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Mouse myeloid leukemic MI cells can be induced to differentiate into mature macrophages and granulocytes by differentiation-stimulating factor (D-factor) in conditioned medium of mouse peritoneal macrophages. Double-stranded RNA's, such as the copolymers of polyinosinic and polycytidylic acids and polyadenylic and polyuridylic acids, could not alone induce differentiation of the cells, but enhanced induction of differentiation by low concentrations of the D-factor and induced a significant amount of interferon. Rabbit antiserum to purified L-cell interferon neutralized the antiviral activity of interferon of MI cells. Simultaneous treatment of MI cells with the anti-interferon serum and copolymer of polyinosine and polycytidylic acids and D-factor abolished the enhancing effect of copolymer of polyinosine and polycytidylic acids on the action of the D-factor. These results suggest that the effect of double-stranded RNA's on induction of differentiation of MI cells is mediated by interferon produced by the cells.

Mouse myeloid leukemia M1 cells were induced to differentiate in vitro into macrophages and granulocytes by various inducers including ascitic fluid. Differentiated M1 cells induced with ascitic fluid expressed a differentiation-associated cell surface glycoprotein with a molecular weight of 180,000 (p180), which can be labeled by lactoperoxidase-catalyzed radioiodination or metabolic labeling with L-[14C]fucose. p180 was also induced by treatment with conditioned medium of hamster embryo cells, dexamethasone, dibutyryl cyclic adenosine 3':5'-monophosphate, and prostaglandin E1. Ascitic fluid, conditioned medium of hamster embryo cells, and dexamethasone induced all the differentiation-associated properties tested, whereas dibutyryl cyclic adenosine 3':5'-monophosphate and prostaglandin E1 induced lysozyme activity and adhesiveness to the substratum but not phagocytosis, locomotive activity, Fc receptors, or morphological changes. The adherent cells induced by dibutyryl cyclic adenosine 3':5'-monophosphate produced a large amount of p180, while the floating cells produced very little, but no difference was detected in the lysozyme activities of the two cell types. These results suggest that p180 is associated with cell-substratum adhesion of differentiated M1 cells.

Mouse myeloid leukemic M1 cells can be induced to differentiate into macrophages and granulocytes in vitro by a factor(s) stimulating differentiation of the cells (D-factor), which is suggested to be a glycoprotein. On the other hand, growth and differentiation of normal precursor cells of macrophages and granulocytes can be stimulated by a glycoprotein termed colony-stimulating factor (CSF). Mouse fibroblast L929 cells were found to produce both the D-factor and CSF. The properties of the D-factor and CSF and the roles of carbohydrates in the molecules of these factors were examined using tunicamycin, a specific inhibitor of asparaginase-linked glycosylation. Although both the D-factor and CSF were produced by L-cells in usual medium containing fetal calf serum, production of D-factor, but not CSF, was reduced by omission of serum from the medium. The activity of the D-factor was slightly decreased by treating the L-cells with tunicamycin (0.5 microgram/ml) in the presence of 2% fetal calf serum, without any decrease in CSF activity. Conditioned medium of L-cells incubated with or without tunicamycin was fractionated by gel filtration on a Sephadex G-200 column. Normal D-factor appeared as a single peak with an apparent molecular weight of 67,000. D-factor produced in the presence of tunicamycin had an apparent molecular weight of 25,000. On the other hand, most of the CSF was eluted in the void volume, even when it was produced in the presence of tunicamycin. The D-factor produced in the presence of tunicamycin was more sensitive than normal D-factor was to trypsin or heat treatment at 70 degrees. The CSF produced in the presence of tunicamycin was resistant to these treatments. These results indicate that the D-factor is distinct from CSF. Furthermore, the results suggest that the D-factor produced by L-cells is also a glycoprotein and that, although carbohydrate is not essential for production or activity of the D-factor, it contributes to stabilizing the protein portion of D-factor.

Mouse myeloid leukemic M1 cells can be induced to differentiate into macrophages and granulocytes in vitro by a protein inducer, differentiation-stimulating factor (D-factor), and by various other compounds. Mouse spleen cells produced D-factors when treated with various mitogens, such as concanavalin A, phytohemagglutinin, pokeweed mitogen, lipopolysaccharide, and synthetic double-stranded polyribonucleotide copolymer of polyinosinic and polycytidylic acids. Concanavalin A, phytohemagglutinin, and pokeweed mitogen stimulated spleen lymphocytes, but not spleen macrophages, to produce a D-factor with an apparent molecular weight of 40,000 to 50,000. On the other hand, lipopolysaccharide and copolymer of polyinosinic and polycytidylic acids stimulated both spleen lymphocytes and spleen macrophages to produce D-factors. Spleen macrophages produced D-factors with molecular weights of 40,000 to 50,000 and 20,000 to 25,000, whereas spleen lymphocytes produced only the larger molecules. In addition to D-factor, colony-stimulating factor (CSF), which stimulates growth and differentiation of normal bone marrow cells, and interferon, were detected in conditioned medium of spleen cells treated with concanavalin A or lipopolysaccharide. On gel filtration of the conditioned medium with Sephadex G-100, CSF was eluted between the larger D-factor and the smaller one. The fraction with interferon activity overlapped that of the larger D-factor. Incubation of the conditioned medium at pH 2 abolished the activity of interferon but did not affect the activity of either D-factor or CSF. The addition of cytochalasin B suppressed the production of interferon but not of D-factor or CSF by the spleen cells. These results indicate that the D-factor is a different substance from CSF or type II interferon.