Stimulation of Mouse Bone Marrow Colony Growth in Vitro by Conditioned Medium

Summary Incubation of culture medium with cells from 8‐day‐old mouse kidney or cells from 16‐ to 18‐day mouse embryos resulted in production of conditioned medium which was capable of stimulating colony growth in vitro of mouse bone marrow cells. A linear relationship was demonstrated between the dose of conditioned medium and the number of colonies developing. A similar relationship was also found between conditioned medium dosage and the size of the colonies grown. The activity of conditioned medium was not lost on extensive dialysis; it showed a high degree of heat stability and was precipitated by 50‐100 saturation with ammonium sulphate. The morphology of cells in colonies grown with conditioned medium was typical of mouse metamyelocytes early in the incubation period but later there was a transition to mononuclear cell types.