Specific binding of a factor inducing differentiation to mouse myeloid leukemic M1 cells

A factor inducing differentiation of mouse myeloid leukemic M1 cells into macrophages (differentiation-inducing factor, D-factor), which was purified to homogeneity from conditioned medium of mouse Ehrlich ascites tumor cells, could be iodinated without detectable loss of biological activity. The binding of 125I-D-factor to M1 cells was specific; the binding was inhibited competitively by D-factor derived from Ehrlich cells and mouse fibroblast L929 cells, but not by other growth factors or D-factor derived from differentiated M1 cells. The latter differs from D-factor of Ehrlich cells and L929 cells in antigenicity and molecular weight. At 21 degrees C, the binding was saturated at 370 pM 125I-D-factor. M1 cells showed a high affinity for 125I-D-factor (dissociation constant, 1.0 X 10(-10) M) and expressed a small number of binding sites (170 per cell). Specific binding of 125I-D-factor was observed only to several clones derived from M1 cells, including those sensitive and resistant to induction of differentiation by D-factor.