(A) The expression level of Fas antigen on whole BM cells. The mice were injected with 5 × 10⁷ of B6 spleen cells (B6/BDF1) or 1 × 10⁸ of D2 cells (D2/BDF1). On day 14 after transfer, the mice were killed to remove their BM cells. Using flow cytometry, the expression level of Fas on these cells was examined. BDF1 represents the uninjected control mice. Four mice were examined in each group and the representative data were shown. (B) The expression level of Fas on hematopoietic progenitor cells. The expression level of c-kit and Fas on the BM cells obtained on day 14 after the transfer of B6 cells (B6/BDF1) was examined after the Lin⁻ populations were gated. The numbers in the figure represent the percentage of c-kit⁺Fas⁺ cells in the Lin⁻ cell populations. BDF1 represents the uninjected control mice. Twelve mice were examined in both groups and the representative data were shown.