Objective: To determine the signal transduction pathways in CD14+ synovial cells from patients with rheumatoid arthritis (RA) after CD40 ligation, and to examine their role in amplifying synovial inflammation in affected joints.
Methods: Expression of messenger RNA was analyzed using quantitative reverse transcription-polymerase chain reaction. Cytokines and chemokines were measured using enzyme-linked immunosorbent assay. Activation of kinases was detected using Western blotting. Nuclear translocation of NF-kappaB was examined using immunohistochemistry. CD14+ synovial cells were enriched using magnetic cell sorting. Fibroblast-like synoviocytes (FLS) were obtained by passaging primary synovial cell culture.
Results: Stimulation of CD14+ synovial cells from RA patients by recombinant soluble CD154 (rsCD154) significantly induced expression of tumor necrosis factor alpha (TNFalpha), interleukin-1alpha (IL-1alpha), and IL-1beta. CD14+ RA synovial cells stimulated with rsCD154 plus interferon-gamma (IFNgamma) induced significantly higher production of IL-6, IL-8, and monocyte chemoattractant protein 1 by FLS compared with unstimulated CD14+ synovial cells, through TNFalpha-, IL-1alpha-, and IL-1beta-mediated pathways. Stimulation with rsCD154 plus IFNgamma induced the activation of ERK-1/2, p38 MAPK, and NF-kappaB. Specific inhibitors of MAPK/ERK-1/2 kinases and p38 MAPK significantly reduced the production of TNFalpha and IL-1beta by rsCD154 plus IFNgamma-stimulated CD14+ synovial cells, and also inhibited production of these cytokines by freshly isolated synovial cells from RA patients.
Conclusion: These data indicate that the CD40-CD154 interaction activates the ERK, p38, and NF-kappaB pathways in CD14+ synovial cells from RA patients to produce TNFalpha, IL-1alpha, and IL-1beta, which in turn amplifies inflammatory responses by stimulating FLS. Inhibition of the CD40-CD154 interaction or its signal transduction pathways would be a strong and efficient strategy for the management of synovial inflammation in RA.