Characterization of a serum factor stimulating the differentiation of myelomonocytic leukemic cells

Abstract

Culture of WEHL‐3B myelomonocytic leukemic cells in semi‐solid agar medium containing serum from mice injected with endotoxin serum (ES) led to the development of maturing granulocytes and macrophages in most leukemic colonies. ES contains high levels of granulocyte‐macrophage colony‐stimulating factor (GM‐CSF), a regulator known to stimulate differentiation of these leukemic cells, but an antiserum which neutralized >85% of the GM‐CSF in ES did not suppress the differentiation‐inducing activity of ES on WEHI‐3B cells. The active factor in endotoxin serum stimulating differentiation in WEHI‐3B leukemic cells (GM‐DF) was separated from most of the GM‐CSF by gel filtration using Ultrogel AcA44..