IL-17 in synovial fluids from patients with rheumatoid arthritis is a potent stimulator of osteoclastogenesis

Geranylgeranylacetone inhibits formation and function of human osteoclasts and prevents bone loss in tail-suspended rats and ovariectomized rats

Vitamin K is used for protecting against osteoporosis. Recently, it has been reported that the inhibitory effect of vitamin K(2) (menatetrenone) on bone resorption may be related to its side chain. Geranylgeranylacetone (GGA), known as teprenone, an antiulcer drug, has almost the same chemical structure as that of the side chain of menatetrenone. We hypothesized that GGA also has an inhibitory effect on osteoclastogenesis both in vitro and in vivo. GGA in pharmacological concentrations directly inhibited osteoclastogenesis from human monocytes induced by soluble receptor activator of nuclear factor-kappaB ligand. In addition, GGA induced degradation of actin rings in mature osteoclasts, which was reversed by adding geranylgeranylpyrophosphatase. Moreover, GGA increased the bone mineral density of total femur, proximal metaphysis, and diaphysis of femur in ovariectomized rats. GGA also prevented bone loss induced by hindlimb unloading in tail-suspended rats. These results indicate that GGA prevents bone loss by maintaining a positive balance of bone turnover through suppression of both the formation and the activity of osteoclasts. Thus, GGA could be used to prevent and improve osteoporosis.

IL-17 enhances the net angiogenic activity and in vivo growth of human non-small cell lung cancer in SCID mice through promoting CXCR-2-dependent angiogenesis

In this study, we examined the biological action of IL-17 on human non-small cell lung cancer (NSCLC). Although IL-17 had no direct effect on the in vitro growth rate of NSCLC, IL-17 selectively augmented the secretion of an array of angiogenic CXC chemokines, including CXCL1, CXCL5, CXCL6, and CXCL8 but not angiostatic chemokines, by three different NSCLC lines. Endothelial cell chemotactic activity (as a measure of net angiogenic potential) was increased in response to conditioned medium from NSCLC stimulated with IL-17 compared with those from unstimulated NSCLC. Enhanced chemotactic activity was suppressed by neutralizing mAb(s) to CXCL1, CXCL5, and CXCL8 or to CXCR-2 but not to vascular endothelial growth factor-A. Transfection with IL-17 into NSCLC had no effect on the in vitro growth, whereas IL-17 transfectants grew more rapidly compared with controls when transplanted in SCID mice. This IL-17-elicited enhancement of NSCLC growth was associated with increased tumor vascularity. Moreover, treatment with anti-mouse CXCR-2-neutralizing Ab significantly attenuated the growth of both neomycin phosphotransferase gene-transfected and IL-17-transfected NSCLC tumors in SCID mice. A potential role for IL-17 in modulation of the human NSCLC phenotype was supported by the findings that, in primary NSCLC tissues, IL-17 expression was frequently detected in accumulating and infiltrating inflammatory cells and that high levels of IL-17 expression were associated with increased tumor vascularity. These results demonstrate that IL-17 increases the net angiogenic activity and in vivo growth of NSCLC via promoting CXCR-2-dependent angiogenesis and suggest that targeting CXCR-2 signaling may be a novel promising strategy to treat patients with NSCLC.

Understanding the IL-23-IL-17 immune pathway

Interleukin (IL)-23 is a heterodimeric cytokine closely related to IL-12. Yet, despite a strong structural relationship that includes a shared p40 subunit, this does not translate into functional similarity. In fact, the opposite is true, in that these two cytokines appear to have profoundly different roles in regulating host immune responses. It is now clear that IL-23 has key roles in autoimmune destruction in experimental allergic encephalomyelitis, collagen-induced arthritis and inflammatory bowel disease. IL-23 drives the development of autoreactive IL-17-producing T cells and promotes chronic inflammation dominated by IL-17, IL-6, IL-8 and tumor necrosis factor as well as neutrophils and monocytes. It is unlikely that IL-23 and its downstream effects evolved just to cause autoimmunity, but its real benefit to the host and the lineage relationship between IL-17-producing cells and T helper 1 cells remain unclear. By comparing the pathophysiological function of IL-12 and IL-23 in the context of host defense and autoimmune inflammation, we are beginning to understand the novel IL-23-IL-17 immune pathway.

Interleukin-17 receptor deficiency results in impaired synovial expression of interleukin-1 and matrix metalloproteinases 3, 9, and 13 and prevents cartilage destruction during chronic reactivated streptococcal cell wall-induced arthritis

OBJECTIVE

To examine the role of interleukin-17 receptor (IL-17R) signaling in cartilage destruction and its interrelationship with synovial IL-1 expression during chronic reactivated streptococcal cell wall (SCW)-induced arthritis.

METHODS

SCW arthritis was repeatedly induced in wild-type (WT) and IL-17R-deficient (IL-17R-/-) mice. At different time points, joint inflammation was assessed by using calipers to measure joint swelling. On day 42, mice were killed, and knee joints were removed for histologic analysis. Quantitative polymerase chain reaction (PCR) analyses for different proinflammatory mediators and matrix metalloproteinases (MMPs) were performed on inflamed synovium from WT and IL-17R-/- mice after 5 repeated injections of SCW fragments.

RESULTS

IL-17R signaling did not play a significant role in acute joint swelling induced by a single injection of SCW fragments directly into the joint. However, repeated local injections of SCW fragments into the knee joints of IL-17R-/- mice resulted in fewer infiltrating cells in the joint compared with WT mice. Moreover, histologic analysis on day 42 revealed a significant suppression of the degree of chondrocyte death and an absence of cartilage surface erosion in IL-17R-/- mice. Quantitative PCR analysis revealed impaired synovial expression of IL-1, IL-6, cyclooxygenase 2, stromelysin (MMP-3), gelatinase B (MMP-9), and collagenase 3 (MMP-13) in IL-17R-/- mice.

CONCLUSION

These data show a critical role of IL-17R signaling in driving the synovial expression of proinflammatory and catabolic mediators, such as IL-1 and different MMPs, during progression from an acute, macrophage-driven joint inflammation to a chronic, cartilage-destructive, T cell-mediated synovitis. Prevention of IL-17R signaling warrants consideration as a therapeutic target in chronic destructive arthritis.

Requirement of IL-17 receptor signaling in radiation-resistant cells in the joint for full progression of destructive synovitis

IL-17 is a proinflammatory cytokine suspected to be involved in inflammatory and autoimmune diseases such as rheumatoid arthritis. In the present study, we report that IL-17R signaling is required in radiation-resistant cells in the joint for full progression of chronic synovitis and bone erosion. Repeated injections of Gram-positive bacterial cell wall fragments (streptococcal cell wall) directly into the knee joint of naive IL-17R-deficient (IL-17R-/-) mice had no effect on the acute phase of arthritis but prevented progression to chronic destructive synovitis as was noted in wild-type (wt) mice. Microarray analysis revealed significant down-regulation of leukocyte-specific chemokines, selectins, cytokines, and collagenase-3 in the synovium of IL-17R-/- mice. Bone marrow (BM) chimeric mice revealed the need for IL-17R expression on radiation-resistant joint cells for destructive inflammation. Chimeric mice of host wt and donor IL-17R-/- BM cells developed destructive synovitis in this chronic reactivated streptococcal cell wall arthritis model similar to wt-->wt chimeras. In contrast, chimeric mice of host IL-17R-/- and donor wt BM cells were protected from chronic destructive arthritis similar as IL-17R-/- -->IL-17R-/- chimeras. These data strongly indicate that IL-17R signaling in radiation-resistant cells in the joint is required for turning an acute macrophage-mediated inflammation into a chronic destructive synovitis.

