IL-2 production by Lyt 1 thymocytes in response to self-Ia antigens

The Lyt 1⁺, 2^-, 3^-(Lyt 1) sub-population of thymocytes in mice represents less than 10% of the total thymocyte population. When tested for function we found that it could respond in MLR both to allogeneic and syngeneic stimulator cells. In the syngeneic response (or SMLR) the Lyt 1 thymocytes proliferated in response to IA(B)E determinants on macrophage-like stimulator cells and produced significant amounts of IL-2 during such cultures. When the SMLR were done in absence of fetal calf serum, proliferation was reduced but IL-2 was still produced in comparable amounts. We found that all types of SMLR (i.e. spleen T versus spleen non-T, etc.) have those same proporties: mediated by Lyt 1 cells; dependent on Ia on the macrophage-like (dendritic) stimulators; produce IL-2 independently of exogenous antigen. We propose that the Ia-dependent physiological signal for IL-2 production. We also propose that the intrathymic Lyt 1 cell may represent an equivalent of the post-thymic Lyt 1-IL-2 producing cells in the periphery.