revealed that IL-17Rh1 (IL-17BR/Evi27), a receptor that binds IL-17E, is up-regulated. Taken together, these data indicate that IL-17E regulates hematopoietic and immune functions, stimulating the development of eosinophils and B lymphocytes. The fact that hIL-17E overexpression results in high levels of circulating eosinophils, IL-4, IL-5, eotaxin, and IgE suggests that IL-17E may be a proinflammatory cytokine favoring Th2-type immune responses.

Contribution of interleukin 17 to human cartilage degradation and synovial inflammation in osteoarthritis

OBJECTIVE

To compare the effect of interleukin (IL)-17, IL-1beta and TNF-alpha on chemokine production by human chondrocytes and synovial fibroblasts isolated from patients with osteoarthritis (OA). The expression of IL-1beta mRNA by OA chondrocytes was also assessed, as well as the presence and expression of IL-17 receptor (IL-17R) in OA chondrocytes and synovial fibroblasts after stimulation with IL-17, IL-1beta and TNF-alpha.

DESIGN

Synovial fibroblasts and chondrocytes isolated from patients with OA were stimulated in vitro with IL-17, IL-1beta or TNF-alpha. Supernatants were collected and immunoassayed for the presence of IL-8, GRO-alpha (CXC chemokines) and MCP-1, RANTES (CC chemokines). The cells were used to detect the presence of IL-17R and the expression of IL-17R mRNA. Stimulated chondrocytes were also used to detect IL-1beta production and mRNA expression.

RESULTS

IL-17 upregulated the release of IL-8 and GRO-alpha both by synovial fibroblasts and chondrocytes, and the release of MCP-1 only by chondrocytes. IL-17 was a weaker stimulator than IL-1beta and TNF-alpha, except for GRO-alpha release which was maximally upregulated by IL-1beta, less by IL-17 and minimally by TNF-alpha. When compared to IL-1beta, IL-17 was more active on chondrocytes than on fibroblasts. In chondrocytes the expression of IL-1beta mRNA was enhanced by IL-17 and TNF-alpha, with a maximum level reached by IL-1beta. IL-17 and TNF-alpha stimulated IL-1beta release in few subjects. Neither IL-17, IL-1beta nor TNF-alpha modulated the presence of IL-17R and the expression of IL-17R mRNA.

CONCLUSIONS

These data suggest that IL-17 could contribute to cartilage breakdown and synovial infiltration in OA by inducing both the release of chemokines by chondrocytes and synovial fibroblasts and, in a less extent, the synthesis of IL-1beta by chondrocytes.

Interleukin 17 induces cartilage collagen breakdown: novel synergistic effects in combination with proinflammatory cytokines

OBJECTIVE

To investigate whether interleukin 17 (IL17), derived specifically from T cells, can promote type II collagen release from cartilage. The ability of IL17 to synergise with other proinflammatory mediators to induce collagen release from cartilage, and what effect anti-inflammatory agents had on this process, was also assessed.

METHODS

IL17 alone, or in combination with IL1, IL6, oncostatin M (OSM), or tumour necrosis factor alpha (TNFalpha), was added to bovine nasal cartilage explant cultures. Proteoglycan and collagen release were determined. Collagenolytic activity was determined by bioassay. Chondroprotective effects of IL4, IL13, transforming growth factor beta1 (TGFbeta1) and insulin-like growth factor-1 (IGF1) were assessed by inclusion in the explant cultures.

RESULTS

IL17 alone stimulated a dose dependent release of proteoglycan and type II collagen from bovine nasal cartilage explants. Suboptimal doses of IL17 synergised potently with TNFalpha, IL1, OSM, and IL6 to promote collagen degradation. This collagen release was completely inhibited by tissue inhibitor of metalloproteinase-1 and BB-94 (a synthetic metalloproteinase inhibitor), and was significantly reduced by IL4, IL13, TGFbeta1, and IGF1. In IL17 treated chondrocytes, mRNA expression for matrix metalloproteinase (MMP)-1, MMP-3, and MMP-13 was detected. Moreover, a synergistic induction of these MMPs was seen when IL17 was combined with other proinflammatory cytokines.

CONCLUSIONS

IL17 can, alone and synergistically in combination with other proinflammatory cytokines, promote chondrocyte mediated MMP dependent type II collagen release from cartilage. Because levels of all these proinflammatory cytokines are raised in rheumatoid synovial fluids, this study suggests that IL17 may act as a potent upstream mediator of cartilage collagen breakdown in inflammatory joint diseases.

Pathogenesis of bone lesions in rheumatoid arthritis

Histopathologic characterization of bone erosions from patients with rheumatoid arthritis (RA) and studies performed in animal models of inflammatory arthritis provide strong evidence that osteoclasts play an important role in focal marginal and subchondral bone loss in inflammatory arthritis. Much has been learned concerning the factors responsible for the induction and activation of osteoclasts associated with the bone erosions in RA. Therapies that target these osteoclast-inducing factors or other aspects of osteoclast-mediated bone resorption represent potential targets for blocking or at least attenuating bone destruction in RA. The demonstration of the role of the newly described osteoclastogenic factor receptor activator of nuclear factor kappaB ligand in RA synovial tissues and the successful prevention of bone erosions in animal models of arthritis with its inhibitor osteoprotegerin provide hope that specific therapies can be developed for preventing bone and joint destruction in RA, particularly in situations in which disease-modifying agents are ineffective in controlling disease activity.

Cytokines in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic disease characterized by synovial inflammation that leads to the destruction of cartilage and bone. In the last decade, there was a lot of successful research in the field of cytokine expression and regulation. It has become clear that pro- and anti-inflammatory cytokines, derived predominantely from cells of macrophage lineage, play a major role in the initiation and perpetuation of the chronic inflammatory process in the RA synovial membrane. Monokines are abundant in rheumatoid synovial tissue, whereas low amounts of lymphokines are found. The involvement of pro-inflammatory cytokines, particularly interleukin (IL)-1 and tumor necrosis factor-alpha, in the pathogenesis of RA is well accepted. Recent data provide evidence that the pro-inflammatory cytokine IL-18 plays a crucial role in the development and sustenance of inflammatory joint diseases. There also appears to be a compensatory anti-inflammatory response in RA synovial membrane. It has become clear in the last few years that T cell-derived cytokines expressed preferentially by Th1 cells contribute to joint destruction and inflammation in RA. However, products from Th2 cells may be protective.

