Inhibitory effects of neutralizing antibodies to cytokines on the SF-mediated proliferation capacity of RA FLSs. Rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLSs; 2–14) at passage 12, at a concentration of 5 × 103 cells per well in a 24-well plate, were cultured in the presence of synovial fluid (SF) at a dilution of 1/10 or in the presence of SF together with anti-granulocyte – macrophage colony-stimulating factor (300 ng/ml), anti-IL-1β (500 ng/ml) or anti-TNF-α (2 μg/ml) neutralizing antibodies. RA FLSs were preincubated for 1 hour with these neutralizing antibodies. Two different SFs were added every 2 days in the presence or absence of neutralizing monoclonal antibody. Cells were harvested every 2 days and their viability was assessed by trypan blue staining. The results are means ± SD obtained from single experiments performed in triplicate cultures. *p < 0.01; **p < 0.05.