Donor CD4 T-cell expansion and activation during reconstitution of naive and M avium–infected TCRα^−/− mice. Naive and day 69 infected CD45.2⁺ TCRα^−/− mice received 1.5 × 10⁶ CFSE-labeled CD45.1⁺ CD4 T cells from naive donors, and tissues were harvested on day 7 after transfer. (A) Representative FACS plots showing the frequency of donor CD4 T cells in different tissues of naive and infected recipient mice (top panels). Numbers represent the percentage of the total recovered cells that were of donor origin. The corresponding histograms of CFSE dilution for each of the gated CD4⁺CD45.1⁺ donor cell populations are shown in the bottom panels. Numbers represent the percentage of donor cells that have fully diluted CFSE. (B) Absolute numbers of donor CD4 T cells recovered from each of the tissues shown in (A). For the PBMCs, the percentage of donor cells is shown. (C) CD69 staining of the donor CD4 T cells recovered in panels A and B. In the case of mediastinal lymph nodes, it was necessary to pool cells from 4 mice to obtain sufficient numbers for staining. Data are representative of 2 independent experiments.