Expression of Cell Adhesion Molecules and Cytokines in Murine Antigen-Induced Arthritis

Adhesion molecules and cytokines are important in chronic inflammatory conditions such as rheumatoid arthritis (RA) by virtue of their role in cell activation and emigration. Using immunohistochemical techniques we studied the expression of adhesion molecules and cytokines in cryopreserved sections of murine knee joint in the course of antigen-induced arthritis, an animal model of human RA. Various adhesion molecules and cytokines are expressed in the arthritic joint tissue. LFA-I, Mac-1, CD44, ICAM-I and P-selectin were strongly expressed in the acute phase and to a lesser degree in the chronic phase of arthritis. VLA-4 and VCAM-I appeared to be moderately expressed on day 1, L-selectin between days 1 and 3. LFA-I, Mac-I, CD44, a4-integrin, ICAM-I and the selectins were found expressed on cells of the synovial infiltrate, LFA-1, Mac-1 and ICAM-I on the synovial lining layer, and VCAM-I and P-selectin on endothelial cells. Expression of E-selectin could be demonstrated throughout the experiment at a low level in cells of the acute cell infiltrate. Cytokines, especially IL-2, IL-4, IL-6, TNF, and IFN-7, were heavily expressed during the acute phase of arthritis in cellular infiltrate. Taken together these data demonstrate that cytokines and their activation of adhesion molecules contribute to cell infiltration and activation during the initial phase of arthritis and to the induction and progression of tissue destruction in arthritic joints. These molecules might be potential targets for novel therapeutic strategies in inflammatory and arthritic disorders.     

Levels of gastrin-releasing peptide and substance P in synovial fluid and serum correlate with levels of cytokines in rheumatoid arthritis

It is well known that cytokines are highly involved in the disease process of rheumatoid arthritis (RA). Recently, targeting of neuropeptides has been suggested to have potential therapeutic effects in RA. The aim of this study was to investigate possible interrelations between five neuropeptides (bombesin/gastrin-releasing peptide (BN/GRP), substance P (SP), vasoactive intestinal peptide, calcitonin-gene-related peptide, and neuropeptide Y) and the three cytokines tumour necrosis factor (TNF)-α, IL-6, and monocyte chemoattractant protein-1 in synovial fluid of patients with RA. We also investigated possible interrelations between these neuropeptides and soluble TNF receptor 1 in serum from RA patients. Synovial fluid and sera were collected and assayed with ELISA or RIA. The most interesting findings were correlations between BN/GRP and SP and the cytokines. Thus, in synovial fluid, the concentrations of BN/GRP and SP grouped together with IL-6, and SP also grouped together with TNF-α and monocyte chemoattractant protein-1. BN/GRP and SP concentrations in synovial fluid also grouped together with the erythrocyte sedimentation rate. In the sera, BN/GRP concentrations and soluble TNF receptor 1 concentrations were correlated. These results are of interest because blocking of SP effects has long been discussed in relation to RA treatment and because BN/GRP is known to have trophic and growth-promoting effects and to play a role in inflammation and wound healing. Furthermore, the observations strengthen a suggestion that combination treatment with agents interfering with neuropeptides and cytokines would be efficacious in the treatment of RA. In conclusion, BN/GRP and SP are involved together with cytokines in the neuroimmunomodulation that occurs in the arthritic joint.     

Immune complex induced arthritis in rats: role of lipid mediators on cell infiltration

We investigated the participation of lipid mediators in an experimental immune complex (IC) arthritis model in rats. The animals were subjected to intraarticular injection of anti-bovine sertLm albumin (BSA) IgG antibodies followed by i.v. injection of BSA. Histopathological analysis of the synovial membranes disclosed infiltration of polymorphonuclear (PMN) cells and vascular congestion. Slight increase in vascular permeability, measured by Evans blue dye extravasation into the joints, was detected after 3 h of arthritis. Cellular influx into the articular cavities was most evident at the sixth hour of arthritis with predominance of PMN. Pretreatment with either indomethacin, a cyclooxygenase inhibitor, or L-660,711, a peptido-leukotriene antagonist, did not inhibit cell infiltration, whereas pretreatment with either L-663,536, a 5-lipoxygenase inhibitor, or L-655,240, a thromboxane antagonist, significantly inhibited the phenomenon. Pretreatment with WEB 2170, a platelet activating factor (PAF) antagonist, also significantly inhibited cell influx. These results suggest that thromboxane, LTB(4) and PAF mediate cell infiltration in this IC arthritis model.     

