Loss of P21 reduces apoptosis of β-thalassemia erythroid cells. (A) Flow cytometric analysis of apoptosis in BM erythroid cells. ∗P < .05 between Hbb^th3/+ and p21^−/−/Hbb^th3/+, and between p21^-/- or p21^−/−/Hbb^th3/+ and WT groups (n = 3 mice for each group). (B) Flow cytometric analysis of apoptosis in splenic erythroid cells. ∗∗P < .01 between Hbb^th3/+ and p21^−/−/Hbb^th3/+, and between Hbb^th3/+ and WT groups; ∗∗∗P < .001 between p21^−/−/Hbb^th3/+ and WT groups (n = 3 mice for each group). (C) Flow cytometric analysis of cell proliferation in BM erythroid cells. ∗P < .05 between Hbb^th3/+ and p21^−/−/Hbb^th3/+groups (n = 3 for each group). (D) Histogram of ROS levels in total BM erythroblasts (TER119⁺) as measured by CM-H₂DCFDA probe; and quantification in (E). ∗∗P < .01 between Hbb^th3/+ and p21^−/−/Hbb^th3/+ groups (n = 3). (F) ROS levels in BM-erythroblast populations within GI to GIV obtained from indicated groups of mice. ∗P < .05 between Hbb^th3/+ and p21^−/−/Hbb^th3/+, and between Hbb^th3/+ and WT groups. All results are shown as mean ± SD.