IL-33 (or IL-1F11) was recently identified as a ligand for the previously orphaned IL-1 family receptor T1/ST2. Previous studies have established that IL-33 and T1/ST2 exert key functions in Th2 responses. In this study, we demonstrate that IL-33 induces the production of pro-inflammatory mediators in mast cells. IL-33 dose and time-dependently stimulated IL-6 secretion by P815 mastocytoma cells and primary mouse bone marrow-derived mast cells (BMMC). This effect was dependent on T1/ST2 binding. In addition, IL-33 also induced IL-1b, TNF-a, MCP-1, and PGD2 production in BMMC. By RNase protection assay, we demonstrated that IL-33 increased IL-6 and IL-1b mRNA expression. These effects of IL-33 appeared to occur independently of mast cell degranulation, The results of this study show for the first time that IL-33, a novel member of the IL-1 family of cytokines, stimulates the production of pro-inflammatory mediators by mast cells in addition to its effect on T helper 2 responses. These findings open new perspectives for the treatment of inflammatory diseases by targeting IL-33.
Interleukin-4, which has been contemplated for the treatment of rheumatoid arthritis and/or osteoarthritis because of its anticatabolic properties, has also been shown to modulate apoptosis. Because inadequate apoptosis is thought to contribute to synovial hyperplasia, we have investigated the ability of IL-4 and other Th2 cytokines to protect human synovial cells from apoptosis. Human synoviocytes or synovial explants were pretreated with IL-4, IL-10, and IL-13 before exposure to NO donor sodium-nitro-prusside (SNP). Apoptosis was evaluated by microscopy, annexin V-FITC, 3-(4,5-dimethylthiazol-2-gl)-5-(3-carboxymethoxylphenyl)-2-(4-sulphophenyl-2H tetrazolium inner salt (MTS) test, pulse field gel electrophoresis, and a method proposed in this study based on 32P Klenow end labeling of high m.w. DNA. Pretreatment by IL-4 or IL-13, but not IL-10, protected human synoviocytes from apoptosis induced by SNP. Even at doses as high as 2 mM SNP, up to 86% and 56% protection was achieved, after IL-4 and IL-13 treatment, respectively. Cell survival was dependent on IL concentration. IL-4 and IL-13 also had antiapoptotic effects on SNP-treated human synovial explants. Effects of IL-4 and IL-13 varied in the presence of phosphatidylinositol-3 kinase and protein kinase C inhibitors, implying the involvement of these pathways in antiapoptotic signaling. Antiapoptotic effects were dramatically inhibited by LY294002, and partially by the protein kinase C inhibitor Gö 6976, while insulin-like growth factor increased synoviocyte survival. The possibility that IL-4 and IL-13 may enhance synovial expansion in vivo by their antiapoptotic effects is discussed.
Higher concentrations of TNF-alpha were found in EF from patients with radiculopathy from HD compared with patients suffering from other type of back pain. These results support the role of TNF-alpha in the pathogenesis of radiculopathy from HD.
Six novel members of the IL-1 family of cytokines were recently identified, primarily through the use of DNA database searches for IL-1 homologues, and were named IL-1F5 to IL-1F10. In the present study, we investigated the effect of IL-1F8 on primary human joint cells, and examined the expression of the new IL-1 family members in human and mouse joints. Human synovial fibroblasts (hSFs) and human articular chondrocytes (hACs) expressed the IL-1F8 receptor (IL-1Rrp2) and produced proinflammatory mediators in response to recombinant IL-1F8. IL-1F8 mRNA expression was increased in hSFs upon stimulation with proinflammatory cytokines, whereas in hACs IL-1F8 mRNA expression was constitutive. However, IL-1F8 protein was undetectable in hSF and hAC culture supernatants. Furthermore, although IL-1β protein levels were increased in inflamed human and mouse joint tissue, IL-1F8 protein levels were not. IL-1F8 levels in synovial fluids were similar to or lower than those in matched serum samples, suggesting that the joint itself is not a major source of IL-1F8. Serum levels of IL-1F8 were similar in healthy donors, and patients with rheumatoid arthritis, osteoarthritis and septic shock, and did not correlate with inflammatory status. Interestingly however, we observed high IL-1F8 levels in several serum samples in all groups. In conclusion, IL-1F8 exerts proinflammatory effects in primary human joint cells. Joint and serum IL-1F8 protein levels did not correlate with inflammation, but they were high in some human serum samples tested, including samples from patients with rheumatoid arthritis. It remains to be determined whether circulating IL-1F8 can contribute to joint inflammation in rheumatoid arthritis.
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