Fig. 4.

PPARγ ligand production by IL-1β-activated HLFs is temporally regulated. HLFs were treated with IL-1β (1 ng/ml) for 24 h, supernatants were removed, the cells were washed with 1× PBS, fresh medium was added; all medium was removed and replaced every 24 h thereafter. Supernatants were tested for PPARγ activity using a PPRE-luciferase reporter (A), IL-6 by ELISA (B), and PGE₂ by EIA (C). In cell lysates, COX-2 protein levels were determined by Western blotting (D). PPARγ ligand production was evident by day 2 after IL-1β treatment, peaked on day 3, and returned to baseline by day 5. By contrast, IL-6 levels peaked on day 1 and returned to baseline by day 3. PGE₂ levels trailed COX-2 induction, peaking on day 2 and then steadily declining. Values are means ± SD of 3–4 independent biological replicates per dose. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001 vs. untreated (by unpaired t-test).