Organ specificity of antithymocyte globulin.

Absorption of horse antimouse thymocyte globulin with either mouse kidney, liver, spleen, mesenteric lymph node, or bone marrow resulted in significant reduction of thymocytotoxicity titre. Absorption with thymus completely removed the thymocytotoxic effect. Cytotoxicity against spleen was removed by absorption with spleen, not by absorption with kidney, liver, or thymus. Absorption by thymus resulted in complete removal of immunosuppressive potency, as judged by duration of survival of H-2 incompatible cardiac allografts, but absorption with the other lymphoid and non-lymphoid tissues did not significantly affect immunosuppressive potency. These studies suggest that horse antimouse thymocyte globulin contained antibodies which were cross-reactive with non-thymic lymphocytes and non-lymphoid tissue but in addition contained antibodies specific for thymus. These thymus specific antibodies were of major importance in determining the immunosuppressive potency of horse antimouse thymocyte globulin.