Thymic cross talk requirements for TEC differentiation. (A) MHC II and Ly51 expression on TECs (CD45^–EpCAM⁺) from wild-type, RAG-1^–/–, TcRα^–/–, Rel-B^–/–, and CD40L^–/– mice. Gates discriminate MHC II^hi and MHC II^lo cTEC and mTEC subpopulations, with the frequencies of each shown at the bottom right of each plot and total TEC numbers at the bottom left. Representative plots from 3 to 5 experiments are shown. (B) Ly51 (green) and MTS-10 (red) staining of thymic sections from wild-type and the various mutant mice. The MTS-10⁺ areas in RAG-1 and RelB were infrequent compared with the other models examined. Representative images from 4 experiments are shown.