Gene transfer of a cell cycle modulator exerts anti-inflammatory effects in the treatment of arthritis

Forced expression of a cyclin-dependent kinase inhibitor gene, p21(Cip1) in the synovial tissues was effective in treating animal models of rheumatoid arthritis. Synovial hyperplasia in the treated joints was suppressed, reflecting the inhibitory effect of p21(Cip1) on cell cycle progression. Additionally, lymphocyte infiltration, expression of inflammatory cytokines, and destruction of the bone and cartilage were inhibited. To determine why the cell cycle regulator gene exerted such anti-inflammatory effects, we investigated gene expression by rheumatoid synovial fibroblasts with or without the p21(Cip1) gene transferred. We have found that p21(Cip1) gene transfer down-regulates expression of various inflammatory mediators and tissue-degrading proteinases that are critically involved in the pathology of rheumatoid arthritis. These molecules included IL-6, -8, type I IL-1R (IL-1R1), monocyte chemoattractant protein-1, macrophage inflammatory protein-3alpha, cathepsins B and K, and matrix metalloproteinases-1 and -3. Down-regulation of IL-1R1 by p21(Cip1) resulted in attenuated responsiveness to IL-1. Inhibition of the inflammatory gene expression by p21(Cip1) was seen even when IL-1 is absent. This IL-1R1-independent suppression was accompanied by reduced activity of c-Jun N-terminal kinase, which was associated with p21(Cip1), and inactivation of NF-kappaB and AP-1. These multiple regulatory effects should work in concert with the primary effect of inhibiting cell cycle in ameliorating the arthritis, and suggest a heretofore unexplored relationship between cyclin-dependent kinase inhibitor gene and inflammatory molecules.     

The M20 IL-1 inhibitor prevents onset of adjuvant arthritis

Cytokines, specifically IL-1 and TNF, have been implicated as important mediators of joint destruction in rheumatoid arthritis (RA). Elevated levels of IL-1 in the joint fluid of patients with RA have been reported, as well as the presence of IL-1 inhibitory activity. We have reported the characterization of an inhibitor derived from a myelomonocytic cell line cloned in our laboratory which is specific for IL-1. This IL-1 inhibitor is protein in nature which specifically inhibits activityin vitro andin vivo. Previous studies showed that the inhibitor reduced acute inflammatory reactions associated with IL-1 (fever, leukocytosis, local foot pad swelling, lymph node enlargement and acute phase reactants). Thus it was of interest to study whether the M20 IL-1 inhibitor could modify adjuvant-induced chronic inflammation in rats, which is often used as a model for human RA. Administration of complete Freund's adjuvant (CFA) into Lewis rats, resulted in a severe adjuvant arthritis (AA) which reached peak severity after 14 days. Daily administration of IL-1 inhibitor, beginning after injection of CFA, abolished the appearance of AA. The parameters investigated were: joint swelling (the increase in diameter of joints), peri-articular erythema, limping of the rats and histological examination. The effect of the M20 IL-1 inhibitor was shown to be dose dependent and the IL-1 inhibitor alone had no adverse effects. These results indicate that the M20 IL-1 inhibitor may have a role in the treatment of AA and may be used to reduce pathological processes in joint inflammation.     

Endogenous IL-11 is pro-inflammatory in acute methylated bovine serum albumin/interleukin-1-induced (mBSA/IL-1)arthritis

OBJECTIVE: To evaluate the role of interleukin-11 (IL-11) in acute mBSA/IL-1-induced inflammatory arthritis. METHODS: IL-11 was administered via intra-articular (IA) injection into knee joints of C57BL/6 mice and joint histology was assessed. The mitogenic response to IL-11 was measured in wild-type (WT) synovial fibroblasts. IL-1 was used as a comparator in both the studies. The severity of acute methylated bovine serum albumin (mBSA)/IL-1 arthritis was determined in WT and IL-11 receptor null (IL-11Ra1-/-) mice. In parallel experiments, a neutralising antibody to IL-11 was administered to WT mice throughout this model. RESULTS: IA injections of IL-11 resulted in mild-to-moderate joint inflammation which was less than that due to IA IL-1. IL-11 had a dose-dependent mitogenic effect on WT synovial fibroblasts (P<0.01). mBSA/IL-1 acute arthritis was reduced in IL-11Ra1-/- versus WT mice (histological arthritis score: 10.1+/-0.5 versus 12.8+/-0.7, respectively; P=0.01). Administration of an IL-11 neutralising antibody to WT mice reduced mBSA/IL-1 acute arthritis scores compared to control antibody (10.6+/-0.7 versus 13.3+/-0.6, respectively; P=0.02). CONCLUSIONS: These data demonstrate that endogenous IL-11 exerts relatively mild but consistent pro-inflammatory effects in acute inflammatory arthritis.     

