Differentiation and maturation of functional T lymphocyte subsets in the thymus. II. Generation of T cell specificities and functions from a single stem cell.

Abstract

Functional differentiation of T cells in the thymus from a single stem cell was investigated by transferring bone marrow cells dirrectly into the thymus (i.t.) of irradiated and reconstituted mice, and assaying the immunologic function of donor drived T cells. To assure the clonality of donor derived T cells, bone marrow cells from two mutually indentifiable strains were 1 : 1 mixed and the limited number of the mixture was transferred i.t. into the recipient mice. As the donor of bone marrow cells, C57BL/6 (H-2^b, Thy-1.2, Lyt-2.2) and B6. Lyt-2.1 (H-2^b, Thy-1.2, Lyt-2.1) mice were used, and B10. Thy-1.1 (H-2^b, Thy-1.1, Lyt-2.2) mice were used as the recipients. Recipient mice were either thymus-shielded and irradiated or whole-body irradiated and reconstituted with 10^7 syngeneic bone marrow cells. The recipient's thymus which contained Thy-1.2^+ cells on day 28 were regarded as positive for donor derived cells, and among these positive thymuses those which contained either Lyt-2.1^+ cells or Lyt-2.2^+ cells were regarded as seeded by a single stem cell (single positive thymus cells). Such single positive thymus cells were treated with anti-Thy-1.1 plus complement to remove recipient-type T cells and the recovered cells were assayed for proliferative response and cytotoxic response in mixed lymphocyte culture against allogeneic lymphocytes. Cells were also assayed for concanavalin A-mediated polyclonal helper T cell (Th) and cytotoxic T cell (CTL) functions. Results indicated that proliferative response to alloantigens was observed only in thymus-shielded recipients, whereas CTL to alloantigens was generated in both thymus-shielded recipients and whole-body irradiated recipients. No general rule of preference for any allogeneic cells was found. Both Th and CTL activities, detectable by polyclonal assays, were generated from a single stem cell in thymus-shielded recipients. However, only CTL but not Th was generated in whole-body irradiated recipients. Moreover, a clone of T cells which responded with CTL to a given allogeneic cells did not necessarily respond with a marked proliferation to the same stimulator cells.