Lessons from animal models of arthritis

There is increasing thought that autoantibodies to systemic self-antigens may provide a principal effector mechanism for the initiation and propagation of joint inflammation. The recent identification of arthritis transfer with antibodies to the self-antigen glucose-6-phosphate isomerase has boosted this interest. Fc receptor involvement in arthritis has been evaluated, identifying pro-inflammatory and inhibitory Fc gamma receptor subtypes, and demonstrating a link between Fc gamma receptor expression, cytokine production, cartilage destruction, and mouse strain susceptibility to immune complex arthritis. Further proof of a key role of interleukin (IL)-1 in arthritis was provided by the occurrence of spontaneous arthritis in IL-1 receptor antagonist knockout mice and elicitation of full-blown arthritis in tumor necrosis factor (TNF)-deficient mice. IL-18 (part of the IL-1 family) is a crucial upstream cytokine that, with IL-12, induces IL-1 and TNF and promotes arthritis and T-cell differentiation. IL-18 neutralization improved arthritis outcome, but its central role in host defense against bacterial infections may complicate therapeutic IL-18 targeting. T helper 1 (Th1) cells may aggravate arthritis and joint destruction through the production of IL-17, which shows joint destructive potential independent of IL-1. Studies have also focused on the control of receptor activator of nuclear factor kappaB ligand, modulation with IL-4, and regulation of downstream mediators in tissue destruction. Gene therapeutic approaches proved efficacious and will provide future ways to control arthritis.

Anatomic localization of immature and mature dendritic cells in an ectopic lymphoid organ: correlation with selective chemokine expression in rheumatoid synovium

It remains to be clarified whether dendritic cells (DC) reach the rheumatoid arthritis (RA) synovium, considered an ectopic lymphoid organ, as mature cells or undergo local maturation. We characterized by immunohistochemistry the DC subsets and used tonsils as a control. Immature and mature DC were defined by CD1a and DC-lysosome-associated membrane protein/CD83 expression, respectively. Immature DC were mainly detected in the lining layer in RA synovium. Mature DC were exclusively detected in the lymphocytic infiltrates. The DC-lysosome-associated membrane protein/CD1a ratio was 1.1 in RA synovium and 5.3 in tonsils, suggesting the relative accumulation of immature DC in RA synovium. We then focused on the expression of CCL20/CCR6 and CCL19/CCR7, CCL21/CCR7 chemokine/receptor complex, which control immature and mature DC migration respectively. A close association was observed between CCL20-producing cells and CD1a(+) cells, suggesting the contribution of CCL20 to CCR6(+) cell homing. Conversely, CCL21 and CCL19 expression was only detected in perivascular infiltrates. The association among CCL19/21-producing cells, CCR7 expression, and mature DC accumulation is in line with the roles of these chemokines in mature CCR7(+) DC homing to lymphocytic infiltrates. The role of DC in disease initiation and perpetuation makes chemokines involved in DC migration a potential therapeutic target.

Novel pathways that regulate tumor necrosis factor-alpha production in rheumatoid arthritis

Clinical intervention studies have clearly shown the benefit in suppressing tumor necrosis factor-alpha (TNF-alpha) rheumatoid arthritis (RA). In consequence, considerable interest has arisen in those pathways that in turn regulate TNF-alpha production, because they may offer further possible therapeutic targets. Several candidate pathways are currently being investigated. They include T cell/macrophage interactions mediated primarily through cell-cell membrane contact; novel cytokine activities; microbial-derived products, in particular bacterial deoxyribonucleic acid sequences; autoreactive T cells, and immunoglobulins. At the subcellular level, there is further interest in targeting signaling and mRNA processing and cytokine cleavage pathways required for optimal TNF-alpha production. The key recent observations in these areas, particularly in the extracellular compartment, are reviewed.

Interleukin-17 inhibits tumor cell growth by means of a T-cell-dependent mechanism

Interleukin 17 (IL-17) is a proinflammatory cytokine produced by activated CD4(+) memory T cells. We previously showed that IL-17 increased the growth rate of human cervical tumors transplanted into athymic nude mice. To address the possible role of T cells in the biologic activity of IL-17 for tumor control, we grafted 2 murine hematopoietic immunogenic tumors (P815 and J558L) transfected with a complementary DNA encoding murine IL-17 into syngeneic immunocompetent mice. We found that growth of the 2 IL-17-producing tumors was significantly inhibited compared with that of mock-transfected tumors. In contrast to the antitumor activity of IL-17 observed in immunocompetent mice, we observed no difference in the in vivo growth of IL-17-transfected or mock-transfected P815 cells (P815-IL-17 and P815-Neo, respectively) transplanted into nude mice. We then showed that IL-17 increased generation of specific cytolytic T lymphocytes (CTLs) directed against the immunodominant antigens from P815 called A, B, C, D, and E, since all mice injected with P815-IL-17 developed a P815-specific CTL response, whereas only 6 of 16 mice immunized with P815-Neo had a specific CTL response against the antigens. The induction of CTLs was associated with establishment of a tumor-protective immunity. These experiments suggest that T lymphocytes are involved in the antitumor activity of IL-17. Therefore, IL-17, like other cytokines, appears to be a pleiotropic cytokine with possible protumor or antitumor effects on tumor development, which often depends on the immunogenicity of tumor models.

Reduction of joint inflammation and bone erosion in rat adjuvant arthritis by treatment with interleukin-17 receptor IgG1 Fc fusion protein

OBJECTIVE

To investigate the role of interleukin-17 (IL-17) in inflammatory arthritis by blockade with an IL-17 receptor/human IgG1 Fc fusion protein (muIL-17R:Fc) in adjuvant-induced arthritis (AIA) in the rat.

METHODS

AIA was induced in 39 DA rats with the use of Freund's complete adjuvant. Rats received either 7.3 or 20 mg/kg of muIL-17R:Fc or phosphate buffered saline intraperitoneally every other day from the time of arthritis induction for approximately 17 days. Paw volume, arthritis severity, and weight were assessed every 3-4 days. Rats were killed between days 21 and 23 post-induction. Ankles were removed for quantitative radiology and histology and for immunohistochemistry for T cells.

RESULTS

Treatment with muIL-17R:Fc attenuated paw volume in a dose-dependent manner. Both the 7.3 and 20 mg/kg doses of muIL-17R:Fc significantly reduced radiographic scores in the treated rats compared with the controls. The 20 mg/kg dose of muIL-17R:Fc significantly reduced histology scores compared with the controls. T cell numbers were unchanged in the muIL-17R:Fc-treated rats as a function of dose.

CONCLUSION

In vivo blockade of IL-17 by muIL-17R:Fc treatment attenuated AIA and reduced joint damage, suggesting that IL-17 plays an important role in the inflammation and joint destruction of AIA. IL-17 may be a potential therapeutic target for inflammatory diseases in humans, such as rheumatoid arthritis.

