Primary engraftment from Id1^−/− versus wild-type marrow. WBM was collected from Id1^−/− and wild-type donors, and transferred intravenously to parallel cohorts of radiation-conditioned hosts, as described for primary transplantations in Figure 3. Doses transferred are indicated on the x-axes. Bone marrow and thymic samples were collected 8 weeks after transplantation and evaluated for specific lineage engraftment as described for Figure 3. Left panels give the fraction of hosts engrafted for each lineage by transplantation dose. Right panels give average numbers of cells produced by grafts in each lineage. Error bars indicate SEM. At least 7 hosts pooled from 2 independent transplantation experiments were evaluated per WBM dose for each genotype. Mice were considered engrafted in B-cell or myeloid lineage if their femora harbored at least 10⁴ donor-type cells expressing CD19 or Ly6G, respectively. For the T lineage, the engraftment threshold was set at 2 × 10⁴ donor cells per thymus, as noted on the y-axes. For all 3 lineages, engraftment thresholds were set based on background levels in controls that were irradiated but did not receive transplants included in each cohort of hosts.