Effects on extramedullary hematopoiesis of 4 weeks of daily IFNα on Jak2^VF chimeric mice. (A) Reduced spleen WCC after IFNα (vehicle 149.6 ± 44.1 × 10⁶ vs IFNα 100 ± 27.1 × 10⁶; P < .01; n = 9-10). (B) Reduced spleen weight after IFNα (vehicle 262 ± 51.2 mg vs IFNα 192 ± 40.6 mg; P ≤ .01; n = 9-10) (C) Representative flow cytometry plots showing maturation of erythropoiesis in WT and vehicle- and IFNα-treated mice. Early erythropoiesis is CD71^high, late erythropoiesis is CD71^mid-lowTer119⁺. (D) Representative histogram plots demonstrating annexin V staining on early erythroid cells. (E) Total early erythropoiesis reduced in IFNα-treated mice (vehicle 87.2 ± 8.0 × 10⁶/spleen vs IFNα 27.6 ± 5.0 × 10⁶/spleen; P < .01; n = 9-10) (F) No change in total late erythropoiesis (vehicle 44.3 ± 5.7 × 10⁶/spleen vs IFNα 54.4 ± 6.0 × 10⁶/spleen; P = .24; n = 9-10). Each data point represents an individual mouse. Data shown are pooled results from 2 independent experiments. (G) Apoptosis in early erythroid precursors increased after IFNα treatment (vehicle 12.3 ± 2.4% vs IFNα 42.4 ± 1.7; P < .01; n = 5). Apoptosis in late erythroid precursors increased after IFNα treatment (vehicle 3.7 ± 0.6% vs IFNα 16.4 ± 1.3; P < .01; n = 5). Results given are mean ± standard deviation.