Shared circulation in parabiosis leads to the transfer of bone phenotype from gld to the wild-type mice

We have previously shown that mice with generalised lymphoproliferative disorder (gld) have increased bone mass in addition to autoimmune disease characterised by the accumulation of double negative (dn) T lymphocytes (CD3(+)CD4(-)CD8(-)CD45R(+)). To further explore the association of the immune disorder with the bone phenotype of gld mice, we established parabiotic circulation between gld and wild-type animals (C57BL/6, B6). One week after the surgery, the proportion of dn T lymphocytes increased in peripheral blood, bone marrow, spleen, and lymph nodes of wild-type members of the B6-gld parabiotic pair and decreased in tissues of gld pair members. The mixing of cells continued during four weeks of parabiosis. Number of osteoclast-like (OCL) cells in bone marrow cultures from a wild-type member of B6-gld parabiotic pair at the end of the first week decreased from 266+/-52 to 120+/-5OCL/cm(2), P<0.05, comparable with gld mice (99+/-21OCL/cm(2)), while the number of osteoblast colonies did not change. After four weeks, number of OCL cells formed from the bone marrow of B6 parabiotic mice was still similar to the number of OCL cells in their gld counterparts (150+/-18 and 131+/-24OCL/cm(2), respectively). In addition, the number of osteoblast colonies in B6 members of B6-gld parabiotic pairs increased (from 6+/-2 to 18+/-1colonies/cm(2), P<0.05) thus resembling the cell cultures of gld mice (18+/-1colonies/cm(2)). Taken together, these data show that the circulation of cells, including dn T lymphocytes established by parabiosis confers the osteoclast and osteoblast phenotype of gld to wild-type animals.

Blocking of interleukin-17 during reactivation of experimental arthritis prevents joint inflammation and bone erosion by decreasing RANKL and interleukin-1

Rheumatoid arthritis is characterized by an intermittent course of disease with alternate periods of remission and relapse. T cells, and in particular the T-cell cytokine interleukin-17 (IL-17), are expected to be involved in arthritic flares. Here, we report that neutralizing endogenous IL-17 during reactivation of antigen-induced arthritis prevents joint inflammation and bone erosion. Synovial IL-17 mRNA expression was clearly up-regulated during primary arthritis and was further enhanced after antigen rechallenge. Neutralization of IL-17 significantly prevented joint swelling at day 1 of flare and significantly suppressed joint inflammation and cartilage proteoglycan depletion at day 4, as assessed by histology. Blocking IL-17 also clearly reduced bone erosions. Cathepsin K, a marker of osteoclast-like activity, and synovial RANKL mRNA expression were both suppressed. The degree of bone erosions strongly correlated with the severity of joint inflammation, suggesting that anti-IL-17 treatment reduced bone erosion by suppressing joint inflammation. Interestingly, blocking IL-17 suppressed synovial expression of both IL-1beta and tumor necrosis factor-alpha, whereas blocking IL-1 did not affect tumor necrosis factor-alpha levels. These data indicate that IL-17 is an important upstream mediator in joint pathology during flare-up of experimental arthritis.

Distinct gene expression patterns of peripheral blood cells in hyper-IgE syndrome

Hyper-immunoglobulin E (IgE) syndrome (HIES) is one of the primary immunodeficiency syndromes. Although the cytokine dysregulation is suggested to play a role in its pathophysiology, the causative gene has not yet been identified. To investigate the pathophysiology and candidate genes involved in this disease, we performed microarray analysis of unstimulated peripheral CD4+ T cells and CD14+ cells, as well as peripheral blood mononuclear cells (PBMNC) stimulated with Staphylococcus aureus isolated from HIES patients and healthy controls. By microarray analysis, 38 genes showed over 2-fold differences between the HIES patients and healthy controls in purified CD14+ cells, although only small differences in the gene expression profiles were observed between the two groups in purified CD4+ T cells. RGC32 expression levels showed the greatest difference between the two groups, and were significantly elevated in HIES compared with those in severe atopic dermatitis or healthy controls using real-time PCR. A significantly larger number of lysosome-related genes were up-regulated, and significantly larger number of genes related to cell growth and maintenance were down-regulated in HIES. After the stimulation of PBMNC with Staphylococcus aureus, 51 genes showed over 3-fold differences between HIES patients and healthy controls. A significantly large number of immunoglobulin-related genes were up-regulated in HIES. The distinct patterns of gene expression profiles and RGC32 expression levels will be useful for understanding the pathophysiology and for diagnosis of HIES, respectively.

The potential role of interleukin-17 in the immunopathology of periodontal disease

BACKGROUND

Interleukin-17 (IL-17) is exclusively produced by activated T cells, and this cytokine can induce inflammatory responses, support immune responses (Th1), and stimulate osteoclastic bone resorption in combination with receptor activator of NF-kappaB (RANK) and RANK ligand (RANKL). These biological functions are relevant to the aetiopathogenesis of periodontitis, and thus we sought to investigate whether IL-17 is produced in periodontal lesions and to assess the relationship of gene expression between IL-17 and other cytokines, and to determine the effect of IL-17 on IL-6 production in human gingival fibroblasts (HGF).

MATERIALS AND METHODS

IL-17 was detected and measured in periodontal tissues obtained as biopsy samples during periodontal surgery and in the cell-free culture supernatants cultured ex vivo, by using Western immunoblotting and enzyme-linked immunosorbent assay, respectively. IL-17 and other cytokine gene expression were investigated by the reverse transcription-polymerase chain reaction (RT-PCR) method. The contribution of IL-17 to IL-6 production by HGF was studied.

RESULTS

IL-17 protein was moderately detected in periodontal tissues. In contrast, IL-17 mRNA was expressed only in nine of 23 periodontitis tissue samples by RT-PCR. The IL-17 mRNA-positive samples simultaneously expressed mRNAs encoding interferon (IFN)-gamma, IL-2, RANK, and RANKL, but not IL-4. IL-10 (Th2 cytokine) was detected more frequently in the samples than IFN-gamma and IL-2 (Th1 cytokine). Recombinant human IL-17 induced IL-6 production from HGF in a dose- and time-dependent fashion.

CONCLUSIONS

These results indicate that IL-17 is produced in periodontal lesions, which may be involved in Th1 modulation and enhance inflammatory reactions via gingival fibroblast-derived mediators in periodontal disease. Thus, IL-17, together with other cytokines, has a potential role in the aetiopathogenesis of periodontal disease.

Osteoprotegerin and the receptor activator of NF-kappa B ligand in the serum and synovial fluid. A comparison of patients with longstanding rheumatoid arthritis and osteoarthritis

We examined OPG and soluble RANKL in the serum (sOPG, sRANKL) and synovial fluid (synOPG, synRANKL) in patients with rheumatoid arthritis (RA) and osteoarthritis (OA). OPG and RANKL were measured in 85 patients (44 with RA, 41 patients with OA) in serum and synovial fluid as well. For measuring of OPG and RANKL ELISA tests were used. The results of OPG and RANKL were compared with clinical and radiological scores. We found a negative correlation for OPG and RANKL in synovial fluids: not only for the whole group of patients (P < 0.003, r = -0.32), but also for the subgroups (RA: P < 0.04, r = -0.28, OA: P < 0.002, r = -0.54). SRANKL and synRANKL were positively correlated in the whole group (P < 0.01, r = 0.25) and in the OA group (P < 0.02, r = 0.35); the RA group was showing a trend (P < 0.063, r = 0.24), however. Serum OPG was lower in RA, synOPG higher in OA. The difference between the two patient groups was only significant for synOPG (P < 0.03, r = 0.056), but not for sOPG (P < 0.09, r = 0.19), sRANKL (P < 0.43, r = 0.85) or synRANKL (P < 0.11, r = 0.22). The synOPG:synRANKL ratio was significantly correlated with the Larsen score (P < 0.004, r = 0.38). Synovial OPG is significantly decreased in rheumatoid joints, whereby synovial RANKL is increased. Lower synOPG could reflect a lower protective effect on bone, thus leading to an earlier and more pronounced bone destruction in RA. However, the effect of different mediators for joint destruction in RA and OA seems not to be important to the pathophysiological changes in the joints. The upregulation of serum OPG might be the result of the inflammation; in contrast, an upregulation of RANKL could not be found in the serum of patients with RA and OA.

