Limiting numbers of thymic progenitors delay T-lineage recovery. (A) CD45.1 WT host mice were sublethally irradiated and intravenously injected with 2.5 × 105 CD45.2 WT BM cells. Immediately thereafter, one group of mice received PBS intrathymically (IV only), whereas another group received 3 × 104 CD45.2 Lin− BM cells intrathymically (IV + IT). Host thymi and spleens were analyzed for donor contributions 4 weeks later. Shown are representative plots of thymic DP (top row), CD4 SP (middle row), and CD8 SP (bottom row) cells from mice in the indicated groups. (B) Mean numbers ± SEM of host and donor thymic DP (top panel), CD4 SP (bottom left panel), and CD8 SP (bottom right panel) cells from the chimeras described in panel A. P values for comparisons of donor DP cell numbers between the 2 groups, .01; of donor CD4 SP cell numbers, .002; of donor CD8 SP cell numbers, .0003. (C) Shown are representative plots of splenic CD4 T (top row), CD8 T (middle row), and B (bottom row) cells from mice in the indicated groups described in panel A. (D) Graphs show the mean number ± SEM of host and donor splenic CD4 T (top left panel), CD8 T (top right panel), and B (bottom panel) cells from the chimeras described in panel A. P values for comparisons of donor CD4 cell numbers between the 2 groups, .007; of donor CD8 cell numbers, .005; of donor B cell numbers, .41. N = 4 or 5 per group.
