Flow cytometric analysis of adhesion molecule expression on donor Sca-1⁺ cells in irradiated and nonirradiated recipient BM 1 hour after transplantation.

In this representative experiment, 50 × 10⁶ PKH2-stained LDBM cells were transplanted into irradiated (A) or nonirradiated (B) mice. Mice were killed 1 hour later, and BM cells were lysed and stained with Sca-1–PE and CD43-biotin, followed by streptavidin-APC. Cells were analyzed flow cytometrically by collecting listmode files containing 300 to 1000 donor Sca-1⁺ events exhibiting low side and forward angle scatter, properties characteristic of primitive hematopoietic cells. In this representative experiment, 1 × 10⁵ (A) and 1.1 × 10⁴ (B) total events were collected, which contained 664 and 597 Sca-1⁺events in histograms A and B, respectively. The frequencies of PKH2⁺ cells were 26% (A) and 1.2% (B) and the frequencies of Sca-1⁺ cells within donor cells were 31% (A) and 25% (B), while the frequencies of CD43⁺ cells within donor Sca-1⁺ cells were 24% (A) and 17% (B). The frequencies of donor cells when all nucleated cells were included in the analysis were 3.8% (A) and 1.1% (B). To avoid collecting very large files, files were sometimes acquired to exclude recipient cells, as shown in panel B.