Joint damage and inflammation in c-Jun N-terminal kinase 2 knockout mice with passive murine collagen-induced arthritis

OBJECTIVE

Previous studies have demonstrated that inhibition of c-Jun N-terminal kinase (JNK) decreases joint destruction in the rat adjuvant arthritis model. The present study was undertaken to investigate whether selective loss of JNK-2 function decreases joint destruction in JNK-2 knockout mice, in order to determine the role of this isoform in inflammatory arthritis.

METHODS

Passive collagen-induced arthritis (CIA) was induced in Jnk2(-/-) and wild-type mice by administering anti-type II collagen antibodies. Arthritis was assessed daily using a semiquantitative clinical scoring system. Fibroblast-like synoviocytes (FLS) were prepared from Jnk2(-/-) and wild-type mice, and JNK protein expression was determined by Western blot analysis. Matrix metalloproteinase 13 (MMP-13) expression was determined by Northern blot analysis, and activator protein 1 (AP-1) binding activity by electromobility shift assay (EMSA).

RESULTS

The JNK protein level in Jnk2(-/-) mice with CIA was 22% of that in wild-type mice with CIA (P < 0.001), and mainly the 46-kd isoform was expressed in the former group. Surprisingly, clinical arthritis was slightly more severe in the Jnk2(-/-) mice. Histologic scores for synovial inflammation were not significantly different. However, Safranin O-stained sections from the Jnk2(-/-) mice exhibited significantly less joint damage. Although joint destruction was decreased in Jnk2(-/-) mice with CIA, EMSA and Northern blot analysis of total joint extracts revealed similar levels of AP-1 binding and MMP-13 expression in Jnk2(-/-) and wild-type mice. The lack of correlation with AP-1 activity and MMP expression was probably because non-FLS cells in the joint may express more JNK-1 than do FLS.

CONCLUSION

JNK-2 is a determinant of matrix degradation, but it has little effect on inflammation in arthritis. Complete inhibition of MMP expression and joint destruction will likely require combined JNK-1 and JNK-2 inhibition.

Expression, modulation and signalling of IL-17 receptor in fibroblast-like synoviocytes of patients with rheumatoid arthritis

Interleukin-17 (IL-17) has been characterized as a proinflammatory cytokine produced by CD4+ CD45RO+ memory T cells. Overproduction of IL-17 was detected in the synovium of patients with rheumatoid arthritis (RA) compared to patients with osteoarthritis. In contrast to the restricted expression of IL-17, the IL-17 receptor (IL-17R/CDw217) is expressed ubiquitously. Using a real-time RT-PCR assay, we detected similar absolute levels of IL-17R mRNA expression in fibroblast-like synoviocytes (SFC) from patients with RA (mean 9 pg/microg total RNA; ranged from 0.1 pg to 96 pg IL-17R mRNA/microg total RNA) compared to synoviocytes of non-RA patients. Analysis of the IL-17R surface expression confirmed the results obtained for IL-17R mRNA expression. Exposure of SFC to IL-17 led to a mRNA induction of CXC chemokines IL-8, GRO-alpha and GRO-beta. An anti-IL-17 antibody blocked these effects of IL-17. The MAPK p38 appears necessary for the regulation of IL-8, GRO-alpha and GRO-beta expression as shown by inhibition with SB203580. The inhibitors genistein (tyrosine kinase inhibitor) and calphostin C (inhibitor of protein kinase C) reduced significantly the IL-17-stimulated mRNA expression of IL-8, GRO-alpha and GRO-beta in SFC, whereas PD98059 (inhibitor of MEK-1/2) was without effect. Pharmacological drugs used in therapy of RA, such as cyclosporin and methotrexate, induced a fourfold increase of IL-17R mRNA expression and augmented the IL-17-stimulated IL-8 expression. Our results support the hypothesis that IL-17/IL-17R may play a significant role in the pathogenesis of RA contributing to an unbalanced production of cytokines as well as participating in connective tissue remodelling.

Soluble and transmembrane isoforms of novel interleukin-17 receptor-like protein by RNA splicing and expression in prostate cancer

Members of the interleukin-17 cytokine family are present in a variety of tissues (1-3), although the founding member, interleukin-17, is expressed exclusively in T cells and B cells (4-8). The cloning and characterization of a novel single-pass transmembrane protein with limited homology to the interleukin-17 receptor is reported. High mRNA levels were detected in prostate, cartilage, kidney, liver, heart, and muscle, whereas transcripts were barely detected in thymus and leukocytes. At least 11 RNA splice variants were found, transcribed from 19 exons on human chromosome 3p25.3-3p24.1. Differential exon usage was found in different tissues by quantitative reverse transcriptase-PCR. Predicted proteins range from 186 to 720 amino acids. Soluble secreted proteins lacking transmembrane and intracellular domains are predicted from several splice isoforms and may function as extracellular antagonists to cytokine signaling by functioning as soluble decoy receptors. Using antibodies directed at the cytoplasmic and extracellular domains of this protein, we investigated its localization and found that it was expressed in a variety of normal human tissues including prostate and in prostate cancer.

Expression of IL-17B in neurons and evaluation of its possible role in the chromosome 5q-linked form of Charcot-Marie-Tooth disease

IL-17B is a recently identified homolog of IL-17. Northern analysis revealed that IL-17B mRNA is expressed at very high levels in spinal cord and at much lower and more variable levels in trachea, prostate, lung, small intestine, testes, adrenal, and pancreas. In developing mouse embryos IL-17B expression was first detected at day 11 and appeared to peak at day 15. In situ analysis of mouse spinal cord, dorsal root ganglia, and brain demonstrated that IL-17B mRNA is primarily expressed by the neurons. Immunohistochemical analysis of human spinal cord, dorsal root ganglia, cerebral cortex, cerebellum, and hippocampus demonstrated that IL-17B protein is primarily localized to the neuronal cell bodies and axons. Radiation hybrid mapping localized the IL-17B gene to a region on human chromosome 5q that is associated with a rare autosomal recessive form of Charcot-Marie-Tooth demyelinating disease. However, no changes were found in the coding regions, splice junctions, intron 1, or the 5' and 3' untranslated regions of IL-17B genes of patients affected with this disease.

The molecular mechanism of osteoclastogenesis in rheumatoid arthritis

Bone-resorbing osteoclasts are formed from hemopoietic cells of the monocyte-macrophage lineage under the control of bone-forming osteoblasts. We have cloned an osteoblast-derived factor essential for osteoclastogenesis, the receptor activator of NF-kappaB ligand (RANKL). Synovial fibroblasts and activated T lymphocytes from patients with rheumatoid arthritis also express RANKL, which appears to trigger bone destruction in rheumatoid arthritis as well. Recent studies have shown that T lymphocytes produce cytokines other than RANKL such as IL-17, granulocyte-macrophage colony-stimulating factor and IFN-gamma, which have powerful regulatory effects on osteoclastogenesis. The possible roles of RANKL and other cytokines produced by T lymphocytes in bone destruction are described.

