NK cells from NKDxIL15tg mice spleens and bone marrow were purified by FACS. NK cells from IL15tg mice spleens were purified by FACS. Gene expression differences were analyzed to identify genes involved in NK cell development. Experiment Overall Design: Immature NK cells from NKDxIL15tg mice and mature NK cells from IL15tg mice were purified by FACS. RNA was made for target synthesis and hybridization to Affymetrix microarrays.