Presence of AKR/J thymocytes induces arrest of early T-cell development within control thymocytes that is overcome by addition of exogenous IL-7. (A) Total thymocytes were isolated from mixed BM chimeras reconstituted with 10% or 90% of AKR/J inoculum at 3 and 9 weeks after transfer and stained using biotin–anti-Thy1.1 and PE–anti-Thy1.2. FACS profiles show the distribution of AKR/J (Thy1.1⁺) versus B10.BR (Thy1.2⁺) donor-derived thymocytes. (B) Total thymocytes were isolated from mixed BM chimeras reconstituted with 10% or 90% of AKR/J BM cells at 6 weeks after transfer and analyzed by 4-color staining using biotin–anti-Thy1.1, PE–anti-Thy1.2, APC–anti-CD4, and FITC–anti-CD8. FACS profiles show the distribution of CD4 versus CD8 within gated Thy1.1⁺ or Thy1.2⁺ thymocytes. (C) Total thymocytes were isolated from mixed BM chimeras reconstituted with 10% or 90% of AKR/J BM cells at 6 weeks after transfer and analyzed by 4-color staining using a cocktail of Cy–(anti-CD4, anti-CD8, anti-TCRαβ) antibodies together with APC–anti-CD25, FITC–anti-CD44, and biotin–anti-Thy1.1 or biotin–anti-Thy1.2. FACS profiles show the distribution of CD25 versus CD44 among gated Thy1.1⁺ or Thy1.2⁺ thymocytes within TN (CD4^–CD8^–TCRαβ^–) cell population. Results (A-C) are representative of 5 independent experiments with n = 3 mice per group of BM chimeric mice. (D) At 9 weeks after transfer, mixed BM chimeras were injected intraperitoneally with PBS or mouse recombinant IL-7 (10 μg/mouse) during 7 consecutive days. Subsequently, cells were recovered from thymus and stained as described in panel B. FACS profiles show the distribution of CD25 versus CD44 within gated Thy1.1⁺ or Thy1.2⁺ thymocytes within TN (CD4^–CD8^–TCRαβ^–) cell population in PBS versus IL-7–treated mice. Results (D) are representative of 2 individual experiments with 2 mice per group of BM chimeric mice. Numbers shown in FACS profiles denote percentages of cells in each quadrant.