Association of CD4+ CD25+ T cells with prevention of severe destructive arthritis in Borrelia burgdorferi-vaccinated and challenged gamma interferon-deficient mice treated with anti-interleukin-17 antibody

CD4+ CD25+ T cells are a population of regulatory T cells responsible for active suppression of autoimmunity. Specifically, CD4+ CD25+ T cells have been shown to prevent insulin-dependent diabetes mellitus, inflammatory bowel disease, and pancreatitis. Here, we present evidence that CD4+ CD25+ T cells also play a major role in controlling the severity of arthritis detected in Borrelia burgdorferi-vaccinated gamma interferon-deficient (IFN-gamma degrees ) C57BL/6 mice challenged with the Lyme spirochete. When B. burgdorferi-vaccinated and challenged IFN-gamma degrees mice were treated with anti-interleukin-17 (IL-17) antibody, the number of CD4+ CD25+ T cells increased in the local lymph nodes. Furthermore, histopathologic examination showed the mice to be free of destructive arthritis. When these anti-IL-17-treated B. burgdorferi-vaccinated and challenged mice were also administered anti-CD25 antibody, the number of CD4+ CD25+ T cells in the local lymph nodes decreased. More importantly, severe destructive arthropathy was induced. In addition, delayed administration of anti-CD25 antibody decreased the severity of the arthritis. These results suggest that CD4+ CD25+ T cells are involved in regulation of a severe destructive arthritis induced with an experimental model of vaccination and challenge with B. burgdorferi.

Interleukin-17 induces hyperresponsive interleukin-8 and interleukin-6 production to tumor necrosis factor-alpha in structural lung cells

Lung epithelial cells contribute to local inflammation by the production of pro-inflammatory mediators like interleukin (IL)-8 and IL-6. Although their production depends on gene transcription, previous studies showed that post-transcriptional mechanisms modulate IL-8 and IL-6 production. Human lung epithelial cells turn from normoresponsive into hyperresponsive IL-8- and IL-6-producing cells when their IL-8 and IL-6 mRNA degradation is reduced. We hypothesized that IL-17, a mediator predominantly released by memory T cells and present in airways of individuals with asthma, would modulate rather than induce IL-8 and IL-6 production by both human lung epithelial cells and fibroblasts. We show here for both cell types that IL-17 was a weak stimulus of IL-8 and IL-6 production, but markedly enhanced IL-8 and IL-6 responses to another stimulus, such as tumor necrosis factor-alpha. This modulatory effect of IL-17 was paralleled by a reduced IL-8 and IL-6 mRNA degradation, with no effect on IL-8 and IL-6 gene transcription. In conclusion, IL-17 particularly affects post-transcriptional regulation of IL-8 and IL-6 expression leading to enhanced IL-8 and IL-6 responses to secondary stimuli, and is only a weak proinflammatory stimulus by itself. This poses the interesting concept that by releasing IL-17 from memory T cells, the adaptive immune system instructs lung structural cells as part of the innate immune system to respond more vigorously.

Neuropeptide substance P stimulates the formation of osteoclasts via synovial fibroblastic cells

The present study was designed to evaluate the effects of neuropeptide substance P (SP) on the formation of osteoclasts via synovial fibroblastic cells. Synovial fibroblastic cells derived from rat knee joint expressed the SP receptor, neurokinin-1 receptor (NK(1)-R). The addition of SP stimulated the proliferation of synovial fibroblastic cells and this effect was inhibited by SP or NK(1)-R antagonists. Increased expression of the receptor activator of nuclear factor kappaB ligand (RANKL) in synovial fibroblastic cells after the addition of SP was demonstrated by reverse transcriptase-polymerase chain reaction and immunofluorescence staining. Osteoprotegerin expression in synovial fibroblastic cells was decreased after incubation with SP. In co-cultures of synovial fibroblastic cells and rat peripheral blood monocytes, SP stimulated osteoclastogenesis. These results suggest that SP in the joint cavity may cause both hypertrophy of the synovium and induction of increased osteoclast formation through the increased expression of RANKL in the synovium.

Levels of interleukin-17 in gingival crevicular fluid and in supernatants of cellular cultures of gingival tissue from patients with chronic periodontitis

BACKGROUND AND AIMS

Interleukin-17 (IL-17) is a T-cell-derived cytokine that may play an important role in the initiation or maintenance of the pro-inflammatory response and has recently been found to stimulate osteoclastic resorption. The purpose of the present study was to determine the presence of IL-17 in gingival crevicular fluid (GCF) samples and in the culture supernatants of gingival cells from patients with chronic periodontitis.

METHOD

GCF samples were collected during 30 s from two sites in 16 patients from periodontally affected sites (probing depth > or =5 mm, attachment loss > or =3 mm). The comparison with healthy controls was carried out by collecting GCF samples from eight healthy volunteers. GCF was collected using a paper strip and ELISA was performed to determine the total amount of IL-17. Supernatant cellular cultures of gingival cells were obtained from periodontal biopsies taken from 12 periodontitis patients and from eight healthy control subjects during the surgical removal of wisdom teeth. Spontaneous and phytohaemagglutinin (PHA)-stimulated levels of IL-17 were determined by ELISA.

RESULTS

The total amount of cytokine IL-17 was significantly higher in the periodontitis group than the control group (45.9 versus 35.6 pg, p=0.005). Significantly higher GCF volume and amount of total proteins were obtained from periodontitis patients as compared with control subjects (0.98 versus 0.36 microl, p=0.0005; 0.12 versus 0.05 microg, p=0.0005, respectively). A higher concentration of IL-17 was detected in culture supernatants from periodontitis patients compared with healthy subjects, either without stimulation (36.28+/-8.39 versus 28.81+/-1.50 microg/ml, p=0.011) or with PHA stimulation (52.12+/-14.56 versus 39.00+/-4.90 microg/ml, p=0.012). Treatment with PHA induced a significant increase in the production of IL-17 in healthy subjects and periodontitis patients (p=0.001 and 0.003).

CONCLUSIONS

The total amount of cytokine IL-17 in GCF samples and in the culture supernatants of gingival cells are significantly increased in periodontal disease.

Mechanisms involved in enhancement of osteoclast formation and function by low molecular weight hyaluronic acid

Hyaluronic acid (HA) is a component of the extracellular matrix that has been shown to play an important role in bone formation, resorption, and mineralization both in vivo and in vitro. We examined the effects of HA at several molecular weights on osteoclast formation and function induced by RANKL (receptor activator of NF-kappa B ligand) in a mouse monocyte cell line (RAW 264.7). HA at M(r) < 8,000 (low molecular weight HA (LMW-HA)) enhanced tartrate-resistant acid phosphatase-positive multinucleated cell formation and tartrate-resistant acid phosphatase activity induced by RANKL in a dose-dependent manner, whereas HA at M(r) > 900,000 (high molecular weight HA (HMW-HA)) showed no effect on osteoclast differentiation. LMW-HA enhanced pit formation induced by RAW 264.7 cells, whereas HMW-HA did not, and LMW-HA stimulated the expression of RANK (receptor activator of NF-kappa B) protein in RAW 264.7 cells. In addition, we found that LMW-HA enhanced the levels of c-Src protein and phosphorylation of ERKs and p38 MAPK in RAW 264.7 cells stimulated with RANKL, whereas the p38 MAPK inhibitor SB203580 inhibited RANKL-induced osteoclast differentiation. This enhancement of c-Src and RANK proteins induced by LMW-HA was inhibited by CD44 function-blocking monoclonal antibody. These results indicate that LMW-HA plays an important role in osteoclast differentiation and function through the interaction of RANKL and RANK.

Interleukin (IL)-17 enhances tumor necrosis factor-alpha-stimulated IL-6 synthesis via p38 mitogen-activated protein kinase in osteoblasts

Inflammatory cytokines are well known to play crucial roles in the pathogenesis of rheumatoid arthritis. Among them, interleukin (IL)-17 is a cytokine that is mainly synthesized by activated T cells and its receptors are present in osteoblasts. The synthesis of IL-6, known to stimulate osteoclastic bone resorption, is reportedly responded to bone resorptive agents such as tumor necrosis factor-alpha (TNF-alpha) in osteoblasts. It has been reported that IL-17 enhances TNF-alpha-stimulated IL-6 synthesis in osteoblast-like MC3T3-E1 cells. We previously showed that sphingosine 1-phosphate (S1-P) mediates TNF-alpha-stimulated IL-6 synthesis in these cells. In the present study, we investigated the mechanism of IL-17 underlying enhancement of IL-6 synthesis in MC3T3-E1 cells. IL-17 induced phosphorylation of p38 mitogen-activated protein (MAP) kinase. SB203580 and PD169316, specific inhibitors of p38 MAP kinase, significantly reduced the enhancement by IL-17 of TNF-alpha-stimulated IL-6 synthesis. IL-17 also amplified S1-P-stimulated IL-6 synthesis, and the amplification by IL-17 was suppressed by SB203580. Anisomycin, an activator of p38 MAP kinase, which alone had no effect on IL-6 level, enhanced the IL-6 synthesis stimulated by TNF-alpha. SB203580 and PD169316 inhibited the amplification by anisomycin of the TNF-alpha-induced IL-6 synthesis. Taken together, our results strongly suggest that IL-17 enhances TNF-alpha-stimulated IL-6 synthesis via p38 MAP kinase activation in osteoblasts.

