Comparison of the relative inhibitory activity of HIG-82-IL-1Ra+ cells to recombinant IL-1Ra when added to HSF cultures 24 hours before stimulation with IL-1β. As in Fig. 1, HSF were plated in multiwell plates and incubated with a range of doses of rIL-1Ra or HIG-82-IL-1Ra+ cells. Twenty-four hours following the addition of the protein or cells, 5 ng recombinant IL-1β was added, and the cultures were incubated an additional 48 hours. PGE2 production at 48 hours after IL-1stimulation for the IL-1Ra treated groups was normalized to control, namely IL-1 stimulated HSF cultures that did not receive IL-1Ra. Shown in the graph is the relationship between PGE2 production at48 hours after IL-1 stimulation, and IL-1Ra concentration immediately before and 48 hours after IL-1 stimulation. PGE2/IL-1Ra levels for cultures receiving the IL-1Ra producing cells are represented by triangles; black indicates before IL-1 stimulation and white indicates 48 hours after. The shaded boxes represent the PGE2/IL-1Ra levels for cultures receiving recombinant IL-1Ra. A single set of data points is shown for the wells receiving the recombinant protein because the IL-1Ra concentration did not change over time. The shaded region between the curves is shown to emphasize the change in IL-1Ra levels over time in the wells receiving the IL-1Ra producing cells. Experiments were performed in triplicate, and each data point repesents the mean value ± SD. HSF, human synovial fibroblast; IL-1Ra, IL-1 receptor antagonist; PGE2, prostaglandin E2.