Fractionation of spleen and serum in attempts to isolate the radiation-leukemia protection factor.

The leukemia induced in C57BL mice by X-irradiation can be prevented by injection of extracts of sheep spleen or serum. These materials have been fractionated by ammonium sulfate precipitation followed by chromatography on Sephadex G-200. Radiation-leukemia protection (RLP) activity precipi tates partially between 0—40%and 40—60% saturation with ammonium sulfate. During chromatography on Sephadex, most of the leukemia protective activity appears to elute with the higher molecular weight proteins of sheep spleen but with the smaller proteins of sheep serum. Cohn fractions III, III—0, IV—1, and IV—4from commercial sources have shown RLP activity on one or more tests. All the preparations tested were heterogeneous on polyacrylamide gel electropherograms. It is suggested that more than one polypeptide exhibits leukemia protection activity.