Mouse myeloid leukemic M1 cells were induced to differentiate in vitro into macrophages and granulocytes by various inducers, such as differentiation stimulating factor (D-factor) in conditioned medium of mouse peritoneal macrophages and mouse embryo cells, dexamethasone, lipopolysaccharide, and polyinosinic acid. Interferon, which was prepared from M1 cells treated with copolymer of polyinosinic and polycytidylic acids and purified by anti-interferon antibody column chromatography, did not itself induce differentiation of M1 cells, but it enhanced the induction of differentiation by D-factor, lipopolysaccharide, or polyinosinic acid. Interferon did not stimulate differentiation of the cells by another inducer, dexamethasone. Interferon alone could induce lysozyme activity in M1 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 copolymer of polyinosinic and polycytidylic acids, containing interferon and D-factor, induced the differentiation of all M1 clone cells, including R-4 and DR-3 clone cells that cannot be induced to differentiate by D-factor alone. The degree of inhibition of cell growth by interferon varied in different clones of cells. Growth of three clones, clones R-1, R-4, and DR-3, that are resistant to inducers of differentiation, was inhibited more than was that of three other clones, S-1, T-22, and B-24, that respond to inducers.


Supported in part by Grants-in-Aid for Cancer Research from the Ministry of Education, Science and Culture, Japan.

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