title: Correlation of the in vivo and in vitro activities of antithymocyte sera (ATS) with the immunizing antigen dose.
abstract: Rabbits were immunized with 1, 3, 10, 30, 100, 300, or 1,000 x 10(6) murine thymocytes per kg according to the method of Levy and Medawar. Thus, 33 individual and 6 pooled antimouse antihymocyte serum (ATS) preparations were obtained and tested for in vivo immunosuppressive (graft-protective) as well as for in vitro thymocytotoxic activity. It was found that: (1) at least 3 x 10(6) thymocytes/kg were necessary for inducing ATS of appreciable immunosuppressive activity; (2) rabbits immunized with 30 x 10(6) thymocytes/kg supplied sera of the most potent immunosuppressive activity; (3) the increase of the immunizing antigen dose over 30 x 10(6) thymocytes/kg resulted in ATS preparations of decreased immunosuppressive activity; (4) the graft-protective activity of an ATS pool corresponded to the average of the activities of the individual ATS preparations from which the pool had been mixed, i.e., the process of pooling itself did not modify the immunosuppressive activity; and (5) there was a good correlation (r = 0.72, P less than 0.001) between the in vivo immunosuppressive (graft-protective) activity and the in vitro thymocytotoxic titre of ATS preparations. The theoretical and practical significance of these results if discussed.
mesh_terms: D000818:Animals; D000941:Antigens; D000961:Antilymphocyte Serum; D003602:Cytotoxicity, Immunologic; D005260:Female; D006085:Graft Survival; D007114:Immunization; D007165:Immunosuppression Therapy; D008297:Male; D051379:Mice; D011817:Rabbits; D016038:Skin Transplantation; D013601:T-Lymphocytes / Q000276:immunology*; D014184:Transplantation, Homologous
chemical_list: D000941:Antigens; D000961:Antilymphocyte Serum