Objective: To examine the cellular mechanisms by which the proinflammatory cytokine interleukin-17 (IL-17) induces the synthesis of 92-kd gelatinase (matrix metalloproteinase 9 [MMP-9]) by human monocyte/ macrophages in primary culture.
Methods: IL-17-stimulated human monocytes isolated from the peripheral blood of healthy donors were cultured in the presence of antiinflammatory cytokines, neutralizing antibodies against IL-1beta, tumor necrosis factor alpha (TNFalpha), or IL-1 receptor antagonist, and with protein kinase inhibitors of diverse specificity. MMP measurements were performed using specific enzyme-linked immunosorbent assays, while the expression of specific messenger RNA was determined by Northern blotting. Detection of phosphorylated proteins and specific transcriptional factors was performed by Western blotting and by gel retardation experiments, respectively.
Results: Biologically active IL-17 was detected in the synovial fluid of patients with rheumatoid arthritis. IL-17-induced MMP-9 production in human monocyte/ macrophages was dependent on endogenous prostaglandin E2 synthesis and related to autocrine stimulation by TNFalpha, but was IL-1beta independent. This activation involves both p42/44 and p38 kinases and nuclear factor kappaB. IL-17-inducible activator protein 1 and signal transducer and activator of transcription 1/3 may transactivate the MMP-9 promoter.
Conclusion: IL-17 may contribute to an unbalanced production of proinflammatory cytokines and MMP-9 in diseased articular joint tissues by interacting with the macrophages in the rheumatoid synovium.