Cellular responsiveness to stimulation in vitro: increased responsiveness to colony stimulating factor of bone marrow...

Addition of low concentrations (10 ng/ml) of saponin or Tween 80 to stimulated cultures of normal mouse bone marrow in agar increased the number of granulocyte-macrophage colonies which developed. Addition of cyclic AMP or dibutyryl cyclic AMP in low concentration (10(-8) to 10(-10) M) also enhanced colony numbers although concentrations above 10(-5) M were inhibitory. enhancement was found when marrow cells were pre-treated with these agents and cultured in their absence. The agents did not stimulate colony development in the absence of colony-stimulating factor and enhancement of colony number occurred only in cultures containing a concentration of colony-stimulating factor which was sub-optimal in terms of maximum colony development. There was no indication of increased colony-stimulating factor production by treated marrow cells under the experimental conditions used to show colony enhancement. It was concluded that the agents caused an increased responsiveness of colony-forming cells to colony-stimulating factor.