Quantitation of absolute numbers of BM cells and CFU-Ss from both hind limbs of STAT5ab^−/− and wild type mice.

(A) BM cellularity was determined after flushing both tibias and femurs from individual mice into phosphate-buffered saline/2% fetal bovine serum. Red blood cells were lysed in 2% acetic acid and nucleated cells were counted with the use of a hemacytometer. Shown is the average BM cellularity from analysis of wild-type (+/+) and STAT5ab^−/− (−/−) mice (n = 13). (B) Total BM cells were injected into irradiated mice (900 rads; ¹³⁷Cs source) at doses of 5 × 10⁴ or 1 × 10⁵ per recipient. Twelve days later the mice were killed and the spleens were collected. The number of CFU-Ss per spleen was determined by manual scoring using a dissecting microscope. The total number of injected cells was then divided by the number of CFU-Ss per spleen to calculate the ratio of CFU-Ss per number of injected cells (CFU-S frequency). The total number of BM cells was then multiplied by the CFU-S frequency to calculate the total number of BM CFU-Ss present in both hind limbs. Shown is analysis of either wild type (+/+) or STAT5ab^−/−(−/−) mice groups from 3 separate comparisons.