Constant exposure to IFN-γ alters the composition of HSPCs. (A) HSPC composition was gated on lineage-negative BM cells by using flow cytometry, LT-HSCs (lin^–cKit⁺Sca1^hiCD34^–Flt3^–), ST-HSCs (lin^–cKit⁺Sca1^hiCD34⁺Flt3^–), MPPs (lin^–cKit⁺Sca1^hiCD34⁺Flt3⁺), common lymphoid progenitors (CLPs; lin^–cKit^intSca1^intIL-7R⁺), CMPs (lin⁻cKit⁺Sca1^–CD34⁺CD16/32^int), GMPs (lin⁻cKit⁺Sca1⁻CD34⁺CD16/32^hi), and MEPs (lin⁻cKit⁺Sca1^–CD34^–CD16/32^lo) (n = 7). The bar graph shows the total cell number of each cell type. Density plots are representative of HSPC gating from 1 set of 4 experiments. (B) The lin^–cKit⁺Sca1^hiCD34^–Flt3⁺CD150⁺ population was used to confirm HSC composition. The bar graph shows the total cell number (n = 5). (C) The function of CMPs, GMPs, and MEPs was analyzed by using a colony-forming assay. Lineage-negative BM cells were plated in triplicate, and the colonies were counted after culture for 7 days. The numbers of each colony are shown. (D) Apoptosis in HSPC was assessed by using Annexin V staining and Fixable Viability Dye eFluor 660. The Annexin V–positive/Viability Dye–negative population represents apoptotic cells. The bar graph shows the percentage of apoptotic cells in the LSK or LK population (n = 4). Density plots are representative of 1 set of 4 experiments. (E) The proliferation of HSPCs was determined by the expression level of Ki-67. The bar graph shows the medium fluorescent intensity (MFI) of Ki-67 cells in the LSK or LK population. Histograms are representative of 1 set of 4 experiments. All experiments were performed at least 3 times. Similar results were obtained from 3 different experiments. Results are expressed as mean ± SD. *P < .05; **P < .01; ***P < .001; ****P < .0001. N.D., not detectable.