Specific in vitro Cytotoxicity of Thymus-derived Lymphocytes sensitized to Alloantigens

Abstract

THE immune response to a specific antigen is characterized by the development of antibody-producing cells and of sensitized lymphocytes active in cell-mediated immunity. Although there is good evidence that antibody-producing cells are bone marrow-derived cells^1–2, the role of thymus-derived cells is less well understood. Development of cell-mediated immunity is impaired in neonatally thymectomized animals³, and it is therefore likely that sensitized lymphocytes are thymus-derived cells. Spleen cell populations of mice immunized with allogeneic cells contain lymphocytes able to destroy in vitro appropriate target cells bearing the sensitizing alloantigens^4–5. Earlier studies demonstrating the in vitro cytotoxic activity of sensitized thymus cells⁶ suggested that cytotoxic cells found in immune spleen cell populations were thymus-derived. As shown recently^7–8 mouse thymus-derived cells in the peripheral lymphoid organs carry a surface marker, the θ alloantigen⁹, and are lysed when incubated in the presence of anti-θ serum and complement. This study was undertaken to test the effect of anti-θ serum on the cytotoxic activity of spleen cells sensitized to alloantigens. Its effect on alloantibody-producing cells present in the same spleen cell populations was tested in parallel.