Novel pro-inflammatory interleukins: potential therapeutic targets in rheumatoid arthritis

Among potential targets for nonspecific anti-inflammatory immunointervention, three pro-inflammatory interleukins (ILs) have recently been found to play a pivotal role in rheumatoid arthritis (RA). IL-15 has both chemoattractant and proinflammatory properties and may promote bone destruction. IL-17, a product of T lymphocytes, has proinflammatory effects and induces production of metalloproteinases such as MMP-1. IL-18 not only has proinflammatory, angiogenic, and chemoattractant effects but also promotes cartilage destruction. These cytokines are potential targets for specific or nonspecific anti-inflammatory therapy. Thus, blocking IL-15 by its receptor reduces the severity of experimental collagen-induced arthritis (CIA). In this model, IL-17 levels fall after administration of anti-inflammatory cytokines such as IL-4 or IL-13. Finally, monoclonal anti-IL-18 antibodies prevent streptococcal cell wall arthritis, and IL-18 binding protein, which is a naturally occurring IL-18 inhibitor, prevents CIA.

Enhancing effect of IL-1, IL-17, and TNF-alpha on macrophage inflammatory protein-3alpha production in rheumatoid arthritis: regulation by soluble receptors and Th2 cytokines

Macrophage inflammatory protein (MIP)-3alpha is a chemokine involved in the migration of T cells and immature dendritic cells. To study the contribution of proinflammatory cytokines and chemokines to the recruitment of these cells in rheumatoid arthritis (RA) synovium, we looked at the effects of the monocyte-derived cytokines IL-1beta and TNF-alpha and the T cell-derived cytokine IL-17 on MIP-3alpha production by RA synoviocytes. Addition of IL-1beta, IL-17, and TNF-alpha induced MIP-3alpha production in a dose-dependent manner. At optimal concentrations, IL-1beta (100 pg/ml) was much more potent than IL-17 (100 ng/ml) and TNF-alpha (100 ng/ml). When combined at lower concentrations, a synergistic effect was observed. Conversely, the anti-inflammatory cytokines IL-4 and IL-13 inhibited MIP-3alpha production by activated synoviocytes, but IL-10 had no effect. Synovium explants produced higher levels of MIP-3alpha in RA than osteoarthritis synovium. MIP-3alpha-producing cells were located in the lining layer and perivascular infiltrates in close association with CD1a immature dendritic cells. Addition of exogenous IL-17 or IL-1beta to synovium explants increased MIP-3alpha production. Conversely, specific soluble receptors for IL-1beta, IL-17, and TNF-alpha inhibited MIP-3alpha production to various degrees, but 95% inhibition was obtained only when the three receptors were combined. Similar optimal inhibition was also obtained with IL-4, but IL-13 and IL-10 were less active. These findings indicate that interactions between monocyte and Th1 cell-derived cytokines contribute to the recruitment of T cells and dendritic cells by enhancing the production of MIP-3alpha by synoviocytes. The inhibitory effect observed with cytokine-specific inhibitors and Th2 cytokines may have therapeutic applications.

Modulation of bronchial epithelial cells by IL-17

BACKGROUND

The induction of epithelial cytokines/chemokines is crucial in the migration of leukocytes, and its regulatory mechanisms remain incompletely defined.

OBJECTIVE

To determine the role of IL-17, a CD4(+) T cell-derived cytokine, in modulation of primary bronchial epithelial cells, the expression of IL-6, IL-8, and intercellular adhesion molecule 1 (ICAM-1) and the potential involvement of mitogen-activated protein (MAP) kinases in IL-17-mediated signaling were examined.

METHODS

The levels of gene expression and protein production for IL-6 and IL-8 in IL-17-treated cells, in the presence or absence of MAP kinase inhibitors, were analyzed by RT-PCR and ELISA, respectively, and activation of MAP kinases was determined by Western blot analyses.

RESULTS

We showed first that IL-17 induced time-dependent expression of IL-6 and IL-8 but not of the chemokines eotaxin and RANTES. In addition, IL-17 induced activation of extracellular signal-regulated kinase 1/2 but not of p38 or JNK kinases. A selective MAP kinase kinase inhibitor, PD98059, inhibited IL-17-induced IL-6 and IL-8. A combination of IL-17 and each of the cytokines IL-4, IL-13, and IFN-gamma further enhanced IL-8 expression. IL-17 alone did not induce ICAM-1 expression and showed no effect on IL-4- or IL-13-induced ICAM-1 expression. In contrast, a combination of IL-17 and IFN-gamma augmented IL-6 and ICAM-1 expression.

CONCLUSION

These findings suggest that IL-17, alone or in combination with other cytokines, modulates airway inflammation via-in part-the expression of epithelial IL-6, IL-8, and ICAM-1.

Pathways by which interleukin 17 induces articular cartilage breakdown in vitro and in vivo

Overexpression of interleukin (IL-)17 has recently been shown to be associated with a number of pathological conditions. Because IL-17 is found at high levels in the synovial fluid surrounding cartilage in patients with inflammatory arthritis, the present study determined the direct effect of IL-17 on articular cartilage. As shown herein, IL-17 was a direct and potent inducer of matrix breakdown and an inhibitor of matrix synthesis in articular cartilage explants. These effects were mediated in part by leukemia inhibitory factor (LIF), but did not depend on interleukin-1 activity. The mechanism whereby IL-17 induced matrix breakdown in cartilage tissue appeared to be due to stimulation of activity of aggrecanase(s), not matrix metalloproteinase(s). However, IL-17 upregulated expression of matrix metalloproteinase(s) in chondrocytes cultured in monolayer. In vivo, IL-17 induced a phenotype similar to inflammatory arthritis when injected into the intra-articular space of mouse knee joints. Furthermore, a related protein, IL-17E, was found to have catabolic activity on human articular cartilage. This study characterizes the mechanism whereby IL-17 acts directly on cartilage matrix turnover. Such findings have important implications for the treatment of degenerative joint diseases such as arthritis.

