Granulocyte-macrophage Colony-stimulating Factor (GM-CSF) and Granulocyte Colony-stimulating Factor (G-CSF) Secretion by Adherent Monocytes Measured by Quantitative Immunoassays

The kinetics of GM-CSF and G-CSF secretion by purified adherent human monocytes were studied by quantitative immunoassays. Interleukin-1 (IL-1); 4-40 ng/ml and E. coli lipopolysaccharide (LPS); 0.1-1.00 ng/ml, were the most effective stimuli and induced dose-dependent secretion of both GM-CSF and G-CSF. Secretion of newly synthesized CSF was detectable 3-6 hours after stimulation and continued for approximately 24 h. Twenty minutes pulse exposure to LPS was sufficient to induce half maximum secretion of GM-CSF, and after 24-36 h the adherent monocytes could not be restimulated. Neither GM-CSF nor TNF could down-regulate the secretion of GM-CSF. IL-3 induced a minor secretion of GM-CSF whereas TNF, G-CSF, M-CSF and IFN-gamma were unable to induce GM-CSF secretion. In addition to LPS and IL-1, GM-CSF and to a minor degree TNF induced G-CSF secretion. Enriched T lymphocytes secreted GM-CSF, but not G-CSF, after stimulation with PHA or staphylococcal enterotoxin A (SEA), whereas LPS and IL-1 were without stimulatory effects. We also noted that enriched T lymphocytes added to LPS-stimulated adherent monocytes at ratios of 1:10 or more inhibited, in a dose-dependent fashion, GM-CSF secretion by 13-55%. These findings add new quantitative data on CSF secretion by human monocytes.