Pure bovine granulocytes as a source of granulopoiesis inhibitor (chalone).

In order to isolate an endogenous inhibitor (chalone) of granulopoiesis, a source of chalone has been employed which consists of pure granulocytes. Optimal conditions for the isolation of these cells from bovine blood using EDTA are described. After incubation of the cells, the conditioned medium was lyophilised and extracted in two separate procedures with water or acetone. Sephadex G-10 chromatography yielded a fraction having a molecular weight under 700 which was capable of inhibiting the colony formation of myelopoietic stem cells in a nontoxic, cell-specific and reversible manner. THE INHIBITORy activity of the fraction was found to be dependent on the addition of 2-mercaptoethanol. Even then, aqueous solutions of the inhibitor are at present not indefinitely stable.