Intrathecal activation of the IL-17/IL-8 axis in opticospinal multiple sclerosis

There are two distinct subtypes of multiple sclerosis in Asians, opticospinal (OS-multiple sclerosis) and conventional (C-multiple sclerosis). In OS-multiple sclerosis, selective and severe involvement of the optic nerves and spinal cord is characteristic, though its mechanisms are unknown. The present study aimed to find out possible differences in the cytokine/chemokine profiles in CSF between OS-multiple sclerosis and C-multiple sclerosis and to delineate the relationships between these profiles and neuroimaging and pathological features. Sixteen cytokines/chemokines, namely interleukin (IL)-1beta, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12 (p70), IL-13, IL-17, interferon (IFN)-gamma, tumour necrosis factor (TNF)-alpha, granulocyte colony-stimulating factor (G-CSF), monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-1beta (MIP-1beta), were measured simultaneously in CSF supernatants from 40 patients with relapsing-remitting multiple sclerosis (20 OS-multiple sclerosis and 20 C-multiple sclerosis) at relapse and 19 control patients with spinocerebellar degeneration (SCD), together with intracellular production of IFN-gamma and IL-4 in CSF CD4+ T cells. In CSF supernatants relative to controls, IL-17, MIP-1beta, IL-1beta and IL-13 were only significantly increased in OS-multiple sclerosis patients, while TNF-alpha was only significantly increased in C-multiple sclerosis patients, using a cut-off level of 1 pg/ml. IL-8 was significantly elevated in both OS-multiple sclerosis and C-multiple sclerosis patients. MCP-1 was significantly decreased in both OS-multiple sclerosis and C-multiple sclerosis patients, while IL-7 was only significantly decreased in C-multiple sclerosis patients. IL-17, IL-8 and IL-5 were significantly higher in OS-multiple sclerosis patients than in C-multiple sclerosis patients. The increases in IL-17 and IL-8 in OS-multiple sclerosis were still significant even after exclusion of the patients undergoing various immunomodulatory therapies. Assays of intracellular cytokine production revealed that both the IFN-gamma+IL-4- T-cell percentage and intracellular IFN-gamma/IL-4 ratio in CSF cells were significantly greater in C-multiple sclerosis patients than in controls. Contrarily, OS-multiple sclerosis patients showed not only a significantly greater percentage of IFN-gamma+IL-4- T cells than controls but also a significantly higher percentage of IFN-gamma-IL-4+ T cells than C-multiple sclerosis patients. Among the cytokines elevated in multiple sclerosis, only IL-8 showed a significant positive correlation with the Expanded Disability Status Scale of Kurtzke score. Both the length of the spinal cord lesions on MRI and the CSF/serum albumin ratio had a significant positive correlation with IL-8 and IL-17 in multiple sclerosis, in which the spinal cord lesions were significantly longer in OS-multiple sclerosis than in C-multiple sclerosis. Three of six spinal cord specimens from autopsied OS-multiple sclerosis cases demonstrated numerous myeloperoxidase-positive neutrophils infiltrating necrotic lesions. These findings strongly suggest that in OS-multiple sclerosis, in addition to the Th1 cell upregulation seen in C-multiple sclerosis, intrathecal activation of the IL-17/IL-8 axis inducing heavy neutrophil infiltration contributes to extensive spinal cord lesion formation.

RANK, RANKL and osteoprotegerin in arthritic bone loss

Rheumatoid arthritis is characterized by the presence of inflammatory synovitis and destruction of joint cartilage and bone. Tissue proteinases released by synovia, chondrocytes and pannus can cause cartilage destruction and cytokine-activated osteoclasts have been implicated in bone erosions. Rheumatoid arthritis synovial tissues produce a variety of cytokines and growth factors that induce monocyte differentiation to osteoclasts and their proliferation, activation and longer survival in tissues. More recently, a major role in bone erosion has been attributed to the receptor activator of nuclear factor kappa B ligand (RANKL) released by activated lymphocytes and osteoblasts. In fact, osteoclasts are markedly activated after RANKL binding to the cognate RANK expressed on the surface of these cells. RANKL expression can be upregulated by bone-resorbing factors such as glucocorticoids, vitamin D3, interleukin 1 (IL-1), IL-6, IL-11, IL-17, tumor necrosis factor-alpha, prostaglandin E2, or parathyroid hormone-related peptide. Supporting this idea, inhibition of RANKL by osteoprotegerin, a natural soluble RANKL receptor, prevents bone loss in experimental models. Tumor growth factor-beta released from bone during active bone resorption has been suggested as one feedback mechanism for upregulating osteoprotegerin and estrogen can increase its production on osteoblasts. Modulation of these systems provides the opportunity to inhibit bone loss and deformity in chronic arthritis.

Cytokines link osteoblasts and inflammation: microarray analysis of interleukin-17- and TNF-alpha-induced genes in bone cells

The novel cytokine interleukin (IL)-17 has been implicated in many infectious and autoimmune settings, especially rheumatoid arthritis. Consistent with its proinflammatory effects on bone, osteoblast cells are highly responsive to IL-17, particularly in combination with other inflammatory cytokines. To better understand the spectrum of activities controlled by IL-17, we globally profiled genes regulated by IL-17 and tumor necrosis factor alpha (TNF-alpha) in the preosteoblast cell line MC3T3-E1. Using Affymetrix microarrays, 80-90 genes were up-regulated, and 19-50 genes were down-regulated with IL-17 and TNF-alpha as compared with TNF-alpha alone. These included proinflammatory chemokines and cytokines, inflammatory genes, transcriptional regulators, bone-remodeling genes, signal transducers, cytoskeletal genes, genes involved in apoptosis, and several unknown or unclassified genes. The CXC family chemokines were most dramatically induced by IL-17 and TNF-alpha, confirming the role of IL-17 as a potent mediator of inflammation and neutrophil recruitment. Several transcription factor-related genes involved in inflammatory gene expression were also enhanced, including molecule possessing ankyrin repeats induced by lipopolysaccharide/inhibitor of kappaBzeta (MAIL/kappaBzeta), CCAAT/enhancer-binding protein delta (C/EBPdelta), and C/EBPbeta. We also identified the acute-phase gene lipocalin-2 (LCN2/24p3) as a novel IL-17 target, which is regulated synergistically by TNF-alpha and IL-17 at the level of its promoter. A similar but not identical pattern of genes was induced by IL-17 and TNF-alpha in ST2 bone marrow stromal cells and murine embryonic fibroblasts. This study provides a profile of genes regulated by IL-17 and TNF-alpha in osteoblasts and suggests that in bone, the major function of IL-17 is to cooperate and/or synergize with other cytokines to amplify inflammation.

The role of T-cell interleukin-17 in conducting destructive arthritis: lessons from animal models

Interleukin-17 (IL-17) is a T cell cytokine spontaneously produced by cultures of rheumatoid arthritis (RA) synovial membranes. High levels have been detected in the synovial fluid of patients with RA. The trigger for IL-17 is not fully identified; however, IL-23 promotes the production of IL-17 and a strong correlation between IL-15 and IL-17 levels in synovial fluid has been observed. IL-17 is a potent inducer of various cytokines such as tumor necrosis factor (TNF)-alpha, IL-1, and receptor activator of NF-kappaB ligand (RANKL). Additive or even synergistic effects with IL-1 and TNF-alpha in inducing cytokine expression and joint damage have been shown in vitro and in vivo. This review describes the role of IL-17 in the pathogenesis of destructive arthritis with a major focus on studies in vivo in arthritis models. From these studies in vivo it can be concluded that IL-17 becomes significant when T cells are a major element of the arthritis process. Moreover, IL-17 has the capacity to induce joint destruction in an IL-1-independent manner and can bypass TNF-dependent arthritis. Anti-IL-17 cytokine therapy is of interest as an additional new anti-rheumatic strategy for RA, in particular in situations in which elevated IL-17 might attenuate the response to anti-TNF/anti-IL-1 therapy.

