Effect of PPAR-γ activation on NK cytolytic activity. (A) PPAR-γ-null NK92 cells were preincubated with different concentrations of 15d-PGJ₂ for 1 hour, and the cells were washed 3 times with RPMI 1640 without serum. The washed cells were incubated with ⁵¹Cr-loaded K562 cells for 4 hours. The detailed procedures are described in “Materials and methods.” (B) Effect of ciglitazone, a synthetic ligand for PPAR-γ, on cytolytic activity of NK92 cells. PPAR-γ-null NK92 cells were preincubated with different concentrations of ciglitazone for 30 minutes. The remaining procedures were identical to those described in panel A. Inhibition of cytolytic activity of PPAR-γ-positive NKL cells by 15d-PGJ₂ but not ciglitazone. NKL cells without IL-4 priming (C) or NKL cells with IL-4 priming (D,E) were pretreated with either 15d-PGJ₂ (3 μM) (C,D) or ciglitazone (3 μM) (E) for 1 hour and then were incubated with or without IL-2 (200 U/mL) for another 1 hour. The cells were washed with RPMI 1640 without serum 3 times and incubated with ⁵¹Cr-loaded K564 cells for 4 hours. The detailed procedures are described in “Materials and methods.” All values are means ± SEM from 3 independent experiments. (F) Effect of 15d-PGJ₂ on conjugation formation. NK92 cells were incubated with 400 nM Ca-AM for green labeling, and K562 cells were labeled red with 250 μM HE. The percentage of conjugated effector or target cells was determined by gating the green and dual-labeled events or the red and dual-labeled events, respectively. Data are shown as a bar presentation of the data obtained from flow cytometry analysis of conjugation formation. Data represent the average from 3 different experiments (mean ± SE).