Interleukin-17 stimulates inducible nitric oxide synthase activation in rodent astrocytes

The effect of interleukin-17 (IL-17) on production of nitric oxide (NO) in rodent astrocytes was investigated. While IL-17 by itself did not induce NO production, it caused a dose-dependent enhancement of IFN-gamma-triggered NO synthesis in both mouse and rat primary astrocytes. In contrast, IL-17 was unable to stimulate NO synthesis in either murine or rat macrophages. IFN-gamma-triggered expression of mRNA for iNOS, but not for its transcription factor interferon regulatory factor-1 (IRF-1), was markedly elevated in IL-17-treated astrocytes. The induction of iNOS mRNA by IL-17 in IFN-gamma-pretreated astrocytes was abolished by antagonists of nuclear factor-kappaB (NF-kappaB) activation--a proteasome inhibitor MG132 and an antioxidant agent PDTC, as well as with specific p38 MAP kinase inhibitor SB203580. While IL-17 stimulated both IL-1beta and IL-6 production in astrocytes, only IL-1 was partly responsible for IL-17-induced NO release. Finally, IL-17 synergized with exogenous IL-1beta and TNF-alpha for astrocyte NO production. Having in mind a well-known neurotoxic action of NO, these results suggest a possible role for IL-17 in the inflammatory diseases of the CNS.

IL-17s adopt a cystine knot fold: structure and activity of a novel cytokine, IL-17F, and implications for receptor binding

The proinflammatory cytokine interleukin 17 (IL-17) is the founding member of a family of secreted proteins that elicit potent cellular responses. We report a novel human IL-17 homolog, IL-17F, and show that it is expressed by activated T cells, can stimulate production of other cytokines such as IL-6, IL-8 and granulocyte colony-stimulating factor, and can regulate cartilage matrix turnover. Unexpectedly, the crystal structure of IL-17F reveals that IL-17 family members adopt a monomer fold typical of cystine knot growth factors, despite lacking the disulfide responsible for defining the canonical "knot" structure. IL-17F dimerizes in a parallel manner like neurotrophins, and features an unusually large cavity on its surface. Remarkably, this cavity is located in precisely the same position where nerve growth factor binds its high affinity receptor, TrkA, suggesting further parallels between IL-17s and neurotrophins with respect to receptor recognition.

Lyme disease and current aspects of immunization

Lyme disease is a tick-borne multisystem disease that affects primarily the skin, nervous system, heart and joints. At least three species of Borrelia burgdorferi sensu lato, namely Borrelia burgdorferi sensu stricto, Borrelia garinii, and Borrelia afzelii, can cause the disease. This review will focus mainly on the pathophysiology of Lyme arthritis, the long-term outcome of Lyme disease, and the recently licensed vaccine against Lyme disease.

Anticytokine therapy for osteoarthritis

Osteoarthritis (OA) is a joint disease that involves degeneration of articular cartilage, weakening of the subchondral bone and limited intra-articular inflammation manifested by synovitis. Since the pathogenesis of OA involves multiple aetiologies, including mechanical, biochemical and genetic factors, it has been difficult to identify unique targets for therapy. Current pharmacological interventions focus primarily on improving symptoms. The rationale for the use of anticytokine therapy in OA is based on evidence from studies in vitro and in vivo that interleukin-1 (IL-1) and tumour necrosis factor (TNF)-alpha are the predominant pro-inflammatory and catabolic cytokines involved in the initiation and progression of articular cartilage destruction. Since the increased levels of catabolic enzymes, prostaglandins, nitric oxide (NO) and other markers in OA fluids and tissues appear to be related to elevated levels of IL-1 and TNF-alpha, therapies that interfere with the expression or actions of these cytokines are most promising. Other cytokines that are anti-inflammatory and are often detected, paradoxically, in OA tissues are also potential therapeutic agents for counteracting the cartilage destruction in OA. Identification of methods for early diagnosis is of key importance, since therapeutic interventions aimed at blocking or reversing structural damage will be more effective when there is the possibility of preserving normal homeostasis. At later stages, cartilage tissue engineering with or without gene therapy will also require anticytokine therapy to block damage to newly repaired cartilage. This review will focus on experimental approaches currently under study that may lead to elucidation of effective strategies for therapy in OA, with special emphasis on anticytokine therapy.

Interleukin-17 enhances tumor necrosis factor alpha-induced synthesis of interleukins 1,6, and 8 in skin and synovial fibroblasts: a possible role as a "fine-tuning cytokine" in inflammation processes

OBJECTIVE

To compare the singular and combined effects of tumor necrosis factor alpha (TNFalpha), interleukin-1beta (IL-1beta), and IL-17 on messenger RNA (mRNA) expression, translation, and secretion of IL-6, IL-8, and IL-1beta in fibroblasts.

METHODS

Fibroblasts were stimulated with the relevant cytokine(s), pulse labeled with 35S-methionine, and the newly synthesized proteins were immunoprecipitated and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Gene expression was determined by Northern blot analysis. Secreted proteins were detected by enzyme-linked immunosorbent assay (ELISA).

RESULTS

IL-17 alone was a weaker stimulator of the transcription, translation, and secretion of other interleukins than was TNFalpha or IL-1beta. IL-17 (10 ng/ml) stimulated the expression of IL-6 mRNA by 1.3-fold, while TNFalpha (1 ng/ml) increased it by 3.7-fold, and IL-1beta (0.1 ng/ml) increased it by >30-fold. Unlike TNFalpha and IL-1beta, IL-17 hardly affected the expression of IL-8 and IL-1beta mRNA. Translation of IL-6 was 6.2 times greater with IL-17, but TNFalpha and IL-1beta stimulated it 28.9- and 174-fold, respectively. ELISA-measured secretion of IL-6 and IL-8 increased by 6.7 and 5.8 times, respectively, with IL-17, compared with 52 and 269 times with TNFalpha stimulation and 1,356 and 1,084 times with IL-1beta stimulation. Yet, when IL-17 was combined with other cytokines, these activities were stimulated much beyond the sum of the individual effects. The combination of IL-17 and TNFalpha induced the expression of IL-6 or IL-1beta mRNA 7 times more than their additive stimulation, and that of IL-8 mRNA 3.8 times more. Likewise, the secretion of IL-6 and IL-8 was 20 times and 5 times higher, respectively, than expected. This synergism started after 4 hours of combined treatment, and decayed after 24-48 hours regardless of cytokine presence. It could be blocked with anti-IL-17 but not with anti-IL-1.

CONCLUSION

Our findings suggest that the primary role of IL-17 is to synergize with TNFalpha and to fine-tune the inflammation process. Therefore, IL-17 may be a potential target for therapeutic intervention.

