Lfng improves the competitive fitness of Lck-deficient and Ptcra-deficient DN3b thymocytes. A, DP thymocyte production in Lfng Tg+ Lck−/− + WT versus Lck−/− + WT mixed chimeras. Left panel, Relative contribution of Lfng Tg+Lck−/−, Lck−/−, and WT donor cells to the DP thymocyte pool in individual thymic lobes. Right panel, Absolute numbers of DP thymocytes derived from Lfng Tg+Lck−/− (diagonal lines), Lck−/− (dots), and WT (gray) donors in individual thymic lobes. B, DP thymocyte production in Lfng Tg+Ptcra−/− + WT versus Ptcra−/− + WT mixed chimeras. Left panel, Relative contribution of Lfng Tg+Ptcra−/−, Ptcra−/−, and WT donor cells to the DP thymocyte pool in individual thymic lobes. Right panel, Absolute numbers of DP thymocytes derived from Lfng Tg+Ptcra−/− (vertical lines), Ptcra−/− (white), and WT (gray) in individual thymic lobes. Chimeras were generated and analyzed after 3 wk as described for Fig. 2.