Mechanisms of thrombocytopenia in the acute phase of antigen-induced arthritis in rabbits.

Arthritis induced in hyperimmune rabbits by the intra-articular injection of the specific antigen was associated with a fall in circulating platelet number that lasted up to 60 days. Pretreatment of the animals with indomethacin and econazol at doses that significantly decreased thromboxane levels in the synovial fluids reduced the arthritis-related thrombocytopenia in the acute phase of arthritis. A similar inhibition was seen when L-655,240, a specific Thromboxane A2 antagonist, and BN 52021, a Platelet Activating Factor antagonist were used. The results suggest that both thromboxane and PAF are involved in the mechanisms leading to thrombocytopenia in this experimental model of arthritis.     

The combined effects of anti-TNFα antibody and IL-1 receptor antagonist in human rheumatoid arthritis synovial membrane

TNFα and IL-1 are the pivotal cytokines involved in rheumatoid arthritis (RA). More recently, the biological therapy targeting TNFα or IL-1 has been impressively effective for many RA patients, however, it remains insufficient in some patients. In the present study, we examined the combined effects of two agents against TNFα and IL-1 in human RA synovial membrane. Synovial explants (an ex vivo model) and synovial fibroblasts (an in vitro model) were prepared from 11 RA patients, and then anti-TNFα antibody (Anti-TNFα) and IL-1 receptor antagonist (IL-1Ra), either alone or in combination, were added to the synovial explants and fibroblasts. IL-6 and MMP-3 production were measured after incubation. As a result, their production significantly decreased by the combination of agents compared with the control group in both the synovial explants and fibroblasts. The efficacy of this combination was also observed for IL-6 production compared with each agent alone in the synovial explants, and for IL-6 and MMP-3 production compared with each agent alone in the synovial fibroblasts. Therefore, the combination of Anti-TNFα and IL-1Ra appears more beneficial in synovial membrane, particularly when compared with a single agent alone.     

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.     

Adenoviral vector-mediated overexpression of IL-4 in the knee joint of mice with collagen-induced arthritis prevents cartilage destruction.

Rheumatoid arthritis is a chronic inflammatory joint disease, leading to cartilage and bone destruction. In this study, we investigated the effects of local IL-4 application, introduced by a recombinant human type 5 adenovirus vector, in the knee joint of mice with collagen-induced arthritis. One intraarticular injection with an IL-4-expressing virus caused overexpression of IL-4 in the mouse knee joint. Enhanced onset and aggravation of the synovial inflammation were found in the IL-4 group. However, despite ongoing inflammation, histologic analysis showed impressive prevention of chondrocyte death and cartilage erosion. In line with this, chondrocyte proteoglycan synthesis was enhanced in the articular cartilage. This was quantified with ex vivo 35S-sulfate incorporation in patellar cartilage and confirmed by autoradiography on whole knee joint sections. Reduction of cartilage erosion was further substantiated by lack of expression of the stromelysin-dependent cartilage proteoglycan breakdown neoepitope VDIPEN in the Ad5E1 mIL-4-treated knee joint. Reduced metalloproteinase activity was also supported by markedly diminished mRNA expression of stromelysin-3 in the synovial tissue. Histologic analysis revealed marked reduction of polymorphonuclear cells in the synovial joint space in the IL-4-treated joints. This was confirmed by immunolocalization studies on knee joint sections using NIMP-R14 staining and diminished mRNA expression of macrophage-inflammatory protein-2 in the synovium tissue. mRNA levels of TNF-alpha and IL-1beta were suppressed as well, and IL-1beta and nitric oxide production by arthritic synovial tissue were strongly reduced. Our data show an impressive cartilage-protective effect of local IL-4 and underline the feasibility of local gene therapy with this cytokine in arthritis.     