Increased interleukin-17 production via a phosphoinositide 3-kinase/Akt and nuclear factor kappaB-dependent pathway in patients with rheumatoid arthritis

Inflammatory mediators have been recognized as being important in the pathogenesis of rheumatoid arthritis (RA). Interleukin (IL)-17 is an important regulator of immune and inflammatory responses, including the induction of proinflammatory cytokines and osteoclastic bone resorption. Evidence for the expression and proinflammatory activity of IL-17 has been demonstrated in RA synovium and in animal models of RA. Although some cytokines (IL-15 and IL-23) have been reported to regulate IL-17 production, the intracellular signaling pathways that regulate IL-17 production remain unknown. In the present study, we investigated the role of the phosphoinositide 3-kinase (PI3K)/Akt pathway in the regulation of IL-17 production in RA. Peripheral blood mononuclear cells (PBMC) from patients with RA (n = 24) were separated, then stimulated with various agents including anti-CD3, anti-CD28, phytohemagglutinin (PHA) and several inflammatory cytokines and chemokines. IL-17 levels were determined by sandwich enzyme-linked immunosorbent assay and reverse transcription–polymerase chain reaction. The production of IL-17 was significantly increased in cells treated with anti-CD3 antibody with or without anti-CD28 and PHA (P < 0.05). Among tested cytokines and chemokines, IL-15, monocyte chemoattractant protein-1 and IL-6 upregulated IL-17 production (P < 0.05), whereas tumor necrosis factor-α, IL-1β, IL-18 or transforming growth factor-β did not. IL-17 was also detected in the PBMC of patients with osteoarthritis, but their expression levels were much lower than those of RA PBMC. Anti-CD3 antibody activated the PI3K/Akt pathway; activation of this pathway resulted in a pronounced augmentation of nuclear factor κB (NF-κB) DNA-binding activity. IL-17 production by activated RA PBMC is completely or partly blocked in the presence of the NF-κB inhibitor pyrrolidine dithiocarbamate and the PI3K/Akt inhibitor wortmannin and LY294002, respectively. However, inhibition of activator protein-1 and extracellular signal-regulated kinase 1/2 did not affect IL-17 production. These results suggest that signal transduction pathways dependent on PI3K/Akt and NF-κB are involved in the overproduction of the key inflammatory cytokine IL-17 in RA.

Th1 shift in CIDP versus Th2 shift in vasculitic neuropathy in CSF

To investigate the intra- and extracellular levels of various cytokines and chemokines in CSF in chronic inflammatory demyelinating polyneuropathy (CIDP) and vasculitic neuropathy (VN), 16 cytokines, IL-1beta, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-10, IL-12 (p70), IL-13, IL-17, IFN-gamma, TNF-alpha, G-CSF, MCP-1 and MIP-1beta, were measured in CSF supernatant by a multiplexed fluorescent bead-based immunoassay and intracellular production of IFN-gamma and IL-4 in CSF CD4+ T cells were simultaneously measured by flow cytometry in 14 patients with CIDP, 8 patients with VN and 25 patients with other noninflammatory neurologic diseases (OND). In the CSF supernatant, a significant increase of IL-17, IL-8 and IL-6, and a significant decrease of IL-4, IL-5 and IL-7 levels were detected in pretreated CIDP as compared with OND. A significant increase of IL-6, IL-8 and IL-10 levels was found in pretreated VN. Both IL-17 and IL-8 levels correlated strongly with CSF protein levels in CIDP, although the correlation of IL-6 levels was weak. In CSF CD4+ T cells, IFN-gamma+ IL-4- cell percentages were markedly elevated in CIDP compared with OND, but not in VN, resulting in a significant increase of intracellular IFN-gamma/IL-4 ratio in CIDP, even in the absence of CSF pleocytosis. The nonresponders to intravenous immunoglobulins (IVIGs) showed a significantly lower IFN-gamma- IL-4+ CD4+ T cell percentage, and tended to have a higher intracellular IFN-gamma/IL-4 ratio than the responders in CSF. Marked upregulation of Th1 cytokine, IL-17, and downregulation of Th2 cytokines, together with infiltration of IFN-gamma-producing CD4+ T cells are useful markers for CIDP, while several Th2 cytokines are upregulated in VN in CSF.

A model of inflammatory arthritis highlights a role for oncostatin M in pro-inflammatory cytokine-induced bone destruction via RANK/RANKL

Oncostatin M is a pro-inflammatory cytokine previously shown to promote marked cartilage destruction both in vitro and in vivo when in combination with IL-1 or tumour necrosis factor alpha. However, the in vivo effects of these potent cytokine combinations on bone catabolism are unknown. Using adenoviral gene transfer, we have overexpressed oncostatin M in combination with either IL-1 or tumour necrosis factor alpha intra-articularly in the knees of C57BL/6 mice. Both of these combinations induced marked bone damage and markedly increased tartrate-resistant acid phosphatase-positive multinucleate cell staining in the synovium and at the front of bone erosions. Furthermore, there was increased expression of RANK and its ligand RANKL in the inflammatory cells, in inflamed synovium and in articular cartilage of knee joints treated with the cytokine combinations compared with expression in joints treated with the cytokines alone or the control. This model of inflammatory arthritis demonstrates that, in vivo, oncostatin M in combination with either IL-1 or tumour necrosis factor alpha represents cytokine combinations that promote bone destruction. The model also provides further evidence that increased osteoclast-like, tartrate-resistant acid phosphatase-positive staining multinucleate cells and upregulation of RANK/RANKL in joint tissues are key factors in pathological bone destruction.

Interleukin-17: the missing link between T-cell accumulation and effector cell actions in rheumatoid arthritis?

The prominence of T cells and monocyte/macrophages in rheumatoid synovium suggests T cells may localize and amplify the effector functions of monocyte/macrophages in rheumatoid disease. However, while T cells are abundant in rheumatoid joints, classic T-cell derived cytokines are scarce, especially when compared to the levels of monokines IL-1 beta and TNF-alpha. For this reason, it has been speculated that monocyte/macrophages may act independently of T cells in rheumatoid disease and that the role of T cells may be more or less irrelevant to core disease mechanisms. The question of T-cell influence requires re-evaluation in light of the characterization of IL-17, a T-cell derived cytokine that is abundant in rheumatoid synovium and synovial fluid. IL-17 has a number of pro-inflammatory effects, both directly and through amplification of the effects of IL-1 beta and TNF-alpha. IL-17 is able to induce expression of pro-inflammatory cytokines and stimulate release of eicosanoids by monocytes and synoviocytes. Furthermore, IL-17 has been implicated in the pathogenesis of inflammatory bone and joint damage through induction of matrix metalloproteinases and osteoclasts, as well as inhibition of proteoglycan synthesis. In animal models of arthritis, intra-articular injection of IL-17 results in joint inflammation and damage. The recognition of IL-17 as a pro-inflammatory T cell derived cytokine, and its abundance within rheumatoid joints, provides the strongest candidate mechanism to date through which T cells can capture and localize macrophage effector functions in rheumatoid arthritis. As such, IL-17 warrants consideration for its potential as a therapeutic target in rheumatoid arthritis.

Bone loss in inflammatory arthritis: mechanisms and treatment strategies

PURPOSE OF REVIEW

Focal bone loss in inflammatory arthritis begins early in the disease process and can contribute to patient morbidity. Current treatment strategies primarily target suppression of the inflammatory cascade with varying success in limiting the progression of focal bone destruction. This review outlines the current understanding of the mechanisms mediating inflammation-induced focal bone loss in rheumatoid arthritis and other inflammatory arthritides and highlights recent studies in animal models of arthritis that have contributed to our knowledge of this process.

