Appearance of T-cell markers in bone marrow rosette-forming cells after incubation with thymosin, a thymic hormone.

After incubation with thymosin, a thymic hormone, normal bone marrow rosette-forming cells acquire T-cell characteristics, including increased sensitivity to azathioprine, anti-lymphocyte serum, and anti-theta serum. This activity of thymosin provides a new sensitive and reproducible bioassay for thymosin, and is well correlated with an in vivo graft-versus-host assay. In addition, incubation of spleen cells from adult thymectomized mice with thymosin in vitro restores to normal their diminished sensitivity to azathioprine and anti-lymphocte serum.