Inhibition of agar colony formation by partially purified granulocyte extracts (chalone)

Granulocytic extracts (GE) of different sources, presumably containing the granulocytic chalone, were prepared in different laboratories and purified to some extent. They specifically inhibited the formation of granulocyte and macrophage colonies in agar. The effect was however most pronounced on granulocyte and mixed granulocyte-macrophage colonies, and less on macrophage types. Addition of GE to bone marrow cells at the time of plating in agar, as well as short incubation of the cells together with GE prior to plating, inhibited subsequent colony formation. The inhibitory effect could easily be reversed by washing the cells with an excess of medium prior to plating during the first hour of preincubation, but not after five hours. Increasing the doses of colony stimulating activity (CSA) (at low doses of GE) released the inhibitory effect, but not at high doses of GE. The inhibitory effect of GE on colony formation was dose dependent down to almost 100% inhibition. No apparent cytotoxic effect of GE on bone marrow cells could be found and lymphoblastic cells were not inhibited. Extracts containing a specific inhibitor of erythropoiesis (EIF) stimulated myelopoietic colony formation in agar.