iNOS gene expression in unstimulated and IL-12- or/and TNF-treated NK cells. NK cells were stimulated for 7 hours in the absence (lane 1) or presence of IL-12 (5 U/mL) (lane 2), IL-12 and TNF (lane 3), or TNF (20 ng/mL) (lane 4), and then mRNA was extracted. The presence of iNOS mRNA was analyzed by RT-PCR, as described in Materials and Methods. Data are from one representative experiment of seven that gave comparable results.