Comparison of the relative inhibitory activity of HIG-82-IL-1Ra+ cells to recombinant IL-1Ra following periodic dilution. Experiments were performed identically to those described for Fig. 3, except that at 24 hour intervals after IL-1 stimulation one half of the conditioned media in each well was removed and replaced with fresh media. As before, the PGE2 and IL-1Ra concentrations in the recovered media were measured using ELISA. Experiments were performed in triplicate, and each data point repesents the mean value ± SD. *P < 0.05 versus corresponding IL-1Ra source at 24 hours. ELISA, enzyme-linked immunosorbent assay; IL-1Ra, IL-1 receptor antagonist; PGE2, prostaglandin E2.