DUAL ACTIVITY OF CSF-1, PRODUCED BY A MURINE HYBRID CELL-LINE AND FROM OTHER SOURCES, ON THE GROWTH OF BONE-MARROW STROMAL CELLS IN CULTURE

Medium conditioned by the cell line A.4.10 was shown to produce a fact or that inhibits the growth of bone marrow (BM) stromal foci in liquid cultures. In this study we demonstrated that CSF-I, present in this c onditioned medium (CM), was largely responsible for this inhibition. T his was concluded from the following findings: 1) the CSF-I activity i n the CM copurified with the inhibitory activity in several biochemica l purification procedures; 2) an antibody against murine CSF-I was abl e to neutralize the CSF-I activity as well as the inhibitory activity in the,A.4.10 CM; and 3) immunopurified murine CSF-I from A.4.10 CM an d from another murine source and recombinant human (rh) CSF-1 were all able to inhibit stromal cell growth. In secondary stromal cultures, i nhibition was demonstrated at high cell densities but not at low densi ties, suggesting that accessory cells may be involved in the effect. W hen the dose rh CSF-I was reduced to half of that required to produce 50% inhibition, stimulation of primary stromal foci growth was demonst rated, supporting observations by others that CSF-1 can act as a growt h factor for BM stromal cells. In this report we thus demonstrate both inhibitory and stimulatory effects of CSF-1 on the growth of BM strom al cells in vitro.