EN
Immunosuppressive proteins were isolated from the sera of cattle suffering from leukosis by employing column chromatography fractionation on DEAE- cellulose, Sephadex G-200 and Sephadex QAE-50A, The resulting three proteins which were homogenous as judged by polyacrylamide gel electrophoresis were found to suppress in vivo the induction of splenic plaque forming cells in mice. The specific activity of the pure proteins were increased to 67-75% in comparison to 31% of the raw material. The pure proteins contain from 15 to 45 µg/mg of hexoses and their molecular weights were approximately the same and were estimated on 70000 by means of SDS polyacrylamide gel electrophoresis.