Studies on colony formation in vitro by mouse bone marrow cells. II. Action of colony stimulating factor

Abstract An analysis was made of some of the processes involved in the stimulation by colony stimulating factor (CSF) of cluster and colony formation by mouse bone marrow cells in agar cultures in vitro . Colony formation was shown to be related to the concentration and not the total amount of CSF. The concentration of CSF determined the rate of new cluster initiation in cultures and the rate of growth of individual clusters. Colony growth depleted the medium of CSF suggesting that colony cells may utilise CSF during proliferation. Bone marrow cells incubated in agar in the absence of CSF rapidly died or lost their capacity to proliferate and form clusters or colonies. CSF appears (a) to be necessary for survival of cluster‐and colony‐forming cells or for survival of their proliferative potential, (b) to shorten the lag period before individual cells commence proliferation and (c) to increase the growth rate of individual clusters and colonies.