Differential engraftment kinetics of young or old BM cells in old or young recipients. 2 × 10⁶ young (⋄) or old (▪) Ly-5.2 BM cells were injected into lethally irradiated young mice, or 3 × 10⁶ young Ly-5.2 BM cells were injected into lethally irradiated old Ly-5.1 mice (○). Shown are the mean ± SEM number of PB leukocytes (A), erythrocytes (B), and platelets (C) counted on the indicated days after transplantation (pooled data from 2 experiments with 10 mice per group). The absence of error bars for specific data points indicates that fewer than 3 animals were available for analysis. Note that the time after transplantation is not depicted on a linear scale. Shaded areas indicate normal ranges of blood cell counts in age-matched B6.SJL control mice. Data for the young-to-young group were collected contemporaneously with those of other groups but were, in part, reported in Szilvassy et al.²³