title: High-level secretion of interleukin 2 by a subset of proliferating thymic lymphoblasts.
abstract: We have characterized the thymocytes that can be induced to secrete interleukin 2 (IL 2) after polyclonal stimulation with Con A. For maximal activation, an important adjunct to the Con A is the phorbol ester TPA. In the presence of TPA, IL 2 production by thymocytes is relatively independent of adherent accessory cells; this allows us to compare the abilities of different thymic subpopulations to make IL 2. The most numerous class that includes IL 2 producers is made up of cells with a typical "medullary" population, the phenotype: moderately small, postmitotic cells that fail to bind peanut agglutinin. In addition, however, a population of large, proliferating lymphoblasts is competent in IL 2 production directly as isolated. Relative to the total "medullary" population, the lymphoblasts are enriched for the ability to make IL 2. They account for a significant proportion of the total IL 2 produced by thymocytes, and demonstrate that this aspect of immunocompetence is not restricted to cells that have finished their intrathymic proliferation. The IL 2-producing lymphoblasts do not bind peanut agglutinin or express thymus-leukemia antigen, but they do express high levels of Lyt-1. Although distinct from most medullary thymocytes, therefore, they are also distinct from the majority of cortical blast cells for which a direct precursor role has been established. They may be a subset of the rare proliferating blast cells in the medulla. Further heterogeneity in the thymic IL 2 producers is demonstrated by their expression of the Lyt-2 glycoprotein. The majority of IL 2 producers are Lyt-2- as are the majority of peripheral T "helper" cells. However, a distinct minority of the thymic IL 2 producers express Lyt-2. Therefore, the ability of some peripheral Lyt-2+ cells to secrete IL 2 may be determined at the time of their initial programming in the thymus.
mesh_terms: D000818:Animals; D000950:Antigens, Ly / Q000032:analysis; D000951:Antigens, Neoplasm / Q000032:analysis; D002470:Cell Survival; D003208:Concanavalin A / Q000494:pharmacology; D007376:Interleukin-2 / Q000096:biosynthesis*; D037102:Lectins / Q000378:metabolism; D008213:Lymphocyte Activation; D008562:Membrane Glycoproteins; D051379:Mice; D008810:Mice, Inbred C57BL; D019887:Peanut Agglutinin; D010641:Phenotype; D013601:T-Lymphocytes / Q000145:classification / Q000276:immunology / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D013950:Thymus Gland / Q000166:cytology* / Q000502:physiology
chemical_list: D000950:Antigens, Ly; D000951:Antigens, Neoplasm; D007376:Interleukin-2; D037102:Lectins; D008562:Membrane Glycoproteins; D019887:Peanut Agglutinin; C028388:thymus-leukemia antigens; D003208:Concanavalin A; D013755:Tetradecanoylphorbol Acetate