Assessment of the Axl/Gas6 pathway in purified mature NK cells. (A) After total RNA was isolated from sorted fresh human CD34⁺ HPCs (34⁺), CD56^bright (bright), or CD56^dim (dim) NK cells, RT-PCR was performed to detect Gas6, Axl, Sky, and Mer mRNA. GAPDH was used as a loading control. The figure represents 1 of 2 experiments performed with separate donors. (B) Purified CD56^bright and CD56^dim NK cells were sorted from human peripheral blood, plated with the same cell numbers, and stimulated with IL-12 and IL-15 in the presence of irrelevant Fc or Axl-Fc for 24 hours. Supernatants were collected and IFN-γ production was measured by ELISA. Results illustrate the mean plus or minus SD from triplicate wells and represent 1 of 3 similar experiments showing no significant difference in the presence or absence of Axl-Fc for CD56^bright or CD56^dim NK cells. (C) CD56^bright and CD56^dim NK cells were prepared as described in panel B and cultured with IL-15 in the presence of irrelevant Fc or Axl-Fc for 24 hours and then mixed with ⁵¹Cr-labeled K-562 target cells at an effector:target ratio of 3:1, again without significant difference. These results are representative of 3 similar experiments.