A potent and selective nonpeptide antagonist of CXCR2 inhibits acute and chronic models of arthritis in the rabbit

Much evidence implicates IL-8 as a major mediator of inflammation and joint destruction in rheumatoid arthritis. The effects of IL-8 and its related ligands are mediated via two receptors, CXCR1 and CXCR2. In the present study, we demonstrate that a potent and selective nonpeptide antagonist of human CXCR2 potently inhibits (125)I-labeled human IL-8 binding to, and human IL-8-induced calcium mobilization mediated by, rabbit CXCR2 (IC(50) = 40.5 and 7.7 nM, respectively), but not rabbit CXCR1 (IC(50) = >1000 and 2200 nM, respectively). These data suggest that the rabbit is an appropriate species in which to examine the anti-inflammatory effects of a human CXCR2-selective antagonist. In two acute models of arthritis in the rabbit induced by knee joint injection of human IL-8 or LPS, and a chronic Ag (OVA)-induced arthritis model, administration of the antagonist at 25 mg/kg by mouth twice a day significantly reduced synovial fluid neutrophils, monocytes, and lymphocytes. In addition, in the more robust LPS- and OVA-induced arthritis models, which were characterized by increased levels of proinflammatory mediators in the synovial fluid, TNF-alpha, IL-8, PGE(2), leukotriene B(4), and leukotriene C(4) levels were significantly reduced, as was erythrocyte sedimentation rate, possibly as a result of the observed decreases in serum TNF-alpha and IL-8 levels. In vitro, the antagonist potently inhibited human IL-8-induced chemotaxis of rabbit neutrophils (IC(50) = 0.75 nM), suggesting that inhibition of leukocyte migration into the knee joint is a likely mechanism by which the CXCR2 antagonist modulates disease.     

Urokinase,a constitutive component of the inflamed synovial fluid,induces arthritis

Urokinase plasminogen activator (uPA) is an important regulator of fibrinolysis in synovial fluid. An increase of uPA activity and expression of its receptor have been reported in joints of patients with rheumatoid arthritis (RA). The aim of the present study was to assess the arthritogenic capacity of uPA and the mechanisms by which this effect is mediated. uPA was injected into the knee joints of healthy mice, and morphological signs of arthritis were assessed 4 days after the injection. The prerequisite of different leukocyte populations for the development of uPA-triggered arthritis was assessed by selective cell depletion. The inflammatory capacity of uPA was assessed in vitro. Finally, levels of uPA were measured in 67 paired blood and synovial fluid samples from RA patients. The synovial fluid from RA patients displayed higher levels of uPA compared with blood samples. Morphological signs of arthritis were found in 72% of uPA-injected joints compared with in only 18% of joints injected with PBS (P < 0.05). Synovitis was characterised by infiltration of CD4-Mac-1+ mononuclear cells, by the formation of pannus and by occasional cartilage destruction. The absence of monocytes and lymphocytes diminished the frequency of synovitis (P < 0.01), indicating an arthritogenic role of both these leukocyte populations. Synthetic uPA inhibitor downregulated the incidence of uPA-triggered arthritis by 50%. uPA induced arthritis, stimulating the release of proinflammatory cytokines IL-6, IL-1beta and tumour necrosis factor alpha. Accumulation of uPA locally in the joint cavity is a typical finding in erosive RA. uPA exerts potent arthritogenic properties and thus may be viewed as one of the essential mediators of joint inflammation.     

Synovial fluids from infected joints contain metalloproteinase--tissue inhibitor of metalloproteinase (TIMP) complexes.

Samples of synovial fluids aspirated from patients with septic arthritis prior to the commencement of any treatment contained active metalloproteinases but no proteinase inhibitory activity. We therefore assayed these samples for proteinase-inhibitor complexes. Although no biologically active alpha 2-macroglobulin or tissue inhibitor of metalloproteinase (TIMP) was present in the fluids, immunoassay of the samples clearly showed that high molecular weight proteinase-TIMP complexes were present. It is proposed that high levels of active metalloproteinases are released from neutrophils into septic synovial fluids and that these proteinases complex all the available TIMP, forming metalloproteinase-TIMP complexes.     