IL-1-independent role of IL-17 in synovial inflammation and joint destruction during collagen-induced arthritis

T cell IL-17 displays proinflammatory properties and is expressed in the synovium of patients with rheumatoid arthritis. Its contribution to the arthritic process has not been identified. Here, we show that blocking of endogenous IL-17 in the autoimmune collagen-induced arthritis model results in suppression of arthritis. Also, joint damage was significantly reduced. In contrast, overexpression of IL-17 enhanced collagen arthritis. Moreover, adenoviral IL-17 injected in the knee joint of type II collagen-immunized mice accelerated the onset and aggravated the synovial inflammation at the site. Radiographic and histologic analysis showed markedly increased joint destruction. Elevated levels of IL-1beta protein were found in synovial tissue. Intriguingly, blocking of IL-1alphabeta with neutralizing Abs had no effect on the IL-17-induced inflammation and joint damage in the knee joint, implying an IL-1 independent pathway. This direct potency of IL-17 was underscored in the unabated IL-17-induced exaggeration of bacterial cell wall-induced arthritis in IL-1beta(-/-) mice. In conclusion, this data shows that IL-17 contributes to joint destruction and identifies an IL-1-independent role of IL-17. These findings suggest IL-17 to be a novel target for the treatment of destructive arthritis and may have implications for tissue destruction in other autoimmune diseases.

High in vivo expression of interleukin-17 receptor in synovial endothelial cells and chondrocytes from arthritis patients

OBJECTIVE

To evaluate the presence of interleukin-17 (IL-17) and the expression of IL-17 receptor (IL-17R) in joint tissues from subjects with different arthritides.

METHODS

Immunohistochemistry was used on frozen synovial and cartilage biopsies to identify cells expressing IL-17 and IL-17R.

RESULTS

IL-17 staining was present only in synovial biopsies of rheumatoid arthritis (RA) (seven out of nine cases). IL-17R was expressed by all synovial biopsies evaluated except for three cases of post-traumatic arthritis (PTA). Vascular endothelial cells mainly expressed IL-17R. The percentage of IL-17R(+) vessels was the highest in RA synovium and the lowest in PTA. Chondrocytes from all types of arthritides were negative for IL-17 staining, but expressed IL-17R; the highest percentage of positive chondrocytes was found in seronegative spondylarthritis and the lowest in RA.

CONCLUSIONS

IL-17-positive cells are found exclusively in RA. On the other hand, synovial endothelial cells and chondrocytes expressing IL-17R are found in the majority of patients with different types of arthritis. This finding suggests a role for a second ligand for IL-17R, which could be either a different cytokine or a different isoform of IL-17.

The combination of tumor necrosis factor alpha blockade with interleukin-1 and interleukin-17 blockade is more effective for controlling synovial inflammation and bone resorption in an ex vivo model

OBJECTIVE

Anti-tumor necrosis factor a (anti-TNFalpha) therapy has shown efficacy in the treatment of rheumatoid arthritis (RA). Since interleukin-1 (IL-1), TNFalpha, and IL-17 have many additive and/or synergistic effects in vitro, we tested whether their combined inhibition by soluble receptors would lead to an enhanced effect on ex vivo models of synovial inflammation and bone destruction.

METHODS

RA synovium and bone explants were cultured for 7 days in the presence of 1 microg/ml soluble TNFalpha receptor (STNFR; as in current therapy), type II soluble IL-1 receptor (sIL-1RII), or sIL-17R either alone or in combination. Their effects on the production of IL-6 and the release of C-telopeptide of type I collagen (CTX), a marker of type I collagen destruction, were measured by enzyme-linked immunosorbent assay.

RESULTS

In synovium, each soluble receptor alone decreased IL-6 production and CTX release by approximately 35% and approximately 55%, respectively. The combination of all 3 receptors was more effective, inhibiting IL-6 production and collagen degradation by up to 70%. Neither sIL-17R, sIL-1RII, or sTNFR alone had no effect (or an effect of <20% inhibition) on IL-6 production in 18%, 33%, and 22%, respectively, of the samples. In bone, sIL-17R, sIL-1RII, and sTNFR decreased IL-6 production by 23%, 50%, and 37%, respectively, while the combination decreased IL-6 production by 75%. A 50% inhibition of CTX release was obtained with sIL-1RII for 63% of the samples versus 38% of the samples with either sTNFR or sIL-17R. However, the combination of all 3 receptors was not more potent than sIL-1RII alone.

CONCLUSION

The inhibitory effect of sTNFR on IL-6 production and collagen degradation in RA synovium and bone was increased in combination with sIL-17R and sIL-1RII. These results support the concept of combination therapy, which may increase the percentage of responding patients as well as the degree of individual patient response.

Pathogenesis of rheumatoid arthritis. The role of T cells and other beasts

The evidence coming from the different experimental approaches reviewed in this article strongly supports the hypothesis that RA is T-cell driven at all stages of the disease. Although the effector phases responsible for the events that lead to joint destruction involve several different cell types, cytokines, and other mediators, T cells still direct operations behind the scenes. Direct experimental proof of this proposition in patients is still lacking, but the development of nondepleting modulating CD4 monoclonal antibodies may provide new tools to test this hypothesis. In this respect, it is encouraging that using one such reagent, we have recently shown that not only did the activity of the disease improve but, more importantly, the inflammatory indices and production of non-T-cell cytokines were reduced. This is not to dissimilar from the results of experiments described in animals, where by blocking synovial T cells, the production of IL-1 beta and TNF alpha could be decreased by more than 90%. From this perspective, it may be predicted that by modulating T cells in the joint, it is possible to achieve our ultimate goal of permanently switching off the disease.

Potential biologic agents for treating rheumatoid arthritis

The encouraging clinical results observed in trials using anti-TNF therapy clearly warrant further studies to determine whether TNF inhibitors are capable of modifying the destructive component of this disease in long-term follow-up studies as well as to assess the safety of long-term use (see the article by Keystone in this issue). It is also reasonable to propose that interfering with the cytokine cascade earlier in the course of disease may be of even greater therapeutic benefit. As the pathogenetic mechanisms in RA are more clearly defined, especially in early disease and in those individuals destined to develop severe disease, the potential of other biologic agents to specifically inhibit these critical pathways may provide better treatments for our patients. Many potential targets in the immune-mediated process of RA are currently being rigorously evaluated in clinical trials. Use of combinations of biologic therapies, perhaps in human patients with RA, should be of considerable interest in future trials.

Uncoupling of inflammatory and destructive mechanisms in arthritis

OBJECTIVE

To update clinicians on recent advances in the differentiation of the mechanisms of inflammation and cartilage destruction in the pathogenesis of rheumatoid arthritis (RA).

METHODS

We present analysis of recent published literature and abstracts that elucidates the independent actions of pivotal proinflammatory cytokines. These experimental data provide the framework for understanding the uncoupling of destructive and inflammatory mechanisms in arthritis.

