Contrasting effects of interferon-gamma and interleukin-4 on the interleukin-6 activity of stimulated human monocytes

Stimulated human monocytes/macrophages are a source of interleukin-6 (IL-6), which is a likely mediator involved in immune and inflammatory reactions. The means to control production of IL-6 by these cells could therefore have therapeutic applications. We report here, for lipopolysaccharide (LPS)-stimulated human monocytes in vitro, that the lymphokine, interferon-gamma (IFN-γ) (100 U/ml), enhanced the level of IL-6 activity, whereas another lymphokine, interleukin-4 (IL-4) (≥0.1 U/ml; ≥1.2 x 10^-11M), suppressed it. The effect of the two lymphokines were manifested at the level of mRNA. The action of the IL-4 was similar to that of the glucocorticoid, dexamethasone, but observed at a lower molar concentration. Such regulation of monocyte IL-6 activity is similar to that found previously for interleukin-1 (IL-1) and tumour necrosis factor-alpha (TNF-α) synthesis.