Flip-flop in the Lyt 2 phenotype of T cells from radiation chimaeras between Thy 1 congenic donor and recipient mice.

We present further evidence that T helper cells change their surface phenotype from Lyt 2- to Lyt 2+, after secondary adoptive transfer. Chimaeras were established with Lyt 2- spleen cells from normal, or carrier-primed A-Thy 1a donors and irradiated, A-Thy 1b recipients. Despite efficient depletion of Lyt 2+ cells from the initial donor, in the fluorescence-activated cell sorter, the majority of chimaeric T cells expressed Lyt 2 and were resistant to monoclonal Thy 1.2 alloantibody and complement treatment. In functional studies, the T helper activity of chimaeras, reconstituted with carrier-primed spleen cells, was present in both Lyt 2+ and Lyt 2- subsets.