Ifnar1 deletion does not impair proliferation or promote death or neonatal HSCs or MPPs. (A,B) Cell cycle distributions of HSCs (CD150⁺CD48^-LSK) and MPPs (CD48⁺LSK) as measured using Ki67/DAPI staining, n = 5-6. (C-F) Percentages of P0 HSCs, MPPs, pGMs, or GMPs in S/G2/M phase of the cell cycle in Ifnar1^+/- and Ifnar1^–/–-mice, as measured by propidium iodine staining, n = 4-9. (G) Percentage of BrdU-positive MPPs (CD48⁺LSK) after a 24 hour pulse between E19 and P0, n = 4-10. (H) Percentage of P14 MPPs (CD48⁺LSK), in S/G2/M phase of the cell cycle as measured by propidium iodine staining n = 5-6. (I) Percentage of Annexin V⁺, DAPI-negative apoptotic HSCs, MPPs, pGM, and GMP in the P0 livers of Ifnar1^+/– and Ifnar1^–/–mice, n = 6-15. For all panels, error bars reflect standard deviation. Representative gating strategies are shown in supplemental Figure 5. ∗∗∗P < .001; ∗P < .05 using two-tailed t test. (J) CFU assays for individually plated MPP2, MPP3, MPP4, or LK cells. Error bars reflect standard deviations from 3 independent experiments with at least 60 cells plated per population per experiment.