FIGURE 1.

The competitive advantage of the Lfng transgene depends on V(D)J recombination. A, Lin⁻ bone marrow progenitors from Lfng Tg⁺ Rag2^−/− (B6.CD45.2) and Rag2^−/− (B6.CD45.1) donors were injected i.v. in equal ratios into lethally irradiated WT hosts (B6.CD45.1;CD45.2). The relative contribution of Lfng Tg⁺Rag2^−/− and Rag2^−/− donors to the DN3 thymocyte pool was assessed 3 wk later by staining total thymocytes with Abs against CD4, CD8, CD25, CD117, CD45.1, and CD45.2. B, Lin⁻ bone marrow progenitors from Lfng Tg⁺ and WT donors were intrathymically injected separately or together as a 50:50 mix into sublethally irradiated WT hosts. The relative contribution of Lfng Tg⁺ and WT donors to the DP and DN3 thymocyte pools was assessed 3 wk later by staining total thymocytes with Abs against CD4, CD8, CD25, CD117, CD45.1, and CD45.2. C, Lfng overexpression enhances DL4-Fc binding by Rag2^−/− DN3a thymocytes. Flow cytometry was used to measure binding of DL4-Fc protein by DN3a (CD117⁻CD25⁺) thymocytes from Lfng Tg⁺Rag2^−/− (dashed line) compared with Rag2^−/− (solid line) mice. Binding of control Fc protein to Lfng Tg⁺ Rag2^−/− DN3a thymocytes is shown for comparison (shaded line). Binding of control Fc protein to Rag2^−/− DN3a thymocytes had a pattern similar to Lfng Tg⁺Rag2^−/− DN3 thymocytes (data not shown). Each experiment was performed at least three times with similar results.