Poly I:C induces MKK3/6 and p38 MAPK activation in human NK cells. (A) Highly purified cultured NK (10 × 10⁶ per sample), (B) NK92 (4 × 10⁶ per sample), and (C) NKL (4 × 10⁶ per sample) cells were stimulated with poly I:C at 37°C for the indicated times. Cell lysates were electrophoresed under reducing condition and blotted with antiphospho-MKK3/6 and anti-MKK3 (top panels) or antiphospho-p38 and anti-p38 Ab (bottom panels). PMA (50 ng/mL)/ionomycin (0.5 μM) (P/I) stimulation was used as positive control. These data are representative of 1 out of at least 4 independent experiments.