Endogenous BM B cells from Rag2°IL2Rβ° and Flt3IL7Rα° mice and B cells generated after reconstitution of these recipient mice. (A) CD19 versus NK1.1 profile of the bone marrow cells of the different recipient mice. Shown are CD3-negative bone marrow lymphocytes. Note that the CD19⁺ in the C57Bl/6 mouse contain Ig^– precursor (pro– and pre–B cells) as well as Ig⁺ immature and mature B cells, while in the Rag2°IL2Rβ° mouse CD19⁺ cells only comprise pro–B cells, as B-cell development is arrested at the transition of the pro– to pre–B-cell stage (according to Hardy et al¹⁷ ) due to the Rag2-mutation. Absolute cell numbers for CD19⁺ and NK1.1⁺CD3^– cells are given. (B) CD19 versus CD25 profiles. Phenotype of the bone marrow B cells from reconstituted Rag°IL2Rβ° and Flt3IL7Rα° mice, then weeks after transplantation with 1 × 10⁴ sorted Lin^–cKit⁺Sca1⁺ cells from wild-type C57Bl/6Ly5.1 mice. Age-matched C57Bl/6Ly5.1 mice were used for control. (C) Profiles of CD19 versus IgM. Shown are CD45.1⁺PI^– cells falling in a lymphocyte gate. One representative analysis of at least 3 experiments is shown. Numbers indicate the absolute cell number in the respective quadrant. The dotted line separates the flow cytometric results from the unmanipulated C57Bl/6Ly5.1 from that of the reconstituted recipient mice.