Pro-resorptive cytokine expression and osteoclastogenesis in the synovial fluid of patients with gouty arthritis. Six paired samples of peripheral blood and synovial fluid were obtained from gouty arthritis patients with knee effusion. (a, b) Expression of mRNA for interleukin (IL)-1α, IL-β, IL-6, tumor necrosis factor (TNF)-α, receptor activator of nuclear factor κB ligand (RANKL) and osteoprotegerin (OPG) in peripheral blood mononuclear cells (PBMCs) and synovial fluid mononuclear cells (SFMCs). Reverse transcription-polymerase chain reaction (RT-PCR) (a) and real-time PCR (b) were performed to determine the mRNA expression of each gene. (c, d) T cell involvement in osteoclastogenesis of SFMCs from patients with gouty arthritis. PBMCs, SFMCs, and T cell-depleted SFMCs (3 × 105 cells/well) were cultured for 10 days in the presence of macrophage colony-stimulating factor (M-CSF; 30 ng/ml) at the different RANKL concentrations and then were stained for tartrate-resistant acid phosphatase (TRAP). TRAP-positive multinucleated cells (MNCs) were counted in triplicate. Results are representative of six independent experiments (a and upper panels in c and d). Data in b and lower panel in c are means ± SEMs. Scale bars in c and d = 50 μm. * = P < 0.05, by Wilcoxon signed rank test.