Characterization of a splenic factor inhibiting DNA-synthesis in lymphocytes in vitro

A factor inhibiting DNA synthesis in lymphocytes from lymph nodes and thymus of guinea pigs and rats has been isolated from the calf spleen. A crude extract was obtained by homogenization of the spleen in saline, centrifugation at 1,200 and 46,000 g, heat precipitation at 60 degrees C, acetone precipitation, followed by lyophilization at the acetone precipitate. The active material was partly purified and characterized by gel chromatography, ion exchange chromatography, ultrafiltration and preparative electrofocusing. The active factor was found to be acidic and heat stable (60 degrees C, 10 min) with a molecular weight between 75,000 and 17,000 daltons. At preparative electrofocusing inhibiting material focused at pH 4.0. The splenic factor inhibited the DNA synthesis in lymphocytes from guinea pigs and rats, but not the DNA synthesis in HeLa cells. During the purification, material which enhanced the uptake of 3H-thymidine in DNA of lymphocytes was separated from the inhibitor. The stimulating factor had a molecular weight below 10,000 daltons as judged by ultrafiltration and gel chromatography. At preparative electrofocusing stimulating material focused around pH 8.5.