Flow cytometry of peripheral blood and bone marrow of 13-week-old well-appearing Eμ-ret (Tg⁺) littermates and transgene-negative (Tg⁻) mice. (A) Density separated peripheral blood lymphocytes were stained for CD45R and IgM expression. Varying amounts of an abnormal population of CD45R⁺sIgM⁻ B precursor cells are present in the Eμ-ret mice. (B) CD45R⁺CD43⁺ gated bone marrow cells from the above Eμ-ret mice along with a Tg⁻ littermate were resolved by BP-1 and CD24 staining into the pro–B cell Fr A through C and early pre–B Fr C′. Eμ-ret mouse 2-7 was an 11-week-old with splenomegaly and adenopathy.