Preparation and characterization of antithymocyte serum and globulin without stem cell activity.

Immunosuppressive antimouse and antihuman thymocyte sera and antihuman T lymphocyte sera, raised in rabbits, inhibited colony formation in vitro by bone marrow stem cells. Absorption of the antisera with fetal liver, or isolation of the gamma-globulin from the antisera, removed the inhibitory effect on bone marrow stem cells but left the anti T lymphocyte activity unimpaired. Absorption with cultured lymphoblasts (B cell lines) failed to remove the affinity of the globulins for B lymphocytes.