T helper cells change their Lyt-1,2 phenotype during an immune response.

Evidence is presented that T helper cells change their Lyt-1,2 phenotype, from Lyt-1+2- to Lyt-1-2+, during a secondary response. In a secondary adoptive transfer the Lyt phenotype of carrier-primed T cells was established before and after secondary challenge using monoclonal antibodies and both positive and negative selection in the fluorescence-activated cell sorter. In a carrier-primed donor, the T helper cells were Lyt-1+2- whereas 3 days after boosting the majority were Lyt-2+, and resistant to treatment with anti-Lyt-1 and complement. Parking experiments in lethally irradiated recipients confirmed that Lyt-2+ T helper cells were generated from Lyt-2- precursors. In a primary response, both Lyt-2- and Lyt-2+ T helper cells were present 4 to 20 days after immunization. Therefore T helper cells do not exhibit invariant expression of the Lyt-1,2 alloantigens.