Effect of HbF, F cells, and percentage HbF/F cell required for functional improvement in RBC survival and deformability. (A) RBC half-life. Left panel shows a representative G^bG mouse injected with biotin, with biotin-labeled F cells (upper right quadrants) and non-F cells (lower right quadrants) determined by FACS. Right panel shows survival of F cells (⊡), compared with the non-F cells (⊙) in G^bG mice (n = 4); wild-type mice (△); and Berkeley mice (○). (B) A cohort of G^bG mice analyzed for RBC survival in vivo, based upon the percentage of HbF/F cell. Each symbol represents a mouse group with HbF percentage and number of mice listed in the adjacent table legend. (C) All G^bG and mock mice (n = 34) that were analyzed for RBC deformability were divided into groups based on proportion of F cells: 0%, 1% to 33%, 33% to 66%, and more than 66%, and deformability of total RBC in these mice was plotted at low (3 Pa, △) and high (28 Pa, ▽) shear stress. Significantly improved deformability over mock controls is denoted by *(P < .05) and **(P < .01). Error bars indicate SEM.