Induction of macrophage production and proliferation by a purified colony stimulating factor [22]

COLONY STIMULATING FACTORS (CSFs) stimulate isolated haemopoietic progenitor cells to differentiate and form granulocyte and/or macrophage colonies in vitro^1,2. There seem to be at least two distinct subclasses of CSF, those stimulating macrophage colony formation and those stimulating granulocytic colony formation. Purified CSF from mouse L cell-conditioned medium is a 70,000 molecular weight glycoprotein, comprising two disulphide-bonded 35,000 MW subunits³. At concentrations as low as 10^-12 M it stimulates macrophage colony formation by murine bone marrow cells. It has similar physicochemical properties to, and shared antigenic determinants with, the CSF from human urine^3-6. This type of CSF has been shown⁶ to share identity with the macrophage growth factor of Virolainen and Defendi⁷ that stimulates proliferation of peritoneal exudate macrophages. The purified CSF was also active⁶ in stimulating macrophage colony formation by peritoneal exudate cells in the agar culture system of Lin and Stewart⁸. We now report that this same kind of CSF is the molecule responsible for the proliferation of mononuclear phagocytes from several haemopoietic and nonhaemopoietic tissues.