Kinetic analysis of engraftment following intravenous transplantation of L-selectin^Pos and L-selectin^Neg bone marrow populations. (A) Progenitors were collected from B6-Thy-1.1-Ly-5.1 mice and transplanted intravenously into sublethally irradiated (6.5 Gy) B6 host mice. Each animal received either 10³ L-selectin^Pos progenitors (▪), 10³ L-selectin^Neg progenitors (○), or 2.5 × 10⁷ normal thymocytes (▵). Thymic lobes were collected on the days indicated and assayed by immunofluorescent staining and flow cytometry for donor-derived (Ly-5.1^Pos Thy-1.1^Pos) thymocytes. Thymic lobes were considered engrafted if they contained equal to or more than 10⁵ donor-derived thymocytes. Each symbol represents the mean donor-derived thymocytes per engrafted thymic lobe observed at that time point from 6 to 18 total lobes assayed over 3 independent sorting and transplantation experiments. Error bars represent SEM. (B) Host mice receiving L-selectin^Pos progenitors for the experiment described in panel A were analyzed for the frequency of engrafted thymic lobes relative to the kinetics of thymocyte expansion. The figure shows the percent positive thymic lobes at each time point (right axis, □) and the mean donor-derived thymocytes per engrafted lobe (left axis, ▪). Error bars represent SEM. (C-D) Bone marrow was collected from the cohort of 62 mice given transplants with L-selectin^Pos progenitors (▪) and 48 mice receiving L-selectin^Neg progenitors (○) for the experiment described in panel A and analyzed by immunofluorescent staining and flow cytometry to identify donor-derived cells expressing either CD19 (B cells) or Ly-6G (granulocytes and macrophages). Each symbol represents the mean donor-derived B cells (C) or Ly-6G cells (D) observed per engrafted femur at the indicated times. Error bars represent SEM. Ly-6G^Pos engraftment following L-selectin^Pos progenitor transplantation was too sporadic for a trend to be extrapolated.