Generation of mature B-1 and B-2 cells in vivo occurs independently of c-kit–mediated signals. A total of 8 × 10⁵ total FL cells from day 13 wildtype or W/W mice were injected intravenously into 4Gy irradiated RAG-2^−/− mice. Twenty-five days after cell transfer, the reconstituted mice were analyzed for the presence of IgM⁺ cells in peripheral blood (PBL), peritoneal cavity (Periton) and spleen (SP). Total cell counts in various tissues are shown on top of each panel. Wildtype C57BL/6 (top row), unreconstituted RAG-2^−/− mice (second row), RAG-2^−/− mice reconstituted with W/W FL cells (third row) or those reconstituted with wildtype FL cells (fourth row) were analyzed by two-color flow cytometry for expression of B220 versus IgM (PBL), and CD5 versus IgM (Periton and SP). Note that CD5⁺IgM⁺ as well as CD5⁺IgM⁺ cells appeared in both types of reconstituted mice (third and fourth row).