Enhanced expansion of myelomonocytic cells in Flt3-ITD hemizygous mice. (A) Typical splenomegaly in Flt3^ITD/ITD (ITD/ITD) and Flt3^−/ITD (−/ITD) but not Flt3^+/ITD (+/ITD) mice. (B) Mean total cellularity of the PB, spleen, and BM for 9 to 18 mice of each genotype. Differential counts were performed on Giemsa-stained smears (PB) and slides after cytospin centrifugation (spleen and BM), on 3 to 5 mice of each genotype, all at 8 to 9 weeks of age. Differential results are displayed as mean ± SD as a proportion of mean total cellularity. (C-D) FACS was used to quantify Mac1^low/+c-Kit^low/+ myelomonocytic immature cells (C) and CD19⁺ B cells (D) in PB, spleen, and BM from age-matched littermates of mutant and WT (+/+) animals (mean ± SD; 6-9 male mice at 8-9 weeks of age per genotype) in at least 2 independent experiments. *P < .05. **P < .01. ***P < .001.