Expression of RANK-L, OPG, RANK, and TRAF6 mRNAs by synovial fluid (SF) neutrophils isolated from patients with rheumatoid arthritis (RA) and by normal blood cells. (a) Purified neutrophils of SF from four patients with RA and of blood from seven normal donors were evaluated by semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analyses. (b) Purified peripheral blood mononuclear leukocytes (PBMLs) and platelets of blood from seven normal donors were evaluated by semi-quantitative RT-PCR analyses. To avoid leukocyte contamination in the platelet suspension, platelets were isolated from the upper part of the platelet-rich plasma (PRP). After centrifugation (600 g, 30 minutes), the pellets were resuspended in Trizol. No contaminating leukocytes in the upper part of the PRP were observed under light microscopy after Wright's stain. Histograms represent mean ± standard error of the mean of ratios of densitometric values for RANK-L/β-actin, OPG/β-actin, RANK/β-actin, and TRAF6/β-actin. OPG, osteoprotegerin; RANK, receptor activator of nuclear factor-kappa-B; RANK-L, ligand of receptor activator of nuclear factor-kappa-B; TRAF6, tumor necrosis factor receptor-associated factor 6.