Stimulation by interferon of induction of differentiation of mouse myeloid leukemic cells.

Mouse myeboidleukemic Ml cells were induced to differen tiate in vitro into macrophages and granubocytes by various inducers, such as differentiation stimulating factor (D-factor) in conditioned medium of mouse peritoneal macrophages and mouse embryo cells, dexamethasone, bipopolysaccharide, and polyinosinic acid. Interferon, which was prepared from Ml cells treated with copolymer of pobyinosinic and polycytidybic acids and purified by anti-interferon antibody column chromatogra phy, did not itself induce differentiation of Ml cells, but it enhanced the induction of differentiation by D-factor, bipopoby saccharide, or polyinosinic acid. Interferon did not stimulate differentiation of the cells by another inducer, dexamethasone. Interferon alone could induce lysozyme activity in Ml cells. The effects of interferon and D-factor or dexamethasone on induction of the lysozyme activity were synergistic. Sera from mice given injections of the copobymer of poby inosinic and pobycytidylic acids, containing interferon and D factor, induced the differentiation of all Ml clone cells, includ ing R-4 and DR-3 clone cells that cannot be induced to differ entiate by D-factor alone. The degree of inhibition of cell growth by interferon varied in different clones of cells. Growth of three clones, clones A-i , R-4, and DR-3, that are resistant to in ducers of differentiation, was inhibited more than was that of three other clones, S-i , T-22, and B-24, that respond to inducers.