title: Thymus-repopulating capacity of cells that can be induced to differentiate to T cells in vitro.
abstract: It was established previously that committed precursors of T cells, which reside in bone marrow and spleen and lack T cell surface differentiation antigens, can be induced by thymopoietin and certain other agents to differentiate rapidly in vitro into T cells bearing typical surface antigens, including Thy-1 and TL (Komuro-Boyse assay). To relate this differentiative step observed in vitro to physiologic events in vivo, a system was devised to trace the migration of precursor cells to the thymus, and their maturation to T cells. Lethally irradiated mice of a TL- strain received spleen cells from TL+ hybrids i.v., and the TL+ population of the thymus was enumerated 13 to 20 days later. Donor TL+ cells first became detectable at 13 days and increased thereafter. Preliminary tests showed that cells capable of migrating to the thymus have a similar density to the cells that are inducible in the Komuro-Boyse assay, this being lower than that of mature of T cells. The thymus-repopulating properties of the donor spleen population were not affected by: 1) pre-treatment in vitro with thymus extract or thymopoietin, which initiates differentiation of T cells precursors, nor b) pre-treatment with anti Thy-1 serum plus complement, which eliminates differentiated T cells. But pre-treatment a) and b) applied in sequence markedly reduced the capacity of spleen cells to repopulate the thymus. These results can be interpreted as follows: induction of Thy-1-TL- precursor cells (pro-thymocyte) in vitro yields Thy-1+TL+ cells (early thymocytes) which have not yet lost their property of repopulating the thymus; therefore, thymus-repopulation was not depleted by treatment a) alone, which induced Thy-1 +TL+ cells, nor by treatment b) alone, which did not affect thymus-repopulation by Thy-1-TL- cells, although treatments a) plus b) did eliminate the newly induced Thy-1+TL+ cells and thus impaired repopulation of the thymus. We conclude that the cell which responds to thymopoietin in the Komuro-Boyse assay by expressing the T cell surface phenotype is the same cell (pro-thymocyte) that normally migrates in vivo from hemopoietic tissues to the thymus and is there induced by thymopoietin to express the phenotype of an early T cell.
mesh_terms: D000818:Animals; D000937:Antigen-Antibody Reactions; D000961:Antilymphocyte Serum / Q000302:isolation & purification; D001853:Bone Marrow / Q000276:immunology; D001854:Bone Marrow Cells; D002454:Cell Differentiation / Q000187:drug effects*; D003601:Cytotoxicity Tests, Immunologic; D000939:Epitopes; D006412:Hematopoietic Stem Cells / Q000166:cytology; D066298:In Vitro Techniques; D051379:Mice; D008809:Mice, Inbred C3H; D011828:Radiation Chimera; D013154:Spleen / Q000276:immunology; D013601:T-Lymphocytes / Q000378:metabolism*; D013949:Thymus Extracts / Q000494:pharmacology*; D013950:Thymus Gland / Q000187:drug effects*; D013997:Time Factors
chemical_list: D000961:Antilymphocyte Serum; D000939:Epitopes; D013949:Thymus Extracts