RECENT FINDINGS

Bone-resorbing osteoclasts have been identified as important effector cells in inflammation-induced bone loss in both experimental animal models and human rheumatoid arthritis and psoriatic arthritis. The RANK/RANKL (receptor activator of nuclear factor-kappaB and RANK ligand) pathway has been shown to be essential for osteoclast differentiation in inflammatory arthritis. In addition, in vitro and in vivo studies have demonstrated that many cytokines and growth factors elaborated by inflamed synovial tissues may contribute to osteoclast differentiation and activation.

SUMMARY

Elucidation of the mechanisms mediating osteoclast differentiation and function has identified new pathways for potential targeted therapeutic intervention for focal bone loss in inflammatory arthritis. Challenges in the application of this approach are that therapies targeting the osteoclast would need to be used in combination with effective anti-inflammatory agents, and that pathways mediating osteoclast differentiation and function would need to remain at least partially functional to allow for continued skeletal remodeling.

IL-15 and the initiation of cell contact-dependent synovial fibroblast-T lymphocyte cross-talk in rheumatoid arthritis: effect of methotrexate

To characterize the molecules responsible for synovial fibroblast-T lymphocyte (TL) cross-talk in rheumatoid arthritis (RA), synovial fibroblasts from patients with established RA (RASFibs) were cocultured with TLs from peripheral blood of early RA patients (RAPBTL). TLs from peripheral blood of healthy controls and from synovial fluid of RA served as controls. Adhesion molecules and cytokines were determined by flow cytometry, ELISA, and real-time PCR. RAPBTL (n = 20) induced an up-regulation of ICAM-1, intracellular IL-8, IL-6, IL-15, and surface IL-15 in cocultured RASFibs. In turn, RAPBTL showed an up-regulation of TNF-alpha, IFN-gamma, IL-17, CD25, and CD69 expression. Responses seen with TLs from peripheral blood of healthy controls (n = 20) were significantly lower, whereas responses with TLs from synovial fluid of RA (n = 20) were maximal. Blocking Abs to IL-15 and CD54, but not an isotype-control Ab, down-regulated the increased TL cytokine and activation marker expression. Abs to CD69, CD11a, IL-17, TNF-alpha, and IFN-gamma significantly decreased the up-regulation of RASFib cytokine and CD54 expression. Cocultures using 0.4- micro m inserts did not result in up-regulation of surface molecules or cytokines. Methotrexate significantly inhibited RASFib/TL cross-talk signals and decreased adhesion of TL to RASFibs. In summary, RASFib production of IL-15 induces the proinflammatory cytokines TNF-alpha, IFN-gamma, and IL-17 in cocultured TLs through a cell contact-dependent mechanism. In turn, these cytokines stimulate the expression of IL-15, IL-8, and IL-6 in RASFibs, thereby creating a feedback loop that favors persistent synovial inflammation. Methotrexate seems to disrupt this loop by decreasing cell adhesion.

Tax protein of human T-cell leukaemia virus type 1 induces interleukin 17 gene expression in T cells

Tax protein of human T-cell leukaemia virus type 1 (HTLV-1) induces the expression of several cellular genes that are involved in T cell activation and proliferation. In this study, it was observed that Tax upregulated the expression of human interleukin 17 (IL17), a cytokine mainly produced by activated CD4(+) memory T cells. Indeed, IL17 mRNA was highly expressed in HTLV-1-infected T cells as well as in Tax-expressing Jurkat T cells, whereas it was not detectable in HTLV-1-negative T cell lines. The clinical relevance of these observations was further demonstrated by quantitative assessment of IL17 expression in lymphocytes isolated from one HTLV-1-infected patient. To define the transcriptional activation of the IL17 gene by Tax, the 5'-flanking region of this gene was cloned and a reporter gene analysis performed. The presence of a Tax-responsive region spanning 614 bp upstream of the initiation start site was identified, in HeLa as well as in Jurkat cells, stimulated with phorbol myristate acetate and Ca(2+) ionophore. Finally, Tax mutants were used to show that the transcriptional activation of the IL17 promoter by Tax was dependent on the CREB/ATF pathway. As IL17 upregulates the expression of several pro-inflammatory cytokines, these observations provide new insights into the involvement of the Tax protein in the pathophysiology of HTLV-1-associated inflammatory disorders.

Involvement of IL-17 in Fas ligand-induced inflammation

Fas ligand (FasL) has been well characterized as a death factor. However, recent studies revealed that ectopic expression of FasL induces inflammation associated with massive neutrophil infiltration. We previously demonstrated that the neutrophil infiltration-inducing activity of FasL is partly dependent on, but partly independent of, IL-1beta. Here we investigated the cytokine profile of peritoneal lavage fluid obtained from mice that received i.p. injections of FFL, a FasL-expressing tumor cell line. We found that FFL injection caused a marked increase of not only IL-1beta but also IL-6, IL-17, IL-18, KC/chemokine CXC ligand 1 and macrophage inflammatory protein (MIP)-2, but not of IL-1alpha, IFN-gamma, TGF-beta or TNF-alpha. The FFL-induced cytokine production was not observed in Fas-deficient lpr mice. Among cells transfected to express individually IL-1beta, IL-6, IL-17, or IL-18, only those expressing IL-1beta and IL-17 induced neutrophil infiltration. In these analyses, as little as 20 pg of peritoneal IL-17 induced neutrophil infiltration. The peritoneal IL-17 levels after FFL-injection were greatly diminished in IL-1-deficient mice. However, the IL-17 level was still above the threshold for neutrophil infiltration. Consistent with this, co-administration of the anti-IL-17 antibody with FFL diminished the peritoneal KC levels and neutrophil infiltration in IL-1-deficient mice. In addition, the expression of IL-17 by the tumor cells inhibited tumor growth in wild-type and nude mice. These results indicate that FasL is an upstream inflammatory factor that induces a variety of other inflammatory cytokines in vivo, and suggest that IL-17 is involved in FasL-induced inflammation in the absence of IL-1beta.

Interleukin-6 family of cytokines as biochemical markers of osseous changes in the temporomandibular joint disorders

The aim of this study was to find out whether there was a correlationship between the concentrations of interleukin-6 (IL-6), IL-11, and IL-17 in synovial fluid and osseous changes in the condyle. The synovial fluid was obtained from 61 patients with temporomandibular joint disorders (TMD) and seven healthy volunteers (controls). The concentrations of IL-6, IL-11, and IL-17 were measured by enzyme-linked immunosorbent assay. IL-6 was detected in 43 of 59 (73%), IL-11 in 23 of 52 (44%) and IL-17 in 14 of 51 (27%) samples of synovial fluid. The concentrations of IL-6 and IL-11 in the joints with osseous changes in the condyle were significantly higher than in the joints without osseous changes (P < 0.05) and also higher than in the joints of the control group (P < 0.05). In addition, there was a correlation of concentrations between IL-6 and IL-11 (P < 0.05). These results suggest that IL-6 and IL-11 may participate in the pathogenesis of TMD and induce osseous changes in the condyle.

Interleukin-17 regulates expression of the CXC chemokine LIX/CXCL5 in osteoblasts: implications for inflammation and neutrophil recruitment

Interleukin (IL)-17 is the founding member of an emerging family of inflammatory cytokines whose functions remain poorly defined. IL-17 has been linked to the pathogenesis of rheumatoid arthritis, and numerous studies implicate this cytokine in inflammation-induced bone loss. It is clear that a major function of IL-17 is to amplify the immune response by triggering production of chemokines, cytokines, and cell-surface markers, ultimately leading to neutrophil chemotaxis and inflammation. As an IL-17 signaling deficiency in mice causes a dramatic reduction in neutrophil chemotaxis and a consequent increased susceptibility to bacterial infection, it is important to define gene targets involved in IL-17-mediated neutrophil trafficking. Here, we demonstrate that IL-17 and tumor necrosis factor alpha (TNF-alpha) cooperatively induce the lipopolysaccharide-inducible CXC chemokine (LIX; a.k.a., CXC chemokine ligand 5, Scya5, or murine granulocyte chemotactic protein-2) in the preosteoblast cell line MC3T3. LIX is induced rapidly at the mRNA and protein levels, likely through the activation of new gene transcription. Conditioned media from MC3T3 cells treated with IL-17 and/or TNF-alpha stimulates neutrophil mobility potently, and LIX is a significant contributing factor to this process. In addition, IL-17 cooperates with bacterial components involved in periodontal disease to up-regulate LIX expression. This study is the first demonstration of LIX expression in bone cells and has implications for inflammatory bone diseases such as arthritis and periodontal disease.

