Delayed hypersensitivity: bone marrow as the source of cells in delayed skin reactions.

Adult Lewis rats were thymectomized, irradiated, and restored with bone marrow from allogeneic (or F(1)) donors. They were passively sensitized to tuberculin by a subsequent transfer of Lewis lymph node cells and were given intradermal skin tests with tuberculoprotein. In 24-hour skin reactions the majority of cells, in successive experiments, were shown to be allogeneic (or F(1)) with the use of isoantibody against the antigens of the transplanted marrow cells and by the indirect fluorescent antibody technique. Our results demonstrate that the non-specific cells making up a large proportion of the infiltrating elements in tuberculin skin reactions probably originate in the bone marrow.