Inhibitory activity in extract from human blood granulocytes was tested on granulocyte-macrophage colony formation in vitro. The inhibition depended on the type of serum used. With mouse BMC and FCS in the cultures, extract corresponding to 2.5x 104 granulocytes/ml reduced the colony number by 35'4'0, and extract from 2 x lo5 cells caused maximal inhibition (80-90%). With HS and mouse BMC the colony number was reduced by only 11-12'70, but stronger inhibition (55%) was observed when the serum concentration was reduced. With both types of sera the total cell number per culture plate was reduced relatively more than the colony number. Human GM-CFC were as sensitive as mouse GM-CFC, and extract from CML granulocytes inhibited less (p < 0.01) than extract from normal cells. Biochemical studies indicated that the inhibitor is a protein with a molecular weight of 30-60000. Lactoferrin, a putative inhibitor of CSF production, did not inhibit spontaneous or CSF-induced colony formation in these studies.
ABBREVIATIONSBMC = bone marrow cells GM-CFC = granulocyte/macrophage colony forming cell CML = chronic myeloid leukemia FCS = fetal calf serum FPLC = fast polypeptide liquid chromatography GCM = granulocyte conditioned medium GCT = stimulator (CSF) for human GM-CFC GRE = granulocyte extract HS = horse serum MW = molecular weight PHA = phytohemagglutinin