Each FLT3 mutant induces splenomegaly. Comparison of spleen size (left) and immunophenotype of spleen cells from mice receiving bone marrow transduced with distinct FLT3 mutants. Two-parameter dot plots (right) show expression of lineage-specific antigens (CD11b, B-220, Thy1.2, CD4, CD8) versus EGFP. Numbers indicate the percentage of cells in each quadrant.