Control of Granulocyte Production: Separation and Chemical Identification of a Specific Inhibitor (Chalone)

It has previously been shown by others that blood serum contains inhibitors of blood cell production acting on the proliferation of granulocy tic and erythrocytic precursor cells in the bone marrow. It is now shown that the active extract from calf blood serum can be further subfractionated into six different components, all of them exhibiting inhibitory effects on the proliferation of rat bone marrow cells in vitro. Ascitic fluid from rats treated intraperitoneally with polyvinylpyrrolidone contains inhibitors which apparently are the same as those found in calf serum. It was further possible to demonstrate that only one of these inhibitors is contained in mature granulocytes where it is actively synthesized from amino acids and subsequently released into the surrounding medium. By chromatography on Sephadex G‐25 of this conditioned medium the inhibiting substance could be obtained in relatively pure form being contaminated only by low amounts of two ninyhdrin‐positive substances. the experiments allow the granulocytic inhibitor to be identified as a polypeptide with a molecular weight below 5000. the results suggest that this substance is the granulocytic chalone.