RESULTS

Tumor necrosis factor-alpha (TNF-alpha) is an important mediator in the inflammation that occurs in RA. Interleukin-1 (IL-1) has a dominant effect on cartilage destruction that occurs later in the disease process. TNF-independent IL-1 production occurs in many RA model situations. Cytokine balance determines the erosive nature of the disease.

CONCLUSION

IL-1 is at least as important as TNF-alpha in promoting the disease process. The pathways by which the inflammatory and destructive changes occur suggest that targeted anticytokine intervention will arrest the cartilage damage that occurs in patients with RA.

Cytokine expression and synovial pathology in the initiation and spontaneous resolution phases of adjuvant arthritis: interleukin-17 expression is upregulated in early disease

The aim of this study was to understand the immune processes controlling the initiation and spontaneous resolution of adjuvant arthritis (AA). We investigated synovial T-cell recruitment and mRNA expression of IL-17 and other important disease related cytokines, IFN-gamma, IL-2, IL-4, TNF and TGF-beta in inguinal lymph node (ILN) and synovial membrane (SM). Arthritis severity was assessed by a numerical rating score and rats were sacrificed every 3--4 days postadjuvant induction. Further assessment involved quantitative radiology and histology of the ankle joints on each day, and the ILN and SM were removed for RNA extraction. Cytokine mRNA expression was measured using RT-PCR and densitometry. Paraffin sections of rat ankle joints were stained for T-cells (CD3) by immunohistochemistry. In the ILN, there was an increase in IL-17, TNF and IFN-gamma expression in the early stages of disease, with a secondary sustained increase in IFN-gamma expression. In the SM, there was expression of T-cell cytokines in early arthritis (day 13), and prolonged TNF and TGF-beta expression, which reflected disease progression. IL-4 mRNA expression increased in the later stages of AA. Synovial T-cell numbers transiently increased at day 6, and remained high from days 13--28. Increased pro-inflammatory cytokine expression, including IL-17, in the ILN reflects the initiating events in the early stage of disease. IL-17 may therefore play an important role in the pathogenesis of AA. The increase in IL-4 (an anti-inflammatory cytokine) in the SM in the later stages of AA suggests that IL-4 is involved in the spontaneous resolution of AA. The initial increase in IFN-gamma in the ILN may reflect a pro-inflammatory response, while the prolonged secondary increase may indicate activation of regulatory T-cells.

Elevation of proinflammatory cytokine (IL-18, IL-17, IL-12) and Th2 cytokine (IL-4) concentrations in patients with systemic lupus erythematosus

Previous studies have indicated that the autoimmune phenomenon might be caused by an imbalance of T helper cell (Th) cytokines. We measured the plasma concentrations of three novel proinflammatory cytokines interleukin (IL)-17, IL-18, IL-12 and a key Th2 cytokine IL-4 in patients with systemic lupus erythematosus (SLE) and correlated the ratio of proinflammatory/Th2 cytokines with SLE disease activity index (SLEDAI). Plasma IL-12, IL-17, IL-18 and IL-4 concentrations of 36 SLE patients and 18 sex- and age-matched control subjects were measured by enzyme linked immunosorbent assay. All were significantly higher in SLE patients than control subjects (IL-12, mean+/-s.d. of 166.7+/-84.5 vs 93.5+/-39.2 pg/ml, P<0.001; IL-17, 76.5+/-45.7 vs 37.6+/-35.3 pg/ml, P=0.002; IL-18, 368.7+/-199. 5 vs 141.1+/-47.1 pg/ml, P<0.001; and IL-4, 27.1+/-15.3 vs 17.3+/-7. 2 pg/ml, P<0.05), and IL-18/IL-4 ratio correlated positively and significantly with SLEDAI score (r=0.435, P=0.006). We propose that SLE is characterized by an elevation of both Th1 and Th2 cytokines: the elevation of proinflammatory cytokine IL-12, IL-17 and IL-18 may trigger the inflammatory process in SLE and the elevation of IL-18/IL-4 ratio suggests an imbalance of cytokine profile to mediate the inflammatory response.

Update on synovitis

Rheumatoid arthritis (RA) is an inflammatory disorder associated with chronic synovitis, eventually leading to cartilage and bone destruction in the joints. Synovitis is associated with the activation of various cells in the synovium including synovial lining cells, interstitial macrophages, endothelial cells, lymphocytes, and fibroblasts. The key mechanisms underlying synovitis include inflammatory cell adhesion and activation, the production of mediators (such as cytokines, chemokines, and growth factors), angiogenesis, joint destruction, fibrosis, and bone resorption. These important events, as well as the role of inflammatory cells, cell surface molecules, and soluble mediators are updated and discussed in this review. Some aspects and strategies of current or future immunotherapy are also discussed because these animal and human trials provide information on the pathogenesis of inflammatory synovitis.

Physiology of cytokine pathways in rheumatoid arthritis

This review has summarized the physiology of some cytokine pathways in RA, emphasizing the redundant and synergistic nature of this network. However, it is important to understand that this system is self-regulating through the action of anti-inflammatory cytokines, opposing cytokines, cytokine receptor antagonists, and possibly naturally occurring antibodies to cytokines (Figure 1). Disease results when an imbalance in the cytokine network develops, either from excess production of pro-inflammatory cytokines or from inadequate presence of natural anti-inflammatory mechanisms. The current therapeutic approaches to RA that are aimed at restoring this balance include the use of monoclonal antibodies to TNFalpha, soluble TNFalpha receptors, and IL-1Ra. Other therapeutic agents that interfere with the cytokine network are in various stages of preclinical and clinical evaluation.

Potential contribution of IL-17-producing Th(1)cells to defective repair activity in joint inflammation: partial correction with Th(2)-promoting conditions

To assess the contribution of cell interactions to the production of cytokines and type I collagen, fixed synovium T cell clones were cocultured on synoviocytes and levels of IL-6, LIF and PICP, a marker of type I collagen synthesis measured. Levels of IL-6 and LIF were higher with Th(1)than with Th(0)and Th(2)clones. Levels of PICP were decreased with Th(1)clones and increased with Th(2)clones. IL-17-producing T cells, all Th(1), were among the highest inducers of cytokine and inhibitors of collagen synthesis. Preincubation of clones in Th(1)conditions (IL-12 plus anti-IL-4) increased IL-6 production, whereas Th(2)conditions (IL-4 plus anti-IL-12) strongly inhibited IL-6 production and restored repair activity. As rheumatoid synovium is infiltrated by Th(1)cells, local cell interactions result in a pro-inflammatory pattern with defective repair, which can be reversed at least in part, by a Th(2)pattern.

