Expression of pro-resorptive cytokines by monosodium urate monohydrate (MSU) crystals. (a) Freshly isolated peripheral blood mononuclear cells (PBMCs) from healthy control subjects were cultured for the indicated times (hours) in the presence of MSU crystals (100 μg/ml). (b) PBMCs from same donors were cultured for the indicated times (that is, 4 hours for cytokines and 72 hours for receptor activator of nuclear factor κB ligand RANKL) at various MSU crystal concentration (μg/ml). (c, d) Monocytes and T cells were isolated from PBMCs by magnetic-activated cell sorting. Freshly isolated monocytes and T cells from healthy control subjects were cultured for the indicated times (hours) in the presence of MSU crystals (100 μg/ml). Total RNA was collected at each time point and at the different MSU crystal concentrations. Reverse transcription-polymerase chain reaction (RT-PCR) was performed to determine the expressions of interleukin (IL)-1α, IL-β, IL-6, tumor necrosis factor (TNF)-α, osteoprotegerin (OPG), and RANKL. Results are representative of three independent experiments.