Surface phenotype of cells constituting the immature NK cell colonies. Thymocytes obtained from day 14 fetus were plated in methylcellulose culture with SF, IL-7, and IL-15. After 14 days of culture, immature NK cell colonies were individually picked, pooled, and stained with MoAbs specific for molecules indicated in each FACS profiles. Stained cells were analyzed by FACS Vantage using CellQuest software. Dotted and solid lines in each profiles represent cell stained with isotype-matched Ig and specific MoAbs, respectively.