IKDCs differ from otherwise similar Ly6C⁺ pDCs with respect to RAG-1 and patterns of gene expression. (A) The B220⁺RAG-1/GFP⁺ population freshly isolated from BM did not include IKDCs. (B) Conversely, BM IKDCs do not express RAG-1 detectable in RAG-1/GFP reporter mice or by RT-PCR. (C) Transcripts for a series of genes were measured in highly purified cells by RT-PCR. (D) Wild-type mice were compared with Id2 gene–targeted animals (Id2^−/−) by flow cytometry. Mean ± SEM values are shown for NK1.1⁺ CD11c⁻ NK cells, B220⁺CD11c⁺CD19⁻Ly-6C⁻ NK1.1⁺ IKDCs, and B220⁺CD11c⁺CD19⁻Ly-6C⁺NK1.1⁻ pDCs in BM. (E) Rigorously sorted DC subsets were placed in overnight cultures with CpG ODN, and supernatants were tested for the 3 indicated cytokines. The results are representative of 3 independent experiments.