Thymus reconstitution in secondary recipients after transfer of primary recipient thymus cells.

T-cell– and mature B-cell–depleted BM cells from C57BL/6 (Ly-5.2) mice were injected intravenously into lethally irradiated primary Ly-5.1 recipient mice. At various times after primary transfer, thymocytes were harvested from the primary Ly-5.1 recipients and injected intravenously into lethally irradiated secondary Ly-5.1 recipient mice, along with the recipient type Ly-5.1 BM cells to ensure recipient survival. Four weeks after reconstitution, donor-derived cells in the thymuses of the secondary recipients were analyzed by flow cytometry. Although few progeny of the original BM cells were present, they could be selected as Ly-5.2⁺ cells and characterized by other markers. Background stainings, in which either a fluorescence-conjugated, isotype-matched control was used or the anti–Ly-5.2 antibody was omitted, gave almost no (less than 0.01%) positive staining. Percentage of donor-derived cells that expressed each indicated lineage marker in the secondary recipient is shown in the upper-right quadrant of each plot. Results shown in this figure are representative of 3 such experiments for each time point that gave similar results. Each experiment included 2 to 3 recipient mice.