Analysis of ID2^gfp expression in NK cell progenitors. (A) BM-derived NKP cells from Id2^gfp/gfp mice, identified by their expression of CD122 and lack of NK1.1, DX5, and the lineage (lin) markers CD3, CD8, CD11b, CD19, Gr-1, and Ter119, were analyzed for ID2^gfp expression (n = 3). (B) ID2^gfp expression in lin⁻Sca-1⁺CD117^{intermediate (int)} BM cells derived from Id2^gfp/gfp mice (n > 5). (C-D) Expression of Sca-1, CD117, CD127, CD135, and ID2^gfp within the lin⁻ BM cells of Id2^gfp/gfp mice. Progenitor populations were electronically gated as indicated (n > 5). For panels A and C, numbers in the plots indicate the percentage of cells within the boxed region. Pre-pro NK a cells represented 0.056% ± 0.017% of lin⁻ BM cells (1893 ± 585 cells/2 femurs, n = 4) and pre-pro NK b cells represented 0.283% ± 0.115% of lin⁻ BM cells (9614 ± 3920 cells/2 femurs, n = 4). (D) CLP (lin⁻Sca-1⁺CD117^intCD127⁺CD135⁺), pre-pro NK a (lin⁻Sca-1⁺CD117^intCD127⁺CD135⁻), and pre-pro NK b (lin⁻Sca-1⁺CD117⁻CD127⁺CD135⁻) cells (gated as in panel C) and mature NK cells (NK1.1⁺CD49b⁺) were analyzed for ID2^gfp expression (n > 5). Mean fluorescence index of GFP of the indicated populations is shown. (E) Multipotent progenitors (MPP, lin⁻Sca1⁺CD117⁺CD135⁺CD127⁻), CLP, pre-pro NK a, and pre-pro NK b progenitor cells were sorted from Id2^gfp/gfp bone marrow by flow cytometry and cultured for 7 days in IL-7 and IL-15 on OP9 stromal cells (n = 2). Numbers indicate the percentage of NK1.1⁺ NK cells in the cultures.