Erythroid-potentiating activity: characterization and target cells.

We established a human T-lymphoblast cell line (Mo) that produces factors stimulating the proliferation of hematopoietic cells. These include a colony-stimulating factor for normal human granulocytes and macrophages, and a factor with erythroid-potentiating activity (EPA) that enhances the proliferation of normal human erythroid progenitors in vitro. Erythroid-potentiating activity has been partially purified and characterized. It is an acidic glycoprotein of 45,000 daltons molecular weight and it has remarkable heat stability. Erythroid-potentiating activity is physically separable from the colony-stimulating factor. Partially purified EPA was found to stimulate the proliferation of human K-562 and murine Friend erythroleukemia cells. These erythroleukemia cell lines may therefore prove useful for studying the action of EPA on target cells. Erythroid-potentiating factors from other human and murine sources stimulated erythroleukemia cell proliferation in a manner indicating some species restriction. Purification and structural analysis of the EPA molecule will ultimately be required in order to determine the details of its biologic action and to define its relationship to other erythropoietic factors.