Leukemogenic effects of the Ptpn11^E76K/+mutation in the stem-cell microenvironment is abolished in Ptpn11^E76K/+Prx1-Cre⁺CCL3^−/− mice. (A) White blood cell counts in the peripheral blood (PB) of Ptpn11^E76K/+Prx1-Cre⁺CCL3^−/−, Ptpn11^E76K/+Prx1-Cre⁺, CCL3^−/−, and Ptpn11^+/+Prx1-Cre⁺ mice (n = 5 mice per group) were determined at the indicated ages. (B-G) Ptpn11^E76K/+Prx1-Cre⁺CCL3^−/−, Ptpn11^E76K/+Prx1-Cre⁺, CCL3^−/−, and Ptpn11^+/+Prx1-Cre⁺ mice were sacrificed at age 12 to 17 months. Spleen weights were documented (n = 7 mice per group) (B). Mac-1⁺Gr-1^hi cells in the BM, spleen, liver, lung, and PB (n = 7 mice per group for BM, spleen, liver, and lung; n = 5 mice per group for PB) (C left), Mac-1⁺Gr-1^low cells in the BM (n = 7 mice per group) (C right), and CD115⁺Gr-1^low cells in the BM, spleen, liver, lung, and PB (n = 7 mice per group for BM, spleen, liver, and lung; n = 5 mice per group for PB) (D) were determined. Femurs, spleens, livers, and lungs were processed for histopathological examination (hematoxylin and eosin staining; n = 3 mice per group). Representative pictures are shown (E). The pool size of HSCs (Lin⁻Sca-1⁺c-Kit⁺CD150⁺CD48⁻Flk2⁻) in the BM (n = 7 mice per group) (F), and the cell-cycle distribution of HSCs in the BM (n = 7 mice per group) (G) were determined by multiparameter fluorescence-activated cell sorting. Data shown are mean ± standard deviation of all mice examined. **P < .01; ***P < .001.