IMMUNOLOGICALLY COMPETENT THYMUS CELLS OF BONE MARROW ORIGIN

EXPERIMENTS with lethally irradiated mice have shown, that the recovery of the immune response to sheep red blood cells (RBC) by transplantation of bone marrow cells is conditioned by the host thymus1,2, and that the thymus promotes differentiation of cells derived from the bone marrow to immunologically competent cells3,4. The tissue in which cells from bone marrow acquire immunological competence under thymic influence has not been identified. That the thymus itself may be the site of this differentiation is suggested by the finding of donor mitotic cells of bone marrow origin in the host thymus of mouse radiation chimaeras5. Although these results show migration of bone marrow-derived cells to the thymus, they do not specify whether the donor cells detected in the thymus have gained any immunological competence. © 1969 Nature Publishing Group.