Immune modulation of the pulmonary hypertensive response to bacterial lipopolysaccharide (endotoxin) in broilers

The lungs of broilers are constantly challenged with lipopolysaccharide (LPS, endotoxin) that can activate leukocytes and trigger thromboxane A2 (TxA2)- and serotonin (5HT)-mediated pulmonary vasoconstriction leading to pulmonary hypertension. Among broilers from a single genetic line, some individuals respond to LPS with large increases in pulmonary arterial pressure, whereas others fail to exhibit any response to the same supramaximal dose of LPS. This extreme variability in the pulmonary hypertensive response to LPS appears to reflect variability in the types or proportions of chemical mediators released by leukocytes. Our research has confirmed that TxA2 and 5HT are potent pulmonary vasoconstrictors in broilers and that broilers hatched and reared together consistently exhibit pulmonary hypertension after i.v. injections of TxA2 or 5HT. Previous in vitro studies conducted using macrophages from different lines of chickens demonstrated innate variability in the LPS-stimulated induction of nitric oxide synthase (iNOS) followed by the onset of an LPS-refractory state. The NOS enzyme converts arginine to citrulline and nitric oxide (NO). It is known that NO produced by endothelial NOS serves as a key modulator of flow-dependent pulmonary vasodilation, and it is likely that NO generated by iNOS also contributes to the pulmonary vasodilator response. Accordingly, it is our hypothesis that the pulmonary hypertensive response to LPS in broilers is minimal when more vasodilators (NO, prostacyclin) than vasoconstrictors (TxA2, 5HT) are generated during an LPS challenge. Indeed, inhibiting NO production through pharmacological blockade of NOS with the inhibitor Nomega-nitro-L-arginine methyl ester modestly increased the baseline pulmonary arterial pressure and dramatically increased the pulmonary hypertensive response to LPS in all broilers evaluated. Innate differences in the effect of LPS on the pulmonary vasculature may contribute to differences in susceptibility of broilers to pulmonary hypertension syndrome (ascites).

Treatment with a neutralizing anti-murine interleukin-17 antibody after the onset of collagen-induced arthritis reduces joint inflammation, cartilage destruction, and bone erosion

OBJECTIVE

Interleukin-17 (IL-17) is a proinflammatory cytokine that is expressed in the synovium of rheumatoid arthritis (RA) patients. This T cell cytokine is implicated in the initiation phase of arthritis. However, the role of IL-17 during the effector phase of arthritis has still not been identified; this was the objective of the present study.

METHODS

Mice with collagen-induced arthritis (CIA) were treated with polyclonal rabbit anti-murine IL-17 (anti-IL-17) antibody-positive serum or normal rabbit serum after the first signs of arthritis. In addition, during a later stage of CIA mice were selected and treated with anti-IL-17 antibody or control serum. Arthritis was monitored visually, and joint pathology was examined radiologically and histologically. Systemic IL-6 levels were measured by enzyme-linked immunosorbent assay, and local synovial IL-1 and receptor activator of NF-kappaB ligand (RANKL) expression was analyzed using specific immunohistochemistry.

RESULTS

Treatment with a neutralizing anti-IL-17 antibody after the onset of CIA significantly reduced the severity of CIA. Radiographic analysis revealed marked suppression of joint damage in the knee and ankle joints. Histologic analysis confirmed the suppression of joint inflammation and showed prevention of cartilage and bone destruction after anti-IL-17 antibody therapy. Systemic IL-6 levels were significantly reduced after anti-IL-17 antibody treatment. Moreover, fewer IL-1beta-positive and RANKL-positive cells were detected in the synovium after treatment with neutralizing IL-17. Interestingly, initiation of anti-IL-17 antibody therapy during a later stage of CIA, using mice with higher clinical arthritis scores, still significantly slowed the progression of the disease.

CONCLUSION

IL-17 plays a role in early stages of arthritis, but also later during disease progression. Systemic IL-6 was reduced and fewer synovial IL-1-positive and RANKL-positive cells were detected after neutralizing endogenous IL-17 treatment, suggesting both IL-1-dependent and IL-1-independent mechanisms of action. Our data strongly indicate that IL-17 neutralization could provide an additional therapeutic strategy for RA, particularly in situations in which elevated IL-17 may attenuate the response to anti-tumor necrosis factor/anti-IL-1 therapy.

Expression of osteoclast differentiation factor and osteoclastogenesis inhibitory factor in rat osteoporosis induced by immunosuppressant FK506

Immunosuppressant drugs are currently required by transplant recipients for the remainder of their lives, despite the many adverse effects associated with these therapies. Acute osteoporosis is one such effect, and a reproducible osteoporosis model has been established through the administration of the immunosuppressant drug FK506 in rats. The cause of this osteoporosis has been shown to be abnormal osteoclast proliferation, altering the process of bone remodeling. However, the reasons why FK506 induces osteoclast proliferation and whether this process is mediated by cytokine changes or an increase in bone resorption factors have been unclear. An investigation was therefore conducted focusing on the recent discoveries of osteoclast differentiation factor (ODF) and osteoclastogenesis inhibitory factor (OCIF). These factors led to elucidation of the osteoclast differentiation-maturation mechanism. An osteoporosis model was produced in rats utilizing intramuscular FK506 injection (1 mg/kg) for 28 consecutive days. Trabecular bone resorption was observed inferior to enchondral ossification in the FK506 group, and tartrate resistant acid phosphatase (TRAP) staining revealed a clear increase in osteoclasts at the site of enchondral ossification, relative to the control group. Real-time PCR and in situ hybridization (ISH) demonstrated minimal differences in OCIF expression between control and the treatment groups. However, Real-time PCR revealed clearly increased ODF expression in the treatment group. ODF expression was also shown to be increased in the treatment group using ISH. This was histologically consistent with a region of osteoclast proliferation inferior to enchondral ossification. The results of this study support the hypothesis that FK506-mediated osteoporosis occurs by action of the drug on osteoclasts, promoting expression of ODF messenger ribonucleic acid (mRNA) and thus prompting osteoclast differentiation and maturation.

Inducible nitric oxide synthase activation by interleukin-17

Interleukin-17 (IL-17) is a proinflammatory T cell cytokine presumably involved in physiological responses to infection, but also in immunopathology of autoimmune disorders such as rheumatoid arthritis. The proinflammatory action of IL-17 depends considerably on its ability to trigger the expression of inducible nitric oxide (NO) synthase (iNOS), an enzyme responsible for the generation of cytotoxic and immunoregulatory free radical NO. Here we discuss the role of IL-17 in the cytokine network controlling iNOS expression, and analyze signaling pathways employed by IL-17 for the initiation of iNOS gene transcription. We also propose biological consequences of IL-17-mediated NO release that could be relevant for the mechanisms or therapy of autoimmune and inflammatory disorders.

Cytokines in the rheumatic diseases

Extensive data has accumulated over the last 10 to 15 years to implicate various cytokines in pathways of pathophysiology in rheumatic diseases. Abnormalities in cytokine production are not the cause of these diseases, but reflect continual production by immune and inflammatory cells. Cytokines are heterogeneous and function in an overlapping and redundant network. An important principle to emerge is that the net biologic response in a diseased organ or tissue reflects a balance between the local levels of proinflammatory and anti-inflammatory cytokines and factors. Thus, a chronic disease may result from the excess production of proinflammatory cytokines or the inadequate production of anti-inflammatory cytokines. This article summarizes the role of cytokines in rheumatic diseases by focusing on each disease and the involved pathways of pathophysiology.

Suppression of osteoclastogenesis in rheumatoid arthritis by induction of apoptosis in activated CD4+ T cells

OBJECTIVE

To examine the suppressive effect of anti-human Fas monoclonal antibody (mAb) on osteoclastogenesis in rheumatoid arthritis (RA) both in vitro and in vivo.

