The presence of Thy-1 on the surface of rat lymphoid stem cells and colony-forming units.

By labeling Thy-1-positive cells of rats with xenoanti-Thy-1 or mouse alloanti-Thy-1 antibody and separating them from Thy-1-negative cells on a fluorescence-activated cell sorter, it was shown that early lymphopoietic stem cells all carry Thy-1-antigen. This was so for both young, adult bone marrow and near-term fetal liver cells. Two kinds of assay were used: long-term radiation chimeras employing B and T cell alloantigens to mark cells of donor origin, and in vivo colony-forming units in the spleens of irradiated recipients (bone marrow only). Thy-1-negative cells gave essentially no B or T progeny, even 6 to 12 months after reconstitution of the chimeras. The kinetics of appearance of Thy-1-positive cells in rat marrow, which peaked at 6-8 weeks of age, were also studied. In rats, Thy-1 is on the surface of pluripotent stem cells and on early progenitors of both B and T lymphocytes.