Regulation of NK function and activation markers by PPAR-γ natural ligand, 15d-PGJ₂. (A) Inhibition of IFN-γ production in human NK cells. Human NK cells were treated with or without different dosages of 15d-PGJ₂ for 30 minutes and then treated with IL-2 for 8 hours. The supernatant was collected to measure IFN-γ concentration. (B) Inhibition of cytolytic activity of human NK cells. Purified human NK cells were pretreated with or without 15d-PGJ₂ (2 μM) for 1 hour and incubated with or without IL-2 (200 U/mL) for an additional 1 hour. The cells were then washed with RPMI 1640 without serum 3 times and incubated with ⁵¹Cr-loaded K564 cells for 4 hours as described in “Materials and methods.” (C) Repression of CD69 expression in activated human NK cells. Freshly isolated human NK cells were treated with different dosages of 15d-PGJ2 or ciglitazone for 30 minutes and then treated with IL-2 (200 U/mL) for 8 hours. The cells were then stained with fluorochrome-conjugated anti-CDs antibodies (APC-anti-CD56, FITC-anti-CD44, and PE-anti-CD69, respectively). Relative expression level of CD69 (mean fluorescence intensity percentage) is presented. Data represent the average from 3 different donors (mean ± SE). ^*Statistically significant changes compared with control samples (P < .05).