Immunosuppressive alpha globulin from bovine thymus. I. Preparation and assay

DEAE chromatography at pH 5.0 of the saline-soluble proteins from bovine thymus glands yields a protein fraction similar in activity to the immunosuppressive alpha-2 globulins previously described from bovine and human serum. Of 32 preparations 16 had consistent and reproducible suppressive activity to DNA synthesis in phytohemagglutinin (PHA)—stimulated lymphocytes in concentrations ranging from 50–600 μg/ml in vitro. In vivo immunosuppression, not directly related to the degree of in vitrolymphocyte suppression, occurred in doses of 4–5 mg per mouse, and was assessed by the hemagglutinin response to sheep red blood cells. A variety of other protein and nucleic acid fractions were not suppressive in these assays; in particular, fractions A and B, which precede the immunosuppressive Fraction C in the elution from DEAE-cellulose, are neither suppressive, nor do they significantly alter the effects of Fraction C.