Humoral factors modulating growth of granulocyte macorphage progenitor cells

The kinetic of production of colony-stimulating activity (CSA) inducing mouse and human colony-forming cells (CFU-C) was tested in different human leukocyte culture systems. Stimulated and unstimulated cultures of spleen single cell suspensions, peripheral mononuclear leukocytes and acute monocytic leukemia (AMoL) cells were investigated. With the exception of the AMoL cells, stimulated cultures always revealed higher CSA levels than unstimulated controls. The spleen cell cultures exhibited the highest overall activity showing three molecular species of 70,000, 35,000 and 10,000 daltons activating human CFU-C to form colonies in the agar culture system. Furthermore it could be demonstrated that colony formation could be inhibited by low molecular weight fibrinogen degradation products obtained by digestion of fibrinogen with granulocyte-derived elastase.