15-Hydroxy-eicosatetraenoic acid (15-HETE) inhibits carrageenan-induced experimental arthritis and reduces synovial fluid leukotriene B4 (LTB4)

15-Hydroxy-eicosatetraenoic acid (15-HETE), a product of arachidonic acid, has no proinflammatory capacity, but can inhibit the formation and the chemotactic response of neutrophils to leukotriene B4 (LTB4), a potent mediator of inflammation. The purpose of the present study was to determine whether intraarticular administration of 15-HETE in carrageenan-induced acute arthritis might decrease the levels of LTB4 in synovial fluid and modify the arthritis. A bilateral acute knee joint arthritis was established in 7 dogs by intraarticular injections of carrageenan every third day. To the right joints, 15-HETE was administered both concomitantly with the carrageenan injections and continuously via an osmotic pump. In samples of synovial fluid obtained on day 0, 3 and 10 PGE2 and LTB4 were determined using reversed phase high performance liquid chromatography combined with radioimmunoassays and neutrophil chemokinesis. In the presence of 15-HETE the clinical severity of arthritis was significantly reduced and the volume of synovial effusate was decreased on an average by 42%. Furthermore, the relative number of neutrophils in histological sections of synovial tissue was decreased by 58%. Intraarticular caragheenan injections induced LTB4 formation, and maximum levels were obtained on day 3 (279.2 +/- 148.2 pg/joint). PGE2 was also present on day 3, but maximum levels were detected on day 10 (9.5 +/- 4.8 ng/joint). In joints injected with both carragheenan and 15-HETE the levels of LTB4 on days 3 and 10 were inhibited by 90% and 83%, respectively. For PGE2 a small but insignificant decrease was found on both day 3 and on day 10. These results show that LTB4 may be an important mediator of acute arthritis induced by carragheenan in dogs, and that intraarticular administration of 15-HETE can modify this arthritis by inhibiting LTB4 formation.     

Interleukin-15 and interferon-gamma participate in the cross-talk between natural killer and monocytic cells required for tumour necrosis factor production

We have characterized the lymphocyte subset and the receptor molecules involved in inducing the secretion of TNF by monocytic cells in vitro. The TNF secreted by monocytic cells was measured when they were co-cultured with either resting or IL-15-stimulated lymphocytes, T cells, B cells or natural killer (NK) cells isolated from the peripheral blood of healthy subjects and from the synovial fluid from patients with inflammatory arthropathies. Co-culture with IL-15-activated peripheral blood or synovial fluid lymphocytes induced TNF production by monocytic cells within 24 hours, an effect that was mainly mediated by NK cells. In turn, monocytic cells induced CD69 expression and IFN-gamma production in NK cells, an effect that was mediated mainly by beta2 integrins and membrane-bound IL-15. Furthermore, IFN-gamma increased the production of membrane-bound IL-15 in monocytic cells. Blockade of beta2 integrins and membrane-bound IL-15 inhibited TNF production, whereas TNF synthesis increased in the presence of anti-CD48 and anti-CD244 (2B4) monoclonal antibodies. All these findings suggest that the cross-talk between NK cells and monocytes results in the sustained stimulation of TNF production. This phenomenon might be important in the pathogenesis of conditions such as rheumatoid arthritis in which the synthesis of TNF is enhanced.     

Angiogenesis in rheumatoid arthritis

There is much evidence that rheumatoid arthritis is closely linked to angiogenesis. Important angiogenic mediators have been demonstrated in synovium and tenosynovium of rheumatoid joints. VEGF (Vascular Endothelial Growth Factor), expressed in response to soluble mediators such as cytokines and growth factors and its receptors are the best characterized system in the angiogenesis regulation of rheumatoid joints. Moreover, other angiogenic mediators such as platelet-derived growth factor (PDGF), fibroblast growth factor-2 (FGF-2), epidermal growth factor (EGF), insulin-like growth factor (IGF), hepatocyte growth factor (HGF), transforming growth factor beta (TGF-beta), tumor necrosis factor alpha (TNF-alpha), interleukin-1 (IL-1), IL-6, IL-8, IL-13, IL-15, IL-18, angiogenin, platelet activating factor (PAF), angiopoietin, soluble adhesion molecules, endothelial mediator (endoglin) play an important role in angiogenesis in rheumatoid arthritis. On the other hand, endostatin, thrombospondin-1 and -2 are angiogenic inhibitors in rheumatoid arthritis. The persistence of inflammation in rheumatoid joints is a consequence of an imbalance between these inducers and inhibitors of angiogenesis.     

Mechanism of hypochlorite-mediated inactivation of proteinase inhibition by alpha 2-macroglobulin.

