IL-15 induces KIR expression in KIR-negative NK cells. KIR-negative NK cells were isolated from adult peripheral blood and stimulated with 10 ng/mL IL-15 for 48 to 120 hours. (A) FACS analysis was performed at baseline before culture and 120 hours after IL-15 stimulation staining with a cocktail of APC-conjugated NCAM16.2 and PE-conjugated DX9, EB6, GL183, and FES172 monoclonal antibodies (n = 9). (B) Proximal coding KIR transcript and distal KIR transcript levels were measured after 48 and 120 hours by quantitative RT-PCR. Values are presented as a ratio of gene expression after 2 and 5 days compared with gene expression at the initial purification (n = 9). Error bars represent the SEM. *P < .05.