Fig. 4.
Radiation susceptibility of congenic stem cells as a surrogate assay for stem cell aging. (A) Schematic diagram of the competitive repopulation assay used for these analyses. (B) Tri-Con and B6.D2 (chr. 2) congenic animals were irradiated by 0, 1, or 2 Gy 2 weeks before BM harvest. Equal numbers of Tri-Con competitor and B6.D2 (chr. 2) donor BM cells (1 × 106 each) were transplanted into lethally irradiated B6.SJL (BoyJ) recipients and the animals subsequently aged up to 20 weeks. Chimerism in peripheral blood was determined at 8, 12, and 20 weeks after transplantation by flow cytometry based on the Ly5.1/Ly5.2 mismatch of the transplanted BM cells. n = 4 for each dose.