Regulation by interleukin-3 of human monocyte pro-inflammatory mediators. Similarities with granulocyte-macrophage colony-stimulating factor

Urokinase-type plasminogen activator (u-PA), tumour necrosis factor-alpha (TNF-α) and interleukin-1 (IL-1) activities were measured for highly purified human monocytes cultured for 18 hr with recombinant human interleukin-3 (IL-3). IL-3 alone stimulated monocyte u-PA activity, but not TNF-α or IL-1 activity. However, IL-3, together with interferon-gamma (IFN-γ), stimulated the TNF-α, but not IL-1, activities of monocytes from several donors. In parallel cultures, granulocyte-macrophage colony-stimulating factor (GM-CSF) behaved similarly. IL-3, like GM-CSF, synergized weakly and sometimes irregularly with lipopolysaccharide (LPS) for increased TNF-α and IL-1 activities. Thus, IL-3 can selectively stimulate monocyte mediator production depending on the costimulus present; however, the stimulatory properties of IL-3 vary from those of IFN-γ and IL-4. The similarities in activity between IL-3 and GM-CSF may be explained by a common or associated IL-3/GM-CSF receptor(s), as suggested by biochemical studies.