IL-17E, a novel proinflammatory ligand for the IL-17 receptor homolog IL-17Rh1

We report identification of interleukin (IL)-17E, a novel member of the IL-17 family of cytokines. IL-17E is a ligand for the recently identified protein termed EVI27/IL-17BR, which we term IL-17 receptor homolog 1 (IL-17Rh1) in light of the multiple reported ligand-receptor relationships. Murine EVI27 was identified through its location at a common site of retroviral integration in BXH2 murine myeloid leukemias. IL-17Rh1 shows highest level expression in kidney with moderate expression in multiple other organs, whereas IL-17E mRNA was detected at very low levels in several peripheral tissues. IL-17E induces activation of NF-kappaB and stimulates production of the proinflammatory chemokine IL-8.

IL-17 derived from juxta-articular bone and synovium contributes to joint degradation in rheumatoid arthritis

The origin and role of IL-17, a T-cell derived cytokine, in cartilage and bone destruction during rheumatoid arthritis (RA) remain to be clarified. In human ex vivo models, addition of IL-17 enhanced IL-6 production and collagen destruction, and inhibited collagen synthesis by RA synovium explants. On mouse cartilage, IL-17 enhanced cartilage proteoglycan loss and inhibited its synthesis. On human RA bone explants, IL-17 also increased bone resorption and decreased formation. Addition of IL-1 in these conditions increased the effect of IL-17. Blocking of bone-derived endogenous IL-17 with specific inhibitors resulted in a protective inhibition of bone destruction. Conversely, intra-articular administration of IL-17 into a normal mouse joint induced cartilage degradation. In conclusion, the contribution of IL-17 derived from synovium and bone marrow T cells to joint destruction suggests the control of IL-17 for the treatment of RA.

Microbial lipopeptides induce the production of IL-17 in Th cells

Naive Th cells can be directed in vitro to develop into Th1 or Th2 cells by IL-12 or IL-4, respectively. In vivo, chronic immune reactions lead to polarized Th cytokine patterns. We found earlier that Borrelia burgdorferi, the spirochaete that causes Lyme disease, induces Th1 development in alpha beta TCR-transgenic Th cells. Here, we used TCR-transgenic Th cells and oligonucleotide arrays to analyze the differences between Th1 cells induced by IL-12 vs those induced by B. burgdorferi. Transgenic Th cells primed with peptide in the presence of B. burgdorferi expressed several mRNAs, including the mRNA encoding IL-17, at significantly higher levels than Th cells primed with peptide and IL-12. Cytometric single-cell analysis of Th cell cytokine production revealed that IL-17 cannot be categorized as either Th1 or Th2 cytokine. Instead, almost all IL-17-producing Th cells simultaneously produced TNF-alpha and most IL-17(+) Th cells also produced GM-CSF. This pattern was also observed in humans. Th cells from synovial fluid of patients with Lyme arthritis coexpressed IL-17 and TNF-alpha upon polyclonal stimulation. The induction of IL-17 production in Th cells is not restricted to B. burgdorferi. Priming of TCR-transgenic Th cells in the presence of mycobacterial lysates also induced IL-17/TNF-alpha coproduction. The physiological stimulus for IL-17 production was hitherto unknown. We show here for the first time that microbial stimuli induce the expression of IL-17 together with TNF-alpha in both murine and human T cells. Chronic IL-17 expression induced by microbes could be an important mediator of infection-induced immunopathology.

What we learn from arthritis models to benefit arthritis patients

Chronic arthritis is characterized by persistent joint inflammation and concomitant joint destruction. Animal models have been of great value in understanding potential pathogenetic pathways and studying therapeutic principles. The first models were based on T cell-driven pathways and taught us that arthritis can be induced by a variety of stimuli. This suggests that the involvement of a single (auto)antigen in rheumatoid arthritis is unlikely and suggests that the regulation of arthritis can best be approached via bystander suppression. Insight into the pivotal role of TNF alpha and IL-1 has emerged from studies employing a range of common and also novel transgenic models. Combination treatment with both TNF and IL-1 blockers is warranted to control both joint inflammation and joint destruction. Novel approaches with viral gene constructs of cytokines and cytokine inhibitors teach us that efficient gene therapy is a possibility for small joints.

IL-17 stimulates intraperitoneal neutrophil infiltration through the release of GRO alpha chemokine from mesothelial cells

IL-17 is a newly discovered cytokine implicated in the regulation of hemopoiesis and inflammation. Because IL-17 production is restricted to activated T lymphocytes, the effects exerted by IL-17 may help one to understand the contribution of T cells to the inflammatory response. We investigated the role of IL-17 in leukocyte recruitment into the peritoneal cavity. Leukocyte infiltration in vivo was assessed in BALB/Cj mice. Effects of IL-17 on chemokine generation in vitro were examined in human peritoneal mesothelial cells (HPMC). Administration of IL-17 i.p. resulted in a selective recruitment of neutrophils into the peritoneum and increased levels of KC chemokine (murine homologue of human growth-related oncogene alpha (GROalpha). Pretreatment with anti-KC Ab significantly reduced the IL-17-driven neutrophil accumulation. Primary cultures of HPMC expressed IL-17 receptor mRNA. Exposure of HPMC to IL-17 led to a dose- and time-dependent induction of GROalpha mRNA and protein. Combination of IL-17 together with TNF-alpha resulted in an increased stability of GROalpha mRNA and synergistic release of GROalpha protein. Anti-IL-17 Ab blocked the effects of IL-17 in vitro and in vivo. IL-17 is capable of selectively recruiting neutrophils into the peritoneal cavity via the release of neutrophil-specific chemokines from the peritoneal mesothelium.

Anti-cytokine therapy in chronic destructive arthritis

Tumor necrosis factor (TNF) and interleukin-1 (IL-1) are considered to be master cytokines in chronic, destructive arthritis. Therapeutic approaches in rheumatoid arthritis (RA) patients have so far focused mainly on TNF, which is a major inflammatory mediator in RA and a potent inducer of IL-1; anti-TNF therapy shows great efficacy in RA patients. However, it is not effective in all patients, nor does it fully control the arthritic process in affected joints of good responders. Directed therapy for IL-1, with IL-1 receptor antagonist, mainly reduces erosions and is marginally anti-inflammatory. It is as yet unclear whether the limited effect is akin to the RA process or linked to suboptimal blocking of IL-1. Analysis of cytokine patterns in early synovial biopsies of RA patients reveals a marked heterogeneity, with variable staining of TNF and IL-1 beta, indicative of TNF-independent IL-1 production in at least some patients. Evidence for this pathway emerged from experimental arthritises in rodents, and is summarized in this review. If elements of the models apply to the arthritic process in RA patients, it is necessary to block IL-1 beta in addition to TNF.