Aged mice mobilize increased numbers of HPCs to PB in response to G-CSF. (A) Frequency of CFCs in 20 μL PB in young and aged mobilized (5-day G-CSF at 100 μg/kg per day intraperitoneally; PB analysis on day 6) and nonmobilized mice, n = 10 for young nonmobilized and mobilized mice, n = 3 for 22-month-old mobilized mice, and n = 7 (3 at 20 months, 1 at 23 months, 3 at 26 months) for mobilized aged mice. (B) White blood cell (WBC) and RBC counts in young and aged mobilized and nonmobilized mice, n = at least 4 per value. (C) CFC frequency in spleen in young and aged mobilized and nonmobilized mice, n = 3. (D) CFC frequency in BM in young and aged mobilized and nonmobilized mice, n = 3. Values shown are mean ± 1 SEM. *P < .05.