Figure 2.

Surface phenotype of Ras–RAG B lineage cells. Lymphocytes isolated from lymph node of Ras–RAG1^−/−, RAG2-deficient chimera, RAG2^−/−, and wild-type (129 Sv/Ev) mice were subjected to FACS^® analyses. Depicted are log-scale dot plots of B220 versus CD43, IgM, CD23, and CD21/CD35. The plots reflect 20,000 collected events, with dead cells excluded by forward and side scatter. Similar results were found in the spleen. Results shown are representative of those obtained in the analysis of six chimeric mice derived from two independent transfected ES clones. The number of B220⁺Ly9.1⁺ cells in these RAG2-deficient chimeras ranged from 5 × 10⁵ to 1.6 × 10⁷ in lymph node and 2 × 10⁶ to 7 × 10⁶ in spleen. Chimeric animals analyzed for evidence of B cell developmental progression showed no gross evidence of malignancy. Older chimeric mice do tend to develop B lineage lymphomas, but such transformed cells are significantly larger in cell size and have markedly altered surface antigen staining characteristics (data not shown). Ras-Rag, activated Ras-complemented-RAG1^–/–, RAG2-deficient chimera; Rag, RAG2^−/− mouse.