T cell activation and enhanced Fas/Fas ligand expression. In addition to a significant T cell expansion in the BM, B6 mice that received TBI + FVB LN treatment (N=10) also had significantly higher proportions of CD11a+ cells, a marker of T cell activation, in both CD4 (P<0.01) and CD8 (P<0.05) subsets, causing net gains of CD11a+CD4+ (P<0.01) and CD11a+CD8+ (P<0.01) T cells in the BM relative to TBI only controls (A). Residual BM cells from TBI + FVB LN treated mice (N=3) showed elevated Fas expression (P<0.01), while BM T cells, especially CD8 T cells, showed higher level of Fas ligand expression (P<0.01) relative to BM cells from untreated control animals (B).