METHODS

For in vitro analysis, activated CD4+ T cells derived from peripheral blood mononuclear cells were left untreated or were treated with humanized anti-human Fas mAb (R-125224) and cocultured with human monocytes. On day 12, the number of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells was counted. For in vivo analysis, tissue derived from human RA pannus was implanted with a slice of dentin subcutaneously in the backs of SCID mice (SCID-HuRAg-pit model). R-125224 was administered intravenously once a week for 3 weeks. The implanted tissue and dentin slice were removed, and the pits formed on the dentin slice were analyzed.

RESULTS

In vitro, coculture of activated CD4+ T cells and peripheral monocytes induced osteoclastogenesis. The number of TRAP-positive multinucleated cells was reduced when activated CD4+ T cells were treated with R-125224. We established a new animal model for monitoring osteoclastogenesis, SCID-HuRAg-pit. We found that with R-125224 treatment, the number of pits formed on the implanted dentin slices was significantly reduced and the number of lymphocytes in the implanted RA synovial tissue was dramatically reduced in this model.

CONCLUSION

This is the first study to demonstrate the suppressive effect of anti-human Fas mAb on osteoclastogenesis in RA synovial tissues through the induction of T cell apoptosis. Induction of apoptosis of infiltrated lymphocytes could be a useful therapeutic strategy for RA, in terms of suppressing both inflammation and bone destruction.

Synergistic effects of vascular IL-17 and TNFα may promote coronary artery disease

Interleukin (IL)-17 is a pro-inflammatory cytokine originally described in T lymphocytes. Increased production of IL-17 has been linked to the induction of cytokines, chemokines and adhesion molecules in various cell types, effects that likely contribute to a number of inflammatory diseases including rheumatoid arthritis. Importantly, in the same pathophysiological conditions production of TNFalpha is also up-regulated and recent studies suggest that cellular signaling pathways induced by IL-17 and TNFalpha converge. Recent studies showed that vascular endothelial and/or smooth muscle cells also express TNFalpha and IL-17, which can be up-regulated in pro-atherogenic pathophysiological conditions in the coronary arteries. TNFalpha has been shown to exert pro-inflammatory vascular effects (e.g., induction of oxidative stress, endothelial apoptosis, up-regulation of adhesion molecules and chemokines), however, the role of vascular IL-17 and its interaction with TNFalpha is much less understood. We propose that increased vascular IL-17 and TNFalpha levels can act synergistically to create a pro-inflammatory microenvironment promoting the development of atherosclerotic vascular disease.

A rapid multiparameter approach to study factors that regulate osteoclastogenesis: demonstration of the combinatorial dominant effects of TNF-alpha and TGF-ss in RANKL-mediated osteoclastogenesis

Macrophages differentiate into osteoclasts in response to the critical cytokine RANKL. However, the efficiency of RANKL-mediated osteoclastogenesis can be profoundly influenced by various cytokines. While studies describing the isolated effects of particular cytokines on osteoclastogenesis have been performed, combinatorial effects of cytokines have not been addressed routinely due to the absence of an efficient assay system. To study the effects of cytokine combinations on osteoclast formation, we performed in vitro assays using either the RAW293 cell line or primary murine splenic macrophages as osteoclast precursors. Using a multiparameter cytokine plating method, we analyzed osteoclastogenesis in response to multiple combinations of the following inflammation-related cytokines: RANKL, IFN-gamma, TNF-alpha, IL-1beta, IL-6, IL-10. We further investigated the role of T-cell-related cytokine combinations on osteoclastogenesis by measuring osteoclast area in response to RANKL with IFN-gamma, IL-2, IL-4, IL-6, TGF-ss, and TNF-alpha. Treatments with RANKL, TNF-alpha, and TGF-ss induced maximal osteoclast formation, suggesting a role for these cytokines in the most aggressive forms of inflammatory bone loss. TNF-alpha alone, however, was unable to induce osteoclast formation in the absence of RANKL despite co-administration of other proinflammatory cytokines. IFN-gamma was a potent inhibitor under all conditions, implicating T cells and NK cells in osteoclast inhibition. These studies demonstrate a rapid screening approach for identifying the potential collective effects of multiple factors on osteoclastic bone resorption.

Functional cooperation between interleukin-17 and tumor necrosis factor-alpha is mediated by CCAAT/enhancer-binding protein family members

Interleukin (IL)-17 is a recently described cytokine involved in the amplification of inflammatory responses and pathologies. A hallmark feature of IL-17 is its ability to induce expression of other cytokines and chemokines. In addition, IL-17 potently synergizes with tumor necrosis factor-alpha (TNFalpha) to up-regulate expression of many target genes, particularly IL-6. Despite the many observations of IL-17 signaling synergy observed to date, little is known about the molecular mechanisms that underlie this phenomenon. In the osteoblastic cell line MC-3T3, we have found that IL-17 and TNFalpha exhibit potent synergy in mediating IL-6 secretion. Here, we show that at least part of the functional cooperation between IL-17 and TNFalpha occurs at the level of IL-6 gene transcription. Both the NF-kappaB and CCAAT/enhancer-binding protein (C/EBP; NF-IL6) sites in the IL-6 promoter are important for cooperative gene expression, but NF-kappaB does not appear to be the direct target of the combined signal. Microarray analysis using the Affymetrix mouse MG-U74v2 chip identified C/EBPdelta as another gene target of combined IL-17- and TNFalpha-induced signaling. Because C/EBP family members are known to control IL-6, we examined whether enhanced C/EBPdelta expression is involved in the cooperative up-regulation of IL-6 by IL-17 and TNFalpha. Accordingly, we show that C/EBPdelta (or the related transcription factor C/EBPbeta) is essential for expression of IL-6. Moreover, overexpression of C/EBPdelta (and, to a lesser extent, C/EBPbeta) could substitute for the IL-17 signal at the level of IL-6 transcription. Thus, C/EBP family members, particularly C/EBPdelta, appear to be important for the functional cooperation between IL-17 and TNFalpha.

Regulation of immune and autoimmune responses by ICOS

Proper T cell activation and function are regulated by the innate immune system, importantly through positive and negative costimulatory molecules in the B7 superfamily. Inducible costimulator (ICOS), the receptor for B7h (also known as B7RP-1), is expressed on T cells after T cell activation. Recently, using ICOS-deficient mice, we have examined the roles of ICOS in immune responses. ICOS is required for humoral immunity. In organ-specific autoimmune responses, however, ICOS has contrast roles in different disease models. On the one hand, ICOS-/- mice exhibited extreme sensitivity to experimental autoimmune encephalomyelitis (EAE); on the other, ICOS gene deletion led to complete resistance to collagen-induced arthritis (CIA) in mice. Our work not only illustrates the complexity of immune regulation by costimulatory molecules, but also suggests novel therapeutic strategies for various autoimmune diseases.

Inhibition of RANKL-induced osteoclast formation in mouse bone marrow cells by IL-12: involvement of IFN-gamma possibly induced from non-T cell population

IL-12 was shown to have the potential to inhibit osteoclast formation in mouse bone marrow cells treated with macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-kappaB ligand (RANKL). When bone marrow macrophages (BMM) were used as osteoclast precursors, IL-12 failed to inhibit M-CSF/RANKL-induced osteoclast formation from BMM. In coculture experiments using transwells, IL-12 did inhibit osteoclast formation from BMM cocultured with whole bone marrow cells. These results indicated that IL-12 indirectly affected M-CSF/RANKL-induced osteoclastogenesis in bone marrow cells and that the inhibition of IL-12 on osteoclast formation was caused by a humoral factor from bone marrow cells treated with IL-12. Experiments with anti-interferon (IFN)-gamma antibody and bone marrow cells from IFN-gamma receptor knockout mice revealed that IFN-gamma might be involved in the inhibition of osteoclast formation in this system. The expression of osteoprotegerin mRNA in bone marrow cells was not affected by treatment with IL-12. The inhibitory effect of IL-12 on osteoclast formation was also seen in the T cell-depleted bone marrow cells of normal mice and the whole bone marrow cells of athymic nude mice, while the inhibitory effect of IL-12 was partially suppressed in the B cell-depleted bone marrow cells. The inhibitory effect of IL-12 on M-CSF/RANKL-induced osteoclastogenesis was not accompanied with cell death, in contrast with our previous finding that the inhibitory effect of IL-12 on M-CSF/TNF-alpha-induced osteoclastogenesis is attributable to Fas and FasL-mediated apoptosis.