Colony inhibiting factor in mature granulocytes from normal individuals and patients with chronic myeloid leukemia

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 2.5 X 10(4) granulocytes/ml reduced the colony number by 35%, and extract from 2 X 10(5) cells caused maximal inhibition (80-90%). With HS and mouse BMC the colony number was reduced by only 11-12%, 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 less than 0.01) than extract from normal cells. Biochemical studies indicated that the inhibitor is a protein with a molecular weight of 30-60,000. Lactoferrin, a putative inhibitor of CSF production, did not inhibit spontaneous or CSF-induced colony formation in these studies.