The proteinase-proteinase inhibitor balance plays an important role in mediating inflammation-associated tissue destruction. alpha 2-Macroglobulin (alpha 2M) is a high-affinity, broad-spectrum proteinase inhibitor found abundantly in plasma and interstitial fluids. Increased levels of alpha 2M and proteinase-alpha 2M complexes can be demonstrated in patients with sepsis, emphysema, peridontitis, rheumatoid arthritis, and other inflammatory diseases. Despite these increased levels, proteolysis remains a significant problem. We hypothesized that a mechanism for inactivating alpha 2M-mediated proteinase inhibition must exist and recently demonstrated that alpha 2M isolated from human rheumatoid arthritis synovial fluid is oxidized and has decreased functional activity. The oxidant responsible for alpha 2M inactivation and the mechanism of such destruction were not studied. We now report that while hypochlorite and hydroxyl radical both modify amino acid residues on alpha 2M, only hypochlorite can abolish the ability of alpha 2M to inhibit proteinases. Hydrogen peroxide, on the other hand, has no effect on alpha 2M structure or function. Protein unfolding with increased susceptibility to proteolytic cleavage appears to be involved in alpha 2M inactivation by oxidation. The in vivo relevance of this mechanism is supported by the presence of multiple cleavage fragments of alpha 2M in synovial fluid from patients with rheumatoid arthritis, where significant tissue destruction occurs, but not in patients with osteoarthritis. These results provide strong evidence that hypochlorite oxidation contributes to enhanced tissue destruction during inflammation by inactivating alpha 2M.     

Soluble IL-6 receptor governs IL-6 activity in experimental arthritis: blockade of arthritis severity by soluble glycoprotein 130

Studies in IL-6-deficient (IL-6(-/-)) mice highlight that IL-6 contributes to arthritis progression. However, the molecular mechanism controlling its activity in vivo remains unclear. Using an experimental arthritis model in IL-6(-/-) mice, we have established a critical role for the soluble IL-6R in joint inflammation. Although intra-articular administration of IL-6 itself was insufficient to reconstitute arthritis within these mice, a soluble IL-6R-IL-6 fusion protein (HYPER-IL-6) restored disease activity. Histopathological assessment of joint sections demonstrated that HYPER-IL-6 increased arthritis severity and controlled intrasynovial mononuclear leukocyte recruitment through the CC-chemokine CCL2. Activation of synovial fibroblasts by soluble IL-6R and IL-6 emphasized that these cells may represent the source of CCL2 in vivo. Specific blockade of soluble IL-6R signaling in wild-type mice using soluble gp130 ameliorated disease. Consequently, soluble IL-6R-mediated signaling represents a promising therapeutic target for the treatment of rheumatoid arthritis.     

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)-α, IL-1, and receptor activator of NF-κB ligand (RANKL). Additive or even synergistic effects with IL-1 and TNF-α 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.     

Effect of long-term treatment with platelet-activating factor on IL-1 and IL-2 production by rat spleen cells

To study the effect of the in vivo administration of platelet-activating factor (PAF) on cytokine production, alzet minipumps loaded with the mediator or solvent alone were connected to the jugular vein and placed under the skin of Sprague-Dawley rats. Over 7 days the animals received total doses of 0.5, 1, 4.5, 9, or 28 micrograms PAF or the solvent alone. The spleen mononuclear cells isolated from Ficoll gradients and the adherent cell fraction were separated before determination of basal and mitogen-stimulated IL-1 and IL-2 production, respectively. Adherent splenocytes from rats having received 28 micrograms PAF exhibited a decreased capability to produce IL-1, as compared to those from vehicle-treated animals. In contrast, adherent splenocytes from rats having received 9 and 4.5 micrograms PAF yielded higher amounts of released and cell-associated IL-1 activity upon LPS stimulation, as compared to those from solvent-treated animals. The PAF antagonist, BN 52021, given orally (5 mg/kg, twice a day throughout the experiments) inhibited the in vivo effect of 28 micrograms PAF. Statistically significant 144 +/- 43% (p less than 0.001, n = 5) and 73 +/- 33%, (p less than 0.01, n = 3) increases in IL-2 production were observed when whole spleen mononuclear cells from rats administered with 1 and 4.5 micrograms PAF, respectively, were stimulated with Con A. BN 52021 markedly inhibited the in vivo effect of 1 microgram PAF on the IL-2 release. Our study demonstrates that PAF can modulate immune functions in vivo and suggests that the specific PAF antagonist, BN 52021, may be used as an immunomodulatory agent.